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Record for a UF thesis. Title & abstract won't display until thesis is accessible after 2010-08-31.

University of Florida Institutional Repository
Permanent Link: http://ufdc.ufl.edu/UFE0022612/00001

Material Information

Title: Record for a UF thesis. Title & abstract won't display until thesis is accessible after 2010-08-31.
Physical Description: Book
Language: english
Creator: Taylor, Joshua
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2008

Subjects

Subjects / Keywords: Materials Science and Engineering -- Dissertations, Academic -- UF
Genre: Materials Science and Engineering thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Statement of Responsibility: by Joshua Taylor.
Thesis: Thesis (Ph.D.)--University of Florida, 2008.
Local: Adviser: Sigmund, Wolfgang M.
Electronic Access: INACCESSIBLE UNTIL 2010-08-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2008
System ID: UFE0022612:00001

Permanent Link: http://ufdc.ufl.edu/UFE0022612/00001

Material Information

Title: Record for a UF thesis. Title & abstract won't display until thesis is accessible after 2010-08-31.
Physical Description: Book
Language: english
Creator: Taylor, Joshua
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2008

Subjects

Subjects / Keywords: Materials Science and Engineering -- Dissertations, Academic -- UF
Genre: Materials Science and Engineering thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Statement of Responsibility: by Joshua Taylor.
Thesis: Thesis (Ph.D.)--University of Florida, 2008.
Local: Adviser: Sigmund, Wolfgang M.
Electronic Access: INACCESSIBLE UNTIL 2010-08-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2008
System ID: UFE0022612:00001


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6b3c8c182760281c22399a394d4c7561844e3133







ADSORPTION OF SODIUM POLYACRYLATE IN HIGH SOLIDS LOADING SLURRIES


By

JOSHUA JAMES TAYLOR
















A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA

2008


































O 2008 Joshua James Taylor




































To my Father and Mother, John and Dina Taylor, who have been an encouragement throughout
all my education.









ACKNOWLEDGMENTS

I would first like to thank my advisor Dr. Wolfgang Sigmund for his guidance and support

which has helped me through this proj ect. I would also like to thank my committee members Dr.

Ronald Baney, Dr. Laurie Gower, Dr. Hassan El-Shall, and Dr. Charles Martin for their

intellectual discussions and advise.

I would like to thank each person in Dr. Sigmund's group who have been a support for me

and offered constructive comments during my research. I would especially like to thank Yi-

Yang Tsai who has offered countless advice and support throughout the last four years.

Additionally, I would like to thank my friends and family who have always been there for

support and encouragement. I especially thank my parents who have always encouraged me to

further my education and have been a support during the challenging times.












TABLE OF CONTENTS


page

ACKNOWLEDGMENTS .............. ...............4.....


LIST OF TABLES ................ ...............7............ ....


LIST OF FIGURES .............. ...............8.....


LIST OF ABBREVIATIONS AND SYMBOLS .............. ...............14....


AB S TRAC T ............._. .......... ..............._ 16...


CHAPTER


1 INTRODUCTION ................. ...............18.......... ......


1.1 Calcium Carbonate Industry ................. ...............18..............
1.2 Sodium Polyacrylate (NaPAA)............... .................18
1.3 High Solids Loading Slurries............... ...............19
1.4 Obj ectives and Approach ................. ...............19...............

2 LITERATURE BACKGROUND AND CHARACTERIZATION ................... ...............20


2.1 Calcium Carbonate .............. ...............20....
2.2 N aPA A ........................... .. .. ... ............2
2.3 Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-
FTIR ) ............... .... .. ......... .. ............. ...........3
2.4 Ultraviolet-Visible Spectroscopy (UV/VIS). ................. ...............40................
2.5 Compression Rheology and Impedance Measurements ................ ................. ......42

3 EXPERIMENTAL METHODS .............. ...............44....


3.1 Adsorption Isotherms................ ..............4
3.2 Turbidity Measurements ................. ...............44....._._ .....
3.3 AT R-FT IR .............. ...............45....
3.4 UV/VIS Spectroscopy .............. ...............45....
3.5 Rheology ............._. ...._... ...............47...

4 SODIUM POLYACRYLATE ADSORPTION ONTO GCC IN HIGH SOLIDS
LOADING SLURRIES .............. ...............48....


4.1 Adsorption Isotherms................ ...............4
4.2 Turbidity of NaPAA ................ ...............53......__ ....
4.3 ATR-FTIR ............... ...............57...
4.3.1 Dry and Wet Samples ................. ...............58.____...
4.3.2 Solvent Exchange ............ ..... .__ ...............61.












4.3.3 Water Structure in High Solids Loading Slurries............... ...............63
4.3.4 NaPAA CH Band Infrared Spectra. ....__ ......_____ .......___ ..........6
4.3.5 NaPAA Carboxylate Group Infrared Spectra ................. ................. ..........68
4.3.6 Carbonate Infrared Spectra............... ...............74
4.3.9 Temperature Dependence ................. ...............78................
4.3.10 Addition of Energy to Aged Slurries ................. ...............79.............
4.4 Probe M olecules .............. ...............82....
4.4.1 Benzoic Acid .............. ...............83....
4.4.2 Gallic Acid............... ...............87..
4.4.3 Propionic Acid............... ...............92..


5 WATER STRUCTURE DEPENDANCE ON SOLIDS LOADING AND AGING...............93


5. 1 AT R-F TIR Water Structure ................. ...............93...............
5.2 W ater Confinement............... ... .................9
5.3 Ions as Water Structure Makers or Breakers .............. ...............98....


6 WATER STRUCTURE MAKING AND BREAKING CHEMICALS ............... .... ...........102


6.1 Calcium Chloride............... ...............10
6.2 Sodium Bicarbonate............... ..............10
6.3 Ethylene Glycol .............. ...............105....
6.4 Propylene Glycol .............. ...............108....


7 SUMMARY AND DISCUSSION ................. ...............112......._ ....


8 CONCLUSIONS AND SUGGESTIONS ................. ......_._....................18


8.1 Conclusions............... ..............11
8.2 Suggestions ......._ ................ ........_ ..........11


LIST OF REFERENCES ..............__.......... ...............120....


BIOGRAPHICAL SKETCH ..........._..__.......... ...............130....










LIST OF TABLES


Table


page


2-1 Several materials used for the ATR crystal. ............. ...............39.....










LIST OF FIGURES


FMure page


2-1 Unit cell of calcium carbonate with space group R3 c. A) An angled top view, B) a
side view with the dotted line through the middle being an edged ................. ................20

2-2 XRD of calcium carbonate powder used in this dissertation. All peaks confirm
calcite structure but only the high intensity peaks are labeled with Miller indices. ..........21

2-3 Number, surface area, and volume distribution of GCC while dispersed with NaPAA
in H20 as dilute samples. .............. ...............22....

2-4 The SEM of GCC particles used in this dissertation. ............. ...............23.....

2-5 Adsorption of polymer onto a surface. Polymer is described as containing tails,
loops, and trains. ............. ...............27.....

2-6 Adsorption confirmations of a polymer. A) Pancake confirmation has an absorbed
layer thickness ~ segment length, B) Confirmation similar to polymer in good
solvent give adsorbs with a layer thickness ~ R,, C) Brush confirmation has an
absorbed layer thickness greater than R,. ............. ...............29.....

2-7 Repeat unit of sodium polyacrylate, NaPAA ................. ...............30........... ..

2-8 Coordination modes of a carboxylate group ................. ...............31........... ..

2-9 IR scattering and adsorption in different IR techniques. ............. .....................3

2-10 ATR-FTIR setup. Sample is placed onto a crystal. The IR beam reflects several
times through the crystal and the evanescent wave interacts at the interface with the
sam pl e. ............. ...............3 5....

2-11 At the interface of the crystal and sample the IR beam penetrates past the surface of
the cry stal and decay s exponenti ally ..........._............ ...............36.

2-12 The electric Hield amplitude at the interface of the crystal and sample. The electric
Hield decays at an exponential rate in the sample. The depth of penetration, Dp, is
determined when the electric Hield is attenuated to 36.8% of its total intensity. ...............37

3-1 Calibration curve for gallic acid. Absorption measurements preformed at a
wavelength of210 nm with a sample thickness of 1 cm. ............. .....................4

3-2 Calibration curve for benzoic acid. Absorption measurements preformed at a
wavelength of 224 nm with a sample thickness of 1 cm. ................ ......_.. .........._.47

4-1 Titration curve of NaPAA. Black curve is the titration of a NaPAA in deionized
water. Red curve is the 1st derivative of the titration curve. ............. .....................4










4-2 Calibration curve for NaPAA with the titration technique. ............. .....................5

4-3 The adsorbed amount of NaPAA compared to the 100% adsorption line. ................... .....5 1

4-4 Langmuir adsorption isotherm of NaPAA by GCC in a 75 wt% solids loading slurry.
This model is a poor fit with a R2 Value Of 0.8187. ........._.._.. ............... 52........_

4-5 Temkin adsorption isotherm of NaPAA by GCC in a 75 wt% solids loading slurry.
This model is a poor fit with a R2 Value Of 0.8529. ........._.._.. ............... 52......_..

4-6 Freundlich adsorption isotherm of NaPAA by GCC in a 75 wt% solids loading
slurry. Freundlich model fits well with a R2 Value Of 0.96. ............... ...................5

4-7 Turbidity of NaPAA in water with increasing monovalent salt concentration. High
concentrations of sodium ions within slurry do not cause the NaPAA to precipitate. ......54

4-8 Turbidity of NaPAA in water with increasing divalent salt concentration. Under
processing condition of GCC slurries there is no indication of NaPAA precipitation. .....55

4-9 Turbidity of NaPAA in water with increasing temperature. NaPAA does not
precipitate with increasing temperature. .............. ...............56....

4-10 Turbidity of NaPAA in water with 10-3M CaCl2 and 10- M CaCl2 OVer a three day
period. At slurry conditions there was no precipitation of NaPAA. ................ ...............57

4-11 IR spectra of the carbonate bending bands located at 1449 cml of a wet and a dry 75
wt% GCC slurry. The wet slurry forms a shoulder at lower wavenumbers indicating
the presents of bicarbonate species ................. ...............58........... ...

4-12 IR spectra of the carbonate stretching bands located at 875 cml of a wet and a dry 75
wt% GCC slurry. The wet slurry has a larger FWHM. ............. .....................5

4-13 Second derivative of the IR spectra of the carboxyl region for a wet and a dry
sample. Band at 1581 cm-l shifts to 1586 cm-l indicated change in coordination............59

4-14 IR spectrum of NaPAA in H20. The OH stretching band overlaps the CH stretching
bands of NaPAA. The OH bending band overlaps part of the COO- band. .....................60

4-15 IR spectrum of NaPAA in D20. Switching from H20 to D20 shifts the stretching
and bending bands so that there is no overlap with the CH or COO- stretching bands
of NaPAA ................. ...............61......__ _.....

4-16 IR spectrum of a 75 wt% GCC slurry with NaPAA. Regions of interests are boxed
and discussed. ............. ...............62.....

4-17 IR spectra of the OH stretching bands of H20 and H20 in a 75 wt% slurry. When
water is in a high solids loading slurry there is a change in the structure of the water










indicated with the FWHM decreasing and the 3183 cm-l shoulder peak shift to
3239 cm l. ........... ...............63......

4-18 IR spectra of the OD stretching bands of D20 and D20 in a 75 wt% slurry. When
D20 is in a high solids loading slurry there is a change in the structure of the water
indicated with the FWHM decreasing and the 2502 cm-l shoulder increasing
i nten sity ................. ...............64........... ....

4-19 IR spectrum of the CH band of NaPAA in D20 ................. ...............66...........

4-20 IR spectrum of the CH bands of NaPAA in a 75 wt% GCC slurry. Two bands are
formed at 2980 cm-l and 2875 cm-l indicating adsorption of the NaPAA onto the
surface of GCC. ............. ...............66.....

4-21 IR spectra of the CH bands of NaPAA in GCC slurries with increasing concentration
of NaPAA. Adsorption limit is between 1 wt% NaPAA and 9 wt% NaPAA. .................67

4-22 IR spectrum of the carboxyl stretching region for NaPAA in D20. The IR spectrum
shows that NaPAA is in the ionic form with a peak at 1570 cm-l for the COO- and no
peak at 1700 cm-l for the C=0. ........._ ...... .... ...............68.

4-23 Second derivative of the IR spectra of the carboxylate region of NaPAA in D20 and
in a 75 wt% GCC slurry. NaPAA adsorbs onto GCC in unidentate, bridging, and
bidentate modes. ............. ...............69.....

4-24 Second derivative of the IR spectra of 75 wt% GCC slurries with increasing
concentration of dispersant. With an excess amount of dispersant there is no
unidentate adsorption mode. ............. ...............70.....

4-25 Second derivative of the IR spectra of the carboxylate region with increasing solids
loading. As the solids loading of the slurries increases there is a shift of the bands
toward a bridging mode. ............. ...............72.....

4-26 Second derivative of the IR spectra of the carboxylate region with aging. The
unidentate band shifts from 1585 cm-l to 1580 cm-l with increasing age indicating a
shift towards the bridging mode. ............. ...............73.....

4-27 ATR-FTIR spectrum of GCC. ............. ...............74.....

4-28 IR spectra of carbonate band of GCC in D20 and in a 75 wt% GCC slurry.
Formation of a shoulder indicates formation of bicarbonates. ................ ................ ...75

4-29 IR spectra of the carbonate band of GCC slurries showing a formation of a shoulder
with increase solids loading. .............. ...............76....

4-30 IR spectra of the carbonate band of GCC in a 75 wt% slurry with aging. ................... ......77










4-3 1 IR spectra of the carbonate band with a slurry at different temperatures. As the
temperature decreases the shoulder shifts from 1311 cm-l to 1335 cm l...........................78

4-32 IR spectra of a 75 wt% GCC slurry before and after a heating cycle. The only
difference of the two spectra is the carbonate band. ....._._._ .... ... .__ ........_.......79

4-33 IR spectra of the OD band in a 75 wt%/ GCC slurry at different temperatures. Lower
temperatures increase the concentration of structured water. .............. ....................8

4-34 IR spectra of the OD band in an aged 75 wt% GCC slurry with addition of energy to
the system. Adding energy to the system partially restores the fluid like water
structure ................. ...............81.................

4-3 5 IR spectra of the carbonate band in an aged 75 wt% GCC slurry with addition of
energy to the system. Adding energy to the system partially restores the carbonate
band to a fresh slurry............... ...............8 1

4-36 Molecular structure of benzoic acid ................. ...............82...............

4-37 Adsorption of benzoic acid onto GCC at varying solids loading. Benzoic acid does
not adsorb onto GCC. ............. ...............83.....

4-3 8 Second derivative of the IR spectra of benzoic acid in D20, 20 wt% GCC slurry, and
57 wt%/ GCC slurry. The bands for the benzene ring and the carboxylate do not
shift, indicating no adsorption............... ...............8

4-39 IR spectrum of the CH bands of benzoic acid in D20 and in a 57 wt% GCC slurry.
Formation of new bands indicates interaction of the CH bonds with GCC...............__.. ...85

4-40 Molecular structure of gallic acid. ............. ...............86.....

4-41 Adsorption of gallic acid onto GCC at varying solids loading............__.. ..........__.. ...87

4-42 Second derivative of the IR spectra of gallic acid in D20 and a 20 wt% GCC slurry.
The bands for the benzene ring and the carboxylate shift, indicating adsorption..............88

4-43 IR spectrum of the CH bands of gallic acid in D20 and in a 67 wt% GCC slurry.
Formation of new bands indicates interaction of the CH bonds with GCC...............__.. ...89

4-44 Second derivative of the IR spectra of gallic acid in a 20 wt% and 67 wt% GCC
slurry. The bands for the benzene ring and the carboxylate shift, indicating change
in the coordination of the benzoic acid with increasing solids loading. ................... .........90

4-45 Molecular structure of propionic acid ................. ...............91...............

4-46 IR spectrum of the CH bands of propionic acid in D20 and in a 70 wt%/ GCC slurry.
Formation of new bands indicates interaction of the CH bonds with GCC..............._._....91










4-47 Second derivative of the IR spectra of propionic acid in D20, 14 wt%/ GCC slurry,
and a 70 wt% GCC slurry. No shift in the carboxylate band indicates that propionic
acid does not adsorb ................. ...............92................

5-1 IR spectra of the OD stretching bands in GCC slurries ranging from 10 wt% to
75 wt%. As the solids loading increases there is an increase in the fluid structure
(2484 cm- ) and decrease in solid structure (2390 cm )~................ ...............93.

5-2 Fluid to solid water structure within different solids loading slurries. There are two
different regions, the first from 10 to 50 wt% and the second above 50 wt%. .................. 94

5-3 IR spectra of the OD band in a 75 wt% slurry with aging. Increasing age causes an
increase in the concentration of structured water in the slurry. ............. ....................95

5-4 Fluid to solid water structure within an aging 75 wt% GCC slurry. The fluid like
water structure decreases with aging becoming more like a slurry without dispersant.....96

5-5 Calculations of the distance between GCC particles in different solids loading
slurries with NaPAA having a radius of gyration of 2 nm, 3 nm, and 4 nm. ................... .97

5-6 Calculations of the distance between NaPAA molecules in different solids loading
slurries with a radius of gyration of 2 nm, 3 nm, and 4 nm ................. ......................98

5-7 Change of pH in an aging 75 wt% GCC slurry over a six day time span. A decrease
in pH is due to the concentration change of species in the slurry ................. ................ .99

5-8 IR spectra of the OD band of a 75 wt% GCC slurry with increase NaPAA. There is a
decrease in the structured water indicating that NaPAA is a water structure breaker in
a GCC slurry. ............. ...............100....

6-1 IR spectra of the OD band of slurries with and without CaCl2. Ca2+ as a water
structure maker prevents the increase in fluid like water of a GCC slurry. .........._........103

6-2 IR spectra of the carbonate band of slurries with and without CaCl2. Ca2+ prevents
some of the interactions with the carbonate species. ................ ...........................103

6-3 IR spectra of the OD band of a 75 wt%/ GCC slurry with 0. 19M sodium bicarbonate
with aging. As a weak structure maker, sodium bicarbonate allows for an increase in
the structured water with aging of a 75 wt% slurry. .......................... ........104

6-4 Rheology of 75 wt% GCC slurries with and without sodium bicarbonate. Sodium
bicarbonate increases the viscosity. ............. ...............105....

6-5 Structure of ethylene glycol ................ ...............106........... ...

6-6 IR spectra of the OD band of a 75 wt% GCC slurry with 0.5M ethylene glycol with
aging. Ethylene glycol as a water structure breaker prevents structure water from
forming while the slurry ages. ............. ...............106....










6-7 IR spectra of the carbonate band of slurries with and without ethylene glycol.
Ethylene glycol prevents interactions with the carbonate species as it ages. ..................107

6-8 Viscosity measurements of 75 wt%/ slurries with and without ethylene glycol.
Ethylene glycol decreases the viscosity more than adding an equal weight amount of
water to the slurry. ............. ...............108....

6-9 Structure of propylene glycol ................. ................ ......... ........ ........ 109

6-10 IR spectra of the OD band of a 75 wt% GCC slurry with 0.43M ethylene glycol with
aging. Propylene glycol as a water structure breaker prevents structured water from
forming while the slurry ages. ............. ...............109....

6-11 Viscosity measurements of 75 wt%/ slurries with and without propylene glycol.
Propylene glycol decreases the viscosity at low shear rates but increases viscosity at
higher shear rates. ................ ...............110................

7-1 Adsorption of NaPAA onto GCC due to an increase in entropy with the release of
structured water. A) NaPAA in solution before adsorbing onto GCC surface, B)
NaPAA adsorption releases structure water from the carboxylate groups and the
calcium as demonstrated in the train of the polymer. ................. .......... ...............1 17









LIST OF ABBREVIATIONS AND SYMBOLS

A absorbance

ATR attenuated total reflectance

a intramolecular expansion factor

b Freundlich exponent

C unadsorbed NaPAA (mg/L)

c concentration of the absorbing species

D, depth of penetration

DRIFTS diffuse reflectance infrared Fourier transform spectroscopy

E electric field amplitude

a molar absorptivity coefficient

FTIR Fourier transform infrared spectroscopy

FWHM full width at half maximum

GCC ground calcium carbonate

IR infrared

K Freundlich constant

L the path length through the sample

1 effective segment length

M molecular weight

Mo segment molecular weight

N number of segments

n refractive index

NaPAA sodium polyacrylate

PCC precipitated calcium carbonate

2n pl










Q adsorbed NaPAA per GCC (mg/g)

SEM scanning electron microscope

T transmittance

6 angle of incidence

UV/VIS Ultravi ol et-vi sibl e

u wavenumber

W wavenumber

XRD x-ray diffraction

z distance from crystal surface









Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

ADSORPTION OF SODIUM POLYACRYLATE INT HIGH SOLIDS LOADING SLURRIES

By

Joshua James Taylor

August 2008

Chair: Wolfgang M. Sigmund
Major: Materials Science and Engineering

The world demand for calcium carbonate has been increasing by 7% per year since 2002

reaching a world capacity of 71.7 megatons in 2007. The demand continues to increase due to

the diverse applications of calcium carbonate such as building materials, medicines, additives to

food, filler for plastics and paper, and more. Calcium carbonate is often stored and transported

by dispersing it into an aqueous medium with a polyelectrolyte to achieve up to 75 wt% solids

loading. One of the most frequently applied dispersants for calcium carbonate is sodium

polyacrylate (NaPAA). Higher solids loading of the calcium carbonate slurries are desired to

increase storage capacity and decrease transportation cost. In order to achieve higher solids

loading slurries the science behind the adsorption of NaPAA onto the calcium carbonate within

high solids loading slurries must be understood. Currently all research which has been

performed on the adsorption of NaPAA onto calcium carbonate has been performed in dilute

systems. The goal of this research is to understand the adsorption of NaPAA onto calcium

carbonate in high solids loading slurries up to 75 wt%/ ground calcium carbonate (GCC).

The adsorption of NaPAA onto calcium carbonate was investigated utilizing several

techniques including adsorption isotherms, turbidity measurements, attenuated total reflectance

Fourier transform infrared spectroscopy (ATR-FTIR), and probe molecule adsorption. The









adsorption of the NaPAA was determined to be due to the chelating ability of the carboxylate

groups with calcium carbonate. The carboxylate groups were determined to adsorb through

unidentate, bidentate, and bridging modes. Also, the mode of adsorption of the carboxylate

group was dependant on the solids loading and age of a slurry system. Further analysis revealed

the CH groups of adsorbed NaPAA were interacting with the surface of the GCC.

Another novel discovery demonstrated that the water structure within a GCC slurry

dispersed with NaPAA is dependant on solids loading and age. With increasing solids loading

there is a decrease in the concentration of structured water. Also, with an increase in age there is

an increase in the concentration of structured water. Chemicals with the ability to either make or

break water structure were introduced into 75 wt%/ solids loading slurries. The water structure

breakers demonstrated that their inclusion in the slurry decreased viscosity and prevented an

increase in the structured water due to aging.









CHAPTER 1
INTTRODUCTION

1.1 Calcium Carbonate Industry

The world capacity for ground calcium carbonate (GCC) reached 71.7 megatons in 2007.

The capacity has grown by 7% per year since 2002 and continues to increase world wide. GCC

is diverse in its applications which include filler in plastics and paper, building materials,

fertilizer, medicines, additive to foods, and more. The paper industry alone accounts for around

38% of the calcium carbonate demand. Transportation and storage of calcium carbonate as

paper fillers are provided in either high solids loading slurries (60-75 wt%) or as dewatered

powder.

Due to calcium carbonate's increasing demand there has also been an increase in published

research concerning calcium carbonate. Improved understanding of calcium carbonate

dispersion in aqueous systems has been desired in order to increase the efficiency of production

and decrease costs. As will be discussed in chapter 2, literature contains many papers concerned

with dilute systems of calcium carbonate but lacks research on high solids loading GCC slurries.

1.2 Sodium Polyacrylate (NaPAA)

Polyacrylic acid and its salt sodium polyacrylate (NaPAA) are one of the most frequently

applied polyelectrolytes in industry and the household. A few examples include laundering

processes, thickening agents, and dispersion of clay and calcium carbonate. NaPAA is used in

the calcium carbonate industry as a dispersant for the mineral because the solids loading can be

increased to 75 wt% while maintaining the desired viscosity. However, the complete role of

stabilization and confirmation of NaPAA in dispersing calcium carbonate at high solids content

is not clear. Previous studies about the adsorption of NaPAA will be discussed in Section 2.2.









1.3 High Solids Loading Slurries

As mentioned above, GCC is dispersed with NaPAA to achieve high solids loading slurries

(75 wt%). The calcium carbonate industry is constantly working to increase solids loading while

maintaining desired slurry properties in order to decrease production costs. In order to achieve

higher solids loading slurries the science behind the adsorption of NaPAA onto the GCC within

high solids loading slurries must be understood. Several published papers have studied the

adsorption of NaPAA onto calcium carbonate but all of the research has been performed on

dilute systems (less than 5 wt%) [1-15]. This is mainly due to the difficulties in measuring

adsorption in high solids content. Therefore, there is a necessity for understanding the

interaction of dispersants with particles in high solids loading slurries.

1.4 Objectives and Approach

This dissertation will focus on understanding the interaction of NaPAA, GCC, and water

within slurries with solids loading up to 75 wt%. Therefore, this work has the following goals:

* Determine adsorption mechanism of NaPAA onto GCC in high solids loading slurries.
* Determine water structure's relationship to solids loading and aging.
* Propose new chemicals for improving GCC dispersion.

There are several analysis techniques that will be utilized to accomplish the listed goals.

Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) will allow for

determination of the chemical interaction from the chemical groups containing a dipole moment.

ATR-FTIR is an excellent technique for high solids loading slurries and will be discussed in

more detail in Section 2.3. Results from the IR spectra will be supplemented with adsorption

isotherms and adsorption of probe molecules in high solids loading slurries. Additional data

from viscosity measurements will aid in the understanding of high solids loading GCC slurries.









CHAPTER 2
LITERATURE BACKGROUND AND CHARACTERIZATION

2.1 Calcium Carbonate

Calcium carbonate is one of the most common and abundant mineral on earth and it has

three different crystalline structures: vaterite, aragonite, and calcite. Of the three crystal

structures calcite is the most stable structure. Calcite has a trigonal crystal system with space

group R3 c, see figure 2-1. Calcite is used in industry as either precipitated calcium carbonate

(PCC) or ground calcium carbonate (GCC).


Z


Figure 2-1. Unit cell of calcium carbonate with space group R3c A) An angled top view, B) a
side view with the vertical dotted line through the middle being an edged.


L Calcium


O Oxygen


* Carbon










PCC is made by direct carbonation of hydrated lime, known as the milk process. High

purity calcium carbonate rock is crushed and heated to form lime and carbon dioxide (equation

2-1). Next, the lime is added to water to form calcium hydroxide (equation 2-2). Finally, the

calcium hydroxide is combined with carbon dioxide and calcium carbonate precipitates out

(equation 2-3).

CaCO3 + Heat CaO + CO2 (2-1)

CaO + H20 Ca(OH)2 (2-2)

Ca(OH)2 + CO2 CaCO3 + H20 (2-3)

PCC's shape and size differ from GCC and allow it to be used in different applications. PCC has

a narrower particle size distribution and the particle shape can be tailored for the application.

During processing the moisture associated with PCC can cause problems.

3600- 0


2500





202J


110
488-
012

100



20 48 60 Be 1ee

o20


Figure 2-2. XRD of calcium carbonate powder used in this dissertation. All peaks confirm
calcite structure but only the high intensity peaks are labeled with Miller indices.



































I I I
) 2 4 E
Diameter (lum)


GCC is removed from the ground and does not go through all the processing steps required

for PCC; therefore, the particles' shape and size distribution differ from PCC. GCC particles

shapes are seen to be irregularly rhombohedral and the size distribution of GCC is wider than
PCC.


110-


8-


6-


4-





0-


- Number
- Surface Area
- volume


Figure 2-3. Number, surface area, and volume distribution of GCC while dispersed with NaPAA
in H20 as dilute samples.
The GCC used in this research was provided by Imerys with a purity of greater than 99%.

X-ray diffraction (XRD) was performed on the particles to determine their structure (figure 2-2)

using the XRD Philips APD 3720. Upon analysis of the diffraction pattern the GCC was
confirmed to be calcite. As mentioned previously the size distribution of GCC is wide;









therefore, particle size measurements were performed with the Coulter LS13320 with a light

diffraction technique at the Particle Engineering Research Center at the University of Florida.

The size distribution is displayed with differential number, surface area, and volume versus

particles size in figure 2-3. The mean sizes for number, surface area, and volume are 0. 13 Clm,

0.56 Clm, and 1.43 Clm, respectively. Ninety percent of the sample contains particles with

diameters less than 0.22 Clm but 90 % of the volume of the GCC particles is provided by particles

larger than 0.23 lm.


Figure 2-4. The SEM of GCC particles used in this dissertation.

For this research the most important measurement for particles size is the surface area

because adsorption of NaPAA occurs at the surface of the particles. The data demonstrates that









90% of the surface area is provided by particles with less than 1.35 Clm diameters. The size

distribution of the particles is also demonstrated with a scanning electron microscope (SEM)

image of the powder, figure 2-4. Also, the specific surface area is important for calculating

adsorption isotherms; therefore, the Nova 1200 instrument in the Particles Engineering Research

Center at the University of Florida was utilized to measure the specific surface area of the GCC

using the Brunauer-Emmett-Teller method. The specific surface area was determined to be

5.36 m2/g which is within the range of published data [16-18].

Calcium carbonate is slightly soluble in water and shows a complex behavior which is due

to the complex chemical equilibrium between the mineral/water interface. The distribution of

ionic species in the system is constantly changing while moving toward equilibrium. The

following equations demonstrate the possible ionic species that form within a calcium carbonate

and water system.

CaCO3(S) & Ca2+ + CO32- (2-4)

H2CO3 & H' + HCO3- (2-5)

HCO3- 4 H+ + CO32- (2-6)

Ca2+ + HCO3~ & CaHCO3+ (2-7)

Ca2+ + OH~ CaOH+ (2-8)

H' + OH- 4 H20 (2-9)

Knez et al. [19] discuss the chemical equilibrium of a calcium carbonate and water system in

relation to pH in detail. They mention that high solution pH promotes the dissociation of

carbonate species (H2CO3 and HCO3-) and if the system is in equilibrium with atmospheric CO2

(GCC slurries are open to the atmosphere during processing) then the activities of all carbonate

species in the solution rise with pH. Since the system is constantly moving toward equilibrium









then the Ca2+ activity must align it self accordingly and the activity of Ca2+ falls with rising pH.

Finally, they conclude that the optimum stability conditions are in the pH range of about 9-11i.

Geoffroy et al. [4] also go into detail about the surface chemistry of calcium carbonate in

water. They focus on the pH range from 8 to 11 which is important for this research since the

pH of GCC slurries prepared in water with NaPAA have a pH of about 10. At pH lower than 8

the calcium carbonate dissolves while at pH higher than 11 the Ca(OH)2 precipitates. Geoffroy

et al. describe the ionic surface sites of calcium carbonate as hydrated forms of -Ca+ and -CO3 -

Equations 2-10 and 2-11 show reactions of the -CaOH surface sites but the pK of the reaction

shown in equation 2-11 is far above the pH of 10.

-CaOH + H -Ca(OH2)' (2-10)

-CaOH + OH -CaO- + H20 (2-11)

Equations 2-12 and 2-13 show the reactions of the -CO3H surface sites but the pK of the reaction

shown in equation 2-13 is far below the pH of 10.

-CO3H + OH -CO3(OH2)- (2-12)

-CO3H + H -CO3H2+ (2-13)

Geoffroy et al. come to the conclusion that the calcium carbonate surface sites within the pH

range of 8 to 11 consist of mainly neutral sites (-CaOH and -CO3H) and ionic sites (-Ca' and

-CO3-). Several other published papers have also discussed these equilibrium reactions which

are present in a calcium carbonate and water system [20-27].

Several papers have been published which include zeta potential measurements of

calcium carbonate in water [6, 16, 19, 23, 24, 26, 28-33]. The measurements of the surface

charge of calcium carbonate are not consistent. Moulin et al. [23] have summarized the results

of many researchers showing that the zeta potential measurements in calco-carbonic equilibrium









conditions have been measured as positive, negative, and variable. The large variation of the

sign of the zeta potential is due to the measurement conditions and the nature of the potential

determining ions in the system. Authors considered the thermodynamic equilibrium within the

liquid phase but did not consider the equilibrium at the gas-liquid interface. Moulin et al. take

into consideration both equilibria when designing their experiment and come to the conclusion

that the values of the zeta potential at the calco-carbonic equilibrium are canceled but is

primarily negative on both sides of the equilibrium. Finally, they determine that the potential

determining ions in the system are not OH- and H+ but are Ca2+ and HCO3 -

Another important aspect of calcium carbonate is the interaction of calcium ions with

water. Published research has shown that calcium prefers to form six-, seven-, and eight-

coordinate structures with water [34-37]. Katz et al. [34] found that the coordination structures

are asymmetrical when the calcium ions coordinate with water in an odd number such as five or

seven. The coordination of calcium with water plays an important role in the adsorption and

coordination of carboxylates as described in Section 2.2.

2.2 NaPAA

Adsorption of polymers onto surfaces is commonly utilized to disperse particles. When

particles with adsorbed polymers approach each other there is a repulsive entropic force due to

the entropy of confining the polymers which is known as steric repulsion. If the steric repulsion

force is greater than the van der Waals attractive force then the particles remain dispersed. The

polymer may take on several different conformations within the solvent and while adsorbed onto

the surface of the particles.

Depending on the segment to segment interactions of a polymer in a solution, it may

assume different conformations. If the segment to segment interactions of the polymer are weak

then the polymer assumes a random coil shape. For a polymer with a random coil shape an









important length scale is the root mean square radius which is known as the radius of gyration,

R,, as given by equation 2-14



R= (2-14)


where 1 is the effective segment length, N is the number of segments, M is the molecular weight,

and Mo is the segment molecular weight. Equation 2-14 is only valid as long as there are no

repulsive, attractive, or excluded volume interactions between the segments of the polymer in the

ideal solvent.


Tail Tail

Lo p










Surface Ta


Figure 2-5. Adsorption of polymer onto a surface. Polymer is described as containing tails,
loops, and trains.

In non-ideal solvents the effective size of the polymer can be smaller or larger than the radius of

gyration and is referred to as the Flory radius, RF, given by equations 2-15 and 2-16

RF = R, (2-15)


RF In11/ (2-16)

where a is the intramolecular expansion factor and is unity when the polymer is in an ideal









solvent. a will exceed unity when the polymer is dissolved into a good solvent and the polymer

swells and expands. If the polymer is in a poor solvent the segment to segment interactions are

strong and the polymer will collapse into a compact structure, a is less than one.

The adsorption of a polymer onto a surface is shown in figure 2-5. The adsorbed part of

the polymer is called a train and the non-adsorbed part of the polymer between two trains is

called a loop. The part of the polymer that is not adsorbed and is only adj acent to one train is

called a tail. Different conformations of the polymer on the surface contain varying

concentrations of each segment. Figure 2-6 demonstrates that a polymer with a high train

concentration adopts a pancake conformation. The layer thickness of a pancake conformation is

about equal to its segment size. As the concentration of trains decreases the polymer reaches a

point at which the layer thickness is similar to the radius of gyration. At this point the surface

area covered per molecule is approximately described by equation 2-17.

2 1
SurfaceArea = xR~ -NI2 (2-17)
S2

As the tail of the polymer extends further from the surface and increases length, the polymer

adopts a brush conformation. Assuming the segment width is close to the segment length, 1, the

fully extended polymer has a projected area approximately described by equation 2-18.

SurfaceArea = NI2 (2-18)

With a good solvent the most important factor for controlling the conformation of an adsorbed

polymer is the concentration of the polymer in the solvent. A low concentration will provide a

pancake conformation while increasing the concentration eventually leads to a brush

conformation.

Polymers whose repeat unit contains an electrolyte group are called polyelectrolytes. The

conformations of polyelectrolytes are similar to non-charged polymers except the polyelectrolyte












Surface


Surface


Pancake


R,


>R,


\l;


Surfarce


Figure 2-6. Adsorption confirmations of a polymer. A) Pancake confirmation has an absorbed
layer thickness ~ segment length, B) Confirmation similar to a polymer in good
solvent adsorbs with a layer thickness ~ R,, C) Brush confirmation has an absorbed
layer thickness greater than R,.


Brush









conformations are also dependant on salt concentration. The charges on the polyelectrolyte

cause the segments of the polymer to repel each other and give the polymer an extended

conformation in salt free water [38, 39]. Addition of salt screens the charges on the

polyelectrolyte and eventually will collapse the polymer into a conformation similar to a non-

charged polymer. Polyelectrolytes are often chosen for dispersion instead of non-charged

polymers because the electrolyte group can be chosen to adsorb onto specific surface sites of a

particle. This research has chosen a polyelectrolyte, NaPAA (molecular weight of 5,967 g/mol

and a 2.04 degree of polydispersity), which is known to have a high affinity to calcium [1, 2, 4-

11, 13-15, 40].

















Na+


Figure 2-7. Repeat unit of sodium polyacrylate, NaPAA.

NaPAA is one of the most commonly used dispersing agents in the papermaking

applications [19]. NaPAA is composed of a long linear hydrocarbon backbone which contains

one carboxyl group for each repeat unit, see figure 2-7. Several published papers have devoted

their research to the interaction of carboxyl groups and/or polyacrylates with surfaces and ions









[12, 36, 40-74]. There are several papers that discuss the adsorption of polyacrylates onto

calcium carbonate [1, 2, 4-15, 75]. A few of the key concepts and papers will be discussed.


R~ RRR






O' O Oa- 6- O~ O` O~ O- O


Mf M+ M; M M

Ionic Bridging Bidentate Unidentate

Figure 2-8. Coordination modes of a carboxylate group.

The carboxylate group has been shown to interact with metal cations and surfaces in four

different modes [4, 11, 36, 49, 59, 76], namely, ionic, bridging, bidentate, and unidentate as

shown in figure 2-8. Several of the papers have investigated the different modes with IR

spectroscopy because the change in bond symmetry can be detected. The ionic, bridging, and

bidentate modes have similar group symmetry. The two oxygen atoms in the bidentate mode are

interacting with one metal cation; therefore, there will be a change in the symmetrical and

asymmetrical vibration frequencies. Since the unidentate mode has one oxygen atom

coordinated with one metal cation the symmetrical and asymmetrical vibration frequencies will

be similar to a carboxylic acid group.

Geffroy et al. [4] and Dobson et al. [49] have shown that adsorption is preferred through

chelation of dicarboxylates. A five member chelate ring (consisting of the metal cation and two

adjacent carboxylates) are the most stable followed by six and seven member chelate rings. Lu

et al. [36] further explains that carboxylate groups interact with calcium ions in









three-dimensional seven- or eight-fold coordination and it is common for calcium ions to

coordinate with both carboxylate groups and water. Katz et al. [34] also demonstrate that both

unidentate and bidentate coordination of carboxylate groups with calcium cations are possible

when the calcium ions bind in seven- and eight-fold coordination.

Since calcium carbonate is slightly soluble in water the dissociation of calcium ions play

an important role on the conformation and shape of the NaPAA. Schweins et al. [13, 14, 71]

have discussed the collapse of NaPAA by calcium ions in three of their papers. The bound Ca2+

ions to the NaPAA chains cause the NaPAA to become much more hydrophobic. Also, all of the

binding modes of the NaPAA with Ca2+ can allow for intramolecular bridging which decreases

the coil dimensions. The collapse of the NaPAA eventually leads to a spherical shape with

different transitional shapes depending on the concentration of NaC1. Another interesting

discovery by Schweins et al. is the expansion of the NaPAA chains with an increase in Na' ions.

Ca2+ ions are strongly bound to the NaPAA but with increasing concentration of Na+ there is a

competition between the Ca2+ ions and the Na+ ions.

Two other papers of interest are written by Geffroy et al. [5] and Sinn et al. [15] who

discuss the heat of exchange of Ca2+ binding onto NaPAA as endothermic. They discuss that the

binding of Ca2+ to NaPAA can not be due to electrostatic forces (screened Coulomb potentials or

counterion exchange) because this would lead to either an exothermic or energetically neutral

process. Since the binding of Ca2+ ions to NaPAA is spontaneous then the free energy of binding

must be negative. In order for the free energy to be negative this process must be driven by an

increase in entropy. The increase in entropy is believed to be due to the release of water

molecules. The total amount of released water molecules can be calculated by subtracting the

rehydration of Na+ from the dehydration of Ca2+ and COO-. Sinn et al. [15] calculate that a









minimal number of six water molecules is required to counterbalance the endothermic binding

heat. The process of Ca2+ binding with NaPAA easily releases at least six water molecules.

Finally, two more papers are of particular interest for the role of NaPAA and ions in high

solids loading slurries. Raviv et al. [12, 77] discuss in two of their papers the role of charged

polymers and ions as providing lubrication to a system. The charged ion or carboxylate group

form water sheaths around them that are tightly bound. When the water sheaths approach each

other there is strong repulsion and the repulsive force can dominate the van der Waals attraction

force. Because the water molecules are tightly bound, removal of water molecules from the

sheath require a large amount of energy but the exchange of water molecules between two

sheaths has a much lower energy barrier. This correlates to the NaPAA and ions acting as highly

effective lubricants.

2.3 Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR)

Infrared (IR) spectroscopy detects the vibrational characteristics of chemical functional

groups having a dipole moment. When an infrared light interacts with matter then the chemical

bonds will stretch, contract, and bend. The chemical functional groups adsorb infrared radiation

in specific wavenumber ranges which allows for determination of specific chemical functional

groups within a sample. The band position and width of the band is an indication of the

interaction of the functional group with its surrounding environment. IR spectroscopy is a

technique which has been used for analyzing the interaction between dispersants and particles.

There are several different IR spectroscopy techniques but the three most common include

transmission, diffuse reflectance (DRIFTS), and attenuated total reflectance (ATR). All three

techniques are able to provide data about the interface but ATR has an advantage over

transmission and DRIFTS. The advantage of ATR can be seen in figure 2-9 which shows the IR

radiation penetration of coated particles for transmission, DRIFTS, and ATR techniques.










Transmission DRIFTS






anticlec


ATR


ATR Crystal

Figure 2-9. IR scattering and adsorption in different IR techniques.

For both the transmission and DRIFTS techniques the IR radiation penetrates through the whole

particle providing greater opportunity for the IR radiation to be absorbed. Also, in DRIFTS it is

difficult to control the interaction of the IR radiation with the sample because the interaction is

dependant on the particle size and sampling depth. Figure 2-9 demonstrates that the interaction

of the IR radiation with a particle using the ATR technique only penetrates into a fraction of the

particle allowing for an increase in the surface to bulk signal.

The IR technique chosen for this research will be required to analyze slurries up to 75 wt%/

solids loading. Transmission IR spectroscopy requires a sample to be transparent. If too much

of the signal is adsorbed while passing through the sample then reliable data cannot be obtained.

Due to the strong scattering of 75 wt% GCC slurries, the transmission technique cannot be

utilized. The sample preparation for the DRIFTS technique requires the sample to be dried and

then mixed with KBr powder. The DRIFTS technique could be used to analyze dried 75 wt%

GCC slurries but the dried samples do not represent the slurries which are discussed in Section

4.3.1. Finally, the ATR technique is ideal for obtaining spectra of liquids, semisolids, thin films,

and solids. ATR allows for measurement of strongly adsorbing samples of any thickness which









is a limitation of the transmission technique. Also, ATR does not require any sample

preparation; the sample is placed directly onto the crystal.





m m1





IR To Detector

ATR Clrystal

Figure 2-10. ATR-FTIR setup. Sample is placed onto a crystal. The IR beam reflects several
times through the crystal and the evanescent wave interacts at the interface with the
sample.

Figure 2-10 demonstrates the ATR accessory that is mounted into the FTIR. A sample is

placed onto the crystal. The IR radiation passes through the ATR crystal with several reflections

until it exits the crystal and travels to the detector. Each time the IR radiation undergoes total

reflection at the crystal surface next to the sample the exponentially decaying evanescent wave

interacts with the sample. An understanding of this phenomenon of total reflection at the

interface of two materials is required for understanding the ATR-FTIR technique.

There are two requirements for total internal reflection to occur (figure 2-11). First, the

crystal must have a higher refractive index than the sample (nl > n2). Second, the incident angle

in the crystal must be greater than the critical angle (6 > 8c). The critical angle is a function of

the refractive indices as shown in equation 2-14

6, = sin-l n21 (2-14)

where n21 82 nz1n = ratio of refractive indices of sample/crystal.



















n,


IR


Figure 2-11i. At the interface of the crystal and sample the IR beam penetrates past the surface of
the crystal and decays exponentially.
As the IR radiation undergoes total reflection it penetrates a small distance beyond the

crystal surface. The IR radiation which penetrates beyond the surface decays exponentially and

is called an evanescent wave. Figure 2-12 shows the electric field amplitude of the evanescent

wave as it passes from the crystal into the sample with refractive indices nl and n2, TOSpectively.

The electric field amplitude decays exponentially with distance from the crystal surface as

described by equation 2-15

E = Eo e-z/Dp (2-15)

where E = electric field amplitude, z = distance from crystal surface, and D, = depth of

penetration. As the evanescent wave decays it also interacts with the sample which is brought

into contact with the surface. Additional to the decay described with equation 2-15, the


Etvarnescent. Ftiieldl


Sample


AIITR
Crystrl









evanescent wave is attenuated by the sample's absorbance which is why it is called attenuated


total reflectance.


Figure 2-12. The electric field amplitude at the interface of the crystal and sample. The electric
field decays at an exponential rate in the sample. The depth of penetration, D,, is
determined when the electric field is attenuated to 36.8% of its total intensity.

The depth at which the evanescent wave penetrates the samples is known as the depth of

penetration (D,). The depth of penetration is defined as the depth at which the attenuation of the


Sarmple


Evanescent
Wave


Clrvstal










evanescent wave is 36.8% of its total intensity. The depth of penetration is described with

equation 2-16


D, (2-16)
2 27tWnZ,(sin 2 1 1,,)/2

where W = wavenumber.

There are several observations of equation 2-16 that will be discussed. The depth of

penetration is inversely proportional to the wavenumber. As the wavenumber increases there is a

decrease in the D,; therefore, the ATR spectra will show peaks that are more intense at low

wavenumbers than at high wavenumbers. Because of this dependence on wavenumber it can be

difficult to compare ATR spectra with library spectra containing transmission or DRIFTS

spectra. In order to avoid any problems, software packages have provided calculations that can

be applied to the ATR spectra to remove the wavenumber dependence.

The depth of penetration is a function of the angle of incidence. As the angle of incidence

decreases the D, increases. There are two possible ways to change the angle of incidence. First,

the angle of the bevel on the ATR crystal could be changed. Second, it can be changed by

changing the angle of the incoming radiation. Some ATR accessories provide the ability to

change the angle of the mirrors in order to change the angle of incidence.

The depth of penetration is a function of refractive index of the sample. The refractive

index of many organic compounds is similar; therefore, there is little change in the D, of

different organic samples and it is considered to be independent of refractive index. Quantitative

analysis is possible with the ATR technique if the refractive indices of samples are the same or

similar.

Equation 2-16 also demonstrates that the depth of penetration is a function of the refractive

index of the ATR crystal. As the refractive index of the ATR crystal increases the D, decreases.









There are several different ATR crystals that can be utilized for measurements and some of the

most common ones are listed in table 2-1. Several different properties of the crystals must be

considered when choosing the correct crystal for a system. The KRS-5 (trade name for thallium

iodide/thallium bromide) crystal has a large range but is toxic and requires handling with gloves.

The KRS-5 has a low refractive index which gives high penetration depths but it is a soft

material and can be easily scratch and bent. Diamond is not easily scratched and is insoluble in

water but is expensive. Zinc selenide (ZnSe) is the most common ATR crystal material due to its

wide range, insolubility in water, difficulty to scratch, and high depth of penetration. Finally,

Silicon (Si) and germanium (Ge) are both difficult to scratch but are usually used when small

penetration depths are desired. This research utilizes the ZnSe crystal for all ATR-FTIR

measurements.

Table 2-1. Several materials used for the ATR crystal.

KRS-5 2.35 20,000 to 250
Diamond 2.42 4,200 to 200
ZnSe 2.42 20,000 to 600
Si 3.42 8300 to 660
Ge 4.0 5500 to 600



After all variables of the ATR-FTIR setup have been determined then the IR spectrum of a

sample is measured. The signal obtained by the FTIR is an interferogram which is then Fourier

transformed into a spectrum. The FTIR spectrum is then analyzed by determining peak

positions, intensities, and full widths at half maximum (FWHM). Peak positions can be difficult

to determine if overlapping occurs but there is a mathematical technique that can be used to

determine the peak positions of overlapping bands. This technique calculates the second

derivative of the IR spectrum. The second derivative contains three features corresponding to

each adsorption peak. There are two upward peaks and one downward peak. The lowest point









of the downward peak corresponds exactly to the peak position in the original IR spectrum. The

second derivative analysis technique will be utilized in this dissertation for determination of the

peak positions of overlapping bands.

The IR spectrum can also be analyzed for quantitative analysis because the height or area

of a peak is directly proportional to the concentration of the molecule within the IR beam. If the

concentration of one component is desired to be known then several standards must be measured.

Then the concentration versus absorbance of the standards is plotted and a calibration curve is

calculated. The calibration curve is linear due to Beer' s law (discussed in Section 2.4).

However, the relative concentrations of two components in two or more spectra can be compared

without determining a calibration curve by utilizing another technique. Since the intensities of

the peaks in a spectrum are proportional to their concentration then the ratio of two peak

intensities is equal to the ratio of their concentrations. The ratio of the peak intensities of one

spectrum can be compared to the ratio of the same peaks in another spectrum in order to

determine the relative change in concentration of the components. The second method is useful

when the components do not follow Beer' s law due to interaction with other species.

ATR-FTIR is a powerful technique to measure the IR adsorption due to the total internal

reflection phenomenon. The phenomenon creates an evanescent wave which decays

exponentially with distance from the crystal. This property of the evanescent wave allows for

analysis of strongly absorbing samples. The ATR-FTIR technique also allows for in situ

measurements of a sample. Due to the advantages of this technique it has been chosen for

analysis of high solids loading slurries in this research.

2.4 Ultraviolet-Visible Spectroscopy (UV/VIS)

UV/VIS spectroscopy is a common technique used to make quantitative absorption

measurements in the UV/VIS spectral region. The technique requires ultraviolet and visible light









beams to pass through a reference and a sample. The light which is absorbed by the sample

promotes electronic transitions form a ground state to an excited state. Depending on the

characteristics of the sample, the energy of the light being absorbed is equal to the energy

required to excite the electron. The instrument then measures the intensity of the light passing

through the sample and compares it to the intensity of the light passing through the reference.

The ratio of the intensity of light passing through the sample to the intensity of light passing

through the reference is the percent transmittance, T. The absorbance, A, is then calculated

using equation 2-17.

A = -log(T) (2-17)

Utilizing the Beer-Lambert law (equation 2-18) provides the relationship of the concentration, c,

to absorbance

A = EXcxL (2-18)

where E is the wavelength-dependent molar absorptivity coefficient with units M1 cm-l and L is

the path length through the sample. A few limitations of the Beer-Lambert law must be noted for

accurate calculations. First, the concentration of the solute species must be below about 0.02 M

to prevent any electrostatic interactions between molecules. Second, readings at high absorbance

values are unreliable and changes in refractive index can occur with high concentrations.

Absorbance readings should be kept below 1.5. Third, solution must be homogenous during

measurement. Fourth, measurements can be erroneous if any suspended particles are in the

solution or if light from other sources enters the equipment.

The Beer-Lambert law is commonly utilized to derive a linear relationship between the

absorbance and concentration. This linear relationship is possible since E is a constant for a

material and L can be kept constant. In order to make a calibration curve, several absorbance










measurements of known concentrations must be performed. The data is then plotted on a

concentration versus absorbance graph and a linear fit is applied to the data. The linear fitted

line can then allow for determination of the unknown concentration with an absorbance

measurement.

2.5 Compression Rheology and Impedance Measurements

Two additional techniques were utilized in the analysis of high solids loading slurries but

they did not provide sufficient results. The data from both techniques did not contradict any of

the results discussed in this dissertation but further analysis of the data would require extensive

modeling and many assumptions; therefore, the following two techniques are briefly discussed in

this section but are not further included in this dissertation.

Compression theology is a technique which relates the volume fraction of a slurry to the

conformation of the dispersant. Kjeldsen et al. [78] utilized this technique to establish a

quantitative link between the molecular structure of superplascticizers and the compression

theology behavior of MgO suspensions. A centrifugal force is applied to a high solids loading

slurry until the consolidation of the slurry reaches steady state. A stress gradient develops in the

slurry which is balanced by the strength of the particle network. Determining the solids volume

fraction profile of the centrifuged sample in relation to the stress gradient gives information

about the strength of the particle networks. Next, a relationship of the solids volume fraction to

the conformation of the dispersant could be modeled but would require several assumptions.

Impedance measurements of high solids loading slurries were performed in order to

provide more insight into the water structure within a slurry. Since the impedance of water is

different than ice, then a change in the impedance of an aging slurry was expected since the

concentration of structured water increases with aging (Section 5.1). Data collected did not









contradict any results in this dissertation but would require extensive modeling in order to

separate the impedance contribution from the water, ions, and calcium carbonate particles.









CHAPTER 3
EXPERIMENTAL METHODS

3.1 Adsorption Isotherms

Slurries were prepared by mixing a dispersant with H20 in a beaker with a stir rod until the

dispersant was uniformly dissolved. Next, GCC was added slowly and mixed with the stir rod

and a spatula. The amount of dispersant was varied between experiments from 0. 1 wt% to

4 wt%/ of the GCC weight. After the GCC, NaPAA, and water have been mechanically stirred,

the samples are centrifuged for 45 minutes at 3,000 rpm in an Eppendorf Centrifuge 5810 using

the swing bucket rotor. After 45 minutes the samples were removed and the supernatant was

decanted into a beaker. Water was added to the supernatant and IM HCI was added until the pH

was two. The water was boiled out of the system and the remaining dispersant was dissolved

into deionized water. This step of changing the pH to 2 and evaporating off the water is

necessary because it removes any carbonate that might be in the system (carbonate will change

the results of the adsorption isotherms). Next, IM HCI was added until the pH was two again.

Finally, 0. 1M NaOH was added in 0.25ml increments and the pH was recorded. The data was

then analyzed and fit to adsorption isotherm models in Section 4-1.

3.2 Turbidity Measurements

The HACH 2100 turbidimeter was utilized to measure the turbidity of each sample

prepared. Sample preparation includes dissolving the dispersant into deionized water at the same

concentration as within a slurry. Next, several conditions are investigated by changing the

following parameters: monovalent salt concentration; divalent salt concentration; temperature;

time. Samples are poured into a glass vial. The outside wall of the glass vial is wiped with a

cloth and oil to decrease light scattering from any defects on the surface of the glass. The glass

vial is placed into the turbidimeter and the turbidity is recorded.









3.3 ATR-FTIR

The Thermo Electron Magna 760 FTIR Microscope was used for the ATR-FTIR

measurements. Samples were placed onto a ZnSe ATR crystal (figure 2-10). The IR spectra

were recorded from 650 cm-l to 4000 cm-l with 128 scans and a resolution of 2 cm- The

MCT/A liquid nitrogen cooled detector was utilized for measurements. A background spectrum

was taken before each measurement and the ATR correction was applied to each sample's FTIR

spectrum.

GCC slurry preparation included the following two steps: 1. Dissolve dispersant into H20

or D20. 2. Using a spatula and stir rod, slowly mix in the GCC powder. For slurries prepared in

D20 the dispersant as received was dried in a furnace at 150oC overnight before dissolving it into

D20. The slurries prepared with water structure makers or breakers were first prepared as

describe above with NaPAA. After the slurry is prepared then a structure maker or breaker

chemical is added to the slurry and mixed.

3.4 UV/VIS Spectroscopy

Slurries with probe molecules were prepared as described above for a slurry except one

extra step. The pH was changed to 9.9 by adding NaOH before mixing in the GCC. Controlling

the pH was to ensure that the amount of deprotonated carboxylate groups were the same as the

number of deprotonated carboxylate groups in a slurry containing NaPAA. The samples were

not disturbed for 24 hrs to allow for the adsorption of the probe molecules. After the allotted

time the samples were centrifuged at 3,000 rpm for 45 minutes. The supernatant was then

decanted into a beaker and diluted with a measured amount of water. The UV/VIS adsorption

intensities were measured at wavelengths of 210 nm and 224 nm for gallic acid and benzoic acid,

respectively, with the Beckman DU 640 spectrophotometer. Next, the measured intensities were

compared to a calibration curve and the amount of probe molecules in the supernatant was









determined. The amount of probe molecules adsorbed was calculated from subtracting the

measured amount in the supernatant from the amount in the slurry.

3.5E-05

3.3E-05
~4 y = 4E-05x
3.1E-05 -~ R == 0.9978


S21.9E-05

El2.7E-05






c 1.7E-05





1L.5E-05


0.50 0.60 0.70 0.80 0.90 1.00

Absorbance

Figure 3-1. Calibration curve for gallic acid. Absorption measurements preformed at a
wavelength of 210 nm with a sample thickness of 1 cm.

The calibration curves for both gallic acid and benzoic acid are given in figures 3-1 and

3-2, respectively. Each curve was determined by preparing several samples with known

concentrations of dissolved probe molecules in water and measuring their UV/VIS absorption

intensities. Earlier experiments had shown that the pH of the system did not affect the intensity

measurements.










1.1E-04

9.5E-05-

8.5E-05

7.5E-05





3.5E-05



2.5E-05




1.5E-05


y= 1E-04x
R2 = 0.9925


O
B

d
O


~I
c,

o
El


0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.8


Absorbance

Figure 3-2. Calibration curve for benzoic acid. Absorption measurements preformed at a
wavelength of 224 nm with a sample thickness of 1 cm.

3.5 Rheology

The modular compact rheometer Physica MCR 300 was the instrument used to measure

the theological properties of the slurries. Measurements were performed with the cup/cylinder

instrument setup. Each sample was pre-sheared to the maximum shear stress before recording

the data used for interpretation. The pre-shearing of the samples was necessary because the

viscosity depends on the history of the slurry just before the measurement data was obtained.


10









CHAPTER 4
SODIUM POLYACRYLATE ADSORPTION ONTO GCC IN HIGH SOLIDS LOADING
SLURRIES

4.1 Adsorption Isotherms

The depletion method is often the chosen technique in literature to measure the

concentration of a solute in order to calculate its adsorption isotherms. Adsorption isotherms

have been published for several dispersants and molecules onto calcium carbonate but all the

experiments have been completed in dilute systems [1, 5, 9, 16, 24, 31, 72, 79-84]. The

following adsorption isotherm experiments were performed with 75 wt% GCC solids loading

slurries.

Potentiometric titration was used to determine the amount of dispersant in the supernatant

after centrifugation. This technique is possible because the NaPAA dispersant contains

carboxylate groups which can be protonated or deprotonated depending on the pH (equation

4-1).

R-COOH + NaOH 4 R-COO- + Na+ + H20 (4-1)

First, the calibration curves for NaPAA had to be determined. This included dissolving a known

amount of dispersant into deionized water, decreasing pH to 2 with 1 M HC1, and then titrating

the sample with 0.1 M NaOH. The amount of NaOH added to the system was then plotted

against the pH of the system (figure 4-1 black curve). Next, the first derivative of the titration

line was taken and then the volume ofNaOH between the two peaks was calculated (figure 4-1

red curve). The volume of NaOH between the peaks is proportional to the amount of dispersant

in the water. This process was repeated for several different known amounts of dispersant. The

data was then plotted with volume of NaOH between peaks versus dispersant amount and a

linear fit was applied to the data (figure 4-2). With the calibration curves determined, the










-Titration
-Derivative








3,6








U 2 4 6 8 10 12 14 16
Volume (mL)

Figure 4-1. Titration curve of NaPAA. Black curve is the titration of a NaPAA in deionized
water. Red curve is the 1st derivative of the titration curve.

amount of dispersant in an unknown sample could be determined by measuring the volume of

NaOH that is needed to titrate the sample.

Adsorption isotherm data was measured from slurries of 75 wt% GCC containing 0. 1 wt%,

0.5 wt%, 1 wt%, 2 wt%, and 4 wt% NaPAA (weight percent of GCC weight). The offered

amount of NaPAA versus adsorbed amount of NaPAA was plotted in figure 4-3 with the 100%

adsorption line.

The adsorption isotherm data was then compared to three models. First, the data was

compared to the linear form of the Langmuir model which does not fit well with a R2 Value Of









0.4 y = 0.0232x
0.35-R2 = 0.9974




0.1 -

0.05 -.

0.2



Voum of0.M aO






Figure 4-2. Calibration curve for NaPAA with the titration technique.

0.82 (figure 4-4). The Langmuir model assumes monolayer adsorption with a surface which

consists of uniform adsorption sites. Second, the data was compared to the linear form of the

Temkin model which also had a poor fit with a R2 Of 0.85 (figure 4-5). Third, the data was

compared to the linear form of the Freundlich model which fits well with a R2 Of 0.96. Next, the

Freundlich constant, K, and Freundlich exponent, b, were calculated from the intercept and slope

of the linear Freundlich model (equation 4-2), respectively.

log(Q) = log(K) + b log(C) (4-2)

where Q is the adsorbed NaPAA per GCC (mg/g) and C is the unadsorbed NaPAA (mg/L). The

non linear Freundlich model (equation 4-3) was fitted with the Freundlich constant and exponent

(figure 4-6).

Q = KCb (4-3)













10 -


+ Experimental
100% aldsorption





0





0 5s 10 15

Offered NaPAA (mg/m2)

Figure 4-3. The adsorbed amount of NaPAA compared to the 100% adsorption line.

The Freundlich model assumes a non-linear relationship between the adsorbed amount and the

concentration of the solute in the liquid. This model represents adsorption with strong solute to

solute interaction. It also indicates that the solute is adsorbing onto a heterogeneous surface. In

agreement with these results, Balaz et al. [85] also demonstrated that adsorption on mineral

surfaces are best fit with the Freundlich model.

The 75 wt% GCC slurry system does not follow the Langmuir isotherm, which is a

common model to describe most adsorption processes, but displays the Freundlich isotherm.

There are several reasons why the system doesn't follow the Langmuir isotherm. First, the

Langmuir isotherm describes a system that is dilute in which the adsorbed molecules do not









y = 0.025x + 7220.4
1.6E+04 = 0.8187


1.2E+04-


8.0E+03-


4I.0E+03-


0.0E+00


0.0E+00


1.0E+-05


2.E+-05


3.0E+-05


C

Figure 4-4. Langmuir adsorption isotherm of NaPAA by GCC in a 75 wt% solids loading slurry.
This model is a poor fit with a R2 Value Of 0.8187.


y = 4.7726I 43.,59
Ri = 0.8529


2,5


20 -


15 -


10





0


10 11 12


In C

Figure 4-5. Temkin adsorption isotherm of NaPAA by GCC in a 75 wt% solids loading slurry.
This model is a poor fit with a R2 Value Of 0.8529.


















~+ *Experimental
Freundlich









0 50 100 150 200 250 300 350

Unadsorbed NaPAA (mg/ml)

Figure 4-6. Freundlich adsorption isotherm of NaPAA by GCC in a 75 wt% solids loading
slurry. Freundlich model fits well with a R2 Value Of 0.96.

interact. Second, it assumes a homogeneous surface. Third, it has a defined adsorption

maximum and assumes linear adsorption at concentrations far below the maximum. Many of

these assumptions do not fit the properties of a 75 wt% GCC slurry. The GCC slurry is a

concentrated system with calcium, carbonate, and sodium ions due to GCC's solubility in water

and the Na+ ions from the NaPAA. Furthermore, as will be demonstrated later, the chemical

interactions within a high solids loading slurry are different than a dilute system.

4.2 Turbidity of NaPAA

Adsorption isotherms indicated that the NaPAA is on the surface of the particles but they

do not distinguish between adsorption and precipitation of the dispersant. Therefore, turbidity

measurements of the dispersant at several conditions were necessary to determine if the NaPAA








400



Ci300


.t 200


1 00-




0. 1 1. 10


Na+ (M)

Figure 4-7. Turbidity of NaPAA in water with increasing monovalent salt concentration. High
concentrations of sodium ions within slurry do not cause the NaPAA to precipitate.

precipitates within a 75 wt% GCC solids loading slurry. First, the impact of the monovalent salt

NaCl on the turbidity was determined because the slurry system contains Na+ from the

dispersant. Samples were prepared with 2.04 g of NaPAA dissolved into 30 ml H20 and the

NaCl concentration was varied. Na+ concentrations started at 0.4 M (slurry conditions) and were

increased above 1 M. There was no increase in turbidity at all salt concentration which indicates

no precipitation (figure 4-7). Second, the impact of the divalent salt CaCl on the turbidity was

determined because the slurry system contains Ca2+ fTOm the CaCO3. The turbidities of the

samples containing concentrations of CaCl2 fr0m 10-4 M to 1.9 x 10-1 M were determined.

Within the processing conditions of the slurry, 10-3 M Ca2+ [20], there was not an increase in

turbidity (no indication of precipitation). When the concentration of CaCl2 WAS above slurry








400-



S300


.) 200



100




1 E-05 0.0001 0.001 0.01 0.1 1 10


Ca '(M)

Figure 4-8. Turbidity of NaPAA in water with increasing divalent salt concentration. Under
processing condition of GCC slurries there is no indication of NaPAA precipitation.
conditions at 1.9 x101 M there was an increase in turbidity and precipitation of the dispersant

(figure 4-8).

During slurry preparation in industry the slurry experiences thermal cycles which could

possible cause the NaPAA to precipitate; therefore, it was necessary to investigate the impact of

temperature on the turbidity of NaPAA. Samples were prepared by dissolving the NaPAA into

deionized water at room temperature. The temperature of the solution was increased up to 85oC

while taking turbidity measurements at 25oC, 40oC, 55oC, 70oC, and 85oC (figure 4-9). There

was no increase in turbidity with increase in temperature which indicates that within processing

temperature conditions there is no precipitation of the dispersant within the slurry.





















S0 2 0608 0






Temperature (C)

Figure 4-9. Turbidity of NaPAA in water with increasing temperature. NaPAA does not
precipitate with increasing temperature.
As a 75 wt% GCC slurry ages, several of its properties change with time. Turbidity

measurements of the NaPAA with respect to time were performed in order to determine if there

was precipitation of NaPAA with aging. Samples were prepared with NaPAA dissolved in water

with two concentrations of CaCl2: 10-3 M CaCl2 which represents the Ca2+ ion concentration in

slurry conditions and 10-1 M CaCl2 which represents an excess concentration of Ca2+ ions. Over

a three day period there was no impact on the turbidity of the 10-3 M CaCl2 (Slurry conditions)

which is an indication of no precipitation. On the third day of the 10-1 M CaCl2 Solution there

was precipitation on the bottom of the container but no increase in turbidity of the liquid (figure

4-10). On the fifth day of the 10-1 M CaCl2 there was precipitation on the bottom of the


400 -
























_ _


25


50


75


400 -

~ 300-



300 -





E-r 100 -


0


S10' M CaCl2
+ 103 M CaCl1,


Time (hrs)

Figure 4-10. Turbidity of NaPAA in water with 10-3 M CaCl2 and 10-1 M CaCl2 OVer a three day
period. At slurry conditions there was no precipitation of NaPAA.
container and the turbidity of the liquid increased. All of the turbidity measurements indicate

that within slurry conditions there is no precipitation of the dispersant.
4.3 ATR-FTIR
ATR-FTIR is a technique that allows for analysis of high solids loading slurries due to the

phenomenon of the evanescent wave described previously in Section 2.3. This technique was
utilized for analysis of the interactions of the carboxylate group, hydrocarbon groups, carbonates,
and the solvent at a variety of conditions.









4.3.1 Dry and Wet Samples

As mentioned before there are several techniques to analyze the GCC slurries but many of

them require either a dilute or dry sample. IR spectra of GCC slurries after drying do not

represent the chemical interactions that have taken place in the slurry. Figures 4-11, 4-12 and

4-13 compare the IR spectrum of a 75 wt% GCC slurry that had been dried and analyzed with

DRIFTS to the spectrum of a 75 wt% GCC slurry analyzed with ATR. Figure 4-11 demonstrates

that in the wet state the carbonate bending band at 1449 cm-l has a lower frequency shoulder that

is not present in the dry sample. This indicates that there are bicarbonate species and chemical

bonds in the slurry (discussed in Section 4.3.6) which are removed upon drying. In the wet state

-75wt% Slurry Dried DRIFTS
1.0- 75wt% Slurry ATR



0.8-









0.2-


0.0 .
1600 1500 1400 1300 1200

Wavenumber (cm-'

Figure 4-1 1. IR spectra of the carbonate bending bands located at 1449 cml of a wet and a dry
75 wt%/ GCC slurry. The wet slurry forms a shoulder at lower wavenumbers
indicating the presents of bicarbonate species.




















































1600 1580 1560
Wavenumber (cm-'


1540


Figure 4-13. Second derivative of the IR spectra of the carboxyl region for a wet and a dry
sample. Band at 1581 cm-l shifts to 1586 cml indicated change in coordination.


-75wt% Slurry Dried DRIFTS
-75wt% Slurry ATR
0.4-










S0.0



9 0 900 850 800
Wavenumber (cm-l

Figure 4-12. IR spectra of the carbonate stretching bands located at 875 cml of a wet and a dry
75 wt% GCC slurry. The wet slurry has a larger FWHM.

-75 wt% Slurry, ATR
-Dried Slurry, DRIFTS


0.0004


0.00








the carbonate stretching band at 875 cm-l has a larger FWHM than the dry state (figure 4-12)

indicating that some of the chemical interactions with the carbonate species in the wet slurry are

not present in the dry state. There is also a change in the antisymmetric stretching band of the

carboxylate group in NaPAA. Figure 4-13 is the second derivative of the IR spectra which

shows a shift in the band at 1581 cm-l in the wet state to 1586 cm-l in the dry state. The shift to a

higher wavenumber indicates that the adsorbed NaPAA in the dry state has unidentate

coordination (coordination of the carboxylate group is described in more detail in Section 4.3.5).

Analysis of the IR spectra demonstrates that the chemical interaction of a slurry are not

represented in a dry slurry; therefore, the best IR technique for this research is the ATR.


OH stretching -NaPAA in H20



0.8-
COO-
I I \stretching



CH
0.4. stretclung
blD I IOH
O bending



0.0-
4000 3500 3000 2500 2000 1500 1000

Wavenumber (cm )

Figure 4-14. IR spectrum of NaPAA in H20. The OH stretching band overlaps the CH
stretching bands of NaPAA. The OH bending band overlaps part of the COO- band.









OD
-tcin NaPAA in DO



0.8-





OD
r(0.4. bending
I I \COO-
~3e i Istretchning
c 0.2- CH
stretching


0.0-
4000 3500 3000 2500 2000 1500 1000

Wavenumber (cm )

Figure 4-15. IR spectrum of NaPAA in D20. Switching from H20 to D20 shifts the stretching
and bending bands so that there is no overlap with the CH or COO- stretching bands
of NaPAA.

4.3.2 Solvent Exchange

The stretching modes of OH in water extend over a range of 2900 cm-l to 3700 cm-l due to

hydrogen bonding in many different energy states. The bending modes of OH in water are

located at 2130 cm-l and 1638 cml as seen in figure 4-14. Also shown in figure 4-14 is the IR

spectrum of NaPAA in H20. As seen in the spectrum the stretching modes of water overlap the

CH stretching of the dispersant and the bending mode of water interferes with the shoulder of the

carboxylate group of the dispersant. In order to analyze these regions the water bands must be

removed without changing the slurry properties. This was accomplished by substituting D20









































CH


with H20. The OD stretching modes of heavy water are at lower wavenumbers, 2200 cm-l to

2700 cm- than the OH stretching modes of water (shown in figure 4-15). Also shown in figure

4-15 is the IR spectrum of NaPAA in D20. Within the spectrum the CH bending is visible and

there is no interference with the carboxylate band. The 75 wt% GCC slurry system was then

analyzed with the ATR-FTIR and its IR spectrum is shown in figure 4-16. The regions of focus

have been boxed and labeled which include the following: CH stretching, OD stretching,

carboxylate group, and the carbonate band.

75 wt% Slurry with D20




0.8-
[CO3]2-






0.4-

r 7COO


~VV-


0.0 CT3
4000 3500 3000 2500 2000 1500 1000

Wavenumber (cm )

Figure 4-16. IR spectrum of a 75 wt% GCC slurry with NaPAA. Regions of interests are boxed
and discussed.









4.3.3 Water Structure in High Solids Loading Slurries

A novel discovery was made upon analysis of the ATR-FTIR measurements of high solids

loading GCC slurries. This discovery demonstrated that the water structure within the high

solids loading slurries is dramatically different than bulk water. This novel discovery is

important because it demonstrates that research performed in dilute solutions does not represent

all the chemical interactions taking place in a high solids loading sample even though the

composition is the same. Figures 4-17 and 4-18 demonstrate that the stretching modes of H20

and D20 dramatically change. For H20 the IR band decreases its FWHM and the shoulder at

3183 cm-l shifts to a higher frequency at 3239 cm- A similar response with D20 and D20 in

-H20
1.0-I -_75wt"/o Slurry


0.8-









0.2-


0.0
3600 3400 3200 3000 2800

Wavenumber (cm-'

Figure 4-17. IR spectra of the OH stretching bands of H20 and H20 in a 75 wt% slurry. When
water is in a high solids loading slurry there is a change in the structure of the water
indicated with the FWHM decreasing and the 3183 cm-l shoulder peak shift to
3239 cml









a 75wt% GCC slurry is shown in figure 4-18. The IR band of D20 in a slurry decreases its

FWHM along with the 2379 cm-l shoulder shifting to 2410 cm-l and the 2492 cm-l shoulder

increasing intensity and shifting to 2502 cm- Nickolov et al. [86] refer to the lower frequency

shoulder as ice-like with stronger hydrogen bonding and the higher frequency shoulder as fluid-

like with weaker and distorted hydrogen bonds. The ice-like water structure has hydrogen bond

coordinations of four while the fluid-like water has hydrogen bond coordinations less than four.

The ice-like structure of both H20 and D20 in a slurry decreases along with an increase in the

fluid-like structure. This will be analyzed and discussed in more detail in chapter 5.

-D20
1.0 -I 75wt%/ Slurry


0.8-









0.2-


0.0 .
2800 2600 2400 2200
Wavenumber (cm-l

Figure 4-18. IR spectra of the OD stretching bands of D20 and D20 in a 75 wt% slurry. When
D20 is in a high solids loading slurry there is a change in the structure of the water
indicated with the FWHM decreasing and the 2502 cm-l shoulder increasing intensity.









4.3.4 NaPAA CH Band Infrared Spectra

The second band to focus on is the CH band of NaPAA located at 2947 cm-l when the

dispersant is dissolved into D20 (figure 4-19). This band is a result of the CH2 and CH

asymmetric stretching bonds within the NaPAA molecule. Focusing on the same region within a

75 wt% GCC slurry there is a decrease in the intensity of the 2947 cm-l band and two new bands

are formed, one at 2980 cm-l and the other at 2875 cm-l (figure 4-20). The appearance of two

new bands was an unexpected finding. The new bands located at 2980 cm-l and 2875 cml are

not present in the IR spectrum of D20 or the IR spectrum of GCC in D20; therefore, it is

concluded that the new bands arise from a shifting of the CH bands and/or an increase in the

symmetric stretching of the CH bands. When the NaPAA is dissolved in the solution the CH

stretching bonds are not restricted but when a carboxylate group adsorbs onto the surface of the

GCC the CH bonds near that carboxylate group are in close proximity to the surface. The close

proximity to the surface could restrict the stretching bonds and cause IR bands to shift. Schmidt

et al. [87, 88] discuss the shift in the IR for CH bands of polymer/water systems due to a change

in temperature with the largest shift being about 12 cml for a 200C temperature difference.

They also derive the theoretical frequency shifts for various numbers of water molecules in the

neighborhood of methyl groups demonstrating a wavenumber shift of ~60 cml for an increase

from 8 to 12 water molecules. They conclude that the hydrophobic interactions of the methyl

groups cause a shift of the CH stretching bands. Al-Hosney et al. [89] demonstrate a shift in the

CH band of 20 cml for wet versus dry conditions of HCOOH adsorbed onto calcium carbonate.

The change in the wavenumber from the 2947 cm-l band to the 2875 cm-l band is 72 cm- This

difference is equivalent to the band difference from the asymmetric to symmetric stretching of

CH2. So the appearance of the two new bands is explained to be a result of NaPAA adsorption

onto the surface of GCC.






















2947


0.00|gga
3100 3050 3000 2950 2900 2850 2800 2750 2700


WiTavenumber (cm-'


Figure 4-19. IR spectrum of the CH band of NaPAA in D20.




0.04 -O


0.03


0.02 -


0.01


2875


2980


2947


0.00 t
3100


305f0 30b00


2950 29b00 2850


28b00 2750 2700


Wavenumber (~cm )
Figure 4-20. IR spectrum of the CH bands of NaPAA in a 75 wt% GCC slurry. Two bands are
formed at 2980 cm-l and 2875 cm-l indicating adsorption of the NaPAA onto the
surface of GCC.









Further investigation of this phenomenon consisted of increasing the concentration of the

NaPAA in a 75 wt% GCC slurry. Figure 4-21 demonstrates that with one weight percent

NaPAA there is formation of two bands at 2980 cm-l and 2875 cm-l while the original band at

2947 cm-l decreases, indicating adsorption of NaPAA. With an increase of NaPAA exceeding

9 wt% the CH band at 2947 cml increases while the other bands remain constant in intensity.

Since the bands at 2980 cm-l and 2875 cm-l indicate adsorption and they do not increase in

intensity above 9 wt% NaPAA then the adsorption limit is between 1 wt% and 9 wt%. Utilizing

equations 2-18 and 2-17, N = 63 and I = 0.27 nm, the monolayer adsorption amount depending

on the NaPAA conformation would be between 2.14 mg/m2 and 4.28 mg/m2, TOSpectively.

746 wt%~ NaPAA
0.05 -37 wt%, NaPAA
---9 wt%~ NaPAA
I w to o NaPAA
-Only NaPAA and D20
0.04







C=0.01



0.00 .




3100 3050 3000 2950 2900 2850 2800 2750 2"00

Wav-enumber (cm L)

Figure 4-21. IR spectra of the CH bands of NaPAA in GCC slurries with increasing
concentration of NaPAA. Adsorption limit is between 1 wt% NaPAA and 9 wt%
NaPAA.








4.3.5 NaPAA Carboxylate Group Infrared Spectra
As mentioned in Section 2.2 the carboxylate group is known to adsorb on several different

surfaces and due to an increase in entropy it adsorbs onto calcium ions. The carboxylate group

ofNaPAA has a resonance form when dissolved in water. This is confirmed in the IR spectra

with the absence of the C=0 band which would be located around 1700 cm-l and the presence of

a COO- band at 1570 cml as seen in figure 4-22. When a 75 wt% GCC slurry is prepared there

is a change in the carboxyl band. Figure 4-23 shows that the 1570 cm-l stretching band is split


-NaPAA in D20
0.1~5










S0.05-






1750 1700 1650 1600 1550 1500

Wavenumber (cm )

Figure 4-22. IR spectrum of the carboxyl stretching region for NaPAA in D20. The IR
spectrum shows that NaPAA is in the ionic form with a peak at 1570 cml for the
COO- and no peak at 1700 cm-l for the C=0.








NaPAA in D20
-75 wt% GCC Slurry
0.0010-



-i 0.0005-



0.0000-

c~ bidentate

-0.0005-1 bridging



-0.0010-
unidentate oc

1600 1580 1560 1540 1520 1500

Wavenumber (cm )

Figure 4-23. Second derivative of the IR spectra of the carboxylate region of NaPAA in D20
and in a 75 wt% GCC slurry. NaPAA adsorbs onto GCC in unidentate, bridging, and
bidentate modes.

into a band at 1581 cm-l and 1567 cm-l along with a band forming at 1524 cm-l with a shoulder.

From the research of Lu et al. [36] and Young et al. [76] they have shown that each band

represents a different mode of interaction. The four possible modes of interaction are ionic,

unidentate, bidentate, and bridging (figure 2-8). Mielczarski et al. [61, 62] assigned the bands at

1575 cm-l and 1540 cm-l to unidentate and bidentate adsorption, respectively. Lu et al. [36]

demonstrate that the bands arise from three-dimensional precipitated calcium dicarboxylate salts

which can either be from the bulk solution or physisorbed at a surface. Therefore, in figure 4-23

the 1581 cm-l band is representative of unidentate coordination, the 1567 cm-l band represents








bridging coordination, and the bands between 1510 cm-l and 1545 cml represent bidentate
coordination with calcium.

Additional slurries with increasing concentrations of NaPAA were prepared and analyzed

with ATR-FTIR. IR spectra of 75 wt% GCC slurries containing 1 wt% and 10 wt% NaPAA are

compared to NaPAA in D20, see figure 4-24. Initially, the NaPAA in D20 shows one band at

1570 cm-l which represents the carboxylate group in the ionic coordination. Next, with the

I wt% NaPAA slurry there is a splitting of the 1570 cm-l stretching band as described above.
NaPAA in D20
-Slurry with 1 wt% NaPAA
0.00010. Slurry with 10 wt%~ NaPAA



-10.0005-



S0.0000-
r\ I bidentatee

-0.0005-



-0.0010.1\ / ~ bridging and
unidentate U ionic


1600 1580 1560 1540 1520 1500

Wavenumber (cm ')

Figure 4-24. Second derivative of the IR spectra of 75 wt% GCC slurries with increasing
concentration of dispersant. With an excess amount of dispersant there is no
unidentate adsorption mode.









The splitting of the band confirms that the adsorption of NaPAA in a 75 wt% GCC slurry is

through unidentate, bridging, and bidentate coordination states with calcium ions on calcium

carbonate. The slurry with 10 wt% NaPAA does not show any unidentate coordination,

indicated with the removal of the 1581 cm-l band, and there is a shift in the band peak at

1524 cm-l to 1515 cml representing bidentate coordination. Also, the band at 1566 cm-l which

represents bridging coordination may also include some NaPAA that has not adsorbed due to

overlap of the 1570 cml band from NaPAA in solution. The IR spectra demonstrate that as the

amount of dispersant increases in a 75 wt%/ solids loading slurry the coordination of the carboxyl

species changes with the removal of the unidentate coordination.

Similar to the results of Section 4.3.3 which showed a change in the water structure with

solids loading, there is a change in the carboxylate coordination at high solids loading. Slurry

samples were prepared with 10, 30, 50, and 70 wt% GCC. The spectra of the IR carboxyl region

are shown in figure 4-25. First, the band representative of the unidentate coordination in the

10 wt% GCC slurry at 1586 cm-l shifts to lower wavenumbers as the solids loading is increased,

eventually to 1578 cm-l in the 70 wt% GCC slurry. Similarly, the band representative of the

bridging coordination in the 10 wt% GCC slurry at 1567 cm-l shifts to lower wavenumbers until

it reaches 1560 cml in a 70 wt% GCC slurry. Also, as the solids loading increases the band

between 1510 cm-l and 1545 cm-l becomes a doublet with band peaks at 1539 cm-l and

1521 cm l, representing the bidentate coordination. As the solids loading increases, the

dispersant shifts towards the calcium bridging mode of adsorption indicated with the decrease in

the unidentate band position and an increase in the bidentate band position. The slight change in

band positions could possibly be due to increased interactions between dispersant molecules due

to their higher concentration in the solvent. This conclusion is important because it supports








-10 wt% Slurry
-30 wt% Slurry
-50 wt% Slurry
0.0008- -70 wt% Slurry



0.00041 unidentate bridging





-0.0004-





-0.0008-1 bidentate

1600 1580 1560 1540 1520
Wavenumber (cm ')

Figure 4-25. Second derivative of the IR spectra of the carboxylate region with increasing solids
loading. As the solids loading of the slurries increases there is a shift of the bands
toward a bridging mode.

previous data which demonstrate that the interactions within a low solids loading slurry is

different than in a high solids loading slurry.

During the first couple of days after a slurry has been prepared there is a change in several

of its properties as mentioned in the introduction. ATR-FTIR was utilized to determine if there

is any change in the interaction of the NaPAA with GCC during the aging process. A 75 wt%

GCC slurry was prepared and analyzed with the ATR-FTIR as it aged while it was less than an

hour old, 24 hours old, and 48 hours old. The IR spectra can be seen in figure 4-26. Initially, the

band representing the unidentate coordination is located at 1585 cm l. As the system ages the









band shifts to 1580 cm- This indicates that while the slurry ages there is a decrease in the

concentration of unidentate coordination of carboxylate groups and an increase in the bridging

and/or ionic coordination of the carboxylate groups. These results would support the idea that as

the system ages there is an increase in the amount of dissolved calcium ions which are then

available for bridging coordination, which require two calcium ions per carboxylate group,

instead of unidentate coordination, which only require one calcium ion per carboxylate group

(figure 2-8).

-75 wt% Slurry Fresh
-75 wt% Slurry Aged 24 hrs
0.0005 -75 wt% Slurry Aged 48 hrs








\increasing age







unidentate bign


1630 1580 1560 1540

Wavenumber (cm ')

Figure 4-26. Second derivative of the IR spectra of the carboxylate region with aging. The
unidentate band shifts from 1585 cm-l to 1580 cm-l with increasing age indicating a
shift towards the bridging mode.








4.3.6 Carbonate Infrared Spectra
The next bands to focus on are the carbonate bands from the GCC. This includes a

stretching band at 875 cm-l and a bending band at 1404 cm-l (figure 4-27) which is in agreement

with literature [90]. When GCC is introduced into a slurry the FWHM for the stretching band



1.0, carbonate ion
bending


0.8-

carbonate ion
0.6-11 stretch~ing


r 0.4-

O combination
c 0.2-
Sbands


Figure 4-27. ATR-FTIR spectrum of GCC.
increases. This is an indication that the carbonates are interacting with other species in the

system. Upon analysis of the carbonate bending band there is a dramatic change in the band (see

figure 4-28). The carbonate bending band at 1404 cm-l in figure 4-27 shifts to 1449 cml for a

75 wt% GCC slurry and the band also forms a low frequency shoulder. These spectra confirm

that the carbonate is interacting with other species in the system. The shoulder that forms on the


0.0-C
3000


2500 2000 1500 1000

Wavenumber (cm ')









-D20 and GCC
- 75wt% Slurry


S0.2~


Figure 4-28. IR spectra of carbonate band of GCC in D20 and in a 75 wt% GCC slurry.
Formation of a shoulder indicates formation of bicarbonates.

carbonate bending band indicates the formation of bicarbonates in the system [86, 91, 92]. Since

CaCO3 is slightly soluble in water then the spectra confirm the dissolution of CaCO3, adding

more ions to the system. These ions play an important role on the adsorption of NaPAA and the

water structure (discussed in Section 5.3). The FWHM and shape of the carbonate bending band

is also dependent on the solids loading. Up to 40 wt% the carbonate bending band is similar to a

mixture of D20 and GCC without NaPAA. Once the solids loading is raised above 40 wt% the

band forms a shoulder which shifts to lower wavenumbers as the solids loading is increased

(figure 4-29). This is another confirmation that high solids loading slurries have different

chemical interactions than dilute systems.


1600 1500 1400 1300 1200
Wavenumber (cm ')


1100









-75wt% Slurry
70wt% Slurry
60wt% Slurry
50wt% Slurry
40wt% Slurry
0.6- -~D20 and GCC


1 increasing solids

0 44









0.0-
1630 1500 1400 1300 1200 1100
Wavenumber (cm ')
Figure 4-29. IR spectra of the carbonate band of GCC slurries showing a formation of a shoulder
with increase solids loading.

There is also a noticeable change in slurry properties over a period of a few days;

therefore, a slurry of 75 wt% GCC in D20 was analyzed with ATR-FTIR over a three day

period. During the three days the carbonate band did not shift but the shoulder became less

pronounced, shifting to higher frequencies as time increased (figure 4-30). The shoulder shifting

over time is an indication of a decrease in the bicarbonate species and affects the water structure

within the slurry (more details in Section 6.2).

If ordering occurs in the system and we assume that the shoulder of the carbonate band is

an indication of this ordering then the shoulder should shift in response to thermal differences. A

slurry of 75 wt% GCC in H20 was prepared and separated into three samples. The first sample








75wt% Slurry Aged <1hr
-75wt% Slurry Aged 25hrs
75wt% Slurry Aged 51hrs

0.6 f-GCC and D20





0.4- mereasmg
age








1630 1500 1400 1300 1200 1100
Wavenumber (cm ')

Figure 4-30. IR spectra of the carbonate band of GCC in a 75 wt% slurry with aging.
was frozen, placed on the ATR crystal, and while it was melting an IR spectrum was measured.

The second sample was poured onto the ATR crystal at room temperature and the IR spectrum

was measured. The third sample was boiled, placed onto the ATR crystal, and the IR spectrum

was measured. These three spectra show that as the temperature decreases (less relative thermal

energy) there is a shift of the shoulder to a higher frequency (figure 4-31i). This supports the idea

that as the age of a slurry increases (shoulder shifts to higher frequencies) there is an increase in

the order of the system.









-Almost Boiling Temperature
Room Temperature Slurry
S-~00C Slurry

0.3-
1311

1319


d~ 0.2-










0.0
1630 1500 1400 1300 1200
Wavenumber (cm ')

Figure 4-31i. IR spectra of the carbonate band with a slurry at different temperatures. As the
temperature decreases the shoulder shifts from 1311 cm-l to 1335 cml

4.3.9 Temperature Dependence

In industry a high solids loading GCC slurry will experience several different thermal

environments while being processed. An experiment was designed to determine if thermal

variation of a slurry has an effect on the IR spectrum of the final slurry. Two 75 wt% GCC

slurries in D20 were prepared at room temperature. The temperature of one sample was raised to

85oC for 15 minutes and then cooled to room temperature before analyzing the sample with

ATR-FTIR. The spectra of both samples were the same except the shoulder of the carbonate

peak was shifted (figure 4-32).









75 wt% Slurry
1.0. -Previously heated
Slurry


0.8-





0.4-










4000 3500 3000 2500 2000 1 500 1000

Wavenumber (cm ')

Figure 4-32. IR spectra of a 75 wt% GCC slurry before and after a heating cycle. The only
difference of the two spectra is the carbonate band.

Also, the structure of the water within a slurry is dependant on the temperature of the

slurry. A 75 wt% GCC slurry was prepared and separated into two samples. The first sample

was analyzed at room temperature with the ATR-FTIR. The second sample was frozen, placed

onto the ZnSe ATR crystal and analyzed as it was melting. As expected, the shoulder at

2379 cml increased in intensity and the shoulder at 2502 cm-l decreased in intensity for the

melting sample which indicates more ice like structure (figure 4-33).

4.3.10 Addition of Energy to Aged Slurries

One technique used by industry to retard slurry aging while it is in storage includes

constant stirring of the slurries. So the effect on the water structure of adding energy to an aged









75 wt% Slurry Room Temperature
_ 7s w% twelting slurry


1.0


0.4-









2700 2600 2500 2400 2300 2200

Wavenumber (cm ')

Figure 4-33. IR spectra of the OD band in a 75 wt% GCC slurry at different temperatures.
Lower temperatures increase the concentration of structured water.

slurry was investigated. First, a 75 wt% slurry was aged for 5 days and then the IR spectrum was

measured. Second, a small amount of energy was added to the slurry with mechanical stirring

which represents the process in industry. As seen in figure 4-34, there is a decrease in the ice-

like structure, reversing the aging process. Third, the aging process is further reversed as more

energy is added to the system through sonication. A similar result is detected in the carbonate

band (figure 4-3 5). As energy is added to the system the shoulder on the carbonate band shifts to

lower frequencies which is the opposite of the aging process in figure 4-30. Even though the

water and carbonate bands are not fully restored to their fresh state, these results indicate that the

aging process includes an entropic component.










75wt% Slurry Aged
3 days
1.0 Same slurry hand
mixed
Same slurry hand
0.8- sonicated






S0.4-


C 0.2-


0.0 .
2800 2600 2400 2200

Wavenumber (cm-)

Figure 4-34. IR spectra of the OD band in an aged 75 wt% GCC slurry with addition of energy
to the system. Adding energy to the system partially restores the fluid like water
structure.


- 75wt% Slurry Aged
3 days
-Same slurry hand
mixed
-Same slurry
sonicated


0.8~



0.6~

0.





a 0.2~
c.



0.0'


1600 1500 1400 1300 1200 1100
Wavenumber (cm l)


Figure 4-35. IR spectra of the carbonate band in an aged 75 wt% GCC slurry with addition of
energy to the system. Adding energy to the system partially restores the carbonate
band to a fresh slurry.








4.4 Probe Molecules

Molecules which contain a carboxylate were chosen to probe the surface of GCC in high

solids loading slurries. The interaction of the probe molecules with the surface of GCC would

provide additional understanding of the interaction between NaPAA and GCC. Benzoic acid and

gallic acid were chosen because their concentrations in a solution could be measured with a
UV/VIS spectrometer. The benzene ring absorbs ultraviolet light causing the electrons transition

from ~n (bonding) to 2*" (anti-bonding).



1 -1i 1F 1 Carbon




120 ..- I Oxygen




C LHydrogen

120" 1.4 A









Figure 4-36. Molecular structure of benzoic acid.




















-1 4 03 4 0 .
Wegh eret C
Fiue43.Asrto fbnocai noG Ca ayn oislaig ezi cdde

no adobonoGC
4..1Bnzi Ai
Bezi cdwscoe sapoemlclebcuei otisabneern n
cabxyi acidgop(iue43) dsrto xeiet o bnocai noGCwr

seciicll perfre todmntaetecroy ru dopinado h yrpoi
adopino h eznern.Asrto fNaA sblee ob det h abxlt

grous inercigwtthcacu ios[,41136.Gfryeal[4goitdealecibn
ter copeaino abxltswt h ufceo act eurdfrasrto.Te
deemn htcroyae dobtruhceain ic thsbe eosrtdta






aiue4-7 dsorption codnton deendsi ondot CCa ayn solids loading, th dopino enzoic acid atiferen








Benzoic acid in D20
20 wt% GCC Slurry
57 wt% GCC Slurry
0.004-









~-0.004


COO-
-0.008
C=


1640 1620 1600 1580 1560 1540 1520
Wavenumber (cm ')

Figure 4-38. Second derivative of the IR spectra of benzoic acid in D20, 20 wt% GCC slurry,
and 57 wt% GCC slurry. The bands for the benzene ring and the carboxylate do not
shift, indicating no adsorption.

solids loading was investigated. Before any adsorption experiments were performed it was

determined that calcium benzoate would not precipitate in the slurry because the concentration of

calcium benzoate was below the precipitation limit of 2.72 g per 100 ml at 200C. Figure 4-37

demonstrates that benzoic acid does not adsorb onto GCC at any solids loading. Since figure

4-37 does not indicate any adsorption, then the ATR-FTIR will be utilized to confirm that the

carboxylate and the benzene ring are not interacting with the surface of the GCC before

centrifugation.









57 wt% GCC Slurry

0.03, -- Benzoic acid in D20












3050 30 95 90 280 20


Waeube c








abene f heC 0 badat100 cm5 .90 Figur 4-8dmntrtsta bnocaidde o



Fgr -9 setu t C ad benzoic acid in D20 does not shf or spliwhe GCC i de oteslto hc is an r
indicaton tato the carboxlates inocte asrinonteto o the G CC paricls. Another posibl


cnineation th at cola use and Csourptio disthrough hydophoicadsrtion withe h the benzene ringh






or the CH groups. The band for a benzene ring is located at 1596 cm-l and does not shift with

increasing solids loading so the benzoic acid is not adsorbing through benzene ring. Figure 4-39









indicates that the CH groups are interacting with the GCC, similar to NaPAA. The IR spectra

could be detecting a small amount of benzoic acid on the surface of the GCC which is within the

error of the adsorption measurements.

The results confirm each other and are in good agreement with Geffroy et al. [4] who

demonstrated that a molecule with one carboxylate group will not adsorb onto the surface of

GCC. Therefore, the next probe molecule chosen contained an OH group which will allow the

molecule to chelate with calcium.









;i* I r C Car1bon



1200 ~1 20~ ii 1.4A Oye







120 1.A








Figure 4-40. Molecular structure of gallic acid.












20

4 15 -





0C 204060

Wegh eret C

Fiue44.Asrto fgli cd noGCa ayn oislaig








adortinofgali ci otoGC neera iffret solds oadng slrisisdmntrtdi

figure 4-41. Teamstount of gallic acid adsorbed is deenaynt n h solids loading o h sur

andli decrse wihan icre ase wegh perben mof C.aculaton wrpeformeesm eao htbezi cd tos


dtrieteadsor be ooae ocnrtion of gallic acid n G i era feet o ids between sue 1.6 dmg/m2 aned



8.5 mg/m2. The range in adsorbed monolayer is due to the different modes of adsorption that the

gallic acid could accompany while adsorbing. Comparing the monolayer adsorption calculations

to figure 4-41 would suggest that the adsorbed amount of gallic acid at 10 wt% would contain 3








Gallic acid in D20
20 wt% Slurry

0.0008-







S-0.0008-



-0.0016-


bridging jbidentate
-0.0024-
1020 1600 1580 1560 1540 1520
Wavenumber (cm ')

Figure 4-42. Second derivative of the IR spectra of gallic acid in D20 and a 20 wt% GCC slurry.
The bands for the benzene ring and the carboxylate shift, indicating adsorption.

adsorbed layers, at 30 wt% would contain 2 adsorbed layers, and at 50 wt%/ and 60 wt% would

contain one monolayer with different modes of adsorption.

The addition of the hydroxyl groups allows for the molecule to chelate with the GCC

surface forming a seven-bond ring through one hydroxyl group, calcium ion, and carboxylate

group (similar results from Geffroy et al. [4]). A seven-member chelate ring is not as stable as a

five-member chelate ring but the chelating ability of gallic acid promotes adsorption unlike

benzoic acid which does have the ability to form a chelate with calcium. A possible adsorption

mechanism for NaPAA is to form an eight-member chelate ring but this is much less stable and

could be a reason why a slurry ages.









-67 wt% GCC Slurry
0.050. -Gallic acid in D20






0.0350




0.030


3~0050 30 90 20 80 20
Waeu be c
Figr4-3IRsetmofteCbadofgliacdiD2anina6wtGCslry
Fomto fnwbad niae ntrcino h C od ihGC









located at43 160 pcm u for the galc acdand D20 system ati an pH of 9.Whn a 20 wt% GCC lry


slgurry with gallicracids tanaye the abenzene band at15 mlshifts to 1594 c idcatin thnat the





benzene ring also plays a role in the adsorption. Figure 4-43 indicates that the CH groups are

interacting with the GCC, similar to NaPAA.








-20 wt% Slurry
67 wt% Slurry

0.0004-





0.00001 -1 bidentate


C- C

S-0.0004-


bridging

1 640 1620 1 600 1580 1560 1540 1520
Wavenumber (cm ')

Figure 4-44. Second derivative of the IR spectra of gallic acid in a 20 wt% and 67 wt% GCC
slurry. The bands for the benzene ring and the carboxylate shift, indicating change in
the coordination of the benzoic acid with increasing solids loading.

The IR spectra for gallic acid demonstrate that with increasing solids loading there is a

change in the adsorption of the gallic acid. Figure 4-44 shows a shift of the carboxylate band at

1547 cml for a 20 wt% GCC slurry to 1560 cml for a 67 wt% GCC slurry. Along with the

carboxylate shift there is a shift of the benzene band from 1594 cm-l to 1584 cml for a 20 wt%/

and 67 wt% slurry, respectively. These results are further conformation that as the solids loading

of a slurry increases the chemical interaction change within the system.









21.1A


) 10


1.5 A


O xygen



Hy'drIogen


1.3


120'


I


Figure 4-45. Molecular structure of propionic acid.


-70 wt% GCC Slurry
-Propionic acid in D20


0.045~


j



r(
1513
O
c;l


0.025~


3050 3000 2950 2900 2850 2800

Wavenumber (cm-'
Figure 4-46. IR spectrum of the CH bands of propionic acid in D20 and in a 70 wt% GCC
slurry. Formation of new bands indicates interaction of the CH bonds with GCC.


SCarlbon


0.040.


0.035~








4.4.3 Propionic Acid

Propionic acid was chosen as a probe molecule because it is similar in structure to the

monomer ofNaPAA (see figure 4-45 for propionic acid structure). Figure 4-46 indicates that the

CH groups are interacting with the GCC, similar to NaPAA. The carboxylate band from

propionic acid in D20 at a pH of 9.9 is located at 1552 cm l. When 14 wt% and 70 wt% GCC

slurries are prepared, the carboxylate bands do not shift (see figure 4-47). This demonstrates

again that the adsorption of a molecule onto the surface of GCC cannot occur through a single

carboxylate group but must include chelation of the molecule with calcium.

Propionic acid in D20
-14 wt% GCC Slurry
-70 wt% GCC Slurry
0.0002-



S0.0000-



S-0.0002-



-0.0004-



-0.0006-

1600 1580 1560 1540 1520
Wavenumber (cm-'

Figure 4-47. Second derivative of the IR spectra of propionic acid in D20, 14 wt% GCC slurry,
and a 70 wt% GCC slurry. No shift in the carboxylate band indicates that propionic
acid does not adsorb.









CHAPTER 5
WATER STRUCTURE DEPENDANCE ON SOLIDS LOADING AND AGING

5.1 ATR-FTIR Water Structure

A novel discovery shows that the water structure within a high solids loading slurry is

distinctly different than bulk water (first discussed in Section 4.3.3 and demonstrated in figures

4-17 and 4-18). When water is introduced into a high solids loading GCC slurry there is a

decrease in the structured water, this is indicated with a decrease in absorbance of the 2379 cml

OD stretching band. The structured water at 2379 cml is representative of water with a


0.8


-75wt% Slurry
70wt% Slurry
60wt% Slurry
- 50wt% Slurry
- 40wt% Slurry
- 30wt% Slurry
20wt% Slurry
- 10wt% Slurry
-D20 and GCC


*


0.2~


2800 2600 2400 2200

Wavenumber (cm-l

Figure 5-1. IR spectra of the OD stretching bands in GCC slurries ranging from 10 wt% to
75 wt%. As the solids loading increases there is an increase in the fluid structure
(2484 cm- ) and decrease in solid structure (2390 cm )~.













1 1.15 yr = 0.004x + 0.8687
~I e~tR2 = 0.91



;211 y = -0.0004 x + 1.0~605
c, R2 = 0.99







0 10 20 30 40 50 60 70 80

Weight Percent GCC

Figure 5-2. Fluid to solid water structure within different solids loading slurries. There are two
different regions, the first from 10 to 50 wt% and the second above 50 wt%.

hydrogen bond coordination of four while the fluid like water at 2484 cml is representative of

water with a hydrogen bond coordination less than four. In order to determine if this

phenomenon occurs only in 75 wt% slurries or if it also occurs at other solids loading, several

slurries were prepared ranging from 10 wt% to 75 wt%. The samples were analyzed with the

ATR-FTIR (figure 5-1) and the ratio of the fluid like band intensity (2484 cm- ) to the solid like

band intensity (2390 cm- ) was calculated for each spectrum. The ratios for each solids loading

are compared in figure 5-2. Initially, there is a change in the water structure when a slurry is

prepared at 10 wt% compared to only a GCC and D20 mixture. From 10 wt% up to 75 wt%

there are two distinct regions. The first region has a constant negative slope which indicates a

linear change in water structure up to 50 wt% solids loading. The second region has a positive








slope which indicates an increase in the fluid like water structure above 50 wt% solids loading.

The change in slope from region one to region two may be due to water confinement and/or ions

in the system which will be discussed in Sections 5.2 and 5.3.

75wt% Slurry Aged <1hr
-75wt% Slurry Aged 25hrs
75wt% Slurry Aged 51hrs
-GCC and D20

1 0.



I ~ mereasmg
0.6- age


S0.4-


0.2-


0.0 .
2800 2600 2400 2200

Wavenumber (cm ')

Figure 5-3. IR spectra of the OD band in a 75 wt% slurry with aging. Increasing age causes an
increase in the concentration of structured water in the slurry.

Aging of slurries is a common problem for industry as mentioned earlier. Investigation of

75 wt% GCC slurries with the ATR-FTIR over a period of several days demonstrated a novel

discovery indicating that the water structure within a high solids loading slurry changes with age

(figure 5-3). Increasing the age of a slurry increases the concentration of structured water

making the slurry more similar to bulk water. As seen in figure 5-4, the decrease in water

structure over a two day period leads to water structure that has a higher concentration of









1.2 1


S 1.0 5






0 20 4060010
Tim (rs
Fiur 5-.Fudt oi ae tutr ihna gn 5wGCsur.Tefudlk







5.2 Water l Conf emen




Ongue o.fli thposil resonsd thate sthue wIRsetra ho an inn 5 t crease in t he fluid likewae






structure is due to an increase in the confinement of water. Since water' s density is higher than

ice then when water molecules are confined within nanometers they behave like water [48, 77,

93-108]. Calculations were performed to determine the distance between calcite particles and

also the NaPAA. The following assumption were made in the calculations: the dispersant has a

radius of gyration of 2 nm to 4 nm [70], dispersant molecules do not adsorb onto calcite

particles, GCC particles have a diameter of 1 Clm, and FCC packing of both calcite particles and









1800
-- Rg of 2nm
S16 00
U -- Rg of 3nm
1400 1 Rg of 4nm

1200




..800





200



0 20 40 60 80

Weight Percent GCC

Figure 5-5. Calculations of the distance between GCC particles in different solids loading
slurries with NaPAA having a radius of gyration of 2 nm, 3 nm, and 4 nm.

dispersant. All of the assumption are not a completely accurate representation of the slurry

system but are necessary for estimating distances. The distance between GCC particles

decreases from 1610 nm to 128 nm with increasing solids loading from 10 wt% to 75 wt%,

respectively (figure5-5). These distances are too large to contribute to the confinement of water

according to literature. Figure 5-6 shows the calculations for the distances between NaPAA

molecules in the dispersing medium without GCC particles. As the solids loading is increased

from 10 wt% to 75 wt%/ the distance between NaPAA molecules changes from 19 nm to 1.5 nm,

respectively. At 75 wt% the confinement of water within 1.5 nm could contribute to the change

in water structure observed for high solids loading samples. Also, due to the Brownian motion









215
-* Rg of 2nm
-eRg of 3nm
p,20 -Rg of 4nm









0 0 0608
WegtPrcn C

Fiur 5-.CluainoftedsacbeweNaAmoeueindfeetsldlaig

slrre wihardu fgrto o m m n m
ofthe GC atce n aA iprattewtrhsls iebtencliin ofr
stutrdwtra h old odn sicesd
5. osa ae tutueMkr rBekr
As seodpsil esnta h Rsetaso nices ntefudlk ae





strucure is6 dalue toteions in the systnem.In arte kon toinerc wthwae molecules i fern od ladnd


formcue water asheth s aound them.n The ionces eite rmt rdeto aetcuedpnigi





the ion is a water structure maker or breaker [86, 95, 109-120]. The high solids loading slurry

systems have a high concentration of ions which include calcium, carbonate, bicarbonate,

sodium, carboxylates, and hydroxyls due to GCC's solubility and the addition of NaPAA. The








concentration of several of these ions is dependent on the solids loading and certain ion

concentrations have not been determined in high solids loading slurries. However, it is possible

to calculate the concentration of sodium ions and the concentration of carboxylate groups

because a known amount of NaPAA is added to the system. Calculations determine that a

75 wt%/ GCC slurry with 1 wt% NaPAA (weight percent of GCC weight) will contain a

concentration of 0.34 M of sodium ions which is extremely high. With such a high concentration

of sodium ions the NaPAA will be completely collapsed with a radius of gyration of 2 nm [70].

Additionally, the GCC is slightly soluble so there is dissolution and formation of calcium ions,

carbonate ions, and bicarbonate ions into the slurry system as indicated with the formation of a














9.4 -



9.2

0 2 4 6 8

Age (days)

Figure 5-7. Change of pH in an aging 75 wt% GCC slurry over a six day time span. A decrease
in pH is due to the concentration change of species in the slurry.








low frequency shoulder on the carbonate band (Higure 4-29). As the age of a slurry increases

there is a change in the concentration of ions in the system along with a change in the water

structure as shown before in Eigures 4-30 and 5-3, respectively. This change in the concentration

of ions in the system with time is also demonstrated with a decrease in the pH with aging (Higure

5-7).

1wt% NaPAA Slurry
-10 wt% NaPAA Slurry
1.0- 40 wt%/ NaPAA Slurry


0.8-






re0.4-


0.2-


0.0-
2700 2600 2500 2400 2300 2200

Wavenumber (cm ')

Figure 5-8. IR spectra of the OD band of a 75 wt% GCC slurry with increase NaPAA. There is
a decrease in the structured water indicating that NaPAA is a water structure breaker
in a GCC slurry.

NaPAA as a polyelectrolyte contains carboxylate groups which Raviv et al. [12, 77] have

shown to cause lubrication of the system due to formation of water sheaths around the

carboxylate groups. Raviv et al. explain that the water molecules which form the sheaths around










the ions are tightly bound to the carboxylate groups but can easily and readily exchange with

other water molecules from other water sheath with which they come in contact. The fluid like

properties of water molecules bound to NaPAA are also confirmed with ATR-FTIR

measurements in Figure 5-8. As the amount of NaPAA is increased within a 75 wt% GCC slurry

there is an increase in the fluid like to solid like water structure ratio. So NaPAA in a GCC

slurry acts as a water structure breaker.

Previously as discussed in Sections 4.3.3 and 5.1 the water structure is dependent on many

variables in the slurry system. As the variables are altered there is also a change in the

concentration and types of ions in the system. The ions in the system could be the reason for the

change in the structure of water due to their water structure making and breaking abilities. In the

following chapter the water structure making and breaking abilities of chemicals will be

analyzed in high solids loading slurries.









CHAPTER 6
WATER STRUCTURE MAKING AND BREAKING CHEMICALS

The previous results have demonstrated that water structure plays an important role in the

dispersion of a high solids loading slurry. Several chemicals which are known to be water

structure makers or breakers have been introduced into high solids loading slurries. The effect of

the chemicals on the slurry's physical properties and water structure are discussed.

6.1 Calcium Chloride

Calcium ions play an important role in the dispersion of GCC as discussed in chapter two.

GCC is slightly soluble in water; therefore, calcium ions are present in the solution and are free

to interact with the NaPAA, carbonates, and dispersing medium. Since calcium is known as a

water structure maker [37], then calcium chloride was introduced to a slurry in order to

determine if calcium ions will change the water structure. Figure 6-1 shows that addition of

0.1 M calcium chloride prevents the decrease in structured water which occurs when a slurry is

prepared. Since it was previously demonstrated in Section 5.1 that the concentration of

structured water increases with aging then the results from figure 6-1 would indicate that during

the aging of a slurry there is an increase in dissolved calcium.

Addition of CaCl2 to the slurry also changes the carbonate band. As seen in figure 6-2 the

slurry with CaCl2 has a carbonate bending band with a smaller FWHM. A similar result was

seen with the carbonate stretching band. This indicates that the excess amount of calcium ions in

the system prevents dissolution of the carbonate.

6.2 Sodium Bicarbonate

As demonstrated in Section 4.3.6 there is an increase in the carbonate species indicated by the

increase in the shoulder of the carbonate band. Since the slurry system contains carbonate ions

along with the sodium ions, which are introduced with the NaPAA, other species are also









-45wt% GCC slurry
-45wt% GCC Slurry with
0.1M CaCI2


0.2.


0.0 .
2800 2600 2400 2200
Wavenumber (cm-)

Figure 6-1. IR spectra of the OD band of slurries with and without CaCl2. Ca2+ as a water
structure maker prevents the increase in fluid like water of a GCC slurry.

-45wt% GCC slurry
0.8'1 45wt% GCC Slurry with
0.1M CaCl2
-50wt% GCC in D20




0.2-







0.0
1630 1500 1400 1300 1200 1100
Wavenumber (cm-l

Figure 6-2. IR spectra of the carbonate band of slurries with and without CaCl2. Ca2+ prevents
some of the interactions with the carbonate species.









present including sodium carbonate and/or sodium bicarbonate. Sodium carbonate is known as a

strong structure maker and sodium bicarbonate as a weak structure maker [86, 113, 114, 121].

Sodium bicarbonate was added to a 75 wt% slurry and the slurry was aged for 64 hrs. Figure 6-3

demonstrates that the OD shoulder at 2379 cml increases with aging which is similar to the

results for an aged slurry. The sodium bicarbonate as a water structure maker does not prevent

the change in water structure for an aging system.

Rheology measurements were performed for a slurry with and without sodium bicarbonate.

Figure 6-4 demonstrates addition of sodium bicarbonate increases the viscosity of the slurry.

75wt% Slurry with
1.0-IF Sodium Bicarbonate
75wt% Slurry with
Sodium Bicarbonate
0.8- Aged 64hrs



0.4-




S0.2-




0.0
2800 2600 2400 2200

Wavenumber (cm ')

Figure 6-3. IR spectra of the OD band of a 75 wt% GCC slurry with 0. 19 M sodium bicarbonate
with aging. As a weak structure maker, sodium bicarbonate allows for an increase in
the structured water with aging of a 75 wt% slurry.









5000
S75 wt% Slurry
4500
-75 wt% Slurry with 0.19M~
4000
Sodium ]Bicarbonate
3500



a4 2000

1r 500



1000

500


0 0.02 0.04 0.06 0.08 0.1


Shear rate (1/s)

Figure 6-4. Rheology of 75 wt% GCC slurries with and without sodium bicarbonate. Sodium
bicarbonate increases the viscosity.

Since there is an increase in the viscosity this indicates that the water structure making ability of

sodium bicarbonate could be a reason for the aging of a 75 wt% slurry.

6.3 Ethylene Glycol

Ethylene glycol is a common additive to water in order to decrease the freezing

temperature (structure shown in figure 6-5). It is also known as a water structure breaker and

each oxygen is known to be fully hydrated with ~2-3 water molecules [122-124]. Figure 6-6

shows the OD band for a 75 wt% GCC slurry containing 0.50 M of ethylene glycol. The water

structure within the slurry does not change with aging due to the addition of ethylene glycol.

Also, the addition of ethylene glycol prevents any changes in the carbonate band with aging as









120*


0. A


Oxy3gen


1.4 A


Figure 6-5. Structure of ethylene glycol.


-75wt% Slurry with
1.0 -Ethylene Glycol
-75wt% Slurry with
Ethylene Glycol
S0.8-1 Aged 64hrs


~40.6-





0.2-


0.0 .
2800 2600 2400 2200
Wavenumber (cm-'

Figure 6-6. IR spectra of the OD band of a 75 wt% GCC slurry with 0.5 M ethylene glycol with
aging. Ethylene glycol as a water structure breaker prevents structure water from
forming while the slurry ages.


C Carbon


Hyidrogen










-75wt% Slurry with
Ethylene Glycol
-75wt% Slurry with
Ethylene Glycol
Aged 64hrs


0.8~


S0.41



S0.2~


1600 1500 1400 1300 1200 1100

Wavenumber (cm ')

Figure 6-7. IR spectra of the carbonate band of slurries with and without ethylene glycol.
Ethylene glycol prevents interactions with the carbonate species as it ages.
shown in figure 6-7. The spectra confirm that addition of a water structure breaker prevents the

aging of the high solids loading system.

Additionally, the theological properties of the slurries were investigated. According to

literature when ethylene glycol is added to water the viscosity increases [125-130]. Upon

addition of 0.5M of ethylene glycol to the slurry system the max viscosity of the slurry decreased

475 Pa-s which is in the opposite direction of a water and ethylene glycol system. Also, the

decrease in the viscosity is greater than the decrease in viscosity due to addition of an equal

weight of water, demonstrated in Figure 6-8. Further, the viscosity of a 48 hour aged slurry with









800 -


75 w~t% Slurryr


700 1 H20 Added to Slurry

600 1 75 wt% Slurry with 0.5M
r_4 I iEthyvlene Glycol




20 so

1- 00

0 0 111




0 0.02 0.04 0.06 0.08 0.1

Shear rate (1/s)

Figure 6-8. Viscosity measurements of 75 wt%/ slurries with and without ethylene glycol.
Ethylene glycol decreases the viscosity more than adding an equal weight amount of
water to the slurry.

ethylene glycol is lower than an aged slurry without ethylene glycol. This is additional

confirmation that nonionic water structure breakers may prevent the aging of a slurry.

6.4 Propylene Glycol

Ethylene glycol is a toxic chemical; therefore, it is commonly substituted with propylene

glycol (see figure 6-9 for chemical structure) which behaves similar to ethylene glycol but is

environmentally safe. Figure 6-10 shows the OD bands of a 75 wt% GCC slurry containing

0.43 M of propylene glycol less than an hour after preparation and after 48 hours of aging.









0 9


C


Carbon


Oxygen



Hydrogen


Figure 6-9. Structure of propylene glycol.


-75 wt% Slurry with
Propylene Glycol
-75 wt% Slurry with
Propylene Glycol
Aged 48hrs


Figure 6-10. IR spectra of the OD band of a 75 wt% GCC slurry with 0.43 M ethylene glycol
with aging. Propylene glycol as a water structure breaker prevents structured water
from forming while the slurry ages.


2700 2600 2500 2400 2300 2200
Wavenumber (cm-'









800
S75 wt% Slurry

700
75 wt% Slurry with 0.4l3Mi

600- Propylene Glycoll


r40




2 00 -1


100






0 0.02 0.04 0.06 0.08 0.1

Shear rate (1/s)

Figure 6-11. Viscosity measurements of 75 wt% slurries with and without propylene glycol.
Propylene glycol decreases the viscosity at low shear rates but increases viscosity at
higher shear rates.

Propylene glycol shows similar results to ethylene glycol indicating no change in water structure

with aging.

Additionally, the theological properties of the slurries were investigated. Similar to

ethylene glycol the literature shows that addition of propylene glycol to water increases the

viscosity of water [131i]. Upon addition of 0.43 M of propylene glycol to a 75 wt%/ GCC slurry

the max viscosity of the slurry decreased 200 Pa-s (figure 6-11). Also, the viscosity of a 48 hour

aged slurry with propylene glycol is less than the viscosity of an aged slurry without propylene









glycol. Propylene glycol as a water structure breaker is additional confirmation that water

structure breakers prevent the aging of 75 wt% GCC solids loading slurries.









CHAPTER 7
SUMMARY AND DISCUSSION

The main obj ective of this dissertation was to determine the mechanism of adsorption for

NaPAA onto GCC in high solids loading slurries. An overview of literature provided some

insight into the behavior of calcium carbonate and NaPAA in water at dilute concentrations.

This was followed by several experiments utilizing adsorption isotherms, turbidity

measurements, probe molecules, and theology. The presented results focused on specific parts

of the NaPAA molecule, including the carboxylate and CH groups, and focused on the

carbonates from GCC. Also, the results in chapters 5 and 6 focus on the water structure within

high solids loading slurries. This chapter summarizes all the results in order to obtain a

comprehensible understanding of the adsorption of NaPAA onto GCC in high solids loading

slurries.

As mentioned in the literature review, calcium carbonate is slightly soluble in water and

the surface shows complex behavior due to the chemical equilibrium of the mineral/water

interface. Geffroy et al. [4] come to the conclusion that within a pH range of 8 toll the surface

of calcium carbonate in water consists mainly of neutral sites (-CaOH and -CO3H) and ionic

sites (-Ca' and -CO3-). Katz et al. [34] determine that the calcium ions form asymmetrical

coordination structures with water. From the literature review it is apparent that the surface of

calcium carbonate in water is heterogeneous, consisting of several different sites with different

charges and hydration states. This is in agreement with the adsorption isotherms performed in

this dissertation. The adsorption of NaPAA in 75 wt% GCC slurries follows the Freundlich

isotherm which is an indication of a heterogeneous surface. Also, several of the sites on the

GCC surface must compete with calcium and sodium ions in the solution for the adsorption of

NaPAA. The ions in solution can precipitate the dispersant and cause the dispersant to be









ineffective. Turbidity measurements of NaPAA in water with varying concentrations of sodium

and calcium ions indicate that NaPAA does not precipitate in slurry conditions. The turbidity

results are only an indication and not a true representation of a high solids loading GCC slurry

because the ionic condition of water in a high solids loading slurry may be different.

Results from the IR spectra of the carbonate band indicated that there is formation of

bicarbonates in 75 wt% GCC slurries. There is little change in the carbonate band up to 50 wt%

GCC but above 50 wt% GCC the band forms a shoulder which continues to extend to lower

wavenumbers as solids loading increases. The shoulder is an indication of bicarbonate formation

and these results demonstrates that a dilute system does not represent a high solids loading

system. Also, it was demonstrated that the IR spectrum of a dried 75 wt% GCC slurry does not

represent an IR spectrum of an aqueous slurry, minus the water, because the dried slurry does not

contain the bicarbonate bands. As a 75 wt% GCC slurry ages there is a shift of the bicarbonate

band to higher wavenumbers which is also accompanies with a decrease in the pH from 9.9 to

9.5. Knez et al. [19] mention that the activity of carbonate species (H2CO3 and HCO3 ) inCreaSCS

with rising pH and the activity of calcium ions decreases with rising in pH. This would be in

agreement with the IR spectra because there is a decrease in the band (decreasing carbonate

activity) with decreasing pH over time. This would also indicate that the activity of calcium ions

in the system increases with aging.

Further investigation of the CH groups of NaPAA would require a solvent exchange. The

OH stretching region of H20 overlaps the CH stretching region of NaPAA; therefore, D20 was

exchanged for H20 allowing for analysis of the CH bands. Surprising results were obtained from

the IR spectra indicating that the CH groups of NaPAA and the probe molecules were interacting

with the GCC. Previous literature has demonstrated that shifts in the CH band are possible due









to temperature changes [87, 88] and aqueous versus dry conditions [89] which were discussed

with more detail in Section 4.3.4. The following is a possible explanation for the interactions of

some CH bonds with the surface of GCC. As a carboxylate adsorbs onto the surface of GCC the

CH bond near the carboxylate is brought into proximity to the surface. The surface restricts the

bending and stretching modes of the CH bond causing a change in the IR spectra. As

demonstrated in figure 4-21 the CH bands indicate that the adsorption limit of NaPAA on GCC

is between 1 wt% and 9 wt%. Calculations of monolayer adsorption are between 2. 14 mg/m2

and 4.28 mg/m2 depending on the conformation of the polymer.

The carboxylate group of NaPAA interacts with cations and surfaces in four different

modes: ionic, bridging, bidentate, and unidentate. Analysis of the IR spectrum of a 75 wt% GCC

slurry demonstrated that the carboxylate groups interact in unidentate, bidentate, and bridging

modes. Probe molecules were utilized in order to determine if the carboxylate group was

directly responsible for the adsorption of NaPAA onto the surface of GCC. Analysis of the IR

spectra for benzoic acid, containing only one carboxylate group, demonstrated that the

carboxylate group does not adsorb at low or high solids loading. Adsorption measurements of

benzoic acid onto GCC support the IR results by indicating no adsorption. The next probe

molecule included propionic acid which also contains a single carboxylate group. Analysis of

the IR spectra also demonstrated no interaction of the carboxylate group with GCC. Finally,

gallic acid which contains a carboxylate group and three OH groups was used as a probe

molecule. Analysis of the IR spectra of the carboxylate group indicated interaction with the

GCC. Adsorption of gallic acid is also confirmed with adsorption measurements. The

interaction of gallic acid with the surface of GCC is possible because the molecule is able to

chelate with the surface through the carboxylate group and an OH group. NaPAA is also










expected to interact through chelation of the carboxylate groups. As discussed in Section 2.2,

literature supports these results with Geffroy et al. [4] and Dobson et al. [49] who also explain

that the adsorption of carboxylates is through chelation and that adsorption does not occur with

molecules which only contain one carboxylate group.

Further investigation of the adsorption of carboxylate groups onto calcium ions could

explain why a decrease in structured water is observed for a 75 wt% slurry compared to bulk

water, Section 4.3.3. There are two papers which could explain indirectly why a high solids

loading slurry demonstrates a change in water structure. One by Geffroy et al. [5] and another

by Sinn et al. [15] which discuss the exchange of calcium ions binding onto NaPAA as

endothermic. As discussed in Section 2.2, the implication of an endothermic binding means the

adsorption process is driven by an increase in entropy. The increase in entropy is believed to be

due to the release of water molecules from the dehydration of the calcium ion and carboxylate

ion. Since the calcium ion is a water structure maker, then dehydration of the ion will release the

structured water that was bound to it.

The water structure is also dependant on the solids loading of the system. Initially when a

10 wt% GCC slurry is prepared there is a decrease in the structured water. As the solids loading

increases to 50 wt% there is a small increase in the structured water. When the solids loading is

increased above 50 wt% and up to 75 wt% there is an increase in the fluid like water structure,

figure 5-2. Also accompanying the change in water structure is a change in the adsorption mode

of the carboxylate. As the solids loading of a slurry sample is increased, the carboxylates which

are adsorbing in a unidentate mode shift their adsorption toward a bridging mode. With the

bridging mode, one carboxylate group is interacting with two calcium ions instead of the

unidentate mode in which one carboxylate group interacts with one calcium ion. The water









structure change could be an indication of the mode of adsorption taking place for the

carboxylate groups.

The water within an aging 75 wt% GCC slurry increases in structured water. The change

could be due to the water structure making ions increasing in concentration over time. A change

in the pH with aging signifies the slurry is not in equilibrium and the concentration of calcium

ions in the system could be increasing over time. This would support the observed increase in

structured water because the calcium ion is a water structure maker. Also, with aging the

coordination mode of the carboxylate group shifts from a unidentate mode closer to a bridging

mode. The increase in calcium ions would provide more ions which are required for a bridging

mode.

Since the previous results indicate that the ions in the system and the water structure are

related to the aging of a system, several chemicals that are known to be water structure makers or

breakers were introduced into high solids loading slurries. Calcium chloride, a water structure

maker, prevented the formation of fluid like water, limited the interactions with the carbonate

species, and increased the viscosity. Sodium bicarbonate, a water structure maker, increased the

viscosity of the slurry by a factor of 8 at a shear rate of 0.01 s^l and did not prevent the increase

in structured water with aging of the slurry. Ethylene glycol, known as a water structure breaker,

decreased the viscosity by a factor of 3.5 at a shear rate of 0.01 s^l and prevented the change in

water structure with aging. Propylene glycol, known as a water structure breaker, also prevented

a change in the water structure but only decreased the viscosity by 1.4 at a shear rate of 0.01 s^l

and at high shear rates ethylene glycol increased the viscosity of the slurry. Results from the

water structure makers and breakers demonstrate that the slurry system's physical properties

depend on the water structure and ions in the system.









From the previous discussion, a model for the adsorption of NaPAA onto GCC is shown in

figure 7-1. Part A illustrates NaPAA in solution before adsorption onto GCC. Structured water

is shown on the surface of the GCC and surrounding the NaPAA. The driving force for the

dispersant to adsorb onto the surface has been determine to be an increase in entropy. The

increase in entropy comes from the dehydration of the carboxylate groups and the calcium ions

as they interact. Part B illustrates that when the dispersant adsorbs, its trains and the surface of

GCC release the structured water. Evidence of a decrease in structured water has been

demonstrated in the IR spectra and discussed.






A -i~




Surface




B



Surface


Structured water

-Dispersant

Figure 7-1. Adsorption of NaPAA onto GCC due to an increase in entropy with the release of
structured water. A) NaPAA in solution before adsorbing onto GCC surface, B)
NaPAA adsorption releases structured water from the carboxylate groups and the
calcium as demonstrated in the train of the polymer.









CHAPTER 8
CONCLUSIONS AND SUGGESTIONS

8.1 Conclusions

This dissertation is the first work to discuss the adsorption of NaPAA onto GCC in high

solids loading slurries. Previous published works have only focused on the analysis of dilute

systems. Several techniques were utilized to investigate slurries up to 75 wt% GCC including

turbidity measurements, adsorption isotherms, theology, and ATR-FTIR. ATR-FTIR was

extensively used because the phenomenon of the evanescent wave in the ATR-FTIR allows for

analysis of dense systems in situ. The following are several novel discoveries and conclusions

from this dissertation.

The chemical interactions and water structure within a dilute system do not represent high

solids loading slurries. The differences in the systems are demonstrated with the carboxylate

group, carbonate species, and the water structure. As the solids loading increases the carboxylate

groups adsorbed in a unidentate mode shift toward a bidentate mode of adsorption. Also, with

increasing solid loading there is formation of bicarbonates within the slurry. A novel discovery

demonstrates that there is a decrease in the concentration of structured water with the

combination of all three components of a slurry: NaPAA, water, and GCC. Increasing solids

loading above 50 wt% increases the fluid like water structure of the slurry. These results

demonstrate the changes which take place as solids loading is increase and are an important

consideration for research of high solids loading slurries.

Additionally, the water structure, carboxylate adsorption mode, and bicarbonate

interactions were demonstrated to change with aging of a slurry. The water increases in

concentration of structured water with aging. The carboxylate adsorption mode shifts from a

unidentate more to a bridging mode along with a decrease in the activity of the bicarbonate










species. With these results several water structure makers and breakers were shown to either

decrease slurry performance (water structure makers) or increase slurry performance (water

structure breakers). Ethylene glycol, a water structure breaker, demonstrated the best results for

improving the properties of a 75 wt% GCC slurry by preventing the water structure change with

age and decreasing the viscosity of the slurry.

Finally, a model for the adsorption of NaPAA onto GCC was proposed and discussed. The

chelating ability ofNaPAA allows for adsorption onto GCC. The adsorption is due to an

increase in entropy due to the release of water molecules from the dehydration of the interacting

carboxylate groups and calcium ions.

8.2 Suggestions

This dissertation has provided several insights into the adsorption of NaPAA onto GCC in

high solids loading slurries. By utilizing these insights a few suggestion are given to improve the

dispersion of high solids loading slurries. First, chapter 6 has already demonstrated that water

structure breaking chemicals could be introduced into a slurry system to improve the properties

slurry. This option would be useful if the dispersant must not be modified. Second, improved

anchoring of the dispersant could be accomplished by adding an OH group to the carbon

adj acent the carboxylate group on each repeat unit. Adding the OH group would allow for a

five-member chelate ring to form with calcium ion which is more stable than the eight-member

ring formed by NaPAA. Third, a water structure breaking chemical group could be added to the

alkyl chain of the dispersant. This would cause the polymer to act as both the water structure

breaker and dispersant.









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BIOGRAPHICAL SKETCH

Joshua Taylor was born in 1980 on October 19 in Santa Barbara, California. He lived in

California for 10 years, Ohio for 6 years, and then finished high school in Florida. He graduated

from Riverview High School in Sarasota, Florida in June of 1999. He then went to the

University of Florida and graduated in 2004 with a Bachelor of Science in chemical engineering.

In 2005, he graduated with a Master of Science in materials science and engineering at the

University of Florida. Joshua Taylor's life is dedicated to Yeshua HaMashiach. Out of love for

Yeshua, he lives a life that is within the standards of the Bible.





PAGE 1

1 ADSORPTION OF SODIUM POLYACRYLATE IN HIGH SOLIDS LOADING SLURRIES By JOSHUA JAMES TAYLOR A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2008

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2 2008 Joshua James Taylor

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3 To my Father and Mother, John and Dina Tayl or, who have been an encouragement throughout all my education.

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4 ACKNOWLEDGMENTS I would first like to thank m y advisor Dr. Wolfgang Sigmund for his guidance and support which has helped me through this project. I would also like to thank my committee members Dr. Ronald Baney, Dr. Laurie Gower, Dr. Hassan El-Shall, and Dr. Charles Martin for their intellectual discussions and advise. I would like to thank each person in Dr. Si gmunds group who have been a support for me and offered constructive comments during my res earch. I would especially like to thank YiYang Tsai who has offered countless advice and support throughout the last four years. Additionally, I would like to thank my friends and family who have always been there for support and encouragement. I especially thank my parents who have always encouraged me to further my education and have been a support during th e challenging times.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS...............................................................................................................4 LIST OF TABLES................................................................................................................. ..........7 LIST OF FIGURES.........................................................................................................................8 LIST OF ABBREVIATI ONS AND SYMBOL S.......................................................................... 14 ABSTRACT...................................................................................................................................16 CHAP TER 1 INTRODUCTION..................................................................................................................18 1.1 Calcium Carbonate Industry............................................................................................. 18 1.2 Sodium Polyacrylate (NaPAA)......................................................................................... 18 1.3 High Solids Loading Slurries............................................................................................ 19 1.4 Objectives and Approach..................................................................................................19 2 LITERATURE BACKGROUND A ND CHARACTERIZATION ....................................... 20 2.1 Calcium Carbonate...........................................................................................................20 2.2 NaPAA..............................................................................................................................26 2.3 Attenuated Total Reflectance Fourier Tr ansform Infrared Spectroscopy (ATRFTIR) ...................................................................................................................................33 2.4 Ultraviolet-Visible S pectroscopy (UV/VIS)..................................................................... 40 2.5 Compression Rheology and Impedance Measurements................................................... 42 3 EXPERIMENTAL METHODS.............................................................................................44 3.1 Adsorption Isotherms........................................................................................................44 3.2 Turbidity Measurements................................................................................................... 44 3.3 ATR-FTIR........................................................................................................................45 3.4 UV/VIS Spectroscopy...................................................................................................... 45 3.5 Rheology...........................................................................................................................47 4 SODIUM POLYACRYLATE ADSORPTION ONTO GCC IN HIGH SOLIDS LOADING SLURRIES .......................................................................................................... 48 4.1 Adsorption Isotherms........................................................................................................48 4.2 Turbidity of NaPAA.........................................................................................................53 4.3 ATR-FTIR........................................................................................................................57 4.3.1 Dry and Wet Samples............................................................................................. 58 4.3.2 Solvent Exchange................................................................................................... 61

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6 4.3.3 Water Structure in High Solids Loading Slurries ................................................... 63 4.3.4 NaPAA CH Band Infrared Spectra......................................................................... 65 4.3.5 NaPAA Carboxylate Group Infrared Spectra......................................................... 68 4.3.6 Carbonate Infrared Spectra..................................................................................... 74 4.3.9 Temperature Dependence.......................................................................................78 4.3.10 Addition of Energy to Aged Slurries....................................................................79 4.4 Probe Molecules...............................................................................................................82 4.4.1 Benzoic Acid..........................................................................................................83 4.4.2 Gallic Acid.............................................................................................................. 87 4.4.3 Propionic Acid........................................................................................................92 5 WATER STRUCTURE DEPENDANCE ON SOLIDS LOADING AND AGING .............. 93 5.1 ATR-FTIR Water Structure.............................................................................................. 93 5.2 Water Confinement.......................................................................................................... .96 5.3 Ions as Water Structur e Makers or Breakers .................................................................... 98 6 WATER STRUCTURE MAKING A ND BREAKING CHEM ICALS............................... 102 6.1 Calcium Chloride............................................................................................................102 6.2 Sodium Bicarbonate........................................................................................................ 102 6.3 Ethylene Glycol..............................................................................................................105 6.4 Propylene Glycol............................................................................................................108 7 SUMMARY AND DISCUSSION.......................................................................................112 8 CONCLUSIONS AND SUGGESTI ONS............................................................................118 8.1 Conclusions.....................................................................................................................118 8.2 Suggestions.....................................................................................................................119 LIST OF REFERENCES.............................................................................................................120 BIOGRAPHICAL SKETCH.......................................................................................................130

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7 LIST OF TABLES Table page 2-1 Several materials used f or the ATR crystal....................................................................... 39

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8 LIST OF FIGURES Figure page 2-1 Unit cell of calcium carbonate with space group cR 3. A) An angled top view, B) a side view with the dotted line th rough the middle being an edged.................................... 20 2-2 XRD of calcium carbonate powder used in this dissertation. A ll peaks confirm calcite structure but only th e high intensity peaks are labe led with Miller indices........... 21 2-3 Number, surface area, and volume distribu tion of GCC while dispersed with NaPAA in H2O as dilute samples....................................................................................................22 2-4 The SEM of GCC particles used in this dissertation. ........................................................ 23 2-5 Adsorption of polymer onto a surface. Po lym er is described as containing tails, loops, and trains.................................................................................................................27 2-6 Adsorption confirmations of a polymer. A) Pancake confirm ation has an absorbed layer thickness ~ segment length, B) Confirmation similar to polymer in good solvent give adsorbs with a layer thickness ~ Rg, C) Brush confirmation has an absorbed layer thickness greater than Rg...........................................................................29 2-7 Repeat unit of sodium polyacrylate, NaPAA..................................................................... 30 2-8 Coordination modes of a carboxylate group. ..................................................................... 31 2-9 IR scattering and adsorption in different IR techniques....................................................34 2-10 ATR-FTIR setup. Sample is placed onto a crystal. The IR b eam reflects several times through the crystal and the evanescent wave interacts at the interface with the sample................................................................................................................................35 2-11 At the interface of the crystal and sample the IR beam penetrates past the surface of the crystal and d ecays exponentially.................................................................................. 36 2-12 The electric field amplitude at the interf ace of th e crystal and sample. The electric field decays at an exponential rate in the sample. The depth of penetration, Dp, is determined when the electric field is a ttenuated to 36.8% of its total intensity................ 37 3-1 Calibration curve for gallic acid. Absorption m easurements preformed at a wavelength of 210 nm with a sample thickness of 1 cm................................................... 46 3-2 Calibration curve for benzoic acid. Absorption m easurements preformed at a wavelength of 224 nm with a sample thickness of 1 cm................................................... 47 4-1 Titration curve of NaPAA. Black curve is the titration of a NaPAA in deionized water. Red curve is the 1st derivative of the titration curve.............................................. 49

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9 4-2 Calibration curve for NaPAA with the titration technique. ............................................... 50 4-3 The adsorbed amount of NaPAA co mpared to the 100% adsorption line. ........................ 51 4-4 Langmuir adsorption isotherm of NaPAA by GCC in a 75 wt% solids loading slurry. This m odel is a poor fit with a R2 value of 0.8187............................................................52 4-5 Temkin adsorption isotherm of NaPAA by GCC in a 75 wt% solids loading slurry. This m odel is a poor fit with a R2 value of 0.8529............................................................52 4-6 Freundlich adsorption isotherm of NaPAA by GCC in a 75 wt% solids loading slurry. F reundlich model fits well with a R2 value of 0.96...............................................53 4-7 Turbidity of NaPAA in water with increasing monovalent salt concentration. High concentrations of sodium ions within slurry do not cause the NaPAA to precipitate. ...... 54 4-8 Turbidity of NaPAA in water with increas ing divalent salt concentration. Under processing condition of GCC slurries there is no indication of NaPAA precipitation...... 55 4-9 Turbidity of NaPAA in water with increasing temperature. NaPAA doe s not precipitate with incr easing temperature............................................................................. 56 4-10 Turbidity of NaPAA in water with 10-3M CaCl2 and 10-1M CaCl2 over a three day period. At slurry conditions th ere was no precipitation of NaPAA.................................. 57 4-11 IR spectra of the carbonate bending bands located at 1449 cm-1 of a wet and a dry 75 wt% GCC slurry. The wet slurry forms a shoulder at lower wavenumbers indicating the presents of bicarbonate species.................................................................................... 58 4-12 IR spectra of the carbonate st retching bands located at 875 cm-1 of a wet and a dry 75 wt% GCC slurry. The wet slurry has a larger FWHM.....................................................59 4-13 Second derivative of the IR spectra of the carboxyl region for a wet and a dry sam ple. Band at 1581 cm-1 shifts to 1586 cm-1 indicated change in coordination............ 59 4-14 IR spectrum of NaPAA in H2O. The OH stretching band overlaps the CH stretching bands of NaPAA. The OH bending band overlaps part of the COOband...................... 60 4-15 IR spectrum of NaPAA in D2O. Switching from H2O to D2O shifts the stretching and bending bands so that there is no overlap with the CH or COOstretching bands of NaPAA...........................................................................................................................61 4-16 IR spectrum of a 75 wt% GCC slurry with NaPAA. Regions of interests are boxed and discussed. ....................................................................................................................62 4-17 IR spectra of the OH stretching bands of H2O and H2O in a 75 wt% slurry. When water is in a high solids loading slurry there is a change in the structure of the water

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10 indicated with the FWHM decreasing and the 3183 cm-1 shoulder peak shift to 3239 cm-1...........................................................................................................................63 4-18 IR spectra of the OD stretching bands of D2O and D2O in a 75 wt% slurry. When D2O is in a high solids loading slurry there is a change in the structure of the water indicated with the FWHM decreasing and the 2502 cm-1 shoulder increasing intensity..............................................................................................................................64 4-19 IR spectrum of the CH band of NaPAA in D2O................................................................ 66 4-20 IR spectrum of the CH bands of NaPAA in a 75 wt% GCC slurry. Two bands are for med at 2980 cm-1 and 2875 cm-1 indicating adsorption of the NaPAA onto the surface of GCC................................................................................................................. .66 4-21 IR spectra of the CH bands of NaPAA in GCC slurries with in creasing concentration of NaPAA. Adsorption limit is be tween 1 wt% NaPAA and 9 wt% NaPAA..................67 4-22 IR spectrum of the carboxyl st retching region for NaPAA in D2O. The IR spectrum shows that NaPAA is in the ionic form with a peak at 1570 cm-1 for the COOand no peak at 1700 cm-1 for the C=O...........................................................................................68 4-23 Second derivative of the IR spectra of the carboxylate re gion of NaPAA in D2O and in a 75 wt% GCC slurry. NaPAA adsorbs onto GCC in unidentate, bridging, and bidentate modes................................................................................................................ .69 4-24 Second derivative of the IR spectra of 75 wt% GCC slurries with increasing concentration of dispersant. W ith an excess amount of dispersant there is no unidentate adsorption mode............................................................................................... 70 4-25 Second derivative of the IR spectra of the carboxylate region w ith increasing solids loading. As the solids loading of the slurri es increases there is a shift of the bands toward a bridging m ode.....................................................................................................72 4-26 Second derivative of the IR spectra of the carboxylate region with aging. The unidentate band shifts from 1585 cm-1 to 1580 cm-1 with increasing age indicating a shift towards the bridging mode........................................................................................ 73 4-27 ATR-FTIR spectrum of GCC............................................................................................ 74 4-28 IR spectra of carbonate band of GCC in D2O and in a 75 wt% GCC slurry. Formation of a shoulder indica tes formation of bicarbonates........................................... 75 4-29 IR spectra of the carbonate band of GCC slurries showing a for mation of a shoulder with increase solids loading............................................................................................... 76 4-30 IR spectra of the carbonate band of GCC in a 75 wt% slurry with aging.......................... 77

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11 4-31 IR spectra of the carbonate band with a slurry at different temperatures. As the tem perature decreases the s houlder shifts from 1311 cm-1 to 1335 cm-1...........................78 4-32 IR spectra of a 75 wt% GCC slurry befo re and after a heating cycle. The only difference of the two spectra is the carbonate band. ..........................................................79 4-33 IR spectra of the OD band in a 75 wt% GCC slurry at different tem peratures. Lower temperatures increase the concen tration of structured water.............................................80 4-34 IR spectra of the OD band in an aged 75 wt% GCC slurry with addition of energy to the system Adding energy to the system partially restores the fluid like water structure..............................................................................................................................81 4-35 IR spectra of the carbonate band in an aged 75 wt% GCC slurry with addition of energy to the system Adding energy to th e system partially restores the carbonate band to a fresh slurry..........................................................................................................81 4-36 Molecular structure of benzoic acid................................................................................... 82 4-37 Adsorption of benzoic acid onto GCC at varying solids loading. Benzoic acid does not adsorb onto GCC. ........................................................................................................83 4-38 Second derivative of the IR spectra of benzoic acid in D2O, 20 wt% GCC slurry, and 57 wt% GCC slurry. The bands for th e benzene ring and the carboxylate do not shift, indicating no adsorption............................................................................................84 4-39 IR spectrum of the CH ba nds of benzoic acid in D2O and in a 57 wt% GCC slurry. Formation of new bands indicates inte raction of the CH bonds with GCC....................... 85 4-40 Molecular structure of gallic acid...................................................................................... 86 4-41 Adsorption of gallic acid onto GCC at varying solids loading.......................................... 87 4-42 Second derivative of the IR spectra of gallic acid in D2O and a 20 wt% GCC slurry. The bands for the benzene ring and the car boxylate shift, indi cating adsorption.............. 88 4-43 IR spectrum of the CH bands of gallic acid in D2O and in a 67 wt% GCC slurry. Formation of new bands indicates inte raction of the CH bonds with GCC....................... 89 4-44 Second derivative of the IR spectra of gallic acid in a 20 wt% and 67 wt% GCC slurry. The bands for the benzene ring a nd the carboxylate shift, indicating change in the coordination of the benzoic ac id with increasing solids loading. ............................ 90 4-45 Molecular structur e of propionic acid. ...............................................................................91 4-46 IR spectrum of the CH bands of propionic acid in D2O and in a 70 wt% GCC slurry. Formation of new bands indicates inte raction of the CH bonds with GCC....................... 91

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12 4-47 Second derivative of the IR spectra of propionic acid in D2O, 14 wt% GCC slurry, and a 70 wt% GCC slurry. No shift in the carboxylate band indica tes that propionic acid does not adsorb........................................................................................................... 92 5-1 IR spectra of the OD stretching bands in GCC slurries ranging from 10 wt% to 75 wt%. As the solids loading increases th ere is an increase in the fluid structure (2484 cm-1) and decrease in solid structure (2390 cm-1).................................................... 93 5-2 Fluid to solid water struct ure within different solids lo ad ing slurries. There are two different regions, the first from 10 to 50 wt% and the second above 50 wt%................... 94 5-3 IR spectra of the OD band in a 75 wt% slurry with aging. In creasing age causes an increase in the concentration of structured water in the slurry. ......................................... 95 5-4 Fluid to solid water structure within an aging 75 wt% GCC slurry. The fluid like water structure decreases with aging becom i ng more like a slurry without dispersant..... 96 5-5 Calculations of the distance between GCC particles in dif ferent solids loading slurries with NaPAA having a radius of gyration of 2 nm, 3 nm, and 4 nm..................... 97 5-6 Calculations of the distance between Na PAA molecules in d ifferent solids loading slurries with a radius of gyrat ion of 2 nm, 3 nm, and 4 nm............................................... 98 5-7 Change of pH in an aging 75 wt% GCC slurry over a six day time span. A decrease in pH is due to the concentration change of species in the slurry. .....................................99 5-8 IR spectra of the OD band of a 75 wt% GCC slurry with increase NaPAA. There is a decrease in the structured water ind icating that NaPAA is a water structure breaker in a GCC slurry....................................................................................................................100 6-1 IR spectra of the OD band of slurries with and without CaCl2. Ca2+ as a water structure maker prevents the increase in fluid like water of a GCC slurry...................... 103 6-2 IR spectra of the carbonate band of slurries with and without CaCl2. Ca2+ prevents some of the interactions w ith the carbonate species........................................................ 103 6-3 IR spectra of the OD band of a 75 wt% GCC slurry with 0.19M sodium bicarbonate with aging. As a weak structure maker, s odium bicarbonate allows for an increase in the structured water with aging of a 75 wt% slurry......................................................... 104 6-4 Rheology of 75 wt% GCC slurries with and without sodium bicarbonate. Sodium bicarbonate increases the viscosity.................................................................................. 105 6-5 Structure of ethylene glycol............................................................................................. 106 6-6 IR spectra of the OD band of a 75 wt% G CC slurry with 0.5M ethylene glycol with aging. Ethylene glycol as a water structure breaker prevents structure water from forming while the slurry ages.......................................................................................... 106

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13 6-7 IR spectra of the carbonate band of slur ries with and without ethylene glycol. Ethylene glycol prevents in teractions with the carbonate species as it ages. .................. 107 6-8 Viscosity measurements of 75 wt% slur ries with and without ethylene glycol. Ethylene glycol decreases the viscosity m ore than adding an equal weight amount of water to the slurry............................................................................................................ 108 6-9 Structure of propylene glycol........................................................................................... 109 6-10 IR spectra of the OD band of a 75 wt% G CC slurry with 0.43M ethylene glycol with aging. Propylene glycol as a water structur e breaker prevents structured water from forming while the slurry ages.......................................................................................... 109 6-11 Viscosity measurements of 75 wt% slurries with and without propylene glycol. Propylene glycol decreases the viscosity at low shear rates but increases viscosity at higher shear rates. ............................................................................................................ 110 7-1 Adsorption of NaPAA onto GCC due to an in crease in entropy with the release of structured water. A) NaPAA in solution before adsorbing onto GCC surface, B) NaPAA adsorption releases structure wa ter from the carboxylate groups and the calcium as demonstrated in the train of the polymer....................................................... 117

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14 LIST OF ABBREVIAT IONS AND SYMBOL S A absorbance ATR attenuated total reflectance intramolecular expansion factor b Freundlich exponent C unadsorbed NaPAA (mg/L) c concentration of the absorbing species Dp depth of penetration DRIFTS diffuse reflectance infrared Fourier transform spectroscopy E electric field amplitude molar absorptivity coefficient FTIR Fourier transfor m infrared spectroscopy FWHM full width at half maximum GCC ground calcium carbonate IR infrared K Freundlich constant L the path length through the sample l effective segment length M molecular weight M0 segment molecular weight N number of segments n refractive index NaPAA sodium polyacrylate PCC precipitated calcium carbonate pi

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15 Q adsorbed NaPAA per GCC (mg/g) SEM scanning electron microscope T transmittance angle of incidence UV/VIS Ultraviolet-visible wavenumber W wavenumber XRD x-ray diffraction z distance from crystal surface

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16 Abstract of Dissertation Pres ented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy ADSORPTION OF SODIUM POLYACRYLATE IN HIGH SOLIDS LOADING SLURRIES By Joshua James Taylor August 2008 Chair: Wolfgang M. Sigmund Major: Materials Science and Engineering The world demand for calcium carbonate has been increasing by 7% per year since 2002 reaching a world capacity of 71.7 megatons in 2007. The demand continues to increase due to the diverse applications of calcium carbonate such as building materials, medicines, additives to food, filler for plastics and paper, and more. Ca lcium carbonate is often stored and transported by dispersing it into an aqueous medium with a polyelectrolyte to ach ieve up to 75 wt% solids loading. One of the most frequently applied dispersants for calcium carbonate is sodium polyacrylate (NaPAA). Higher solids loading of the calcium carbonate slu rries are desired to increase storage capacity and decrease transpor tation cost. In order to achieve higher solids loading slurries the science behind the adsorption of NaPAA onto the ca lcium carbonate within high solids loading slurries must be underst ood. Currently all research which has been performed on the adsorption of NaPAA onto calcium carbonate has been performed in dilute systems. The goal of this research is to understand the adsorption of NaPAA onto calcium carbonate in high solids loading slurries up to 75 wt% ground calcium carbonate (GCC). The adsorption of NaPAA onto calcium carbona te was investigated utilizing several techniques including adsorption isotherms, turbid ity measurements, attenuated total reflectance Fourier transform infrared sp ectroscopy (ATR-FTIR), and probe molecule adsorption. The

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17 adsorption of the NaPAA was determined to be due to the chelating ab ility of the carboxylate groups with calcium carbonate. The carboxylate groups were determined to adsorb through unidentate, bidentate, and bri dging modes. Also, the mode of adsorption of the carboxylate group was dependant on the solids loading and age of a slurry system. Furt her analysis revealed the CH groups of adsorbed NaPAA were inte racting with the surface of the GCC. Another novel discovery demonstrated that the water structure within a GCC slurry dispersed with NaPAA is dependant on solids load ing and age. With increasing solids loading there is a decrease in the concentration of structured water. Also, with an increase in age there is an increase in the concentration of structured water. Chemicals with the ability to either make or break water structure were introduced into 75 wt % solids loading slurries The water structure breakers demonstrated that their inclusion in the slurry decreased viscosity and prevented an increase in the structur ed water due to aging.

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18 CHAPTER 1 INTRODUCTION 1.1 Calcium Carbonate Industry The world capacity for ground calcium carbona te (GCC) reached 71.7 m egatons in 2007. The capacity has grown by 7% per year since 2002 and continues to increase world wide. GCC is diverse in its applications which include filler in plastics and paper, building materials, fertilizer, medicines, additive to foods, and mo re. The paper industry alone accounts for around 38% of the calcium carbonate demand. Transportation and storage of calcium carbonate as paper fillers are provided in either high solid s loading slurries (60-75 wt%) or as dewatered powder. Due to calcium carbonates increasing demand th ere has also been an increase in published research concerning calcium carbonate. Im proved understanding of calcium carbonate dispersion in aqueous systems has been desired in order to increase the efficiency of production and decrease costs. As will be discussed in ch apter 2, literature contains many papers concerned with dilute systems of calcium carbonate but lacks research on hi gh solids loading GCC slurries. 1.2 Sodium Polyacrylate (NaPAA) Polyacry lic acid and its salt sodium polyacrylat e (NaPAA) are one of the most frequently applied polyelectrolytes in industry and the household. A few examples include laundering processes, thickening agents, and dispersion of clay and calcium carbonate. NaPAA is used in the calcium carbonate industry as a dispersant fo r the mineral because the solids loading can be increased to 75 wt% while maintaining the desired viscosity. However, the complete role of stabilization and confirmation of NaPAA in disp ersing calcium carbonate at high solids content is not clear. Previous studies about the adsorp tion of NaPAA will be discussed in Section 2.2.

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19 1.3 High Solids Loading Slurries As m entioned above, GCC is dispersed with NaPAA to achieve high solids loading slurries (75 wt%). The calcium carbonate industry is constantly working to incr ease solids loading while maintaining desired slurry properties in order to decrease production costs. In order to achieve higher solids loading slurries th e science behind the adsorption of NaPAA onto the GCC within high solids loading slurries must be understood. Several published pape rs have studied the adsorption of NaPAA onto calcium carbonate but all of the research has been performed on dilute systems (less than 5 wt%) [1-15]. This is mainly due to the difficulties in measuring adsorption in high solids content. Therefore, there is a necess ity for understanding the interaction of dispersants with par ticles in high solids loading slurries. 1.4 Objectives and Approach This dissertation will focus on understanding the interaction of NaPAA, GCC, and water within slurries with solids loading up to 75 wt%. Therefore, this work has the following goals: Determine adsorption mechanism of NaPAA onto GCC in high solids loading slurries. Determine water structures relations hip to solids loading and aging. Propose new chemicals for improving GCC dispersion. There are several analysis techniques that will be utilized to accomplish the listed goals. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) will allow for determination of the chemical interaction from the chemical groups containing a dipole moment. ATR-FTIR is an excellent technique for high solids loading slurries and will be discussed in more detail in Section 2.3. Results from the IR spectra will be supplemented with adsorption isotherms and adsorption of probe molecules in high solids loading slurries. Additional data from viscosity measurements will aid in the understanding of high solids loading GCC slurries.

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20 CHAPTER 2 LITERATURE BACKGROUND AND C HARACTERIZATION 2.1 Calcium Carbonate Calcium carbonate is one of the most comm on and abundant mineral on earth and it has three different crystalline structures: vaterite aragonite, and calcite. Of the three crystal structures calcite is the most st able structure. Calcite has a tr igonal crystal system with space group cR 3, see figure 2-1. Calcite is used in i ndustry as either precipitated calcium carbonate (PCC) or ground calcium carbonate (GCC). Figure 2-1. Unit cell of cal cium carbonate with space group cR 3. A) An angled top view, B) a side view with the vert ical dotted line through th e middle being an edged.

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21 PCC is made by direct carbona tion of hydrated lime, known as the milk process. High purity calcium carbonate rock is crushed and h eated to form lime and carbon dioxide (equation 2-1). Next, the lime is added to water to fo rm calcium hydroxide (equa tion 2-2). Finally, the calcium hydroxide is combined with carbon dioxide and calciu m carbonate precipitates out (equation 2-3). CaCO3 + Heat CaO + CO2 (2-1) CaO + H2O Ca(OH)2 (2-2) Ca(OH)2 + CO2 CaCO3 + H2O (2-3) PCCs shape and size differ from GCC and allow it to be used in different applications. PCC has a narrower particle size distributi on and the particle shap e can be tailored for the application. During processing the moisture associ ated with PCC can cause problems. Figure 2-2. XRD of calcium carbonate powder used in this dissertation. All peaks confirm calcite structure but only th e high intensity peaks are labeled with Miller indices.

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22 GCC is removed from the ground and does not go through all the proc essing steps required for PCC; therefore, the particles shape and si ze distribution differ from PCC. GCC particles shapes are seen to be irregularly rhombohedral and the size distribution of GCC is wider than PCC. 0246 0 2 4 6 8 10 PercentDiameter (m) Number Surface Area Volume Figure 2-3. Number, surface area, and volume di stribution of GCC while dispersed with NaPAA in H2O as dilute samples. The GCC used in this research was provided by Imerys with a purity of greater than 99%. X-ray diffraction (XRD) was perfor med on the particles to determin e their structure (figure 2-2) using the XRD Philips APD 3720. Upon analysis of the diffraction pattern the GCC was confirmed to be calcite. As mentioned previously the size distribution of GCC is wide;

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23 therefore, particle size measurements were performed with the Cou lter LS13320 with a light diffraction technique at the Particle Engineering Research Center at the University of Florida. The size distribution is displayed with differe ntial number, surface area, and volume versus particles size in figure 2-3. The mean sizes for number, surface area, and volume are 0.13 m, 0.56 m, and 1.43 m, respectively. Ninety perc ent of the sample contains particles with diameters less than 0.22 m but 90 % of the volume of the GCC particles is provided by particles larger than 0.23 m. Figure 2-4. The SEM of GCC partic les used in this dissertation. For this research the most important meas urement for particles size is the surface area because adsorption of NaPAA occurs at the surface of the particles. The data demonstrates that

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24 90% of the surface area is provided by particle s with less than 1.35 m diameters. The size distribution of the particles is also demonstrated with a s canning electron microscope (SEM) image of the powder, figure 2-4. Also, the sp ecific surface ar ea is important for calculating adsorption isotherms; therefore, the Nova 1200 instrument in the Particles Engineering Research Center at the University of Florida was utiliz ed to measure the specific surface area of the GCC using the Brunauer-Emmett-Teller method. The sp ecific surface area was determined to be 5.36 m2/g which is within the rang e of published data [16-18]. Calcium carbonate is slightly soluble in water and shows a complex behavior which is due to the complex chemical equilibrium between th e mineral/water interface. The distribution of ionic species in the system is constantly changing while moving toward equilibrium. The following equations demonstrate th e possible ionic species that fo rm within a calcium carbonate and water system. CaCO3(s) Ca2+ + CO3 2(2-4) H2CO3 H+ + HCO3 (2-5) HCO3 H+ + CO3 2(2-6) Ca2+ + HCO3 CaHCO3 + (2-7) Ca2+ + OHCaOH+ (2-8) H+ + OHH2O (2-9) Knez et al. [19] discuss the chemical equilibrium of a calcium carbonate and water system in relation to pH in detail. They mention that high solution pH promotes the dissociation of carbonate species (H2CO3 and HCO3 -) and if the system is in equilibrium with atmospheric CO2 (GCC slurries are open to the atmosphere during processing) then the ac tivities of all carbonate species in the solution rise with pH. Since the system is constantly moving toward equilibrium

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25 then the Ca2+ activity must align it self accordingly and the activity of Ca2+ falls with rising pH. Finally, they conclude that the optimum stability conditions are in the pH range of about 9-11. Geoffroy et al. [4] also go into detail about the surface chemistry of calcium carbonate in water. They focus on the pH range from 8 to 11 which is important for this research since the pH of GCC slurries prepared in water with NaPAA have a pH of about 10. At pH lower than 8 the calcium carbonate dissolves while at pH higher than 11 the Ca(OH)2 precipitates. Geoffroy et al. describe the ionic surface sites of calcium carbonate as hydrated forms of Ca+ and CO3 -. Equations 2-10 and 2-11 show reactions of the CaOH surface sites but the pK of the reaction shown in equation 2-11 is far above the pH of 10. CaOH + H+ Ca(OH2)+ (2-10) CaOH + OHCaO+ H2O (2-11) Equations 2-12 and 2-13 show the reactions of the CO3H surface sites but the pK of the reaction shown in equation 2-13 is far below the pH of 10. CO3H + OHCO3(OH2)(2-12) CO3H + H+ CO3H2 + (2-13) Geoffroy et al. come to the conclusion that th e calcium carbonate surfac e sites within the pH range of 8 to 11 consist of main ly neutral sites (CaOH and CO3H) and ionic sites (Ca+ and CO3 -). Several other published papers have also discussed these equilibrium reactions which are present in a calcium carbona te and water system [20-27]. Several papers have been published whic h include zeta potential measurements of calcium carbonate in water [6, 16, 19, 23, 24, 26, 28-33]. The measurements of the surface charge of calcium carbonate are not consistent. Moulin et al. [ 23] have summarized the results of many researchers showing that the zeta potential measurements in calco-carbonic equilibrium

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26 conditions have been measured as positive, nega tive, and variable. The large variation of the sign of the zeta potential is due to the measur ement conditions and the na ture of the potential determining ions in the system. Authors cons idered the thermodynamic equilibrium within the liquid phase but did not consider the equilibrium at the gas-liquid interface. Moulin et al. take into consideration both equilibria when designing their experiment and come to the conclusion that the values of the zeta pot ential at the calcocarbonic equilibrium are canceled but is primarily negative on both sides of the equilibriu m. Finally, they determine that the potential determining ions in the system are not OHand H+ but are Ca2+ and HCO3 -. Another important aspect of calcium carbonate is the interaction of calcium ions with water. Published research has shown that ca lcium prefers to form six-, seven-, and eightcoordinate structures with water [34-37]. Katz et al. [34] found that th e coordination structures are asymmetrical when the calcium ions coordinate with water in an odd number such as five or seven. The coordination of calcium with water plays an important role in the adsorption and coordination of carboxylates as described in Section 2.2. 2.2 NaPAA Adsorption of polymers onto surfaces is commonly utilized to disperse particles. When particles with adsorbed polymers approach each other there is a repulsive entropic force due to the entropy of confining the polymers which is known as steric repu lsion. If the steric repulsion force is greater than the van der Waals attractive force then the pa rticles remain dispersed. The polymer may take on several different conformati ons within the solvent and while adsorbed onto the surface of the particles. Depending on the segment to segment interactions of a polymer in a solution, it may assume different conformations. If the segment to segment interactions of the polymer are weak then the polymer assumes a random coil shape. For a polymer with a random coil shape an

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27 important length scale is the root mean square ra dius which is known as the radius of gyration, Rg, as given by equation 2-14 660M M l Nl Rg (2-14) where l is the effective segment length, N is the number of segments, M is the molecular weight, and M0 is the segment molecular weight. Equation 2-14 is only valid as long as there are no repulsive, attractive, or excluded volume interacti ons between the segments of the polymer in the ideal solvent. Figure 2-5. Adsorption of polymer onto a surface. Polymer is described as containing tails, loops, and trains. In non-ideal solvents the effective size of the polym er can be smaller or larger than the radius of gyration and is referred to as the Flory radius, RF, given by equations 2-15 and 2-16 g FRR (2-15) 5 3ln FR (2-16) where is the intramolecular expansi on factor and is unity when the polymer is in an ideal

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28 solvent. will exceed unity when the polymer is di ssolved into a good solvent and the polymer swells and expands. If the polymer is in a poor solvent the segment to se gment interactions are strong and the polymer will collapse into a compact structure, is less than one. The adsorption of a polymer onto a surface is sh own in figure 2-5. The adsorbed part of the polymer is called a train a nd the non-adsorbed part of the polymer between two trains is called a loop. The part of the polymer that is not adsorbed and is only adjacent to one train is called a tail. Different conformations of the polymer on the surface contain varying concentrations of each segment. Figure 2-6 de monstrates that a polym er with a high train concentration adopts a pancake conformation. Th e layer thickness of a pancake conformation is about equal to its segment size. As the concentr ation of trains decreases the polymer reaches a point at which the layer thickness is similar to th e radius of gyration. At this point the surface area covered per molecule is approx imately described by equation 2-17. 2 22 1 NlRaSurfaceAreg (2-17) As the tail of the polymer extends further from the surface and increases length, the polymer adopts a brush conformation. Assuming the segment width is close to the segment length, l, the fully extended polymer has a projected ar ea approximately descri bed by equation 2-18. 2NlaSurfaceAre (2-18) With a good solvent the most important factor fo r controlling the conformation of an adsorbed polymer is the concentration of the polymer in the solvent. A low concentration will provide a pancake conformation while increasing the c oncentration eventually leads to a brush conformation. Polymers whose repeat unit contains an elec trolyte group are called polyelectrolytes. The conformations of polyelectrolyte s are similar to non-charged polym ers except the polyelectrolyte

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29 Figure 2-6. Adsorption confirma tions of a polymer. A) Pancake confirmation has an absorbed layer thickness ~ segment length, B) C onfirmation similar to a polymer in good solvent adsorbs with a layer thickness ~ Rg, C) Brush confirmation has an absorbed layer thickness greater than Rg.

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30 conformations are also dependant on salt concen tration. The charges on the polyelectrolyte cause the segments of the polymer to repel each other and give the polymer an extended conformation in salt free water [38, 39]. Addition of salt scre ens the charges on the polyelectrolyte and eventually will collapse th e polymer into a conformation similar to a noncharged polymer. Polyelectrolytes are often chosen for dispersion instead of non-charged polymers because the electrolyte group can be chos en to adsorb onto specific surface sites of a particle. This research has chosen a polyelectrolyte, NaPAA (molecular weight of 5,967 g/mol and a 2.04 degree of polydispersity), which is known to have a high affinity to calcium [1, 2, 411, 13-15, 40]. Figure 2-7. Repeat unit of sodium polyacrylate, NaPAA. NaPAA is one of the most commonly used dispersing agents in the papermaking applications [19]. NaPAA is composed of a long linear hydrocarbon backbone which contains one carboxyl group for each repeat unit, see figure 2-7. Several published papers have devoted their research to the in teraction of carboxyl group s and/or polyacrylates w ith surfaces and ions

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31 [12, 36, 40-74]. There are several papers that discuss the adsorption of polyacrylates onto calcium carbonate [1, 2, 4-15, 75]. A few of the key concepts and papers will be discussed. Figure 2-8. Coordination modes of a carboxylate group. The carboxylate group has been shown to interact with metal cations and surfaces in four different modes [4, 11, 36, 49, 59, 76], namely, ionic, bridging, bident ate, and unidentate as shown in figure 2-8. Several of the papers ha ve investigated the di fferent modes with IR spectroscopy because the change in bond symmetry can be detected. The ionic, bridging, and bidentate modes have similar group symmetry. The two oxygen atoms in the bidentate mode are interacting with one metal cation; therefore, there will be a change in the symmetrical and asymmetrical vibration frequencies. Since the unidentate mode has one oxygen atom coordinated with one metal cati on the symmetrical and asymmetrical vibration frequencies will be similar to a carboxylic acid group. Geffroy et al. [4] and Dobson et al. [49] have shown that ad sorption is preferred through chelation of dicarboxylates. A five member chel ate ring (consisting of the metal cation and two adjacent carboxylates) are the most stable follow ed by six and seven member chelate rings. Lu et al. [36] further explai ns that carboxylate groups inte ract with calcium ions in

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32 three-dimensional sevenor eight-fold coordination and it is common for calcium ions to coordinate with both carboxylate groups and water. Katz et al. [ 34] also demonstrate that both unidentate and bidentate coordi nation of carboxylate groups with calcium cations are possible when the calcium ions bind in se venand eight-fold coordination. Since calcium carbonate is slight ly soluble in water the dissociation of calcium ions play an important role on the conforma tion and shape of the NaPAA. Schweins et al. [13, 14, 71] have discussed the collapse of NaPAA by calcium ions in three of their papers. The bound Ca2+ ions to the NaPAA chains cause the NaPAA to become much more hydrophobi c. Also, all of the binding modes of the NaPAA with Ca2+ can allow for intramolecula r bridging which decreases the coil dimensions. The collapse of the NaPA A eventually leads to a spherical shape with different transitional shapes depending on the co ncentration of NaCl. Another interesting discovery by Schweins et al. is the expansi on of the NaPAA chains with an increase in Na+ ions. Ca2+ ions are strongly bound to the NaPAA but with increasing concentration of Na+ there is a competition between the Ca2+ ions and the Na+ ions. Two other papers of interest are written by Geffroy et al. [5] and Sinn et al. [15] who discuss the heat of exchange of Ca2+ binding onto NaPAA as endotherm ic. They discuss that the binding of Ca2+ to NaPAA can not be due to electrostatic forces (screened Coulomb potentials or counterion exchange) because this would lead to either an exothermic or energetically neutral process. Since the binding of Ca2+ ions to NaPAA is spontaneous then the free energy of binding must be negative. In order for the free energy to be negative this proce ss must be driven by an increase in entropy. The increa se in entropy is believed to be due to the release of water molecules. The total amount of released wate r molecules can be calcu lated by subtracting the rehydration of Na+ from the dehydration of Ca2+ and COO-. Sinn et al. [15] calculate that a

PAGE 33

33 minimal number of six water molecules is requ ired to counterbalance the endothermic binding heat. The process of Ca2+ binding with NaPAA easily releases at least six water molecules. Finally, two more papers are of particular interest for the ro le of NaPAA and ions in high solids loading slurries. Raviv et al. [12, 77] discuss in two of th eir papers the role of charged polymers and ions as providing lubrication to a system. The charged ion or carboxylate group form water sheaths around them that are tightly bound. When the water sheaths approach each other there is strong repulsion and the repulsive force can domina te the van der Waals attraction force. Because the water molecules are tight ly bound, removal of water molecules from the sheath require a large amount of energy but th e exchange of water molecules between two sheaths has a much lower energy barrier. This correlates to the NaPAA and ions acting as highly effective lubricants. 2.3 Attenuated Total Reflectance Fourier Tran sform Infrared Spectroscopy (ATR-FTIR) Infrared (IR) spectroscopy detects the vibra tional characteristics of chemical functional groups having a dipole moment. When an infrared light interacts with matter then the chemical bonds will stretch, contract, and bend. The chemi cal functional groups adsorb infrared radiation in specific wavenumber ranges which allows for determination of specific chemical functional groups within a sample. The band position and width of the band is an indication of the interaction of the functional group with its surrounding enviro nment. IR spectroscopy is a technique which has been used for analyzing the interaction between disp ersants and particles. There are several different IR spectroscopy techniques but the three most common include transmission, diffuse reflectance (DRIFTS), and attenuated total reflectance (ATR). All three techniques are able to provide data about the interface but ATR has an advantage over transmission and DRIFTS. The advantage of ATR can be seen in figure 2-9 which shows the IR radiation penetration of coated particles for transmission, DRIFTS, and ATR techniques.

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34 Figure 2-9. IR scattering and adso rption in different IR techniques. For both the transmission and DRIFTS techniques the IR radiation penetrates through the whole particle providing greater opportunity for the IR radiation to be absorbed. Also, in DRIFTS it is difficult to control the interaction of the IR radiation with the sa mple because the interaction is dependant on the particle size and sampling depth. Figure 2-9 demonstrates that the interaction of the IR radiation with a particle using the ATR technique only penetrates into a fraction of the particle allowing for an increase in the surface to bulk signal. The IR technique chosen for this research will be required to analyze slurries up to 75 wt% solids loading. Transmission IR sp ectroscopy requires a sample to be transparent. If too much of the signal is adsorbed while pa ssing through the sample then reli able data cannot be obtained. Due to the strong scattering of 75 wt% GCC sl urries, the transmission technique cannot be utilized. The sample preparation for the DRIFTS technique requires the sample to be dried and then mixed with KBr powder. The DRIFTS tec hnique could be used to analyze dried 75 wt% GCC slurries but the dried samples do not represen t the slurries which are discussed in Section 4.3.1. Finally, the ATR technique is ideal for obt aining spectra of liquids, semisolids, thin films, and solids. ATR allows for measurement of st rongly adsorbing samples of any thickness which

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35 is a limitation of the transmission technique Also, ATR does not require any sample preparation; the sample is placed directly onto the crystal. Figure 2-10. ATR-FTIR setup. Sample is placed onto a crystal. The IR beam reflects several times through the crystal and the evanescent wave interacts at the interface with the sample. Figure 2-10 demonstrates the ATR accessory that is mounted into the FTIR. A sample is placed onto the crystal. The IR radiation passes through the ATR crystal with several reflections until it exits the crystal and travel s to the detector. Each time the IR radiation undergoes total reflection at the crysta l surface next to the sample the e xponentially decaying evanescent wave interacts with the sample. An understanding of this phenomenon of total reflection at the interface of two mate rials is required for understanding the ATR-FTIR technique. There are two requirements for total internal re flection to occur (figure 2-11). First, the crystal must have a higher refr active index than the sample (n1 > n2). Second, the incident angle in the crystal must be greater than the critical angle ( > c). The critical angle is a function of the refractive indices as shown in equation 2-14 c = sin-1 n21 (2-14) where n21 = n2/ n1 = ratio of refractive indices of sample/crystal.

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36 Figure 2-11. At the interface of the crystal and sa mple the IR beam penetrates past the surface of the crystal and d ecays exponentially. As the IR radiation undergoes total reflection it penetrates a small distance beyond the crystal surface. The IR radiation which pene trates beyond the surface decays exponentially and is called an evanescent wave. Figure 2-12 shows the electric field amplitude of the evanescent wave as it passes from the crystal into the sample with refractive indices n1 and n2, respectively. The electric field amplitude d ecays exponentially with distance from the crystal surface as described by equation 2-15 E = Eo e-z/Dp (2-15) where E = electric field amplitude, z = distance from crystal surface, and Dp = depth of penetration. As the evanescent wave decays it also interacts with the sample which is brought into contact with the surface. Additional to the decay desc ribed with equation 2-15, the

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37 evanescent wave is attenuated by the samples absorbance which is why it is called attenuated total reflectance. Figure 2-12. The electric field amplitude at the interface of the crystal and sample. The electric field decays at an exponentia l rate in the sample. The depth of penetration, Dp, is determined when the electric field is a ttenuated to 36.8% of its total intensity. The depth at which the evanescent wave penetr ates the samples is known as the depth of penetration (Dp). The depth of penetration is defined as the depth at which the attenuation of the

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38 evanescent wave is 36.8% of its total intensity. The depth of penetra tion is described with equation 2-16 2/12 21 2 1) (sin2 1 n Wn Dp (2-16) where W = wavenumber. There are several observations of equation 2-16 that will be discussed. The depth of penetration is inversely proportiona l to the wavenumber. As the wavenumber increases there is a decrease in the Dp; therefore, the ATR spectra will show peaks that are more intense at low wavenumbers than at high wavenumbers. Because of this dependence on wavenumber it can be difficult to compare ATR spectra with library spectra containing tr ansmission or DRIFTS spectra. In order to avoid any problems, software packages have provided calculations that can be applied to the ATR spectra to remove the wavenumber dependence. The depth of penetration is a function of the a ngle of incidence. As the angle of incidence decreases the Dp increases. There are two possible ways to change the angle of incidence. First, the angle of the bevel on the ATR crystal could be changed. Second, it can be changed by changing the angle of the incoming radiation. Some ATR accessories provide the ability to change the angle of the mi rrors in order to change the angle of incidence. The depth of penetration is a function of re fractive index of the sample. The refractive index of many organic compounds is similar; th erefore, there is little change in the Dp of different organic samples and it is considered to be independent of refractive index. Quantitative analysis is possible with the ATR technique if th e refractive indices of samples are the same or similar. Equation 2-16 also demonstrates that the depth of penetration is a function of the refractive index of the ATR crystal. As the refractiv e index of the ATR crystal increases the Dp decreases.

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39 There are several different ATR crystals that can be utilized for measurements and some of the most common ones are listed in ta ble 2-1. Several different properties of the crystals must be considered when choosing the correct crystal for a system. The KRS-5 (trade name for thallium iodide/thallium bromide) crystal ha s a large range but is toxic and requires ha ndling with gloves. The KRS-5 has a low refractive index which give s high penetration dept hs but it is a soft material and can be easily scratch and bent. Di amond is not easily scratche d and is insoluble in water but is expensive. Zinc se lenide (ZnSe) is the most common ATR crystal material due to its wide range, insolubility in water, difficulty to scratch, and high depth of penetration. Finally, Silicon (Si) and germanium (Ge) are both difficult to scratch but are usually used when small penetration depths are desired. This research utilizes the ZnSe crystal for all ATR-FTIR measurements. Table 2-1. Several materials used for the ATR crystal. Z Refractive index (n) Range (cm-1) KRS-5 Diamond ZnSe Si Ge 2.35 2.42 2.42 3.42 4.0 20,000 to 250 4,200 to 200 20,000 to 600 8300 to 660 5500 to 600 After all variables of the ATR-FTIR setup have been determined then the IR spectrum of a sample is measured. The signal obtained by the FT IR is an interferogram which is then Fourier transformed into a spectrum. The FTIR spect rum is then analyzed by determining peak positions, intensities, and full widths at half maximum (FWHM). Peak positions can be difficult to determine if overlapping occurs but there is a mathematical technique that can be used to determine the peak positions of overlapping ba nds. This technique calculates the second derivative of the IR spectrum. The second deriva tive contains three fe atures corresponding to each adsorption peak. There are two upward peaks and one downward peak. The lowest point

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40 of the downward peak corresponds exactly to the p eak position in the origin al IR spectrum. The second derivative analysis technique will be utilized in this dissertation for determination of the peak positions of overlapping bands. The IR spectrum can also be analyzed for quan titative analysis because the height or area of a peak is directly proportional to the concentra tion of the molecule within the IR beam. If the concentration of one component is desired to be known then severa l standards must be measured. Then the concentration versus absorbance of the standards is plotted a nd a calibration curve is calculated. The calibration curve is linear du e to Beers law (discussed in Section 2.4). However, the relative concentratio ns of two components in two or more spectra can be compared without determining a calibration curve by utilizing another techni que. Since the intensities of the peaks in a spectrum are propor tional to their concentration then the ratio of two peak intensities is equal to the ratio of their concentr ations. The ratio of the peak intensities of one spectrum can be compared to the ratio of the same peaks in another spectrum in order to determine the relative change in concentration of the components. The second method is useful when the components do not follow Beers law due to interaction with other species. ATR-FTIR is a powerful technique to measure the IR adsorption due to the total internal reflection phenomenon. The phenomenon cr eates an evanescent wave which decays exponentially with distance from the crystal. Th is property of the evanescent wave allows for analysis of strongly absorbing samples. The ATR-FTIR technique also allows for in situ measurements of a sample. Due to the advantag es of this technique it has been chosen for analysis of high solids loading slurries in this research. 2.4 Ultraviolet-Visible Spectroscopy (UV/VIS) UV/VIS spectroscopy is a common technique used to make quantitative absorption measurements in the UV/VIS spectral region. The technique requires ultrav iolet and visible light

PAGE 41

41 beams to pass through a reference and a sample. The light which is absorbed by the sample promotes electronic transitions form a ground st ate to an excited state. Depending on the characteristics of the sample, the energy of th e light being absorbed is equal to the energy required to excite the electron. The instrument then measures the intensity of the light passing through the sample and compares it to the intens ity of the light passing through the reference. The ratio of the intensity of light passing thr ough the sample to the intensity of light passing through the reference is the percent transmittance, T. The absorbance, A, is then calculated using equation 2-17. )log( TA (2-17) Utilizing the Beer-Lambert law (equation 2-18) provi des the relationship of the concentration, c, to absorbance LcA (2-18) where is the wavelength-dependent molar absorptivity coefficient with units M-1 cm-1 and L is the path length through the sample. A few limitati ons of the Beer-Lambert law must be noted for accurate calculations. First, th e concentration of the solute species must be below about 0.02 M to prevent any electr ostatic interactions between molecules. Second, re adings at high absorbance values are unreliable and changes in refractive index can occur with high concentrations. Absorbance readings should be kept below 1.5. Third, solution must be homogenous during measurement. Fourth, measurements can be er roneous if any suspende d particles are in the solution or if light from other so urces enters the equipment. The Beer-Lambert law is commonly utilized to derive a linear re lationship between the absorbance and concentration. This linear relationship is possible since is a constant for a material and L can be kept constant. In orde r to make a calibration curve, several absorbance

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42 measurements of known concentrations must be performed. The data is then plotted on a concentration versus absorbance graph and a linear f it is applied to the data. The linear fitted line can then allow for determination of th e unknown concentration with an absorbance measurement. 2.5 Compression Rheology and Impedance Measurements Two additional techniques were utilized in the analysis of high solids loading slurries but they did not provide sufficient re sults. The data from both tec hniques did not contradict any of the results discussed in this dissertation but furt her analysis of the data would require extensive modeling and many assumptions; ther efore, the following two techniqu es are briefly discussed in this section but are not further included in this dissertation. Compression rheology is a technique which rela tes the volume fraction of a slurry to the conformation of the dispersant. Kjeldsen et al [78] utilized this technique to establish a quantitative link between the molecular structur e of superplascticizers and the compression rheology behavior of MgO suspensions. A centrif ugal force is applied to a high solids loading slurry until the consolidation of the slurry reaches steady state. A stress gradient develops in the slurry which is balanced by the strength of the particle network. Dete rmining the solids volume fraction profile of the centrifuged sample in relation to the stress gradient gives information about the strength of the particle networks. Next, a relationship of the solids volume fraction to the conformation of the dispersant could be modeled but would requir e several assumptions. Impedance measurements of high solids loadi ng slurries were performed in order to provide more insight into the water structure with in a slurry. Since the impedance of water is different than ice, then a change in the impeda nce of an aging slurry was expected since the concentration of structured water increases with aging (Section 5.1). Data collected did not

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43 contradict any results in this dissertation but would require extensive modeling in order to separate the impedance contribu tion from the water, ions, and calcium carbonate particles.

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44 CHAPTER 3 EXPERIMENTAL METHODS 3.1 Adsorption Isotherms Slurries were prepared by mixing a dispersant with H2O in a beaker with a stir rod until the dispersant was uniformly dissolved. Next, GCC was added slowly and mixed with the stir rod and a spatula. The amount of dispersant wa s varied between experiments from 0.1 wt% to 4 wt% of the GCC weight. After the GCC, NaPAA, and water have been mechanically stirred, the samples are centrifuged for 45 minutes at 3, 000 rpm in an Eppendorf Centrifuge 5810 using the swing bucket rotor. Afte r 45 minutes the samples were removed and the supernatant was decanted into a beaker. Water was added to th e supernatant and 1M HCl was added until the pH was two. The water was boiled out of the syst em and the remaining dispersant was dissolved into deionized water. This step of changing the pH to 2 and evaporating off the water is necessary because it removes any carbonate that might be in the system (carbonate will change the results of the adsorption isotherms). Next, 1M HCl was added until the pH was two again. Finally, 0.1M NaOH was added in 0.25ml incremen ts and the pH was recorded. The data was then analyzed and fit to adsorption isotherm models in Section 4-1. 3.2 Turbidity Measurements The HACH 2100 turbidimeter was utilized to measure the turbidity of each sample prepared. Sample preparation includes dissolving the dispersant into deionized water at the same concentration as within a slurry. Next, several conditions are invest igated by changing the following parameters: monovalent sa lt concentration; divalent salt concentration; temperature; time. Samples are poured into a glass vial. The outside wall of the glass vial is wiped with a cloth and oil to decrease light scattering from an y defects on the surface of the glass. The glass vial is placed into the turbidimeter and the turbidity is recorded.

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45 3.3 ATR-FTIR The Thermo Electron Magna 760 FTIR Microscope was used for the ATR-FTIR measurements. Samples were placed onto a ZnSe ATR crystal (figure 2-10). The IR spectra were recorded from 650 cm-1 to 4000 cm-1 with 128 scans and a resolution of 2 cm-1. The MCT/A liquid nitrogen cooled detector was uti lized for measurements. A background spectrum was taken before each measurement and the ATR correction was applied to each samples FTIR spectrum. GCC slurry preparation included the following two steps: 1. Dissolve dispersant into H2O or D2O. 2. Using a spatula and stir rod, slowly mi x in the GCC powder. For slurries prepared in D2O the dispersant as received was dried in a furnace at 150C overnight before dissolving it into D2O. The slurries prepared with water structure makers or breakers were first prepared as describe above with NaPAA. After the slurry is prepared then a structure maker or breaker chemical is added to the slurry and mixed. 3.4 UV/VIS Spectroscopy Slurries with probe molecules were prepared as described above for a slurry except one extra step. The pH was changed to 9.9 by adding NaOH before mixing in the GCC. Controlling the pH was to ensure that the amount of depr otonated carboxylate groups were the same as the number of deprotonated carboxylat e groups in a slurry containing NaPAA. The samples were not disturbed for 24 hrs to allow for the adsorpti on of the probe molecules. After the allotted time the samples were centrifuged at 3,000 rpm for 45 minutes. The supernatant was then decanted into a beaker and diluted with a meas ured amount of water. The UV/VIS adsorption intensities were measured at wavelengths of 210 nm and 224 nm for gallic acid and benzoic acid, respectively, with the Beckman DU 640 spectrophotometer. Next, the measured intensities were compared to a calibration curve and the amount of probe mol ecules in the supernatant was

PAGE 46

46 determined. The amount of probe molecules ad sorbed was calculated from subtracting the measured amount in the supernatan t from the amount in the slurry. Figure 3-1. Calibration curve for gallic acid Absorption measurements preformed at a wavelength of 210 nm with a sample thickness of 1 cm. The calibration curves for both gallic acid and benzoic acid ar e given in figures 3-1 and 3-2, respectively. Each curve was determin ed by preparing severa l samples with known concentrations of dissolved probe molecules in water and measuring their UV/VIS absorption intensities. Earlier experiments had shown that th e pH of the system did not affect the intensity measurements.

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47 Figure 3-2. Calibration curve for benzoic acid. Absorption measurements preformed at a wavelength of 224 nm with a sample thickness of 1 cm. 3.5 Rheology The modular compact rheometer Physica MCR 300 was the instrument used to measure the rheological properties of the slurries. Me asurements were performed with the cup/cylinder instrument setup. Each sample was pre-sheared to the maximum shear stress before recording the data used for interpretation. The pre-shearing of the samples was necessary because the viscosity depends on the history of the slurry just before the measurement data was obtained.

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48 CHAPTER 4 SODIUM POLYACRYLATE ADSORPTION ONTO GC C IN HIGH SOLIDS LOADING SLURRIES 4.1 Adsorption Isotherms The depletion method is ofte n the chosen technique in literature to measure the concentration of a solute in order to calculat e its adsorption isotherms. Adsorption isotherms have been published for several dispersants and molecules onto calcium carbonate but all the experiments have been completed in dilute sy stems [1, 5, 9, 16, 24, 31, 72, 79-84]. The following adsorption isotherm experiments were performed with 75 wt% GCC solids loading slurries. Potentiometric titration was used to determine the amount of dispersant in the supernatant after centrifugation. This technique is possi ble because the NaPAA dispersant contains carboxylate groups which can be protonated or deprotonated depending on the pH (equation 4-1). R-COOH + NaOH R-COO+ Na+ + H2O (4-1) First, the calibration curves for NaPAA had to be determined. This included dissolving a known amount of dispersant into deionized water, decr easing pH to 2 with 1 M HCl, and then titrating the sample with 0.1 M NaOH. The amount of NaOH added to the system was then plotted against the pH of the system (figure 4-1 black curve). Next, the first derivative of the titration line was taken and then the volume of NaOH be tween the two peaks was calculated (figure 4-1 red curve). The volume of NaOH between the peaks is proportiona l to the amount of dispersant in the water. This process was repeated for se veral different known amount s of dispersant. The data was then plotted with volume of NaOH between peaks ve rsus dispersant amount and a linear fit was applied to the da ta (figure 4-2). With the calibration curves determined, the

PAGE 49

49 0246810121416 0 2 4 6 8 10 12 pHVolume (mL) Titration Derivative Figure 4-1. Titration curve of NaPAA. Black curve is the titr ation of a NaPAA in deionized water. Red curve is the 1st derivative of the titration curve. amount of dispersant in an unknown sample coul d be determined by measuring the volume of NaOH that is needed to titrate the sample. Adsorption isotherm data was measured from slurries of 75 wt% GCC containing 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, and 4 wt% NaPAA (wei ght percent of GCC weight). The offered amount of NaPAA versus adsorbed amount of Na PAA was plotted in fi gure 4-3 with the 100% adsorption line. The adsorption isotherm data was then compared to three models. First, the data was compared to the linear form of the Langmuir model which does not fit well with a R2 value of

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50 Figure 4-2. Calibration curve for Na PAA with the titration technique. 0.82 (figure 4-4). The Langmuir model assume s monolayer adsorption with a surface which consists of uniform adsorption sites. Second, th e data was compared to the linear form of the Temkin model which also had a poor fit with a R2 of 0.85 (figure 4-5). Third, the data was compared to the linear form of the Freundlich model which fits well with a R2 of 0.96. Next, the Freundlich constant, K, and Fre undlich exponent, b, were calculate d from the intercept and slope of the linear Freundlich model (equation 4-2), respectively. log(Q) = log(K) + b log(C) (4-2) where Q is the adsorbed NaPAA per GCC (mg/g) and C is the unadsorbed NaPAA (mg/L). The non linear Freundlich model (equation 4-3) was f itted with the Freundlich constant and exponent (figure 4-6). Q = KCb (4-3)

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51 Figure 4-3. The adsorbed amount of NaP AA compared to the 100% adsorption line. The Freundlich model assumes a non-linear rela tionship between the adsorbed amount and the concentration of the solute in the liquid. This model represents adsorption with strong solute to solute interaction. It also indicates that the solute is adsorbin g onto a heterogeneous surface. In agreement with these results, Balaz et al. [85] also demonstr ated that adsorption on mineral surfaces are best fit with the Freundlich model. The 75 wt% GCC slurry system does not follow the Langmuir isotherm, which is a common model to describe most adsorption proce sses, but displays the Freundlich isotherm. There are several reasons why the system doesn t follow the Langmuir isotherm. First, the Langmuir isotherm describes a system that is di lute in which the adsorbed molecules do not

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52 Figure 4-4. Langmuir adsorption isotherm of NaPAA by GCC in a 75 wt% solids loading slurry. This model is a poor fit with a R2 value of 0.8187. Figure 4-5. Temkin adsorption isotherm of Na PAA by GCC in a 75 wt% solids loading slurry. This model is a poor fit with a R2 value of 0.8529.

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53 Figure 4-6. Freundlich adsorp tion isotherm of NaPAA by GCC in a 75 wt% solids loading slurry. Freundlich model fits well with a R2 value of 0.96. interact. Second, it assumes a homogeneous su rface. Third, it has a defined adsorption maximum and assumes linear adsorption at concen trations far below the maximum. Many of these assumptions do not fit the properties of a 75 wt% GCC slurry. The GCC slurry is a concentrated system with calcium, carbonate, and sodium ions due to GCCs solubility in water and the Na+ ions from the NaPAA. Furthermore, as will be demonstrated later, the chemical interactions within a high solids loading sl urry are different than a dilute system. 4.2 Turbidity of NaPAA Adsorption isotherms indicated that the NaPAA is on the surface of the particles but they do not distinguish between adsorpti on and precipitation of the disp ersant. Therefore, turbidity measurements of the dispersant at several conditions were necessa ry to determine if the NaPAA

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54 Figure 4-7. Turbidity of NaPAA in water with increasing monovalent sa lt concentration. High concentrations of sodium ions within sl urry do not cause the NaPAA to precipitate. precipitates within a 75 wt% GCC so lids loading slurry. First, the impact of the monovalent salt NaCl on the turbidity was determined b ecause the slurry system contains Na+ from the dispersant. Samples were prepared with 2.04 g of NaPAA dissolved into 30 ml H2O and the NaCl concentration was varied. Na+ concentrations started at 0.4 M (slurry conditions) and were increased above 1 M. There was no increase in turbidity at all sa lt concentration which indicates no precipitation (figure 4-7). Sec ond, the impact of the divalent salt CaCl on the turbidity was determined because the slurry system contains Ca2+ from the CaCO3. The turbidities of the samples containing concentrations of CaCl2 from 10-4 M to 1.9 x 10-1 M were determined. Within the processing conditions of the slurry, 10-3 M Ca2+ [20], there was not an increase in turbidity (no indication of precipitati on). When the concentration of CaCl2 was above slurry

PAGE 55

55 Figure 4-8. Turbidity of NaPAA in water with increasing divalent salt concentration. Under processing condition of GCC slurries there is no indication of NaPAA precipitation. conditions at 1.9 x10-1 M there was an increase in turbidity and precipitation of the dispersant (figure 4-8). During slurry preparation in industry the slu rry experiences thermal cycles which could possible cause the NaPAA to precipitate; therefore, it was necessary to investigate the impact of temperature on the turbidity of NaPAA. Sample s were prepared by dissolving the NaPAA into deionized water at room temperature. The temp erature of the solution was increased up to 85C while taking turbidity measurements at 25C, 40C, 55C, 70C, and 85C (figure 4-9). There was no increase in turbidity with increase in temperature which i ndicates that within processing temperature conditions there is no precipitation of the disp ersant within the slurry.

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56 Figure 4-9. Turbidity of NaPAA in water w ith increasing temperat ure. NaPAA does not precipitate with increasing temperature. As a 75 wt% GCC slurry ages, several of it s properties change with time. Turbidity measurements of the NaPAA with respect to time were performed in order to determine if there was precipitation of NaPAA with aging. Samples were prepared with NaPAA dissolved in water with two concentrations of CaCl2: 10-3 M CaCl2 which represents the Ca2+ ion concentration in slurry conditions and 10-1 M CaCl2 which represents an excess concentration of Ca2+ ions. Over a three day period there was no im pact on the turbidity of the 10-3 M CaCl2 (slurry conditions) which is an indication of no precipita tion. On the third day of the 10-1 M CaCl2 solution there was precipitation on the bottom of th e container but no increase in turbidity of the liquid (figure 4-10). On the fifth day of the 10-1 M CaCl2 there was precipitation on the bottom of the

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57 Figure 4-10. Turbidity of NaPAA in water with 10-3 M CaCl2 and 10-1 M CaCl2 over a three day period. At slurry conditions th ere was no precipitation of NaPAA. container and the turbidity of the liquid increased. All of the turbidity measurements indicate that within slurry conditions there is no precipitation of the dispersant. 4.3 ATR-FTIR ATR-FTIR is a technique that allows for analysis of high solids loading slurries due to the phenomenon of the evanescent wave described prev iously in Section 2.3. This technique was utilized for analysis of the in teractions of the carboxylate group, hydrocarbon groups, carbonates, and the solvent at a variety of conditions.

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58 4.3.1 Dry and Wet Samples As mentioned before there are several techniqu es to analyze the GCC slurries but many of them require either a dilute or dry sample. IR spectra of GC C slurries after drying do not represent the chemical interactions that have taken place in the slurry. Figures 4-11, 4-12 and 4-13 compare the IR spectrum of a 75 wt% GCC sl urry that had been dried and analyzed with DRIFTS to the spectrum of a 75 wt% GCC slurry an alyzed with ATR. Figure 4-11 demonstrates that in the wet state the carbonate bending band at 1449 cm-1 has a lower frequency shoulder that is not present in the dry sample. This indicates that there are bicarbonate species and chemical bonds in the slurry (discussed in Section 4.3.6) which are removed upon drying. In the wet state 16001500140013001200 0.0 0.2 0.4 0.6 0.8 1.0 75wt% Slurry ATRLog (1/R) (a.u.)Wavenumber (cm-1) 75wt% Slurry Dried DRIFTS Figure 4-11. IR spectra of the carbo nate bending bands located at 1449 cm-1 of a wet and a dry 75 wt% GCC slurry. The wet slurry fo rms a shoulder at lower wavenumbers indicating the presents of bicarbonate species.

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59 950900850800 0.0 0.2 0.4 Log (1/R) (a.u.)Wavenumber (cm-1) 75wt% Slurry ATR 75wt% Slurry Dried DRIFTS Figure 4-12. IR spectra of the carbo nate stretching bands located at 875 cm-1 of a wet and a dry 75 wt% GCC slurry. The wet slurry has a larger FWHM. 1600158015601540 -0.0004 0.0000 0.0004 d2A/d2 (a.u.)Wavenumber (cm-1) Dried Slurry, DRIFTS 75 wt% Slurry, ATR Figure 4-13. Second derivative of the IR spect ra of the carboxyl region for a wet and a dry sample. Band at 1581 cm-1 shifts to 1586 cm-1 indicated change in coordination.

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60 the carbonate stretching band at 875 cm-1 has a larger FWHM than the dry state (figure 4-12) indicating that some of the chemi cal interactions with the carbonate species in the wet slurry are not present in the dry state. There is also a ch ange in the antisymmetric stretching band of the carboxylate group in NaPAA. Figur e 4-13 is the second derivativ e of the IR spectra which shows a shift in the band at 1581 cm-1 in the wet state to 1586 cm-1 in the dry state. The shift to a higher wavenumber indicates that the adsorb ed NaPAA in the dry state has unidentate coordination (coordination of the carboxylate group is described in more detail in Section 4.3.5). Analysis of the IR spectra demonstrates that the chemical interaction of a slurry are not represented in a dry slurry; ther efore, the best IR technique fo r this research is the ATR. 4000350030002500200015001000 0.0 0.2 0.4 0.6 0.8 1.0 bending OH stretching COO-Log (1/R) (a.u.)Wavenumber (cm-1) NaPAA in H2O OH stretchingCH stretching Figure 4-14. IR spectrum of NaPAA in H2O. The OH stretching band overlaps the CH stretching bands of NaPAA. The OH bending band overlaps part of the COOband.

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61 4000350030002500200015001000 0.0 0.2 0.4 0.6 0.8 1.0 bending OD COOOD stretching stretching CH stretching Log (1/R) (a.u.)Wavenumber (cm-1) NaPAA in D2O Figure 4-15. IR spectrum of NaPAA in D2O. Switching from H2O to D2O shifts the stretching and bending bands so that there is no overlap with the CH or COOstretching bands of NaPAA. 4.3.2 Solvent Exchange The stretching modes of OH in wa ter extend over a range of 2900 cm-1 to 3700 cm-1 due to hydrogen bonding in many different energy states. The bending modes of OH in water are located at 2130 cm-1 and 1638 cm-1 as seen in figure 4-14. Also shown in figure 4-14 is the IR spectrum of NaPAA in H2O. As seen in the spectrum the stretching modes of water overlap the CH stretching of the dispersant and the bending mode of water inte rferes with the shoulder of the carboxylate group of the dispersant. In order to analyze these re gions the water bands must be removed without changing the sl urry properties. This was accomplished by substituting D2O

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62 with H2O. The OD stretching modes of heavy water are at lower wavenumbers, 2200 cm-1 to 2700 cm-1, than the OH stretching modes of water (show n in figure 4-15). Also shown in figure 4-15 is the IR spectrum of NaPAA in D2O. Within the spectrum th e CH bending is visible and there is no interference with the carboxylate band. The 75 wt% GCC slurry system was then analyzed with the ATR-FTIR and its IR spectrum is shown in figure 4-16. The regions of focus have been boxed and labeled which include the following: CH stretching, OD stretching, carboxylate group, and the carbonate band. 4000350030002500200015001000 0.0 0.2 0.4 0.6 0.8 1.0 [CO3]2COOOD CH Log (1/R) (a.u.)Wavenumber (cm-1) 75 wt% Slurry with D2O Figure 4-16. IR spectrum of a 75 wt% GCC slurry with NaPAA. Regions of interests are boxed and discussed.

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63 4.3.3 Water Structure in High Solids Loading Slurries A novel discovery was made upon analysis of the ATR-FTIR measurem ents of high solids loading GCC slurries. This discovery demonstr ated that the water structure within the high solids loading slurries is dramatically different than bulk wa ter. This novel discovery is important because it demonstrates that research performed in dilute solutions does not represent all the chemical interactions taking place in a high solids loading sample even though the composition is the same. Figures 4-17 and 4-18 demonstrate that the stretching modes of H2O and D2O dramatically change. For H2O the IR band decreases its FWHM and the shoulder at 3183 cm-1 shifts to a higher frequency at 3239 cm-1. A similar response with D2O and D2O in 36003400320030002800 0.0 0.2 0.4 0.6 0.8 1.0 Log (1/R) (a.u.)Wavenumber ( c m -1 ) 75wt% Slurry H2O Figure 4-17. IR spectra of the OH stretching bands of H2O and H2O in a 75 wt% slurry. When water is in a high solids loading slurry there is a change in the structure of the water indicated with the FWHM decreasing and the 3183 cm-1 shoulder peak shift to 3239 cm-1.

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64 a 75wt% GCC slurry is shown in figure 4-18. The IR band of D2O in a slurry decreases its FWHM along with the 2379 cm-1 shoulder shifting to 2410 cm-1 and the 2492 cm-1 shoulder increasing intensity and shifting to 2502 cm-1. Nickolov et al. [86] refer to the lower frequency shoulder as ice-like with st ronger hydrogen bonding and the highe r frequency shoulder as fluidlike with weaker and distorted hydrogen bonds. The ice-like water structure has hydrogen bond coordinations of four while th e fluid-like water has hydrogen bond c oordinations less than four. The ice-like structure of both H2O and D2O in a slurry decreases along with an increase in the fluid-like structure. This will be analyzed and discussed in more detail in chapter 5. 2800260024002200 0.0 0.2 0.4 0.6 0.8 1.0 Log (1/R) (a.u.)Wavenumber (cm-1) D 2 O 75wt% Slurry Figure 4-18. IR spectra of the OD stretching bands of D2O and D2O in a 75 wt% slurry. When D2O is in a high solids loading slurry there is a change in the structure of the water indicated with the FWHM decreasing and the 2502 cm-1 shoulder increasing intensity.

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65 4.3.4 NaPAA CH Band Infrared Spectra The second band to focus on is the CH band of NaPAA located at 2947 cm-1 when the dispersant is dissolved into D2O (figure 4-19). This band is a result of the CH2 and CH asymmetric stretching bonds with in the NaPAA molecule. Focusing on the same region within a 75 wt% GCC slurry there is a decrea se in the intensity of the 2947 cm-1 band and two new bands are formed, one at 2980 cm-1 and the other at 2875 cm-1 (figure 4-20). The appearance of two new bands was an unexpected finding. The new bands located at 2980 cm-1 and 2875 cm-1 are not present in the IR spectrum of D2O or the IR spectrum of GCC in D2O; therefore, it is concluded that the new bands arise from a shifting of the CH bands and/or an increase in the symmetric stretching of the CH bands. When th e NaPAA is dissolved in the solution the CH stretching bonds are not restricted but when a carboxylate group adsorbs onto the surface of the GCC the CH bonds near that carboxylate group are in close proximity to the surface. The close proximity to the surface could restrict the stretc hing bonds and cause IR bands to shift. Schmidt et al. [87, 88] discuss the shift in the IR for CH bands of polymer/water systems due to a change in temperature with the la rgest shift being about 12 cm-1 for a 20C temperature difference. They also derive the theoretical frequency shifts for various numbers of water molecules in the neighborhood of methyl groups demonstr ating a wavenumber shift of ~60 cm-1 for an increase from 8 to 12 water molecules. They conclude th at the hydrophobic intera ctions of the methyl groups cause a shift of the CH stretching bands. Al -Hosney et al. [89] dem onstrate a shift in the CH band of 20 cm-1 for wet versus dry conditions of HC OOH adsorbed onto calcium carbonate. The change in the wavenumber from the 2947 cm-1 band to the 2875 cm-1 band is 72 cm-1. This difference is equivalent to the band difference fr om the asymmetric to symmetric stretching of CH2. So the appearance of the two new bands is explained to be a result of NaPAA adsorption onto the surface of GCC.

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66 Figure 4-19. IR spectrum of the CH band of NaPAA in D2O. Figure 4-20. IR spectrum of the CH bands of NaPAA in a 75 wt% GCC slurry. Two bands are formed at 2980 cm-1 and 2875 cm-1 indicating adsorption of the NaPAA onto the surface of GCC.

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67 Further investigation of this phenomenon consis ted of increasing the concentration of the NaPAA in a 75 wt% GCC slurry. Figure 4-21 demonstrates that with one weight percent NaPAA there is formation of two bands at 2980 cm-1 and 2875 cm-1 while the original band at 2947 cm-1 decreases, indicating adsorption of NaP AA. With an increase of NaPAA exceeding 9 wt% the CH band at 2947 cm-1 increases while the other bands re main constant in intensity. Since the bands at 2980 cm-1 and 2875 cm-1 indicate adsorption and they do not increase in intensity above 9 wt% NaPAA then the adsorption limit is between 1 wt% and 9 wt%. Utilizing equations 2-18 and 2-17, N = 63 and l = 0.27 nm, the monolayer adsorption amount depending on the NaPAA conformation w ould be between 2.14 mg/m2 and 4.28 mg/m2, respectively. Figure 4-21. IR spectra of the CH bands of NaPAA in GCC slur ries with increasing concentration of NaPAA. Adsorption limit is between 1 wt% NaPAA and 9 wt% NaPAA.

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68 4.3.5 NaPAA Carboxylate Group Infrared Spectra As mentioned in Section 2.2 the carboxylate group is known to adsorb on several different surfaces and due to an increase in entropy it ad sorbs onto calcium ions. The carboxylate group of NaPAA has a resonance form when dissolved in water. This is confirmed in the IR spectra with the absence of the C=O band which would be located around 1700 cm-1 and the presence of a COOband at 1570 cm-1 as seen in figure 4-22. When a 75 wt% GCC slurry is prepared there is a change in the carboxyl band. Figure 4-23 shows that the 1570 cm-1 stretching band is split 175017001650160015501500 0.00 0.05 0.10 0.15 Log (1/R) (a.u.)Wavenumber (cm-1) NaPAA in D2O Figure 4-22. IR spectrum of the car boxyl stretching region for NaPAA in D2O. The IR spectrum shows that NaPAA is in the ionic form with a peak at 1570 cm-1 for the COOand no peak at 1700 cm-1 for the C=O.

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69 160015801560154015201500 -0.0010 -0.0005 0.0000 0.0005 0.0010 ionic bridging bidentate unidentate NaPAA in D2Od2A/d2 (a.u.)Wavenumber (cm-1) 75 wt% GCC Slurry Figure 4-23. Second derivative of the IR spect ra of the carboxylate re gion of NaPAA in D2O and in a 75 wt% GCC slurry. NaPAA adsorb s onto GCC in unident ate, bridging, and bidentate modes. into a band at 1581 cm-1 and 1567 cm-1 along with a band forming at 1524 cm-1 with a shoulder. From the research of Lu et al. [36] and Young et al. [76] they have shown that each band represents a different mode of interaction. The four possible modes of interaction are ionic, unidentate, bidentate, and bridgi ng (figure 2-8). Mielczarski et al [61, 62] assigned the bands at 1575 cm-1 and 1540 cm-1 to unidentate and bidentate adsorption, respectively. Lu et al. [36] demonstrate that the bands aris e from three-dimensional precip itated calcium dicarboxylate salts which can either be from the bulk solution or physisorbed at a surface. Therefore, in figure 4-23 the 1581 cm-1 band is representative of uni dentate coordination, the 1567 cm-1 band represents

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70 bridging coordination, and the bands between 1510 cm-1 and 1545 cm-1 represent bidentate coordination with calcium. Additional slurries with increasing concentra tions of NaPAA were prepared and analyzed with ATR-FTIR. IR spectra of 75 wt% GCC sl urries containing 1 wt% and 10 wt% NaPAA are compared to NaPAA in D2O, see figure 4-24. Initially, the NaPAA in D2O shows one band at 1570 cm-1 which represents the carboxylate group in the ionic coordination. Next, with the 1 wt% NaPAA slurry there is a splitting of the 1570 cm-1 stretching band as described above. 160015801560154015201500 -0.0010 -0.0005 0.0000 0.0005 0.0010 bidentate bridging and ionic unidentate NaPAA in D2Od2A/d2 (a.u.)Wavenumber (cm-1) Slurry with 1 wt% NaPAA Slurry with 10 wt% NaPAA Figure 4-24. Second derivative of the IR sp ectra of 75 wt% GCC slurries with increasing concentration of dispersant. With an excess amount of dispersant there is no unidentate adsorption mode.

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71 The splitting of the band confirms that the adsorption of NaPAA in a 75 wt% GCC slurry is through unidentate, bridging, and bidentate coor dination states with calcium ions on calcium carbonate. The slurry with 10 wt% NaPAA doe s not show any unidentate coordination, indicated with the re moval of the 1581 cm-1 band, and there is a shift in the band peak at 1524 cm-1 to 1515 cm-1 representing bidentate coordina tion. Also, the band at 1566 cm-1 which represents bridging coordination may also include some NaPAA that has not adsorbed due to overlap of the 1570 cm-1 band from NaPAA in solution. The IR spectra demonstrate that as the amount of dispersant increases in a 75 wt% solid s loading slurry the coordination of the carboxyl species changes with the removal of the unidentate coordination. Similar to the results of Section 4.3.3 which showed a change in the water structure with solids loading, there is a change in the carboxylate coordination at high solids loading. Slurry samples were prepared with 10, 30, 50, and 70 wt % GCC. The spectra of the IR carboxyl region are shown in figure 4-25. First, the band representative of the unidentate coordination in the 10 wt% GCC slurry at 1586 cm-1 shifts to lower wavenumbers as the solids loading is increased, eventually to 1578 cm-1 in the 70 wt% GCC slurry. Similarly, the band representative of the bridging coordination in the 10 wt% GCC slurry at 1567 cm-1 shifts to lower wavenumbers until it reaches 1560 cm-1 in a 70 wt% GCC slurry. Also, as the solids loading increases the band between 1510 cm-1 and 1545 cm-1 becomes a doublet with band peaks at 1539 cm-1 and 1521 cm-1, representing the bidentate coordination. As the solids loading increases, the dispersant shifts towards the ca lcium bridging mode of adsorption indicated with the decrease in the unidentate band position and an increase in the bidentate band position. The slight change in band positions could possibly be du e to increased interactions be tween dispersant molecules due to their higher concentration in the solvent. This conclusion is important because it supports

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72 16001580156015401520 -0.0008 -0.0004 0.0000 0.0004 0.0008 bridging bidentate unidentated2A/d2 (a.u.)Wavenumber (cm-1) 70 wt% Slurry 10 wt% Slurry 30 wt% Slurry 50 wt% Slurry Figure 4-25. Second derivative of the IR spectra of the carboxylate region with increasing solids loading. As the solids loading of the slur ries increases there is a shift of the bands toward a bridging mode. previous data which demonstrate that the interactions within a low solids loading slurry is different than in a high solids loading slurry. During the first couple of days after a slurry ha s been prepared there is a change in several of its properties as mentioned in the introduction. ATR-FTIR was utilized to determine if there is any change in the interaction of the NaP AA with GCC during the aging process. A 75 wt% GCC slurry was prepared and analyzed with the ATR-FTIR as it aged while it was less than an hour old, 24 hours old, and 48 hours ol d. The IR spectra can be seen in figure 4-26. Initially, the band representing the unidentate c oordination is located at 1585 cm-1. As the system ages the

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73 band shifts to 1580 cm-1. This indicates that while the slu rry ages there is a decrease in the concentration of unidentate coor dination of carboxylate groups a nd an increase in the bridging and/or ionic coordination of the carboxylate groups. These results would support the idea that as the system ages there is an in crease in the amount of dissolved calcium ions which are then available for bridging coordina tion, which require two calcium ions per carboxylate group, instead of unidentate coordina tion, which only require one ca lcium ion per carboxylate group (figure 2-8). 1600158015601540 0.0000 0.0005 increasing age bridging unidentate 75 wt% Slurry Aged 48 hrs d2A/d2 (a.u.)Wavenumber (cm-1) 75 wt% Slurr y Fresh 75 wt% Slurry Aged 24 hrs Figure 4-26. Second derivative of the IR spectra of the carboxylate region with aging. The unidentate band shifts from 1585 cm-1 to 1580 cm-1 with increasing age indicating a shift towards the bridging mode.

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74 4.3.6 Carbonate Infrared Spectra The next bands to focus on are the carbonate bands from the GCC. This includes a stretching band at 875 cm-1 and a bending band at 1404 cm-1 (figure 4-27) whic h is in agreement with literature [90]. When GCC is introduced into a slurry the FWHM for the stretching band 30002500200015001000 0.0 0.2 0.4 0.6 0.8 1.0 combination bands bending carbonate ion carbonate ion stretching Log (1/R) (a.u.)Wavenumber (cm-1) Figure 4-27. ATR-FTIR spectrum of GCC. increases. This is an indication that the car bonates are interact ing with other species in the system. Upon analysis of the car bonate bending band there is a dr amatic change in the band (see figure 4-28). The carbonat e bending band at 1404 cm-1 in figure 4-27 shifts to 1449 cm-1 for a 75 wt% GCC slurry and the band also forms a lo w frequency shoulder. These spectra confirm that the carbonate is interacting with other specie s in the system. The shoulder that forms on the

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75 160015001400130012001100 0.0 0.2 0.4 0.6 75wt% SlurryLog (1/R) (a.u.)Wavenumber (cm-1) D2O and GCC Figure 4-28. IR spectra of carbonate band of GCC in D2O and in a 75 wt% GCC slurry. Formation of a shoulder indica tes formation of bicarbonates. carbonate bending band indicates the formation of bicarbonates in th e system [86, 91, 92]. Since CaCO3 is slightly soluble in water then the spectra confirm the dissolution of CaCO3, adding more ions to the system. These ions play an important role on the adsorption of NaPAA and the water structure (discussed in Section 5.3). The FWHM and shape of the carbonate bending band is also dependent on the solids loading. Up to 40 wt% the carbonate bending band is similar to a mixture of D2O and GCC without NaPAA. Once the solid s loading is raised above 40 wt% the band forms a shoulder which shifts to lower wave numbers as the solids loading is increased (figure 4-29). This is anothe r confirmation that high solids lo ading slurries have different chemical interactions than dilute systems.

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76 160015001400130012001100 0.0 0.2 0.4 0.6 75wt% Slurry 40wt% Slurry 50wt% Slurry 60wt% Slurry 70wt% Slurryincreasing solidsLog (1/R) (a.u.)Wavenumber (cm-1) D2O and GCC Figure 4-29. IR spectra of the carbonate band of GCC slurries s howing a formation of a shoulder with increase solids loading. There is also a noticeable change in slu rry properties over a period of a few days; therefore, a slurry of 75 wt% GCC in D2O was analyzed with ATR-FTIR over a three day period. During the three days the carbonate band did not shift but th e shoulder became less pronounced, shifting to higher frequencies as time increased (figure 4-30). The shoulder shifting over time is an indication of a decrease in the bicarbonate species and aff ects the water structure within the slurry (more details in Section 6.2). If ordering occurs in the system and we assume that the shoulder of the carbonate band is an indication of this ordering th en the shoulder should shift in re sponse to thermal differences. A slurry of 75 wt% GCC in H2O was prepared and separated into three samples. The first sample

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77 160015001400130012001100 0.0 0.2 0.4 0.6 Log (1/R) (a.u.)Wavenumber (cm-1) GCC and D2O increasing age 75wt% Slurry Aged <1hr 75wt% Slurry Aged 25hrs 75wt% Slurry Aged 51hrs Figure 4-30. IR spectra of th e carbonate band of GCC in a 75 wt% slurry with aging. was frozen, placed on the ATR crystal, and while it was melting an IR spectrum was measured. The second sample was poured onto the ATR crysta l at room temperature and the IR spectrum was measured. The third sample was boiled, pl aced onto the ATR crystal, and the IR spectrum was measured. These three spectra show that as the temperature decreases (less relative thermal energy) there is a shift of the shoulder to a higher frequency (f igure 4-31). This supports the idea that as the age of a slurry increases (shoulder shif ts to higher frequencies) there is an increase in the order of the system.

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78 16001500140013001200 0.0 0.1 0.2 0.3 Room Temperature SlurryLog (1/R) (a.u.)Wavenumber (cm-1) Almost Boiling Temperature ~0 C Slurry 1311 1319 1335 Figure 4-31. IR spectra of the carbonate band with a slurry at different temperatures. As the temperature decreases the s houlder shifts from 1311 cm-1 to 1335 cm-1. 4.3.9 Temperature Dependence In industry a high solids loading GCC slurry will experience several different thermal environments while being processed. An expe riment was designed to determine if thermal variation of a slurry has an e ffect on the IR spectrum of th e final slurry. Two 75 wt% GCC slurries in D2O were prepared at room temperature. The temperature of one sample was raised to 85C for 15 minutes and then cooled to room te mperature before analyzing the sample with ATR-FTIR. The spectra of both samples were th e same except the shoulder of the carbonate peak was shifted (figure 4-32).

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79 4000350030002500200015001000 0.0 0.2 0.4 0.6 0.8 1.0 Previously heated SlurryLog (1/R) (a.u.)Wavenumber (cm-1) 75 wt% Slurry Figure 4-32. IR spectra of a 75 wt% GCC slurry before and after a heating cycle. The only difference of the two spectra is the carbonate band. Also, the structure of the water within a slur ry is dependant on the temperature of the slurry. A 75 wt% GCC slurry was prepared and separated into two samples. The first sample was analyzed at room temperature with the AT R-FTIR. The second sample was frozen, placed onto the ZnSe ATR crystal and analyzed as it was melting. As expected, the shoulder at 2379 cm-1 increased in intensity and the shoulder at 2502 cm-1 decreased in intensity for the melting sample which indicates more i ce like structure (figure 4-33). 4.3.10 Addition of Energy to Aged Slurries One technique used by industry to retard slu rry aging while it is in storage includes constant stirring of the slurries. So the effect on the water structure of adding energy to an aged

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80 270026002500240023002200 0.0 0.2 0.4 0.6 0.8 1.0 75 wt% Slurry Room Temperature 75 w% Melting SlurryLog (1/R) (a.u.)Wavenumber (cm-1) Figure 4-33. IR spectra of the OD band in a 75 wt% GCC slurry at different temperatures. Lower temperatures increase the concentration of structured water. slurry was investigated. First, a 75 wt% slurry was aged for 5 days and then the IR spectrum was measured. Second, a small amount of energy was added to the slurry wi th mechanical stirring which represents the process in i ndustry. As seen in figure 4-34, there is a decrease in the icelike structure, reversing the aging process. Third, the aging process is further reversed as more energy is added to the system th rough sonication. A similar result is detected in the carbonate band (figure 4-35). As energy is added to the sy stem the shoulder on the carbonate band shifts to lower frequencies which is the opposite of the ag ing process in figure 4-30. Even though the water and carbonate bands are not fully restored to th eir fresh state, these results indicate that the aging process includes an entropic component.

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81 2800260024002200 0.0 0.2 0.4 0.6 0.8 1.0 Log (1/R) (a.u.)Wavenumber (cm-1) Same slurry hand sonicated 75wt% Slurry Aged 3 days Same slurry hand mixed Figure 4-34. IR spectra of the OD band in an aged 75 wt% GCC slurry with addition of energy to the system. Adding energy to the system partially restores the fluid like water structure. 160015001400130012001100 0.0 0.2 0.4 0.6 0.8 Log (1/R) (a.u.)Wavenumber (cm-1) Same slurry sonicated 75wt% Slurry Aged 3 days Same slurry hand mixed Figure 4-35. IR spectra of the carbonate band in an aged 75 wt % GCC slurry with addition of energy to the system. Adding energy to th e system partially restores the carbonate band to a fresh slurry.

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82 4.4 Probe Molecules Molecules which contain a car boxylate were chosen to prob e the surface of GCC in high solids loading slurries. The in teraction of the probe molecule s with the surface of GCC would provide additional understanding of the interactio n between NaPAA and GCC. Benzoic acid and gallic acid were chosen because their concentr ations in a solution could be measured with a UV/VIS spectrometer. The benzene ring absorbs ultr aviolet light causing the electrons transition from (bonding) to (anti-bonding). Figure 4-36. Molecular st ructure of benzoic acid.

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83 Figure 4-37. Adsorption of benzoic acid onto GCC at varying solids loading. Benzoic acid does not adsorb onto GCC. 4.4.1 Benzoic Acid Benzoic acid was chosen as a probe molecule because it contains a benzene ring and a carboxylic acid group (figure 4-36). Adsorption experiments for benzoic acid onto GCC were specifically performed to demonstrate the carboxyl group adsorpti on and/or the hydrophobic adsorption of the benzene ring. Adsorption of NaPAA is believed to be due to the carboxylate groups interacting with the calcium ions [2, 4, 11, 36]. Geffroy et al. [4] go into detail describing the complexation of carboxylates with the surface of calcite required for adsorption. They determine that carboxylates adso rb through chelation. Since it has been demonstrated that adsorption coordination depends on solids loading, the adsorption of benzoic acid at different

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84 1640162016001580156015401520 1640162016001580156015401520 1640162016001580156015401520 -0.008 -0.004 0.000 0.004 C C COO20 wt% GCC Slurry Wavenumber (cm-1) 57 wt% GCC Slurryd2A/d2 (a.u.) Benzoic acid in D2O Figure 4-38. Second derivative of th e IR spectra of benzoic acid in D2O, 20 wt% GCC slurry, and 57 wt% GCC slurry. The bands for th e benzene ring and th e carboxylate do not shift, indicating no adsorption. solids loading was investigated. Before any adsorption experiments were performed it was determined that calcium benzoate would not precipitate in the slurry becau se the concentration of calcium benzoate was below the precipitation lim it of 2.72 g per 100 ml at 20C. Figure 4-37 demonstrates that benzoic acid does not adsorb onto GCC at any solids loading. Since figure 4-37 does not indicate any adsorption, then the AT R-FTIR will be utilized to confirm that the carboxylate and the benzene ring are not intera cting with the surface of the GCC before centrifugation.

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85 305030002950290028502800 0.00 0.01 0.02 0.03 Benzoic acid in D2O Log (1/R) (a.u.)Wavenumber (cm-1) 57 wt% GCC Slurry Figure 4-39. IR spectrum of the CH bands of benzoic acid in D2O and in a 57 wt% GCC slurry. Formation of new bands indicates inte raction of the CH bonds with GCC. Slurry samples with benzoic acid were prepared at a pH of 9.9 in order to represent the pH condition of a NaPAA and GCC slurry. Additional confirmation of the pH of the slurry was the absence of the C=O band at 1700 cm-1. Figure 4-38 demonstrates that benzoic acid does not adsorb onto the GCC with increasing solids loading. The carboxylate band at 1548 cm-1 for benzoic acid in D2O does not shift or split when GCC is added to the solution which is an indication that the carboxylate is not adsorbi ng onto the GCC particles. Another possible interaction that could cause adsorption is through hydrophobic ad sorption with the benzene ring or the CH groups. The band for a benzene ring is located at 1596 cm-1 and does not shift with increasing solids loading so the benzoic acid is not adsorbing through benzene ring. Figure 4-39

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86 indicates that the CH groups are interacting with the GCC, similar to NaPAA. The IR spectra could be detecting a small amount of benzoic acid on the surface of the GCC which is within the error of the adsorption measurements. The results confirm each other and are in good agreement with Geffroy et al. [4] who demonstrated that a molecule with one carboxy late group will not adsorb onto the surface of GCC. Therefore, the next probe molecule ch osen contained an OH group which will allow the molecule to chelate with calcium. Figure 4-40. Molecular st ructure of gallic acid.

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87 Figure 4-41. Adsorption of gallic acid onto GCC at varying solids loading. 4.4.2 Gallic Acid Gallic acid was chosen as a probe molecule for the same reason that benzoic acid was chosen but it also includes thr ee hydroxyl groups (figur e 4-40). Hydroxyl groups were chosen in order to determine if hydrogen bonding would play an important role in adsorption. The adsorption of gallic acid onto GCC in several different solids loading slurries is demonstrated in figure 4-41. The amount of gallic acid adsorbed is dependant on the solids loading of the slurry and decreases with an increase weight percent of GCC. Calculations were performed to determine the adsorbed monolayer concentr ation of gallic acid is between 1.6 mg/m2 and 8.5 mg/m2. The range in adsorbed monolayer is due to the different modes of adsorption that the gallic acid could accompany while adsorbing. Comparing the monolayer adsorption calculations to figure 4-41 would suggest that the adsorbed amount of gallic acid at 10 wt% would contain 3

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88 162016001580156015401520 -0.0024 -0.0016 -0.0008 0.0000 0.0008 bidentate bridging 20 wt% Slurry C C d2A/d2 (a.u.)Wavenumber (cm-1) Gallic acid in D2O Figure 4-42. Second derivative of the IR spectra of gallic acid in D2O and a 20 wt% GCC slurry. The bands for the benzene ring and the car boxylate shift, indi cating adsorption. adsorbed layers, at 30 wt% would contain 2 ad sorbed layers, and at 50 wt% and 60 wt% would contain one monolayer with di fferent modes of adsorption. The addition of the hydroxyl groups allows fo r the molecule to chelate with the GCC surface forming a seven-bond ring through one hydr oxyl group, calcium ion, and carboxylate group (similar results from Geffroy et al. [4]). A seven-member chelate ring is not as stable as a five-member chelate ring but the chelating abil ity of gallic acid promotes adsorption unlike benzoic acid which does have the ability to form a chelate with calcium. A possible adsorption mechanism for NaPAA is to form an eight-member chelate ring but this is much less stable and could be a reason why a slurry ages.

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89 3050300029502900285028000.030 0.035 0.040 0.045 0.050 67 wt% GCC SlurryWavenumber (cm-1) Gallic acid in D2OLog (1/R) (a.u.)Wavenumber (cm-1) Figure 4-43. IR spectrum of th e CH bands of gallic acid in D2O and in a 67 wt% GCC slurry. Formation of new bands indicates inte raction of the CH bonds with GCC. Analysis of the IR spectra indicates that ga llic acid adsorbs onto the surface of GCC. Figure 4-42 demonstrates that the carboxylate band at 1550 cm-1 shifts to 1547 cm-1 when a 20 wt% GCC slurry is prepared. The carboxylate shif t is a confirmation that the gallic acid is chelating with the surface of the GCC. Another important band includes the benzene ring band located at 1600 cm-1 for the gallic acid and D2O system at a pH of 9. When a 20 wt% GCC slurry with gallic acid is analy zed the benzene band shifts to 1594 cm-1 indicating that the benzene ring also plays a role in the adsorption. Figure 4-43 indicates th at the CH groups are interacting with the GCC, similar to NaPAA.

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90 1640162016001580156015401520 -0.0004 0.0000 0.0004 bidentate bridging 67 wt% Slurry C C d2A/d2 (a.u.)Wavenumber (cm-1) 20 wt% Slurry Figure 4-44. Second derivative of the IR spect ra of gallic acid in a 20 wt% and 67 wt% GCC slurry. The bands for the benzene ring and the carboxylate shift, indicating change in the coordination of the benzoic acid with increasing solids loading. The IR spectra for gallic acid demonstrate th at with increasing solids loading there is a change in the adsorption of the gallic acid. Figure 4-44 shows a shift of the carboxylate band at 1547 cm-1 for a 20 wt% GCC slurry to 1560 cm-1 for a 67 wt% GCC slurry. Along with the carboxylate shift there is a shift of the benzene band from 1594 cm-1 to 1584 cm-1 for a 20 wt% and 67 wt% slurry, respectively. These results ar e further conformation that as the solids loading of a slurry increases the chemical in teraction change within the system.

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91 Figure 4-45. Molecular stru cture of propionic acid. 3050300029502900285028000.020 0.025 0.030 0.035 0.040 0.045 70 wt% GCC SlurryWavenumber (cm-1)Log (1/R) (a.u.) Propionic acid in D2O Figure 4-46. IR spectrum of the CH bands of propionic acid in D2O and in a 70 wt% GCC slurry. Formation of new bands indicates interaction of the CH bonds with GCC.

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92 4.4.3 Propionic Acid Propionic acid was chosen as a probe molecule because it is similar in structure to the monomer of NaPAA (see figure 4-45 for propionic ac id structure). Figure 4-46 indicates that the CH groups are interacting with the GCC, similar to NaPAA. The carboxylate band from propionic acid in D2O at a pH of 9.9 is located at 1552 cm-1. When 14 wt% and 70 wt% GCC slurries are prepared, the carboxy late bands do not shift (see figur e 4-47). This demonstrates again that the adsorption of a molecule onto the surface of GCC cannot occur through a single carboxylate group but must include chelati on of the molecule with calcium. 16001580156015401520 -0.0006 -0.0004 -0.0002 0.0000 0.0002 14 wt% GCC Slurryd2A/d2 (a.u.)Wavenumber (cm-1) Propionic acid in D2O 70 wt% GCC Slurry Figure 4-47. Second derivative of th e IR spectra of propionic acid in D2O, 14 wt% GCC slurry, and a 70 wt% GCC slurry. No shift in the carboxylate band indica tes that propionic acid does not adsorb.

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93 CHAPTER 5 WATER STRUCTURE DEPENDANCE ON S OLIDS LOADING AND AGING 5.1 ATR-FTIR Water Structure A novel discovery shows that the water structur e within a high solid s loading slurry is distinctly different than bulk water (first discu ssed in Section 4.3.3 and demonstrated in figures 4-17 and 4-18). When water is introduced in to a high solids loading GCC slurry there is a decrease in the structured wate r, this is indicated with a decrease in absorbance of the 2379 cm-1 OD stretching band. The structured water at 2379 cm-1 is representative of water with a 2800260024002200 0.0 0.2 0.4 0.6 0.8 1.0 75wt% Slurry 10wt% Slurry 20wt% Slurry 30wt% Slurry 40wt% Slurry 50wt% Slurry 60wt% Slurry 70wt% Slurryincreasing solids Log (1/R) (a.u.)Wavenumber (cm-1) D2O and GCC Figure 5-1. IR spectra of the OD stretching bands in GCC slurries ranging from 10 wt% to 75 wt%. As the solids loading increases there is an increase in the fluid structure (2484 cm-1) and decrease in solid structure (2390 cm-1).

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94 Figure 5-2. Fluid to solid water structure within different solids loading slurries. There are two different regions, the first from 10 to 50 wt% and the second above 50 wt%. hydrogen bond coordination of four wh ile the fluid like water at 2484 cm-1 is representative of water with a hydrogen bond coordi nation less than four. In order to determine if this phenomenon occurs only in 75 wt% slurries or if it also occurs at other solids loading, several slurries were prepared ranging fr om 10 wt% to 75 wt%. The samples were analyzed with the ATR-FTIR (figure 5-1) and the ratio of the fluid like band intensity (2484 cm-1) to the solid like band intensity (2390 cm-1) was calculated for each spectrum. The ratios for each solids loading are compared in figure 5-2. Initially, there is a change in the water structure when a slurry is prepared at 10 wt% compared to only a GCC and D2O mixture. From 10 wt% up to 75 wt% there are two distinct regions. The first region has a constant negative slope which indicates a linear change in water structure up to 50 wt% so lids loading. The second region has a positive

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95 slope which indicates an increase in the fluid like water structur e above 50 wt% solids loading. The change in slope from region one to region tw o may be due to water c onfinement and/or ions in the system which will be discussed in Sections 5.2 and 5.3. 2800260024002200 0.0 0.2 0.4 0.6 0.8 1.0 increasing age Log (1/R) (a.u.)Wavenumber (cm-1) GCC and D2O 75wt% Slurry Aged <1hr 75wt% Slurry Aged 25hrs 75wt% Slurry Aged 51hrs Figure 5-3. IR spectra of the OD band in a 75 wt % slurry with aging. Increasing age causes an increase in the concentration of structured water in the slurry. Aging of slurries is a common problem for indus try as mentioned earlier. Investigation of 75 wt% GCC slurries with the ATR-FTIR over a period of several days demonstrated a novel discovery indicating that the water structure within a high solids loading sl urry changes with age (figure 5-3). Increasing the age of a slurry increase s the concentration of structured water making the slurry more similar to bulk water. As seen in figure 5-4, the decrease in water structure over a two day period leads to water structure that has a higher concentration of

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96 Figure 5-4. Fluid to solid wate r structure within an aging 75 wt% GCC slurry. The fluid like water structure decreases with aging becomi ng more like a slurry without dispersant. structured water than a 40 wt% GCC slurry. The change in water structure could be a result of water confinement and/or ions in the system. 5.2 Water Confinement One of the possible reasons that the IR spectra show an in crease in the fluid like water structure is due to an increase in the confinement of water. Since water s density is higher than ice then when water molecules ar e confined within nanometers th ey behave like water [48, 77, 93-108]. Calculations were performed to determ ine the distance between calcite particles and also the NaPAA. The following assumption were made in the calculations: the dispersant has a radius of gyration of 2 nm to 4 nm [70], dispersant molecules do not adsorb onto calcite particles, GCC particles have a diameter of 1 m, and FCC packing of both calcite particles and

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97 Figure 5-5. Calculations of the distance betw een GCC particles in different solids loading slurries with NaPAA having a radius of gyration of 2 nm, 3 nm, and 4 nm. dispersant. All of the assumption are not a co mpletely accurate repres entation of the slurry system but are necessary for estimating dist ances. The distance between GCC particles decreases from 1610 nm to 128 nm with increasi ng solids loading from 10 wt% to 75 wt%, respectively (figure5-5). These distances are too large to contri bute to the confinement of water according to literature. Figure 5-6 shows the calculations for the distances between NaPAA molecules in the dispersing medium without GCC particles. As the solids loading is increased from 10 wt% to 75 wt% the distance between NaP AA molecules changes from 19 nm to 1.5 nm, respectively. At 75 wt% the confinement of water within 1.5 nm could contribute to the change in water structure observed for hi gh solids loading samples. Also, due to the Brownian motion

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98 Figure 5-6. Calculations of the distance betw een NaPAA molecules in different solids loading slurries with a radius of gyr ation of 2 nm, 3 nm, and 4 nm. of the GCC particles and NaPAA dispersant the water has less time between collisions to form structured water as the solids loading is increased. 5.3 Ions as Water Structure Makers or Breakers As second possible reason that the IR spectra show an increase in the fluid like water structure is due to the ions in the system. Ions are known to in teract with water molecules and form water sheaths around them. The ions either promote or destroy wate r structure depending if the ion is a water structure maker or breaker [86, 95, 109-120]. The high solids loading slurry systems have a high concentration of ions which include calcium, carbonate, bicarbonate, sodium, carboxylates, and hydroxyls due to GCCs so lubility and the addition of NaPAA. The

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99 concentration of several of th ese ions is dependent on the so lids loading and certain ion concentrations have not been determined in high solids loading slurries. However, it is possible to calculate the concentration of sodium i ons and the concentration of carboxylate groups because a known amount of NaPAA is added to the system. Calculations determine that a 75 wt% GCC slurry with 1 wt% NaPAA (weight percent of GCC weight) will contain a concentration of 0.34 M of sodium ions which is extremely high. With such a high concentration of sodium ions the NaPAA will be completely collapsed with a radius of gyration of 2 nm [70]. Additionally, the GCC is slightly soluble so ther e is dissolution and formation of calcium ions, carbonate ions, and bicarbonate ions into the slurry system as indicated with the formation of a Figure 5-7. Change of pH in an aging 75 wt% GCC slurry over a six day time span. A decrease in pH is due to the concentration change of species in the slurry.

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100 low frequency shoulder on the carbonate band (figur e 4-29). As the age of a slurry increases there is a change in th e concentration of ions in the system along with a change in the water structure as shown before in figur es 4-30 and 5-3, respectively. Th is change in the concentration of ions in the system with time is also demonstrat ed with a decrease in th e pH with aging (figure 5-7). 0.0 0.2 0.4 0.6 0.8 1.0 270026002500240023002200 40 wt% NaPAA SlurryWavenumber (cm-1) 1 wt% NaPAA SlurryLog (1/R) (a.u.) 10 wt% NaPAA Slurry Figure 5-8. IR spectra of the OD band of a 75 wt% GCC slurry with increase NaPAA. There is a decrease in the structured water indicati ng that NaPAA is a water structure breaker in a GCC slurry. NaPAA as a polyelectrolyte contains carboxylat e groups which Raviv et al. [12, 77] have shown to cause lubrication of the system due to formation of water sheaths around the carboxylate groups. Raviv et al. explain that th e water molecules which form the sheaths around

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101 the ions are tightly bound to the carboxylate groups but can eas ily and readily exchange with other water molecules from other water sheath with which they come in contact. The fluid like properties of water molecules bound to NaP AA are also confirmed with ATR-FTIR measurements in Figure 5-8. As the amount of NaPAA is increased within a 75 wt% GCC slurry there is an increase in the fluid like to solid like water structure ratio. So NaPAA in a GCC slurry acts as a water structure breaker. Previously as discussed in Sections 4.3.3 a nd 5.1 the water structure is dependent on many variables in the slurry system. As the variab les are altered there is also a change in the concentration and types of ions in the system. The ions in the system could be the reason for the change in the structure of water due to their wa ter structure making and br eaking abilities. In the following chapter the water structure making a nd breaking abilities of chemicals will be analyzed in high solids loading slurries.

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102 CHAPTER 6 WATER STRUCTURE MAKING AND BREAKING CHEMICALS The previous results have dem onstrated that wa ter structure plays an important role in the dispersion of a high solids loading slurry. Several chemicals which are known to be water structure makers or breakers have been introduced into high solids loading sl urries. The effect of the chemicals on the slurrys physical propert ies and water structure are discussed. 6.1 Calcium Chloride Calcium ions play an important role in the dispersion of GCC as discus sed in chapter two. GCC is slightly soluble in water; therefore, ca lcium ions are present in the solution and are free to interact with the NaPAA, carbonates, and di spersing medium. Since calcium is known as a water structure maker [37], then calcium chlori de was introduced to a slurry in order to determine if calcium ions will change the water structure. Figure 6-1 shows that addition of 0.1 M calcium chloride prevents the decrease in structured water which occurs when a slurry is prepared. Since it was previously demonstrated in Section 5.1 that the concentration of structured water increases with ag ing then the results from figure 6-1 would indicate that during the aging of a slurry there is an increase in dissolved calcium. Addition of CaCl2 to the slurry also changes the carbona te band. As seen in figure 6-2 the slurry with CaCl2 has a carbonate bending band with a sm aller FWHM. A similar result was seen with the carbonate st retching band. This indicates that the excess amount of calcium ions in the system prevents dissol ution of the carbonate. 6.2 Sodium Bicarbonate As demonstrated in Section 4.3.6 there is an in crease in the carbonate species indicated by the increase in the shoulder of the carbonate band. Since the slurry system contains carbonate ions along with the sodium ions, which are introduced with the NaPAA, other species are also

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103 2800260024002200 0.0 0.2 0.4 0.6 0.8 1.0 Log (1/R) (a.u.)Wavenumber (cm-1) 50wt% GCC in D2O 45wt% GCC slurry 45wt% GCC Slurry with 0.1M CaCl2 Figure 6-1. IR spectra of the OD ba nd of slurries with and without CaCl2. Ca2+ as a water structure maker prevents the increase in fluid like water of a GCC slurry. 160015001400130012001100 0.0 0.2 0.4 0.6 0.8 Log (1/R) (a.u.)Wavenumber (cm-1) 50wt% GCC in D2O 45wt% GCC slurry 45wt% GCC Slurry with 0.1M CaCl2 Figure 6-2. IR spectra of the carbonate band of slurries wi th and without CaCl2. Ca2+ prevents some of the interactions w ith the carbonate species.

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104 present including sodium carbonate and/or sodium bicarbonate. Sodium carbonate is known as a strong structure maker and sodium bicarbonate as a weak structure maker [86, 113, 114, 121]. Sodium bicarbonate was added to a 75 wt% slurry and the slurry was aged for 64 hrs. Figure 6-3 demonstrates that the OD shoulder at 2379 cm-1 increases with aging which is similar to the results for an aged slurry. The sodium bicarbon ate as a water structure maker does not prevent the change in water structure for an aging system. Rheology measurements were performed for a sl urry with and without sodium bicarbonate. Figure 6-4 demonstrates addition of sodium bicarbonate increases th e viscosity of the slurry. 2800260024002200 0.0 0.2 0.4 0.6 0.8 1.0 75wt% Slurry with Sodium Bicarbonate Aged 64hrsLog (1/R) (a.u.)Wavenumber ( c m -1 ) 75wt% Slurry with Sodium Bicarbonate Figure 6-3. IR spectra of the OD band of a 75 wt% GCC slurry with 0.19 M sodium bicarbonate with aging. As a weak structure maker, sodium bicarbonate allows for an increase in the structured water with aging of a 75 wt% slurry.

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105 Figure 6-4. Rheology of 75 wt% GCC slurries with and without sodium bicarbonate. Sodium bicarbonate increases the viscosity. Since there is an increase in the viscosity this i ndicates that the water st ructure making ability of sodium bicarbonate could be a reason for the aging of a 75 wt% slurry. 6.3 Ethylene Glycol Ethylene glycol is a common additive to water in order to decrease the freezing temperature (structure shown in figure 6-5). It is also known as a water structure breaker and each oxygen is known to be fully hydrated with ~2-3 water molecules [122-124]. Figure 6-6 shows the OD band for a 75 wt% GCC slurry cont aining 0.50 M of ethylene glycol. The water structure within the slurry does not change with aging due to the additi on of ethylene glycol. Also, the addition of ethylene glycol prevents an y changes in the carbonate band with aging as

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106 Figure 6-5. Structur e of ethylene glycol. 2800260024002200 0.0 0.2 0.4 0.6 0.8 1.0 Log (1/R) (a.u.)Wavenumber (cm-1) 75wt% Slurry with Ethylene Glycol Aged 64hrs 75wt% Slurry with Ethylene Glycol Figure 6-6. IR spectra of the OD band of a 75 wt% GCC slurry with 0.5 M ethylene glycol with aging. Ethylene glycol as a water structure breaker prevents structure water from forming while the slurry ages.

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107 160015001400130012001100 0.0 0.2 0.4 0.6 0.8 Log (1/R) (a.u.)Wavenumber (cm-1) 75wt% Slurry with Ethylene Glycol Aged 64hrs 75wt% Slurry with Ethylene Glycol Figure 6-7. IR spectra of the carbonate band of slurries with and w ithout ethylene glycol. Ethylene glycol prevents interactions with the carbonate species as it ages. shown in figure 6-7. The spectra confirm that addition of a wate r structure breaker prevents the aging of the high solids loading system. Additionally, the rheological properties of the slurries were investigated. According to literature when ethylene glycol is added to water the visc osity increases [125-130]. Upon addition of 0.5M of ethylene glycol to the slurry system the max viscosity of the slurry decreased 475 Pas which is in the opposite direction of a water and ethylene glycol system. Also, the decrease in the viscosity is greater than the de crease in viscosity due to addition of an equal weight of water, demonstrated in Figure 6-8. Furt her, the viscosity of a 48 hour aged slurry with

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108 Figure 6-8. Viscosity measurements of 75 wt% slurries with and without ethylene glycol. Ethylene glycol decreases the viscosity more than adding an equal weight amount of water to the slurry. ethylene glycol is lower than an aged slurry without ethylene glycol. This is additional confirmation that nonionic wate r structure breakers may prevent the aging of a slurry. 6.4 Propylene Glycol Ethylene glycol is a toxic chem ical; therefore, it is comm only substituted with propylene glycol (see figure 6-9 for chemical structure) which behaves simila r to ethylene glycol but is environmentally safe. Figure 6-10 shows the OD bands of a 75 wt% GCC slurry containing 0.43 M of propylene glycol less than an hour afte r preparation and after 48 hours of aging.

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109 Figure 6-9. Structur e of propylene glycol. 270026002500240023002200 0.0 0.2 0.4 0.6 0.8 1.0 75 wt% Slurry with Propylene Glycol 75 wt% Slurry with Propylene Glycol Aged 48hrsLog (1/R) (a.u.)Wavenumber (cm-1) Figure 6-10. IR spectra of the OD band of a 75 wt% GCC slurry with 0.43 M ethylene glycol with aging. Propylene glycol as a water st ructure breaker prevents structured water from forming while the slurry ages.

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110 Figure 6-11. Viscosity measurem ents of 75 wt% slurries with and without propylene glycol. Propylene glycol decreases the viscosity at low shear rates but increases viscosity at higher shear rates. Propylene glycol shows similar results to ethylene glycol indicating no cha nge in water structure with aging. Additionally, the rheological properties of the slurries were investigated. Similar to ethylene glycol the literature shows that addition of propylene glycol to water increases the viscosity of water [131]. Upon addition of 0.43 M of propylene glycol to a 75 wt% GCC slurry the max viscosity of the slurry decreased 200 Pas (figure 6-11). Also, the viscosity of a 48 hour aged slurry with propylene glycol is less than the viscosity of an aged slurry without propylene

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111 glycol. Propylene glycol as a water structure breaker is additional confirmation that water structure breakers prevent the aging of 75 wt% GCC solids loading slurries.

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112 CHAPTER 7 SUMMARY AND DISCUSSION The main objective of this dissertation was to determine the mechanism of adsorption for NaPAA onto GCC in high solids loading slurries An overview of literature provided some insight into the behavior of cal cium carbonate and NaPAA in water at dilute concentrations. This was followed by several experiments utilizing adsorption isotherms, turbidity measurements, probe molecules, and rheology. The presented results focused on specific parts of the NaPAA molecule, including the car boxylate and CH groups, and focused on the carbonates from GCC. Also, the results in chapte rs 5 and 6 focus on the water structure within high solids loading slurries. This chapter summarizes all the results in order to obtain a comprehensible understanding of the adsorption of NaPAA onto GCC in high solids loading slurries. As mentioned in the literature review, calcium carbonate is slightly soluble in water and the surface shows complex behavior due to the chemical equilibrium of the mineral/water interface. Geffroy et al. [4] come to the conclu sion that within a pH range of 8 to11 the surface of calcium carbonate in water consists mainly of neutral sites (CaOH and CO3H) and ionic sites (Ca+ and CO3 -). Katz et al. [34] determine that the calcium ions form asymmetrical coordination structures with water. From the lite rature review it is appa rent that the surface of calcium carbonate in water is heterogeneous, consis ting of several different sites with different charges and hydration states. This is in agreement with the ad sorption isotherms performed in this dissertation. The adsorption of NaPAA in 75 wt% GCC slurries follows the Freundlich isotherm which is an indication of a heterogene ous surface. Also, seve ral of the sites on the GCC surface must compete with calcium and sodium ions in the solution for the adsorption of NaPAA. The ions in solution can precipitate th e dispersant and cause the dispersant to be

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113 ineffective. Turbidity measurements of NaPAA in water with varying concentrations of sodium and calcium ions indicate that NaPAA does not precipitate in sl urry conditions. The turbidity results are only an indication and not a true re presentation of a high solids loading GCC slurry because the ionic condition of water in a high solids loading slurry may be different. Results from the IR spectra of the carbonate band indicated that th ere is formation of bicarbonates in 75 wt% GCC slurries There is little change in the carbonate band up to 50 wt% GCC but above 50 wt% GCC the band forms a s houlder which continues to extend to lower wavenumbers as solids loading increases. The sh oulder is an indication of bicarbonate formation and these results demonstrates that a dilute system does not represent a high solids loading system. Also, it was demonstrated that the IR spectrum of a dried 75 wt% GCC slurry does not represent an IR spectrum of an aqueous slurry, mi nus the water, because the dried slurry does not contain the bicarbonate bands. As a 75 wt% GCC slurry ages there is a shift of the bicarbonate band to higher wavenumbers which is also accomp anies with a decrease in the pH from 9.9 to 9.5. Knez et al. [19] mention that the activity of carbonate species (H2CO3 and HCO3 -) increases with rising pH and the activity of calcium ions d ecreases with rising in pH. This would be in agreement with the IR spectra because there is a decrease in the band (decreasing carbonate activity) with decreasing pH over time. This would also indicate that the activity of calcium ions in the system increases with aging. Further investigation of the CH groups of NaPAA would require a solvent exchange. The OH stretching region of H2O overlaps the CH stretching region of NaPAA; therefore, D2O was exchanged for H2O allowing for analysis of the CH bands. Surprising results were obtained from the IR spectra indicating that th e CH groups of NaPAA and the probe molecules were interacting with the GCC. Previous literature has demonstrat ed that shifts in the CH band are possible due

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114 to temperature changes [87, 88] and aqueous ve rsus dry conditions [89] which were discussed with more detail in Section 4.3.4. The following is a possible explanation for the interactions of some CH bonds with the surface of GCC. As a carboxylate adso rbs onto the surface of GCC the CH bond near the carboxylate is brought into proxi mity to the surface. The surface restricts the bending and stretching modes of the CH bond cau sing a change in the IR spectra. As demonstrated in figure 4-21 the CH bands indica te that the adsorption limit of NaPAA on GCC is between 1 wt% and 9 wt%. Calculations of monolayer adsorption are between 2.14 mg/m2 and 4.28 mg/m2 depending on the conformation of the polymer. The carboxylate group of NaPAA interacts with cations and surfaces in four different modes: ionic, bridging, bidentate, and unidentate. Analysis of th e IR spectrum of a 75 wt% GCC slurry demonstrated that the carboxylate groups interact in unidentate, bidentate, and bridging modes. Probe molecules were utilized in order to determine if the carboxylate group was directly responsible for the adsorption of NaP AA onto the surface of GCC. Analysis of the IR spectra for benzoic acid, containing only one carboxylate group, de monstrated that the carboxylate group does not adsorb at low or high solids loading. Adsorption measurements of benzoic acid onto GCC support the IR results by indicating no adsorption. The next probe molecule included propionic acid which also contains a single carboxylate group. Analysis of the IR spectra also demonstrated no interacti on of the carboxylate group with GCC. Finally, gallic acid which contains a carboxylate gr oup and three OH groups was used as a probe molecule. Analysis of the IR spectra of the carboxylate group indicate d interaction with the GCC. Adsorption of gallic acid is also confirmed with adsorption measurements. The interaction of gallic acid with the surface of GCC is possible becau se the molecule is able to chelate with the surface through the carboxylat e group and an OH group. NaPAA is also

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115 expected to interact through ch elation of the carboxylate groups. As discussed in Section 2.2, literature supports these results with Geffroy et al. [4] and Dobson et al. [49] who also explain that the adsorption of carboxylat es is through chelation and that adsorption does not occur with molecules which only contai n one carboxylate group. Further investigation of the adsorption of carboxylate groups onto calcium ions could explain why a decrease in structured water is observed for a 75 wt% slurry compared to bulk water, Section 4.3.3. There are two papers which could explain indirectly why a high solids loading slurry demonstrates a change in water structure. One by Geffroy et al. [5] and another by Sinn et al. [15] which discuss the excha nge of calcium ions binding onto NaPAA as endothermic. As discussed in Section 2.2, the implication of an endothermic binding means the adsorption process is driven by an increase in entropy. The increase in entropy is believed to be due to the release of water molecules from th e dehydration of the calcium ion and carboxylate ion. Since the calcium ion is a water structure maker, then dehydrat ion of the ion will release the structured water that was bound to it. The water structure is also depe ndant on the solids loading of the system. Initially when a 10 wt% GCC slurry is prepared there is a decrease in the structured water. As the solids loading increases to 50 wt% there is a small increase in the structured water. When the solids loading is increased above 50 wt% and up to 75 wt% there is an increase in the fluid like water structure, figure 5-2. Also accompanying the change in wate r structure is a change in the adsorption mode of the carboxylate. As the solids loading of a slurry sample is increased, the carboxylates which are adsorbing in a unidentate mode shift their adsorption toward a bridging mode. With the bridging mode, one carboxylate group is interacting with two calcium ions instead of the unidentate mode in which one carboxylate group interacts with one calcium ion. The water

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116 structure change could be an indication of the mode of adsorption taking place for the carboxylate groups. The water within an aging 75 wt% GCC slurry in creases in structured water. The change could be due to the water structure making ions increasing in concentration over time. A change in the pH with aging signifies the slurry is no t in equilibrium and the concentration of calcium ions in the system could be increasing over ti me. This would support the observed increase in structured water because the calcium ion is a water structure maker. Also, with aging the coordination mode of the carboxylat e group shifts from a unidentat e mode closer to a bridging mode. The increase in calcium ions would provi de more ions which are required for a bridging mode. Since the previous results indicate that the i ons in the system and the water structure are related to the aging of a system, several chemicals that are known to be wa ter structure makers or breakers were introduced into hi gh solids loading slurries. Calc ium chloride, a water structure maker, prevented the formation of fluid like wate r, limited the interactio ns with the carbonate species, and increased the viscos ity. Sodium bicarbonate, a water structure maker, increased the viscosity of the slurry by a factor of 8 at a shear rate of 0.01 s-1 and did not prevent the increase in structured water with aging of the slurry. Ethylene glycol, know n as a water structure breaker, decreased the viscosity by a factor of 3.5 at a shear rate of 0.01 s-1 and prevented the change in water structure with aging. Propylene glycol, known as a water structure breaker, also prevented a change in the water structure but only decreased the viscosity by 1.4 at a shear rate of 0.01 s-1 and at high shear rates ethylene glycol increased the viscosity of the slurry. Results from the water structure makers and breakers demonstrate that the slurry systems physical properties depend on the water structure and ions in the system.

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117 From the previous discussion, a model for th e adsorption of NaPAA onto GCC is shown in figure 7-1. Part A illustrates NaPAA in solution before adsorption onto GCC. Structured water is shown on the surface of the GCC and surrounding the NaPAA. The driving force for the dispersant to adsorb onto the surface has been determine to be an increase in entropy. The increase in entropy comes from the dehydration of the carboxylate groups and the calcium ions as they interact. Part B illustra tes that when the dispersant adsorbs, its trains and the surface of GCC release the structured water. Evidence of a decrease in structured water has been demonstrated in the IR spectra and discussed. Figure 7-1. Adsorption of NaPAA onto GCC due to an increase in entropy with the release of structured water. A) NaPAA in solution before adsorbing onto GCC surface, B) NaPAA adsorption releases structured water from the carboxylate groups and the calcium as demonstrated in the train of the polymer.

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118 CHAPTER 8 CONCLUSIONS AND SUGGESTIONS 8.1 Conclusions This dissertation is the first work to disc uss the adsorption of NaPAA onto GCC in high solids loading slurries. Previous published work s have only focused on the analysis of dilute systems. Several techniques were utilized to investigate slurries up to 75 wt% GCC including turbidity measurements, adsorption isotherms, rheology, and ATR-FTIR. ATR-FTIR was extensively used because the phenomenon of the ev anescent wave in the ATR-FTIR allows for analysis of dense systems in situ. The followi ng are several novel disc overies and conclusions from this dissertation. The chemical interactions and water structure within a dilute system do not represent high solids loading slurries. The differences in the systems are demonstrated with the carboxylate group, carbonate species, and the water structure. As the solids loadi ng increases the carboxylate groups adsorbed in a unidentate mode shift toward a bidentate mode of adsorption. Also, with increasing solid loading there is formation of bicarbonates within the slurry. A novel discovery demonstrates that there is a decrease in the concentration of structured water with the combination of all three components of a slurry : NaPAA, water, and GCC. Increasing solids loading above 50 wt% increases the fluid like wa ter structure of the slurry. These results demonstrate the changes which take place as solid s loading is increase and are an important consideration for research of high solids loading slurries. Additionally, the water structure, carboxylate adsorption mode, and bicarbonate interactions were demonstrated to change with aging of a slurry. The water increases in concentration of structured water with aging. The carboxylate adsorption mode shifts from a unidentate more to a bridging m ode along with a decrease in th e activity of the bicarbonate

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119 species. With these results several water structure makers and breakers were shown to either decrease slurry performance (water structure makers) or increase slurry performance (water structure breakers). Ethylene glycol, a water structure breaker, demonstrated the best results for improving the properties of a 75 wt% GCC slurry by preventing the water structure change with age and decreasing the vi scosity of the slurry. Finally, a model for the adsorption of NaPAA onto GCC was proposed and discussed. The chelating ability of NaPAA allows for adsorption onto GCC. The adsorption is due to an increase in entropy due to the re lease of water molecules from th e dehydration of the interacting carboxylate groups and calcium ions. 8.2 Suggestions This dissertation has provided several insigh ts into the adsorption of NaPAA onto GCC in high solids loading slurries. By utilizing these insights a few suggestion ar e given to improve the dispersion of high solids loading slurries. First, chapter 6 has already de monstrated that water structure breaking chemicals could be introduced in to a slurry system to improve the properties slurry. This option would be us eful if the dispersant must not be modified. Second, improved anchoring of the dispersant could be acco mplished by adding an OH group to the carbon adjacent the carboxylate group on each repeat un it. Adding the OH group would allow for a five-member chelate ring to form with calcium ion which is more stable than the eight-member ring formed by NaPAA. Third, a water structur e breaking chemical group could be added to the alkyl chain of the dispersant. This would cause the polymer to act as both the water structure breaker and dispersant.

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130 BIOGRAPHICAL SKETCH Joshua Taylor was born in 1980 on October 19 in Santa Barbara, California. He lived in California f or 10 years, Ohio for 6 years, and then finished high school in Florida. He graduated from Riverview High School in Sarasota, Florid a in June of 1999. He then went to the University of Florida and graduated in 2004 with a Bachelor of Science in chemical engineering. In 2005, he graduated with a Ma ster of Science in materials science and engineering at the University of Florida. Joshua Taylors life is dedicated to Yeshua HaMashiach. Out of love for Yeshua, he lives a life that is wi thin the standards of the Bible.