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Mechanisms of the destabilization of kaolinite clay suspensions with aluminum sulfate

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Title:
Mechanisms of the destabilization of kaolinite clay suspensions with aluminum sulfate
Creator:
Chen, Ching-Lin, 1937-
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English
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xvi, 173 leaves : illus. ; 28 cm.

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Subjects / Keywords:
Adsorption ( jstor )
Aluminum ( jstor )
Coagulation ( jstor )
Copyrights ( jstor )
Dosage ( jstor )
Ions ( jstor )
Kaolinite ( jstor )
pH ( jstor )
Sulfates ( jstor )
Turbidity ( jstor )
Aluminum sulphate ( lcsh )
Clay ( lcsh )
Dissertations, Academic -- Environmental Engineering Sciences -- UF
Environmental Engineering Sciences thesis Ph. D
Sedimentation and deposition ( lcsh )
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bibliography ( marcgt )
non-fiction ( marcgt )

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Thesis:
Thesis - University of Florida.
Bibliography:
Bibliography: leaves 168-172.
General Note:
Manuscript copy.
General Note:
Vita.

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MECHANISMS OF THE DESTABILIZATION

OF KAOLINITE CLAY SUSPENSIONS

WITH ALUMINUM SULFATE











By

CHING-LIN CHEN


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













UNIVERSITY OF FLORIDA


June, 1966














ACKNOWGLEDGMENTS


The author wishes to express his sincere appreciation to his committee chairman, Dr. A. P. Black, for his enthusiastic assistance and continual inspiration throughout the course of this graduate research work. Specific acknowledgment is also due to Dr. J. J. Morgan for his guidance and encouragement.

The author is deeply indebted to Professor John E. Kiker, Jr., and Dr. H. A. Bevis for their advice and assistance in the scheduling of course work in the entire period of graduate study. Sincere thanks are due also to Professor Thomas deS. Furman and Dr. Hugh D. Putnam who gave their time and advice whenever requested.

Specific appreciation is also extendea to Dr. J. E. Singley and

Mrs. Annie L. Smith for their many valuable suggestions and corrections in writing this paper, to Mrs. Janice G. Larson for her excellent typing of this dissertation, and to all the author's colleagues in the water chemistry laboratory for their help and friendship.

The author also wishes to express his gratitude for the support of this investigation by Water Supply and Pollution Control Research Grant WP-139 from the Public Health Service of the United States.














CONTENTS

Page

ACKNO9LEDCMENTS ............ . . . . . . . . . . . ii


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


LIST OF FIGURES . . ................ . . . . . . . ix

ABSTRACT .. . . . . . ....... . . . . . . . . . . . . . xiv

CHAPTER


i. INTRODUCTION .............


II. HISTORICAL REVIEvI ............ . . . . . .

III. THEORETICAL CONSIDERATIONS . .. ..........


Chemistry of Aqueous Aluminum .........
Hydrolytic Reactions of Aluminum Ion
Alkalimetric Titration Curves .
Charge of Specific Hydrolysis Products Aging Effect ..................
Complex Formation ..........
Characteristics of Kaolinite Clays . . .
Structure and Chemical Composition of
Kaolinite Clays. .........
Size and Shape of Clay Particles . . .


Origin of Surface Charge on Clay Particles . . .
Cation Exchange Capacity of Clay Particles . . .
Adsorption Sites of Clay Particles . . . ....
Mechanisms of Destabilization ....... . ...
Coagulation . .................
Flocculation ...... ..................
Aluminum-Clay Interactions ...........
Reduction of Zeta Potential . . . . . . ..
Adsorption ....... ...................
Charge Reversal . . . . . . . . . . . . . . ..

IV. EXPERIMENTAL MATERIALS AND PROCEDURES . . . . ....

Materials ....... ................. . .
Kaolinite Clay . .. ............ ..
Aluminum Sulfate ............. . . ...
Reagents for pH Adjustment . . . . . . ....
Reagents for Aluminum Determination . . ....


. . . . . . . . . 0


. . . 6 0 . . . . * . .










Page


Procedures ....................
Preparation of Kaolinite Clay Suspensions . .
Preparation of Aluminum Sulfate Solutions . .
Alkalimetric Titrations ... ...........
Destabilization Experiments........
Electrophoretic Mobility Determinations . . .
Determination of Residual Aluminum ..
Adsorption Computations ...........
Aluminum-Clay Kinetic Experiments ......


V. RESULTS AND DISCUSSION ............... 51

Variable pH Series .... ................. 51
Role of pH on Aluminum Sorption ..... ... 51
Relationship Between Mobility and Residual
Turbidity ............ . . . ... 60
Effect of Initial Clay Concentration on
Destabilization .. .......... . . .. 64
Log (Al) vs. pH . . . . . . . . . . . . . . 69
Constant pH Series .............. . . ... 70
Destabilization at Constant pH 3 . . . . . 70 Destabilization at Constant pH 5 . . . . . 77 Destabilization at Constant pH 8 . . . . . 83
Kinetics of Aluminum-Clay Interactions . . . .. 99
AluminumAdsorption Rate.. . �........ 99
Effect of Mixing Time on Residual Turbidity . . 99
Effect of Agitation intensity on Residual
Turbidity ......... . . . 0 . 0 . . . 110


VI. SUMARY AND CONCLUSIONS .


. . . . . . . . . . . 12


APPENDIX . . . .......... ... . . ... ....... 115

LIST OF REFERENCES............. . . . . . . . . . . 167

BIOGRAPHICAL SKETCH ................. . ..... . 173












LIST OF TABLES


Table Page

1. Hydrolysis Equilibria of Aluminum .. . . . . . . . . 13

2. Calculated Equilibrium pH Values for Successive States in One Reaction for the Hydrolysis of A1+.. at Al . . . 14 3. Complex Formation Reactions of Aluminum . . . . . . . . . 26 4. Analysis of Aluminum Sulfate ... .............. 40

5. Kaolinite Clay Suspensions .................... 42

6. Comparison of pH Values for Maximum Hydrolysis and
Maximum Adsorption of Aluminum Ion ........... 61

7. The Empirical Constants of the Freundlich Adsorption
isotherm Equation ..... ................... . . . 96

8. The Destabilization of a Kaolinite Clay Suspension
with a Dosage of 3 g/1 of Aluminum Sulfate . . . . . . . 116

9. The Destabilization of a Kaolinite Clay Suspension
with a Dosage of 5 mg/l of Aluminum Sulfate . . . . . . . 117 10. The Destabilization of a Kaolinite Clay Suspension with a Dosage of 7 mg/1 of Aluminum Sulfate . . . . . . . 119 11. The Destabilization of a Kaolinite Clay Suspension with a Dosage of 10 mg/1 of Aluminum Sulfate . . . . . . 121 12. The Destabilization of a Kaolinite Clay Suspension with a Dosage of 15 mg/1 of Aluminum Sulfate . . . . . . 123 13. The Destabilization of a Kaolinite Clay Suspension with a Dosage of 20 mg/ of Aluminum Sulfate . . . . . . 125 14. The Destabilization of a Kaolinite Clay Suspension with a Dosage of 30 mg/1 of Aluminum Sulfate ....... .127 15. The Destabilization of a Kaolinite Clay Suspension with a Dosage of 50 mg/1 of Aluminum Sulfate . . . . . . 129 16. Adsorption Data for Freundlich Isotherm Plot. Kaolinite Clay Concentration = 61.5 mg/l. pH = 4.0 . . . .. . . 131












17. Adsorption Data for Freundlich Isotherm Plot.
Kaolinite Clay Concentration = 61.5 mg/1. pH = 4.5 . � . 132

18. Adsorption Data for Freundlich Isotherm Plot.
Kaolinite Clay Concentration = 61.5 mg/l. pH = 5.0 . . . 133

19. Effect of pH on Aluminum Residual. Kaolinite Clay
Concentration =61.5 mg/l ...... ............... . 134

20. Construction of Formation Function Curve for Aluminum
Sulfate Solution .................... . . . . . 135

21. The Effect of Total Number of Paddle Revolutions and
intensity of Agitation upon the Destabilization of a
Kaolinite Clay Suspension with Aluminum Sulfate. Initial
Clay Concentration = 63.3 mg/i. pH = 3.0 . . . . . . . . 138

22. The Effect of Total Number of Paddle Revolutions and
intensity of Agitation upon the Destabilization of a
Kaolinite Clay Suspension with Alumunum Sulfate. Initial
Clay Concentration = 63.3 mg/1. pH = 5 t 0.05 . . . . . 139

23. The Effect of Total Number of Paddle Revolutions and
Intensity of Agitation upon the Destabilization of a
Kaolinite Clay Suspension with Aluminum Sulfate. Initial
Clay Concentration = 63.3 mg/l. pH = 8 t 0.1. . . . . . 140

24. The Effect of Total Number of Paddle Revolutions and
Intensity of Agitation upon the Destabilization of a
Kaolinite Clay Suspension with Aluminum Sulfate. Initial
Clay Concentration = 31.7 mg/i. pH = 3.0 ........ . . 141

25. The Effect of Total Number of Paddle Revolutions and
Intensity of Agitation upon the Destabilization of a
Kaolinite Clay Suspension with Aluminum Sulfate. Initial
Clay Concentration = 31.7 mg/i. pH = 5 � 0.05 . . . . . 142

26. The Effect of Total Number of Paddle Revolutions and
Intensity of Agitation upon the Destabilization of a
Kaolinite Clay Suspension with Almtinum Sulfate. Initial
Clay Concentration = 31.7 mg/l. pH = 8 + 0.1 ........ 143

27. The Effect of pH on Aluminum Residual After Separation
by High-Speed Centrifuge ...... ................. 144

28. The Effect of Aluminum Concentration on Aluminum
Residual After Separation by High-Speed Centrifuge . . . 145


Table


Page









Table Page
29. The Effect of Time on the Adsorption of Aluminum by
Kaolinite Clay ..... .. ...................... 146
30. The Effect of pH on the Electrophoretic Mobility of Kaolinite Clay Particle ..... ................. 147
31. The Zone of Aluminum Floc Formation ... ........... .148
32. The Effect of pH and Anion on the Electrophoretic
Mobility of Aluminum Floc .... .. ............... 149

33. The Effect of pH on the Electrophoretic Mobility of
Kaolinite Clay Particle with a Dosage of 50 mg/1
Aluminum Sulfate ..... .. ..................... 150
34. Adsorption Data for Freundlich Isotherm Plot. Kaolinite Clay Concentration = 15.8 mg/1 ... ........... . . . . 151
35. Adsorption Data for Freundlich Isotherm Plot. Kaolinite
Clay Concentration = 31.7 mg/l ... ................. 152
36. Adsorption Data for Freundlich Isotherm Plot. Kaolinite
Clay Concentration = 47.5 mg/1 ... ........... . . . .153
37. Adsorption Data for Freundlich Isotherm Plot. Kaolinite
Clay Concentration = 63.3 mg/l ..... ............... 154
38. The Destabilization of a Kaolinite Clay Suspension with
Aluminum Sulfate. Initial Clay Concentration = 15.8 mg/1 155
39. The Destabilization of a Kaolinite Clay Suspension with
Aluminum Sulfate. Initial Clay Concentration = 31.7 mg/1 156
40. The Destabilization of a Kaolinite Clay Suspension with
Aluminum Sulfate. Initial Clay Concentration = 47.5 mg/1 157
41. The Destabilization of a Kaolinite Clay Suspension with
Aluminum Sulfate. Initial Clay Concentration = 63.3 mg/1 158
42. The Destabilization of a Kaolinite Clay Suspension with
Aluminum Sulfate. Initial Clay Concentration = 15.8 mg/l.
Final pH = 5 t 0.05 . . . . . . .............. 159
43. The Destabilization of a Kaolinite Clay Suspension with
Aluminum Sulfate. Initial Clay Concentration = 31.7 mg/l.
Final pH = 5 0.05 ........................ 160











4.4. The Destabilization of a Kaolinite Clay Suspension with
Aluminum Sulfate. Initial Clay Concentration = 47.5 mg/i.
Final pH = 5 1 0.05 .... ............... . . . . . .161

45. The Destabilization of a Kaolinite Clay Suspension with
Aluminum Sulfate. Initial Clay Concentration = 63.3 mg/i.
Final pH = 5 1 0.05 ...... .................... .162

46. The Destabilization of a Kaolinite Clay Suspension with
Aluminum Sulfate. Initial Clay Concentration = 15.8 mg/i.
Final pH = 8 t 0.1 . . . . .......... . . . . . . 163

47. The Destabilization of a Kaolinite Clay Suspension with
Aluminum Sulfate. Initial Clay Concentration = 31.7 mg/l.
Final pH = 8 � 0.1 .... ... .................... .164

48. The Destabilization of a Kaolinite Clay Suspension with
Aluminum Sulfate. Initial Clay Concentration = 47.5 mg/l.
Final pH = 8 � 0.1 . . . . ........ . . . . . . . . 165

49. The Destabilization of a Kaolinite Clay Suspension with
Aluminum Sulfate. Initial Clay Concentration = 63.3 mg/i.
Final pH = 8 t 0.1 ..... .................. . . . 166


viii


Table


Page













LIST OF FIGURES


Figure Page

1. Solubility Curve for Aluminum Hydroxide .. ......... ... 15

2. Alkalimetric Titration Curves for Aluminum Sulfate Solutions ......... ........................ . 19

3. Alkalimetric Titrations of Aluminum and Aluminum in the Presence of Sodium Bicarbonate or Sodium Sulfate . . . . 20 4. Formation Function Curves for Aluminum Sulfate Solutions 21

5. Stepwise Conversion of the Tripositive Aluminum Ion to
the Negative Aluminate ion. (From Stumm and Morgan25). . 22

6. The Effect of the Time of Aging of Aluminum Sulfate
Solutions at 90% on the Coagulation Values of Silver
Chloride, Silver Bromide and Silver Iodide Sols in
statu nascendi. (From Matijevic et al.20). . . . . . . . 24

7. The Change of pH in Solutions of Al(NO ) When Aged at 900C. (From Matijevic et al.20)... .. ..... ... 25

8. Schematic Diagram of the Cry al Structure of Kaolinite
Unit Cell. (From van Olphen ) ..... ............. 28
9. The Structure of Stern-Gouy Double Layer and the
Corresponding Potentials ....... ................ 32

10. Potential Energy of Interaction ... .......... . . . . 33

11. Critical Zeta Potential Curve. (From Tambo29) ... . 314 12. The Effect of pH on the Destabilization of Kaolinite Clay
Suspension. Aluminum Sulfate Dosage = 3 mg/l. Clay
Concentration = 61.5 mg/l ..... ............... . 52

13. The Effect of pH on the Destabilization of Kaolinite Clay
Suspension. Aluminum Sulfate Dosage = 5 mg/l. Clay
Concentration = 61.5 mg/l ..... ................ ... 53

14. The Effect of pH on the Destabilization of Kaolinite Clay Suspension. Aluminum Sulfate Dosage = 7 mg/l. Clay
Concentration = 61.5 mg/1 . . . .............. 54












15. The Effect of pH on the Destabilization of Kaolinite
Clay Suspension. Aluminum Sulfate Dosage = 10 mg/i.
Clay Concentration = 61.5 mg/1 .... .............. . . 55

16. The Effect of pH on the Destabilization of Kaolinite
Clay Suspension. Aluminuma Sulfate Dosage = 15 mg/1.
Clay Concentration = 61.5 mg/i . . . . . . . . . . . . . . 56

17. The Effect of pH on the Destabilization of Kaolinite
Clay Suspension. Aluminum Sulfate Dosage = 20 mg/1.
Clay Concentration = 61.5 mg/1 .... ................ 57

18. The Effect of pH on the Destabilization of Kaolinite
Clay Suspension. Aluminum Sulfate Dosage = 30 mg/1.
Clay Concentration = 61.5 mg/i ... .............. . . 58

19. The Effect of pH on the Destabilization of Kaolinite
Clay Suspension. Aluminum Sulfate Dosage = 50 mg/i.
Clay Concentration = 61.5 mg/1 . 59

20. The Effect of pH on the Adsorption Isotherms. Kaolinite
Clay Concentration = 61.5 mg/l. (The figures on the
right side are pH values) ................... . . 62

21. The Effect of pH on the Freundlich Adsorption Isotherms
of Kaolinite Clay Suspensions. Kaolinite Clay Concentration = 61.5mg/l... . . . . . . . . . . .. 63

22. The Effect of Initial Clay Concentration on the
Destaailization of Kaolinite Clay Suspensions with
Aluminum Sulfate. Aluminum Sulfate Dosage = 5 mg/1 . . . 65

23. The Effect of Initial Clay Concentration on the
Destabilization of Kaolinite Clay Suspensions with
Aluminum Sulfate. Aluminum Sulfate Dosage = 10 mg/1 . . . 66

24. The Effect of Initial Clay Concentration on the
Destabilizat on of Kaolinite Clay Suspensions with
Aluminum Sulfate. Aluminum Sulfate Dosage = 30 mg/1 . . . 67

25. The Effect of Initial Clay Concentration on the
Destabilization of Kaolinite Clay Suspensions with
Aluminum Sulfate. Aluminum Sulfate Dosage = 50 mg/1 . . . 68

26. The Entire Log (All - pH Domain for a Kaolinite Clay
Suspension. Clay Concentration = 61.5 mg/1 . . . . . . . 71


Figure


Page










Figure


27. The Destabilization of
with Aluminum Sulfate.
= 15.8 mg/i. Final pH

28. The Destabilization of
wA +,h Aluminum Sulfate.
= 31.7 mg/l. Final p-i

29. The Destabilization of
with Aluminum Sulfate.
4 47.5 mg/l. Final pM

30. The Destabilization of
with Aluminum Sulfate.
= 63.3 mg/l. Final pH

31. The Destabilization of
with Aluminum Sulfate.
= 15.8 mg/l. Final pH

32. The Destabilization of
with Aluminum Sulfate.
= 31.7 mg/i. Final pH

33. The Destabilization of
with Aluminum Sulfate.
- 47.5 mg/l. Final pH

34. The Destabilization of
with Aluminum Sulfate.
= 63.3 mg/l. Final pH


a Kaolinite Clay Suspension Initial Clay Concentration of Suspension = 3.0 ........

a Kaolinite Clay Suspension initial Clay Concentration of Suspension = 3.0 ...........


a Kaolinite Clay Suspension initial Clay Concentration of Suspension = 3.0 .

a Kaolinite Clay Suspension Initial Clay Concentration of Suspension = 3.0 ..


a Kaolinite Clay Suspension initial Clay Concentration of Suspension = 5.0 1 0.05 ....

a Kao!Lnite Clay Suspension Initial Clay Concentration of Suspension = 5.0 t 0.05 ....

a Kaolinite Clay Suspension Initial Clay Concentration of Suspension = 5.0 � 0.05 ....

a Kaolinite Clay Suspension Initial Clay Concentration of Suspension = 5.0 � 0.05 ....


35. The Effect of Initial Clay Concentration on the
Destabilization of Kaolinite Clay Suspensions with
Aluminum Sulfate. Final pH of Suspensions = 5.0 t 0.05


72 73


74 75 78 79 80



81 84


36. Freundlich Adsorption Isotherm. Kaolinite Clay
Concentration = 15.8 mg/1 . . . . . . . . . . . ....

37. Freundlich Adsorption Isotherm. Kaolinite Clay
Concentration = 31.7 mg/l ................

33. Freundlich Adsorption Isotherm. Kaolinite Clay
Concentration = 47.5 mg/ .... ................

39. Freundlich Adsorption Isotheim. Kaolinite Clay
Concentration = 63.3 mg/l ......... . . . . . .


Page












40. The Effect of Initial Clay Concentration on the
Freundlich Adsorption Isotherms of Aluminu-Kaolinite
Systems. pH = 5.0 t 0.05 .... ....... ......... 89

41. The Effect of pH on Aluminum Residual After Separation
by High-Speed Centrifuge ........ ................ 90

42. The Destabilization of a Kaolinite Clay Suspension with
Aluinum Sulfate. Initial Clay Concentration = 15.8 mg/1.
Final pH of Suspension = 8 t 0.1 ... ............ ...91

43. The Destabilization of a Kaolinite Clay Suspension with
Aluninum Sulfate. Initial Clay Concentration = 31.7 mg/i.
Final pH of Suspension = 8 Z 0.1 ... ............ ...92

44. The Destabilization of a Kaolinite Clay Suspension with
Aluminurm Sulfate. Initial Clay Concentration = 47.5 mg/1.
Final pH of Suspension = 8 0.1 ............. 93

45. The Destabilization of a Kaolinite Clay Suspension with
Aliuminum Sulfate. Initial Clay Suspension = 63.3 mg/1.
Final pH of Suspension = 8 t 0.1 ... ........... . . 94

46. The Effect of Initial Clay Concentration on the
Destabilization of Kaolinite Clay Suspensions with
Aluminum Sulfate. Final PH of Suspensions = 8 t 0.1 � � 95

47. The Effect of Initial Aluminum Concentration on Aluminum
Residual After Separation by High-Speed Centrifuge . . . 98

48. The Effect of Time on th.e Adsorption of Aluminum by
Kaolinite Clay Particles. initial Aluminum Concentration = 1.6 mg/i. Clay Concentration = 63.3 mg/1 . . . . 100

49. The Effect of Time of Mixing, Expressed as Total Number
of Paddle Revolutions, on the Destabilization of Two
Kaolinite Clay Suspensions with 5 mg/! of Aluminum
Sulfate at 40 rpm Agitation Intensity. pH = 3.0 .... 101

50. The Effect of Time of Mixing, Expressed as Total Number
of Paddle Revolutions, on the Destabilization of Two
Kaolinite Clay Suspensions with 5 mg/i of Aluminum
Sulfate at 40 rpm Agitation Intensity. pH = 5.0 t 0.05 . 102

51. The Effect of Tire of Mixing, Expressed as Total Number
of Paddle Revolutions, on the Destabilization of Two Kaolinite Clay Suspensions with 30 mg/l of Aluminum
Sulfate at 40 rpm Agitation Intensity. pH = 8 t 0.1 . . 103


Figure


Page











52. The Effect of Time of Mixing, Expressed as Total Number
o Paddle Revolutions, on the Destabilization of Two
Kaolinite Clay Suspensions with 5 -g/1 of Al-minum
Sulfate at 100 rpm Agitation Intensity. pH = 3.0 . . . . 104
53. The Effect of Time of Mixing, Expressed as Total Number
of Paddle Revolutions, on the Destabilization of Two
Kaolinite Clay Suspensions wit h 5 mg/i of Aluminum
Sulfate at 100 rpm Agitation Intensity. pH = 5.0 + 0.05 105 54. The Effect of Time of i Ex, rssed as Total Nuxber
of Paddle Revolutions, on the Destabilization of Two Kaolinite Clay Suspensions with 30 Mg/l of Aluminum
Sulfate at 100 rpm Agitation Intensity. pH = 8 t 0.1 . . 106

55. The Effect of Time of Mixing, Expressed as Total Number
of Paddle Revolutions, on the Destabilization of a Kaolinite Clay Suspension with 5 mg/l of Aluminum
Sulfate at Two Agitation Intensities. pH = 3.0 ..... 107

56. The Effect of Time of MEing, xpressed as Total Number
of Paddle Revolutions, on the Destabilization of a Kaolinite Clay Suspension with 5 mg/l of Aluminum
Sulfate at Two Agitation intensities. pH = 5.0 � 0.05 108

57. The Effect of Time of Mixing, Expressed as Total Number
of Paddle Revolutions, on the Destabilization of a Kaolinite Clay Suspension with 30 mg/1 of Aluminum
Sulfate at Two Agitation Intensities. pH = 8 t 0.1 . . . 109


Figure


Page











Abstract of Dissertation Presented to the Graduate Council in
Partial Fulfillment of the Reauirements for the Degree of Doctor of Philosophy

..C....TS.S 0T DE2 ITS LIZTTON OF KAOLINITE

CLAY SUZPEXSiOXS Wl- ALUviNUM SULFATE By

Chinz-lin Chen

June, 1966

Chairman: Dr. A. P. Black
Major Department: Bioenvironmental Engineering

Three major experimental approaches were used in this study to elucidate the mechanisms involved in the specific aluminum-clay interactions and subsequent destabilization of dilute kaolinite clay suspensions: (1) In one series the dosage of aluminum sulfate was maintained at some selected constant value while the final pH of the suspension was varied from 3 to 10. (2) in another series the final pH of the suspension was maintained at a constant value of 3, 5 or 8 with the aluminum sulfate dosage va-.yig from I mg/l to 50 mg/l. (3) in a series of kinetic experiments both the time of mixing and the intensity of agitation were varied.

Neither aluminum adsorption nor charge reversal of clay particles was demonstrated at pH 3 within the limits of the aluminum sulfate dosage used. However, the electrophoretic mobility of the clay particles was found to be reduced to a constant minimum value as the dosage of aluminum sulfate increased. Consequently, the mechanism involved in the destabilization of kaolinite clay suspensions at this pH value is believed to be due to a reduction of the repulsive potential between the


X _V











negatively charged clay particles through compression of the electrical dou'ole-laycr, which in turn is due to the incorporation of hydrogen and. hydratcd metallic aluminum ions into the Gouy diffuse layer.

At tH 5, a very narrow: zone of coagulation was found at the isoelectric oH point which marked the beginning of a charge reversal zone with tche subsequent restabilization of the suspension as the dosage of aluminum sulfate increased. The Freundlich adsorption isotherm model was found best to describe the adsorption of the hydrolyzed aluminum polynuclear comolex ions by the kaolinite clay particles. Therefore, it is postulated that the mechanism of the destabilization at this pH value is a reduction of the zeta potential of the clay particles through the specific adsorption of the hydrolyzed aluminum polynuclear complex ions onto the clay surface, with the subsequent reduction of the surface potential of the clay particles.

t is shown from the experimental results that at pH 8 physical enmeshment might account for the mechanism of the destabilization of the kaolinite clay suspensions when rapid and abundant precipitation of

aluminum hydroxides occurs i.e., when the dosage of aluminum sulfate exceeds 40 mg/l. However, when the dosage of aluminum sulfate is less than 40 .nz/_ at this pH, a mechanism of mutual coagulation between

_oidal aluminum hydroxides and clay particles better describes the phenomena of the destabilization.

in all cases investigated, the residual turbidity curve as a

function of the time of mixing shows that the turbidity could be reduced to a constant minimum value by stirring the suspension system with a










total of 2,000 paddle revolutions. The constant minimum value of the residual turbidity appears to be dependent on such factors as the final pH of the suspension, the aluninum sulfate dosage, the intensity of agitation and the clay concentration.

The effect of the initial clay concentration on the destabilization process was found to follow Soluchowski's theory at pH 3 and pH 5, whereas it had little effect at pH 8 when the aluminum sulfate dosage was higher than 50 mg/l.














i. iNTRO2UCTICN


The need of scientif'ic control for the removal of natural clay

turbidity from the raw water of public water supply systems has for many years been a challenging problem in the field of water cherstry. In order to provide a sound solution to this problem, the mechanisms involved in the destabilization of clay suspensions must be clearly

deonstrated. Theref'ore, the present research has been initiated in an attempt co elucidate the echanisms by hfich an inorganic coagulant effects the destabilization of dilute clay suspensions under controlled conditions.

Aluminum sulfate has been idely and effectively used as a coagulant to remove clay turbidity from water for many years. The mechanisms involved have been investigated and several theories have been proposed. However, due to the lack of specific controls in the investigations and a good understanding of the chemstry of aluminum, the proposed mechanisms have had to be revised through the years, and as yet are not well es tablished.

Electrophoretic tecuimques have been used throughout this study

in an atte::.t to reveal any significant relationships between the electrophoretic obility measurements and the residual turbidity data, and also to elucidate the charge reversal phenomena due to the adsorption of the aluminum hydrolysis products.


-1-














11. H737:0.'RCAL REVIEW


3oeore the turn of the centary, water treatment employing coagulation was an art and not a science. The early patents of that period contain no definitive data or present even the simplest of the reactions n-volved. As the water works industry began to grow to meet the needs of a rapidly expanding population, increased emphasis was placed upon bot> bacteriological and chemical qality. in 1914, the first quality standards to apply to water used on interstate e carriers were developed, and in 1923-25 the U.S. Public Health Service initiated what were really the first definitive studies of water coagalation. They were done by Therlmlt, Clark and Liller, and published in Public Health Reorts.16 They concluded that:

1. there ast be present a certain minimum quantity of aluminum or ferric cation in the -ater being coagulated;

2. they called attantion to the applicability of the SchulzeHardy rule and pointed out that an anion of strong coagulating power, such as sulfate ion, should be present;

they found that the h .rolysis products of both aluminum and ferric .ulfate w re not pure hydrates bat contained combined sulfate and tha- Ln consequence the pH mast be properly adjusted.

in 1928, Bartow and Peterson7 published their studies on the

eff..ct of some selected s ts on the rate of coagulation arn. the optinum precipitation of alum floc. So:.e of the salts studied were found to


-2-







-3-


broaden the pH range of rapid coagulation toward the low pH side.

In 1928, in a very important paper which remained unnoticed for many years, Mattson8 was able to demonstrate the relationship between the microelectrophoretic mobility of colloidal particles and the aluminum salt dosage. Mattson found that the positively charged sol, formed by the hydrolysis of the aluminum salt, exhibits its greatest effect on the zeta potential of the clay particle at a pH of about 5.2. He further showed that the hydrolysis products of aluminum and ferric salts are more effective than the trivalent metallic ions, Al++ and Fe', in reducing or neutralizing the zeta potential of the colloidal particles.

Black and his associates (1933-34) initiated the use of a pilot plant and refined jar test techniques to demonstrate the effect of some selected ions on the pH zone of rapid coagulation. They found that

the zone of rapid floc formation was considerably broadened on the acid side by the sulfate ion and to a much lesser degree by the chloride ion. Further, using both ferric sulfate and ferric chloride, they showed that in the pH zone from 6.5 to 8.5, floc formation was markedly retarded or even inhibited. They ascribed the existence of this zone to the reversal of the charge on the floc, and emphasized that adsorption is an important mechanism of turbidity removal.
12
In 1949, Langelier and Ludwig made some basic studies on the

mechanisms of flocculation, using synthetic clay suspensions, and came to the conclusion that the base exchange capacity and the size of clay particles were important factors in the flocculation process. They were perhaps the first workers to distinguish between the terms coagulation,











which they characterized as "perikinetic" and flocculation, which they called "orthokinetic" coagulation. For the first time, they used the

term "binder alum" to characterize its bridging functions in floc formation.

In 1959, Pilipovich et al.13 reintroduced the long neglected

microelectrophoretic technique to the study of water coagulation. They investigated the effects of pH, alum dosage, zeta potential, and base exchange capacity of clay particles on the coagulation of clay suspensions with alum, and concluded that the optimum coagulation dosage for clays with low base exchange capacity is lower than that for clays with high base exchange capacity. They further confirmed Mattson' 8 view that the hydrolysis products of aluminum salts are more effective than the trivalent metallic aluminum ion, A+4+, in producing good coagulation.

Black and Hannah14 summarized the results of their electrophoretic studies on the coagulation of three synthetic clay suspensions with aluminum sulfate as follows:

The zeta potential of clay particles was found to be dependent
on the pH and on the alum dosage. An amount of alum equivalent to
several times the base exchange capacity of the clay suspension
was required to neutralize the particle charge. Clarification was
best in the range pH 7.5 - 8.5 where the particles were negative, rather than at pH values where the particle charge had been neutralized. Fair coagulation was often obtained below pH 4.5 where
the particles were nearly.neutral..........instances, residual
turbidities changed sharply without any accompanying change in
mobility values.

In a series of five papers, Packham presented his extensive

studies on the coagulation of dispersed clays with aluminum salts.1519 He concluded that anions have a great effect on the pH range of optimum

coagulation, while cations have very little influence except under







-5-


conditions wherein they can produce insoluble hydroxides. Packham also concluded that the mechanism of the coagulation of dilute clay suspensions with aluminum salts is simply a physical enmeshment of the clay particles by the precipitation of the insoluble aluminum hydroxide. Thus, he came to another conclusion, namely that those factors which bring about the maximum precipitation of aluminum hydroxide will also bring about the optimum coagulation of clay suspension.

Matijevic et al.20-23 employed microelectrophoretic mobility

measurements in their studies of coagulation and for the characterization of the hydrolysis products of A1+++. They applied the well-known SchulzeHardy rule in demonstrating that the predominant species of the product of aluminum hydrolysis in the acid range is a tetravalent octanuclear complex, A18(OH)20++++. They further showed, by using both coagulation techniques and microelectrophoretic techniques, that the hydrolyzed aluminum species can reverse the charge of the negatively charged silver halide sols, AgI and AgBr, while the hydrated trivalent metallic aluminum ion cannot. This charge reversal was found to coincide with the optimum coagulation of silver halide sols. Matijevic et al. have asserted that the hydrolyzed aluminum species are more strongly adsorbed

than the trivalent aluminum ion.

In 1962, Mackrle24 confirmed his hypothesis that the initial phase of coagulation is accomplished by the following successive steps:

1. the hydrolysis of coagulant added;

2. the crystallization of the aluminum or ferric hydrous oxides;

3. the compensation of the negative charges on the colloidal






-6-


particles;

4. the mutual coagulation of the hydrous oxides and the colloidal impurities in the water; and

5. the formation of "microflocs."

These microflocs are then removed from the water by the agglomeration or matual collision of the particles. He further showed that the zeta potential is pH-dependent, and that the low zeta potential zone of the hydrous oxides identified the pH range of the optimum coagulation.

Stumm and Horgan (1962) reemphasized the importance of chemical

theory in their explanation of the basic mechanisms of colloid stability and coagulation.25 From their studies of the alkalimetric titrations of aluminum in the presence of various ion groups, such as phosphate, pyrophosphate, oxalate and salicylate, they concluded that for certain anions specific chemical equilibria, such as complex formation, may be more important than double-layer compaction through counter ion adsorption. However, if the anions are weak coordinators with the coagulating metal ions, the copacting of the diffuse part of the double layer generally will be more important than chemical interaction for the destabilization of colloids. In addition to alkalimetric titration studies, they also suggested a laboratory technique for coagulation study which allows constant pH and alkalinity to be maintained throughout each experiment, thus facilitating the interpretation of specific chemical effects in a

coagulation process.

In the studies of turbidity removal with ferric sulfate, Black and Walter 6 again demonstrated the significant effect of the base exchange







-7-


capacity of the clay on the coagulant dosage for producing charge reversal at low pH range, although the base exchange capacities of the clay suspensions were not found to be directly or proportionally related to the coagulant dosage which is required to accomplish satisfactory coagulation. Further, they gave strong support to the view that the "overdosed isoelectric point" marks the beginning of the zone of efficient orthokinetic coagulation, or flocculation.

Kim et al. investigated the effects of cation exchange capacity, pH and alkalinity on the coagulation process and concluded that:

1. The optimum final pH of coagulation depends upon the initial

alkalinity present in the suspension. As the alkalinity of the suspension is increased, the optimum final pH decreases.

2. The optimum final pH of coagulation is independent of alum dosage, but the pH range for good coagulation broadens with increasing alum dosage.

3. When the cation exchange capacity of the suspension is greater than about 10 ge/l, a pH value near the isoelectric point favors coagulation.

4. Low concentration (less than 100 ppm) kaolinite suspensions can best be treated by maintaining pH at an isoelectric point that is a function of suspension alkalinity.

Based on recent studies of the coagulation and flocculation of

several river sediment suspensions vith aluminum sulfate, Black and Chen28 postulated that both coagulation and flocculation are strongly controlled by the properties of the coagulant. The characteristics of clay particles,






-8-


such as base exchange capacity, particle size, total surface area and particle charge density, may influence the coagulant dosage required to achieve a good coagulation, but not the basic mechanisms of coagulation and flocculation for a particular coagulant. They further suggested that different mechanisms of destabilization are involved in various pH zones which are controlled by the hydrolytic reactions of aluminum ion.

Tambo29 fully discussed the validity of double-layer theory for understanding and controlling the stability and the instability of colloidal suspensions. He further emphasized that the critical zeta potential is without doubt not only a definite value but is dependent on the conditions of the suspension. There exist two factors to control the critical zeta potential; (1) the kinetic energy of a suspended particle, and (2) the maximum interaction energy. Based on the assumption of the existence of a critical zeta potential in the coagulation ofc! natural water, Tambo showed that the measurement of the zeta potential, i.e., electrophoretic studies of coagulation, is one of the most important tools for investigating and controlling coagulation.

The effect of particle size on the destabilization of colloidal suspensions in water has been extensively studied by Vilaret.30 As a result of his investigation he demonstrated the following several phenomenal

1. The optimum coagulating and flocculating dosage of a cationic polymer increases directly with an increase in the total surface area of the system, which in turn is inversely proportional to the size of the suspended particles.






-9-


2. No optimum dosage was observed during coagulation vith nonhydrolyzing metal ions, and thus particle size has no marked effect on the required coagulant dosage.

3. When a hydrolyzing coagulant, such as aluminum sulfate, is used, the particle size has an effect on the required dosage, although the relationship has not been so well defined as with high polymers.

4. Particle size has a definite effect on the kinetics of the destabilization process with the time required for optimum destabilization decreasing vith decreasing size of suspended particles.














III. THEORETICAL CONSIDERATIONS


Chemistry of Aqueous Aluminum


Since any explanation of the basic mechanisms of colloid stability and coagulation, either by chemical theory or physical theory, should concern itself with the chemical composition of the coagulant being used, a comprehensive exploration and understanding of the chemistry of aluminum is very essential for the present investigation. It is believed that
4
the chemistry of aluminum in very dilute aqueous solutions (less than 10mole/liter) is very different from that of high concentrations. Therefore, the present discussion will be limited to solutions having a concentration range of 10-6 mole/liter to 1074 mole/liter, which is in the practical range encountered in water coagulation. Hyvdrolytic Reactions of Aluminum Ion

When aluminum ion is present in dilute aqueous solution, it is

very easily hydrolyzed, and the hydrolytic reactions are very complicated. Brosset et al.31,32 investigated the hydrolysis of aluminum ion, AI*, by potentiometric titration techniques and concluded that in the acid range the main product of Al hydrolysis is a polynuclear complex with a stoichiometric ratio of OH- to Al(III) of 2.5:1. With reference to the behavior of aged solutions and crystallographic evidence, they suggested that the trivalent polynuclear complex (Al6(OH)15) + is the most likely main product. On the other hand, in the alkaline range the assumption of


- 10 -






- 11 -


the existence of a single complex (AI(OH) 4)- and solid A1(OH)3 explains the Brosset data31 very well.

Based on the ionic strength effect of the Schulze-Hardy rule, 21
Matijevic and his coworkers initiated the use of the critical coagulation concentration of aluminum salt solutions for silver iodide sole (both aged and in statu nascendi) and silver bromide sole (in statu nascendi) for determining the actual charge of ionic species in solution. By using the new electrolytic coagulation techniques they were able to identify the main hydrolysis products between the possible complexes, such as (Al 6(OH)I,5V and Al8(OH)20)''++, all of which have a stoichiometric ratio of OH" to Al(III) of 2.5 to 1. They postulate the polynuclear tetravalent species [Al8(OH)20)1+++ as the most

likely formula of the complex in the pH range 4 to 7. However, at pH values below 4, the critical coagulation concentration corresponds to that of trivalent counterions indicating the presence of the simple hydrated aluminum ion.

In addition to the complexes (Al6(OH) 5r and [Al 8(OH)2013~is more highly polymerized and hydrolyzed aluminum ions containing 6, 7, 10 or even 13 aluminum atoms in the complex, such as (Al7(OH)I7f1+Hi and [Al13 (OH)341+++++ have been postulated by several other investigators.33,34,35

Frink and Peech36 propose a completely different picture, in postulating that the hydrolysis of the aluminum ion in dilute aqueous solutions proceeds according to the simple monomeric hydrolysis mechanism, Al' + H 20 " Al(OH)+ + H. They further attempt to show that, without controlling pH, aluminum hydroxide Al(OH)3 begins to






-12-


precipitate upon diluting the solution to a concentration of aluminum salt lower than 10-5 mole/liter, which is considered to be the critical value of the supersaturation of Al(OH)3�
Packham suggested two functional types of reactions which are
thought to be involved in aluminum hydroxide precipitation as follows:18
1. Ligand exchange reactions.
(Al(H2)' + H~ 0- tAl(12) (OH))' + H30O+ (1a) (H20)5 (OH'"+ H 20 = A(H2O)4(OH)21* + H0* (lb) (Al(H20)4(OH)2)* + H20 4- (Al(H20)3(OH)3) + H36+ (ic) (Al(H20)3 (OH)3)+ H 20 0 tAl( O)2(OH)4)" + H30+ (1d) (tA(H20)6x+++ +X" (A(Yo)4 + 2H2o (2) LAl(H20)4(OH)2)+ x (Al (H2o)4 X + 2OH . (3)

2. Olation reactions.

2 H- A /OH\ (4a)
25 j Ho o) (H2o)4 AloH/',, 0


+ 2H 0
2

((HO,)4A'(OH)2A'(H,0 + H20


,(H20)4A1(OH)2A1(H20) 3(OH)) '+ H O (4b)






- 13 -


f(H20)4 A(OH)2A2(H20)3(OH))++ + (Al(H 20)5(OH))+ H20
(H20)4A( OH\ I ,OH + 2Hv (4c) Al Al(H2f)4111# 29YT OH' I '%OH'
H2.0


Table 1 shows the composition of several of the ionic and molecular species which have been suggested for aluminum and equilibrium constants for the reactions by which they may be formed.



Table 1

Hydrolysis Equilibria of Aluminum


Log of Equilibrium
No. Equilibria Constant* (250C) References


1 (Al(0H2)6)]+++ + H20 2 AlOH]++ +H 0+ -503 37 2 2A1'4- +2H20 # (A12(OH)2+++ 4- 2H -6.27 37 3 Al++ + 3H20 2 Al(OH)3(S) + 3He -9.10 38 4 Al(OH)3(S) + H2o (Al(OH)) + H -12.74 38 5 8Al+++ + 20H20 a (Al8(OH )20)"+H+ 2oe -- 21 6 6Al++ + 15H20 - (AI6(OH)5]+++ + 15e1 -47.00 32 7 AI(OH)3(S) Al+++ + 30H- -32.96 39


Additional constapts can be found in the works by Bjerrum, Schwarzenbach and Sillen,u and Latimer.41

Ligand - H.0 molecules are ommitted from subsequent reactions for brevity.






-14-


Figure 1 is a general plot of the concentrations of the various aluminum species at different pH values. The solubility of aluminum h.'roxide Al(OH)3 is defined by the boundary of the shaded area on the figure.

Table 2 presents calculated data for equilibrium pH values for which the molar ratio of tAl1 or [ Al6(OH)15+'1 to tAITI has been predetermined. The reaction formula and equilibrium constant used for this calculation are listed in line No. 6 of Table 1.


Table 2

Calculated Equilibrium pH Values for Successive States in One
Reaction for the Hydrolysis of Al+++ at AlT.'



AlT ( AlT pH

0.99 0.01 4.23 0.90 0.10 4.31 0.80 0.20 4.35 0.70 0.30 4.38
0.60 0.40 4.42 0.50 0.50 4.46 0.40 0.60 4.50 0.30 0.70 4.56 0.20 0.80 4.63 0.10 0.90 4.75
0.01 0.99 5.16


to 50


is equivalent
the calculation.


A concentration of 1.5 x 10-4 mole/liter, which m1l of Al (SO ) . 18H20, is assumed for (AlT]in is the total alufflinum concentration.






- 15 -


0

-1


-2


-3


-4
B








-7


.8


-9 E


-10
4 5 6 7 8 9 10 Z PH

Figo - Solubility C~lve for Alwdnum Hydroxides
As A16(OH)15 D: +"

BI Al(OH)+2 9: A1(OH),

C, A'2(oH)24






- 16 -


Alkalimetric Titration Curves

The information yielded from the results of the alkalimetric

titrations of aluminum in aqueous solutions is very valuable for understanding aluminum hydrolysis phenomena and the composition of the various hydrolysis product species as functions of pH value. Figure 2 shows typical alkalimetric titration curves for aluminum sulfate solutions with different total concentrations of aluminum. The titration curves for aluminum sulfate solution and aluminum in the presence of

sodium bicarbonate NaHCO3 or sodium sulfate Na2SO4 solution are shown in Figure 3The average number of bound hydroxide ions per aluminum ion

applied, the formation function fi, can be calculated from the data of alkalimetric titrations. The computation of the function for aluminum sulfate solution may be illustrated in the following way.

Assume that the series of aluminum hydrolysis product species can be represented by the general formula (Alm(OH)n(So4) ) 3m-n-2p

where m and n may equal to any small positive integral number excluding zero.

p may equal to any small positive integral number including zero.

The total aluminum concentration at any pH is given by





- 17 -


The electroneutrality at any pH is given by
IH') + tNa+) + 3 (Al] + I(3m-n-2p) ( Alm(OH)(SO4) 3m-n-2p] 4p %I
-2 (SO4 + ( 1o1 (6) The total concentration of sulfate ion at any pH is given by S S04 - ( Al [T) "1p fAlm(OH)n(SO4 ) p3mn-2pl (7) The combination of equations (6) and (7) leads to

(H+) + (Na+J + 3 (Al+++ + (3m-n-2p)Al(OH)n(O4)p3mn-2P

P 3 A'T 2 1p tAl(OH )n( S0) p3mn2pj + OH-) (8) The combinations of equations (5) and (8) leads to tH+ + [Na+ + 3[Al+++I+I(3m-n-2p) Alm(OH)n(S)p3m'n'2p)

3 (Ai++ + 3 m Al.(OH)n(SO4)p3m-n2p - 2Xp [Alm(OH)n (304) 3D1-n-2p..J. (Qif) (9) The simplification and rearrangement of equation (9) leads to

(H+) + tNa+} - [OH"1 = Xn (Alm(OHn (S4)p 3Mn2p) (10) Now, the formation function n at any pH can be given by

- (0H1 bound
n [Al T) (U)

n (Alm(OH) n(SO4)3mn'2p (12)


t ej~ + t[Na+J - OH-)la







- 18 -


Since the parameters on the right side of equation (13) are known from alkalimetric titration data, the formation function R can be easily evaluated.

Some of the computed formation function R data are plotted as

functions of pH in Figure 4.


Charge of Specific Hydrolysis Products

Since there is a random behavior in the arrangement of the structure of the hydrolysis product in the hydrolytic reactions, only the statistical charge average of the hydrolysis products can be evaluated from formation function Ta data. However, because the best available data indicate the existence of some active predominant hydrolysis products throughout the entire series of reactions, a general discussion of the charge of some specific hydrolysis products is feasible and it provides valuable information for an understanding of the electrokinetic characteristics of the flocs formed by the interaction of the polymeric species with clay particles in the destabilization process. The charge of the various aluminum hydrolysis products which are assumed to be formed at different pH values can be summarized in a hypothetical scheme as shown in Figure 5.


Aging Effect

When solutions of aluminum salts are aged, either at ordinary room temperatures or at elevated temperatures, certain aqua-complexes may be formed by hydrolysis of the aged solutions. These aging reactions are more rapid in solutions having higher concentration of hydroxide ion,
































0.1 1 NaOH (meq)

Fig. 2 - Alkalimetric Titration Curves for Aluminum Sulfate Solutions.














10-----9 . . /


S-.... 50 ppm A(SO,,.18 H20
7 - 50 PM A'l(SO,)3<.8 H.0 and
6 1.5 x 16-3M NaH{C03
-50 PPM A'2(SO,6)3.18 H.0 anid
5 1.5 x 10-3 K NaSO,


!3 I i I I S I I I I I I! 1
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8
0.1 N NaOH (meq)

Fig. 3 - Alkalimetric Titrations of Aluminum and Aluminum in the Presence of Sodium Bicarbonate
or Sodium Sulfate.













10


9 It.





-- --- 5 0- l





-- -1. x 10~ K Al T







flu 1 ~bound (AlT)

Fig. 4- Formation Function Curves for Aluminum Sulfate Solutions.





- 22 -


(A(,H0)6)3+
(a)
( OHO
(Al(HO)(OH )j 2+ oH" ( A(Ho)U(oH)2 +


OH"


OH"


aq.)


{A16(O)15)3'
(d)


I
(A18(ou)20)4+ (aq.)
(e)

I OH"
A.I(OH)3(H20)3 (a)
(i)

I oW (Al(oH) 41"
(g)


Fig. 5 w Stepwise Conversion of the Tripositive Aluminum Ion to the
Negative Aluminate Ion. (From Stumm and Morgan.5)







- 23 -


or at elevated te perature. 25

It has been shown that this aging effect causes a decrease in the critical coagulating concentrations of aluminum ions and simultaneously an increase in the hydrogen ion concentration of the solutions of aluminum salts.20 Figure 6 and Figure 7 show the effect of this aging process on the coagulating concentration and pH of aged aluminum so" nations.


Complex Formation

The formation of soluble and insoluble complexes by specific

chemical interactions of aluminum ions with anionic functional groups, such as sulfates and phosphates, has considerable significant effect on 42
the flocculation process throu-.h a cross-linking or bridging mechanism. It is especially important when metal ions are employed to flocculate hydrophilic colloidal suspensions.25 Some of the complex formation reactions of aluminum ions and their equilibrium constants are listed in Table 3Characterstics of Kaolinite Clays


Clays comprise the major portion of the colloidal material

which, suspended in natural waters, the water chemist terms natural turbidity. Langelier and Ludwig12 were among the first to initiate the use of synthetic clay suspensions for the investigation of the water coagulation. Black and Chen have demonstrated the applicability of the results from synthetic clay suspension studies to natural 28
river sediment suspensions. Therefore, for simplicity in






- 24 go


AgN03 a 0-OO0lN
HCl,HBr or KI(M 13) o.oo














N41






mm 8 - - k 4 m mwq m mint


300


600


900


Tim of A"g A1Z(So4)3 at 90C (min.)

Fig. 6 - The Effect of the Time of Aging of Aluminum Sulfate Solutions
at 90 on the Coagulation Values of Silver Chloride, Silver
Bromide and Silver Iodide Sole in statu nasoendi.(From Matijevlo


.6


0






- 25 -


5.0









Concentration of Al(NO, 3 aged at 900:

0.002 N

4.0





0.002 N

3.5 .0N
0 300 600 90o
Time of Aging AI(N03)3 at 90�C (min.) Fig. 7 - The Change of pl in SolutiqDs of AI(NO3)3 When Aged at 90C.
(krom Matijevic =.rid a.)






- 26 -


Table 3

Complex Formation Reactions of Aluminum25


Log of Equilibrium
No. Equilibrium Constants (25�C)

I Ai +p AlPOIS 22
1 n + P0 P" 0n 4 (S)

2 Al + P207 _- jAlP207

3 i++ + F" = (AlF)Y 6.13

4 Al++ + 3 Acetate "Al(Acetate)jJ -5 A+' + 3 Oxalate-" t (Al(Oxalate)--" 16.3

6 Al+' + Salicylate'- = tA1 Salicylate)+ 14


designing the laboratory experiments comprising the present investigations, kaolinite clay suspensions have been used. A general description of the characteristics of kaolinite clays will therefore be useful.


Structure and Chemical Composition of Kaolinite Clays

Kaolinite may be described as a two-layer clay whose particles are made up of a single tetrahedral silicon sheet topped by a slightly distorted octahedral aluminum sheet. The two layers are joined by condensation and splitting off of water between adjoining hydroxyl groups in the vertex position. Thus a single oxygen linkage remains and is shared by the two layers, resulting in a primary valence bond between the sheets.

The atomic charges in the structural units are balanced, and the






- 27 -


chemical composition of a typical structural unit may be expressed as

(OH)8A14Si 4010. Kaolinite is often referred to as having a 1:1 lattice, and the extent of atom substitutions in the lattices is relatively small.43. A schematic diagram of the crystal structure of kaolinite is shown in Figure 8.


Size and Shape of Clay Particles

Due to the existence of the strong valence bond between the two unit layers of kaolinite clay, these clay particles commonly are quite resistant to natural mechanical cleaving forces. Consequently,

natural kaolinite clays are usually composed of fairly large unit particles, larger than three microns. A kaolinite clay particle may be described as a thin, plate-like, hexagonal crystal. Origin of Surface Charge on Clay Particles

The surface charge on clay particles, which are hydrophobic

colloids, may be produced, according to van Olphen44 in either of two ways. The first source of surface charge which he suggests is the net result of imperfections within the interior of the crystal lattice of the particle. The second source suggested is the preferential adsorption of certain specific ions on the particle surface.


Cation Exchange Capacity of Clay Particles

The cation exchange capacity of a clay is its ability to exchange cations with the solution phase. The aluminum layer in kaolinite clay seems to have amphoteric properties and will produce more hydrogen ions by dissociation as the pH of the system increases. Therefore, kaolinite






- 28 -


Octahedral She

















Tetrahedral Sheet


\i/\1/ \IY/\1




/I \/ I/\
6


(OH)




~(Al)




(o) + 2 (OH)









(s)

(0)


Formula of unit cell: (,A2(OH)4(Si205))2 Unit cell dimensions:
0
A = 5.15 A

B = 8.9X

C = 7.2
Unit cell weights 516

Fig. 8 - Schematic Diagram of thp,.Crystal Structure of Kaolinite Unit
Cell. (From van Olphern?').







- 29 -


clays have variable cation exchange capacities depending upon the pH of the system. The cation exchange capacity of kaolinite clays may vary from 3 to 15 milliequivalents per 100 grams at pH 7.0.45


Adsorption Sites of Clay Particles

According to van Olphen44 kaolinite clay has a nonexpandable lattice and thus a smaller "c-spacing." Such a structure tends to physically prevent the accommodation of cations in the interior of the clay particle. Therefore, all cations must be adsorbed on the exterior surface of the clay particle.


Mechanisms of Destabilization


In the field of colloid science at least two different theories have been historically advanced to explain the basic mechanisms involved in the stability and instability of colloidal systems. The first theory is the so-called chemical theory which assumes that colloids are aggregates of definite chemical structural units, and assumes the existence of specific chemical interactions between specific ions in both phases of colloids and solutions. According to this theory the destabilization of colloids is the result of the precipitation of insoluble complexes formed by those specific chemical interactions. The second theory, termed the physical theory or double-layer theory, emphasizes the importance of the electric double layers surrounding the colloidal particles in the solutions and the significant effects of counter-ion adsorption and zeta potential reduction in the destabilization of colloidal systems. These two theories may appear at first






- 30 -


sight to be different, but they are not mutually exclusive. As a matter of fact, both mechanisms must be employed in order for a comprehensive understanding and for effective control of the phenomena of colloid stability and instability. Under the present heading only a general discussion of the destabilization mechanisms of the hydrophobic colloids, to which clay colloids are classified, will be given. Coagulation

Definition. According to La Mert4 coagulation can be best defined as follows: "We propose that coagulation be used for the general kinetic process obeying the simple Smoluchowski equation independent of E, whereby colloidal particles are united (L. coagulare - to be driven together) as typified by the effects of electrolytes upon gold sols. Coagulation is brought about primarily by a reduction of the repulsive potential of the electrical double layer in accordance with the ideas advanced by Derjaguin, Landau, Verwey and Overbeck."

Double-Layer Theory. The electric double-layer surrounding a colloid may be created by the preferential adsorption of counterions onto the clay surface as a result of the charge deficiency within the clay lattice, or the direct ionization of some of the molecules on the colloid surface. Among the many theories47'48 which describe the structure of the electric double-layer, the Stern-Gouy diffuse doublelayer theory has been found most acceptable in the case of clay colloid

systems. In this particular model, part of the counterions remains in a compact layer, Stern layer, on the charged colloid surface in consequence of the existence of strong electrostatic forces as well as van der Waals






- 31 -


forces, while the other part of the counterions extends into the bulk of the solution and constitutes the so-called diffuse Gouy-Chapman layer. Figure 9 shows the structure of the Stern-Gouy double-layer and the corresponding potentials. The potential at the surface of the particle itself is generally designated as 1A, while the potential at the boundary between the Stern and the Gouy part of the double-layer is designated as 9l. The potential at the plane of shear which essentially separates the hydration water from the bulk of solution is distinguished as the zeta, ', potential. It is this zeta potential which controls the stability and instability of the colloid system.

Critical Zeta Potential. According to the findings of electrophoretic studies on water coagulation,14928 the zeta potential of colloids need not be reduced to zero in order that coagulation may take

place, and this fact has led to the concept of a critical zeta potential. The theoretical derivation of the critical zeta potential is based on the principle that the total kinetic energy, Ek, of the colloid particle should be large enough to overcome the energy barrier, which is the maximum interaction energy, Emax, between two approaching colloidal particles (see Figure 10). Tambo concluded from his derivation of the cr tical zeta potential for the coagulation of ordinary natural water, which have inverse values of the thickness of the Debye-Hiickel ionic atmosphere (Kvalues) in the range of l05.5 to 106.5 cm1, that 12 mV may be used as a threshold value for the coagulation of most waters in water supply systems.29 Figure 11 shows his critical zeta potential as a function of K value.







- 32 -


G


G

0


Oouy layer


layer


solvent


-- Plane of shear


I




Distance from the surface of clay Fig. 9 -The Structure of Stem-Gouy Double Layer and the Corresponding
Potentials.







- 33 -


Stern layer Gouy layer


-. Plane of shear Repulsive potential energy curve








face of clay particle



4





F . 1I


Fig. 10 - Potential Energy of Interaction.






- -


106.5 1O6,3


F, - Potential (mV) Fig. 11 - Critical Zeta Potential Curve. (From TambO9).






- 35 -


Flocculation

Definition. It is important that a distinction be made between the terms coagulation and flocculation to account for the different forces involved. According to La Mer flocculation should be defined as follows:46 "We propose that the term flocculation should be restricted more in accordance with original usage corresponding to the Latin meaning of floc (L. flocculus - a small tuft of wool or a loosely

fibrous structure). Flocculation is usually brought about by the action of high molecular weight materials (potato starch and polyelectrolytes in general) acting as linear polymers which bridge and

unite the solid particles of the dispersion into a random structure which is three dimensional, loose, and porous."

Bridging Mechanism. Interparticle bridging action has been proposed by many investigators49,50,51 as the basic mechanism in the flocculation of colloidal dispersions with polyelectrolytes. This same mechanism may also serve to explain the flocculation of clay suspensions with hydrolyzing metal coagulants. According to the bridging theory the polymer molecules are postulated to have part of themselves attached on the adsorption sites of the suspended particles and with other parts of the chains extended into the bulk of the solution.

When these extended chain segments are adsorbed on the vacant adsorption sites of other suspended particles, bridges are established. Consequently, the particles are bound together and form small packets which

can grow into big porous structural units until the shear gradient imposed by agitation in the system serves to prevent further growth.







- 36 -


Enmeshment Mechanism. The rapid flocculation of clay suspensions with aluminum salts has been explained by Packham19 and Eackrle24 as due to the physical enmeshment of the clay particles by the precipitation of the insoluble aluminum hydroxide. Under this enmeshment theory, it is postulated that the pH zone of optimum precipitation of aluminum hydroxide is the controlling factor in producing optimum flocculation.


Aluminum-Clay Interactions


The following experimental phenomena which take place in the

interactions between aqueous aluminum ions and clay particles in dilute

suspensions are believed to be most significant on the destabilization of the dilute clay suspensions.


Reduction of Zeta Potential

Depending upon the characteristics of the different types of

counterions involved in the aluminum-clay-water systems, the repulsive zeta potential of the clays may be reduced in three different ways, as follows:

1. by the compression of the double-layer thickness in consequence of the incorporation of the simple cationic counterions into the diffuse Gouy double-layer;

2. by the specific adsorption of the cationic hydrolyzed species on the clay surface with a concurrent reduction in the surface potential of the clay particles; and

3. by the reduction of the particle surface charge, which is







- 3? -


acco-z 2nied by a reduction in the particle surface potential, as a result of the partial neutralization of particle charge by the attachment of aluminum hydroxides through physical enmeshment or mutual coagulation nech 2ism.

in general, the decrease in zeta potential is related to a decrease in the thickness of the electrical double-layer. The extent to Vrdch the double-layer thickness may be compressed depends upon the conc tration and valence of the added counteions in the colloid system. Adsorption

The acua-comolex ions of aluanum hydrolysis products may be adsorbed orito the adsorption sites of the clay particles by specific meoInisns. Thre are many types of adsorption models available for descritbing the various types of physical adsorptions.48 Among those the Freu.ndlich adsorption >:dl is considered to best describe the case of the adsorption of the soluble aluminum hydrolysis products by kaolinite clay suspensions.

Adsorption Iechanisns. The adsorption process may be described by one or more of the folloTing postulated mechanisms:

1. Hydro3en bonding betwee-n the clay rnd the counterion.

2. Adsorption through the agency of the residual valence forces

in cl. lattices.

3.A specific chemical reaction taking place on the surface of

the clay between the adsorbed ion and the clay with the subsequent formatio-. of an isoluble complex.

4. Dipole effect of the counterions.







-38 -


Freundlich Adsorption Isotherm. The Freundlich adsorption isotherm equation may be written
1/n

(rx) = KC 1n(14) or log (x) = log K + 1 log C (15)

where x = weight of material adsorbed

m = weight of adsorbent

C = equilibrium concentration of the material being adsorbed

n,K = empirically derived constants Charge Reversal

The phenomena of charge reversal of the clay particles in the

coagulation of clay suspensions with metal ion coagulants, such as aluminum salts and ferric salts, have been demonstrated by many investigators.14,26s28 The pH range of charge reversal generally corresponds to the range of the formation of the polynuclear hydrolysis products. Consequently, it has been postulated that the charge reversal is caused by the specific adsorption of a sufficient amount of the hydrolyzed polynuclear species onto the surface of colloids.21 In addition to the above findings, a zone of redispersion of colloids has also been revealed to be consistent with the zone of charge reversal.















IV. EXPER14NTr.L 1,LTSRIkL AND PROCEDURES


Materials


Kaolinite Clay

The kaolinite clay used in preparing the clay suspensions in thi. investigation was the particular species, Kaolinite 4, supplied by Ward's National Science Establish ent. This was the same clay used by Bla,; and his cowor.:ers in their previous coagulation studies.14,26,51 The base exchange capacity of this clay is 8.7 milliequivalents per 1'j grams, which was deterined by Hannah using the ammonium acetate m_thod.52 In addition, the surface area of the kaolinite clay calculated from B.E.T. nitrogen gas adsorption data53 was reported by Birkner to be 15.8 m2/gm.


Aluminum, Sulfate

The coagulant used in this study was reagent grade aluminum sulate h a chernIcal formula Al,,(S04)3 * 18H20. The chemical analysis of this material is given in Table 4.


R:,-ents for pH Adjustment

Standardized 0.1 N HCl nd 0.1 N NaOH solutions were used to adjust the final -;D values of ;h clay suspensions. WP.i:ts for Ainu,-, Deter:.Liation

T?.* reage..ts used for determining the total aluminum are







- 40 -


Table 4

Analysis of Aluminum Sulfate


Constituent


Per Cent by Weight


Al n(SO )18H0
Assay (A12(54)3 .820 Insoluble Matter

Chloride (Cl) Arsenic (As) Substances not Precipitated by NH4.OH (as S04) Heavy Metals (as Pb) Iron (Fe) pH of 5% Solution at 2&C


103.0
0.003 0.0008

0.00003

0.10

0.0005

0.0005

2.4


Analyzed by J. T. Baker Chemical Company, Phillipsburg, N. J.



described in the following sections:54

Standard 100 ppnm Aluminum Solution. Dissolve 1.757 gma of aluminum potassium sulfate in distilled water containing 50 ml of 5 N hydrochloric acid and dilute to 1 liter.

1 Per Cent p-Nitrophenol. This indicator solution was obtained directly from W. H. Curtin and Company.

5 N Amrronium Hydroxide. Dilute 33 ml concentrated ammonium hydroxide to 100 ml with distilled water.

0.5 iC Hydrochloric Acid. Dilute 4.5 ml of concentrated hydrochloric acid to 100 ml with distilled water.






- 41 -


1 Per Cent Thio - n y-i)e ic Acid. Tne thioglycollic acid used was an analytical grade cheacal supplied by Eastuman Kodak Company.

Alurlnon Reagent. Dissolve 0,25 U. of alninon in 250 ml of

distl - d :ter, warning the solution. Add 5 gm of gm acacia followed by 37 gn of arnoniu.. acetate and 126 r1 of 5 N hydrochloric acid. Dilute to 500 m.1 and then filter under suction.


Pro cedures


Preparation of Kaolinite Clay aSspensions

Before it was suspended in denineralized water, the kaolinite clay was pulverized in a l nill for a period of 24 hours and sieved through a 200 mesh screen, which has an average open ng of 0.074 millimeter. One hundred twenty grams of the sieved kaolinite clay powder was susnended in 0 liters of dewiieralzed ter in a polyethylene carboy. The suspension waj vigorously stirred for 12 hours Aith a high-speed mixer

-ipp ,with a long stainless steel shaft and propeller, after which

the suspension was allowed o settle quiescently for 24 hours to separate

a large size fractions. The supernan"t portion of the settled clay suspension was then. &phoned off and stored in another polyethylene carl~y. The particle size 2 a clay suspension thus prepared will have a size range smaler tL tio microns as estimated from the Stokes law. ,1-orous -ixz vas startad io hours before and was continued through the entire process of pipetting various size aliquots of the settled clay suspension :-'o n'd _idual 2 -- :1 t phylene bottles, which were then stoppered, labelled and stored until needed. 'hen these different size







- 42 -


aliquots were diluted to two liters with demineralized water, the various values of clay concentration and initial clay turbidity as shoun in Table

5 were obtained.



Table 5

Kaolinite Clay Suspensions



Clay Concentration (mag/l) Initial Turbidity (units)


15.8 20 18.8 24 31.7 41 37.2 51

47.5 67 61.5 102 63.3 104 73.9 125


The clay concentrations were determined gravietrically.



Preparation of Alu.inun Sulfate Solutions

All aluminum sulfate solutions were prepared by dissolving an appropriate amount of reagent grade aluminum sulfate in demineralized water. Those solutions having concentration levels higher than 10 mg Alum/ml were prepared every tuo weeks, while those having concentrations lower than 10 mg Alum/m-l were prepared at much shorter intervals, the











criterion being the maintenance of constant pH values, which were neasured daily.


Aki ic T~.tations

3 ndardiza"ion of 0.i N Sodiun, Hy _de Solution. The 0.1 N

sodium hydro de solution wiich a-s used for both alkalimetric titration and -H ad ust .t was orecisely standardized by praary standard potassium acid ohthalate soluticn XHC C

Tit tion of' Al)-ninua Sulfate Solution. Danidneralized water was used to prepare the aluninum -,ilate Solu iono for titration experiments. A Teflon-covered magnetic bar and a rTag.etic stirrer were used to mix the solu ion thoroughly for three minutess after the drop-ose addition of the standardized 0.1 N sodium hvdzir _de solution. pH value of the solution

1.-s detenTe2--ned by th-e 3 cc'dw . la G -H Y~cter. The same procedure was repeatd until a pH value of 10 was recorded. Through the entire titration process a pure nitrogen gas flow 'as babblod through the solution ding titrated� The temperature^ of the solution was maintained constant at 250C

Titration of Di>D, Ko-n...'te 'D Susosion. The procedure for titrating the dilute kaoLni ie clay suspensions, which had different dosages of aluIum sulfate solution, with the standardized 0.1 N sodium Sroxie solution Tas Si ilar to that used for the alum solutions.





The dsstabilizatio'- :qerin.nts i$rich have be=- conducted in this nvst~ion may be grouped into four different series as follows:







-44-


1. With the dosage of aluminum sulfate fixed at a selected constant value, but varying the final pH of the clay suspension.


2. With the final pH of the clay value of pH 3, but varying the dosage of ferent clay concentrations were used.

3. With the final pH of the clay value of pH 5, but varying the dosage of clay concentrations were used.

4. With the final pH of the clay value of pH 8, bat varying the dosage of


suspension fixed at a constant aluminum sulfate. Four difsuspension fixed at a constant aluminum sulfate. Four different



suspension fixed at a constant aluminum sulfate. Four different


clay concentrations were used.

Although there are some differences among the four series of experiments, the preparation of clay } rking suspension, function and intensity of agitation, sampling, residual turbidity measurements and pH measurements, as described in the following sections, were exactly the same in all series.

Preparation of Clay Iiorking Suspensions. Six bottles of the

kaolinite clay stock suspensions were used for each series of jar tests. The contents of the bottles were quantitatively transferred to separate two-liter volumetric flasks in which about one liter of the demineralized water had been placed. Appropriate anounts of 0.1 N HC or 0.1 N NaOH wnere added to the flasks to yield the desired final pH values, and the flasks were then filled to the mark -ith additional demineralized water. A Teflon-covered magnetic bar was then placed in each flask and the flasks were then placed on magnetic stirrers. The suspensions were thoroughly







- 453 -


mixed for five minutes. One-liter graduated cylinders were then used to measure one liter of the suspension from each flask and this was

transferred to a 48-oz square jar. The jars were placed on the multiple laboratory stirrer which was manufactured by Phipps and Bird, Inc. The suspensions remaining in the flasks were retained for the electrophoretic mobility determinations.

Function and Intensity of Agitation. The suspension in the 48-oz square jars was agitated by the stainless steel paddles on the multiple laboratory stirrer at a speed of 100 revolutions per minute for two minutes before and after the addition of appropriate dosages of aluminum sulfate. The speed was then reduced to 10 revolutions per minute for a period of 28 minutes. The suspensions were then allowed to settle quiescently for 10 minutes in order to separate the settleable flocs.

In addition, a second combination of mixing was used, which consisted of a 20-minute period of 100 rpm rapid mixing followed by a 10minute period of 10 rpm slow mixing, followed by a period of 10-minute sedimentation. In all cases, a final pH of 5 was used.

Sampling. At the end of the prescribed sedimentation period

250 ml samples were withdrawn from each jar by an apparatus similar to that described by Cohen55 at a level approximately one inch below the surface of the supernatant in the jar. The samples so obtained were used for residual turbidity and residual aluminum determinations.

initial and Residual Turbidity Measurements. The initial and residual turbidities of the samples were measured with a Lumetron











Model 450 Filter Photometer.- The use of a 650 mp red filter with a 75 mm light path in the cell was found to give sufficiently accurate readings of the turbidity values. The calibration of the Photometer was accomplished by comparing the optical density readings with the turbidity readings for each sample.56 The optical density readings from the Photometer were plotted against the turbidity readings from a Jackson Candle Turbidimeter by the method described in Standard Methods.

The initial turbidity of each clay suspension was determined by averaging the turbidity values of four samples of each suspension in

which no coagulant or other reagent had been added.

In each destabilization experiment, the residual turbidity of each sample was measured promptly at the end of the sedimentation period.

pH Measurements. The destabilized suspensions which remained in the jars after the sampling process were used for the final pH determinations. All the pH determinations were made with a Beckman Model G pH Meter.


Elect-'ophoretic Mobility Determinations

Sample Preparation. Prior to t-he addition of the predetermined amount of aluminum sulfate, each of the remaining one-liter samples of



Manufactured by Photovolt Corp., New York, N. Y.

Manufactured by Beckman Instruments, Inc., Fullerton, Calif.


- 46 -







- 47



the clay suspensions which were retained from the destabilization experiment was placed on a magnetic stirrer and mixed vigorously for five minutes. Mixing was continued for another five minutes after the

dosing of aluminum sulfate, and then the electrophoretic mobility of the particles was immediately determined.

Measurements of Particle Electrophoretic Mobility. Throughout

the entire course of this investigation, the Briggs microelectrophoresis cell was used to determine the electrophoretic mobilities of particles. The calibration of the cell as well as the procedure for determining particle mobilities were the same as those described and recommended in detail by Black and Smith.58-60

Specific Conductance Determinations. A Model IB-2A Impedance Bridge with a pipette-form conductivity cell having a cell constant
-i
of 1 cm was used for the measurements of the resistance of the clay suspensions. The specific conductance values were then calculated from these resistance data according to the procedure described in

Standard Methods.57

pH Mieasure-ents. The pH of each sample was measured with a

Beckman Model G pH Meter immediately after the mobility determination of the same sample was made

Calculation of Mobility Values. The electrophoretic mobilities of particles were calculated from the equation:58



Manufactured by Heath Company, Benton Harbor, Michigan.






- 48 -


= dX
ti


(16)


where- = mobility, in /sec/v/c.

d = distance across a square of the Howard counter at a

given magnification, in p
2
X = cross sectional area of the cell, in cm t time for traveling across d, in seconds

I = current density, in amperes

R = specific resistance of the suspension, in ohms

centimeters


Determination of Residual Aluminum

Standard Curve Calibration. A standard curve was prepared on the Lumetron Model 450 Filter Photometer by using standards containing

0.0 to 1.5 mg/l aluminum, Al, prepared by dilution of the standard 100 ppm aluminum solution. A separate calibration curve was plotted for each new batch of aluminon reagent. The optical density readings of the standards were obtained by using a 530 mu filter and a 3.75 mm light path in the cell.

Separation of Clay Particles. After the destabilization experiment was completed, a 250 ml sample of the supernatant was withdrawn from each jar as described in the previous section of sampling. A 100 ml of this sample was transferred into two 50-ml plastic centrifuge tubes, and then they were immediately centrifuged with a Model HR-I International High-Speed Refrigerated Centrifuge for 10 minutes at a speed



Manufactured by International Equipment Company, Boston 35,


Mass.






- 49 -


. 90 .,. to allow a combo'setc senaration of the clay particle from the _ quid. -he va .l" of 9,30 r m is equivalent to 4,600 x g.

Procedures fc Al- -e nati 3. The procedures for

deterAMnin the res a alLL-n'a in the sample were basically the same as those developed by Packham.4 The successive steps used in the

determinaticn+ were as follows:

I. A 50 ml an[ s e of the center gate, which was estimated to contain less t1.an 0.075 mg of alminun, was pipetted into a l00-I volmmetric flask. The volume of s.o e was reduced to 25 ml or 10 ml when the aluminum, concentration was estimated to possibly exceed

0.075 n, and a dilution 2ac.r Was U.L to calculate the actual con;,ntration of aluminum in the samie.

2. One drop of 1 r ccnc p-Nitroph1-:nol indicator solution was add d to the sample. Five N za-onium hydroxide was added drop by drop until the solution turned yellow.

3. The yellow coloration was then discharged by the dropwise addition. of 0.5 N hydrochloric acid.

4. To the sclution 16 drops of the freshly prepared 1 per cent thioglycolliL. acid and 10 nI of aliinon reagent was added. Demineralized water was then used t3 make up the volume to approximately 95 ml.

5. The flask was then nmmersed in boiling water for 20 minutes, after which it was removed from the boiling water and cooled rapidly L- cold i-a.iing water to around 2000. iLnally, the solution in the flask was made up to 100 i-l with1 dc. .neralized water.

6. The optical density -alues of tp processed samples were






- 50 -


determined with the L.ietron Photometer, using a 530 Mil filter and a

3.j A li-ht path in the coll.

Each jar test consisted of six individual experiments so that a total of six samples and one blank was prepared for every series of residual al=uninm determinations.


Adsorntion Coi-wtations

The difference between the total aluminum added to the clay

suspension and the total aluminum still remaining in the centrifugate of the suspension was calculated and reported as the adsorption value. A!Lminui-Ciay Xinetic Experiments

Aluminum Adsorption Rate. The adsorption rate of aluminum by kaolinite clay was determined by measuring the residual total aluminum in the centrifugate of the clay suspension at successive time intervals after the addition of a predetermined amount of aluminum. The adsorption values were computed in the same manner as that described in the previous section.

Duration and Intensity of Agitation. In order to evaluate the effects of the initial clay concentrations and the duration and intensity of agitation on the destabilization of the kaolinite clay suspensions at different pH values, the suspensions were mixed at a given intensity of agitation for a predetermined period of time, following which a oeriod of 15 minutes was used to allow the destabilized suspensions to settle quiescent1y. Samples for residual turbidity determinationis ucre then withdrawn by the same method as described in the previous section, and the determinations immediately made.














V. RESULTS AND DISCUSSION


Variable iH Series


The series of studies in which the pH value is varied was performed using two different approaches. In the first, the destabilization experiments were performed on kaolinite clay suspensions which had the same clay concentration value of 61.5 mg/l. The final pH of the destabilized suspensions was varied from 3 to 10, while the dosages of aluminum sulfate used were 3, 5, 7, 10, 15, 20, 30 and 50 mg/l. The experimental results of this part of the study are shown in Figures 12 to 19.

In the second approach, the experiments were conducted using

kaolinite clay suspensions having three different initial clay concentrations and in the neutral to slightly alkaline pH range of from pH 6 to 8with dosages of 5, 10, 30 and 50 mg/l of aluminum sulfate. Figures 22 to 25 show the results obtained for the second series.


Role of pH on Alminrum Sorption

The aluminum sorption curves as depicted in Figures 12 to 19

reveal several significant phenomena which are discussed in the following sections:

1. Only a small fraction of the aluminum ions was adsorbed on kaolinite clay particles at pH values below pH 4 and above pH 9, and practically '.o sorption of aluminum ions by the clay particles was


- 51 -






- 52..


*0

0,-)
#o


04
4

o -2
0)

100


8o
4

S 6040

, 20


0




o 3




-4
2-t






0
2 3 4 5 6 7 8 9 10
pH Fig. 12 - The Effect of pH on the Destabilization of Kaolinite Clay
Suspension. Aluminum Sulfate Dosage - 3 mg/l. Clay
Concentration - 61.5 mg/l.







- 53 -


0 1
0

"-4
o


o




100


7-4 9
.71~ Vk


4) 4


o -t

o 2


.
0 C
0
2


Fig. 13 - The Effect ol
Suspension.
centration -


3 4 5 6 7 8 9 10
pH

pH on the Destabilization of Kaolinite Clay Aluminum Sulfate Dosage 3 mg/l. Clay Con61.5 mg/l.









4 2

.0
o
o 0


4->
0 U) -2


o .4


100


80
r4

.0 60


40









to
20


0


10 8 ~'~ 6
H






0

2 3 4 5 6 7 8 9 10
pH Fig. 14 - The Effect of pH on the Destabilization of Kaolinite Clay
Suspension. Aluminum Sulfate Dosage = 7 mg/1. Clay Concentration = 61.5 mg/i.









- 55 -


2 3 4 5 6 7 8 9 10 11 pH


The Effect of pH on the Destabilization of Kaolinite Clay
Suspension. Aluminum Sulfate Dosage = 10 mg/1. Clay Concentration = 61.5 g/i .


H
0


-r4 >r

00


100.


w



r4



-4


U)


1)


0

0


Fig. 15 -








- 56 -


2 3 4 5 6 7 8 9 10 pH


The Effect of pH on the Destabilization of Kaolinite Clay Suspension. Aluminum Sulfate Dosage = 15mg/l. Clay Concentration = 61.5 mg/1.


43 0U

S0 '4 ,4






-p


,04


'3) r- ..
o





0


Fig. 16 -







- 57 -


0 C





4)
10

go

-r4







H



4-)
E-


.s.'Ju I


8060 4o


0


0


12-


0






0-- 0
0
0
)Ni l I
Cr- 0


2 3 4 5 6 7 8 9 10 pH

Fig. 17 - The Effect of pH on the Destabilization of Kaolinite Clay
Suspension. Aluminum Sulfate Dosage = 20 mg/l. Clay Concentration = 61.5 mg/1.







- 58 -


o
000

o..



WI











00
0
00










2d 4 406


S 20









r, O 8Cd 4



2 3 4 5 6 7 8 9 176 pH

Fig. 18 - The Effect of pH on the Destabilization of Kaolinite Clay
Suspension. Aluminum Sulfate Dosage = 30 mg/1. Clay Concentration = 61.5 mg/l.







- 59 -


2

,0
o

0 0


-H
0o -2-.
-4


100

80





cd 4000
10

20D


0

" 328-.

E


2 3 4 5 6 7 8 9 10 pH

Fig. 19 - The Effect of pH on the Destabilization of Kaolinite Clay
Suspension. Aluminum Sulfate Dosage = 50 rag/l. Clay Concentration = 61.5 mg/l.







- C'. -


observed at pH 3 and pH 10. These data are believed to support the hypotheses21 that the predominant species at pH values below pH 4 is the simple trivalent aluminum ion, A!+++, while in the alkaline pH range aluminum is present mainy as the negatively charged aluminate ion, Al(OH)4-. It would appear that these two species are not strongly adsorbed by the clay particles.

2. In the range from pH 4 to pH 9, two peaks were found on the alu num sorption curves when inteimediate dosages of aluminum sulfate were used. The pH value of the first peak at the lower pH values is found to correspond very well -o the equilibrium pH at which 99 per cent of the added alumLnum ions is present as A16(OH)15.. as proposed by Brosset and his coworkers.32 The second peak of the aluminum sorption curve on the higher pH side is believed to represent the pH value at which maximum precipitation of aluminum hydroxide occurs. A comparison between the calculated and observed values for four different

dosages is shown in Table 6.

A series of aluminm adsorption isotherms based on the interpolated data from Figures 12 to 19 is shown in Figure 20. The Freundlich adsorption is therm plots of these data at three selected pH values

are sho.in in Figure 21.


Relatiorship Bet-:een Mobility and Residual Turbidity

The relationships between the electrophoretic mobility values and residual turbidity shown in Figures 12 to 19 are not so readily defined and correlated. However, there are several interesting and






- 61 -


:7abl e 6

Comparison of pH Values for 1 _ximum Hydrolysis
and Maximum Adsorption of Aluminum Ion


Experimental pH
Dosage of Ecuilibrijan pH at Which for Maximum Alui(nun 6 Al (OH)1.5 Aludnum Adsorp- Discrepancy Sulfate 6 A 99 tion in Acid Between the (ng/l) T) pH Range two pH Values


3 5.57
r 5.49

7 5.45 -- -10 5.39 5.25 -0.14 15 5.35 5.35 0.00 20 5.29 5.35 0.06 30 5.23 5.25 0.02

50 5.16 -- --


significant conclusions which may be drawn from them. Among them the most important are the follow ing:

1. At pH values below poH 4, the electrophoretic mobilities of the clay particles gradually become more positive with increasing alum dosages. This change identified a zone of fair to good turbidity removal, tered by Langelier and Ludwig, who first observed it, perikinetic or electrokinetic coagulation.

2. The firz electric point appeared in the pH range from 4 to 5. This isoelectric pH value decreased with an increase in the







-62-


4.0 7.0


3.6 / 6.5
/
/
3.2 //
/
r-4
2.8 6 / 6.
/
( * /
0
0) / /5.5 2.0 5.0


1.6 4.8

01.2 / 24.6

0.8
4.5


4.0
0.0 3.0
0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0
Dosage of Aluminum (mg/l)

Fig. 20 - The Effect of pH on the Adsorption Isotherms. Kaolinite Clay
Concentration = 61.5 mg/l. (The figures on the right side are
pH values).















-1.0 1-


PH = 5.0 O


-2.0





-3.0


-4.0


0 pH = 4.o
0 0


0) 0 GOPH=4.0


-1.2 -0.8 -0.4 0 0
Log C
Fig. 21 - The Effect of pH on the Freundlich Adsorption Isotherms
Kaolinite Clay Concentration = 61.5 mg/1.


0.4 0.8 1.2 of Kaolinite Clay Suspensions.


-ij






- 64-


dosage of aluminun, sulfate. The second isoelectric point appeared in the range from pH 6 to pH 8, the pH value increasing with increasing alum dosage. Therefore, the charge reversal zone falling between the two isoelectric pH va!aes was broadened with an increase in the dosage of alum~num sulfate. In addition, the first isoelectric pH, when the mobility changed from negative to positive, marked the beginning of a redispersion zone essentially identical with the zone of charge reversal, first pointed out by Black and Hannah. The second isoelectric pH at which the mobility changed from positive to negative identified the beginning of a pl zone of optimum turbidity removal.

3. The maximum charge reversal was generally accompanied by maximum redispersion. Moreover, the pH value of the maximum charge reversal was slightly decreased from 5.7 to 4.9 with an increase in the aluminum sulfate dosage from 3 mg/l to 50 mg/l.



Effec. of Initial Clay Concentration on Destabilization

The data shown in Figures 22 to 25 were mostly obtained within pH range from 6 to 8 within which the aluminum hydroxide has been supposed to be the most predominant aluminum species. Those curves showed that when the dosages of aluminum sulfate were less than 30 mg/l the initial clay concentration had an influence on all of the clay

mobility, the residual turbidity and the total aluminum consumption measurements. Clay suspensions with higher concentration of clay particles were more readily destabilized than those with lower clay concentrations. However, when a high dosage of aluminum sulfate, specifically 50 mg/l was used, the initial clay concentration had practically






- 65 -


2




H
o 0


o
Xo %
-3 -2
0) -4..





100




060 Initial Turbidity = 24
z 40 Initial Turbidity = 51
0




------Initial Turbidity = 125
201


4
o -I

,- II I .






3
Fig. 22 - Te Effect ofInitial ClyCne t ron nth Detbidity=2
tionof aoliiteCla Iupnitn i t T uiy m = ul51 e Aumiu SuInfaialDosrbidity = 2..
2



0
0


HP



5.5u6.0u6.5u7.0t7.5o8.0e8=559.0 9.







- 66 -


o~ o

o 0-0

U


100


ri O.


0







rZ

4.)
0


o f I II I 5.5 6.0 6.5 7.0 7.5 pH


Fig. 23 -


8.0 8.5 9.0 9.5


The Effect of Initial Clay Concentration on the Destabilization of Kaolinite Clay Suspensions with Aluminum Sulfate. Aluminum Sulfate Dosage = 10 mg/l.








- 67 -


H .0
0
0 0





o:~


100


rHECd


CO
4 ) +
0










E-


4 1. I I - I I I I..I
5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5
PH
The Effect of Initial Clay Concentration on the Destabilization of Kaolinite Clay Suspensions with Aluminum Sulfate. Aluminum Sulfate Dosage = 30 mg/i.


Fig. 24 -







-68-


0 0

0 I0


o10 0O


-o
:.4 E



0






0
0 SC




0.)
0 O-


80 60 40


20


0


32 24


16


5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 pH


The Effect of Initial Clay Concentration on the Destabilization of Kaolinite Clay Suspensions with Aluminum Sulfate. Aluminum Sulfate Dosage = 50 mg/1.


Fig. 25 -






- 69 -


no effect on the values of the three determinations. In addition, the a!uninum consumption curves reveal that all three clay concentration curves are quite similar in the pH range above pH 7.5.

The simple physical e eshn.ent mechanism as proposed by Packham to desci-be the coagulation of the dilute clay suspensions with aluminum salts19 is applicable only in those systems in which the concentrations of the applied aluminum ion are sufficiently high so that abundant amount of aluminum hydroxide flocs can be rapidly formed to sweep down the suspending clay particles. However, for low alum dosages, mutual coagulation as proposed earlier by Black61 would appear to be better mechanism for describing the destabilization of dilute clay suspensions

with aluminunm salts in the neutral pH range.

7dhen a clay suspension can be destabilized by the physical enmeshnent mechanism, the concentration of clay particles may have very little effect. However, the clay concentration becomes a critical factor when mutual coagulation is the controlling mechanism of the destabilization process. The experimental results shown in Figure 25, using

30 mg/l alminum sulfate dosage, support the assumption of the validity of a physical enmsh=ent mechanism, while the results in Figures 22 to 24, using aluminum sulfate dosages less than 30 mg/1, can be better understood by assuming mutual coagulation as the mechanism of destabilization.


Log tA! vs. pH

The destabilization of a dilute clay suspension with aluminum

salts is largely controlled by the hydrolytic reactions of the aluminum






- 70 -


ions, which in tuarn are fPunctions of the pH and the concentration of aluminum ions oresent in the system. Consequently, a more comprehensive understanding of the destabilization of a clay suspension may be achieved through a study of the log t Al3 - pH plot in which the various regions of coagulation and flocculation are very well defined by both pH value and the logarithm of the molar concentration of aluminum. The experimental results of the variable pH series of this study are summarized and plotted in the form of log (Al) - pH as shown in Figure 26.


Constant oH Series


In the constant pH series, three different final pH values, namely, pH 3, pH 5 and pH 8, were chosen for investigation in an attempt to elucidate the various mechanisms involved in the destabilization processes in those pH ran=es within which the existence of different predominant alminum ion species have been proposed.21'32 The trivalent metallic aluminum ion, Ai- is the main species in the region below pH 4. In the range between PH 4 and pH 6, the formation of hydrolyzed -olynuclear comolexes, such as Al6(OH)+++ or

8 (OH) 20 , has been proposed. In the neutral pH zone from pH 6 to pH 8, insoluble aluinum hydroxide, Al(OH) 3, or colloidal basic salts are believed to be the principal species present. Destabilization at Constant oH 3
the results of this series of experiments are shown in Figures

27 to 30. -he curves of particle electrophoretic mobility and aluminum adsorption are quite similar for the four clay suspensions which had






- 71 -


-3.50
Coagulation and
-3.75 Flocculation Region

-4.00
S t abili zation
-4.25 -Region







Hp
-50

Coagulation Region


-5.00

-5-25
Region of no Coagulation

-5.50 I I I
3 4 5 6 7 8 9 10 pH

Fig. 26 - The Entire Log (Al) - pH Domain for a Kaolinite Clay
Suspension. Clay Concentration = 61.5 mg/l.







- 72 -


I -


0 5 10 15 20 25 30 35
Aluminum Sulfate Dosage (mg/1)


40 45 50


The Dastabilization of a Kaolinite Clay Suspension with
Aluminum Sulfate. Initial Clay Concentration = 15.8 mg/i. Final pH of Suspension = 3.0.


4

4--
oo
QV o
4 C 00


4-)
0
i


100


43



,0 NA


-e
0








0 E-


Fig. 27 -






-73-


H



c4

10

o

r4f







on
%.10





Fig. 2


2


1


0


1


2 i0


0 5 10 15 20 25 30 35
Aluminum Sulfate Dosage (mg/i)


40 45


The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration a 31.7 mg/i. Final pH of Suspension - 3.0.







m 74 -


0 " 00


Q cno 6 1 A ' 0 5 10 15 20 25
Aluminum Sulfate


A I


D 3o Dosage (xug/)


40 45 50


The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration - 47.5 m/l. Final pH of Suspension - 3.0.


o
0U

o -4 0W


0


-2(


4% W14


20-


0


32 24


Fig. 29 -






- 75 -


0 2


4

.6


8


0 5 10 15 20 25
Aluminum Sulfate


30
Dosage


35 (mg/1)


40 45


The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration a 63.3 mg/l. Final pH of Suspension w 3.0.


..4)

0 "


o


100


.4
H0


1 -


,0 0 _


2


0


0.-


Fig. 30 -






- 76 -


different initial clay concentrations, namely, 15.8, 31.7, 47.5 and 63.3 mg/. When the residual turbidity is expressed as per cent of the initial clay turbidity, the clay suspension which had the highest clay concentration was found to have the lowest residual turbidity.

The addition of aluminu:-i sulfate in dosages from 5 mg/l up to

50 mg/l had no effect upon either the residual turbidity or the adsorption of aluminiu ions for any one of the four clay suspensions. However, increasing the dosage of aluminum sulfate decreased the negative mobility of the floc particles at all dosages employed from -2.5 P/sec/ v/cm to about -0.3 L/sec/v/cm.

According to MatijEvc1 the hydrated trivalent metallic aluminiun. ion does not reverse the charge of negative silver halide sols, and this same behavior has been shown to take place in the kaolinite clay suspensions, as revealed in Fi-ures 27 to 30. Also, no adsorption of

the trivalent Al+-+ ion was found at this pH value throughout the entire range of dosages employed.

The reduction in the negative mobility of the clay particles by an increase in aluminum ion concentration is believed to be brought about by the reduction of the doule-ayer thickness of the clay particle in consequence of an increase of the ionic strength in the suspension system. Therefore, the behavior of the trivalent metallic

alumaziu ions in the clay colloidal systems is simply to intensify the ionic atmosohere surrounding every clay particle to compress the doublelayer of the particle with a reduction in the double-layer thickness. As a result of this reduction in the thickness of the double-layer







- 77 -


surrounding a clay particle, the zeta potential of the clay particle is reduced, as shown by much lo-: :egatve mobility values.

Although the electrophoretic mobility curves in all four clay suspensions investigated are aLost identical, the percentages of

initial turbidity remaining ater coagulation were not the same, and the curves show an in-irerse relationship between concentration and final turbidity. These differences in residual turbidity at different initial clay concentrations may be explained by the Smoluchowski theory62 which is based upon the probability factor in particle collisions during the process of coagulation. Accor:: ng to this theory, where all variables except clay concentration are held constant, the suspension which has higher initial clay concentration should be easier to destabilize with

a greater reduction in clay turbidity.


Destabilization at Constant oH 5

Figures 31 to 34 show the results of the series of experiments in which the final pH values were maintained at constant pH 5. The predominant species at this p: value is believed to be either the polynuclear complex, A!6(OH)1 or Al8(OH)20 , as proposed by Brosset32
.21l.
and Matijevic respectively.

2:o types of agitation were used to bring about destabilization in tiLs series. The first type was tw-o minutes of rapid mixing at

- rp-: followed by a oeriod of 28 minutes of slow mixing at a speed of I' rpm, followed by a 10 -inute sedimentation period. The results :or this series are shown in the solid line curves in Figures 31 to 34. The second type employed 20 minutes of rapid mixing at 100 rpm followed






- 78 -


4 2

00
,$4



100

800
-2

o -.4-t4
0









0




0.
8













4
0


0 5 10 15 20 25 30 35 40 45 50 Aluminum Sulfate Dosage (mg/i) Fig. 3 - The Destabilization of a Kaolinite Clay Suspension with
Aluminum Sulfate. Initial Clay Concentration - 15.8 mg/l.
Final pH of Suspension = 5.0 ! 0.05.






- 79 -


4


4
2

Zo 0
.0
o -.
0 0 0



-2





4-)
0. 10


0




o
J.f

60


c-40
.4
U)
20


0


16
0
,--, 12


W' 8
0


4

0
0 5 10 15 20 25 30 35 40 45 50 Aluminum Sulfate Dosage (mg/i)

Fig. 32 - The Destabilization of a Kaolinite Clay Suspension with
Aluminum Sulfate. Initial Clay Concentration 31.7 mg/l.
Final pH of Suspension -5.0 - 0.05.






-80-


0 5 10 15 20 25 30
Aluminum Sulfate Dosage


35 40 45 50 (mg/i)


The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 47.5 mg/l. Final pH of Suspension = 5.0 � 0.05.


W4
4-) .0

o +3

0 40








ow


Fig. 33 -






- 81 -


4 .-4



H ..4






O0
o


0 5 10 15 20 25 30 35 40 45 Aluminum Sulfate Dosage (mg/i)

The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration a 63.3 mg/l. Final pH of Suspension = $.0 � 0.05.


- -,,,r p" " -'. ,,-..,.,q .,. .,,..,.


Fig. 34 -











by a period of 10 minutes of slou mixing and 10 minutes sedimentation. The dash line curves in Figures 31 to 34 show the experimental results obtained with this type of mixing. The second type of mixing provides more kinetic margy for the particles and thus results in better turbidity removal. The differences in the percentage of the initial turbidity remaining after coagulation at different initial clay concentrations may, as before, be accounted for in terms of Smoluchowski's theory.

The electrophoretic mobility curves show that the aluminum

hydrolysis products formed at this pi value are capable of reversing the originally negative charge of the clay particles. These charge reversal phenomena, which occurred in the case of all of the four sus21
pensions, support the theonr proposed by Matijevic and much earlier,
8
by Mattson, that the hydrolyzed alu.inum species are able to reverse the charge of the negatively charged sols. The mechanism for this charge reversal nay be the over-neutralization of the surface charge of

the clay particle by the strongly adsorbed multivalent hydrolyzed aluminm: species in consequence of a specific adsorption of the hydrolyzed aluminum ions by the ions on the clay surface.

A very narrow zone of coagulation appears at the point where the ..obility values change from negative to positive. Beyond this point, the clay s ensign was again stabilized. This same phenomenon was fully demonstrated by 3lack and his associates in their studies of the dosabilization of dilute clay suspensions with labelled polymers. Consequently, the polym.erization tendency of the aluminum hydroxo






- 83 -


25
complexes as proposed by Stumm and Morgan can be indirectly supported by the present experimental results. Figure 35 summarizes the effect of the initial clay concentration on the destabilization of kaolinite clay suspensions with aluminum sulfate at pH 5.

The aluminum adsorption data shown in Figures 31 to 34 may also be plotted as Freundlich adsorption isotherms. Figures 36 to 39 show the plots of these Freundlich adsorption isotherms. Figure 40 shows the effect of the initial clay concentration on the Freundlich adsorption isotherm. The concave inflection at the right ends of the adsorption curves as shown in Figures 31 to 34 may be due to the presence of colloidal aluminum hydroxides which can be removed by centrifuge separation since, as shown in Figure 41, 12 per cent of the aluminum added was removed by centrifuging.

The empirical constants of the Freundlich adsorption isotherm equation for each of the four clay suspensions investigated were calculated, using the sample linear regression equation,63 and the calculated results are shown in Table 7. Destabilization at Constant pH 8

The experiments in this series were performed using four different kaolinite clay suspension concentrations, varying from 15.8 mg/l to 63.3 mg/1l. Figures 42 to 45 show the individual results for each of the four clay suspensions investigated. A summary of these is shown in Figure 46.

It is clearly demonstrated that the aluminum consumption curves are only slightly influenced by the difference in initial clay


















.0




0 00( 0 4) P4. -0 :1
4) H 94)






4J
















H








0
E














Fig. 35--


o 5 10 15 20 25 30 35 40 45 50 Aluminum Sulfate Dosage (mg/l)


The Effect of Initial Clay Concentration on the Destabilization of Kaolinite Clay Suspensions with Aluminum Sulfate. Final pH of Suspensions = 5.0 t 0.05.




Full Text

PAGE 1

MECHANISMS OF THE DESTABILIZATION OF KAOLINITE CLAY SUSPENSIONS WITH ALUMINUM SULFATE By CHING-LIN CHEN A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA June, 1966

PAGE 2

acknowledgments The author wishes to express his sincere appreciation to his committee chairman, Dr. A. P. Black, for his enthusiastic assistance and continual inspiration throughout the course of this graduate research work. Specific acknowledgment is also due to Dr. J. J. Morgan for his guidance and encouragement. The author is deeply indebted to Professor John E. Kiker, Jr. , and Dr. H. A. Bevis for their advice and assistance in the scheduling of course work in the entire period of graduate study. Sincere thanks are due also to Professor ThonaS deS. Furman and Dr. Hugh D. Putnam who gave their time and advice whenever requested. Specific appreciation is also extended. to Dr. J. a. Singley and Mrs. Annie L. Smith for their many valuable suggestions and corrections in writing this paper, to Mrs. Janice G. Larson for her excellent typing of this dissertation, and to all the author's colleagues in the water chemistry laboratory for their help and friendship. The author also wishes to express his gratitude for the support of this investigation by Water Supply and Pollution Control Research Grant WP-139 from the Public Health Service of the United States. ii

PAGE 3

CONTENTS Page . ii ACKNOWLEDGMENTS . LIST OF TABLES . LIST OF FIGURES . ABSTRACT . . . . CHAPTER I . INTRODUCTION II. HISTORICAL REVIEW III. THEORETICAL CONSIDERATIONS Chemistry of Aqueous Aluminum Hydrolytic Reactions of Aluminum Ion . . . Alkaline trie Titration Curves Charge of Specific Hydrolysis Products . . Aging Effect Complex Formation Characteristics of Kaolinite Clays Structure and Chemical Composition of Kaolinite Clays Size and Shape of Clay Particles ...... Origin of Surface Charge on Clay Particles Cation Exchange Capacity of Clay Particles Adsorption Sites of Clay Particles . . . . Mechanisms of Destabilization Coagulation Flocculation Aluminum-Clay Interactions Reduction of Zeta Potential Adsorption Charge Reversal IV. EXPERIMENTAL MATERIALS AND PROCEDURES Materials Kaolinite Clay Aluminum Sulfate .... Reagents for pH Adjustment Reagents for Aluminum Determination . . . . v . ix . xiv . 1 . 2 . 10 . 10 . 10 . 16 . 18 . 18 . 23 . 23 . 26 . 27 . 27 . 27 . 29 . 29 • 30 . 35 . 36 . 36 . 37 • 38 . 39 . 39 . 39 • 39 . 39 . 39 iii

PAGE 4

Page Procedures ^1 Preparation of Kaolinite Clay Suspensions ... 41 Preparation of Aluminum Sulfate Solutions ... 42 Alkalimetric Titrations 43 Destabilization Experiments 43 Electrophoretic Mobility Determinations .... 46 Determination of Residual Aluminum 48 Adsorption Computations 50 Aluminum-Clay Kinetic Experiments 5° V. RESULTS AND DISCUSSION 51 Variable pH Series 51 Role of pH on Aluminum Sorption 51 Relationship Between Mobility and Residual Turbidity 6° Effect of Initial Clay Concentration on Destabilization 64 Log (Al) vs. pH 69 Constant pH Series 7° Destabilization at Constant pH 3 70 Destabilization at Constant pH 5 77 Destabilization at Constant pH 8 83 Kinetics of Aluminum-Clay Interactions 99 Aluminum Adsorption Rate 99 Effect of Mixing Time on Residual Turbidity . . 99 Effect of Agitation Intensity on Residual Turbidity HO VI. SUMMARY AND CONCLUSIONS 112 APPENDIX 11 5 LIST OF REFERENCES l6 7 BIOGRAPHICAL SKETCH 173 iv

PAGE 5

Table 1 . 2 . 34. 5 . 6 . 7. 8 . 9. 10 . 11 . 12'. 13. 14. 15. 16 . LIST OF TABLES Page Hydrolysis Equilibria of Aluminum Calculated Equilibrium pH Values for Suc ces sive States in One Reaction' for the Hydrolysis of AT H_+ at Al^ . . . Complex Formation Reactions of Aluminum Analysis of Aluminum Sulfate Kaolinite Clay Suspensions Comparison of pH Values for Maximum Hydrolysis and Maximum Adsorption of Aluminum ron 13 14 26 40 42 61 The Empirical Constants of the Freundlich Adsorption Isotherm Equation The Destabilization of a Kaolinite Clay Suspension with a Dosage of 3 mg/l of Aluminum Sulfate .... The Destabilization of a Kaolinite Clay Suspension with a Dosage of 5 rag/l of Aluminum Sulfate H7 The Destabilization of a Kaolinite Clay Suspension with a Dosage of 7 mg/l of Aluminum Sulfate 119 The Destabilization of a Kaolinite Clay Suspension with a Dosage of 10 mg/l of Aluminum Sulfate . . The Destabilization of a Kaolinite Clay Suspension with a Dosage of 15 mg/l of Aluminum Sulfate 123 The Destabilization of a Kaolinite Clay Suspension with a Dosage of 20 mg/l of Aluminum Sulfate 125 The Destabilization of a Kaolinite Clay Suspension with a Dosage of 3 O mg/l of Aluminum Sulfate . . The Destabilization of a Kaolinite Clay Suspension with a Dosage of 5 0 mg/l of Aluminum Sulfate 129 Adsorption Data for Freundlich Isotherm Plot. Kaolinite Clay Concentration = 61.5 mg/l. pH = 4.0 131 v

PAGE 6

Table Page 17 . 18 . 19. 20 . 21 . 22 . 23 . 24 . 25 . 26 . 27 . 28 . Adsorption Data for Freundlich isotnerm Plot. Kaolinite Clay Concentration =61.5 mg/l. pH = 4.5 • • • ^32 Adsorption Data for Freundlich Isotherm Plot. Kaolinite Clay Concentration = 61.5 mg/l. pH = 5*0 • • • ^33 Effect of pH on Aluminum Residual. Kaolinite Clay Concentration = 61.5 nig/l '34 Construction of Formation Function Curve for Aluminum Sulfate Solution 135 The Effect of Total Number of Paddlo Revolutions and Intensity of Agitation upon the Destabilization of a. Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 63.3 m g/l* pH = 3*9 The Effect of Total Number of Paddle Revolutions and Intensity of Agitation upon the Destabilization of a. Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 63.3 ^g/l. pH = 5 1 0.05 139 The Effect of Total Number of Paddle Revolutions and Intensity of Agitation upon the Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 63.3 mg/l. pH = 8 I 0.1 The Effect of Total Number of Paddle Revolutions and Intensity of Agitation upon the Destabilization of a. Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 31*7 nig/l. pH = J.O The Effect of Total Number of Paddle Revolutions and Intensity of Agitation upon the Destabilization of a. Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 31*7 rog/l. pH = 5 0.05 ^2 The Effect of Total Number of Paddle Revolutions and Intensity of Agitation upon the Destabilization of a^ Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 31*7 mg/l. pH = 8 + 0.1 143 The Effect of pH on Aluminum Residual After Separation by High-Speed Centrifuge LLWr The Effect of Aluminum Concentration on Aluminum Residual After Separation by High-Speed Centrifuge . . . 145 vi

PAGE 7

Table Pa S e 29. The Effect of Time on the Adsorption of Aluminum by Kaolinite Clay 30. The Effect of pH on the Electrophoretic Mobility of Kaolinite Clay Particle 31 . The Zone of Aluminum Floe Formation 1^8 32. The Effect of pH and Anion on the Electrophoretic Mobility of Aluminum Floe 1^9 33 . The Effect of pH on the Electrophoretic Mobility of Kaolinite Clay Particle with a Dosage of 50 mg/l Aluminum Sulfate 1^0 y±. Adsorption Data for Freundlich Isotherm Plot. Kaolinite Clay Concentration = 15.8 mg/l 151 35. Adsorption Data for Freundlich Isotherm Plot. Kaolinite Clay Concentration = 31*7 mg/l 152 36 . Adsorption Data for Freundlich Isotherm Plot. Kaolinite Clay Concentration = 47.5 mg/l 153 37. Adsorption Data for Freundlich Isotherm Plot. Kaolinite Clay Concentration = 63.3 mg/l ^54 38 . The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = I 5.8 mg/l 155 39. The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 3I.7 mg/l 156 40. The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration =47*5 mg/l 157 41. The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 63.3 mg/l 158 42. The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 15.8 mg/l. Final pH = 5 ± 0.05 159 43 . The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 3I.7 mg/l. Final pH = 5 1 0.05 160 vii

PAGE 8

Table Page 44 . The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 47-5 mg/l. Final pH = 5 0*05 45. The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 63.3 mg/l. Final pH = 5 0.05 162 46. The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 15.8 mg/l. Final pH = 8 t 0.1 ^°3 47. The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 31.7 mg/l* Final pH = 8 i 0.1 1^ 48. The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 47.5 mg/l. Final pH = 8 t 0.1 1^5 49. The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 63.3 mg/l. Final pH = 8 ± 0.1 166 viii

PAGE 9

LIST OF FIGURES Figure 1. Solubility Curve for Aluminum Hydroxide 2. Alkalimetric Titration Curves for Aluminum Sulfate Solutions 3 . Alkalimetric Titrations of Aluminum and Aluminum in the Presence of Sodium Bicarbonate or Sodium Sulfate .... 4 . Formation Function Curves for Aluminum Sulfate Solutions 5 . Stepwise Conversion of the Tripositive Aluminum Ion to the Negative Aluminate Ion. (From Stumm and Morgan ? ) . . 6 . The Effect of the Time of Aging of Aluminum Sulfate Solutions at 90% on the Coagulation Values of Silver Chloride, Silver Bromide and Silver Iodide Sols in statu nascendi. (From Matijevic et al. ) 7 . The Change of pH in Solutions of A1(N0 L When Aged at 90°C. (From Matijevic et al. ) 8 . Schematic Diagram of the Crystal Structure of Kaolinite Unit Cell. (From van Olphen^) 9 . The Structure of Stem-Gouy Double Layer and the Corresponding Potentials 10. Potential Energy of Interaction 29 11. Critical Zeta Potential Curve. (From Tambo ) 12. The Effect of-pH on the Destabilization of Kaolinite Clay Suspension. Aluminum Sulfate Dosage = 3 mg/l. Clay Concentration =61.5 mg/l 13 . The Effect of pH on the Destabilization of Kaolinite Clay Suspension. Aluminum Sulfate Dosage = 5 m s/l* Clay Concentration = 61.5 mg/l 14. The Effect of pH on the Destabilization of Kaolinite Clay Suspension. Aluminum Sulfate Dosage = 7 mg/l. Clay Concentration = 61.5 J&g/l • • Page 15 19 20 21 22 24 25 28 32 33 34 52 53 54

PAGE 10

Page Figure 15. The Effect of pH on the Destabilization of Kaolinite Clay Suspension. Aluminum Sulfate Dosage = 10 mg/1. Clay Concentration = 61.5 mg/l 55 16. The Effect of pH on the Destabilization of Kaolinite Clay Suspension. Aluminum Sulfate Dosage = 15 mg/l. Clay Concentration = 61.5 Mg/l 5° 17. The Effect of pH on the Destabilization of Kaolinite Clay Suspension. Aluminum Sulfate Dosage = 20 mg/l. Clay Concentration = 61.5 mg/l ^7 18. The Effect of pH on the Destabilization of Kaolinite Clay Suspension. Aluminum Sulfate Dosage = 3® mg/l. Clay Concentration = 61.5 mg/l 5° 19. The Effect of pH on the Destabilization of Kaolinite Clay Suspension. Aluminum Sulfate Dosage = 50 mg/l. Clay Concentration = 61.5 mg A 59 20. The Effect of pH on the Adsorption Isotherms. Kaolinite Clay Concentration = 61.5 mg/l. (Tne figures on the right side are pH values) 62 21. The Effect of pH on the Freundlich Adsorption Isotherms of Kaolinite Clay Suspensions. Kaolinite Clay Concentration = 61.5 Mg/l °3 22. The Effect of Initial Clay Concentration on the. Destabilization of Kaolinite Clay Suspensions with Aluminum Sulfate. Aluminum Sulfate Dosage = 5 Mg/l • • • °5 23. The Effect of Initial Clay Concentration on the Destabilization of Kaolinite Clay Suspensions with Aluminum Sulfate. Aluminum Sulfate Dosage = 10 mg/l ... 60 24. The Effect of Initial Clay Concentration on the. Destabilization of Kaolinite Clay Suspensions with Aluminum Sulfate. Aluminum Sulfate Dosage = 30 mg/l ... 67 25. The Effect of Initial Clay Concentration on the. Destabilization of Kaolinite Clay Suspensions with Aluminum Sulfate. Aluminum Sulfate' Dosage = 50 mg/l ... 68 26. The Entire Log ^Al") pH Domain lor a Kaolinite olay Suspension. Clay Concentration =61.5 Mg/l ?1 x

PAGE 11

Figure Page 27. The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = I 5.8 mg/1. Final pH of Suspension = 3.0 72 28. The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 3 I .7 mg/l. Final pH of Suspension = 3.0 73 29. The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 47.5 mg/l. Final pH of Suspension = 3.0 74 30 . The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 63.3 mg/l. Final pH of Suspension = 3-0 75 31. The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = I 5.8 mg/l. Final pH of Suspension = 5-0 t 0.05 .... 78 32. The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 31.7 mg/l. Final pH of Suspension = 5.0 ± 0.05 .... 79 33 . The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 47.5 mg/l. Final pH of Suspension = 5.0 I 0.05 .... 80 34 . The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 63.3 mg/l. Final pH of Suspension = 5.0 ± 0.05 .... 81 35 . The Effect of Initial Clay Concentration on the Destabilization of Kaolinite Clay Suspensions with Aluminum Sulfate. Final pH of Suspensions =5.0-0.05 . 84 36 . Freundlich Adsorption Isotherm. Kaolinite Clay 37 . Freundlich Adsorption Isotherm. Kaolinite Clay . . . 86 38 . Freundlich Adsorption Isotherm. Kaolinite Clay 39. Freundlich Adsorption Isotherm. Concentration = 63.3 mg/l . . . Kaolinite Clay . . . 88 xi

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Page Figure 40. 41. 42. 43. 44. 45. 46. 4748. 49. 50. 51 . The Effect of Initial Clay Concentration on the Freundlich Adsorption Isotherms of Aluminum-Kaolinite Systems. pH = 5«0 0.05 The Effect of pH on Aluminum Residual After Separation by High-Speed Centrifuge The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 15.8 mg/1. Final pH of Suspension =8-0.1 The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 31.7 mg/1. Final pH of Suspension =8-0.1 The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate . Initial Clay Concentration = 47.5 mg/1. Final pH of Suspension =8-0.1 The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Suspension = 63.3 mg/l. Final pH of Suspension = 8 a 0.1 The Effect of Initial Clay Concentration on the. Destabilization of Kaolinite Clay Suspensions with Aluminum Sulfate. Final pH of Suspensions = 8 ± 0.1 . . 95 The Effect of Initial Aluminum Concentration on Aluminum Residual After Separation by High-Speed Centrifuge ... 98 The Effect of Time on the Adsorption of Aluminum by Kaolinite Clay Particles. Initial Aluminum Concentration =1.6 mg/1. Clay Concentration = 63.3 mg/l .... 100 The Effect of Time of Mixing, Expressed as Total Number of Paddle Revolutions, on the Destabilization of Two Kaolinite Clay Suspensions with 5 mg/l of Aluminum Sulfate at 40 rpm Agitation Intensity. pH =3*0 .... 101 The Effect of Time of Mixing, Expressed as Total Number of Paddle Revolutions, on the Destabilization of Two Kaolinite Clay Suspensions with 5 mg/l of Aluminum Sulfate at 40 rpm Agitation Intensity. pH = 5*0 0.05 . 102 The Effect of Time of Mixing, Expressed as Total Number of Paddle Revolutions, on the Destabilization of Two Kaolinite Clay Suspensions with 30 mg/l of Aluminum Sulfate at 40 rpm Agitation Intensity. pH = 8 t 0.1 . . 103 xii

PAGE 13

Figure 52. The Effect of Time of Mixing, Expressed as Total Number of Paddle Revolutions, on the Destabilization of Two Kaolinite Clay Suspensions with 5 mg/l of Aluminum Sulfate at 100 rpm Agitation Intensity. pH = 3.0 . . . . 53 . The Effect of Time of Mixing, Expressed as Total Number of Paddle Revolutions, on the Destabilization of Tito K aolinite Clay Suspensions with 5 mg/l of Aluminum^ Sulfate at 100 rpm Agitation Intensity. pH = 5-0 0.05 54-. The Effect of Time of Mixing, Expressed as Total Number of Paddle Revolutions, on the Destabilization of Tito Kaolinite Clay Suspensions with 30 mg/l of Aluminum Sulfate at 100 rpm Agitation Intensity. pH = 8 I 0.1 . . 55. The Effect of Time of Mixing, Expressed as Total Number of Paddle Revolutions, on the Destabilization of a Kaolinite Clay Suspension with 5 mg/l of Aluminum Sulfate at Two Agitation Intensities. pH = 3*° 56. The Effect of Time of Mixing, Expressed as Total Number of Paddle Revolutions, on the Destabilization of a Kaolinite Clay Suspension with 5 mg/l of Aluminum Sulfate at Two Agitation Intensities. pH = jj.O ± 0.05 . 57. The Effect of Time of Mixing, Expressed as Total Number of Paddle Revolutions, on the Destabilization of a Kaolinite Clay Suspension with 30 mg/l of Aluminum Sulfate at Two Agitation Intensities. pH = 8 i 0.1 . . . Page 104105 106 107 108 109 xiii

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Abstract of Dissertation Presented to the Graduate Council in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy MECHANISMS OF THE DSSTA3ILIZATI0N OF KAOLINITS CLAY SUSPENSIONS WITH ALUMINUM SULFATE BY Ching-lin Chen June, 1966 Chairman: Dr. A. P. Black Major Department: Bioenvironmental Engineering Three major experimental approaches were used in this study to elucidate the mechanisms involved in the specific aluminum-clay interactions and subsequent destabilization of dilute kaolinite clay suspensions: (1) In one series the dosage of aluminum sulfate was maintained at some selected constant value while the final pH of the suspension was varied from 3 to 10. (2) In another series the final pH of the suspension was maintained at a constant value of 3> 5 or 8 with the aluminum sulfate dosage varying from 1 mg/l to 50 mg/i. ( 3 ) In a series of kinetic experiments both the time of mixing and the intensity of agitation were varied. Neither aluminum adsorption nor charge reversal of clay particles was demonstrated at pH 3 within the limits of the aluminum sulfate dosage used. However, the electrophoretic mobility of the clay particles was found to be reduced to a constant minimum value as the dosage of aluminum sulfate increased. Consequently, the mechanism involved in the destabilization of kaolinite clay suspensions at this pH value is believed to be due to a reduction of the repulsive potential between the xuv

PAGE 15

negatively charged clay particles through compression of the electrical double-layer, which in turn is due to the incorporation of hydrogen and hydrated metallic aluminum ions into the Gouy diffuse layer. At pH 5, a very narrow zone of coagulation was found at the isoelectric pH point which marked the beginning of a charge reversal zone with the subsequent restabilization of the suspension as the dosage of aluminum sulfate increased. The Freundlich adsorption isotherm model was found best to describe the adsorption of the hydrolyzed aluminum polynuclear complex ions by the kaolinite clay particles. Therefore, io is postulated that the mechanism of the destabilization at this pH value is a reduction of the zeta potential of the clay particles through the specific adsorption of the hydrolyzed aluminum polynuclear complex ions onto the clay surface, with the subsequent reduction of tne surface potential of the clay particles. It is shown from the experimental results that at pH B pnysical enmeshment might account for the mechanism of the destabilization of tne kaolinite clay suspensions when rapid and abundant precipitation of aluminum hydroxides occurs i.e., when the dosage of aluminum sulfate exceeds 40 mg/l. However, when the dosage of aluminum sulfate is less than 40 mg/l at this pH, a mechanism of mutual coagulation between colloidal aluminum hydroxides and clay particles better describes the phenomena of the destabilization. In all cases investigated, the residual turbidity curve as a function of the time of mixing shows that the turbidity could be reduced to a constant minimum value by stirring the suspension system with a xv

PAGE 16

total of 2,000 paddle revolutions. The constant minimum value of the residual turbidity appears to be dependent on such factors as the final oH of the suspension, the aluminum sulfate dosage, the intensity of agitation and the clay concentration. The effect of the initial clay concentration on the destabilization process was found to follow Smoluchowski* s theory at pH 3 an ^ pH 5, whereas it had little effect at pH 8 when the aluminum sulfate dosage was higher than 50 mg/l. xvi

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I. INTRODUCTION The need of scientific control for the removal of natural clay turbidity from the raw water of public water supply systems has for many years been a challenging problem in the field of water cnemistry . In order to provide a sound solution to this problem, the mechanisms involved in the destabilization of clay suspensions must be clearly demonstrated. Therefore, the present research has been initiated in an attempt zo elucidate the mechanisms by which an inorganic coagulant effects the destabilization of dilute clay suspensions under controlled conditions. Aluminum sulfate has been widely and effectively used as a coagulant to remove clay turbidity from water for many years. The mechanisms involved have been investigated and several theories have been proposed. However, due to the lack of specific controls in the investigations and a good understanding of the chemistry of aluminum, the proposed mechanisms have had to be revised through the years, and as yet are not well established. Electrophoretic techniques have been used throughout this study in an attempt to reveal any significant relationships between the electrophoretic mobility measurements and the residual turbidity data, and also to elucidate the charge reversal phenomena due to the adsorption of the aluminum hydrolysis products. 1 -

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II. HISTORICAL REVIEW Before the turn of the century, water treatment employing coagulation was an art and not a science. The early patents of that period contain no definitive data or present even the simplest oi the reactions involved. As the water works industry began to grow to meet the needs of a raoidly expanding population, increased emphasis was placed upon both bacteriological and chemical quality. In 191^, the first quality standards to apply to water used on interstate carriers were developed, and in 192>25 the U.S. Public Health Service initiated what were really the first definitive studies of water coagulation. They were done by Theriault, Clark and Miller, and published in Public He alth Reports . 1 They concluded that: 1 . there must be present a certain minimum quantity of al um inum or ferric cation in the water being coagulated; 2. they called attention to the applicability of the SchulzeHardy rule and pointed out that an anion of strong coagulating power, such as sulfate ion, should be present; 3 . they found that the hydrolysis products of both aluminum and ferric sulfate were not pure hydrates but contained combined sulfate and that in consequence the pH must be properly adjusted. In 1928, Bartow and Peterson^ published their studies on the effect of some selected salts on the rate of coagulation and tne optimum precipitation of alum floe. Some of the salts studied were found to 2 -

PAGE 19

3 broaden the pH range of rapid coagulation toward the low pH side. In 1928, in a very important paper which remained unnoticed for O many years, Mattson was able to demonstrate the relationship between the microelectrophoretic mobility of colloidal particles and the aluminum salt dosage. Mattson found that the positively charged sol, formed by the hydrolysis of the aluminum salt, exhibits its greatest effect on the zeta potential of the clay particle at a pH of about 5*2. He further showed that the hydrolysis products of aluminum and ferric salts are | j more effective than the tri valent metallic ions, Al and Fe , in reducing or neutralizing the zeta potential of the colloidal particles. Black and his associates (1933-3^) initiated the use of a pilot plant and refined jar test techniques to demonstrate the effect of some 9-11 selected ions on the pH zone of rapid coagulation. They found that the zone of rapid floe formation was considerably broadened on the acid side by the sulfate ion and to a much lesser degree by the chloride ion. Further, using both ferric sulfate and ferric chloride, they showed that in the pH zone from 6.5 to 8 . 5 , floe formation was markedly retarded or even inhibited. They ascribed the existence of this zone to the reversal of the charge on the floe, and emphasized that adsorption is an important mechanism of turbidity removal. 12 In 1949, Langelier and Ludwig made some basic studies on the mechanisms of flocculation, using synthetic clay suspensions, and came to the conclusion that the base exchange capacity and the size of clay particles were important factors in the flocculation process. They were perhaps the first workers to distinguish between the terms coagulation,

PAGE 20

4 which they characterized as "perikinetic" and flocculation, which they called "orthokinetic" coagulation. For the first time, they used the term "binder alum" to characterize its bridging functions in floe formation. In 1959, Pilipovich et al. 1 ^ reintroduced the long neglected microelectrophoretic technique to the study of water coagulation. They investigated the effects of pH, alum dosage, zeta potential, and base exchange capacity of clay particles on the coagulation of clay suspensions with alum, and concluded that the optimum coagulation dosage for clays with low base exchange capacity is lower than that for clays with Q high base exchange capacity. They further confirmed Mattson's view that the hydrolysis products of aluminum salts are more effective than the trivalent metallic aluminum ion, Al +++ , in producing good coagulation. Black and Hannah^ summarized the results of their electrophoretic studies on the coagulation of three synthetic clay suspensions with aluminum sulfate as follows: The zeta potential of clay particles was found to be dependent on the pH and on the alum dosage. An amount of alum equivalent to several times the base exchange capacity of the clay suspension was required to neutralize the particle charge. Clarification was best in the range pH 7-5 8.5 where the particles were negative, rather than at pH values where the particle charge had been neutralized. Fair coagulation was often obtained below pH 4.5 where the particles were nearly neutral. In many instances, residual turbidities changed sharply without any accompanying change in mobility values . In a series of five papers, Packham presented his extensive 15-19 studies on the coagulation of dispersed clays with aluminum salts. He concluded that anions have a great effect on the pH range of optimum coagulation, while cations have veiy little influence except under

PAGE 21

conditions wherein they can produce insoluble hydroxides. Packhara also concluded that the mechanism of the coagulation of dilute clay suspensions with aluminum salts is simply a physical enmeshment of the clay particles by the precipitation of the insoluble aluminum hydroxide. Thus, he came to another conclusion, namely that those factors which bring about the maximum precipitation of aluminum hydroxide will also bring about the optimum coagulation of clay suspension. Matijevic et al . 20 " 2 5 employed microelectrophoretic mobility measurements in their studies of coagulation and for the characterization | j., j, of the hydrolysis products of Al . They applied the well-known SchulzeHardy rule in demonstrating that the predominant species of the product of aluminum hydrolysis in the acid range is a tetravalent octanuclear complex, A1 q(OH) 20 ++++ . They further showed, by using both coagulation techniques and microelectrophoretic techniques, that the hydrolyzed aluminum species can reverse the charge of the negatively charged silver halide sols, Agl and AgBr, while the hydrated tri valent metallic aluminum ion cannot. This charge reversal was found to coincide with the optimum coagulation of silver halide sols. Matijevic et al. have asserted that the hydrolyzed aluminum species are more strongly adsorbed than the tri valent aluminum ion. In 1962, Mackrle confirmed his hypothesis that the initial phase of coagulation is accomplished by the following successive steps: 1 . the hydrolysis of coagulant added; 2 . the crystallization of the aluminum or ferric hydrous oxides; 3 . the compensation of the negative charges on the colloidal

PAGE 22

6 particles; 4. the mutual coagulation of the hydrous oxides and the colloidal impurities in the water; and 5. the formation of "microflocs. " These microflocs are then removed from the water by the agglomeration or mutual collision of the particles. He further showed that the zeta potential is pK-dependent, and that the low zeta potential zone of the hydrous oxides identified the pH range of the optimum coagulation. Stumm and Morgan (1962) reemphasized the importance of chemical theory in their explanation of the basic mechanisms of colloid stability and coagulation. 2 -^ From their studies of the alkalimetric titrations of aluminum in the presence of various ion groups, such as phosphate, pyrophosphate, oxalate and salicylate, they concluded that for certain anions specific chemical equilibria, such as complex formation, may be more important than double-layer compaction through counter ion adsorption. However, if the anions are weak coordinators with the coagulating metal ions, the compacting of the diffuse part of the double layer generally will be more important than chemical interaction for the destabilization of colloids. In addition to alkalimetric titration studies, they also suggested a laboratory technique for coagulation study which allows constant pH and alkalinity to be maintained throughout each experiment, thus facilitating the interpretation of specific chemical effects in a coagulation process. In the studies of turbidity removal with ferric sulfate. Black and Whiter^ again demonstrated the significant effect of the base exchange

PAGE 23

7 capacity of the clay on the coagulant dosage for producing charge reversal at low pH range, although the base exchange capacities of the clay suspensions were not found to be directly or proportionally related to the coagulant dosage which is required to acoonplish satisfactory coagulation. Further, they gave strong support to the view that the "overdosed isoelectric point" marks the beginning of the zone of efficient ortho kinetic coagulation, or flocculation. Kim et al. 2 ^ investigated the effects of cation exchange capacity, pH and alkalinity on the coagulation process and con eluded that! 1. The optimum final pH of ooagulation depends upon the initial alkalinity present in the suspension. As the alkalinity of the suspension is increased, the optimum final pH decreases. 2. The optimum final pH of coagulation is independent of alum dosage, but the pH range for good coagulation broadens with increasing alum dosage. 3. When the cation exchange capacity of the suspension is greater than about 10 ne/l, a pH value near the isoelectric point favors ooagulation. 4. Low concentration (less than 100 ppm) kaolinite suspensions can best be treated by maintaining pH at an isoelectric point that is a function of suspension alkalinity. Based on recent studies of the coagulation and flocculation of 28 several river sediment suspensions with aluminum sulfate. Black and Chen postulated that both coagulation and flocculation are strongly controlled by the properties of the coagulant. The characteristics of clay particles,

PAGE 24

8 such as base exchange capacity, particle size, total surface area and particle charge density, may influence the coagulant dosage required to achieve a good coagulation, but not the basic mechanisms of coagulation and flocculation for a particular coagulant. They further suggested that different mechanisms of destabilization are involved in various pH zones which are controlled by the hydrolytic reactions of aluminum ion, Tambo 2 ^ f ully discussed the validity of double-layer theory for understanding and controlling the stability and the instability of colloidal suspensions. He further emphasized that the critical zeta potential is without doubt not only a definite value tut is dependent on the conditions of the suspension. There exist tw> factors to control the critical zeta potential; (l) the kinetic energy of a suspended particle, and (2) the maximum interaction energy. Based on the assumption of the existence of a critical zeta potential in the coagulation ofc natural water, Tambo showed that the measurement of the zeta potential, i.e. , electrophoretic studies of coagulation, is one of the most important tools for investigating and controlling coagulation. The effect of particle size on the destabilization of colloidal 30 suspensions in water has been extensively studied by Vilaret. As a result of his investigation he demonstrated the following several phenomena: 1. The optimum coagulating and flocculating dosage of a cationic polymer increases directly with an increase in the total surface area of the system, which in turn is inversely proportional to the size of the suspended particles.

PAGE 25

9 2. No optimum dosage was observed during coagulation with nonhydrolyzing metal ions, and thus particle size has no marked effect on the required coagulant dosage. 3 . When a hydrolyzing coagulant, such as aluminum sulfate, is used, the particle size has an effect on the required dosage, although the relationship has not been so well defined as with high polymers. 4. Particle size has a definite effect on the kinetics of the destabilization process with the time required for optimum destabilization decreasing with decreasing size of suspended particles.

PAGE 26

III. THEORETICAL CONSIDERATIONS Chemistry of Aqueous Aluminum Since any explanation of the basic mechanisms of colloid stability and coagulation, either by chemical theory or physical theory, should concern itself -with the chemical composition of the coagulant being used, a comprehensive exploration and understanding of the chemistry of aluminum is very essential for the present investigation. It is believed that the chemistry of aluminum in very dilute aqueous solutions (les3 than 10 mole/liter) is very different from that of high concentrations. Therefore, the present discussion will be limited to solutions having a concentration range of 10”^ mole/liter to 10”^ mole/liter, which is in the practical range encountered in water coagulation. Hydrolytic Reactions of Aluminum Ion When aluminum ion is present in dilute aqueous solution, it is very easily hydrolyzed, and the hydrolytic reactions are very complicated. Brosset et al.-^' , ^ 2 investigated the hydrolysis of aluminum ion, Al +>k , by po ten tiome trie titration techniques and concluded that in the acid | | | range the main product of A1 hydrolysis is a polynuclear complex with a stoichiometric ratio of OH” to Al(IIl) of 2 . 5 * 1 » With reference to the behavior of aged solutions and crystallographic evidence, they suggested that the tri valent polynuclear complex (Al^(OH)^^J is the most likely main product. On the other hand, in the alkaline range the assumption of 10 -

PAGE 27

11 \ the existence of a single complex [Al(OH)^] and solid Al(OH)^ explains 31 the Brosset data very well. i Based on the ionic strength effect of the Schulze-Hardy rule, Matijevic and his coworkers initiated the use of the critical coagulation concentration of aluminum salt solutions for silver iodide sols » (both aged and in statu nascendi) and silver bromide sols (in statu nascendi) for determining the actual charge of ionic species in solution. By using the new electrolytic coagulation techniques they were able to identify the main hydrolysis products between the possible complexes, such as (Al^(OH)^^] and [a1q(0H) 2 q} , all of which have a stoichiometric ratio of OH to Al(lll) of 2.5 to 1. They postulate the polynuclear tetravalent species [a1q( 0H) 20 ) ++++ as the most likely formula of the complex in the pH range 4 to 7. However, at pH values below 4, the critical coagulation concentration corresponds to that of trivalent counterions indicating the presence of the simple hydrated aluminum ion. In addition to the complexes [A1^(0H)^^J and [A1 q(0H) 2 qJ more highly polymerized and hydrolyzed aluminum ions containing 6, 7* 10 or even 13 aluminum atoms in the complex, such as ( Aly(0H)^r,j and (Al 1 ^(0H)^]" H " t_H ", have been postulated by several other investigators. 33 ’ 34 ’ 35 Frink and Peecrr^ propose a completely different picture, in postulating that the hydrolysis of the aluminum ion in dilute aqueous solutions proceeds according to the simple monomeric hydrolysis mechanism, Al*** + H 2 0 ^ A1(0H) ++ + H + . They further attempt to show that, without controlling pH, aluminum hydroxide Al(OH)^ begins to

PAGE 28

12 precipitate upon diluting the solution to a concentration of aluminum salt lower than 10”^ mole/liter, which is considered to be the critical value of the supersaturation of A1(0H)^. Packham suggested two functional types of reactions which are thought to be involved in aluminum hydroxide precipitation as follows: Ligand exchange reactions. (A1(H 2 0)^ + h 2 0 2 (ai(h 2 0) 5 (oh)] ++ + h/ (la) (A1(H 2 0) 5 (0H)) ++ + H 2 0 s [Al(H 2 0) if (0H) 2 ) + + 1^0+ (lb) (A1(H 2 0) 4 (OH) 2 ) + + h 2 0 * [ai(h 2 o) 3 (oh) 3 ) + ^0+ (lc) (ai(h 2 0) 3 (oh) 3 )+ h 2 0 * (ai(h 2 o) 2 (oh) 4 )“ + ^0+ (Id) [A1(H 2 0) 6 ) +++ + x“ (Al(iy>) 4 xf + 2H 2 0 (2) [A1(H 2 0) 4 (0H) 2 ) + + X* (A1(H 2 0) 4 Xj + + 2 OH" , (3) Olation reactions. OH 2 (A1(H 2 0)-(OH)) ++ = )*l(H 8 0U ++t+ (4a) + 2H 0 2 ((H20) 4 A1(OH) 2 A1(H 2 0) 4 )^ + H 2 0 2 C(H 2 0) 2f Al(0H) 2 Al(H 2 0) 3 (0H)} +++ + (4b)

PAGE 29

13 ((H 2 0) 4 A1(OH) 2 A1(H 2 0) 3 (OH)}^ + [Al(H 2 0) 5 (OH)) ‘2 3 H 2° 0H n f .OH (H °). Ai 24 N 0H' I / 0H \ i H-H-+ + 2H 2 0 (4c) H 2° Table 1 shows the composition of several of the ionic and molecular species which have been suggested for aluminum and equilibrium constants for the reactions by which they may be formed. Table 1 Hydrolysis Equilibria of Aluminum No. Equilibria Log of Equilibrium Constant* (25°C) References 1 (ai(h 2 0) 6 ) + ' h ‘ + h 2 0 * (aioh] 44 -t ** h 3 o + -5.03 37 2 2A1 +++ + 2H 2 0 2 (A1 2 (0H) 2 ) +++ + 2H + -6.27 37 3 ai 444 + 3H 2 o 52 ai(oh) 3 (s) + 3H + -9.10 38 4 ai(oh) 3 (s) + h 2 0 ^ (ai(oh) 4 )" + H + -12.74 38 5 8A1 +++ + 20H 2 0 * (Al 8 (0H) 20 )‘ hHH '+ 20H + — 21 6 6A1* 44 + 15H 2 o (ai 6 (oh) 15 ) +++ + 15H + -47.00 32 7 A1(0H) 3 (S) Al 4 " 44 + 30H" -32.96 39 i(( Additional constants can be found in the works by Bjerrum, Schwarzenbach and Sillen, ® and Latimer. Ligand H 2 0 molecules are ommitted from subsequent reactions for brevity.

PAGE 30

14 Figure 1 is a general plot of the concentrations of the various aluminum species at different pH values. The solubility of aluminum hydroxide Al(OH)^ is defined by the boundary of the shaded area on the figure. Table 2 presents calculated data for equilibrium pH values for which the molar ratio' of (Al* * ' ) or [ Al^(OH)^' ' ' ] to (Al^] has been predetermined. The reaction formula and equilibrium constant used for this calculation are listed in line No. 6 of Table 1. Table 2 Calculated Equilibrium pH Values for Succe ssiv e States in One Reaction for the Hydrolysis of Al' 1 H at Al^. la***) 6 (AWOHhh^) PH [ a1 t ) I a 1 t] 0.99 0.01 4.23 0.90 0.10 4.31 0.80 0.20 ^•35 0.70 0.30 4.38 0.60 0.40 4.42 0.50 0.50 4.46 0.40 0.60 4.50 0.30 0.70 4.56 0.20 0.80 4.63 0.10 0.90 4.75 0.01 0.99 5. 16 A concentration of 1.5 x 10 mole/liter, which is equivalent to 5° mg/1 of Al (S0^) . 18H 9 0, is assumed for (Al^Jin the calculation. [a!^] is the total aluminum concentration.

PAGE 31

15 Fig. 1 Solubility Curre for Aluminum^ Hydroxide . Ai Al 6 (OH) 15 3 D! Al +3 Bl A1(0H) +2 El Al(0H) 4 ci ai 2 (oh) 2 + ^

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16 Alkalimetric Titration Curves The information yielded from the results of the alkalimetric titrations of aluminum in aqueous solutions is very valuable for understanding aluminum hydrolysis phenomena and the composition of the various hydrolysis product species as functions of pH value. Figure 2 shows typical alkalimetric titration curves for aluminum sulfate solutions with different total concentrations of aluminum. The titration curves for aluminum sulfate solution and aluminum in the presence of sodium bicarbonate NaHCO^ or sodium sulfate Na 2 S 0 ^ solution are shown in Figure 3 . The average number of bound hydroxide ions per aluminum ion applied, the formation function n, can be calculated from the data of alkalimetric titrations. The computation of the function for aluminum sulfate solution may be illustrated in the following way. Assume that the series of aluminum hydrolysis product species can be represented by the general formula (Al m (OH V SO,) p )^ where m and n may equal to any small positive integral number excluding zero. p may equal to any small positive integral number including zero. The total aluminum concentration at any pH is given by (A1 t ) = Ul^) 4-r m (Al m (0H) n (S0 4 ) p 3m n " 2p ) ( 5 )

PAGE 33

17 The electroneutrality at any pH is given by (H + ) + (Na + ) + 3 (Al* 4 *) +5(3i-n-2p) (Al m (0H) n (S0 lt ) p 3 "n 2p ) = 2 ( S V") + ( 0H ") (6) The total concentration of sulfate ion at any pH is given by K"J “ I K) rp (' a m (OH, n (SO A ) p 3! *" , ’' 2P ] (7) The combination of equations (6) and (7) leads to (h + ) + (lia + } + 3 [a 1 T++ ) +I(3»>-n-2p)[Al nl (OH) n (S0 lt ) p :3, "" n " 2p ] “ 3[A1 T ) 2Xp(Al m (0H) n (S0^) p 3n, ' n 2p ] + (OH') (8) The combinations of equations (5) and (8) leads to (h + ) + (na + ) + 3[Al +++ ] + X(3m-n-2p)(Al m (0H) n (S0 lt ) p :3 ” , n 2p J. 3 (ai^) + 3S«. (a m (0H) n (so 1> ) p 3 m n 2p ) . 25p ( Alm( oH) n (s° lt ) p 3m n 2p )+ (OH') (9) The simplification and rearrangement of equation (9) leads to ( H + ) + (na + ) (OH') = In (Al m (0H) n (S0 4 ) p 3m n 2p ) (10> Now, the formation function n at any pH can be given by n = n = n = toH~] bound l PST ;n(A 1 m (°H) n (S0 4 ) p 3nl n 2p ) (.Alj] (h + ) Hr ( Na + J (oh") 1 a1 t) ( 11 ) ( 12 ) (13)

PAGE 34

18 Since the parameters on the right side of equation (13) are known from alkalimetric titration data, the formation function n can be easily « \ evaluated . Some of the computed formation function n data are plotted as functions of pH in Figure 4. Charge of Specific Hydrolysis Products Since there is a random behavior in the arrangement of the structure of the hydrolysis product in the hydrolytic reactions, only the statistical charge average of the hydrolysis products can be evaluated from formation function n data. However, because the best available data indicate the existence of some active predominant hydrolysis products throughout the entire series of reactions, a general discussion of the charge of some specific hydrolysis products is feasible and it provides valuable information for an understanding of the electrokinetic characteristics of the floes formed by the interaction of the polymeric species with clay particles in the destabilization process. The charge of the various aluminum hydrolysis products which are assumed to be formed at different pH values can be summarized in a hypothetical scheme as shown in Figure 5* Aging Effect When solutions of aluminum salts are aged, either at ordinary room temperatures or at elevated temperatures, certain aquacomplexes may be formed by hydrolysis of the aged solutions. These aging reactions are more rapid in solutions having higher concentration of hydroxide ion.

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19 o Hd n C o # 0 rH O in u +j rt CO I 3 (< o t bO a a a

PAGE 36

20 td s s= SB O Hd v -p s 5 I r'* h0 K Alkalimetric Titrations of Aluminum and Aluminum in the Presence of Sodium Bicarl of Sodium Sulfate.

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21 Hd to El Formation Function Curves for Aluminum Sulfate Solutions

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22 Fig. 5 Stepwise Conversion of the Tri positive Aluminum Ion to the Negative Aluminate Ion. (From Stumm and Morgan? 5)

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23 25 or at elevated temperatures . It has been shown that this aging effect causes a decrease in the critical coagulating concentrations of aluminum ions and simultaneously an increase in the hydrogen ion concentration of the solutions of aluminum salts. ^ Figure 6 and Figure 7 show the effect of this aging process on the coagulating concentration and pH of aged aluminum solutions . # Complex Formation The formation of soluble and insoluble complexes by specific chemical interactions of aluminum ions with anionic functional groups, such as sulfates and phosphates, has considerable significant effect on 42 the flocculation process through a cross-linking or bridging mechanism. It is especially important when metal ions are employed to flocculate 25 hydrophilic colloidal suspensions. Some of the complex formation reactions of aluminum ions and their equilibrium constants are listed in Table 3 • Characteristics of Kaolinite Clays Clays comprise the major portion of the colloidal material which, suspended in natural waters, the water chemist terms natural ~ 1~2 turbidity. Langelier and Ludwig were among the first to initiate the use of synthetic clay suspensions for the investigation of the water coagulation. Black and Chen have demonstrated the applicability of the results from synthetic clay suspension studies to natural 28 river sediment suspensions.'” Therefore, for simplicity in

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24 0 300 600 900 Time of Aging Al^SO^ at 90°C (min.) Fig. 6 The Effect of the Time of Aging of Aluminum Sulfate Solutions at 90° on the Coagulation Values of Silver Chloride, Silver Bromide and Silver Iodide Sols in statu nascendi.(Froa Matijevio aftd Iezak% °)

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25 Time of Aging Al(NO^)^ at 90°C (min.) Fig. 7 The Change of pH in Solutions of Al(NO ) When Aged at 90°C. (From Matijevic and Tazak. ) ^ *

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26 Table 3 Complex Formation Reactions of Aluminum ,25 No. Equilibrium Log of Equilibrium Cons tan ts ( 2 5° C ) 1 Al^ + PO^ AlPO^ (S) 22 2 ^ + vr" = t Aip 2 o ?r — 3 Al +++ + F” * (a1f} ++ 6.13 A A1 N *" + 3 Acetate” [a 1( Acetate)^ — 5 Al +++ + 3 Oxalate”" Z (Al(Oxalate)} 16.3 6 Al 4 ” 4 " 4 " + Salicylate ^ (a 1 Salicylate] 4 " 1A designing the laboratory experiments comprising the present investigations, kaolinite clay suspensions have been used. A general description of the characteristics of kaolinite clays will therefore be useful. Structure and Chemical Composition of Kaolinite Clays Kaolinite may be described as a two-layer clay whose particles are made up of a single tetrahedral silicon sheet topped by a slightly distorted octahedral aluminum sheet. The two layers are joined by condensation and splitting off of water between adjoining hydroxyl groups in the vertex position. Thus a single oxygen linkage remains and is shared by the two layers, resulting in a primary valence bond between the sheets. The atomic charges in the structural units are balanced, and the

PAGE 43

27 chemical composition of a typical structural unit may be expressed as (OH)gAl^Si^O^Q. Kaolinite is often referred to as having a 1:1 lattice, and the extent of atom substitutions in the lattices is relay's tively small. . A schematic diagram of the crystal stricture of kaolinite is shown in Figure 8. Size and Shape of Clay Particles Due to the existence of the strong valence bond between the two unit layers of kaolinite clay, these clay particles commonly are quite resistant to natural mechanical cleaving forces. Consequently, natural kaolinite clays are usually composed of fairly large unit particles, larger than three microns. A kaolinite clay particle may be described as a thin, plate-like, hexagonal crystal. Origin of Surface Charge on Clay Particles The surface charge on clay particles, which are hydrophobic hh colloids, may be produced, according to van Olphen in either of two ways. The first source of surface charge which he suggests is the net result of imperfections within the interior of the crystal lattice of the particle. The second source suggested is the preferential adsorption of certain specific ions on the particle surface. Cation Exchange Capacity of Clay Particles The cation exchange capacity of a clay is its ability to exchange cations with the solution phase. The aluminum layer in kaolinite clay seems to have amphoteric properties and will produce more hydrogen ions by dissociation as the pH of the system increases. Therefore, kaolinite

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28 Octahedral Sheet A A A A $ A 6(0H) / \ i v i / \ I v I / m/m/ \ i / \ i / v / V \ / v\ \ / A \ / A 8 i 6 h 8 $ 4(0) 2 (OH) Tetrahedral Sheet Formula of unit cell: (Al 2 (0H)^(Si 2 0^)J , o 5.15 A Unit cell dimensions: A B = 8.9 ft C » 7.2 X Unit cell weight: 516 Fig. 8 Schematic Diagram of theCrystal Structure of Kaolinite Unit Cell. (From van Olpherv 41 ).

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29 clays have variable cation exchange capacities depending upon the pH of the system. The cation exchange capacity of kaolinite clays may 45 vary from 3 to 15 milliequivalents per 100 grams at pH Adsorption Sites of Clay Particles According to van Olphen^ kaolinite clay has a nonexpandable lattice and thus a smaller "c-spacing." Such a structure tends to physically prevent the accommodation of cations in the interior of the clay particle. Therefore, all cations must be adsorbed on the exterior surface of the clay particle. Mechanisms of Destabilization In the field of colloid science at least two different theories have been historically advanced to explain the basic mechanisms involved in the stability and instability of colloidal systems. The first theory is the so-called chemical theory which assumes that colloids are aggregates of definite chemical structural units, and assumes the existence of specific chemical interactions between specific ions in both phases of colloids and solutions . According to this theory the destabilization of colloids is the result of the precipitation of insoluble complexes formed by those specific chemical interactions. The second theory, termed the physical theory or double-layer theory, emphasizes the importance of the electric double layers surrounding the colloidal particles in the solutions and the significant effects of counter-ion adsorption and zeta potential reduction in the destabilization of colloidal systems. These two theories may appear at first

PAGE 46

30 sight to be different, but they are not mutually exclusive. As a matter of fact, both mechanisms must be employed in order for a comprehensive understanding and for effective control of the phenomena of colloid stability and instability. Under the present heading only a general discussion of the destabilization mechanisms of the hydrophobic colloids, to which clay colloids are classified, will be given. Coagulation 46 Definition According to La Mer coagulation can be best defined as follows: "We propose that coagulation be used for the general kinetic process obeying the simple Smoluchowski equation independent of 0, whereby colloidal particles are united (L. coagulare to be driven together) as typified by the effects of electrolytes upon gold sols. Coagulation is brought about primarily by a reduction of the repulsive potential of the electrical double layer in accordance with the ideas advanced by Derjaguin, Landau, Verwey and Overbeck." Double-Layer Theory . The electric double -layer surrounding a » colloid may be created by the preferential adsorption of counterions onto the clay surface as a result of the charge deficiency within the clay lattice, or the direct ionization of some of the molecules on the colloid surface. Among the many theories ’ which describe the structure of the electric double -layer, the Stem-Gouy diffuse doublelayer theory has been found most acceptable in the case of clay colloid systems. In this particular model, part of the counterions remains in a compact layer, Stem layer, on the charged colloid surface in consequence of the existence of strong electrostatic forces as well as van der Waals

PAGE 47

31 forces, while the other part of the counterions extends into the bulk of the solution and constitutes the so-called diffuse Gouy-Chapman layer. Figure 9 shows the structure of the Stem-Gouy double -layer and the corresponding potentials. The potential at the surface of the particle itself is generally designated as while the potential at the boundary between the Stern and the Gouy part of the double -layer is designated as ££ . The potential at the plane of shear which essentially separates the hydration water from the bulk of solution is distinguished as the zeta, g , potential. It is this zeta potential which controls the stability and instability of the colloid system. Critical Zeta Potential . According to the findings of electrophoretic studies on water coagulation, ’ the zeta potential of colloids need not be reduced to zero in order that coagulation may take place, and this fact has led to the concept of a critical zeta potential. The theoretical derivation of the critical zeta potential is based on the principle that the total kinetic energy, E^» of the colloid particle should be large enough to overcome the energy barrier, which is the maximum interaction energy, E > between two approaching colloidal ITIclX particles (see Figure 10). Tambo concluded from his derivation of the critical zeta potential for the coagulation of ordinary natural water?, which have inverse values of the thickness of the Debye-Huckel ionic atmosphere (Rvalues) in the range of 10^*^ to 10^’^ cm \ that 12 mV may be used as a threshold value for the coagulation of most waters in water supply systems. Figure 11 shows his critical zeta potential as a function of Y, value.

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Potential Surface of Clay Particle 32 i© |0 i. i 0 0 0 | 0 i© i 0 © | 0 |© |0 0 © 0 © | 0 |0 !© i © 0 © | 0 P 0 0 1® i© i 0 © 4 k — Stern layer Bound solvent e 0 © © 0 0 m 0 Gouy layer Distance from the surface of clay Fig. 9 The Structure of Stem -Gouy Double Layer and the Corresponding Potentials.

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33 Fig. 10 Potential Energy of Interaction

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34 29 Fig. 11 Critical Zeta Potential Curve. (From Tambo. ) .

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35 Flocculation Definition . It is important that a distinction be made between the terms coagulation and flocculation to account for the different forces involved. According to La Mer flocculation should be defined as follows: "We propose that the term flocculation should be restricted more in accordance with original usage corresponding to the Latin meaning of floe (L. flocculus a small tuft of wool or a loosely fibrous structure). Flocculation is usually brought about by the action of high molecular weight materials (potato starch and polyelectrolytes in general) acting as linear polymers which bridge and unite the solid particles of the dispersion into a random structure which is three dimensional, loose, and porous." Bridging Mechanism . Interparticle bridging action has been proposed by many inves tigato rs ^ 5 ^ as the basic mechanism in the flocculation of colloidal dispersions with polyelectrolytes. This same mechanism may also serve to explain the flocculation of clay suspensions with hydrolyzing metal coagulants. According to the bridging theory the polymer molecules are postulated to have part of themselves attached on the adsorption sites of the suspended particles and with other parts of the chains extended into the bulk of the solution. When these extended chain segments are adsorbed on the vacant adsorption sites of other suspended particles, bridges are established. Consequently, the particles are bound together and form small packets which can grow into big porous structural units until the shear gradient imposed by agitation in the system serves to prevent further growth.

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36 Enmeshment Mechanism . The rapid flocculation of clay suspensions 19 24 with aluminum salts has been explained by Fackham and Mackrle as due to the physical enmeshment of the clay particles by the precipitation of the insoluble aluminum hydroxide. Under this enmeshment theory, it is postulated that the pH zone of optimum precipitation of aluminum hydroxide is the controlling factor in producing optimum flocculation. Aluminum-Clay Interactions The following experimental phenomena which take place in the interactions between aqueous aluminum ions and clay particles in dilute suspensions are believed to be most significant on the destabilization of the dilute clay suspensions. Reduction of Zeta Potential Depending upon the characteristics of the different types of counterions involved in the aluminum-clay-water systems, the repulsive zeta potential of the clays may be reduced in three different ways, as follows : 1. by the compression of the double-layer thickness in consequence of the incorporation of the simple cationic counterions into the diffuse Gouy double -layer; 2. by the specific adsorption of the cationic hydrolyzed species on the clay surface with a concurrent reduction in the surface potential of the clay particles; and 3. by the reduction of the particle surface charge, which is

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37 accompanied by a reduction in the particle surface potential, as a result of the partial neutralization of particle charge by the attachment of aluminum hydroxides through physical enmeshment or mutual coagulation mechanism. In general, the decrease in zeta potential 'is related to a decrease in the thickness of the electrical double-layer. The extent to which the double -layer thickness may be compressed depends upon the concentration and valence of the added counterions in the colloid system. Adsorption The aqua-complex ions of aluminum hydrolysis products may oe adsorbed onto the adsorption sites of the clay particles by specific mechanisms. There are many types of adsorption models available for describing the various types of physical adsorptions. Among those tne Freundlich adsorption model is considered to best describe the case of the adsorption of the soluble aluminum hydrolysis products by kaolinite clay suspensions. Adsorption Mechanisms . The adsorption process may be descrioed by one or more of the following postulated mechanisms: 1. Hydrogen bonding betweenthe clay and the counterion. 2. Adsorption through the agency of the residual valence forces in clay lattices. j. A specific chemical reaction taking place on the surface of the clay between the adsorbed ion and the clay with the subsequent fonnation of an insoluble complex. 4. Dipole effect of the counterions.

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33 Freundlich Adsorption Isotherm , The Freundlich adsorption isotherm equation may be written l/n (m) = KC (1*0 or log (|) = log K + jjlog C (15) where x = weight of material adsorbed m = weight of adsorbent C = equilibrium concentration of the material being adsorbed n,K = empirically derived constants Charge Reversal The phenomena of charge reversal of the clay particles in the coagulation of clay suspensions with metal ion coagulants, such as aluminum salts and ferric salts, have been demonstrated by many investiga26 28 tors. * 9 The pH range of charge reversal generally corresponds to the range of the formation of the polynuclear hydrolysis products. Consequently, it has been postulated that the charge reversal is caused by the specific adsorption of a sufficient amount of the hydrolyzed polynuclear species onto the surface of colloids. In addition to the above findings, a zone of redispersion of colloids has also been revealed to be consistent with the zone of charge reversal.

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IV. EXPERIMENTAL MATERIALS AND PROCEDURES Materials Kaolinite Clay The kaolinite clay used in preparing the clay suspensions in this investigation was the particular species, Kaolinite 4, supplied by Ward's National Science Establishment. Tnis was the same clay used , „ . 14,26, by Black and his coworkers in their previous coagulation studies. The base exchange capacity of this clay is 8.7 milliequivalents per 100 grains, which was determined by Hannah using the ammonium acetate method.' 32 In addition, the surface area of the kaolinite clay calculated from B.E.T. nitrogen gas adsorption data was reported by Birkner to be 15*8 nf/gm. Aluminum Sulfate The coagulant used in this study was reagent grade aluminum sul fate with a chemical formula Al^SO^ • 18^0. The chemical analysis of this material is given in Table 4. Reagents for pH Adjustment Standardized 0.1 N HC1 and 0.1 N NaOH solutions were used to adjust the final pH values of the clay suspensions. Reagents for Aluminum Determination The reagents used for determining the total aluminum are -39 -

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40 Table 4 * Analysis of Aluminum Sulfate Constituent Per Cent by Weight Assay {^Al^SO^ • 18H 2 °) 103.0 Insoluble Matter 0.003 Chloride (Cl) 0.0008 Arsenic (As) 0.00003 Substances not Precipitated by NH^*0H (as S0^) 0.10 Heavy Metals (as Pb) 0.0005 Iron (Fe) 0.0005 pH of 5$ Solution at 25°C 2.4 ^Analyzed by J. T. Baker Chemical Company, Phillipsburg, N. J. Cij, described in the following sections: Standard 100 ppm Aluminum Solution . Dissolve 1.757 gm of aluminum potassium sulfate in distilled water containing 50 ®1 of 5 N hydrochloric acid and dilute to 1 liter. 1 Per Cent p-Nitrophenol . This indicator solution was obtained directly from W. H. Curtin and Company. 5 N Ammonium Hydroxide . Dilute 33 ^ concentrated ammonium hydroxide to 100 ml with distilled water. 0.5 N Hydrochloric Acid . Dilute 4.5 ml of concentrated hydrochloric acid to 100 ml with distilled water.

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I Per Cant Thiog-Iy collie Acid . The thioglycollic acid used was an analytical grade chemical supplied by Eastman Kodak Company. Aluminon Reagent . Dissolve 0,25 gai of aluminon in 250 ml of distilled rater, rarming the solution. Add 5 gm of gum acacia followed by 87 gm of ammonium acetate and 126 ml of 5 N hydrochloric acid. Dilute to 500 ml and then filter under suction. Procedures Preparation of Kaolinite Clay Suspensions Before it ras suspended in demineralized rater, the kaolinite clay ras pulverized in a ball mill for a period of 24 hours and sieved through a 200 mesh screen, which has an average opening of 0.074 millimeter. One hundred twenty grams of the sieved kaolinite clay powder ras suspended in 40 liters of demineralized water in a polyethylene carboy. The suspension ras vigorously stirred for 12 hours rath a high-speed mixer equipped with a long stainless steel shaft and propeller, after which the suspension was alio rad to settle quiescently for 24 hours to separate the large size fractions. The supernatant portion of the settled clay suspension was then siphoned off and stored in another polyethylene carboy. The particle size cf a clay suspension thus prepared will have a size range smaller than two microns as estimated from the S'tokes law T . Vigorous mixing was started two hours before and was continued through the entire process of pipetting various size aliquots of the settled clay suspension into individual 250 ml polyethylene bottles, which were then stoppered, labelled and stored until needed. When these different size

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42 aliquots were diluted to two liters with demineralized water, the various values of clay concentration and initial clay turbidity as shown in Table 5 were obtained. Table 5 Kaolinite Clay Suspensions $ Clay Concentration (mg/l) Initial Turbidity (units) 15.8 20 18.8 24 31.7 41 37.2 51 4 7.5 67 61.5 102 63.3 104 73.9 125 >jc The clay concentrations Preparation of Aluminum Sulfate were determined gravimetrically. Solutions All aluminum sulfate solutions xrere prepared by dissolving an appropriate amount of reagent grade aluminum sulfate in demineralized water. Those solutions having concentration levels higher than 10 mg Alum/ml were prepared every two x-jeeks, -while those having concentrations lower than 10 mg Alum/ml were prepared at much shorter intervals, the

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criterion being the maintenance of constant pH values, which, were measured daily. Alkaline trie Titrations Standardization of 0.1 N Sodium Hydroxide Solution . The 0.1 N sodium hydroxide solution which was used for both alkalimetric titration and pH adjustment was precisely standardized by primary standard potassium acid pht'nalate solution, KKCE,. 0 . Titr tion of Aluminum Sulfate Solution ,, Demineralized water was used to prepare the aluminum sulfate solutions for titration experiments. A Tefloncovered magnetic bar and a magnetic stirrer were used to mix the solution thoroughly for three minutes after the drop vise addition of the standardized 0.1 N sodium hydroxide solution. pH value of the solution was determined by the Beckman Model G pH Meter. The same procedure was repeated until a pH value of 10 was recorded. Through the entire titration process a pure nitrogen gas flow was bubbled through the solution being titrated. The temperature of the solution was maintained constant, at 25°C. Titration of Dilu t e Kaolin! te "lay Suspension . The procedure for titrating the dilute kaolinite clay suspensions, which had different dosages of aluminum sulfate solution, with the standardized 0.1 N sodium hydroxide solution was similar to that used for the alum solutions. Destabil ization Experiments The destabilization experiments which have been conducted in this investigation may be grouped into four different series as follows:

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44 1. With the dosage of aluminum sulfate fixed at a selected constant value, bat varying the final pH of the clay suspension. 2. With the final pH of the clay suspension fixed at a constant value of pH 3, but varying the dosage of aluminum sulfate. Four different clay concentrations were used. 3 . With the final pH of the clay suspension fixed at a constant value of pH 5» hut varying the dosage of aluminum sulfate. Four different clay concentrations were used. 4. With the final pH of the clay suspension fixed at a constant value of pH 8 , but varying the dosage of aluminum sulfate. Four different clay concentrations were used. Although there are some differences among the four series of experiments, the preparation of clay working suspension, function and intensity of agitation, sampling, residual turbidity measurements and pH measurements, as described in the folio-ting sections, were exactly the same in all series. Preparation of Clay Working Suspensions . Six bottles of the kaolinite clay stock suspensions were used for each series of jar tests. The contents of the bottles were quantitatively transferred to separate two-liter volumetric flasks in which about one liter of the demineralized water had been placed. Appropriate amounts of 0.1 N HC1 or 0.1 N NaOH were added to the flasks to yield the desired final pH values, and the flasks were then filled to the mark with additional demineralized water. A Tefloncovered magnetic bar was then placed in each flask and the flasks were then placed on magnetic stirrers. The suspensions were thoroughly

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45 mixed for five minutes. One-liter graduated cylinders were then used to measure one liter of the suspension from each flask and this was transferred to a 48-oz square jar. The jars were placed on the multiple laboratory stirrer which was manufactured by Phipps and Bird, Inc. The suspensions remaining in the flasks were retained for the electrophoretic mobility determinations. Function and Intensity of Agitation . The suspension in the ij-8-oz square jars was agitated by the stainless steel paddles on the multiple laboratory stirrer at a speed of 100 revolutions per minute for two minutes before and after the addition of appropriate dosages of aluminum sulfate. The speed was then reduced to 10 revolutions per minute for a period of 28 minutes. The suspensions were then allowed to settle quiescently for 10 minutes in order to separate the settleable floes. In addition, a second combination of mixing was used, which consisted of a 20-minute period of 100 rpm rapid mixing followed by a 10minute period of 10 rpm slow mixing, followed by a period of 10-minute sedimentation. In all cases, a final pH of 5 was used. Sampling . At the end of the prescribed sedimentation period 250 ml samples were withdrawn from each jar by an apparatus similar to that described by Cohen^ at a level approximately one inch below the surface of the supernatant in the jar. The samples so obtained were used for residual turbidity and residual aluminum determinations. Initial and Residual Turbidity Measurements . The initial and residual turbidities of the samples were measured with a Lumetron

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46 Model 450 Filter Photometer. The use of a 650 ro4 red filter with a 75 mm light path in the cell was found to give sufficiently accurate readings of the turbidity values. The calibration of the Photometer was accomplished by comparing the optical density readings with the turbidity readings for each sample." 50 The optical density readings from the Photometer were plotted against the turbidity readings from a Jackson Candle Turbidimeter by the method described in Standard 57 Methods . The initial turbidity of each clay suspension was determined by averaging the turbidity values of four samples of each suspension in which no coagulant or other reagent had been added. In each destabilization experiment, the residual turbidity of each sample was measured promptly at the end of the sedimentation period. pH Measurements . The destabilized suspensions which remained in the jars after the sampling process were used for the final pH determinations. All the pH determinations were made with a Beckman Model G pH Meter. Electrophoretic Mobility Determinations Sample Preparation . Prior to the addition of the predetermined amount of aluminum sulfate, each of the remaining one-liter samples of "Manufactured by Photo volt Corp., New York, N. Y. ^Manufactured by Beckman Instruments, Inc., Fullerton, Calif.

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the clay suspensions which were retained from the destabilization experiment was placed on a magnetic stirrer and mixed vigorously for five minutes. Mixing was continued for another five minutes after the dosing of aluminum sulfate , and then the electrophoretic mobility of the particles was immediately determined. Measurements of Particle Electrophoretic Mobility . Throughout the entire course of this investigation, the Briggs microelectrophoresis cell was used to determine the electrophoretic mobilities of particles. The calibration of the cell as well as the procedure for determining particle mobilities were the same as those described and recommended in detail by Black and Smith. Specific Conductance Determinations . A Model IB-2A Impedance Bridge with a pipette-form conductivity cell having a cell constant of 1 cm * was used for the measurements of the resistance of the clay suspensions. The specific conductance values were then calculated from these resistance data according to the procedure described in 57 Standard Methods . pH Measurements . The pH of each sample was measured with a Beckman Model G pH Meter immediately after the mobility determination of the same sample was made Calculation of Mobility Values . The electrophoretic mobilities C?Q of particles were calculated from the equation: $ Manufactured by Heath Company, Benton Harbor, Michigan.

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48 -T2= dX tIR ( 16 ) where -°= mobility, in n/sec/v/cm d = distance across a square of the Howard counter at a given magnification, in n 2 X = cross sectional area of the cell, in cm t ~ time for traveling across d, in seconds I = current density, in amperes R s = specific resistance of the suspension, in ohmcentimeters Determination of Residual Aluminum Standard Curve Calibration . A standard curve was prepared on the Lumetron Model 450 Filter Photometer by using standards containing 0.0 to 1.5 mg/l aluminum, Al, prepared by dilution of the standard 100 ppm aluminum solution. A separate calibration curve was plotted for each new batch of aluminon reagent. The optical density readings of the standards were obtained by using a 530 mp. filter and a 3*75 mm light path in the cell. Separation of Clay Particles . After the destabilization experiment was completed, a 250 ml sample of the supernatant was withdrawn from each jar as described in the previous section of sampling. A 100 ml of this sample was transferred into two 50-ml plastic centrifuge tubes, and then they were immediately centrifuged with a Model HR-1 Inter* national High-Speed Refrigerated Centrifuge for 10 minutes at a speed Manufactured by International Equipment Company, Boston 35, Mass.

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49 c i 9,000 rpm to allow a complete separation of the clay particle from the liquid. The value of 9,000 rpm is equivalent to 4,600 x g. Procedures fcr Alur tnum Determinations . The procedures for determining the residual aluminum in the sample were basically the same as those developed by Packham.'^' The successive steps used in the aluminum determinations were as follows: 1. A 50 ml sample of the centrifugate, which was estimated to contain less than 0.075 mg of aluminum, was pipetted into a 100-ml volumetric flask. The volume of sample was reduced to 25 ml or 10 ml when the aluminum concentration was estimated to possibly exceed 0.075 rag, and 3 . dilution factor was used to calculate the actual concentration of aluminum in the sample. 2. One drop of 1 ..or cent p-Nitrophenol indicator solution was added to the sample. Five N ammonium hydroxide was added drop by drop tin til the solution turned yellow. 3. The yellow coloration was then discharged by the dropwise addition of 0.5 N hydrochloric acid. 4. To the solution 16 drops of the freshly prepared 1 per cent thioglycollic acid and 10 ml of aluminon reagent was added. Demineralized water was then used to make up the volume to approximately 95 ml* 5. The flask was then immersed in boiling water for 20 minutes, after which it was removed from the boiling water and cooled rapidly in cold running water to around 20°C. Finally, the solution in the flask was made up to 100 ml with demineralized water. 6. The optical density values of the processed samples were

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50 determined with the Lunetron Photometer, using a 530 mufilter and a 3.75 mm light path in the cell. Each jar test consisted of six individual experiments so that a total of six samples and one blank was prepared for every series of residual aluminum determinations. Adsorption Computations The difference between the total aluminum added to the clay suspension and the total aluminum still remaining in the centrifugate of the suspension was calculated and reported as the adsorption value. --luminun-Clay Kinetic Experiments Aluminum Adsorption Rate . The adsorption rate of aluminum by kaolinite clay was determined by measuring the residual total aluminum in the centrifugate of the clay suspension at successive time intervals after the addition of a predetermined amount of aluminum. The adsorption values were computed in the same manner as that described in the previous section. Duration and Intensity of Agitation . In order to evaluate the effects of the initial clay concentrations and the duration and intensity of agitation on the destabilization of the kaolinite clay suspensions at different pH values, the suspensions were mixed at a given intensity of agitation for a predetermined period of time, following which a period of 15 minutes was used to allow the destabilized suspensions to settle quiescently. Samples for residual turbidity determinations were then withdrawn by the same method as described in the previous section, and the determinations immediately made.

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V. RESULTS AND DISCUSSION Variable pH Series The series of studies in which the pH value is varied was performed using Wo different approaches. In the first, the destabilization experiments were performed on kaolinite clay suspensions which had the same clay concentration value of 61.5 mg/l. The final pH of the destabilized suspensions was varied from 3 to 10, while the dosages of aluminum sulfate used were 3> 5 j 7> 10, 15» 20, 30 and 50 mg/l. The experimental results of this part of the study are shown in Figures 12 to 19. In the second approach, the experiments were conducted using kaolinite clay suspensions having three different initial clay concentrations and in the neutral to slightly alkaline pH range of from pH 6 to 8 with dosages of 5> 1°, 30 and 50 mg/l of aluminum sulfate. Figures 22 to 25 show the results obtained for the second series. Role of pH on Aluminum Sorption The aluminum sorption curves as depicted in Figures 12 to 19 reveal several significant phenomena which are discussed in the following sections: 1. Only a small fraction of the aluminum ions was adsorbed on kaolinite clay particles at pH values below pH 4 and above pH 9> and practically no sorption of aluminum ions by the clay particles was 51 -

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2 Fig. 12 The Effect of pH on the Destabilization of Kaolinite Clay Suspension. Aluminum Sulfate Dosage = 3 nig/l. Clay Concentration =61.5 mg/l.

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2 1 0 -1 -2 .00 80 60 40 20 0 4 3 2 1 0 53 of pH on the Destabilization of Kaolinite Clay Aluminum Sulfate Dosage * 5 ng/l« Clay Con* 61.5 mg/l.

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4 2 0 -2 -4 .00 80 60 40 20 0 8 6 4 2 0 54 of pH on the Destabilization of Kaolinite Clay . Aluminum Sulfate Dosage = 7 mg/l. Clay Con=61.5 rag/ 1 *

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4 2 0 -2 -4 100 . 80 60 40 20 0 8 6 4 2 0 The 55 O o <0 r o Effect of pH on the Destabilization of Kaolinite Clay ension. Aluminum Sulfate Dosage = 10 mg/l. Clay Conration =61.5 rog/l •

PAGE 72

56 Fig. 16 The Effect of pH on the Destabilization of Kaolinite ClaySuspension. Aluminum Sulfate Dosage = 15mg/l. Clay Concentration =61.5 mg/1.

PAGE 73

57 Fig. 17 The Effect of pH on the Destabilization of Kaolinite ClaySuspension. Aluminum Sulfate Dosage = 20 mg/l. Clay Concentration =61.5 mg/l.

PAGE 74

58 Fig. 18 The Effect of pH on the Destabilization of Kaolinite Clay Suspension. Aluminum Sulfate Dosage = 3° m sA* Clay Con. centration =61.5 mg/l»

PAGE 75

59 Fig. 19 The Effect of pH on the Destabilization of Kaolinite ClaySuspension. Aluminum Sulfate Dosage = 50 m s/l* Clay Concentration =61.5 mg/l.

PAGE 76

cu observed at pH 3 and pH 10. These data are believed to support the 21 hypotheses that the predominant species at pH values below pH 4 is ( ) { the simple tri valent aluminum ion, A1 , while in the alkaline pH range aluminum is present mainly as the negatively charged aluminate ion, A1(0H) ; , . It would appear that these two species are not strongly adsorbed by the clay particles . 2. In the range from pH 4 to pH 9 > two peaks were found on the aluminum sorption curves when intermediate dosages of aluminum sulfate were used. The pH value of the first peak at the lower pH values is found to correspond very well to the equilibrium pH at which 99 per cent of the added aluminum ions is present as Al^(OH)^^ as proposed 32 by Brosset and his coworkers. The second peak of the aluminum sorption curve on the higher pH side is believed to represent the pH value at which maximum precipitation of aluminum hydroxide occurs. A comparison between the calculated and observed values for four different dosages is shown in Table 6. A series of aluminum adsorption isotherms based on the interpolated data from Figures 12 to 19 is shoxm in Figure 20. The Freundlich adsorption isotherm plots of these data at three selected pH values are shown in Figure 21. Relationship Between Mobility and Residual Turbidity The relationships between the electrophoretic mobility values and residual turbidity shown in Figures 12 to 19 are not so readily defined and correlated. However, there are several interesting and

PAGE 77

61 Table 6 Comparison of pH Values for Maximum Hydrolysis and Maximum Adsorption of Aluminum Ion Experimental pH Dosage of Equilibrium pH at Which for Maximum Aluminum 6 £ Al^(OH), ^ Aluminum AdsorpDiscrepancy Sulfate TatI — ^ = ^ tion in Acid Between the (mg/l) L^tJ pH Range two pH Values 3 5.57 — — =: 5.49 — — 7 5.45 — — 10 5-39 5.25 -0.14 15 5-35 5*35 0.00 20 5.29 5,35 0.06 30 5.23 5.25 0.02 50 5.16 — — significant conclusions which may be drawn from them. Among them the most important are the following: 1. At pH values below pH 4, the electrophoretic mobilities of the clay particles gradually become more positivewith increasing alum dosages. This change identified a zone of fair to good turbidity removal, termed by Langelier and Ludwig, who first observed it, perikinetic or electro kinetic coagulation. 2. The firs. oelectric point appeared in the pH range from 4 to 5. This isoelectric pH value decreased with an increase in the

PAGE 78

Total Aluminum Adsorbed (mg/l) 62 Fig. 20 The Effect of pH on the Adsorption Isotherms. Kaolinite ClayConcentration =61.5 mg/l. (The figures on the right side are pH values ) .

PAGE 79

63 o rH I CM I 0 ^ i (§) 3 d CM CO to c o •H to c a to 3 CO >> 0 ) rH O 0 ) P •rl c • H rH O tJ « o to tl) ,C O P O o to to •O H °^C o •rl P a P o to T) •dc •c o •rl rH T5 00 • O I CM CO £ c tl) p p c o 1 § O P 0 o 0) P «H .rl «H C W -rl rH 0 ) O JC. cfl E« 1 CM to •rl IP Clay Concentration = 61.5 mg/l.

PAGE 80

64 dosage of aluminum sulfate. The second isoelectric point appeared in the range from pH 6 to pH 8, the pH value increasing with increasing alum dosage. Therefore, the charge reversal zone falling between the two isoelectric pH values was broadened with an increase in the dosage of aluminum sulfate. In addition, the first isoelectric pH, when the mobility changed from negative to positive, marked the beginning of a redispersion zone essentially identical with the zone of charge reversal, first pointed out by Black and Hannah.^ The second isoelectric pH at which the mobility changed from positive to negative identified the beginning of a pH zone of optimum turbidity removal. 3. The maximum charge reversal was generally accompanied by maximum redispersion. Moreover, the pH value of the maximum charge reversal was slightly decreased from 5.? to 4.9 with an increase in the aluminum sulfate dosage from 3 mg/l to 50 mg/l. Effect of Initial Clay Concentration on Destabilization The data shown in Figures 22 to 25 were mostly obtained within pH range from 6 to 8 within which the aluminum hydroxide has been supposed to be the most predominant aluminum species. Those curves showed that when the dosages of aluminum sulfate were less than 30 mg/l the initial clay concentration had an influence on all of the clay mobility, the residual turbidity and the total aluminum consumption measurements . Clay suspensions with higher concentration of clay particles were more readily destabilized than those with lower clay concentrations. However, when a high dosage of aluminum sulfate, specifically 50 mg/l was used, the initial clay concentration had practically

PAGE 81

65 Fig. 22 The Effect of Initial Clay Concentration on the Destabilization of Kaolinite Clay Suspensions with Aluminum Sulfate. Aluminum Sulfate Dosage = 5 rog/l.

PAGE 82

66 pH Fig. 23 The Effect of Initial Clay Concentration on the Destabilization of Kaolinite Clay Suspensions with Aluminum Sulfate. Aluminum Sulfate Dosage = 10 mg/l.

PAGE 83

2 1 0 -1 -2 .00 80 60 40 20 0 20 16 12 8 4 67 .5 6.0 6.5 7.0 7.5 pH 8.0 8.5 9.0 9.5 of Initial Clay Concentration on the Destabiliza>linite Clay Suspensions with Aluminum Sulfate, llfate Dosage = 30 mg/l.

PAGE 84

68 5-5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 PH Fig. 25 The Effect of Initial Clay Concentration on the Destabilization of Kaolinite Clay Suspensions with Aluminum Sulfate. Aluminum Sulfate Dosage = 50 mg/l.

PAGE 85

69 no effect on the values of the three determinations. In addition, the aluminum consumption curves reveal that all three clay concentration curves are quite similar in the pH range above pH 7»5« The simple physical enmeshment mechanism as proposed by Packham to describe the coagulation of the dilute clay suspensions with alumi19 num salts is applicable only in those systems in which the concentrations of the applied aluminum ion are sufficiently high so that abundant amount of aluminum hydroxide floes can be rapidly formed to sweep down the suspending clay particles. However, for low alum dosages, mutual coagulation as proposed earlier by Black^“ would appear to be better mechanism for describing the destabilization of dilute clay suspensions with aluminum salts in the neutral pH range. When a clay suspension can be destabilized by the physical enmeshment mechanism, the concentration of clay particles may have very little effect. However, the clay concentration becomes a critical factor when mutual coagulation is the controlling mechanism of the destabilization process. The experimental results shown in Figure 25 , using 50 mg/l aluminum sulfate dosage, support the assumption of the validity of a physical enmeshment mechanism, while the results in Figures 22 to 2^, using aluminum sulfate dosages less than 30 mg/l, can be better understood by assuming mutual coagulation as the mechanism of destabilization. Log (Al) vs. pH The destabilization of a dilute clay suspension with aluminum salts is largely controlled by the hydrolytic reactions of the aluminum

PAGE 86

70 ionSj which in turn are functions of the pH and the concentration of aluminum ions present in the system. Consequently, a more comprehensive understanding of the destabilization of a clay suspension may be achieved through a study of the log ( Al) pH plot in which the various regions of coagulation and flocculation are very well defined by both pH value and the logarithm of the molar concentration of aluminum. The experimental results of the variable pH series of this study are summarized and plotted in the form of log (Al) pH as shown in Figure 26. Constant pH Series In the constant pH series, three different final pH values, namely, pH 3 j pH 5 and pH 8, were chosen for investigation in an attempt to elucidate the various mechanisms involved in the destabilization processes in those pH ranges within which the existence of dif21,32 The ferent predominant aluminum ion species have been proposed.' trivalent metallic aluminum ion, Al ' , is the main species in the region below pH 4. In the range between pH 4 and pH 6, the formation of hydrolyzed polynuclear complexes, such as A1^(0H) 1 ^ +++ or Alg ( OH ) ^ Q _r "~ r , has been proposed. In the neutral pH zone from pH 6 to pH 8, insoluble aluminum hydroxide, A1(0H) , or colloidal basic salts are believed to be the principal species present. Destabilization at Constant pH 3 The results of this series of experiments are shown in Figures 27 to 30. The curves of particle electrophoretic mobility and aluminum adsorption are quite similar for the four clay suspensions which had

PAGE 87

Log Molar Al 71 PH Fig. 26 The Entire Log (Al) pH Domain for a Kaolinite Clay Suspension. Clay Concentration = 61. 5 mg/l.

PAGE 88

Total Aluminum Consumed Residual Turbidity Electrophoretic Mobility (mg/l) (10) ($ T. ) (p/sec/v/cra) 72 pier. 2? The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 15.8 mg/l. Final pH of Suspension = 3.0.

PAGE 89

2 1 0 -1 -2 .00 80 60< 40 20 0 32 24 16 8 73 o—o n o ... o -o _Q_ o—o— 6—o — 65 10 ± ± 15 20 25 30 35 40 45 50 Aluminum Sulfate Dosage (mg/l) 3 Destabilization of a Kaolinite Clay Suspension with orainum Sulfate. Initial Clay Concentration 31.7 mg/l. nal pH of Suspension =3.0.

PAGE 90

74 Fig. 29 The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration **47.5 mg/l« Final pH of Suspension *» 3.0.

PAGE 91

75 Fig. 3° . The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 63.3 mg/ 1. Final pH of Suspension =3.0.

PAGE 92

76 different initial clay concentrations, namely, 1 5*&, 3l*?» ^7*5 63.3 mg/1. When the residual turbidity is expressed as per cent of the initial clay turbidity, the clay suspension which had the highest clay concentration was found to have the lowest residual turbidity. The addition of aluminum sulfate in dosages from 5 m oA U P to 50 mg /1 had no effect upon either the residual turbidity or the adsorption of aluminum ions for any one of the four clay suspensions. However, increasing 'the dosage of aluminum sulfate decreased the negative mobility of the floe particles at all dosages employed from -2.5 p/sec/ v/cm to about -O .3 p/sec/v/cra. According to Matijevie~ x the hydrated trivalent metallic aluminum ion does not reverse the charge of negative silver halide sols, and this same behavior has been shown to take place in the kaolinite clay suspensions, as revealed in Figures 27 to 30 . Also, no adsorption of the trivalent Al^ ion was found at this pH value throughout the entire range of dosages employed. The reduction in the negative mobility of the clay particles by an increase in aluminum ion concentration is believed to be brought about by the reduction of the double -layer thickness of the clay particle in consequence of an increase of the ionic strength in the suspension system. Therefore, the behavior of the trivalent metallic aluminum ions in the clay colloidal systems is simply to intensify the ionic atmosphere surrounding every clay particle to compress the doublelayer of the particle with a reduction in the double -layer thickness. As a result of this reduction in the thickness of the double-layer

PAGE 93

77 surrounding a clay particle, the zeta potential of the clay particle is reduced, as shown by much lower negative mobility values. Although the electrophoretic mobility curves in all four clay suspensions investigated are almost identical, the percentages of initial turbidity remaining after coagulation were not the same, and the curves show an inverse relationship between concentration and final turbidity. These differences in residual turbidity at different initial 62 clay concentrations may be explained by the Smoluchowski theory which is based upon the probability factor in particle collisions during the process of coagulation. According to this theory, where all variables except clay concentration are held constant, the suspension which has higher initial clay concentration should be easier to destabilize with a greater reduction in clay turbidity. Destabilization at Constant pH 5 Figures 31 to 34 show the results of the series of experiments in which the final pH values were maintained at constant pH 5* The predominant species at this pH value is believed to be either the polynuclear complex, Al^(0H)-, ; ‘ ' ' or Alg(0H) 20 ‘ ‘ , as proposed by Brosset-' 21 and Matijevic respectively. Two types of agitation were used to bring about destabilization in this series. The first type was two minutes of rapid mixing at 100 rpm followed by a period of 28 minutes of slow mixing at a speed of 10 rpm, followed by a 10 minute sedimentation period. The results for this series are shown in the solid line curves in Figures 31 to 34. The second type employed 20 minutes of rapid mixing at 100 rpm followed

PAGE 94

4 2 0 -2 -4 100 80 60 40 20 0 16 12 8 4 T 78 5 10 15 20 25 30 35 40 Aluminum Sulfate Dosage (mg/l) 3 Destabilization of a Kaolinite Clay Suspension with ominum Sulfate. Initial Clay Concentration = 15.8 mg/l. nal pH of Suspension * 5.0 t 0.05.

PAGE 95

79 pj_g t 32 The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 31.7 mg/1. Final pH of Suspension = $.0 0.0$,

PAGE 96

Total Aluminum Adsorbed Residual Turbidity Electrophoretic Mobility (mg/l) (10) (* T ) (n/sec/v/cra) 80 Fig. Final pH of Suspension = 5*° 1 0.05.

PAGE 97

81 Fig. 34 The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 63.3 mg/l. Final pH of Suspension = 5«° 0.05.

PAGE 98

82 by a period of 10 minutes of slow mixing and 10 minutes sedimentation. The dash line curves in Figures 31 to 34 show the experimental results obtained with this type of mixing. The second type of mixing provides more kinetic energy for the particles and thus results in better turbidity removal. The differences in the percentage of the initial turbidity remaining after coagulation at different initial clay concentrations may, as before, be accounted for in terms of Smoluchowski' s theory. The electrophoretic mobility curves show that the aluminum hydrolysis products formed at this pH value are capable of reversing the originally negative charge of the clay particles. These charge reversal phenomena, which occurred in the case of all of the four sus21 pensions, support the theory proposed by Matijevic, and much earlier, g by Mattson, that the hydrolyzed aluminum species are able to reverse the charge of the negatively charged sols. The mechanism for this charge reversal may be the over-neutralization of the surface charge of the clay particle by the strongly adsorbed multivalent hydrolyzed aluminum species in consequence of a specific adsorption of the hydrolyzed aluminum ions by the ions on the clay surface. A very narrow zone of coagulation appears at the point where the mobility values change from negative to positive. Beyond this point, the clay suspension was again stabilized. This same phenomenon was fully demonstrated by Black and his associates'^ in their studies of the destabilization of dilute clay suspensions with labelled polymers. Consequently, the polymerization tendency of the aluminum hydroxo

PAGE 99

83 complexes as proposed by Stumm and Morgan 2 "’ can be indirectly supported by the present experimental results. Figure 35 summarizes the effect of the initial clay concentration on the destabilization of kaolinite clay suspensions with aluminum sulfate at pH 5» The aluminum adsorption data shown in Figures to 3 ^ ma y a l so be plotted as Freundlich adsorption isotherms. Figures 36 to 39 show the plots of these Freundlich adsorption isotherms. Figure 40 shows the effect of the initial clay concentration on the Freundlich adsorption isotherm. The concave inflection at the right ends of the adsorption curves as sho\m in Figures 3± to 3 ^ ma y De due to the presence ox colloidal aluminum hydroxides which can be removed by centrifuge separation since, as shown in Figure 41, 12 per ceno of tne aluminum added was removed by centrifuging. The empirical constants of the Freundlich adsorption isotherm equation for each of the four clay suspensions investigated were calculated, using the sample linear regression equation, and the calculated results are shown in Table 7. Destabilization at Constant pH 8 The experiments in this series were performed using four different kaolinite clay suspension concentrations, varying from 15.8 mg/l to 63.3 mg/l. Figures 42 to 45 show the individual results for each of the four clay suspensions investigated. A summary of these is shown in Figure 46. It is clearly demonstrated that the aluminum consumption curves are only slightly influenced by the difference in initial clay

PAGE 100

4 2 0 -2 -4 .00 80 60 40 20 0 16 12 8 4 0 84 10 15 20 25 30 35 40 45 50 Aluminum Sulfate Dosage (mg/l) i Effect of Initial Clay Concentration on the Destabilization Kaolinite Clay Suspensions with Aluminum Sulfate. Final pH Suspensions = 5 *° 0 . 05 .

PAGE 101

0*0 85 CO • VPv I — I It e o •rl -P rt U -P c a) o c o o !$* 5 •H 5 rH O tt) X 0 ) Xi p o 10 c o •H -P & o to < x o T) 0 ) (W/ x ) Sai VO to £

PAGE 102

0.0 86 CM (W/ x ) 201 rH C O •rl -P nJ U -P c 0 ) o c o o rt* rH O -p rH O Oj C o •pH •P O W 5 o •H rH •d & c^ho *tH

PAGE 103

0.0 87 to 6 r-d C o •H P nJ P C
PAGE 104

0.0 88

PAGE 105

89 o -du> £ (W/ x ) 2oi

PAGE 106

90 Fig. 41 The Effect of pH on Aluminum Residual After Separation by High-Speed Centrifuge.

PAGE 107

4 2 0 -2 -4 .00 80 60 40 20 0 32 24 16 8 0 > _ 91 Destabilization of a Kaolinite Clay Suspension with *inum Sulfate. Initial Clay Concentration = 15-8 rag/ 1. al pH of Suspension = 8 t 0.1.

PAGE 108

4 2 0 -2 -4 .00 80 60 40 20 0 32 24 16 8 0 92 10 15 20 25 30 35 Aluminum Sulfate Dosage (mg/l) le Destabilization of a Kaolinite Clay Suspension with Luminum Sulfate. Initial Clay Concentration * 31.7 mg/l, Lnal pH of Suspension = 8 1 0.1.

PAGE 109

Total Aluminum Consumed Residual Turbidity Electrophoretic Mobility (mg/l)(10) ($ T. ) (n/sec/v/cm) 93 Fig. 44 The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 47.5 mg/l. Final pH of Suspension = 8 t 0.1.

PAGE 110

94 Fig. 45 The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Suspension 63.3 «g/l. Final pH of Suspension = 8 I 0.1.

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Total Aluminum Consumed Residual Turbidity Electrophoretic Mobility (mg/1) (10) (* T ) (p/sec/v/cra) 95 Fig. 46 The Effect of Initial Clay Concentration on the Destabilization of Kaolinite Clay Suspensions with Aluminum Sulfate . Final pH of Suspensions = 8 0.1.

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Table 7 The Empirical Constants of the Freundlich Adsorption Isotherm Equation Kaolinite Clay Concentration (mg/1) log K K x (10) 2 1 n n 15.8 -1.64 2.29 0.73 1.37 31.7 -1.76 1.74 0.68 1.47 47.5 -1.82 1.51 0.65 1.54 63.3 -1.84 1.45 O .63 1.59 * The form of the Freundlich isotherm used is log I = ^ log C + log K concentrations . This minor effect of the clay concentration on the aluminum consumption can be attributed to the active precipitation of the colloidal aluminum hydroxide in the suspension. Practically, these appear as straight lines which may simply demonstrate the increasing tendency of the precipitation of the aluminum hydroxide corresponding to the increase in the dosage of aluminum sulfate. Therefore, instead of the effect of aluminum adsorption, the rate of precipitation of the aluminum hydroxide is the major controlling factor in the process of destabilization at this pH value. This theory is supported by the work 18 of Packham. Figure 4? shows the aluminum residual as a percentage of the aluminum added, after the separation of the colloidal aluminum hydroxides by centrifugation. There is an inflection point in each of the electrophoretic

PAGE 113

97 mobility curves shown in Figure 46 at a low aluminum sulfate dosage . This particular point of inflection seems to mark the first effect of the colloidal aluminum hydroxide on the mobility value when compared with the aluminum residual curve shown in Figure 47. At dosages higher than that at the inflection point, the mobilities reach a constant value, very close to zero, but either positive or negative, depending on the clay concentration. This slightly positive or negative value of floe mobility probably is due to the small net charge remaining on the floe as a result of a mutual coagulation between clay particles and aluminum hydroxide colloids. Consequently, the sign of the mobility value may be determined by the clay concentration in the suspension, with positive values for suspensions with very low concentrations of clay particles, while for suspensions with high concentrations of clay particles the mobility values always show zero or slightly negative values. This phenomenon was repeatedly shown in the previous electrojh 28 phoretic studies of coagulation by Black and his associates. Â’ The results of the measurements of the residual turbidity values as depicted in Figure 46 show that in the aluminum sulfate dosage range from 10 mg/l to 40 mg/l the initial clay concentration has an important effect on the removal of turbidity, whereas in the ranges below 10 mg/l or above 40 mg/l the clay concentration has little effect. The mechanism of physical enmeshment in destabilizing the clay suspension as proposed by Packham may account for the very slight effect of the initial clay concentration at aluminum sulfate dosages higher than 40 mg/l at pH 8. However, mutual coagulation is a better mechanism

PAGE 114

Aluminum Residual (^5 Al_) 98 Fig. 47 The Effect of Initial Aluminum Concentration on Aluminum Residual After Separation by High-Speed Centrifuge.

PAGE 115

99 to describe the destabilization phenomena at intermediate dosages of aluminum sulfate at this pH. Kinetics of Aluminum-Clay Interactions Aluminum Adsorption Rate The investigation of the aluminum adsorption rate was carried out at a constant final pH value of 5 with the temperature maintained at 25°C. The concentration of the kaolinite clay suspension was 63.3 mg/l. An aluminum sulfate dosage of 20 mg/l (1.6 mg/l of aluminum) was added to the system. The results as depicted in Figure 48 show that about 0.67 rng/l of total aluminum, which was equal to 41.9 per cent of the total added aluminum, was adsorbed by the kaolinite clay particles during the first one minute after the addition of the aluminum sulfate to the suspension. The adsorption increased slightly with time. At the end of a 60-minute period, the adsorption value was O .76 mg/l which was equal to 47.5 per cent of the added aluminum ion concentration. Therefore, the adsorption of aluminum hydrolysis products, which are proposed to be actively formed at this pH, can be demonstrated to be a rapid process. Effect of Mixing Time on Residual Turbidity In Figures 49 to 54, the residual turbidity was plotted against the total number of paddle resolutions at which the turbidity measurements were made. The total number of paddle revolutions is computed from the total time of mixing (in minutes) and the mixing rate (in

PAGE 116

Total Aluminum Adsorbed (mg/l) 100 Time (min.) Fig. 48 The Effect of Time on the Adsorption of Aluminum by Kaolinite Clay Particles. Initial Aluminum Concentration = 1.6 mg/l. Clay Concentration = 63.3 mg/l.

PAGE 117

Residual Turbidity (T) 101 Fig. 49 The Effect of Time of Mixing, Expressed as Total Number of Paddle Revolutions, on the Destabilization of Two Kaolinite Clay Suspensions with 5 nig/l of Aluminum Sulfate at 40 rpm Agitation Intensity. pH = 3.0.

PAGE 118

102 Fig. 50 The Effect of Time of Mixing, Expressed as Total Number of Paddle Revolutions, on the Destabilization of Two Kaolinite Clay Suspensions with 5 rag/l of Aluminum Sulfate at 40 rpm Agitation Intensity. pH = 5 *° 0 . 05 *

PAGE 119

Residual Turbidity (T) 103 Fig. 51 The Effect of Time of Mixing, Expressed as Total Number of Paddle Revolutions, on the Destabilization of Two Kaolinite Clay Suspensions with 30 mg/l of Aluminum Sulfate at 40 rpm Agitation Intensity. pH = 8 t 0.1.

PAGE 120

Residual Turbidity (T) 104 Fig. 52 The Effect of Time of Mixing, Expressed as Total Number of Paddle Revolutions, on the Destabilization of Two Kaolinite Clay Suspensions with 5 mg/l of Aluminum Sulfate at 100 rpm Agitation Intensity. pH = 3*0*

PAGE 121

Residual Turbidity (T) 105 Fig. 53 The Effect of Time of Mixing, Expressed as Total Number of Paddle Revolutions, on the Destabilization of Two Kaolinite Clay Suspensions with 5 mg/l of Aluminum Sulfate at 100 rpra Agitation Intensity. pH = 5*° 0.05 .

PAGE 122

Residual Turbidity (T) 106 Fig. 54 _ The Effect of Time of Mixing, Expressed as Total Number of Paddle Revolutions, on the Destabilization of Two Kaolin! te Clay Suspensions with 30 mg/l of Aluminum Sulfate at 100 rpm Agitation Intensity. pH = 8 t 0.1.

PAGE 123

Residual Turbidity (T) 10 ? p^g. 55 _ The Effect of Time of Mixing, Expressed as Total Number of Paddle Revolutions, on the Destabilization of a Kaolinite Clay Suspension with 5 mg/l °f Aluminum Sulfate at Two Agitation Intensities. pH = 3.0.

PAGE 124

Residual Turbidity (T) 108 Fig. 56 The Effect of Tine of Mixing, Expressed as Total Number of Paddle Revolutions, on the Destabilization of a Kaolinite Clay Suspension with 5 ng/l of Aluminum Sulfate at Two Agitation Intensities. pH = 5*0 0.05.

PAGE 125

Residual Turbidity (T) 109Fig. 57 The Effect of Time of Mixing, Expressed as Total Number of Paddle Revolutions, on the Destabilization of a Kaolinite Clay Suspension with 30 mg/l of Aluminum Sulfate at Two Agitation Intensities. pH = 8 0,1.

PAGE 126

no revolutions per minute). It is clearly demonstrated that the residual turbidity curves in all cases investigated reached a constant minimum value when the suspension systems were stirred with a total of 2,000 paddle revolutions. However, the final constant minimum value of the residual turbidity curves appears to be dependent on such factors as the pH of the suspension, the coagulant dosage, the intensity of agitation and the clay concentration . Since interparticle collision is a prerequisite to particle agglomeration, the initial rate of the reduction of turbidity should be very rapid as the initial number of particles is relatively high. According to this theory, the rate of the reduction of turbidity is diminished as the number of the suspended particles is reduced because of the formation of the particle agglomerates and the subsequent sedimentation of the larger floes. Effect of Agitation Intensity on Residual Turbidity Two stirring rates were used in this series of kinetic experiments. Figures 55 to 57 show the results obtained from the investigations on the high clay concentration suspensions at three different pH values, namely, pH 3> pH 5 and pH 8. In all cases, the agitation at a rate of h-0 rpm was more effective in the reduction of turbidity than that at a rate of 100 rpm. The difference in the residual turbidities affected by different rates of agitation was reduced in the following order:

PAGE 127

Ill pH 3 > pH 5 > pH 8 This might be attributed to the different mechanisms involved in the destabilization processes at the three pH values investigated. At pH 3 the results of this investigation have supported an electrokinetic coagulation mechanism. Therefore, a moderate rate of mixing gives a better reduction in turbidity than a high rate of mixing, which produces greater shear forces in the fluid and thus makes the aggregated particles more susceptible to break-up action. Although a little bridging effect may be provided by the aluminum hydrolysis polynuclear complexes in the destabilization mechanism at pH 5» the aggregated particles at this pH value still cannot withstand the strong shear forces produced by a high rate of mixing. Consequently, a rather low rate of mixing is favored for better turbidity reduction at pH 5* However, the difference in the rate of mixing has a smaller effect in the reduction of turbidity at pH 8, at which pH the flocculated particles have stronger floe structures and are more resistant to break-up.

PAGE 128

VI. SUMMARY AND CONCLUSIONS Chemical grade aluminum sulfate at concentrations up to 50 rog/l was used as a coagulant to investigate the mechanisms involved in the destabilization of dilute kaolinite clay suspensions at various clay concentrations and over a pH range from 3 to 10. Within the aluminum sulfate concentration limits used in this investigation, the pH range from 3 to 10 can be roughly divided into four different regions in which different predominant aluminum species are present. In the region below pH 4, the hydrated metallic aluminum ion is the most active aluminum species, while in the region between pH 4 and pH 6 a hydrolyzed aluminum polynuclear complex, such as A1 6 (0H) 15 H+ , A1 ? (0H ) Vf ** + *. Alg(OH) 20 W+ and Al^OH)^^, is the predominant aluminum species. In the neutral pH range roughly from 6 to 8, colloidal aluminum hydroxide is the main aluminum species, while the alumina te ion, A1(0H)^", is the predominant species in the region above pH 8. Three major experimental approaches were used to elucidate the mechanisms involved in the specific aluminumclay interactions with the subsequent destabilization of the clay suspensions. They were conducted in the following ways: 1. In one series, the dosage of aluminum sulfate was maintained at some selected constant value while the pH was varied. 2. In another series, the final pH value of the suspension was 112 -

PAGE 129

113 maintained at a constant value of 3* 5 or 8 . The choice of these three particular pH values was based on both the available literature of aqueous aluminum chemistry and the experimental results obtained from the first approach above. In this series, the aluminum sulfate dosage was varied. 3 . In the series of kinetic studies, both the time of mixing and the intensity of agitation were varied. According to the experimental results obtained, several important and significant conclusions can be drawn as follows: 1. The mechanism involved in the destabilization of the kaolinite clay suspension at pH 3 is due ho a reduction of the repulsive potential between the negatively charged clay particles through a compression of the double layer. This is due to the incorporation of hydrogen and hydrated aluminum ions into the Gouy diffuse layer. 2. The destabilization of kaolinite clay suspensions at pH 5 can be attributed to a reduction of the zeta potential of the clay particles through the specific adsorption of the hydrolyzed multivalent aluminum polynuclear complex ions onto the clay surface with the subsequent reduction of the surface potential of the clay particles. 3 . Physical enmeshment may account for the destabilization of kaolinite clay suspensions at pH 8 where rapid and abundant precipitation of aluminum hydroxides occurs. However, when the dosage of aluminum sulfate is less than 40 mg/l at this pH, a mechanism of mutual coagulation between colloidal aluminum hydroxides and clay particles better describes the phenomena of the destabilization.

PAGE 130

114 4. The Freundlich adsorption isotherm model was found best to describe the adsorption of the hydrolyzed aluminum polynuclear complex ions by the kaolinite clay particles. 5. The residual turbidity curve as a function of the time of mixing shows that the turbidity can be reduced to a constant minimum value by stirring the suspension system with a total of 2,000 paddle revolutions . 6. The constant minimum value of the residual turbidity curve appears to be dependent on such factors as the pH of the suspension, the coagulant dosage, the intensity of agitation and the clay concentration . 7. The effect of the initial clay concentration on the destabilization process was found to follow SmoluchowskiÂ’ s theory at pH 3 an( i pH 5, whereas it had little effect at pH 8 when the aluminum sulfate dosage was higher than 50 mg/l.

PAGE 131

APPENDIX

PAGE 132

116 CO i — ! § E-. 0 C •H 0 rH > S rt ( — I O rt rH CD O -P •H rH C rt •ri *H l-l -P O *rl rt C « H rt • cp CD O -P rt G «P •H "3 -P CO CTJ SJ •H rH •H rQ ct3 *P CO 0) Q 0) E-i o •H 4-> <1) / — » ft s>> e O -P o x : -ri^ CX rH > O -H " — ft £> •P O o £ <0 0) i— l « tp O o Q) -p •H CD rH cvj Ov cv H a. Ov O rH •H rO o CO • CVJ • rv • •S ^ § / — ' 0 C rH T> •H — ni cn o 00 VO •H £ bO CVJ CVJ CVJ 1 — 1 rH CO 0 e • • • • • CD (X H ^ . •H «P -p •H T5 £> -P -H ^ g-g £ CD rH a nj •rH tn -p co rt -p a> c CJ H T> rH 33 Cl) O T) O' rt fl u) »
PAGE 133

Table 9 The Destabilization of a Kaolinite Clay Suspension with a Dosage of 5 mg/l of Aluminum Sulfate. Initial Clay Concentration =61.5 mg/l* 117 o •H -p P 5 -. O JS P. rH O -H' P -P O P rH W J3 o S o >» -P 6.45 0.06 92 0.00 6.50 0.06 89 0.04 6.44 -0.59

PAGE 134

Final pH of HC1 NaOH Residual Turbidity Residual Final pH of Electrophoretic Destabilized Added Added as per cent of * Aluminum Mobility Mobility Suspension (meq/l) (meq/l) Initial Turbidity (mg/l) Sample (p/sec/v/cm) 118 as sO 00 -3“ UN rH rH co CA o Os ON O CO O • • • • • • • • o CM ON CM 0J CA CM . On On 00 00 oo ON 00 o o UN as 3 o CNco CnrH • • • • • • • CNCNc^ co co Os On 5$ o -3" o

PAGE 135

119 O r— I < 1 > r — i •s E-i o •H -P (1) ^ G >» s O -P o G -P * — s 0< rH > On o o OCO o p}CV. o p O -P NO CNVO CO cv pt CNrH 1 1 c h O o • • • • • • • • • 1 1 • •H •P O © O o o o o rH rP rH rH o 5 o s « © H a. 1 1 • 1 • H «< W w O 1 — 1 o !>> -p © VO to EG -P rP o o VA o CO Pt On ON S G< rP 0* tp VO rH CO o CVJ rH VO 1 1 CN# ^ | C* • • • • • • • • • 1 t • INo © c s CO CO pjPivo u-\ V\ vrv VO CH o •H pH © • to (H oi to to a s vo rH 6 flj • r — 1 JZ vO 0} P P P rH CO ip ON co VO o vo cvj rH o 4-> 3 ’i'ts vo VO pjco rP 1 — 1 o o o o •H ii w p e • • • • • • • • • • • • * c o o O o o O o o o o o o c o O -P •P -P to a} a g © -P G. C £ *>> to 0 ) 3 O •P t M -P •G O -P cn c •P G o O -P -P >»o G G X rt rP t>j p © G £<0 3 O ctJ H rP vo CNOn O o rv VO On CVJ 1 i — 1 rH G rP co vO VO ON ON ON On 00 00 1 © O -P d © iP 3 ftrt 1 •P rP c rt G -a •A to -P •P *P to d .p rP -P © G O *P d G US M (G H nj • G rP vn »T\ VO VO VO VO G to to •P © 3 UQ (O

PAGE 136

Final pH of HCl NaOH Residual Turbidity Residual Final pH of Electrophoretic Destabilized Added Added as per cent of * Aluminum Mobility Mobility Suspension (meq/l) (meq/l) Initial Turbidity (mg/l) Sample (p/sec/v/cm) 120 vO vO rH o ca CA vO (V CTv • • • • • rH 1 CM 1 (A 1 "T CA 1 o o o o rH VO oVO On • • • • • CVa00 00 o O CVo o CTv VO CNON • • • • • VO CVCNCO 00

PAGE 137

The Destabilization of a Kaolinite Clay Suspension with a Dosage of 10 mg/l of Aluminum Sulfate. Initial Clay Concentration =61.5 mg/l* 121 o P P O u O P JZ P ' O. P O P' f-i & P O O S 0 ) . • P w O !>> P <1) KPP O NO CM CO P. P Q. rH VO O NO • • • • P -O 3 a 0 co CO CO -3-3£ P P Xi O P O P ^ C r1 CO 3 X) P CO a> pO * p P Xi P P C ,0 O C-. o 3 E-i S* <0 P O. CO P (0 P cO P C O P W O XI o' CO X) 0) ss <=0 e Xi P CD P Xi CT a xi J i — I c0 CO P c o c a C w « P © P< Pn a co CM o I On co o ) NO CM NO CO p o I NO CO CO oCNoo CO o d VO CM NO CM d CO d ON NO CM £n& CO On ON CM CM O ON CO ON o p CM ON CNCM CO NO CM O CM O CO CO CNCN. p NO NO NO NO VO p 00 o CO 00 ON co CH CO CO • NO S' On O CO ON o On NO 0 • NO 0 • CN0 • § • On O • O rH • 0 0 0 0 O 0 NO {>On rH 0 0 00 O 00 0 OO vn On CO On On CM CNrH -3. • • • • • • • • • • CO CO CO d . 3 -3" d NO NO VO VO 6.83 0.11 95 0.06 6.7? O.52

PAGE 138

Final pH of HC1 NaOH Residual Turbidity Residual Final pH of Electrophoretic Destabilized Added Added as per cent of * Aluminum Mobility Mobility Suspension (meq/l) (meq/l) Initial Turbidity (mg/l) Sample (n/sec/v/cm) 122 o vp\ ft Ov VP, $ 1 VP, Ov VP, O1 vO CvrH rH • • • • 1 • • 1 • • o o rH 1 CM 1 rH 1 CM 1 1 O o o 3 ON CM 00 VO rH r\ CV1 1 — 1 Cv1 o CM • • • • 1 • • 1 • • CvCV00 On Ov o o rH rH VO rH 81*0 c^ s s £ o 00 o 00 o 00 O o’ o o o o o o CM O vr, Cv3 o r\ CP VP, vO vp. vP, CO C'l rH • O 3 VO i— I vO VO O 05 00 VO 00 3 o 00 On rH O CM CM o o o o -dN Ov Ov Ov Ov Ov OCCvCM o VP\ O • o I — I VP\ l>cm CM c o •H w G & OT 3 OT 0) Si +> o •H £ -P » — I OJ •H -P M

PAGE 139

The Destabilization of a Kaolinite Clay Suspension with a Dosage of 15 mg/l of Aluminum Sulfate. Initial Clay Concentration =61.5 mg/l. 123 o •H -P © P O -P x .h p< O *H u £> 4-> O O ^ CD r— I w rH o !>> -p © S rl rl C V ca 00 SO 00 >A O -dPr rH P. rH o CA 00 o | 1 CsCS) rH •H £ rH £t c3 cd o co • ca • ca • • •3• -3• SA 1 1 • »A • SO • so £ •»H X! -H .O P rH m s XS •H W © EC $ •H X! •H g £ Vh O •P c © o p CD rH P, cd •H W +> cd *H G H -a h ec ©^ O x! cr* cd x) © sc a T3 rH 00 CS) (V o o rH CO so CS) dCS1 — 1 o Csc-dca 00 -d00 ca o CM o £NVT> ca oOs on vO Os Os 00 00 Os CSo o rH rH O S' S' o 0) 00 vr-S o cs) rH "d o* Os CS) 1 — 1 o o "d © • • • • EC -<3 e o o o o , 73 O N *rl W rH P. -H X) G o •iH w c os o 8 5 5 o Os 00 o Os SA Os 00 1 O
PAGE 140

Final pH of HC1 NaOH Residual Turbidity Residual Final pH of Electrophoretic Destabilized Added Added as per cent of + Aluminum Mobility Mobility Suspension (meq/l) (meq/l) Initial Turbidity (mg/l) Sample (p/sec/v/cm) 124 o o oCVJ 1 1 vrv c*• rH 1 1 • O • o i Cv. VO VO VO CvC't -3• • • • • 0^ CM CVJ CVJ CVJ 1 1 1 1 1 o VO VO oOv VO Ov O CVJ • 00 o d 9 Ov O vrv VO Ov Ov vO 00 • Ov o VO VO 3 ; 00 o CVJ c? US Sr 00 • d o o O o o VO I iH I • cvj o 00 Ov x! -p o -p* •H iH ctJ •H -P •H C H rH CO CVJ vrv 00 CVo o VO Cvl ON -3* Ov Ov cvj rv vO 00 • • • • • • • • • • vO VO CvCVCv00 Ov Ov Ov OV ian'

PAGE 141

125 c •H o r-A © I — I X rt P hfl e o CV) P O © • bOP rt ~~to bD a 6 ^a rt • P Xi vO P P S II c o P P rt G P G (D O G O % P O P rt P P P G G O •H to C © ft to G CO (H O £ O rt M P cti Pi o c o P P cd N P rH *H X> 05 P to a) Q 05 Xi E-i © P rt P i — I G CO o p P to G ^ O P x: p Ot P O P' G XI P O © i — I w cX) CVo o (VI CO VO -4xh cv o CA CVI cvj • • • • • • • o o o o rH rH rH I I I C^. CV o xt VTA oa 00 O rH CO rH p O 00 o rH • • • • • • • • rH o rH rH rH o rH 1 CVJ 1 P o !>> p © Gi P I — i Or fH Gr P E p x c3 now .s s O ca UA 00 Cv o VPv o rA o VO Ov o CVCO rH VO O -4 cv o 1 — i vO o ov [Vo 00 cv rH • • • • • • • • • • • • • • • oa 4-3-4 UA VTA VO VO VO tv. CV 00 C30 o) G X p W © . . OS < C H e to g s o o ov oa rH F'VTA 00 VO 00 5 CV CO VO VO UA 00 CO CvCv cv VTA CVVTA CO • • • • • • • • • • • • • • rH rH rH rH o O o O o o o o o o >1 •» p !>» p p P xl o •H p T5 X p G G rO G © U P o 2, < — 1 G cTH eg © i — 1 G Or cd X •H •rl to -P n rt •H © G os M VO N N N 400 M © rH VO VO O0v Ov Ov Ov Ov Cv Ov cS VO O -4 I X P G5 © . O X O' rt X © 525 < e O -3* vO 00 ON o CVJ -3* CV. ov rH rH rH rH rH iH CVJ CVJ CV] CV) CV) • • • • • • • • • • • o o o o o O o o o o o X © 1 — 1 00 VA o rH 1 — 1 X a i* OV CV) rH o o X © • • • • w < e o o o o X P © O CO G P o G5 P P OrP CO G P rt © up o. C to to P © G Ui Q co CO o • UA VO • a • cv UA • CVJ 00 • cv) o • CVJ CVJ • 3a • o rH • O 00 • o ov • rH -3• o 00 • o CV) • OA OA -3X)-3UA UA UA VO VO VO CvCv 00

PAGE 142

Table 13 Continued 126 o -P -p > O +5 P» rP O *P * U £> -P O O S CD i — I ca o t>> -P CD o CO o rH CM O ffi -P P on c on 0^ NO O' ftp D< • • • • • • •H CO CO O' On ON ON "p 'o co .s s >N •p •H •£ O -P c CD O -P •P TJ •P s> u £ u CD H P, P -H CO -P P *p C H Xi H CD H tf coo wee "O ACNr\co4 • • • • • 00 00 On On O' O O • O rp CM O rH c O •H CO C a JA P CO CD w -p O *>> -p •p ! +> •H c

PAGE 143

The Destabilization of a Kaolinite Clay Suspension with a Dosage of 30 rag/l of Aluminum Sulfate. Initial Clay Concentration = 61.5 mg/l. 127 o -C T rH cm 0 NO 0 On 0 CN CM ON O on P» CM 0 rH .pC'y rN cn r\ t>rH 0 O T . • • • • • • • • • • • U X O O O 0 O rH rH rH rH rH O rH 1 — 1 -P C a> 1 1 02 to » 40 CM CM rH On NO CO CNCM ON O On NO S -r rH rH NO O CN CNCO ON CM NO CN, CM 00 P-4 rH U. • • • • • • • • • • • • • •H £5 COi C^ -p-3" -it -ppun, UN, NO NO NO ni C C S CO £ *3 § O 0 Ovr> C^ON ON co NO O CO 3 c rH nfr CM rH CN CM rH on cn rH CN. XS rH • • • • • • . • • • • • •rl £ to CM CM CM CV2 rH rH r — 1 1 — 1 1 — 1 rH rH 0 CO pi E 0) I-H CP
PAGE 144

Final pH of HC1 NaOH Residual Turbidity Residual Final pH of Electrophoretic Destabilized Added Added as per cent of * Aluminum Mobility Mobility Suspension (meq/l) (meq/l) Initial Turbidity (mg/l) Sample (n/sec/v/cm) 128 CM vO o vcv rH CM ON VA Cvo VO i — 1 o rH • • • • • • • O o o o iiii o VO 3vrv o O CM o orH • • • • • • • Cvoo 00 Ov Ov o 3 00 o NO CO 00 O rv vo rH o rH • • • • • • • o o o i — 1 CM CM CM CM vO cm 3 o rH O'V oo 00 VO c^ Ov O CM • CO 00 IN-3Ov

PAGE 145

The Destabilization of a Kaolinite Clay Suspension with a Dosage of 50 mg/l of Aluminum Sulfate. Initial Clay Concentration = 61.5 mg/l. 129 o •H 0 ) . — ' U £ o -P o iC O -H U X> -P O O 2 W CD r*H w o o 0) -P CD PC -H rH CU rH Q. o o o NO CM rv On rH O rH NO o rv C" 00 O 0^ o rH aP ccJ cO O CO • • cn • -3• •3• -3• • •3• • VT\ • NO rH ^ 3 C h" TP -H"-. •a e m in 3 S CD rH Pi << £ * •H nd O •H as s s i — i p* cC CD 2 P< -0 •H co co nj CD Pi £ *H nd •H i — I ct 5 •H -P •rH C & o I vO i — 1 • o I o o -dn VO CM On CM CM CM O CM 3 CO CO £ € 5 • • n n w n ON oojCM o NO NO NO T) H CD"--O O* xl
PAGE 146

Final pH of HC1 NaOH Residual Turbidity Residual Final pH of Electrophoretic Destabilized Added Added as per cent of ^ Aluminum Mobility Mobility Suspension (meq/l) (meq/l) Initial Turbidity (mg/l) Sample (p/sec/v/cm) 130 0 O CM O CM On UN H O ON O CM NO NO CM UN ON CM • • • • • • • • • O O O O rH on ON ON ON 1 1 1 1 1 1 1 rH ON 00 0 0 O 00 <\J UN CV2 00 cr\ CM ON O O CM • • • • • • . • • • cn Cn 00 00 ON ON O rH O rH 00 3 ON ON ON 'A O UN O ON CM CNCM -3“ O CN. NO • • • • • • • • • O O rH rH ON ON ON ON •dON UN C'on CN iH ININon 0 cn O CM UN INUN Cn CM O UN UN UN UN NO NO CN. 00 • • • • • • • • O O O O 0 O O O ON O rH (A CM O CM -300 rH cv -3On CM O • • • • • • • • CNCN 00 00 00 CO On O !>00 • O CM CM • o rH CM o I— I II c o •rl to C a to 3
PAGE 147

131 Table 16 Adsorption Data for Freundlich Isotherm Plot. Kaolinite Clay Concentration = 61.5 nig/l. pH = 4.0. X (mg/1) X/M (io) 3 C 2 (mg/l)( 10) 3 Log X/M Log C 0.05 0.813 190 -3.09 0.72 0.05 0.813 350 -3.09 -0.46 0.06 0.976 500 3.01 -0.30 0.07 1.138 730 -2.94 -0.14 0.06 0.976 114-0 3.01 0.06 0.08 1.301 1520 -2.89 0.18 0.08 1.301 2320 -2.89 0.37 0.20 3.252 38 OO -2.49 0.58 * n The = (i) log C form of the + log k. Freundlich isotherm used is X/M = kC 1 / 1 * or log X/M

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132 Table 17 * Adsorption Data for Freundlich Isotherm Plot. Kaolinite Clay Concentration = 61.5 mg/l. pH = 4.5* X (mg/ 1 ) X/M do ) 3 C (mg/i) c 10 y Log X/M Log C 0.08 1.301 160 -2.89 -0.80 0.09 1.463 310 2.83 0.51 0.16 2.602 400 -2.58 -0.40 0.16 2.602 640 -2.58 -0.19 0.24 3.902 960 -2.41 0.02 0.24 3.902 1360 -2.41 0.13 0.30 4 . 8?8 2100 -2.31 0.32 0.64 10 .407 ' 3360 -1.98 0.53 *The form of the Freundlich isotherm used is X/M log X/M = (I) log C + log k. n kC 1 / n or

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133 Table 18 Adsorption Data for Freundlich Isotherm Plot.* Kaolinite Clay Concentration =61.5 mg/l. pH = 5.0. X (mg/l) X/M do ) 3 C (mg/l)(10) 3 Log X/M Log C 0.16 2.602 80 -2.58 -1.10 0.2 4 3.902 160 -2 .41 -0.80 0.40 6.504 160 -2.19 -0.80 0.66 IO.732 140 -1.97 -0.85 0.80 13. 008 400 -1.89 -0.40 0.90 14.634 700 -I.83 -0.15 1.12 18.211 1280 -1.74 0.10 1.84 29.919 2160 -1.52 0.33 The form of the Freundlich isotherm used is X/M = kC 1 ^ 1 or log X/M = (I) log C + log k. n

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134 Table 19 Effect of pH on Aluminum Residual. Kaolinite Clay Concentration =61.5 mg/l* Total Aluminum Added (mg/l) pH 0.24 0.40 0.56 ' 0.80 1.20 1.60 2.40, '• 4.00 Fraction of Aluminum Remaining in Solution 3.0 0.980 0.950 1.000 1.000 1.000 1.000 1.000 0.990 3-5 0.917 0.925 0.982 0.975 0.983 0.987 1.000 0.990 4.0 0.792 0.875 0.893 0.912 0.950 0.950 0.967 0.950 4.5 0.667 0.775 0.714 0.800 0.800 0.850 0.875 0.840 5.0 O.334 0.400 0.286 0.175 O.334 0.437 0.533 0.540 5-5 0.042 0.025 0.054 0.150 0.292 0.375 0.517 0.445 6.0 0.000 0.000 0.036 0.200 O.383 0.412 0.567 0.300 6.5 0.021 0.000 O.O36 0.112 0.267 0.431 0.500 0.060 7.0 0.125 0.012 0.036 0.100 0.217 0.350 0.317 0.000 7.5 0.417 0.437 0.143 0.200 0.283 0.250 0.175 0.080 8.0 0.687 0.837 0.393 0.400 0.458 0.400 0.267 0.240 8.5 0.896 0.950 0.643 0.600 0.717 0.750 0.667 0.762 9.0 1.000 1.000 0.804 0.800 0.850 0.881 0.842 0.920 9.5 1.000 1.000 0.929 0.912 0.942 0.950 0.933 0.950 10.0 1.000 1.000 1.000 0.987 0.983 0.994 0.996 0.970

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135 Table 20 Construction of Formation Function Curve for Aluminum Sulfate Solution.* Al^ = 1.5 x 10“^ M. PH C H + ) (mole/l) ( OH”) (Na + ) , (mole/l) (mole/l) (10) , (H + MNa + M0|-I 5 JoHlbpd ’ (mole/l) (10 )° *• TJ 4.40 4.0 x 10"5 2.5 x 10" 10 0 40 0.267 4.46 3.5 x 10' 5 2.9 x 10' 10 10 45 O.3OO 4.54 2.9 x 10" 5 3.5 x 10" 10 30 59 0.393 4.60 2.5 x 10" 5 4.0 x 10" 10 49 74 0.493 4.62 2.4 x 10" 5 4.2 x 10' 10 79 103 0.687 4.66 2.2 x 10"5 4.6 x 10 -10 110 132 ' 0.880 4.70 2.0 x 10" 5 5.0 x 10" 10 195 215 1.433 4.86 1.4 x 10" 5 7.2 x 10" 10 323 337 2.247 4.91 1.2 x 10” 5 8.1 x 10" 10 359 371 2.473 5.01 9.8 x 10" 6 1.0 x 10~ 9 377 387 2.580 5.10 7.9 x 10" 6 1.3 x 10 -9 389 397 2.647 5.20 6.3 x 10 -6 1.6 x 10~ 9 399 405 2.700 5.26 5.5 x 10' 6 1.8 x 10" 9 403 409 2.727 5.33 4.7 x 10' 6 2.1 x 10‘ 9 408 413 2.753 5.40 4.0 x 10“ 6 2.5 x IQ' 9 411 415 2.767 5.54 2.9 x 10" 6 3.5 x 10~ 9 417 420 2.800 5.61 2.5 x 10' 6 4.1 x 10" 9 420 423 2.820 5. 80 1.6 x 10" 6 6.3 x 10‘ 9 426 428 2.853

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136 Table 20Continued PH 1h + ) (mole/l) [0H“] [Na + ] , (mole/l) (mole/l)(10) (H + J+(Na + )-(0H“] (mole/l) (10)° (0H“1 bound n ' l^ T J 6.00 1.0 x 10"° 1.0 x 10" 8 430 4312.873 6.21 6.2 x 10" 7 1.6 x 10" 8 435 436 2.907 6.36 4.4 x 10" 7 2.3 x 10 -8 439 439 2.927 6.48 3.3 x 10" 7 3.0 x 10' 8 443 443 2.953 6.60 2.5 x 10“ 7 4.0 x 10 -8 447 447 2.980 6.72 1.9 x 10" 7 5.2 x 10" 8 450 450 3.000 6.86 1.4 x 10~ 7 7.2 x 10" 8 454 454 3.027 6.96 1.1 x 10 -7 9.1 x 10' 8 460 460 3.067 7.06 8.7 x 10" 8 1.1 x 10' 7 464 464 3.093 7.19 6.5 x 10" 8 1.5 x 10' 7 470 470 3.133 7.25 5.6 x 10" 8 1.8 x 10‘ 7 474 474 3.160 7.35 4.5 x 10" 8 2.2 x IQ" 7 479 479 3.193 7.42 3.8 x 10“ 8 2.6 x 10' 7 485 485 3-233 7.51 3.1 x 10" 8 3.2 x 10" 7 490 490 3.267 7.57 2.7 x 10‘ 8 3.7 x 10‘ 7 495 495 3.300 7. 72 1.9 x 10' 8 5.2 x 10" 7 505 505 3.367 7.82 1.5 x 10“ 8 6.6 x 10' 7 516 516 3.440 7.92 1.2 x 10" 8 8.3 x 10" 7 527 527 3.513 8.02 9.5 x 10" 9 1.0 x 10" 6 538 537 3.580 8.12 7.6 x 10" 9 1.3 x 10 -6 555 554 3-693 8.26 5.5 x 10 -9 1.8 x 10" 6 578 576 3.840

PAGE 153

137 Table 20 Continued PH (h + 1 (mole/l) (OH"] ( Na + ) , (mole/l) (mole/l)(10) (H + ]+(Na + I-(0H"] (mole/1) (10) (OH"] bound n t A1 T ) 8.33 4.7 x 10" 9 2.1 x 10' 6 598 596 3.973 8.40 4.0 x 10" 9 2.5 x H O 1 On 625 622 4.147 8.?2 1.9 x 10" 9 5.2 x 10" 6 687 682 4.547 9.08 8.3 x 10' 10 1.2 x 10' 5 708 696 4.640 9-37 4.3 x 10" 10 2.3 x 10~ 5 730 707 4.713 9.57 2.7 x 10" 10 3-7 x 10" 5 758 721 4.807 9.71 1.9 x 10“ 10 5.1 x J— ' O 1 781 730 4.867 9.84 1.4 x 10" 10 6.9 x H O 1 809 740 4.933 9-91 1.2 x 10" 10 8.1 x H O 1 v_n 833 752 5.013 10.08 8.3 x 10 -11 1.2 x 10-* 890 770 5.133 10.35 4.5 x 10' 11 2.2 x 10" 4 1036 816 5.W) 10.57 2.7 x 10' 11 3-7 x 10" 4 1262 892 5.947 * Temperature = (25 i 0 . 5 ) °C.

PAGE 154

138 Table 21 The Effect of Total Number of Paddle Revolutions and Intensity of Agitation upon the Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate.* Initial Clay Concentration = 63.3 m g/l* pH = 3-0 Intensity of Agitation, 40 rpm Intensity of Agitation, 100 rpm Total Number of Revolutions Residual Turbidity Total Number of Revolutions Residual Turbidity 0 104 0 104 400 35 200 64 1000 19 500 56 2000 11 1000 50 3000 10 2000 37 4000 12 3000 38 5000 13 4000 36 6000 15 5000 40 6000 40 The dosage of aluminum sulfate is 5 mg/l.

PAGE 155

139 Table 22 The Effect of Total Number of Paddle Revolutions and Intensity of Agitation upon the Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate.* Initial Clay Concentration = 63.3 mg/l. pH = 5 + 0.05 Intensity of Agitation, 40 rpm Intensity of Agitation, 100 rpm Total Number of Revolutions Residual Turbidity Total Number of Revolutions Residual Turbidity 0 104 0 104 400 73 200 88 1000 24 500 76 2000 11 1000 45 3000 8 2000 ' 30 4000 8 3000 28 5000 9 4000 30 6000 7 5000 29 6000 30 * The dosage of aluminum sulfate is 5 mg/l.

PAGE 156

140 Table 23 The Effect of Total Number of Paddle Revolutions and Intensity of Agitation upon the Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 63.3 mg/l. pH = 8 ± 0.1 Intensity of Agitation, 40 rpra Intensity of Agitation, 100 rpra Total Number of Revolutions Residual Turbidity Total Number of Revolutions Residual Turbidity 0 104 0 104 400 20 200 68 1000 5 500 26 2000 1 1000 14 3000 2 2000 11 4000 2 3000 12 5000 3 4000 14 6000 2 5000 13 6000 13 >r The dosage of aluminum sulfate is 30 mg/l.

PAGE 157

Table 24 The Effect of Total Number of Paddle Revolutions and Intensity of Agitation upon the Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 3I.7 mg/l. pH = 3.0 Intensity of Agitation, 40 rpm Intensity of Agitation, 100 rpm Total Number of Revolutions Residual Turbidity Total Number of Revolutions Residual Turbidity 0 41 0 41 400 31 200 33 1000 22 500 2000 14 1000 30 3000 10 2000 24 4000 10 3000 22 5000 9 4000 25 6000 10 5000 24 6000 21 The dosage of aluminum sulfate is 5 mg/l.

PAGE 158

142 Table 25 The Effect of Total Number of Paddle Revolutions and Intensity of Agitation upon the Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate.* Initial Clay Concentration = 31,7 mg/l. pH = 5 0.0 5 Intensity of Agitation, 40 rpm Intensity of Agitation, 100 rpm Total Number of Revolutions Residual Turbidity Total Number of Revolutions Residual Turbidity 0 41 0 41 400 39 200 39 1000 38 500 40 2000 37 1000 40 3000 35 2000 38 4000 31 3000 37 5000 27 4000 35 6000 20 5000 33 6000 32 *The dosage of aluminum sulfate is 5 mg /!•

PAGE 159

143 Table 26 The Effect of Total Number of Paddle Revolutions and Intensity of Agitation upon the Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate/ Initial Clay Concentration = 3I.7 mg/l. pH = 8 ± 0.1 intensity of Agitation, 40 rpm Intensity of Agitation, 100 rpm Total Number of Revolutions Residual Turbidity Total Number of Revolutions Residual Turbidity 0 41 0 41 400 31 200 3^ 1000 6 500 33 2000 2 1000 19 3000 2 2000 5 4000 1 3000 8 5000 2 4000 12 6000 2 5000 11 6000 12 The dosage of aluminum sulfate is 30 mg/l.

PAGE 160

1 44 Table 27 The Effect of pH on Aluminum Residual After Separation by HighSpeed Centrifuge.^ Initial Aluminum Concentration =4.00 mg/l. Aluminum Residual PH As mg/l As Percent of Initial Concentration 3.01 3-98 99.4 4.00 3-99 99.9 4.61 3-90 97.5 5.10 3-25 87*3 5.61 3.00 75.0 5.96 2.61 65.1 6.57 2.11 52.6 6.63 1.31 32.8 7.44 0.33 9.4 7.96 I.03 25.8 8.67 3 .75 93.8 9.18 3-95 98.8 10.10 3.98 99.4 * With a speed of 9 >000 rpm and a period of 10 minutes.

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145 Table 28 The Effect of Aluminum Concentration on Aluminum Residual After Separation by High-Speed Centrifuge. pH = 8.0. Initial Aluminum Concentration (mg/1) Aluminum Residual As mg/l As Percent of Initial Concentration 0.40 0.40 100 0.80 0.75 92.6 1.60 1.34 83.8 2.40 1..18 48.8 3.20 0.68 21.1 4.00 0.60 15.0 * With a speed of 9,000 rpm and a period of 10 minutes.

PAGE 162

146 Table 29 The Effect of Time on the Adsorption of Aluminum by Kaolinite Clay. Clay Concentration = 63.3 mg/l. Aluminum Dosage = 1.60 mg/l. pH = 5.0 Temp. = 25°C. Time Aluminum Residual Aluminum Adsorbed (Min. ) (mg/l) (mg/l) 0 1.60 0.00 1 0.94 0.66 3 0.94 0.66 5 0.94 0.66 10 0.90 0.70 20 0.89 0.71 30 0.87 0.73 50 0.87 0.73 60 0.84 0.76

PAGE 163

147 Table 30 The Effect of pH on the Electrophoretic Mobility of Kaolinite Clay Particle.* Clay Concentration = 63.3 mg/l. pH of Suspension HC1 Added (raeq/l) NaOH Added (meq/l) Electrophoretic Mobility (p/sec/v/cra) 3.14 1.37 -2.96 3.77 0.78 -2.67 4.34 0.64 -2.83 5.22 0.57 -2.88 5-74 0.49 -2.90 6.23 O .34 -2.99 6.6 9 0.20 -2.91 7.04 0.10 -3.02 7.78 0.00 -3.00 8.30 0.03 -3.12 8.76 0.06 3. 16 9.12 0.10 -2.91 9.52 0.20 -3-19 10.07 0.50 -3.34 * A total of 50 Ppm NaHC0 3 was added to the suspension before the pH was adjusted with 0.1 N HC1 or 0.1 N NaOH.

PAGE 164

Table 31 The Zone of Aluminum Floe Formation. Temperature = 25°C. Concentration of Aluminum (mole/liter) Low pH Limit High pH Limit Presence of Visible Floe 1.0 x 10~ 3 4.40 9.20 Yes 5.0 x 10 44.50 8.90 Yes 3.0 x 10* 4 4.55 Q HA ^ • y\J Yes 1.5 x 10 4 4.90 8.60 Yes 1.0 x 10 4 5.00 8.50 No 7.5 x 10" 3 6.00 8.30 No 6.0 x 10“ 5 7.00 8.20 No £ The zone aluminum sulfate is defined by the solution. evidence of Tyndall effect in

PAGE 165

149 Table 32 The Effect of pH and Anion on the Electrophoretic Mobility of Q Aluminum Floe. Aluminum Concentration = 1.5 x 10~^ M. Temp. = 25 C. ai 2 (so 4 ) 3 • 1 8 H 2 0 A1(N0 3 V 9 H 2 0 A1(N0 3 ) 2.25 x 3 * 9 H 2 0 and 10" 4 M Na 2 S0 4 pH Mobility (li/sec/v/cm) PH Mobility (p/sec/v/ cm) pH Mobility ((i/sec/v/cm) 5.00 0.89 5.25 2.76 5.00 1.45 5.32 0.97 5.6 7 2.85 5.66 1.56 5.3^ 0.87 6.15 2.88 6.08 1.71 5.60 I.03 6.29 2.80 6.14 1.56 5.62 0.94 6.82 2.70 6.47 1.40 6.00 1.18 6.93 2.52 6.50 1.35 6,26 1.02 7.39 2.35 6.51 1.45 6.40 1.16 7.50 2.40 7.3^ 1.31 6.42 I.23 7.61 2.19 7.43 1.34 6.5^ 1.13 7.70 2.20 7.67 1.28 6.87 1.16 7.86 2.01 7.96 1.05 7.22 1.01 8.13 1.91 8.32 0.87 7.3*11.02 8.40 1.28 8.50 . 0.51 7 .76 1.02 8.42 1.18 7.91 1.01 7.9 6 1.08 8.22 0.90 8.46 0.54 8.58 0.74 8.71 -0.77

PAGE 166

150 Table 33 The Effect of pH on the Electrophoretic Mobility of^Kaolinite Clay Particle with a Dosage of 50 mg/l Aluminum Sulfate. Clay concentration = 63.3 mg/l. Temperature = 25 C. pH of Clay Suspension NaOH Added (meq/l) HCl Added (meq/l) Electrophoretic Mobility (p/sec/v/cm) 3.14 1.37 -0.41 3.72 0.78 0.30 4.13 0.64 -0.09 4.41 0.59 0.37 4.52 0.54 1.14 4.57 0.49 1.78 4.70 O .34 1.78 5.08 0.12 1.49 5.70 0.10 ' 1.54 6.10 0.05 1.41 6.40 0.15 I .30 6.61 0.25 1.24 6.81 0.30 1.23 6.98 0.35 1.13 8.00 O .56 O .32 8.22 0.61 0.42 9.04 0.77 -3.14 9.7 6 1.01 -4.09 A total of 50 pH was adjusted with mg/l NaHC0 3 was 0.1 N HCl or 0.1 added to the N NaOH. suspensions before the

PAGE 167

Table 3^ Adsorption Data for Freundlich Isotherm Plot. Kaolinite Clay Concentration = 15.8 mg/l. pH = 5 t 0.05. Temp. = (25 t 0.5) C. X (rag/l) x/m (10) 3 C (mg/l) ( 10 ) 3 Log X/M Log C 0.03 1.899 50 -2.72 -1.30 0.08 5.063 170 -2.20 -0.77 0.16 10.127 240 -1.99 -0.62 0.25 15.823 ' 310 -1.80 -0.51 0.29 18.354 520 -1.74 -0.28 O.36 22.785 1240 -1.64 0.09 0.44 27.848 1980 -1.56 O.3O 0.57 36.076 2630 -1.44 0.42 1.05 66.456 2950 -1.18 0.47 * log X/M The form of = (|) log C the Freundlich + log k. isotherm used is X/M = kC 1 / 11 or

PAGE 168

152 Table 35 * Adsorption Data for Freundlich Isotherm Plot. Kaolinite Clay Concentration = J1.7 gg/l. pH = 5 t 0.05. Temp. = (25 t 0.5) C. X X/M (10) 3 c (mg/D (mg/l)(10) 3 Log X/M Log C 0.04 1.262 40 -2.90 -1.40 0.15 4.732 100 -2.32 1.00 0.19 5-994 210 -2.22 -0.68 0.32 10.095 240 -2.00 -0.62 O.38 11.938 430 -1.92 -0.37 0.48 15.143 1120 -I.83 0.0 5 0.6? 21.137 1750 -1.67 0.24 0.78 24.607 2430 -1.61 0.39 I.36 42.905 2650 -1.37 0.42 l/n *The form of the Freundlich isotherm used is X/M = kC ' or log X/M = (I) log C + log k. n

PAGE 169

153 Table 36 * Adsorption Data for Freundlich Isotherm Plot. Kaolinite Clay Concentration =47.5 mg/l. pH = 5 t 0.05. Temp. = (25 t 0.5)°C. X (mg/1) X/M (10) 3 C (mg/l)( 10) 3 Log X/M Log C 0.05 1.053 30 -2.98 -1.52 0.17 3-579 80 -2.45 1.10 0.23 4.842 170 2.31 -0.77 0.35 7.368 210 2.13 0.68 0.47 9.894 340 -2.00 -0.47 0.62 13.052 980 1.88 0.01 0.73 15.368 1690 -1.81 0.23 1.02 21.473 2180 -1.67 O .34 1.53 32.210 2470 -1.49 0.39 jjt l/n The form of the Freundlich isotherm used is X/M = kC ' or log X/M = (i) log C + log k. n

PAGE 170

154Table 37 * Adsorption Data for Freundlich Isotherm Plot. Kaolin! te Clay Concentration = 63.3 gg/l* pH = 5 0.05. Temp. = (25 t 0.5) C. X (mg/1) X/M ( 10) 3 C (mg/l)( 10) 3 Log X/M Log C 0.06 0.948 20 3.02 1.70 0.18 2.844 70 -2.55 -1.15 0.26 4.107 140 -2.39 -0.85 O .38 6.003 180 -2.22 -0.74 O .56 8.846 250 -2.05 -0.60 0.76 12.007 840 -1.92 -0.08 0.94. 14.850 1480 -I.83 0.17 1.25 19.747 1950 -1.70 0.29 1.79 28.278 2210 -1.55 0.34 *The form of the Freundlich isotherm used is X/M = k C^ n log X/M = (— ) log C + log k. n or

PAGE 171

The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 15.8 mg/l. Final pH = 3.0 Temperature = (25 0 ^ 5)°C 155 o •H 0 U o H " e o P. rH O -H ?H -P o > * . -P •H *H -P 73 O .H •H 73 JO -P -H " C JO 03 !h V 0 H —I P td Q> 1 — { 3 fttj W -P p 0 Eh 73 •H to ctf .H rH rH 1 — 1 rH rH rH rH rH rH rH 0 U* • • • • • • • • • • K n CO VO 3 “ c\) 0 c 0. e • • • • • • • • • • P.W 0 0 0 0 0 O rH CV) cn 3 iH < cd •p o Eh Initial turbidity of the suspension = 20.

PAGE 172

The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 3I.7 mg/l. 156 o o CA o + 1 iA co II 0 P 2 •p rt p 0 & 0 Eh O • CA II S ft rH as c •H ft s o o ft -P 0 U >»' O -P > X ft~-~ft 1 — I O O ft 0 P ,0 W -P O-'rH ft cS -P O E-< n 0 . to C o o to e CTl 3 xs •H CO 0 01 >> p •rl Xl ft X> P 3 Eh CO » O ft X3 ft s 0 Eh P 0 H ft aS •H co p> cO .H C H X 5 H W 0 -^. O xl cr 1 cd xs 0 s : e I 5 rH < cB P> O Eh XI ^ 0 H •H ft to R* ft^ VO • C\) I o ca • ft 1 ca o ft 1 1 — 1 C\ o I £ 3 • • o o I I o o *A cv) CO CO • • o o I I o o • o {>CA O CA rH 0 CO 0 O 0 CV! 4 * CA CO vO 3 CO O • • • • • • • • • 0 O O O 0 rH CO CA • 3 000 VO VO VO ft ft 1 — I ft o VO vO VO VO VO CO VO PVO CA 0 ^ C~\ C~\ rH 1 — I rH rH rH rH rH rH rH 1 — 1 • • • • • • • • • • rH rH rH rH rH rH rH rH rH i — 1 0 CO CA O VO rH 0 (\J 0 O 0 0 CO CA CO vO 3 CO O • • • • • • • • • • 0 0 O O O O rH CO CA • 4 Initial turbidity of the suspension = 41.

PAGE 173

The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration =47.5 mg/l. Final pH = 3.0 Temperature = (25 t 0.5)°C 157 ca M3 CO I VO -3• I 1 I Ov] I — 1 I — ! I o ON o ; co o i i — i C"o I & o I i — ! CA O I CO CO VA CO • o I T3
PAGE 174

The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate Initial Clay Concentration = 63.3 mg/l. Final pH = 3^° Temperature = (25 0 e 5)°C 158 o •H * -P CD O -P JS H ' P. rS O *H U •P o
PAGE 175

The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 15.8 mg/l. Final pH = 5 t 0.05. Temp. = (25 t 0.5)°C. 159 o P P 0 U w S o S v X P~-ft i> O i—t G P O P X 0 OO © S J — I w CO § •H m) S 0) pl J3H p G-^ < O ha 0 g cd <; P o Eh P S cd B h'' P CH TJ •H''— P g W) « P B 0) Pi C * •if £ TO x> u Pd ^ Eh p Eh 1 — ! c 3 ^ T? * P -if CO 0 Pi P P OCco cm • • cm H 1 1 o I cc ^ ^ N O*A NO CnCO CO w\ ^5NO VO • «*•••• <— t H (H P p iH r — I O O O CmcOvO'AONVO^-C^-'A _ opcococm^j-Nm© o o o O o o !N. ^ H CO H CM ^ CO cm cm Nim CO On no on • ••••• O O P P CO CO i o^mo>mococmoco I O ON OOO On O O On P P p p p p cm oo co co oo 00 cm 00 co OnOnOnOnOnOnOnOnCOCO -td w 0 01 O "0 0 rtTl S 55 < ^ TJ bT\ 0 0 1 — 1 0 ty 1 — 1 < — 1 0 0 "Cf 0 O 0 0 ffl •o g • • • C N-' O 0 0 c •rj S 0 H pd P">~ H H M c a g OhW I — 1 “=< cd P 0 Eh cm co no p cm oo cm H N cm o n >n o o o h co 00 cm o o o o 0 CO vm 0 NO 0 CO 0 0 0 0 CO —X. vm 00 NO -4CO 0 0 0 0 0 0 0 1 1 CO cm •3" Td T 5 C d C a , — s s. l H 4 g O 0 rH H fcd tO g p c P X •2 s £ O p 0 0 1 — i CO «H 4 Vo P O • 0 • •H P 0 p Td 0 C P G P 0 0 pd 0 X P g C g G pd 0 •rH 0 pd G P s « — 1 P •r~i P p g P 0 p 0 CO 0 1 — 1 CO 0 0 cd. X P P! P p P P O p 0 •tH P c 3: 0 0 P * 0 * 0 * P » p pd pd C G P P g g O O P P

PAGE 176

160 o p ni «tH cn § •H S 2 XJ rH -P •ri tO £ e c oo • •H rH 0 CA ? I. a n! El O O VA O + 1 VA CV 0 J-r 5 03 £ O O •H P 0 U >»' o P > x: •h-'--. ftrH O O -H 0 Sr ,0 0 -P O 0 s d. Q) — 1 1 w i c 03 a I E-< W G 0 O CO -H &2 H P O C 0 0 0 -P C •H O C O •H rH !>* O Cti n5 rH iX O 03 r — ! Ctf «H -H O -P •H C C 0 H •H P 01 CO •H rH •H x> 03 -p 0 0 Q 0 X3 Eh VA o O + 1 VA II & rH 03 C •rl , c*< os < p o Eh *3 g *rl 0 0 H ' 01 A VA O CO NO CV CO N ffl 4 AOCO O O I CA H On vr\ ^ 1A tA 0 • • • • (— i r— i r 1 rH s 0 rN X> rH o 3 VA ON cv CO co oCO NO . — 1 Sr-n. o iH 1 — 1 CA CA -V NO OCA < o to • • • • • • • • • 1 — i n e X} ' — ' o o O o o o o o o rH >> -P •H •rH VS H H ^~-rl Eh rH 0 '6&. G — X2 •* •rl -JE 0 E 0 03 T3 rH SO 0 — o t 3 a* cS t3 0 S3 < S T3 H -jH 0 — H o-d o' o k •a ® < 6 t o o jrr o rH -V CA A’ NA CA NA o a rH CV cv -3* rH VD o o o o o o rH rH CV cv CA VA O ^A gA ON C0 NO On VO CA ON O' on CO CO OOONCANACACArHAOnOncO OnOnOnOnOnCO CA -3" ON NO NO o CA rX O . — i CV NA CA (H CO a O O o O rH CV A CA • * • • • • • • o o o o O o O O On O O TS 0 H . B .. rH pH tiO rA < p o Eh o CO VA o NO rH o A! o O o o CV -4VA CO NO -X cv O • • • • • • • • • o o O o O o rH CV CA -3& o I — I a ^^With 20 minutes of rapid mixing (100 rpm) followed by 10 minutes of slow mixing (10 rpm) and 10 minutes of settlement.

PAGE 177

The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 47.5 mg/l. Final pH =5+0.05 Temperature = (25 t °»5)°C 161 £ o o •H -p © P >>' O -P > X. P.H O O -H © P X W -P o"-~o S =1 © I — l w H X) CTS *4 •p o e-< H § 3 C rl U H''•ri a to WPS © rH ' — ' Pi C $ •H X5 S p Eh '"h •H i — I Eh 05 P^ XJ — » H H •ri CO © CP 1-H X H CP CD O XS O' ij p o s S X rH H ©-~-OP O' SP 2 C S H < CO -p o H NA A£ CO MO ON O O Oi N ^ CO 4o o o I I H H rH AOn lA CA 4• • • H H H a <1> ^ o NA CN* CA NA ACN! CA C\} rH £-4 o O rH CM CA -pMO CnO O &0 • . • • • • • • • CO £ o o o o O O O o rH CA NA O OCONH4ffl<>CON OOOHCMCAONMOHjjO O rl N N CA ntn CA AH H ON >A ^4 ON O O O' CO A ON ON On 0^04 ON On 00 CO On O CN) O A00 CO On On On CO 00 CA On NA ArH MO AO rH CN) NA CA rH CO NO O O O O r — l CV2 CN) CA • • • • • • • • o o O O O O o O -PCN H O O O •H T3 ^ 0 rH o co NA o MO ( i o CV? O o 0 •H — o o CN) -3NA CO vO -bCN) o 1 • < rH hO O, £ • o • o • o • o • O • o • rH • CN) • CA • AMO C o •H W C a CO 3 CO Q

rH 05 •H +> c H X 6 p e a p o i — i bJD C X I H co Cp o CO CD -p p c CO CN) £ •P CD S O I — l H O «P a p o o H bO C H X i TS H P. P P cp ° -P CO C CD 0) -p a P CD C H •H -H a -p © CN) CO X, Cp -P o •H ^ CO * © * -P P c o H a p o H to c •H a a § Cp O co © -P P c 10 minutes of settlement.

PAGE 178

The Destabilization of a Ka Unite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 63.3 mg/l. 162 na O • o + 1 NA S3 a i — 1 © C •H b o o O NA O , +1 vn .£2. 11 © £ d p © P © a s © © •p P © P >A O -P > S3 *H P.rH O O *P © P SO © P o O S i © — pH W % •H "d S ©• aJ < P O Eh pH co "d pH S3 O © O' © "d © s 4 •r-i S &0 0 O O rH rH CM On CM so WPS • • • • • • • • • • 0 H ^ 0 0 O 0 0 O O rH rH CM 2 TS « < © d 5c © O pH » 0 pH -d* pH O O 1 — 1 Cp *P * rH O •H # Cp / s T5 * i! S •bi II 1 1 c$ s}CA 17 pH 00 tv 00 (V 00 3 81 -3(V G & p O O. d p-n •H P O Eh .H CO O Eh G O 1 — 1 pH ©•s£c a O pH d w © to to * •H * CA CA CM VA NO CM NA NA 3 CM d © to 5 © H ON ON 00 NO CO ON On ON CO c X © « © S3 •H X i CA On ON CM CO ON «P 0 u "d •H T3 P P. © O rH CM CA 1 — 1 CO NO / — s p. P O O O O rH CM CM CA © • • • » • • • • Eh p cp O 0 O O O O O O £ •H

u G -P « •H -P •H c M © © P E d © C H •d p B P © cu m S 3 Cp P O o pH hfl C •H l E S o pH CO «P o CO © p d c © © p d c
PAGE 179

The Destabilization of a Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 15.8 mg/l. Fi n al pH = 8 ± 0.1 _ Temperature = (25 t 0.5)°C 163 o •H P © e o u >»O P > 31 p O O -H © U P CO P o-~-. O S a. © . — rH w CO O p O E-i 1 — I cti 3 -a •H CO © Pi c •H 1 x 0 e p •rl Pi •H p p * £ •H +> -H Si o 3 EiH P erf © P P, Ctf •H 10 p 5 to P P c 0 © Pi T5 P P ©•"O T 3 O* K trf © < e I 1 — 1 erf P O Eh ca 1 VO ca ca 1 co XA CO CO CO £ 1-1 0 rH 0 XA . — •! 3 -^0 1 — 1 Ov vO < co m . • • • 1 — i C E O w 0 O 0 O rH o o CK CO XA VO XA Ov CA Ov CA Ov O Ov CO VO | © p P ’ O O O 1 — 1 CO 0 VO . — i P txO • • < g< B CU ' — O O 0 p CO -=}CO CA CO AAO A! • CA -3" CA AP CO CA O • CA S' AOV CA CO CA rH Tf H CA O 0 rH XA XA W ©^ g O VO VO vO VO XA Ofl O' erf arf © O P • rH • co • CA • XA • S
PAGE 180

The Destabilization of Kaolinite Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 31*7 mg/l. 164o ITS o + 1 XA CO CD 3 P 3 U o s § c •H T5 O &-< i — I CTJ P •H to 0 I C i — f a5 -P o E-* C i — I •H * • — £ W) -a; T3 H « © S3 < g TJ rH rH CD--. O -a O* S3 ffl *=C S no rH . CA I CNJ CCO I CO o r— I I XA CA O O O O XA CO o XA OA VO CO CO CA ON 00 CO CO 00 i — ! CO CA do o I — i o rH CO XA CO CA CO O I o o 0 r-H O vn rH INNO VP* , — 1 3 ~~'O rH ON CO rH < 10 txQ • • • • • • • t — 1 oj -P c e O W O o o o o rH CO CA & XA 00 XA VO XA ON XA CA CO CQ NO XA Hxa •n tj ^ • & > P •H 'G •H e $ a •H -P •H C H

PAGE 181

Table 48 The Destabilization of a Kaolinitj Clay Suspension with Aluminum Sulfate. Initial Clay Concentration =47.5 mg/l. Final pH = 8 ± 0.1 Temperature = (2 5 ± 0.5) C 165 o •H P o O P > A P.P O O P " U A P O' o S 0 rH W e o 0 CO CO cm cp I VO cp cp i CO o I o I CO -3o I cp i oo i p •H "d •H g 3 Eh ctf S x5 P co o (3 £ xl •H S 5 a^ P w P cd P C H P O w x$ 0xs X3 cr 1 I ^ 0 H 2 P"-. p P b.0 p. e p.^ P -a; nJ P o p o CO cc CM NO rH o o o rH ON NO CV ON • • • • • • • o o o o I — 1 cv CM o o p ON CM CP CP NO 00 NO NO oON On O P • rH o On NP NO »P CM P P NO d P CP H* o o p CM *A 32 0 a NO NO NO NO vr\ ODD 1 O rH p CM CP =3Cfl x) 0 53 < S • o • O • o • o o • O o o o 1 — 1 o CM O o co NO CM • • • • • • o o o rH CM CP o o oNO c o p CO c a co 3 co o A p o & p xJ p € 3 p P rt •rl P P c p

PAGE 182

The Destabilization of a Kaolin! te Clay Suspension with Aluminum Sulfate. Initial Clay Concentration = 63.3 mg/l. 166 O H ' ^ •p e 0 0 u ^ 0 -p > c^cv MO MO UA CO P,H 0 ^v 1 1 rH 0 A CA A! O O H w 0 1 — 1 / — . w MA * O +1 1 U~\ c cm •H TS 5 a> 3 E H O UA cm CA ON CO 11 ; 1 — 1 pi O 0 00 ON MO 1 — ! CO < co do • • • • • • • <0 C S O 0 O 0 1 1 00 00 fn rH O 2 rt 0 -p -p oj 0 fn Eh a s H S cu id 3 ^ Eh S CH O 0VO CO ON H $ 'd •H'"" O CA VA MO O'O •H E dO • • • • • * • » p s OH — « < O O O O 0 1 1 rH o +! CO II P, 5 >5 . * •p •H -P •o O •rH •H T5 £> -P •H U c rO fl 0 Eh 0 2 H u H a5
PAGE 183

LIST OF REFERENCES

PAGE 184

LIST OF REFERENCES 1. Theriault, E. + J. and Clark, W. M. An Experimental Study of the Relation of H Concentration to the Formation of Floe in Alum Solutions. Public Health Reports , 38:181 (1923). 2. Miller, L. 3. On the Composition of the Precipitate from Partly Alkalinized Solutions. Public Health Reports , 2§.:1995 (1923). 3. Miller, L. B. Adsorption by Aluminum Hydroxide Considered as a Solid Solution Phenomenon. Public Health Reports , 39:25 (1924). 4. Miller, L. B. A Study of the Effect of Anions upon the Properties of Alum Floe. Public Health Reports , 40:351 (1925). 5. Miller, L. B. Some Properties of Iron Compounds and Their Relation to Water Clarification. Public Health Reports , 40:1413 (1925). 6. Miller, L. B. Notes on the Clarification of Colored Waters. Public Health Reports , 40:1472 (1925). 7. Bartow, E. and Peterson, B. Effect of Salts on the Rate of Coagulation and the Optimum Precipitation of Alum Floe. Ind. Eng. Chem ., 20:51 (1928). 8. Mattson, S. Cataphoresis and the Electrical Neutralization of Colloidal Material. J . Phvs . Chem . , 32 : 1532 (1928). 9. Black, A. P. and Rice, Owen. Formation of Floe by Aluminum Sulfate. Ind. Eng. Chem ., 25:811 (1933)* 10. Black, A. P., Bartow, E. and Sansbury, W. Formation of Floe by Ferric Coagulants. Ind. Eng. Chem ., 2j5:898 (1933)* 11. Black, A. P. Coagulation with Iron Compounds. Jour. AWWA , 26 : 1713 (1934). 12. Langelier, W. F. and Ludwig , H. F. Mechanism of Flocculation in the Clarification of Turbid Waters. Jour. AWWA , 41:163 (1949). 13. Pilipovich, J. B., Black, A. P., Eidsness, F. A. and Steams, T. W. Electrophoretic Studies of Water Coagulation. Jour, AWWA , 50:1467 (1958) 168 -

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169 14. Black, A. P. and Hannah, S. A. Electrophoretic Studies of Turbidity Removal by Coagulation with Aluminum sulfate, uoar. ^2:433 (1961). 15. Packham, R. F. The Coagulation Process I. The Effect of pH on the Coagulation of Dilute Mineral Suspensions with Aluminum Sulfate. Technical Publication No. 14 , British Water Research Association. 16. Packham, R. F. The Coagulation Process II. The Isolation and Examination of the Fine Suspended Solids from Nine English. Rivers . Technical Publication No. 15 * British Water Research Association. I?. Packham, R. F. The Coagulation Process III. The Effect of pH on the Precipitation of Aluminum Hydroxide. Technical Publication No. 17 , British Water Research Association. 18. Packham, R. F. The Coagulation Process IV. The Effect of Electrolytes and Temperature on Coagulation with Aluminum Compounds . Technical Publication No. 20 , British Water Research Association. 19. Packham, R. F. Some Studies of the Coagulation of Dispersed Clays with Hydrolyzing Salts. J . Colloid 5ci . , 20:81 (19o5) • 20. Matijevic, E. and Tezak, B. Coagulation Effects of Aluminum Nitrate and Aluminum Sulfate on Aqueous Sols of Silver Halides in Statu Nascendi. J. Phys. Chem ., 57:951 (1953)* 21. Matijevic, E., Mathai, K. G., Ottewill, R. H. and Kerker, M . . Detection of Metal Ion Hydrolysis by Coagulation. III. Aluminum. J. Phys. Chem ., 65:826 (1961). 22. Matijevic, E., Janauer, G. E. and Kerker, M. Reversal of Charge of Lyophobic Colloids by Hydrolyzed Metal Ions. I. Aluminum Nitrate. J. Colloid Sci ., 19:333 (1964). 23. Matijevic, E. and Stryker, L. J. Coagulation and Reversal of Charge of Lyophobic Colloids by Hydrolyzed Metal Ions. IH. Aluminum Sulfate. Preprint. 24. Mackrle, S. Mechanism of Coagulation in Water Treatment. Jour« San. Eng. Div. Proceedings ASCE , 88 (May 1962 ) . 25. Stumm, W. and Morgan, J. J. Chemical Aspects of Coagulation. Jour. AWWA , j>4:971 (1962). Discussion, p. 992, Black, A. P. 26. Black, A. P. and Walters, J. V. Electrophoretic Studies of Turbidity Removal with Ferric Sulfate. Jour. AWWA , j56:99 (1964).

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170 27. Kira, W . , Ludwig, H. F. and Bishop, W. D. Cation-Exchange Capacity and pH in the Coagulation Process. Jour. AWWA , J57:327 (1965)* 28. Black, A. P. and Chen, C. L. Electrophoretic Studies of Coagulation and Flocculation of River Sediment Suspensions with Aluminum Sulfate. Jour. AWWA , jj7:354 (1965)* 29. Tarabo, N. A Fundamental Investigation of Coagulation in Water ’Works (1). Memoirs of Faculty of Engineering , Hokkaido University, Sapporo, Japan, 11:585 (August 1965) ~ 30. Vilaret, M. R. Effect of Particle Size on the Destabilization of Colloidal Suspensions in Water. Ph.D. Dissertation, Dept, of Bioenvironmental Engineering, University of Florida, Gainesville, Florida (1965). 31. Brosset, C. On the Reactions of the Aluminum Ion with Water. Acta Cheraica Scandinavica , 6:910 (1952). 32. Brosset, C., Biedermann, G. and Sillen, L. G. Studi^^on the Hydrolysis of Metal Ions. XI. The Aluminum Ion, A1 . Ac Cheraica Scandinavica , 8:1917 (1954). 33Hsu, P. H. and Bates, T. F. Mineral Mag ., 22:749 (1964). 34. Rausch, W. V. and Bale, H. D. Small-Angle X-Ray Scattering from Hydrolyzed Aluminum Nitrate Solutions. J . Chem . Phys . , 40/3391 (1964). 35 . Biedermann, G. Svensk Keraisk Tidskr , 76:19 (1964). 36 . Frink, C. R. and Peech, M. Hydrolysis of the Aluminum Ion in Dilute Aqueous Solutions. Inorganic Chem ., 2:473 (1963). 37 . Kubota, H. Properties and Volumetric Determination of Aluminum Ion. Thesis, University of Wisconsin (1956). 38 . Szabo, Z. G., Czanyi, L. J. and Kavai, M. Determination of the Solubility Products of Metal Hydroxide Precipitates. Z. Anal . Chen., 147 :401 (1955)* 39 . Gayer, K. K., Thompson, L. C. and Zajicek, 0. T. The Soluoility of Aluminum Hydroxide in Acidic and Basic Media at 25°C. Can. J. Chem . , 36:1268 (1958). 40. Bjerrum, J., Schwarzenbach, G. and Sillen, L. G. Stability Constants of Metal-ion Complexes. The Chemical Soc. (London) (1958) .

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1?1 41. Latimer, W. M. Oxidation Potentials . Second Edition, Prentice Hall , Englewood Cliffs, N. J. (1961) . 42. LaMer, V. K. and Smellie, R. H. Flocculation, Subsidence and Filtration of Phosphate Slimes. J . Colloud Sci . , li:7Q4 (1956) • 43. Toth, S. J. Chemistry of the Soil , Chapter 3 , Reinhold Publishing Corporation, New York (i 960 ) . 44 . Olphen, H. An Introduction to Clay Colloid Chemistry . Interscience Publishers, .London-New York ( 1963 ). 45. Seatz, L. F. Chemistry of the Soil , Chapter 8 , Reinhold Publishing Corporation, New York (i960). 46. LaMer, V. K. and Healey, T. W. The Role of Filtration in Investigating Flocculation and Redispersion of Colloidal Dispersions. J, Phys. Chem ., 67:2417 (1963). 47. Kruyt, H. R. Colloid Science , Elsevier Publishing Company, AmsterdamLondon-New York (1952). 48. Mysels, K. J. Introduction to Colloid Chemistry . Interscience Publishers , ('London-New York (1959). 49. LaMer, V. K. and Smellie, R. H. Thee j of Flocculation, Subsidence, and Refiltration Rates of Colloidal Dispersions Flocculated by Polyelectrolytes . Ninth National Conference on Clays and Clay Minerals , 295 (19617. 50. Michaels, A. S. and Morelos, 0. Polyelectrolyte Adsorption by Kaolinite. Ind. and Eng. Chem ., 47:1801 (1955). 51. Black, A. P., Birkner, F.B. and Morgan, J. J. Destabilization of Dilute Clay Suspensions with Labeled Polymers. Jour. AWVIA , 57 : 159-7 (1965) . 52. Replaceable Bases in Soils Devoid of Carbonates. Official Methods of Analysis of the Association of Official Agricultural Chemists , George Banta Publishing Co., Menasha, Wis. 8 th ed., pp. 39-42 (1955) . 53 . Birkner, F. B. The Destabilization of Dilute Clay Suspensions with Labelled Polymers. Ph.D. Dissertation, Department of Bioenviron.antal Eng., University of Florida, Gainesville, Florida (1965). 54. Packham, R. F. The Absorptiometric Determination of Aluminum in Water. Proc, Soc. Water Treatment and Examination, 7:102 (1958)*

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172 55Cohen, J. M. Improved Jar Test Procedure. Jour &WA , 49:1425 (1957). 56 . Lumetron Photoelectric Colorimeter Model 450 for Nessler Tubes , Photovolt Corp., 95 Madison Ave., New York 16, N. Y. 57 . Standard Methods for the Examination of Water and Wastewater , APHA, AWWA and WPCF, New York (12th ed., 1965). 58 . Black, A. P. and Smith, A. L. Determination of the Mobility of Colloidal Particles by Microelectrophresis . Jour. A/JVIA , j>4:926 ( 1962 ) . 59. Black, A. P. and Smith, A. L. Improvements in Instrumentation and Techniques for Microelectrophoresis . Jour. AWl-IA , j)7:485 (1965). 60. Black, A. P. and Smith, A. L. Suggested Method for Calibration of Briggs Microelectrophoresis Cells. Jour. AVAJA , ^8:445 (1966). 61. Black, A. P. Basic Mechanisms of Coagulation. Jour. A/M A , .£2:492 (I960). 62. Smoluchowski, von M. Versuch einer mathematischen Theorie der Koagulations -Kine tik Kolloider Losungen. Z. Physik. Chemie ., XCII:129 (1916). 63 . Sneaecor, G. W. Statistical Methods , The Iowa State University Press, Ames, Iowa (1962).

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BIOGRAPHICAL SKETCH Ching-lin Chen was born on July 1?> 1937 » l n Hsin-Chu City, Taiwan (Formosa). He entered the College of Engineering in the National Taiwan University in September, 1956, and received the degree of Bachelor of Science in Civil Engineering in June, I960. In July, I960, he attended the Chinese Reserve. Military Officer Training Corps and served in the Chinese Air Force as a second lieutenant officer from October, I960 to September, 1961. He joined the faculty of the National Taiwan University as a teaching assistant in the Department of Civil Engineering in October, 1961. He continued in that position until September, 1962, when he was granted a graduate research assistantship to enroll in the Graduate School of the University of Florida. He received the degree of Master of Science in Engineering in December, 1963 from the University of Florida, and since then he has been appointed as a research assistant by the Department of Chemistry. He is presently a candidate for the degree of Doctor of Philosophy in Bioenvironmental Engineering at the University of Florida. He is a registered civil engineer in Taiwan, and is a member of the Chinese Institute of Engineers, the Chinese Civil Engineers Association, the American Water 'Works Association, the American Chemical Society, and the Sigma Xi honor society. 173 -

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This dissertation was prepared under the direction of the chairman of the candidate's supervisory committee and has been approved by all members of that comm_ttee. It was submitted to the Dean of the College of Engineering and to the Graduate Council, and was approved as partial fulfillment of the requirements for the degree of Doctor of Philosophy. June 21, 1966 Dean, Graduate School Supervisory Committee: Chairman