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Status of phosphatic clay waste disposal ( FGS: Open file report 14 )
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 Material Information
Title: Status of phosphatic clay waste disposal ( FGS: Open file report 14 )
Series Title: ( FGS: Open file report 14 )
Physical Description: 29 p. : ill., maps ; 28 cm.
Language: English
Creator: Yon, J. William
Florida Geological Survey
Publisher: Florida Geological Survey
Place of Publication: Tallahassee Fla
Publication Date: 1983
 Subjects
Subjects / Keywords: Geology -- Florida   ( lcsh )
Sewage -- Purification -- Phosphate removal   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: J. William Yon.
Bibliography: Includes bibliographical references (p.28-29).
General Note: Cover title.
 Record Information
Source Institution: University of Florida
Rights Management:
The author dedicated the work to the public domain by waiving all of his or her rights to the work worldwide under copyright law and all related or neighboring legal rights he or she had in the work, to the extent allowable by law.
Resource Identifier: aleph - 001545487
oclc - 22438713
notis - AHF9007
System ID: UF00001013:00001

Table of Contents
    Main
        Copyright
    Front Cover
        Page i
        Page ii
    Title Page
        Title Page
    Geology and mining
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
    Physical settling
        Page 7 (MULTIPLE)
        Page 8
        Page 9
        Page 10
    Chemical settling
        Page 11 (MULTIPLE)
        Page 12
        Page 13
        Page 14
        Page 15
    Consolidation predictions
        Page 16 (MULTIPLE)
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
    Summary
        Page 22 (MULTIPLE)
        Page 23
        Page 24
        Page 25
        Page 26
    Conclusions and recommendations
        Page 27
    References
        Page 28
        Page 29
Full Text






FLRD GEOLOSk ( IC SUfRiW


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State of Florida
Department of Natural Resources
Elton J. Gissendanner, Executive Director




Division of Resource Management
Casey J. Gluckman, Director




Florida Geological Survey
C. W. Hendry, Jr., Chief









Open File Report 14

Status of Phosphatic Clay Waste Disposal

by

J. William Yon


Florida Geological Survey
Tallahassee, Florida
1983
































3 1262 04543 6333








nowli

^'It^'1--








OPEN FILE REPORT 14


STATUS OF PHOSPHATIC CLAY WASTE DISPOSAL





By

J. William Yon


Florida Department of Natural Resources
Bureau of Geology

November, 1983












Florida Bureau of Geology library
903 W. Tennessee St.
Tallahassee, FL 32304





:J'"ir;a Burxu or Geclcgy :
j93 W. Tennessee St.
Status of Phosphatic Clay Waste Disposal Talahassee. FL 32304


The Department of Natural Resources has the responsibility, under Chapter

211, Part II, Florida Statutes, for administering the reclamation of certain

lands mined for solid minerals in Florida. Currently, these minerals include

phosphate, clay, and heavy minerals. However, only phosphate will be discussed

as the purpose of this report is to present information on the present conven-

tional method for reclaiming phosphate clay waste storage areas and research

relating to clay waste dibposals

GEOLOGY

Phosphate occurs in Florida as a sedimentary rock in the form of calcium

phosphate. There are several kinds of phosphate deposits in Florida, but those

known as the land pebble phosphate are the most important commercially. The

land pebble phosphate deposits, also known as the Bone Valley Formation, were

formed during the Miocene and Pliocene geologic epochs. Commercial deposits of

land pebble phosphate occur in Polk, Hillsborough, Hardee, Manatee, and DeSoto

counties in central Florida, and in Columbia and Hamilton counties in northern

Florida. (Figure 1). As shown in figure 2., the phosphate ore zone, five to

fifty feet thick, is overlain by the 0 to ten foot thick leach zone, ten to

thirty feet of overburden, and top soil. (Florida Bureau of Geology, Phosphate

Land Reclamation Study Commission Report, 1978, 32 p.)

MINING

Before mining, a program of extensive drilling is conducted to explore for

and determine the economic potential of the deposit. If an area is determined

to contain commercial deposits and is to be mined, the vegetation is removed.

Phosphate mining is done by the open-pit method using large, electrically-

operated, walking draglines. Mining is conducted in adjacent cuts 200-300 feet

wide and up to several thousand feet long. As the first mine cut is made the

overburden is removed and placed on top of the natural ground adjacent to the





















.Wht* Si r
I

Sn COLUNYa



", o wow.u -



Sccun ..Cenrt-ra
*\ d-i dsntcti



maw"tt '" COMTno




Scaoe, miles cOUNTY

'















FIGURE 1 Map of phosphate-producing counties.
USBM, p. 17, 1983.


--I-















GEOLOGIC AGE FORMATION LITHOLOGIC SECTION MINING MINERALOGY
TERM


TOPSOIL


PLEISTOCENE TERRACES '


PLIOCENE
and
UPPER MIOCENE


MIDDLE MIOCENE


9* I


BONE VALLEY

FORMATION


4* 1


HAWTHORN

FORMATION


.* .* 10'.."
- -
S. LEACHED ZONE ":
:;* .,- L. ''-; ;.0 ?p e* *
.. .".. ....
*. ** .
.. 0 ...

O ..-.


:T ::. .'.ORE ZONE ;- _.
.......,. .. ....



,*, -- :..-.......... .-- -
..* O;o*.* ~ o.. O....e. .S *
.--. -.~I. ..--.. -. .


OVERBURDEN


T


*SUBSTITUTIONS FOR ALUMINUM INCLUDE Uranium,Strontium and Barium.


ORGANIC SAND


SAND


ALUMINUM PHOSPtATES(Crondoliite-
Wovellite) x
SAND
CLAYS (Koolinite-AttoouIqite)


IRON PHOSPHATE(Vivianite)
CALCIUM PHOSPHATES (Apaite Group)
SAND
CLAY (Montmorillonit,)


LIMESTONE(Colcite)
SAND(Quortz)
CLAY(MontmorillonitsAnapuzgite)
CALCIUM PHOSP?9ATES(Apatite Group)


EXPLANATION


CLAY

SAND

P* PEBBLE


M LIMESTONE

i..f LEACH O
[oo0 ROCK


**
SUBSTITUTIONS FOR CALCIUM INCLUDE Uronium, StrontiumSodium, eoad, Magnes;um and Manganese.

SUBSTITUTIONS FOR FLOURIDE INCLUDE Chlorides and Hydroxyls
SUBSTITUTIONS FOR PHOSPHATE INCLUDE Oxides otVanadium, Arsenic,Silicon and COrbon


FIGURE 2 Columnar Section of the Central Florida Phosphate District, Phosphate Land
Reclamation Study Commission Report, p. 4, 1978.


RECENT


UNNAMED


L







mining operation. When mining progresses beyond the initial cut, the overburden

removed to make the phosphate ore accessible is cast back into the preceding

mined-out cut. The phosphate matrix is then removed by the dragline, slurried

with water under high pressures, and hydraulically transported by pipeline to a

washer plant where the pebble phosphate is removed from the sand and clay asso-

ciated with it.

BENEFICIATION

The process of separating the phosphate rock from the matrix is known as

beneficiation and produces two waste products, quartz sand and phosphatic clay.

The quartz sand is disposed of by pumping it back to mined-out cuts left during

the mining process. The phosphatic waste clay is near collodial size material,

0.002 mm in particle size, and has a tendency to remain in suspension for long

periods of time when mixed with water. As the clay wastes mixed with water

leave the beneficiation plant, the slurry is about three percent solids by

weight. The clay wastes are composed of montmorillonite(smectite), attapulgite

(palygorskite), kaolinite, illite, phosphate minerals, and silt size material.

All of the above clay minerals occur in a complex combination in the natural

state and causes numerous varation in settling characteristics of phosphatic

clays (USBM, p. 17, 1983). The USBM (p. 17, 1983) states that the phosphatic

clays containing greater amounts of attapulgite settle much slower than those

clays which contain lesser amounts of this particular clay mineral.

CONVENTIONAL STORAGE AND RECLAMATION OF CLAY WASTE PONDS

As shown in figure 3, phosphatic clay wastes are placed in conventional

storage areas which are surrounded by dams of varying heights. Although most

of the settling areas have holding capacities of approximately two years and

are used alternately with other settling areas to permit periods of natural





















r---I

Phosphatic clays

(3 % to 5% solids


Initial settling area used
at start of mining
operation.


Active settling area


FIGURE 3 Conventional clay disposal process.
USBM, p. 22, 1983.


(modified







settling (USBM, p. 21, 1983), they may remain in service for the life of the

mine as a water reservior. Once a storage area is filled with clay and no

longer used as a water reservior, it is taken out of service and reclamation can

begin.

The reclamation of waste clay settling ponds is a time consuming process

because of the water retention properties of the clay materials. The two most

frequently used methods to reclaim a settling pond by the phosphate industry are

dewatering by decanting and by capping the clays, i.e., pumping sand tailings

onto the semi-liquid clays.

The decanting process begins by removing surface water as fast as possible

through water control structures. As soon as dewatering of the surface area is

feasible, perimeter drainage ditches are dug inside the dams and into the

interior of the settling ponds to further enhance the drying of the-clays.

Continual maintenance and deepening of these channels is required to maintain

the dewatering process. As the clay dries, a crust forms which is capable of

supporting light farm machinery for cultivating the area. Due to the instabi-

lity of the substrate, conventional settling ponds are usually reclaimed for

pasture.

Sand tailings often are pumped into settling ponds, capping the clays which

speeds up the process of dewatering. However, if the sand is added to the clay

before a sufficient surface crust has been formed, "mud waves" often develop as

the clays are pushed ahead of the sand.

CLAY WASTE RESEARCH

The phosphate industry, because of the environmental concern of government

and the phosphate industry over the traditional method of storing waste clays,

was encouraged to condust research for accelerating the consolidation of clays

and improve land stability and minimize above ground storage.

Since 1972, the USBM, the phosphate industry, and others have conducted

numerous studies related to the phosphatic waste clay problem. In 1975, the

6







USBM, in their publication, "The Florida'Phosphate Slimes Problem--A Review and

Bibliography" (USBM IC 8668, 1975, 41p.) lists the research conducted on

phosphate slimes. The list below is comprised of methods cited in the USMB

publication and some other methods used for dewatering waste clays:

1. Filtration
2. Centrifugation
3. Freezing
4. Drying
5. Electrical Dewatering
6. Bacteriological Dewatering
7. Mechanical Thickeners
8. Chemical Flocculation- and Addition of Sand Tailings
9. Mixing with Sand Tailings
10. Dredge and Mix with Sand Tailings
11. Rotary Trommel and Flocculation
12. Reverse Osmosis
13. Pre-thickening of clay and cap with sand and/or overburden.

Of the above methods, mixing with sand tailings, dredge and mix with sand

tailings, chemical flocculants, and capping of pre-thickened clays in mine cuts

appear to be the most promising. For convenience, these processes are combined

into two broad categories, 1)physical settling and 2) chemical settling, and are

reviewed in the discussion that follows:

PHYSICAL SETTLING

Physical settling enhances the dewatering of phosphatic clays by mixing

sand with the clay or capping pre-thickened clay with sand and/or overburden.

Sand-clay mix has been developed to the extent that the process is now an opera-

tional technique for at least two operators.

Sand Spray Process:

In early 1972, Brewster Phosphates began experimenting with the sand spray

method of mixing sand with clay (Figure 4). Clay slurries of three to five per-

cent solids were placed in mined-out cuts and allowed to settle to 15 percent

solids. Subsequently, sand tailings were sprayed over the clays from spray

nozzles attached to a floating pipeline. As the sand settled through the clay,













r--. -. Standby
Phosphatic clays I settling ar
(3% to 5% solids)


Initial clay settling


Tailing


Disposal area


Sand capping


FIGURE 4 Sand-spraying process for clay disposal.
UswB, p. 25, 1983.







the water trapped within the clay was released. After the initial sand-clay

mix, more clay was introduced into the mine cuts and a second sand tailing

spraying was conducted to produce a clay solids content in excess of 35 percent.

Brewster Phosphates is presently using a sand-clay mixing technique which

is significantly different from the sand-spray process described above. Clays

at three to.five percent solids are placed in mine cuts and upon .consolidating

to 15 percent solids in three to four months slurried sands are discharged into

the mine cuts containing the clay from several points. The discharge points are

such that only one unit is discharging at a given time. As the sand interacts

with the clay, movement of the clay may take place. To counteract this move-

ment, the discharge of sand is stopped at that point and changed to another unit

placed along the bank of the mine cut. (B. Sapp pers. comm., 1983).

Approximately two years after filling the mine cuts, the clays begin to con-

solidate to 35 to 50 percent solids and available overburden peaks are used to

cover the sand-clay material. (B. Sapp pers. comm., 1983).

Dredge Mix:

CF Industries in Hardee County is presently experimenting with a dredge-mix

technique for disposal of phosphatic clay wastes and ensuing reclamation of

mined-out lands (Figure 5). The dredge mix method involves placing clays in a

holding pond and allowing them to settle to approximately 15-18 percent solids.

Then the clays are dredged out and mixed in a hopper with sand tailings before

being placed in mined-out cuts. The mix is pumped at approximately 30-32 per-

cent total solids content and can be placed above or below the water level.

After the ini tial fill, with the sand-clay mix, the material is allowed to

settle and the process is repeated until the mine cut is filled. Ardaman and

Associates, Inc., under the sponsorship of Florida Institute of Phosphate

Research monitored and collected data during the filling of a 110-acre sand-clay




BOOK TIGHTLY BOUND


Tailing sand (30 % solids)


Prethickened
clays


Disposal area


Figure 5 CF Industries, Inc. process for clay disposal.
(modified USBM, p. 25, 1983)








mix site at CF Industries, Hardee County Mine. In a final report on the area,

Ardaman and Associates (1982, p. 6-1) reported that at the end of a two year

study period the sand-clay mix averaged 34 percent clay solids. They (Ardaman

and Assoc., Inc., 1982, p. 6-1) also stated that reclamation can begin in the

area within one to two years after filling is complete, provided the site is

kept well drained.

Capping Process:

International Minerals and Chemical Corporation, Agrico, and Mobil Chemical

Company are experimenting with the technique of placing prethickened clays from

an initial settling pond in mine cuts surrounded by dikes (Lawyer, 1982, p. 141),

(Figure 6). After the mine cuts are filled above ground with prethickened 18

percent clay solids, a one and one-half foot cap of sand clay mix is placed over

the clays. At this point the clays are permitted to further consolidate for

one year before final capping with an additional seven foot layer of sand

tailings or overburden.

Five years after the final filling of the pits, the clays will consolidate

to 36 percent and that the ultimate clay consolidation will reach approximately

42 percent (Lawyer, pers. comm., 1983).

CHEMICAL SETTLING

Over a period of several years the USBM has experimented with chemical

flocculants as a means for rapidly dewatering phosphatic clays. They state

that, (USBM, p. 27, 1983)

"Flocculation is a technique in which discrete, colloidal-sized par-
ticles are agglomerated by an appropriate reagent and, as a result,
settle out of suspension. Hundreds of commercial flocculating
reagents have been tested singly or in combination with others, in an
effort to select a flocculant that will result in the formation of
stable flocs that will not reslurry readily and that will cause rapid


---- I I ---C`3-~CBL~CC~9~





BOOK TIGHTLY BOUND


Prethickened
clays


After


Add
thickened c


Disposal area


FIGURE 6 International Minerals and Chemicals Corp. process for
clay disposal. (modified USBM, p. 26, 1982)









settling and dewatering of phosphatic clays. Frequently, successful
flocculating reagents evaluated in the laboratory on-a specific clay
proved unpredictable in field tests owing to the variables encountered
in the field test conditions. These variables are...clay mineralogy;
age of the clay slurries; method of flocculant introduction; dilution
of the clay slurries; pH of the slurry; mixing shear; conditioning and
contact time."

Estech General Chemical Corporation, Enviro-Clear Process:

Estech has been experimenting with the Enviro-Clear thickening process for

rapidly dewatering waste phosphatic clays. The process, as shown in figure 7,

involves single flocculation for the treatment and disposal of three percent

waste clays.

Phosphatic clays, chemical flocculant, and dewatered tailings are mixed

together in a surge tank. After mixing, the material is passed into the

thickener where additional agglomeration takes place. The thickened solids

leave the bottom of the thickener and are pumped to mine cuts for further de-

watering. The water released from the clay passes out the top of the thickener

and is recycled into the mining operational system. The flocculated clays mixed

with sand continue to consolidate and eventually reach 30 to 35 percent solids.

Estech has built a full-scale plant at their Watson Mine in Polk County and have

been encouraged by preliminary field disposal tests.

U.S. Bureau of Mines Rotary Trommel and FlocculationProcess:

The rotary trommel and chemical flocculation developed by the U.S. Bureau

of Mines is presently being field tested (Figure 8). The process involves

mixing a chemical flocculant, polyethylene oxide (PEO) with clay waste con-

taining three percent solids and subjecting them to static and rotating screens

which rapidly dewaters the clays to 24 percent solids. Pit tests indicate that

clay solids greater than 30 percent can be achieved in several months. Some

clays require oxidation and treatment with lime in addition to PEO to achieve

flocculation.


-- s --a~a-CP--r~~~-~p~--~--U~m~vii~Cj7~



















Phosphatic clays


Recycle water


Surge tank


Disposal area


FIGURE 7: Estech Chemical Corp. process for clay disposal.
USBM, p. 30, 1983.


sands





























(PEO)


Hydrosieve


Mixing tank


Recycle
water to plant


screen


Phosphatic
L clay solids


Recyc:e
water


Disposal area


FIGURE 8 Rotary screen process for clay
USBM, p. 28, 1983


disposal.


-- ---~^~-~.1~-^9~-r~aa~naELgsS~iQg~BS







Gardinier, Inc. Process:

Gardinier, Inc., has been experimenting with a process utilizing double

flocculation for the treatment and disposal of waste clays (J. Taylor, 1982, p.

249-64) (Figure 9). The process involves adding flocculants to clay waste at

one to six percent solids which causes the waste clay to agglomerate and settle.

The thickened clays, consisting of 12 to 15 percent solids, are then pumped to

another station where more flocculant is added to the thickened clay. The

double flocculated material is then deposited in mine cuts where it continues

to dewater until the mixture reaches 30 to 40 percent solids after a few weeks.

The mine cuts are stage filled for approximately one year allowing the material

to be exposed to the atmoshpere to enhance drying of the material. After the

mine-cuts are filled with the thickened clay, they are capped with sand tailings

and overburden.

CONSOLIDATION PREDICTIONS

Dr. James E. Lawyer of International Minerals and Chemical Corporation has

done an in depth comparison of the consolidation predictions of the various

systems used by the phoshpate industry to dispose of phosphatic waste clay.

(Table 1). The comparison is based on a site specific standard Central Florida

phosphate mine using a value of 10,700 tons per acre of waste clay, 24 feet of

matrix, and 26 feet of overburden. Based on data from table 1, graphs (Figures

10-12) showing the comparison of percent clay solids as a function of time were

constructed. Except for conventional clay settling ponds, most of the tech-

niques achieve approximately thirty five percent clay solids after 5 to 8 years.

(Figure 10-12). This is the percent solids required if the waste clays are to

fill the available void space in the mine cuts to allow ultimate disposal at

approximately ground level over 85 percent of the area mined.


























































FIGURE 9 Gardinier, Inc., process for clay disposal.
USBM, p. 29, 1983.















17

17


_ IC__ IY_________PP_A~a~~





U


TABLE I COMPRISOM OF CONSOLIDATION PREDICTIONS OF VARIOUS WASTE DISPOSAL SYSTEMS


Acres of Above Ground Settling Total
Ponds Effective

Acres of in-Pit Storage (IPS)

Initial Slim Height Above Ground of
In-Pit Storage

Initial % Solids of Clay In in-Pit Storage

% Solids of Clay in In-Pit Storage at Time
of Final Fill

S Solids of Clay In in-Pit Storage 5 Years
After Final Fill

Height of Slims Above Ground of In-PIt
Storage 5 Years After Final Fill

Ultimate % Clay Solids

Ultimate Height Above Ground of
Final Surface

Turnaround Tim Between Initial
--- Mining and Reclamatlon

o of Total Slimes Stored in In-Pit Storage

S of Slims Ultimately Stored at or
Below Ground Level


Source: Dr. James Lawver, 1983.


A
TWT
350E

1750


15*

3-5


25

28

8.7

31


5

IOY

83

75


B

350E

1750

15'

3-5

25

28

8,7

40


0

IIY

83

91


C D
T5I3 3WTa
278E

1845 1750

0' 10I

3-5 12-14


12-15 30

36 35

-13 7

42 36

0 6

4Y BY

41 85

67 72


E

450E

1680

10I

15-18


30.3

35.7

7

36

6

8Y

83


72


F

450E

1695


10'

15-18


23,5


36.3

-3.0

42

0


8Y

82


90


G H
3W0T -35W"


440

1750


101

12-14


>30


>35

<10

>40

+2


6-8Y

>80

>88


1750


10l

18-22


>30


>35

<10

>40

<5


>5Y

>80

>88


CODE

A = Conventional System
B Conventional Cap
C = Brewster Cap
D Estech
E CF
F IMC-Agrico-MoblI Cap
G = Gardinler Cap
H = U.S.B.4.

BASIS

9,700 TPA Product
10,700 TPA Slmes
26,100 TPA Tailings

24 ft. MTX
26 ft. Overburden
50 ft. Pit

Production Rate
1.1 X 106 tpy slimes
2.7 X 106 tpy tailings
1.0 X 106 tpy product

Mining Rate 103 Acres/Year
for 20 Years




CONSOLIDATION PREDICTIONS FOR CLAY WASTE STO.RRGE
SOURCE- OR. JAMES LRWVER, 1983
50

A CONVENTIONAL
S---" CONVENTIONAL + CRP
.P
E 40
R D
C -'
E
N 0
N -'
T
30
C
L c
LR o I'

Y
20
0
L
I A Initial percent solids at time of in-pit
o storage.
S 10 B Percent solids at time of final fill.
C Percent solids five years after final fill.
D Percent solids ten years after final fill.


0A[
0 ----------------------------

0 5 10 !5
TIME (YERRS)
FIGURE 10






CONSOLIDATION PREDICTIONS FOR CLAY
SOURCE- OR. JAMES LAWVER,


WASTE STORAGE
1983


0- ESTECH
G--- U.S.B.M.
*-- GRRDINIER D



-- c


a 1-
-7


*o


A Percent solids
and at time of
B Percent solids
C Percent solids
D Percent solids


reached after undergoing flocculation
in-pit storage.
at time of final fill.
five years after final fill.
ten years after final fill.


TIME (YERRS)


50


30


C
L

Y

S
0
L
I
O0
S





i




CONSOLIDATION PREDICTIONS F0R CLRY WNSTE STORAGE


SOURCE- DR. JAMES LAWYER,


1983


A--- IMC-AGRICO-MOBIL
Q---S CF INDUSTRIES
-- BREWSTER PHOSPHATE E- E E



D ^ ------------------ El
S --- D
B--"'/ ,^



A Initial percent solids at time of in-pit'sto.
B Percent solids reached after pre-consolidatic
C at time of in-pit storage.
/ C Percent solids at time of final fill.
SD Percent solids five years after- final fill.
S / E Percent solids ten years after final fill.
B -


/C


rage.
on and


TIRE (YERRS)
FIGURE 12


50


30 -


20





10


w








Field measurements by Brewster Phosphate at their Fort Lonesome Mine

(B. Sapp, pers. comm., 1983) and Ardaman and Associates, Inc. (FIPR, 80-03-006,

1982, 122 pp.) at C.F. Industries Hardee Complex Mine are presented in figure

13. Comparison of figure. 13 with figure 12 shows a slight differencee between

the field measurements and Lawyers computer model prediction. This difference

may exist because of different size areas and pit depths.

SUMMARY

Much research work has been done since 1972 in an attempt to solve the

problem of rapidly dewatering phosphatic clays. Research efforts conducted on

dewatering phosphatic clays is to reduce the area needed for storing these clays

and the height of storage dams, with an ultimate goal of returning the land to

approximate the original surface elevations. To date, research efforts have not

greatly reduced the area needed for storing phosphatic clays as up to 85 percent

of the mined land is required for waste clay storage. However, if a feasible

technique can be developed which will consolidate clay waste to greater than 50

percent, a stable land mass can be created, and the land would have greater

economic and environmental qualities.

The efforts toward dewatering phosphatic clay can be classified generally

as follows:

A. Conventional Settling Technology

1. Stage Filling with subsequent dewatering.
2. Longtime dewatering of clays by ditching and subsequent capping
with sand or overburden.

B. Physical settling Technology

1. Pre-thickening of clay in settling pond plus quartz sand cap or
overburden.
2. Pre-thickening of clay in settling pond before dredging and
admixing with quartz sand.
3. Pre-thickening of clay in mine cuts before addition of quartz sand
by spraying.

22


_ 1




ACTUAL CONSOLIDATION RATES FOR CLRY WASTE STORAGE
SOURCE- BREWSTER PHOS., RRODMAN AND ASSOC., 1983
50

-- BREWSTER PHOSPHATE
E---8 CF INDUSTRIES

E +0
R
C
E D
N
T
30 D





S 20 *'
S
0
L
I B
D / A Initial percent solids at time of in-pit storage
S. 10 B Percent solids reached after initial fill.
C Percent solids reached after pre-consolidation and
at time of in-pit storage.
D Percent solids at time of final fill.


0 A

0 5 10 1

TIME (YERRS)
FIGURE 13








C. Chemical Settling Technology

1. Flocculation with addition of sand or overburden cap.
2. Flocculation plus addition of quartz sand to form a mix.
3. Flocculation minus addition of quartz sand.

Of the methods tested for dewatering clays, admixing of sand with the

phosphatic clays is one of the most promising techniques. According to

A. L. Holmes (Pers. comm., 1983) of C. F. Industries and Bobby Sapp (Pers.

comm.,1983) of Brewster Phosphates, their sand-clay mix processes are at full

scale field operation mode. Both companies have indicated that the method they

are using may be suited only for their particular mine. Williams (1981, 15 p.)

states that admixing of sand and clay is not a proven technique because research

has not provided sufficient data to be able to predict a .final landform that a

sand-clay mixture will ultimately acquire. He (William, 1981, 15 pp.) also says

that adopting standardized proportions for a sand-clay mix is impossible because

ore bodies vary drastically in the constituent parts of sand, clay, and

phosphate (Table 2).

In the list that follows, the advantages and disadvantages of sand-spray,

sand-clay mix and capping are cited%

(Mobil Chemical Company, EIS, 1981, p. 2-50, Lawyer 1982, p. 225-48, USMB, 1983,
p. 24, 28):

(Advantages)
Reduce the number of acres devoted to conventional settling ponds.
Reduce the risk of dam failure.
Enhance the drainage characteristics of the soil over conventional clay
areas.
Reduce reclamation time.
Expedite the initial consolidation rate of the clay.
Make possible the storing of clays at or near ground level elevation behind
low level dams.
Dispose of sand and clay at the same disposal site.
Rapid recovery of water for reuse in the beneficiation process.

(Disadvantages)
Still require above ground dams even though they are low level.
Still risk dam failure and probable damage.
Still require considerable acreage for storage purposes.

S 24















TABLE 2
SUMMARY OF MATRIX SAND/CLAY RATIOS


Mine


Grace

Estech

Beker

AMAX

Borden

Brewster

CF Industries

Farmland

Mississippi Chemical

Mobil


Four Corners

Duette

Manatee

Pine Level

SBig Four
Ft. Lonesome

Hardee Co.

Hardee

Hardee Co.

South Fort Meade


Source: Mobil Chemical Company, EIS, 1981, p. 2-36)


Company


Matrix
Sand/Clay
Rati os


4.5:1

4.2:1

4.0:1'

3.75:1

3.2:1

2.5-3:1

2.6:1

2.5:1

2.2:1

1.2:1








(Disadvantages, continued)


Low weight bearing capacity.
'Restricted variety of land forms and land uses.
Logistics of providing the required sand for disposal.
Creation of mud waves in capping and sand-spray methods.
Difficulty. of- poper clay-capping techniques.
"Turn-around" time for proper clay thickening.

The chemical methods under study or presently operational-are considered to

have both advantages and disadvantages, which are listed below:

(USBM, 1983, p. 29, J. Lawyer, pers. comm., 1983, Raden, 1982, p. 216-21,
Taylor, 1982, p. 249-64):

(Advantages)
Rapid recovery of water for reuse in the beneficiation process.
Eliminate the need for numerous conventional settling ponds.
Induce rapid settling of clays which makes possible the storing of clays at
or near ground level elevations behind low level dams.
Speed up reclamation.
Obtain the necessary clay solids to suspend all sand tailings produced into
homogenous mixture that will not segregate.
Clays dewatered using PEO do not readily reslurry.

(Disadvantages)
Reuse of reclaimed water from the process may effect the beneficiation
process. (Froth Flotation)
Changing mineralogy of clays causes difficulties in flocculant performances.
Low weight bearing capacity.
Restricted variety of land forms and land uses.
Still risk dam failure and probable damage from the stored material.
Still require considerable acreage for storage purposes.
Unknown impact of flocculant chemicals on ground water quality.

Regardless of whether physical or chemical settling techniques are used,

other factors should be considered with regard to planning for clay waste

disposal at any particular mine. According to Carrier (USBM, 1982, p. 500) and

the U.S. Bureau of Mines (1983, p.32) each mine site waste disposal plan will

have its unique characteristics because of the following variables:

1. Thickness of overburden.
2. Amount of clay in matrix.
3. Ratio of sand to clay in'matrix.
4. Mineralogy and chemical composition of the clays in the deposit.
5. Volume of available below ground storage which includes the volume of
both the overburden and matrix.





CONCLUSIONS AND RECOMMENDATIONS


Based on the review of published data, field observation, and personal com-

munications with the phosphate industry, the following conclusions and recommen-

dations are presented:

1. The conventional above ground storage of clay waste requires the use of
approximately two-thirds of the land mined*.

2. The physical and chemical dewatering of waste clays that.are presently
being considered will reduce the time between initial storage and reclamation of
the areas where waste clays are stored.

3. Because overburden is currently being placed back in the mine cuts,
approximately 85 percent of the mined area is required for placing waste clays
at 35 percent solids (at approximately 10,000 tons of clay per acre).

4. After reaching 35 percent solids, the time factor for achieving addi-
tional consolidation of the clay waste is similar for all techniques.

5. Each mine has certain characteristics (as detailed by Carrier and USBM)
which will affect the waste disposal plan for that mine.

6. In a new mine an initial settling pond will be necessary for storing
clays until enough void space becomes available for utilizing sand mix and/or
flocculation.

7. An initial settling pond will be necessary for pre-thickening clays to
be used in sand mix, flocculation, and capping technique.

8. Initially, it will be necessary to store waste clays behind elevated
dams if ground level is achieved and topographic lows are to be avoided over the
total area.

9. Regardless of the presently recognized techniques being used for clay
waste storage, the stability of the land will be such that land use of the areas
may be limited Lo agricultural uses.

10. Research on the physical and chemical methods of dewatering clay
wastes, with regard to chemical methods of dewatering clays, research should be
conducted to determine whether flocculants create ground water quality problems.

11. As previously mentioned, the current method of mining requires placing
up to 50 percent of the overburden in the mine cuts. If a different mining
method can be perfected to remove the overburden the amount of land required for
clay storage can be greatly reduced. To determine if this approach is
realistic, research should be conducted which addresses both the technical
aspects and associated costs of the new method.

12. Research should be conducted to improve land stability and the agrono-
mics of the lands after reclamation is complete.

13. The ultimate research goal for rapidly dewatering clays should be to
perfect a technique that will achieve clay solids of about 50 percent.

14. THE TECHNIQUE USED FOR DEWATERING WASTE CLAYS IS NOT AS IMPORTANT AS
THE ULTIMATE GOAL OF ACHIEVING A STABLE LAND SURFACE AND MINIMIZING ABOVE GROUND
CLAY STORAGE.











Ardaman and
1982


Carrier, W.
1982


Associates, Inc.
Field Evaluation of Sand-Clay Mix Reclamation, December 1982:
Florida Institute of Phosphate Research, p. 6-1.

D. III ..
Predicting Consolidation of Phosphatic Clay Waste:
Proceedings, Consolidation and Dewatering of Fine Particles
Conference, U.S. Bureau of Mines Symposium, University of Alabama,
August, 1982, p. 492-519.


Florida Department of Natural Resources
1978 Phosphate Land Reclamatidn and Study Commission
Report on Phosphate Mining and Reclamation, 32 p.

Gordon F. Palm and Associates
1983 Evaluation of Clay Disposal and Land Reclamation Techniques,
Sand-clay Method vs Sand-cap Method, Suwannee River Mine,
Occidental Chemical and Agricultural Products, Inc.,
White Springs, Florida, 137 p.


Lawyer, J. E.
1982 Progress Report 6:
Reclamation Study:
Corporation, 141 p.


IMC-Agrico-Mobil Slime Consolidation and
International Minerals and Chemical


Lawyer, J. E. ,
1982 The Clay Waste Problem in a Nutshell:
Proceedings, Consolidation and Dewatering of Fine Particles
Conference, U.S. Bureau of Mines Symposium, University of Alabama,
August, 1982, p. 225-248.


Mobil Chemical Company
1981 Mobil Chemical Company
South Fort Meade Mine
Polk County, Florida:
U.S. Environmental Protection Agency,
Environmental Impact Statement,
EPA 904/9-81-075.


Raden, D. J.
1982 Dewatering Phosphate Clay Waste Using the Enviro-Clear Thickener:
Proceedings Consolidation and Dewatering of Fine Particles
Conference, U.S. Bureau of Mines Symposium, University of Alabama,
August, 1982, p. 205-224.

Taylor, J. W.
1982 Thickening, Disposal, Dewatering, Consolidation of Slimes from
Phosphate Washeries in Florida:
Proceedings, Consolidation and Dewatering of Fine Particles
Conference, U.S. Bureau of Mines Symposium, University of Alablama,
August, 1982, p. 249-264.




I


William, J.
1981 Predicting Physical Properties of Mistures of Sand and Phosphatic
Clay: Proceedings of the Progress in the Dewatering of Fine
Particles Conference, U.S. Bureau of Mines Symposium, U.S. Bureau
of Mines, University of Alabama, April 1981, 18 p.

U.S. Bureau of Mines
1975 The Florida Phosphate Slimes Problem, A.Review and a Bibliography:
Inf. Cir. 8668, 41 p.

1982 The Florida Phosphate Industry's. Technological and Environmental
Problems, A Review:. Inf. Cir. 8914, 42 p.