EPA-600/2-76-045
March 1976
Environmental Protection Technology Series
ELIMINATION OF WASHER SLIMES FROM THE
PRODUCTION OF PHOSPHATE CHEMICALS
Industrial Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park. North Carolina 27711
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into five series. These five broad
categories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series. This series describes research performed to develop and
demonstrate instrumentation, equipment, and methodology to repair or prevent
environmental degradation from point and non-point sources of pollution. This
work provides the new or improved technology required for the control and
treatment of pollution sources to meet environmental quality standards.
EPA REVIEW NOTICE
This report has been reviewed by the U.S. Environmental
Protection Agency, and approved for publication. Approval
does not signify that the contents necessarily reflect the
views and policy of the Agency, nor does mention of trade
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recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-76-045
March 1976
ELIMINATION OF WASHER SLIMES
FROM THE PRODUCTION OF
PHOSPHATE CHEMICALS
by
Raybon C. Cannon, Roger S. Ribas, J. David Nickerson,
and Robert A. Weisback
USS Agr1-Chemicals Division
U.S. Steel Corporation
658 DeKalb Industrial Way
Decatur, Georgia 30033
for
State of Florida
Department of Environmental Regulation
Tallahassee, Florida 32301
GRANT S802684
ROAP No. 21AZR-007
Program Element No. 1BB036
EPA Project Officers: Robert R. Swank, ERL, Athens,
and Edmond Lomasney, EPA Region IV, Atlanta
Industrial Environmental Research Laboratory
Office of Energy, Minerals, and Industry
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
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CONTENTS
Page
Sections
I Conclusions 1
II Recommendations 5
III Introduction 6
IV Matrix Characterization 15
V Upgrading Methods 23
VI Calcination and Digestion Studies 27
VII Discussion of Results 41'
VIII References 57
IX Glossary 58
X Appendices 59
111
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FIGURES
Page.
1 Conventional Phosphoric Acid Process 10
2 Matrix Sample Locations 16
3 Comparison of Digestion Methods 34
4 Metals Solubility of Low-Clay Fractions 35
5 Metals Solubility of Clay Fraction 36
6 Hydrochloric Acid Digestion of USSAC Matrix 72
7 Hydrochloric Acid Digestion of Borden Matrix 73
8 Hydrochloric Acid Digestion of American Cyanamid 74
Matrix
9 Hydrochloric Acid Digestion of IMC Matrix 75
10 Hydrochloric Acid Digestion of Mobil Matrix 76
11 Phosphoric-Sulfuric Acid Digestion of USSAC Matrix 77
12 Phosphoric-Sulfuric Acid Digestion of Borden Matrix 78
13 Phosphoric-Sulfuric Acid Digestion of American 79
Cyanamid Matrix
14 Phosphoric-Sulfuric Acid Digestion of IMC Matrix 80
15 Phosphoric-Sulfuric Acid Digestion of Mobil Matrix 8l
16 Effect of Calcination Time on Metals Solubility of 38
Clay Fraction
17 Calculation of P209/A1 Ratio Versus Clay Removal 44
18 P205/Metal Ratios of USSAC Matrix 82
19 P205/Metal Ratios of Borden Matrix 83
20 P20s/Metal Ratios of American Cyanamid Matrix 84
21 P20s/Metal Ratios of IMC Matrix 85
22 P20s/Metal Ratios of Mobil Matrix 86
23 P205/Metal Ratios of USSAC Matrix 87
24 PaOs/Metal Ratios of Borden Matrix 88
25 P20s/Metal Ratios of American Cyanamid Matrix 89
26 P20s/Metal Ratios of IMC Matrix 90
27 P205/Metal Ratios of Mobil Matrix 91
IV
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TABLES
No. Page
1 Mineralogical Composition of Phosphate Slimes 8
2 Chemical Composition of Phosphate Slimes 8
3 Study of Sampling Representativeness 15
4 Chemical Composition of Matrix Samples 18
5 Particle Size Distribution USSAC Matrix 1?
6 Mineralogical Characteristics of Matrix Samples 19
7 Particle Size, P205 and Metals Distribution in 21
Matrix
8 Chemical Composition of Clay Fractions 24
9 Effect of Impactor RPM on Matrix Disintegration 6l
10 Time Effect of Ceramic Tumbling 62
11 Loading Effect of Ceramic Tumbling 63
12 Comparison of Impactor Grinding Versus Tumbling 64
13 Experimental Conditions of Sand Separation 65
14 Sand Separation Tests at USS Agri-Chemicals 66
15 Sand Separation Tests at Minnesota Resources 6?
Research Center
16 Conditions of Calcination-Digestion Study 30
17 Results of Calcination-Digestion Study 31
18 Summary of Variable Response 32
19 Differential Thermal Analysis of Matrix Samples 68
20 Calcination of Clay Fraction at Two Consecutive 69
Temperatures
21 Calcination of Matrix at Two Consecutive 70
Temperatures
22 Calcination of Clay fraction with Mineralizers 40
23 Optimum Performance Summary 55
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SECTION I
CONCLUSIONS
Bench-scale studies of various Florida phosphate
matrix samples established that calcination at 800°C
or higher eliminates the interference of clay in the
digestion and filtration steps. Filtration rates of
the resulting gypsum slurries were equal or better
than those at present commercial plants using bene-
ficiated phosphate rock. The acid solubilities of
iron, aluminum, and magnesium minerals were reduced
to 30-605S of the total, depending on the type of
matrix. Although apparently all minerals containing
iron, aluminum, and magnesium entered, at least in
part, into the reactions forming the acid-insoluble
derivatives, the metals present in clay minerals gave
the best response, resulting in the highest degree
of insolubilization.
The response pattern of the clay fractions to the
calcination treatment was consistently different from
that of the low-clay fractions. While the clay frac-
tions exhibited a solubility minimum at 900-1000°C,
the metals of the low-clay fractions became increasingly
less soluble the higher the calcination temperature.
For this reason, better overall metals rejection was
obtained when the matrix was divided into a clay and
low-clay fraction, and the fractions calcined separately
at different temperatures. All types of clay investi-
gated - montmorillonite, attapulgite, kaolin, and
mixtures of the three - gave the described response
pattern.
- 1 -
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Despite the relatively good reduction in metals solu-
bility, only one out of the five test matrix samples
met the stipulated quality of phosphoric acid to be
produced. Most problematic was the solubility of
aluminum which responded the least to the calcination
treatment but was generally present in all matrix
samples at the highest concentration.
An evaluation of the calcination performance in terms
of P205-to-metal ratios shows the results more clearly
Present commercial phosphoric acid production yields
P205-to-metal ratios of 40, 50, and 100 for iron,
aluminum and magnesium, respectively. These ratios
were met by the calcination process in three out of
five cases for iron and magnesium, and was approached
in one for aluminum.
Attempts to improve the metals insolubilization by
addition of mineralizers such as magnesium oxide,
lithium fluoride, fluorspar or phosphoric oxide gave
only marginal improvements. The additive concept has
been reviewed in depth in Appendix C, and suggests
a variety of possible approaches to insolubllizing
metal impurities in phosphate matrices. However,
only a few exploratory tests were conducted inci-
dental to the primary study and the results were
inconclusive, but this area probably merits further
study.
- 2 -
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Attempts to upgrade the matrix by dry methods involved
selective crushing and air classification to remove a
substantial amount of metal-containing minerals. How-
ever, since a certain loss of phosphate could not be
avoided, the P209~to-metal ratios improved very little.
Furthermore, the predominant mineral removed by this
method was clay, i.e., the matrix component which
responded best to the calcination treatment\ thus,
the overall gain in P205-to-metal ratios in the pro-
duced phosphoric acid was very small.
The proposed matrix calcination process encountered
another problematic development. During the course
of the investigation, the suddenly emerging energy
shortage placed an unexpected economic penalty on
the process. Fuel costs for calcination not only
became excessive, rather fuel simply became unavail-
able. Fuel requirements were higher than initially
anticipated because of the poor draining tendency
of phosphate matrix. Most samples retain 20%
moisture even after several months storage above
ground. For this reason, every effort was made to
reduce the mass to be calcined by separation of inert
matrix components such as sand prior to the calcination.
Difficulties with sand separation were encountered
at USS Agri-Chemicals and at the Minnesota Minerals
Research Center. However, earlier reported pilot-
plant work by W. R. Grace and Company substantiated
the feasibility of performing the separation by
electrostatic means if the drying and clay removal
is carried out simultaneously in a fluidized bed,
- 3 -
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as described in U. S. patent 3,329,351. A similar
process was recently patented to Cities Service
Company, U. S. patent 3,806,046.
In summary, the calcination method was capable of
producing an acceptable phosphoric acid from good
quality matrix, but failed to reject metal impurities
sufficiently to permit processing of poor-to-average
quality matrix.
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SECTION II
RECOMMENDATIONS
Since the ultimate goal set for the matrix calcination pro-
cess, as outlined in Section III, was only partly met,
efforts to make the process viable would have to focus
predominantly on the aluminum problem, attempting the eli-
mination by either physical separation or chemical insolu-
bilization. A potentially improved insolubilization might
be achieved by calcination in a reducing atmosphere, and/or
by calcination in an agitated or fluidized bed instead of
the static calcination method employed in the work of this
report.
As described in Appendix C (Reference 97), carbon was found
to lower the minimum temperature for mullite formation in
clays. A similarly attractive effect was observed by cal-
cining in an atmosphere of steam and/or carbon dioxide
(Reference 95, 96), which also enhanced the rate of mullite
formation.
The problem of acid soluble aluminum in the form of wavel-
lite and crandallite might be resolved by addition of calcium
oxide or carbonate. This reagent should displace aluminum
from these minerals as the oxide and yield acid insoluble
corundum. Also, increasing the calcination temperature to
1200-1300 °C might increase the acid insolubility of aluminum
by improving the crystallinity of the formed compounds. How-
ever, judging from spot tests, it appears unlikely that
interference of silica, forming calcium silicate, can be
avoided, thus, impractical amounts of lime may be required
to achieve the desired formation of corundum.
In view of the limited chances for success by presently known
improvement methods and the high fuel requirements due to
poor draining of the matrix, continuation of the project
does not appear justified at this time.
- 5 -
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SECTION III
INTRODUCTION
The Florida phosphate industry recovered in 197^ ap-
proximately 37 million tons of phosphate rock by strip
mining and beneficiation. Of this amount, about 21
million tons were chemically converted to phosphoric
acid. Both of these operations require the disposal
of enormous quantities of waste by-products. The
mining operation must dispose of some 32 million tons
of waste clay minerals, as a dilute 3-5 percent slurry,
which is allowed to settle for decades in diked
settling ponds. The chemical operation produces and
disposes of, as by-product, more than 23 million tons
of gypsum per year in above-ground disposal sites.
These disposal methods create long-term environmental
effects and, in some cases, pose immediate pollution
hazards to rivers and lakes.
In addition to the environmental problems, the mining
and disposal methods result in considerable waste
of water, mineral, and land resources. For mining
and beneficiation, billions of gallons of fresh water
from deep wells are required for makeup each year,
with approximately 25-35 percent of the mined phosphate
values discarded in the slimes. In 15 years, a plant
producing 2 million tons of phosphate rock per year
will require about 4,500 acres of land for slimes
disposal ponds, which remain unusable without applying
- 6 -
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expensive reclamation procedures. The gypsum by-product
from phosphoric acid manufacture is not considered a
potential pollutant, as are its soluble fluorine and
acid contents^ however, the gypsum does create an
aesthetically undesirable problem by marring the land
surface indefinitely.
In today's Florida phosphate strip-mining operations,
the overburden is first removed and the underlying
phosphatebearing matrix recovered. The matrix,
actually a mixture of about equal parts of phosphate
mineral, sand, and the so-called phosphate slimes
containing mainly clay, is pumped as a slurry from
the mine site to a beneficiation plant where it is
washed, scrubbed, and beneficiated to produce an up-
graded phosphate pebble and phosphate rock concentrate.
During this operation, the clay and phosphate rock
fines, as they are separated from the product, are
collected and pumped from the washer plant as a dilute
3-5 percent by weight solids slurry to settling ponds
built over mined areas. Dams reaching 35 feet in
height are required to impound these slimes, since
for every acre-foot of matrix, a volume of slimes
equivalent to about 1.25 acre-feet is produced. A
typical mineral and chemical composition of these
slimes is given in Tables 1 and 2.
- 7 -
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TABLE 1
MINERALOGICAL COMPOSITION OF PHOSPHATE SLIMES
Fluorapatite 20-25
Quartz 30-35
Montmorillonite 20-25
Attapulgite 5-10
Wavellite 4- 6
Feldspar 2- 3
Heavy minerals 2-3
Dolomite 1- 2
Miscellaneous 0- 1
TABLE 2
CHEMICAL COMPOSITION OF PHOSPHATE SLIMES
Typical Analyses, % Rangea
P205 9.06 9-17
Si02 45.68 31-46
Fe203 3.98 3- 7
A1203 8.51 6-18
CaO 14.00 14-23
MgO 1.13 1-2
C02 0.80 0- 1
F 0.87 0- 1
Loss on ignition 10.60 9-16
Ca3(POtt)2 19.88 19-37
- 8 -
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The beneficiated phosphate rock is next converted into
phosphoric acid by digestion with sulfuric acid to
solubilize the phosphate values. This process also
dissolves a major portion of the iron, aluminum,
magnesium and fluorine associated with the phosphate.
The phosphoric acid and gypsum are then separated by
filtration. Soluble fluorides and phosphates con-
tained in the wet gypsum cake are dissolved in the
pond waters. Figure 1 schematically outlines the
basic operations from mine to phosphoric acid which
are required to produce merchant-grade phosphate
values by conventional methods.
For three major reasons, the matrix, which of course
includes the slimes, cannot be directly used as feed
to digestion. First, the impurity content of the
matrix, particularly iron, aluminum, and magnesium
is considerably higher than in beneficiated phos-
phate rock, and it is largely solubilized by sulfuric
acid. Phosphoric acid of unacceptable quality results,
Secondly, if the clays are not removed from the matrix
before digestion, a much more dilute phosphoric acid
must be produced to overcome the thickening effect
of the clays on the digestion slurry. Thirdly, the
presence of colloidal clays makes filtration of the
gypsum economically unacceptable due to blinding of
filters and extremely slow filtration rates.
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o
I
FIG. 1
CONVENTIOK1AL PROCESS
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This project was initiated because it became apparent
that after-the-fact methods would not result in complete
solutions to industry waste disposal problems. New
concepts and techniques are necessary to meet domestic
needs and the environmental control required to
continue and extend the life of the Florida phosphate
industry. The waste disposal problems of the industry
are detailed below to emphasize the magnitude and the
necessity of finding solutions to these problems.
The techniques used in the recovery of Florida phos-
phate have not changed in basic concept for the last
20 years. Despite the many suggested new methods
for slimes disposal, none have been economically
attractive. Several proposals have involved manu-
facture of products, such as lightweight aggregate,
tile, etc., from slimes, and wallboard from gypsum.
Products from these materials are at best marginally
economical in a few cases, and the market volumes can
by no means be projected to result in an industry-wide
solution to the problems. The proposal of the matrix
calcination process was based on the concept that new
technology needs to be developed which would eliminate
slimes formation in the first place, and which would
better utilize available resources, thereby contri-
buting to the establishment of a more acceptable
economic situation to encourage change.
- 11 -
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The techniques used by the Florida phosphate industry
so far have the following disadvantages from the stand-
point of water and mineral conservation, environmental
hazard, and land usage:
1. Large volumes of water are required for mining and
beneficiation, with makeup requirements of some 80
billion gallons per year,
2. approximately 15 million tons of phosphate values
are discarded as waste each year,
3. the present slimes disposal systems tie up land
resources indefinitelyj for example, at the present
production rate of 37 million tons per year, about
82,000 acres of slimes ponds are required for 15
years operation,
4. retaining dams around each 50-400-acre slimes dis-
posal pond require continual maintenance and checking,
with the ever present possibility of dam breakage
and resultant river, lake, and stream pollution,
5. annual above-ground disposal of some 23 million
tons of gypsum by-product per year is aesthetically
unattractive and becomes a permanent feature of the
topography, and
- 12 -
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6. the soluble acid content, and particularly the
soluble fluorine content, of the gypsum disposal
ponds and piles are potential hazards since they
may enter the environment by leaching and run-off
during heavy rainfall, by seepage, and by evapora-
tion from the surface of the ponds.
Consequently, a dry-mining calcination-digestion con-
cept was developed, based on the laboratory observation
that calcination of phosphate matrix to certain tem-
peratures eliminates the interference of clay in the
phosphoric acid process and simultaneously decreases
the acid solubility of most metal impurities. The
original concept involved a total of five steps I
1. Dry mining of the matrix,
2. upgrading by dry methods,
3. calcination,
4. digestion to produce phosphoric acid, and
5. return of gypsum and acid insoluble by-
products to the mining pits.
Successful completion of all phases of this concept
would result in a new process with the following
benefits:
1. Closed-loop operation where all of the major
mining and chemical plant by-products would
be disposed of in mine pits without above-
ground-level dikes and ponds,
2. the utilization of at least 90 percent of
the actually mined phosphate values,
3. a major reduction in the deep-well water
makeup requirements, and
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4. complete elimination of slimes pond environ-
mental hazard and potential fluorine runoff,
leaching, and evaporation from gypsum ponds.
A literature search of publications relating to
the postulated reactions of the matrix calcination
was initiated to establish prior art before the
beginning of extensive laboratory work and to
aid in planning of the experimental phase. The
search covered Chemical Abstracts Volumes 41-77
(1947-1972). It is presented as Appendix C.
Only a few references were found which deal
directly with the chemical nature of acid-in-
soluble iron, aluminum, or magnesium compounds
formed by calcination.
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SECTION IV
MATRIX CHARACTERIZATION
A total of five phosphate matrix samples were eval-
uated in the course of studying the matrix calcination-
digestion process. The samples were selected to re-
present all major types of typical Florida matrix, and
were taken directly from mining sites of five major
mining companies in Florida as indicated in Figure 2.
Preparation of the samples for process studies involved
air drying to 0.5-3$ moisture, crushing with a jaw
crusher to 3/16 in., and blending in a 55-gal drum
tumbler. The stainless-steel drum used for the
blending was equipped with baffles to avoid rolling
of the charge. Subsamples were withdrawn while the
drum was in motion. A test for representativeness
as shown in Table 3 confirmed the efficiency of the
blending equipment.
TABLE 3
STUDY OF SAMPLING
Blending
Time, min
30
30
60
60
P20g
9.70
9.68
9.81
9.79
REPRESENTATIVENESS
Fe
1.11
1.10
0.96
1.12
%
Al
1.78
1.71
1.62
1.63
Mg
0.38
0.33
0.33
0.33
H20
2.77
2.84
2.68
2.62
Ref. No.
320-15-1
320-15-2
320-15-3
320-15-4
In this test, four 20-lb samples were withdrawn, two
each after 30 and 60 minutes of blending, respectively,
Each sample was analyzed after riffling and grind-
ing to -100 mesh (Tyler). Chemical compositions of
- 15 -
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FIGURE 2
MATRIX SAMPLE LOCATIONS
A. BORDEN C. IMC
B. AM. CYANAMID D. MOBIL
E. USSAC
- 16 -
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all matrix samples are listed in Table 4. A typical
particle size distribution of the crushed or ground
matrix is presented in Table 5.
TABLE 5
PARTICLE SIZE DISTRIBUTION
US SAC MATRIX
Ground Matrix
Crushed Matrix
Screen Analysis % Screen Analysis %
( TyLer )
+60 0.24
-60+100 16.65
-100+200 29.13
-200 53.98
(Tyler)
+3
-3+4
-4+8
-8+10
-10+16
-16+28
-28+60
-60+100
-100+200
-200
1.86
0.40
0.59
0.40
1.19
24.73
19.71
25.52
11.87
13.73
The mineralogical compositions of the matrix samples
were determined by X-ray diffractionjx»2 and microscopic
examination. Separation into various mineral fractions
for the purpose of identification was performed by
classification according to differences in hardness,
gravity, acid solubility, and streak. A comparison
of major mineralogical characteristics of all matrix
samples is listed in Table 6. The terminology of data
in this table follows the customary practice of the
phosphate mining industry designating the -150 mesh
fraction as slimes, the'-14+150 mesh fraction as
flotation feed, and the +14 mesh fraction as pebble.
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TABLE 4
CO
I
Acid Insol.
CaO
SO,,
Org. Matter
F
C02
Fe
Al
Mg
Na
K
Moisture
Pa09/Fe,
wt. Ratio
P.O./A1,
wt . Ratio
wt . Ratio
USSAC
9.67
63.87
13.41
0.31
0.15
1.19
0.30
1.18
2.23
0.40
0.21
0.72
-
8.2
4.3
24.2
CHEMICAL COMPOSITION OF
Borden
20.09
39.87
29.40
0.67
0.19
2.13
-
0.419
1.17
0.125
-
NF
0.53
48.0
17.2
160.7
MATRIX SAMPLES
American
Cyanamid
15.70
51.80
21.33
0.57
0.19
1.48
-
0.517
1.32
0.157
-
NF
0.58
30.4
11.9
109.0
0.79
3.05
0.144
NF
0.57
15.6
4.0
85.2
1.84
1.32
0.153
NF
0.45
8.6
11.9
102.7
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TABLE 6
MINERALOGICAL CHARACTERISTICS OF MATRIX SAMPLES
Clay1
% in Matrix
1
f-1
VO
1
Matrix
Source
USSAC
Borden
American
Cyanamid
IMC
Mobil
Type
Montmorillonite
Kaolin
Montmorillonite
Kaolin
Attapulgite
Montmorillonite
Attapulgite
%
27.4
2.2
7.3
-
23.4
Slimes*
33.0
8.8
17.5
35.7
69.3
PZ09
9.7
20.4
18.9
12.1
6.9
Pebble
0
4.5
39.5
2.9
1.1
Peed3
52.2
87.7
43.0
61.5
29.6
Pebble*
% weathered
no pebble
nil
25
75
nil
1 Clay = -ly
a Slimes = +ly -150 mesh
3 Peed = -14+150 mesh material
* Pebble = +14 mesh material
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The main purpose of evaluating several matrix samples
was to establish the response of different matrix types
and components to the calcination treatment. As evident
from Table 6, the matrix samples contained montmoril-
lonite, attapulgite or kaolin clay, or a mixture of all
three. Further differences were the presence of
weathered and unweathered pebble, as well as one case
of iron in solid solution in the pebble. The distri-
bution of P205 and metals is listed in Table 7. Detailed
results of the matrix characterization are as follows.
USS Matrix, Rockland Mine
The USSAC sample was a high quartzite, high aluminum
matrix with very little pebble phosphate. Its clay
content was about average for a Florida matrix, being
nearly all montmorillonite. There was a substantial
amount of aluminum in minerals other than clay.
Listed in decreasing order of occurrance, the follow-
ing components were found:
Quartz Apophyllite
Apatite Illmenite
Montmorillonite Wavellite
Staurolite Rutile
Feldspar 111ite Traces
Borden Matrix, Tenerock Mine
The sample is representative of the older mining opera-
tions in the northern section of the Florida phosphate
field. Because of its high phosphate content, this
area has been mined very intensively. Its clay content
was mainly kaolin. The sample contained an above
average amount (87$) of -14+150 mesh material which
normally is used as flotation feed. Its sand fraction
was very fine, usually -40 mesh.
- 20 -
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TABLE 7
PARTICLE SIZE, P209 AND METALS DISTRIBUTION IN MATRIX SAMPLES
(ATC 320-39)
I
ro
Borden
Pebble
Feed
+ly Slimes
-ly Slimes
American Cyanamid
Pebble
Peed
+ly Slimes
-ly Slimes
IMC
Pebble
Peed
Slimes
Mobil
Pebble
Feed
+ly Slimes
-ly Slimes
4.5
86.7
6.6
2.2
33.5
20.6
13.0
9.2
7.4
87.5
4.2
0.9
0.56
0.54
7.85
9.52
2.1
38.4
42.4
17.1
0.43
0.26
1.54
2.00
4.9
58.0
25.9
11.2
0.125
0.085
0.375
0.446
4.8
64.9
21.8
8.5
2.85
61.50
35.65
P205
33.5
20.6
13.0
9.2
31.4
6.6
21.6
20.3
32.0
8.3
17.1
18.4
13.8
5.0
1.3
PsO,
Distr.
7.4
87.5
4.2
0.9
65.5
15.0
11.7
7.8
7.5
42.3
50.2
2.9
59.4
33.3
4.4
Al
Al
Distr
39.45
43.01
10.29
7.25
31.4
6.6
21.6
20.3
65.5
15.0
11.7
7.8
0.71
0.25
5.91
6.12
19.5
7.5
42.2
30.8
0.59
0.19
0.98
1.29
45.9
15.9
19.8
18.4
0.168
0.050
0.497
0.879
32.8
10.6
25.3
31.3
0.93
0.54
8.33
0.8
10.0
89.2
1.09
29.62
45.92
23.37
18.4
13.8
5.0
1.3
2.9
59.4
33.3
4.4
0.59
0.73
3. '41
1.34
0.3
10.3
74.5
14.9
0.53
0.39
1.88
2.54
0.4
7.3
54.7
37.6
0.626
0.300
0.777 '
1.190
0.9
12.2
48.8
38.1
Fe
0.43
0.26
1.54
2.00
0.59
0.19
0.98
1.29
0.48
0.21
1.65
0.53
0.39
1.88
2.54
Fe
Distr.
4.9
58.0
25.9
11.2
45.9
15.9
19.8
18.4
1.9
17.4
80.7
0.4
7.3
54.7
37.6
Mg
Distr,
0.088
0.035
0.322
1.8
15.5
82.7
-------
American Cyanamid Matrix, Haynsworth Mine
The sample from American Cyanamid originated from the
southwestern location of the phosphate field and repre-
sented the newer mining areas toward Manatee County.
This matrix had a more typical distribution of apatite,
sand, and clay. It had a high pebble content, which
contained an iron impurity in solid solution. The sand,
fraction was present in rather coarse form. Most of
the clay was a mixture of montmorillonite, attapulgite,
and kaolin.
IMC Matrix, Clear Springs Mine
The matrix from IMC was quite similar to the USSAC
sample, except for weathering. The Clear Springs Mine
is located in the lateritic weathering belt, and con-
sequently about half of the pebble showed strong weather-
ing. Similar to the USSAC matrix, the clay fraction
consisted almost exclusively of montmorillonite, and
constituted about one-third of the matrix. The sand
fraction contained both coarse and fine sand.
Mobil Matrix, Ft. Meade
Mobil's mine is located near the southeastern end of
the lateritic weathering belt. The weathering is mainly
evident in the flotation feed fraction. Since the
sample contained fQ% clay, it cannot be considered a
representative matrix sample. The Mobil matrix was
evaluated mainly because it contained primarily attapul-
gite clay and therefore gave an indication of the cal-
cination performance of attapulgite.
- 22 -
-------
SECTION V
MATRIX UPGRADING METHODS
Any removal of nonphosphate matrix components prior to
the calcination step improves the process economics by
reducing fuel requirements. In the case of clay removal,
an additional benefit of eliminating some of the iron
and aluminum can also be realized. Preparatory mea-
sures to apply any upgrading treatment included drying
of the matrix to less than 3% moisture and crushing to
3/16 in.
CLAY SEPARATION
i
The removal of clay from the predried matrix was most
efficiently accomplanished by air classification. This
method floats the lighter clay particles from the phos-
phate and sand fractions of the matrix. Consequently,
the preparatory treatment such as drying and particle
size reduction is very crucial for the success of the
operation.
The apparatus used for the air classification study
consisted of a cylindrical fluidization chamber
(4x24 in.) supplied with 40-50 ftVmin of air through
a perforated disc at the bottom. The temperature of
the air was controlled by an electric heater.
Unground matrix was treated in 14 runs. Only 15 min-
utes were required per run to remove all fines from
the samples. However, the clay removal did not exceed
24$ of the total clay present in the sample.
- 23 -
-------
Grinding of the matrix improved the clay removal sub-
stantially, but the run time during air classification
had to be doubled to remove all fines. Chemical com-
positions of the air-classified clay fractions are
listed in Table 8.
TABLE 8
CHEMICAL COMPOSITION OP CLAY FRACTIONS
*
(ATC 320-23)
Concentration, % Clay
P20S Fe Al Mg Removal,
Clay, Unground Matrix 7.18 1.24 5.26 0.99 24
Clay, Ground Matrix 10.32 1.14 4.90 0.77 96
Matrix Sample 9.67 1.19 2.25 0.40
The particle size reduction was tested with an impactor
(6-in. hammer mill without screens) at 2000 and 4000
rpm and with a ball mill (6x8 in.) charged with ceramic
cylinders, operated at 65 rpm, which approached
critical speed. Results are tabulated in Tables 9
and 10 (Appendix A). Loading variation of the ball
mill had little effect on the grinding and air classifi-
cation performance as evident from data of Table 11
(Appendix A). A comparison of impactor versus ball
mill grinding is listed in Table 12 (Appendix A).
A third variation was tested by use of a 24-inch drum
tumbler. It was operated without load (balls or
cylinders) at the same percent of critical speed as
the ceramics ball mill. Three runs of 45 minutes
each, followed by the standard air classification
treatment, achieved approximately 68$ removal of the
dust fraction (-150 mesh).
- 24 -
-------
SAND SEPARATION
Samples for studies of sand separation by electrostatic
means were predried to approximately 10% moisture,
crushed in an impactor at 2000 rpm, and dried to 0.5-3%
moisture in a fluidized bed at 65°C. Each sample was
then given a two-stage light grind in the ball mill
followed by dedusting in a fluidized bed to remove
80-90$ of the dust fraction (-150 mesh).
All experiments were carried out with a UNIVERSAL
ELECTROSTATIC SEPARATOR Model 1700. Test conditions
and results are listed in Tables 13 and 14 (Appendix
A). In the operation of the electrostatic separation,
the middling and tail fractions were passed through
the separator three times. A concentrate fraction
was collected on each pass, and the three concen-
trates combined. The water-washed matrix samples
were run for comparison purposes.
Additional electrostatic separation tests were per-
formed at the Mineral Resources Research Center of
the University of Minnesota. A free-fall separator
was used consisting of a pair of parallel plate
electrodes, one foot wide and three feet long,
separated by 7 in», with a potential difference of
60,000 volts.
For all tests, the sample to be tested was held in
an oven until it reached 105°C. It was delivered
by a SYNTRON feeder and passed through a plastic
chute mounted midway between the electrodes at a
- 25 -
-------
rate of about 0.2 ton per hour distributed over the
one-foot width of the electrodes. The products
were collected in a series of one-inch-wide product
pans numbered from 1 (negative electrode) to 12
(positive electrode). The pans were positioned 5
inches below the lower edge of the electrodes, with
the divider between pans 6 and 7 midway between the
two electrodes. After examining the products of the
first three tests, the samples were grouped in the
following manner;
Phosphate Concentrate .' Pan 1-3
Middling 1 : Pan 4-5
Middling 2 : Pan 6-8
Quartz Tailing : Pan 9-12
Analytical results and percent metals distribution
of the Minnesota tests are reported in Table 15
(Appendix A). The only variable in the four tests
was the method of scrubbing. In test A the sample
was used as received, in test B the sample was Jigged
over a screen, in test C it was subjected to shear
scrubbing, and in test E to attrition scrubbing.
- 26 -
-------
SECTION VI
CALCINATION AND DIGESTION STUDIES
Matrix samples for the calcination and digestion study
were obtained by withdrawing a 10-kg portion of the
predried stock matrix from a drum blender while rotat-
ing. After riffling into two 5-kg samples, one portion
was ground to -100 mesh and the other subdivided into
200 to 300-g portions by additional riffling.
CALCINATION PROCEDURE
All calcinations were carried out in a THERMOLYNE
furnace, Model F-A1520M. The charge temperature was
measured by a thermocouple immersed in the sample,
which indicated a temperature Constance of +_ 5°C, as
monitored by a continuous recorder.
In the standard procedure for calcination of matrix,
approximately 150-200 g of the sample was placed in the
preheated furnace in a Vycor dish. Warmup of the sample
to the specified temperature required 20-30 minutes.
The listed calcination times do not include this warm-
up period. After completion of heating, the sample
was removed from the hot furnace, allowed to cool to
ambient temperature, ground if necessary, and screened
before the subsequent digestion in acid.
DIGESTION PROCEDURE
The digestion of the calcined matrix with sulfuric
acid was performed in a 1-liter cylindrical poly-
propylene reactor equipped with four vertical 3/8-in.
baffles, spaced equally around the wall. Agitation
- 27 -
-------
was provided by a stainless-steel stirrer with a blade
length of three-fourths of the reactor diameter. The
rate of agitation was adjusted to the minimum required
to keep the solids suspended. A lid with appropriate
cutouts for the stirrer shaft, and for the rock and
acid additions was installed to minimize evaporation.
Control of temperature was achieved by a thermostat-
regulated water bath in which the reactor was immersed.
In a typical digestion experiment, a pool of 30% P209
chemically pure phosphoric acid (150 g) was heated
in the reactor to 75-85°C. Matrix (150-200 g) and
hot (75°C) sulfuric acid (25% H2SCU) were added con-
tinuously over a period of approximately 60 minutes.
Every 10 minutes a 2-ml sample was withdrawn to
determine free sulfuric acid concentration. Lengthen-
ing or shortening of the reactant addition time
decreased or increased the free sulfuric acid in the
reactor slurry. After all reactants were added, the
digestion mixture was cured for 15 or 60 minutes while
maintaining temperature and agitation. Water was added
very slowly to compensate for loss by evaporation.
The hot slurry was then filtered through a polypropylene
test leaf of 0.1 ft2 filter area and washed with three
100-ml portions of water. Filtration rates were deter-
mined at 15 in. vacuum.
Major process parameters for the combined calcination-
digestion study were established in a preliminary
screening experiment where a total of seven variables
where evaluated for their dominance in the over-all
process. Each variable was tested at two levels as
shown below.
-------
Variable Level
. Temperature, °C 980 1095
Calcination (2. Time, minute 20 60
. Particle Size, mesh -100 -6
. Temperature, °C 65 85
. Cure Time, minute 15 60
. Acid Strength, % SO* 1.5 4.0
7. Particle Size, mesh -100 -20
Digestion
These variables were studied at two levels according
to a fractional factorial design using a one-eighth
replicate of the 27 factorial3. The design required
sixteen experiments, which were run with the USSAC
matrix using the previously described standard cal-
cination and digestion procedures.
Experimental conditions and results of the study are
listed in Table 16. Table 17 shows the same results
expressed on a P209-to-metals ratio basis. As evident
from the data, the main variables of the process were
calcination temperature, particle size in calcination
and digestion, and acid strength in digestion. This
conclusion was based on statistical evaluation (t-Test)
of the experimental data. Table 18 summarizes the
response of the P205 and metal solubilities according
to the specific variables. The numbers in parentheses,
giving the statistical confidence level, indicate
whether respective pairs of averages are truly dif-
ferent .
Subsequent work in the calcination-digestion study
was carried out over a. temperature range of 700-1100°C,
at a fixed particle size of -100 mesh for both cal-
cination and digestion, and at an acid strength of
2.5$ S04 during digestion.
- 29 -
-------
TABLE 16
U)
o
Experiment
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
CONDITIONS OF CALCINATION - DIGESTION STUDY
(ATC 324-10-1)
Experimental Conditions
Calcination
Particle
Size, Mesh
-6
-6
-100
-6
-6
-100
-100
-100
-100
-100
-100
-6
-100
-6
-6
-6
Time,
Mln
20
60
20
20
60
60
20
20
60
60
20
20
60
60
20
60
Temp . ,
°C
1095
980
1095
980
1095
1095
1095
980
1095
980
980
980
980
1095
1095
980
Particle
Size, Mesh
-100
-100
-100
-100
-100
-20
-20
-20
-100
-20
-100
-20
-100
-20
-20
-20
Digestion
Sulfate
%
4.0
1.5
1.5
4.0
1.5
1.5
4.0
4.0
4.0
1.5
1.5
1.5
4.0
4.0
1.5
4.0
Temp . ,
°C
65
65
85
85
85
65
85
65
65
85
65
85
85
85
65
65
Cure Time,
Min
15
60
60
60
15
15
15
60
60
60
15
15
15
60
60
15
-------
TABLE 1?
RESULTS OF CALCINATION - DIGESTION STUDY
(ATC 324-10-1)
Experiment
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Extraction Performance, % of Total
paos
94.6
95.9
93.1
87.2
97.2
78.0
73.7
76.9
89.9
85.5
78.6
79.3
76.2
51.0
44.2
32.4
Fe
20.0
46.4
38.8
42.6
25.2
12.1
16.3
18.7
18.0
24.6
25.3
13.1
22.8
13.5
15.5
7.3
Al
42.7
32.2
57.0
36.1
44.4
43.9
41.4
36.1
58.5
40.2
36.7
20.1
1 37.2
38.6
38.5
23.9
41.4
41.1
51.8
39.3
45.5
57.1
45.5
30.0
47.7
32.5
28.9
16.4
33.9
26.6
26.6
16.4
Weight
PaOs/Fe
37.9
28.7
19.6
16.7
31-3
53.5
36.7
33-3
41.1
28.1
25.4
48.3
27.2
31.1
26.7
35.5
Ratio Extracted
PaOs/Al
9.5
12.8
7.0
10.4
9.4
7.6
7.7
9.2
6.6
9.1
9.2
16.9
8.8
5.7
4.9
5.8
PaOs/Mg
48.6
92.8
43.7
53-1
51.5
32.9
39.1
55.0
39.9
52.1
58.8
100.2
54.5
39.9
34.6
40.9
- 31 -
-------
TABLE 18
SUMMARY OP VARIABLE RESPONSE1
Average Extraction, % of Total
P203
E3 <«
75*8 (60)
7?'.7 (55)
sgii (99>5)
81-5 (Qc)
72.7 l w
73.8 ,70,
80.4 170;
78.'o (55)
Pe
23-0 ,„)
22.1 OD;
Ilii (65)
19:9 (80)
•^ * / QQ C \
O/> o \ ^> * *s /
29.9
OK 1
Wig <85)
g:| «,
z?:l »5'
Al
qlj <:
fQ7 R^
4o!o (60)
Hs'.i (99<5)
35-3 ^Qii\
43.1 ^9H;
39.1
39-3
39.1
39-4
42ii (88)
J3S_
01 7
(9^)
S:J ««
42*.8 (98)
41 '.2 (95)
Sii (65)
36.2
36.4 ~
35.6 m
36.9 w;
Particle Size:
-6 mesh
-100
Calcination Time:
20 min.
60 min.
Calcination Temperature:
980°C
1100°C
Digestion Particle Size:
-20 mesh
-100 mesh
Sulfate Concentration:
1.5%
4.0?
Digestion Temperature
65°C
85°C
Cure Time:
15 min.
60 min.
Averages listed for each category are statistically equal unless the confidence
level is 90% or greater. Statistical confidence limits are shown in parentheses.
-------
Most matrix samples and matrix components were checked
by differential thermal analysis (DTA) for specific
temperatures at which reactions or phase transformations
took place. A DELTATHERM Model 2000 was used for all
DTA work. Results are summarized in Table 19 (Appendix
A).
All calcination samples were prescreened for P205 and
metals solubilities by a hydrochloric acid digestion
to establish the general trend of solubility response.
An oxidizer such as hydrogen peroxide or nitric acid
was added to facilitate the digestion. Areas of
specific interest were then evaluated in detail by
the more time-consuming but more representative phos-
phoric-sulfuric acid method described above. Both
methods indicated the relative response of the
solubilities to the calcination treatment, as shown
in Figure 3, and therefore were useful to interpret
data. However, only the phosphoric-sulfuric acid
digestion is representative on an absolute level,
which is required for yield predictions, etc.
Initial calcination tests (Figures 4 and 5) scanning
the full temperature range from 700 to 1200°C estab-
lished that the low-clay fraction (+150 mesh) of the
matrix responded differently in the calcination
treatment as compared to the clay fraction (-150 mesh).
Also, sintering occured at temperatures above 1100°C.
Consequently, all subsequent studies were carried
out with the matrix separated into low-clay and clay
fractions as well as with the total matrix, and
the temperature was limited to 1100°C. Results of
these calcination experiments are summarized
- 33 -
-------
FIGURE 3
COMPARISON OF DIGESTION
.METHODS
HCL DIGESTION
DIGESTION
100
90
- Mg
£70
X
LU
60
LU
O
or
Es.o
40
30
20
10
I
I
I
100
90
80 S
700 800 900 1000 1100
800 900 1000
70
60
50
40
30
20
10
o
<
cr
X
LU
LU
O
a:
CALCINATION TEMPERATURE,
ATC 324-42
-------
100
FIGURE 4
METALS SOLUBILITY OF
LOW-CLAY FRACTION
a 90
o
Q 80
70
60
Q
ui
o
<
Of.
X
"J 50
UJ
o 40
UJ
30
20
10
j
700
800
900
1000
1100
1200
CALCINATION TEMPERATURE., °C
ATC 322-42
- 35 -
-------
FIGURE 5
METAL SOLUBILITY OF
OF CLAY FRACTION
CO
ai
CD
*-«
Q
o
a
LJ
a:
X
LJ
LJ
U
LJ
Q.
100
90
80
70
60
50
40
30
20
10
I
I
I
700 800 900 1000
CALCINATION TEMPERATURE, UC
1100
1200
ATC 321-26
-------
graphically in Figures 6-10 (Appendix B), using the
hydrochloric acid digestion method. Figures 11-15
(Appendix B) show the same experiments evaluated by
the phosphoric-sulfuric acid method.
A detailed evaluation of the time effect of the cal-
cination on the clay fraction (USSAC) covering a
range of 0.5 to 8 hours is presented in Figure 16.
A similar, though less detailed, study was made
with the clay fraction where the final calcination
temperature was approched stepwise. This test is
reported in Table 20 (Appendix A)„
Comparable studies with the complete matrix (USSAC)
were performed to confirm the applicability of the
results from the clay fraction to the total matrix.
The results are listed in Table 21 (Appendix A).
In each experiment, the matrix was heated in a
porcelain crucible to the indicated temperature at
a rate of 10°C per minute. Cooling to ambient pro-
ceeded at 3°C per minute.
Several calcination tests were performed with the
addition of so-called mineralizers which are cited
in the literature to either promote solid state
reactions or to lower the minimum temperature at
which these reactions proceed. The additives tested
in this study were magnesium oxide, lithium fluoride,
fluorspar (calcium fluoride), and phosphoric oxide.
These additives were premixed with the test samples
in a pulverizer prior to calcination at the In-
dicated concentration. After calcination, metals
solubilities were determined by the hydrochloric
- 37 -
-------
FIGURE 16
EFFECT OF CALCINATION TIME ON
METALS SOLUBILITY OF CLAY FRACTION
o
HI
*•*•
Q
o
x
Q
o
X
111
I-
UJ
O
D£
UU
Q.
40
30 _
20 _
IA1, 1000°C
, 1000°C
Fe, 1000°C
23456
CALCINATION TIME, HR
9 10
ATC 321-17
- 38 -
-------
acid method. The results in Table 22 include, in the
case of phosphoric oxide addition, the added phosphate
in the P203 column. However, the P205-to-metal ratios
were calculated excluding the added phosphate.
- 39 -
-------
TABLE 22
-Cr
O
CALCINATION OP
CLAY FRACTION AT 1000°C WITH MINERALIZERS
(ATC 321-20)
Calcination
Time, hr
2
1
2
4
8
2
2
2
2
2
2
Mineralizer,
Wt. %
% Extraction(HCl Digestion)
P20S
none
3.
3.
3.
3.
0.
2.
2.
5.
10.
17.
8$
8*
8*
8*
5%
0%
0%
4*
MgO
MgO
MgO
MgO
LiP
LiF
CaP2
CaP2
P205
P203
94.1
93.9
85.8
93.0
94. 61
97. 61
Al
73.0
67.6
64.4
66.8
67.2
77.8
61.3
78.5
93.7
100
100
Pe
41.9
41.9
36.9
38.8
36.6
55.6
61.5
51.8
65.6
61.1
75.3
Mg
63.7
77. 91
72. 91
72. 91
71. 71
80.2
88.7
74.4
84.1
94.8
97.0
P20s/Metal
Al
1.8
2.0
2.0
2.0
2.0
1.5
2.0
1.6
1.4
1.2"
l.l2
7
7
8
7
8
I
5
4
4
3
Weight Ratio
Pe
.0
.2
.1
.7
.1
.9
.4
.6
.5
.52
.92
Mg
11.0
2.71
2.81
2.81
2.91
7.7
7.0
8.8
8.0
6.72
6.92
10verall (includes P20B in clay plus P20S added)
2Net (includes only P205 from clay)
-------
SECTION VII
DISCUSSION OF RESULTS
The matrix samples used in this project were selected
to reflect the major types of phosphate deposits found
in the Florida Bone Valley formation. Variations in
this deposit involve mainly the different types of clay,
attapulgite, montmorillonite and kaolin, and weathering
of the pebble fraction. All these requirements were
met by the samples as evident from Table 6 (page 19).
Matrix Upgrading
From the beginning of the project it was apparent that
the removal of nonphosphate components from the matrix
prior to calcination was highly desirable for two rea-
sons. First, to minimize fuel costs of the calcination
and second, to eliminate some of the metal impurities
such as iron, aluminum, and magnesium.
Essentially all methods - other than wet scrubbing -
for separation of matrix components require a nearly
dry matrix. Due to the high water table found in the
Florida phosphate field, the matrix deposits contain
from 30 to 6Q% by weight water. Drainage of the water
from piled matrix is generally poor and depends mainly
on the degree of clay contamination. Most matrix sam-
ples do not drain to less than 205? on piling above
ground.
All matrix samples had to be dried to 3-5$ moisture
before separation tests could be performed. Mild
attrition prior to or combined with air classification
proved most effective in removing the major portion
-------
of clay from the matrix. The problem was really not
how much clay could be removed rather than to achieve
the removal at a minimum ,phosphate loss. This correla-
tion is evident from Table 8 (page 24) which lists the
composition of material separated by air classification
over a fluidized bed. The clay content can be judged
from the aluminum concentration. Accordingly, only
4.9$ of the matrix phosphate was lost when 20% of the
original clay content was removed using unground matrix.
When approximately 80$ of the clay was removed by grind-
ing the matrix prior to air classification, the phosphate
loss Increased to 27.'
Any successful method for the clay separation is highly
dependent on finding selective grinding treatment which
breaks up the clay particles and removes them from the
phosphate pebble without disintegrating phosphate
particles.
Of the series of grinding methods evaluated, namely,
disk grinding, Impact grinding, and tumbling In a
ball mill, the latter provided the most selective
disintegration. As evident from Table 12 (Appendix
A), at approximately equal clay removal (80$), the
phosphate loss upon air classification was 31.3$ with
impact crushing but only 18.3$ with tumbling. A two-
step treatment in which the matrix was slightly ground
by tumbling, dedusted by air classification, and the
whole process repeated once more, gave better results
than a more intensive one-step process.
- 42 -
-------
The clay removal for the purpose of reducing fuel cost
in the calcination is readily accomplished. However,
there are two other reasons for the clay separation
which require a better than 90% clay removal to be ef-
fective. One is the objective of improving the P205/A1
ratio of the matrix. Calculation of the P205/A1 ratio
as a function of clay removal indicates that a sub-
stantial improvement is realized only at a clay removal
exceeding 80$, as shown in Figure 17. The other reason
for attempting a clay removal of more than 90% is related
to the separation of sand by electrostatic methods.
The sand separation by dry methods is limited to electro-
static separation techniques. However, work at USS
Agri-Chemicals and at the Mineral Resources Research
Center at the University of Minnesota established that
the presence of small quantities of clay can be quite
detrimental to the efficiency of the process. Residual
clay coating of the phosphate particles interfered
with the development of different electrostatic charges
on the phosphate and sand particles.
When a vigorous wet scrubbing was applied to the test
matrix prior to electrostatic treatment, the inter-
ference was completely eliminated, as evident from
Tests A and C of Table 15 (Appendix A).
The problem of clay interference in the electrostatic
sand separation can be mininized or completely
eliminated by combining the drying and grinding steps.
Such a process was described by Joe D. Clary et al.
in U. S. patent 3,329,351. In this case, the wet
matrix was introduced into a vertical attrition
column positioned on top of a fluidized bed dryer.
-------
FIGURE 17
CALCULATION OF P2Os/AL RATIO
VERSUS CLAY REMOVAL
4=-
-fr
100
90
80
>
9 70
O
LU
O
o:
60
50
40
30
20
10
ASSUMPTIONS
Matrix contains 25% clay, 9.67% P20Sl
and 2.23% Al. P20S is equally dis-
tributed between clay and non-clay
fractions.
O 85% of Al is in clay.
A All of Al is in clay.
10 15 20 25
CALCULATED P205/AL WEIGHT RATIO
30
35
ATC 326-13
-------
A high-velocity air stream was recirculated through
the column which provided impact grinding by blowing
the matrix against an impinger plate and carrying
-1/4 in. material out through the top where it was
separated into dust (clay) and matrix in cyclones.
Sand contained in the phosphate fraction was success-
fully separated by electrostatic treatment.
Consultation with one of the engineers who operated
this process at the pilot-plant level (800 pounds per
hour) revealed that no problems with clay coating
were observed. Consequently, no additional effort
was made during the course of this project to over-
come the clay interference encountered at USS Agri-
Chemicals and at the Minnesota Mineral Resource
Research Center. It is most likely the combined
drying and grinding operation of the Clary process
which prevents the formation of clay coating.
Apparently, particle size reduction at the elevated
temperature in the presence of a high-velocity air
stream alleviates the problem.
Calcination and Digestion Performance
The major objective of this project was to achieve a
digestion of matrix which would produce a filtrable
gypsum slurry and to insolubilize the metals to yield
a phosphoric acid of acceptable purity level. The
present commercial phosphoric acid production was
selected as a reference. Current processes recover
about 65% of the total P205 value from the matrix
and yield an acid quality corresponding to the
following P20s-to-metal weight ratios before con-
centration or clarification of the acid.
-------
P20s/Fe = 40
P20S/A1 = 50
P205/Mg = 100
Expressing the metal solubilization relative to that
of P205 gives a more Informative number than absolute
solubility figures, since it is the ratio of P20S to
metal which actually determines the quality of the
acid. For this reason, most of the data in this re-
port representing metals solubility are expressed as
the P205-to-metal ratio as well as in concentration
percent.
The process performance in calcination and digestion
is subject to a large number of process variables.
Major process parameters were established in a series
of screening experiments, where a total of seven
variables were evaluated for their dominance in the
over-all process. As described in more detail in
Section VI, the estimated variables were studied at
two levels according to a fractional factorial design
using a one-eighth replicate of the 27 factorial3.
The results, as summarized in Table 18,revealed that
the major variables were calcination temperature,
particle size in calcination and digestion, and,to
a lesser degree, acid strength in the digestion. To
simplify and optimize the experimental work, all sub-
sequent tests were carried out at only one particle
size (-100 mesh), and at a fixed acid strength of
2.5% SCU~. The smaller particle size (-100 mesh)
was selected because of the improved P205 extraction.
- 46 -
-------
A comparison with Table 17 (page 31) shows that in the
screening experiments the stipulated P203/Pe ratio (>40)
was met in experiment Nos. 6, 9, and 12, and for PaOs/Mg
(>100) in experiment No. 2. The best P205/A1 ratio was
16.9 in experiment No. 2, which is far from the stipulated
value of 50.
From the results of the screening experiments it became
apparent that the greatest improvement in metals rejec-
tion would be necessary for aluminum. Consequently,
subsequent work was aimed mainly at identifying the
minerals containing aluminum and to characterize their
behavior during calcination and digestion.
The objective of obtaining well-filtering digestion
slurries was readily accomplished. All test slurries
filtered equally well or better than commercial process
gypsum slurries (350 GPH/ft2). Thus, no detailed eval-
uation of the influence of calcination parameters on
the filtration rate was made. The calcination treatment
apparently completely destroyed the tendency of clays
to swell and interfere in the filtration.
To identify the calcination response of different matrix
components, the matrix was separated into a -150 mesh
fraction, which consisted mainly of clay, and a +150
mesh fraction containing most of the phosphate. These
two fractions are referred to as the " clay" and the
11 low-clay" fractions.
-------
A full scan of the temperature response of these two
fractions by differential thermal analysis'* (DTA) indi-
cated reactions or phase transformations as listed in
Table 19 (Appendix A). As evident from the data, DTA
does not produce a specific pattern according to the
type of clay. Thermal changes up to 150°C are due to
surface water. The endotherm at 235-240°C represents
loss of water of hydration. Reactions or transforma-
tions affecting the acid solubility of iron, aluminum,
and magnesium occur at temperatures from 800 to 1200°C.
These do not follow a consistent pattern5, although
some trends can be recognized. Montmorillonite clay,
for example, gives an endotherm-exotherm combination
at 850°C. This so-called S curve is claimed in the
literature to be associated with the formation of
spinel (MgAl204). However, the curve for the total
matrix from which the montmorillonite clay originated
does not exhibit this pattern. No particular DTA peak
is associated with apatite. Similarly, wavellite
(4 A1PCU-2A1(OH)3-9H20) in the matrix (IMC) does not
show the same response as a sample of pure wavellite.
For these reasons, differential thermal analysis was
used in this work only to a limited degree.
Calcination tests with the USSAC matrix using the
low-clay and the clay fractions showed that the
practical temperature range can be limited to 800-
1100°C. As evident from Figures 4 and 5 (pages 35, 36),
no substantial decrease in acid solubility of iron,
aluminum, and magnesium occurred below 800°C.
- 48 -
-------
As a matter of fact, there was indication that the
solubility actually increased up to about 800°C.
Above 800°C a strong decrease was observed, reaching
a minimum at 875°C for the low-clay fraction and at
900°C for the clay fraction. Calcination tempera-
tures above 1100°C. caused sintering. Thus, cal-
cination tests were limited to 1100°C since it was
felt that a sintered charge posed unacceptable
economic penalties.
The effect of calcination time on the acid solubility
of iron, aluminum, and magnesium was evaluated in a
more detailed study. The results are presented in
Figure 16 (page 38). Accordingly, a calcination time
of 30 minutes is sufficient to achieve minimum metals
solubility. The curves for the 1000°C calcination
show a distinct minimum at 1 hour, after which the
solubility increases again. This response is probably
less a function of time, rather, it seems to be the
result of the temporary exposure of the samples to
800-900°C during warmup. Additional tests confirmed
that the minimum acid solubility produced by calcina-
tion at 875°C is not permanent. Reheating to above
875°C leads to increased solubility, as apparent from
data of Table 20 (Appendix A ) .
The phenomenon of reversible metals solubility dis-
credits the commonly claimed spinel formation as the
reason for a change of aluminum and magnesium solubility.
\
If spinel were the acid-insoluble aluminum and magnesium
compound formed during heating to 875°C, subsequent
exposure to higher temperatures would not affect its
acid solubility.
-------
Based on the above observations, the series of matrix
samples was calcined over a temperature range of 700-
1100°C, using the total matrix as well as the separated
low-clay and clay fractions. Calcination times were
one hour. Most samples (Figures 6-10, Appendix B)
followed the general pattern of a minimum solubility
around 875-1000°C. This trend was particularly con-
sistent in the clay fractions. All three types of
clay, montmorillonite, attapulgite, and kaolin
responded in the same manner. However, for unex-
plained reasons, the clay fraction of the USSAC matrix
(montmorillonite) showed the minimum solubility 100°C
lower than all others.
The low-clay fractions' gave a minimum only in two cases
(USSAC, IMC); the others exhibited a continuous decrease
in solubility with increasing temperature up to 1100°C.
It is possible that the minimum of the USSAC and IMC
samples was caused by the presence of some residual
clay.
The total matrix samples usually produced the additive
result of the low-clay and clay fractions, as would be
expected. One exception was the Borden matrix which
did not reflect the strong reduction in solubility
indicated by the separate clay and low-clay fractions.
Because of the difference in optimum temperatures for
the low-clay and the clay fractions, the best over-all
metal rejection was achieved when each fraction was
calcined Individually at the respective temperatures.
Subsequent digestion could then be performed with the
combined fractions. Another exception - this time in
- 50 -
-------
a positive way - was the aluminum response of the IMC
matrix. As evident from Figure 9 (Appendix B), the
aluminum solubility of the total matrix was lower than
the corresponding additive total of the low-clay and
clay fractions.
In summary, all three metals responded to the calcina-
tion treatment. At optimum conditions, iron, aluminum,
and magnesium solubilities were reduced to 30-60$ of
the total present. Depending on the type of mineral ir>
which the metal was present, either of three metals
could give the greatest reduction in solubility. Clay
fractions showed usually a greater response than the
low-clay fractions. Of the various types of clay, the
response decreased in the order montmorillontie, atta-
pulgite, kaolin. The poor response of allophane - an
amorphous form of montmorillonite - as in the case of
the American Cyanamid matrix (Figure 8, Appendix B)
may be due to the presence of wavellite.
The better response of the clay fractions as compared
to the low-clay fractions is most likely due to the
fact that clays contain a mixture of metal ions in
close proximity to silicate. And, the metal ions are
relatively mobile. Whereas, metals in the phosphate
form such a wavellite, geothite, etc., depend on
particle-particle interaction to form the acid-insoluble
compound. Consequently, higher temperatures are
necessary to provide the required mobility. This is
in agreement with the results showing that the low-
clay fractions give the better insolubilization the
higher the temperature.
- 51 -
-------
No positive identification of species representing the
acid-insoluble metal derivatives was made. Only mullite
(3Al203»2Si02) appeared as an X-ray active form6. Most
other acid-insoluble species formed at 875°C were X-ray
inactive. Crystalline phases appeared at 1000-1100°C,
but these were associated with an increase in solubility
and therefore could not represent the sought-after com-
pounds .
The calcination treatment caused volatilization and/or
decomposition of several matrix components. A typical
weight loss of the dry matrix ranged from 7 to 9%. The
volatilized compounds consisted of silicon tetrafluoride,
formed by the interaction of fluoroapatite with silicates
or quartz, and carbon dioxide resulting from the decom-
position of carbonates and from oxidation of organic
matter. Fluoride volatilization during calcination
amounted to 25% of the matrix fluoride at 980°C and 325?
at 1100°C. The evolution of fluoride occurred very
rapidly. It was usually completed within 10 minutes.
Attempts to improve the metals insolublization by addi-
tives were essentially futile. So-called mineral!zers7
and fluxes which promote solid-state reactions or lower
the temperature at which these reactions proceed gave
only marginal or no improvements at all. As listed
in Table 22 (page 40), magnesium oxide, lithium fluoride,
fluorspar (CaF2), and phosphoric oxide were tested.
There are indications that reducing agents might be
effective to decrease the solubility of iron.
- 52 -
-------
All preceding experimental results were obtained by
the use of a hydrochloric acid digestion, aided by the
addition of an oxidizer such as nitric acid or hydrogen
peroxide. This method was selected for the initial
scanning of the bulk of calcination samples in place
of the time-consuming phosphoric-sulfuric digestion
which gives a more representative indication of plant-
scale performance. A comparison of both methods
established the suitability of the hydrochloric acid
digestion as demonstrated in Figure 3 (page 3*0- Both
methods reflected the response to calcination relative
to the temperature dependence and therefore were use-
ful to interpret data. The only difference was in the
absolute level of solubility. Predictions relative to
yield have to be based on the phosphoric-sulfuric acid
digestion data presented in Figures 11-15 (Appendix B).
As a rule, the phosphoric-sulfuric acid digestion gives
a slightly better metals rejection than the hydrochloric
acid method. In particular, the solubility of iron is
often greatly reduced as in the case of the American
Cyanamid (Figure 13, Appendix B) and the IMC (Figure 14,
Appendix B) matrices.
Chemically pure phosphoric acid was used in these diges-
tions. Since the plant-scale process employs wet-process
acid, that is, acid containing iron, aluminum, and
magnesium, one might expect a better metals rejection
than with chemically pure acid. A brief test indicated
a marginal difference between the two acids, if any.
- 53 -
-------
Data of the preceding studies were expressed as percent
solubilizatlon of the total metals of the matrix or its
fraction. This unit is best suited to discuss the
calcination performance and follow the effect of process
parameters. The process performance with respect to acid
quality is better recognized in terms of P205-to-metals
ratio. Therefore, results of the calcination-digestion
experiments were also expressed in relation to the phos-
phate solubilization which is actually the true measure
of acid quality. Figures 18-22 (Appendix B) summarize
the finding for the hydrochloric acid digestion and
Figures 23-27 (Appendix B) for the phosphoric-sulfuric
acid digestion. It becomes immediately apparent that
despite the relatively good metals insolubllization, the
quality of the produced phosphoric acid is in most cases
short of the stipulated specifications. Although aluminum
gave, on a percentage basis, reduction in solubility
similar to that of iron and magnesium, on a P20s/metal
basis it is mainly aluminum which failed to reach the
goal. The reason for this is the relatively high
aluminum level of most matrix samples.
For example, in the case of the USSAC matrix, which
contained P205-to-metal ratios of 8.2, 4.3, and 24.2,
respectively, for iron, aluminum, and magnesium, the
necessary improvement factors to reach the stipulated
quality were 4.8 for'iron, 11.6 for aluminum, and 4.2
for magnesium. A similar situation existed for the
other matrix samples.
- 54 -
-------
A comparison of the total matrix versus low-clay frac-
tions revealed that the clay removal sometimes improved
the P20s-to-metal ratios (USSAC, Borden, Mobil) and
sometimes worsened them (P205/Pe in American Cyanamid,
IMC matrix). This is due to the different behavior of
metal-containing minerals on air classification. If
the clay separation removed a substantial portion of
those minerals which did not respond to calcination,
the PaOs-to-metal ratio of the remaining low-clay frac-
tion improved, and vice versa. The following summary
(Table 23) shows which fraction - low-clay or total
matrix - gave the best P20s-to-metal ratios, and at
what calcination temperature.
TABLE 23
OPTIMUM PERFORMANCE SUMMARY
P205-to-Mstal Ratio Calcination
Source
USSAC
BORDEN
AM. CYANAMID
IMC
MOBIL
Fraction
Low-Clay
Total Matrix
Low-Clay
Total Matrix
Low-Clay
Fe
18
143
51
79
24
Al
18
41
15
8
14
Mg
68
280
108
97
9
Temp. °C
900
900
1000
1000
1000
As evident from the data, the stipulated specifications
were met in three out of five cases for iron and mag-
nesium, and was approached in one case for aluminum.
- 55' -
-------
The matrix from the Mobil mine can not be considered
a typical phosphate matrix. As described in more detail
in SECTION IV, this sample was evaluated only because
it contained attapulgite clay. It is doubtful that this
matrix could be upgraded by any method, including wet
processing.
-------
SECTION VIII
REFERENCES
1. Brown, G., Ed., " X-ray Identification and Crystal
Structures of Clay Minerals" , Mineralogical Society,
London, 1961.
2. Black, C. A., et al, Ed., " Methods of Soil Analysis" ,
Part I, American Society of Agronomy, Madison, 1965-
3. Natrella, M. G., "Experimental Statistics" ,
Washington, United States Department of Commerce,
1963, PP 12/1-12/21.
A 27 factorial design consists of a series of experi-
ments which contains all the combinations of the seven
variables at the high and the low level.
4. Grim, R. E., "Clay Mineralogy" , McGraw-Hill, New
York, 1953.
5. Mdivnishvili, 0. M., Soobshch. Akad. Nauk Gruz. SSR,
No. 1, pp 67-71 (1972).
6. Krylov, G. M. and Nikonovich, G. V., Doklady Akad.
Nauk Uzbek. SSR, No. 10, pp. 31-3^ (I960).
7. Palmer, V. R., Anales Soc. Cient. Argentina, 152, pp
127-137 (1951).
- 57 -
-------
SECTION IX
GLOSSARY
Beneficiation - Upgrading of ore by removal of inert
material.
Flotation - Separation of ore and inert material in an
aqueous slurry.
Lateritic Weathering - Transformation of ore particles
on the surface only.
Matrix - Total ore body as mined from the deposit.
Middling - Middle fraction of a sample series.
Mineralizer - Additive which facilitates a solid-solid
reaction or lowers the minimum temperature at which the
reaction takes place.
Phosphate Concentrate - Phosphate ore enriched by separa-
tion of inerts.
Riffling - Method of splitting a sample into two or more
portions of equal composition by use of a mechanical device,
Slimes - Pine fraction (-150 mesh) from phosphate matrix
suspended in water.
Tailing - End fraction of beneficiation process. In the
case of phosphate ore, the tailing is mainly sand.
- 58 -
-------
SECTION X
APPENDICES
Page
A. Supplementary Tables 60
B. Supplementary Figures 71
C. Literature Search 92
- 59 -
-------
APPENDIX A
SUPPLEMENTARY TABLES
- 60 -
-------
TABLE 9
EFFECT
OF IMPACTOR RPM
ON MATRIX DISINTEGRATION
(ATC 322-39)
%
Treatment
Mode
Sample
" As Is"
Disintegrated
at 2000
RPM &
dedusted
Disintegrated
at 4000
RPM &
dedusted
Tyler
Mesh
+48
-48+100
-100+200
-200
+48
-48+100
-100+200
-200
Clay
+48
-48+100
-100+200
-200
Clay
PZ09
8.90
10.59
9.04
7.87
8.82
10.54
9.58
7.85
7.68
8.65
10.31
10.08
'8.95
8.90
Weight
40.05
40.59
13.25
6.11
38.09
40.96
13-53
0.70
6.72
20.46
47.84
11.00
0.32
20.38
P205
Distn.
37.47
44.85
12.63
5-05
35.20
45.25
13.60
0.52
5.43
18.34
51.09
11.50
0.31
18.76
Dedusting
Efficiency
39.54
82.48
- 61 -
-------
TABLE 10
15
30
45
TIME EFFECT OF
(ATC
Tyler
Mesh
+48
-48+100
•100+200
•200
+48
-48+100
•100+200
•200
+48
-48+100
•100+200
•200
CERAMIC
322-39)
Pa09
9.33
10.48
8^42
8.58
9.85
10.51
8.8?
8.42
9.90
10.19
10.56
8.82
TUMBLING
%
Weight
24.98
49.63
17.11
8.28
16.78
48.23
22.08
12.91
14.58
51.54
22.73
11.15
Pa09
Distn.
24.07
53.72
14.88
7.33
16.89
51.89
20.06
11.16
14.30
52.14
23.83
9.73
- 62 -
-------
TABLE 11
LOADING EFFECT OF CERAMIC TUMBLING
(ATC 322-39)
Charge, g
650
1500
2000
Tyler
Mesh
+48
-48+100
-100+200
-200
+48
-48+100
-100+200
-200
+48
-48+100
-100+200
-200
P209
10.08
10.47
8.54
8.73
9.90
10.19
10.56
8.82
10.03
10.63
8.70
8.69
Weight
16.17
51.08
21.27
11.48
14.58
51.54
22.73
11.15
21.81
52.41
17.61
8.17
P20;,
Distn.
16.63
54.60
18.57
10.20
14.30
52.14
23.83
9.73
21.90
55.70
15.30
7.10
- 63 -
-------
TABLE 12
COMPARISON OF IMPACTOR GRINDING VERSUS CERAMIC TUMBLING
(ATC 322-39)
Method
4000 RPM
Impactor
Tyler
Mesh
+48
-48+100
-100+200
-200
P209
7.57
9.65
10.76
10.08
Weight
12.36
15.16
12.47
29.92
P209
Dlstn.
9.74
45.13
13-87
31.26
Clay
Removal
^80
Ceramic
Tumbling,
2000 g
45 min
+48
-48+100
-100+200
-200
9.48
11.04
8.85
7.73
24.75
44.53
7.64
23-03
24.15
50.57
6.99
18.29
-------
TABLE 13
o\
ui
EXPERIMENTAL CONDITIONS OP ELECTROSTATIC SAND SEPARATION
Experiment No .
320-47-1
-7
-13
-15
-16
-18
-19
-20
-23
Electrode
Dielectric Rotary
Huff Rotary
Huff Rotary
Huff Rotary
Huff Rotary
Huff Rotary
Huff Rotary
Huff Rotary
Huff Rotary
Electrode
4:oo
3:00
1:00
1-.30
H30
1:30
3100
1:30
1:30
Position1
3.5
2.0
2.0
2.0
2.0
2.0
2.0
2.0
1.2
Voltage
20,000
20,000
22,000
22,000
22,000
22,000
2^,000
16,000
Peed
Roller
Dielectric
Dielectric
Brass
Brass
Brass
Brass
Brass
Brass
Brass
1 Listed as clock position and distance between electrodes in inches.
-------
TABLE
o\
ox
Experiment No,
320-47-4
-7
-13
-15
-16
-18
-19
-20
-23
SAND SEPARATION TESTS AT USS AGRI -CHEMICALS
Matrix x Pretreatment
Am. Cyanamid Washed
Am. Cyanamid Washed
Am. Cyanamid Washed
Am. Cyanamid Dedusted
Am. Cyanamid Dedusted
IMC Washed
IMC Washed
IMC Dedusted
IMC Dedusted
Cut
Tailings
Middling
Concentrate
T
M
C
T
M
C
T
C
T
C
T
C
T
M
C
T
C
T
C
Weight
22.0
72.0
6.0
23.8
61.2
15.0
27.2
45.4
27.4
57.6
47.7
52.3
40.0
60.0
9.4
40.9
49.7
46.9
53.1
56.2
43-8
Pa09
5.02
9.55
14.70
8.25
7.91
9.20
7.65
10.43
11.72
10.25
10.47
10.65
9.91
5.66
10.32
6.00
5.29
11.72
7.63
11.12
9.14
11.41
Distn.
12.4
77.7
9.9
24.0
59.2
16.8
20.7
47.3
32.0
57.1
42.9
49.5
50.5
26.7
73.3
6.6
25.3
68.1
37.8
62.2
50.7
49.3
-------
TABLE 15
SAND SEPARATION TESTS AT MINNESOTA RESOURCES RESEARCH CENTER
(ATC 320-40)
o\
—]
Weight
6.3
48.7
33.8
11.2
11.5
30.1
35.3
23.1
30.9
9.1
7.2
52.8
20.1
9.5
11.7
58.7
Pa0s
10.8
10.06
9.74
10.09
15.51
12.15
8.63
8.01
22.75
17.03
3.14
0.98
19.87
16.11
10.31
6.73
Distn.
6.80
49.00
32.90
11.30
17.23
35.33
29.53
17.91
75.43
16.63
2.42
5.55
37.36
14.33
11.33
36.99
Al
1.92
1.42
1.02
0.917
0.977
0.913
0.652
0.747
0.345
0.293
0.088
0.020
0.795
0.892
0.686
0.569
Al
Distn.
9.60
54.92
27.38
8.17
14.18
34.81
29.11
21.90
70.86
17.88
3.97
7.28
24.28
12.90
12.14
50.68
Fe
1.13
0.854
0.672
0.592
0.638
0.644
0.552
0.564
0.570
0.473
0.237
0.179
0.662
0.704
0.633
0.516
Fe
Distn.
9.10
53.33
29.10
8.46
12.33
32.77
32.94
21.96
53.17
12.99
5.14
28.70
23.05
11.61
12.82
52.51
0.429
0.323
0.232
0.200
0.224
0.221
0.166
0.204
0.159
0.120
0.028
0.013
0.179
0.217
0.172
0.139
Mg
Distn.
9.51
55.28
27.46
7.75
13.07
33.67
29.65
23.62
71.01
15.94
2.90
10.14
22.64
13.21
12.58
51.57
Fraction'
Ac
AM2
AT
Be
BMa
BT
Cc
CMi
CMa
CT
EC
EM!
EM2
ET
A = Sample tested as received
B = Sample was wet washed by Jigging over a screen
C = Sample was subjected to shear scrubbing
E - Sample was attrition scrubbed
c = Concentrate
Mi = Middlings
M2 = Middlings
T = Tailings
-------
TABI£ 19
DIFFERENTIAL THERMAL ANALYSIS OF MAIRIX SAMPUSS1
(ATC 328-21)
ON
CD
USSAC Clay
(montmorillonite )
USSAC Matrix
BC Clay
(montmorlllonlte, kaolin)
IMC Matrix
Borden Clay
(kaolin)
Mobil Clay
(attapulglte)
Mobil Clay + Apatite,
•^50:50
American Cyanandd Clay
(allcphane, wavelllte)
Wavellite, fron
Montgcraery Co., Ark/
115- 135- 150- 170- 235- 330- 535- 850- 870-
120 140 155 180 2^0 3*K) 500 51*0 575 JJO 810 860 880 930 960 1100
+
(S-curve)
+ - +
(S-curve)
1 - * Bidothennic
+ = Exothermic
-------
TABLE 20
a\
vo
CALCINATION OP CLAY FRACTION AT TWO CONSECUTIVE TEMPERATURES
(ATC 321, p. 23)
Calcination
Time, hr
1
1
1
1
1
1
1
1
Temp . ,
°C
875
715
875
715
1000
875
1000
1000
% Extraction(HCL-HN03 Digest.)
P205
-
83.0
90.8
91.1
93.0
Al
30.4
30.3
66.0
65.2
70.3
Pe
11.9
11.1
32.0
31.9
35.9
Mg
14.6
14.6
54.6
52.4
57.3
P205/Metal Weight Ratio
Al
3.8
3.8
1.9
2.0
1.9
Pe
22.0
24.0
9.0
9.1
8.2
41.0
41.0
12.0
13-0
12.0
-------
TABLE 21
CALCINATION OP MATRIX AT TWO
CONSECUTIVE
TEMPERATURES
(ATC 328-17, 18)
Calcination
Time, hr.
Uncalcined
1/2
1 1
o 2
1 1/2
1
2
4
1
1
1
1
1
1
Temp . ,
°C
Matrix
875
875
875
1000
1000
1000
1000
715
875
715
1000
875
1000
% Extraction (HC1
Al
93.7
42.0
40.9
40.2
60.8
77.0
89.9
91.4
38.8
77.0
64.1
Pe
103.0
59.3
55.8
56.2
71.1
80.9
90.0
87.6
56.0
82.2
76.0
Digestion)
Mg
97.5
• 40.0
39.0
37.7
51.0
70.2
84.9
87.2
39.2
72.8
55.9
P20S
Al
4.6
11.7
12.1
12.3
8.1
6.4
5-5
5.4
12.7
6.4
7.7
/Metal Weight
Pe
8.0
14.4
15.3
15.2
12.0
10.5
9.5
9.7
15.2
10.4
11.2
Ratio1
Mg
24.7
66.0
67.8
70.1
51.8
37.6
31.1
30.3
67.3
36.3
47.3
P205 extraction assumed in all cases.
-------
APPENDIX B
SUPPLEMENTARY FIGURES
- 71 -
-------
FIGURE 6
HYDROCHLORIC ACID DIGESTION
US&AC MA111X
-4
f\J
3 lot
~
H
-J . 90
X)
D:
x
UJ
LU
O
cr
SOL
70
60l_
50
40
30
TOTAL MATRIX
FRACTION
_L
I
I
J
I
700 800 900 1000 1100
700 800 900 1000 1100
CALCINATION TEMPERATURE, °C
.CLAY FRACTION
(Montmorillonite)
J
700 800
900 1000 1100
ATC 321-49
-------
FIGURE 7
HYDROCHLORIC ACID DIGESTION
OF BORDEN MATRIX
TOTAL MATRIX
LOW-CLAY FRACTION
CLAY FRACTION
(Kaolin)
I
uo
I
V)
UJ
CD
1—4
Q
_J
O
X
^*
2
o
<
oc
X
at
UJ
o
cc.
UJ
o.
100
90
80
70
60
50
40
Fe
30
I
700 800 900 1000 1100
I
I
I
J
700 800 900 1000 1100
CALCINATION TEMPERATURE,
I
j_
j
700 800
900 1000 1100
ATC 321-49
-------
FIGURE 8
HYDROCHLORIC ACID DIGESTION
OF AMERICAN CYANAMID MATRIX
UJ
I!)
O
s
OL
X
oc
li!
O-
90
80
70
60
50
40
30
TOTAL MATRIX
LOW-CLAY FRACTION
700 800 900 1000 1100
700 800 900 1000 1100
CALCINATION TEMPERATURE,, °C
CLAY FRACTION
(Allophane, Wavellite)
I
I
_L
700 800
900 1000 1100
ATC 321-49
-------
FIGURE 9
HYDROCHLORIC ACID DIGESTION
OF IMC MATRIX
VJI
I
CO
111
a
_i
x
a
5
cc
01
100
90
80
70
60
01
£ 50
LU
40
30
TOTAL MATRIX
LOW-CLAY FRACTION
Fe
DAI
I
I
I
J_
J
I
I
700 800 900 1000 1100
700 800 900 1000 1100
CALCINATION TEMPERATURE, °C
CLAY FRACTION
(Montmorillonite, Kaolin)
L
_L
I
I
700 800 900 1000 1100
ATC 321-49
-------
FIGURE 10
HYDROCHLORIC ACID DIGESTION
OF MOBIL MATRIX
I
a\
fe 10°
UJ
O
Q 90
o
a
X
LU
LU
O
0£
UJ
Q.
80
70
60
50
40
30
TOTAL MATRIX
LOW-CLAY FRACTION
I
I
L
I
I
I
I
700 800 900 1000 1100
700 800 900 1000 1100
CALCINATION TEMPERATURE., °C
CLAY FRACTION
(Attapulgite)
I
j_
_L
700 800
900 1000 1100
ATC 321-49
-------
FIGURE 11
PHOSPHORIC-SULFUR 1C ACID
DIGESTION OF USSAC MATRIX
TOTAL MATRIX
LOW-CLAY FRACTION
100
90
e> 80
o
O
tn
o
Q.
a
LJ
§
ce:
X
UJ
UJ
o
a:
UJ
a.
70
60
50
40
Fe
30
20 _
800
900
1000 1100
800
CALCINATION TEMPERATURE, °C
900 1000 1100
ATC 324-40
- 77 -
-------
30
20
FIGURE 12
PHOSPHORIC-SULFUR1C ACID
DIGESTION OF BORDEN MATRIX
TOTAL MATRIX
LOW-CLAY FRACTION
100
90
-------
FIGURE 13
PHOSPHORIC-SULFURIC ACID DIGESTION
OF AMERICAN CYANAMID MATRIX
TOTAL MATRIX
LOW-CLAY FRACTION
100
90
I-
tn
o
-------
FIGURE 14
PHOSPHORIC-SULFUR1C ACID
DIGESTION OF IMC MATRIX
TOTAL MATRIX
LOW-CLAY FRACTION
100.
^ 90
V)
UJ
2 80
o
CO
CM
70
O
a.
ro
Q
UJ
l-
u
cc.
X
UJ
60
50
UJ
o
a: 40
in t\i
a.
30
20
J
800
900
1000
1100
800
900
CALCINATION TEMPERATURE, °C
1000 1100
ATC 324-46
- 80 -
-------
FIGURE 15
PHOSPHORIC-SULFURIC ACID
DIGESTION OF MOBIL MATRIX
TOTAL MATRIX
LOW-CLAY FRACTION
100
90
tO
UJ
2 80
Q
O
to
2
m
X
a
UJ
70
60
2 50
I-
UJ
o
ui 40
Q_
30
20
800
Fe
900
1000
1100
800
900
CALCINATION TEMPERATURE, C
1000 1100
ATC 324-48
- 81 -
-------
FIGURE 18
P205/METAL RATIOS OF
USSAC MATRIX
TOTAL MATRIX
LOW-CLAY FRACTION
oo
ro
o
- 50
V)
UJ
1C
x 40
v^ ^u
Q
Ul
H 35
^
25
UJ
15
in
O
CM
Q. 5
0 -
CLAY FRACTION
(Montmori1lonite)
Al
J I
L
J_
I
J
700 800 900 1000 1100
700 800 900 100-0 1100
CALCINATION TEMPERATURE, °C
200
L80
L60
L40
L20
.00
80
60
40
20
0
0
i-
V)
UJ
o
Q
_J
O
a:
0
Ul
EXTRAC1
0
P
H-
C9
UJ
_J
Ul
•»>.
in
O
CM
Q.
700 800 900 1000
1100
ATC 321-49
-------
FIGURE 19
P205/METAL RATIOS OF
BQRDEN MATRIX
oo
U)
S 50
CO
in
245
£40
35
X 30
LU
25
CD
*•*
LU
20
15
LLJ
10
in
O
TOTAL MATRIX
700 800 900 1000 1100
LOW-CLAY FRACTION
700 800 900 1000 1100
CALCINATION TEMPERATURE., °C
CLAY FRACTION
Y_ FRACTH
(Kaolin)
200 «
CO
LU
180 2
Q
160 i
s^
140 2
u
oc
120 x
LU
o
100 H
<
GC.
80
60
40
20
700 800 900
CD
»«i
LU
LU
in
O
1000 1100
Alt 321-49
-------
FIGURE 20
P205/METAL RATIOS OF
AMERICAN CYANAMID MATRIX
oo
-t=-
CO
UJ
050
045
Q
UJ40
u
<
£35
S 30
25
<
cc.
to
•-*
UJ
20
15
m
Q.
I
TOTAL MATRIX
LOW-CLAY FRACTION
J
700 800 900 1000 1100
700 800 900 1000 1100
CALCINATION TEMPERATURE, °C
CLAY FRACTION
(Allophane, Wavellite)
I
I
I
I
CO
LU
Cfl
200
180
160 S
140
100
80
x
UJ
120 2
X
(£>
»—«
UJ
3:
in
O
60 uj
40
20
700 800 900 1000 1100
ATC 321-49
-------
FIGURE 21
RATIOS OF
IMC MATRIX
oo
VJl
tn
ui
ID
Q
UJ
5
QC
50
45
40
"
GJ 30
o
£ 25
20
ui
£
UI
15
10
i
i
°- 5
in
O
TOTAL MATRIX
LOW-CLAY FRACTION
Mg
3A1
I
I
_L
I
I
I
J
700 800 900 1000 1100
700 800 900 1000 1100
CALCINATION TEMPERATURE, °C
CLAY FRACTION
(Montmorillonite, Kaolin)
200
180
160
140
120
100
80
60
40
20
o
X
a
ui
(£
X
<
a:
ui
ui
^
in
O
700 800 900 1000 1100
ATC' 321-49
-------
FIGURE 22
P2Os/METAL RATIOS OF
MQBIL MATRfX
oo
CT\
o
50 _
to
LU
CD
545
_J
O
5 40l_
Q
UJ
t 35
a:
ul 30
o
£25
LLI
in
O
CM
a.
20
15
10
5
0
TOTAL MATRIX
LOW-CLAY FRACTION
l
j_
j
j
700 800 900 1000 1100
700 800 900 1000 1100
CALCINATION TEMPERATURE, °C
CLAY FRACTION
(Attapulgite)
j_
_L
l
50
20
15
10
_ 0
700 800 900 1000 1100
z
o
UJ
<£>
45 5
_i
40 3
s
35 s
a:
\-
30 2
O
25 £
cr
i-
i
H-*
UJ
in
O
CM
o.
-------
FIGURE 23
P205/METAL RATIOS OF
USSAC MATRIX
TOTAL MATRIX
LOW-CLAY FRACTION
w 150
LU
<3
o 140
co 130
ts
I
"^120
o
^110
g 100
o
< 90
^
UJ 80
70
60
50
40
CO
<
LU
O
CM
a- 20
10 .
§
RAW
-*f-
800 900 1000
I // 1 _l 1
RAW 800 900 1000
. 150 w
LLJ
IE
. 140 5
. 130 %
x
. 120 ^
o
. HO -£*
. 100 Q
t-
o
_ 90 <
H-
80 "J
o
»—*
70 t
60 H
50 |
40 <
LLJ
. 30
in
O
rg
. 20 cT
_ 10
CALCINATION TEMPERATURE, °C
ATC 324-40
- 87 -
-------
FIGURE 24
P2Os/METAL RATIOS OF
BQRDEN MATRIX
TOTAL MATRIX
140L
in
V)
2 lid
o
tu
I-
o
tu
10C_
90
80
« 70.
H
^ 60.
I 50
LU
in
401
20U
10
LOW-CLAY FRACTION
-ss-
o
300 p
CO
LU
280 £
n
260
O
CO
240
220 g
200
180
160
^^
a.
I
Q
HI
U
cc
X
UJ
140 2
<
120 K
l-
100 2
111
3:
80 _,
£
60 £
•—
m
40 OM
a.
20
RAW
800 900 1000 1100 RAW 800 900 1000 1100
CALCINATION TEMPERATURE,, °C
ATC 322-44
-------
FIGURE 25
RATIOS OF
AMERICAN CYANAMID MATRIX
TOTAL MATRIX
LOW-CLAY FRACTION
o 150
k-4
C/>
g 140
i-*
a
*, 130
120
o* 110
o.
•5 100
UJ
o
I
(S
»—»
LU
90
80
70
60
50
40
30
20
10
Fe
O
0
150
o
C/3
140 g
130
120
110
100
90
80
70
60
50
40
30
20
10
o
co
o
O-
UJ
o
a.
UJ
o
UJ
UJ
in
O
CM
a.
RAW
i T.T + * o n
800 900 1000 1100 RAW
800 900 1000 1100
CALCINATION TEMPERATURE, C
- 89 -
324-43
-------
FIGURE 26
P205/METAL RATIOS OF
IMC MATRTV
fc150
in
(D
5140
gf130
(N
o
x
Q 100
111
o
90 .
Lu 80
<
a:
70
60 .
to
2 50
UJ
in
o
40
30
20 .
10 .
TOTAL MATRIX
-OW-CLAY FRACTION
A
Pe
0
O
j i
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
V)
tu
(S
o
CM
O
a.
o
DC
LU
O
LU
in
O
CM
a.
RAW
800 900 1000 1100 RAW
800 900 1000 1100
CALCINATION TEMPERATURE, °C
ATC 324-46
- 90 -
-------
2 150
Ul
140
^120
gTllO
CO
X
o
LU
UJ
2
u.
IS
^^
LU
3:
I
ID
80
70
60
50
40
30
20
10
FIGURE 27
P205/METAL RATIOS OF
MOBIL MATRIX
TOTAL MATRIX
LOW-CLAY FRACTION
-5 f-
RAW
800 900 1000 1100
•f-
150
140
130
120
110
100
90
80
70
60
50
40
30
20
10
RAW
800 900 1000 1100
CALCINATION TEMPERATURE;
LU
CD
O
CO
o
a.
O
a:
X
LU
O
in
O
eg
a.
ATC 324-48
- 91 -
-------
APPENDIX C
LITERATURE SEARCH
INTRODUCTION
SUMMARY 95
1. Rock Phosphate, Apatite, and Tricalciuni Phosphate 95
2. Clay Minerals and Clays 97
3. Aluminum Phosphate Minerals and Aluminum Phosphates 108
k. Aluminum Silicate Minerals and Aluminum Silicates 109
5. Aluminum Oxide 109
6. Iron Oxide Minerals and Iron Oxides 109
7. Iron Phosphate Minerals and Iron Phosphates 110
8. Magnesium Carbonate Minerals and Magnesium Oxide 110
9. Magnesium Silicate Minerals 112
10. Magnesium Phosphates 113
11. Binary and Ternary Systems of A1203, Fe203, MgO and Si02 113
12. Acid-Resistant Ceramics, Cements, and Enamels 114
BIBLIOGRAPHY 115
- 92 -
-------
INTRODUCTION
This report contains 'the materials from a literature survey of Chemical
Abstracts, covering Volumes 1)1-77 (19^7-1972), for data relating to the
EPA matrix process.
It was noted during the early stage of this work that very little
information is available in the literature under the heading of "rock
phosphate" which can be considered directly applicable to the proposed
matrix process. Since, in general, Florida phosphate rock contains
aluminum, iron, and magnesium minerals as the detrimental contaminants,
these minerals, as well as many related materials listed below, were
used as the key words in the reference scanning.
Actinolite CaO3(Mg,Fe)oUSi02
Aluminum Metaphosphate Al(P03)3
Aluminum Oxide A1203
Aluminum Phosphates
Aluminum Silicates
Ankerite 2CaC03-MgC03.FeC03
Apatite 3Ca3(P04)2«Ca(F,Cl)2
Apophyllite -- - — K20.8CaO. l6Si02«F- 16H20
Barbosalite Fe(ll)Fe( IIl)2(P04)2(OH)2
Ceramics
Corundum
-------
Iron Silicates
Kaolinite -------------------------- . Al203'2Si02»2H20
Limonite --------------------------- Fe203«3H20
Magnesite -------------------------- MgC03
Magnesium Oxide -------------------- MgO
Magnesium Silicates
Millisite -------------------------- 2CaO.Na2O6Al203'^P205. 17H20
Montmorillonite -------------------- (Mg,Ca)0- A1203« 5Si02-nH20
Mullite ---------------------- ...... 3Al203-2Si02
Phosphate Rock
Phosphoric Acid
Phosphorite
Staurolite ------------------------- 2FeO- 5Al203'HSi02«H20
Tremolite -------------------------- 2CaO- 5MgO- 8Si02«H20
Turgite ---------------------------- Hydrous Eerric Oxide
Vivianite -------------------------- Fe3( P04)2-8H20
Wavellite --------- ..... ----- .......
Special attention was paid to their high- temperature chemistry, struc-
tural changes, formation of new phases, and changes in acid solubility
of the metal impurities versus temperature of calcination.
Copies of abstracts from about 600 references were obtained initially,
and 277 of them were selected for this report during the final
screening. The selected abstracts were then edited, shortened, and
grouped into a report form to meet our particular needs.
- 94 -
-------
SUMMARY
Specific trends and results of the literature references are summarized
in this section according to certain aspects which are of particular
interest to the matrix process. Numbers in parentheses denote the re-
ference as listed in the bibliography section.
1. Rock Phosphate, Apatite, and Tricalcium Phosphate
a. Fertilizer fromJ|igh-Al Phosphate Ores
Leached-zone ore, containing about 15 PgOsj 10 A1203, H CaO,
and 1.2% F was calcined at 1000-1150°C. and extracted with a
mixture of k2$ HN03 and 50$ H2S04 at 80-100°C. The filtrate
contained about 90$ of the P20s and 60$ of the A1203 originally
present in the ore. The calcining step rendered a large propor-
tion of the Al insoluble in the extracting acid (l). A Senegal
ore, a mixture of crandallite and millisite, was calcined and
ground, and the powder heated at 1000°C. for 2 hr. with petroleum
coke under H2 atmosphere. About 59$ of the P205 was volatilized
and 15$ converted to ferrophosphorus. The P-Ca3(P04)2 present
in the residue was completely recovered as H3P04 with 2N H2S(>4(2).
b. High-Temperature Chemistry of Phosphate Rock
The calcination of Florida phosphate rock at 1000°C. caused
considerable volatilization of F. However, the volatilization
of Si with F was not observed. The growth of apatite crystals
in the rock was remarkable, and the crystal quality of quartz
accompanying the rock was lowered. The decomposition rate of
phosphate by HCl was decreased (ij-). A phosphorite after heating
to 300°C. contained Calo( P04)6'F2 1J.5, Ca(P03)2 26.5, Mg(PQ3)2
19.0, Fe,Al(P03)3 11.7, CaS04 1J.9, CaSiF6 1.1, Si02 5.8 and
MgO + (Fe,Al)203 O.U$. Starting at 800°C., the formation of
Ca3(P04)2 took place. At 300-700°C., compounds did not undergo
structural changes, but at 800-900°C. their structural changes
were considerable. After 900°C., Ca3(P04)2 remained stable.
- 95 -
-------
Melting and further heating at 900-1100°C. lead to structural
transformation (5).
c. Enrichment Processes for Calcined Phosphate Rock
Phosphate ore was thermally dried, while simultaneously subjected
to attrition, air-classifying the dried ore to produce pebble
phosphate and fine particles of phosphate rock, Si02, and
agglomerated clay, and separating the pebble phosphate as a
final product (6). Rock phosphate was partially disintegrated
by calcination and H20- quench ing. The disintegrated mass was
made into a pulp and particles of finer size and lower density
were stripped from the pulp by countercurrent washing. The
concentrate that remained after washing was enriched in P20s ( T) •
d. Thermal Synthesis, Thermal Decomposition, and HgSO^ Decomposi-
tion of Apatite
Apatite was synthesized by heating a stoichiometric mixture of
CaHP04, CaC03, and CaF2 to 1000-1200°C. (9). The addition of
catalytic amounts of Si02 to fluorapatite increased the vola-
tility of F on heating in steam. A1P04, LiOH, and CaCl2
decomposed apatite to form B-Ca3(P04)2, Li3P04 and CaO, Ca2P04Cl,
or Ca10(P04)6(Cl,F)2, respectively ( 10, ll). The decomposition
rate of apatite increased in dilute H2S04 with increasing H+
concentration, and reached a maximum at 5-7$ H2S04, depending
on temperature. Then, with increasing H2S04 concentration, the
rate decreased due to the formation of a gypsum coating, with a
minimum at 60 and 50$ H2S04 at 25 and 90°C., respectively (13).
e. High-Temperature Chemistry of Tricalcium Phosphate
Tricalcium phosphate did not form a hydrate with a definite
structure by the reaction of Ca salts with phosphate in aqueous
solution, but formed a hydroxyapatite which was converted to
3-Ca3(P04)2 at 700-800°C. Contrary to many other reports,
3-Ca3(P04)2 was fairly soluble in citric acid. However, the
solubility was reduced remarkably by a small amount of admixtures,
expecially of MgO. The effect of A1203 and Fe203 was similar,
- 96 -
-------
'but not as intense as MgO (lk} 15). The rate of H2 reduction
of CaaCPO^g was enhanced greatly in the presence of A1203. The '
equilibrium constants in the presence of Si02 and Al20a were
~10~10 (at 1500°C.) and ~10~10 (at 1300°C. ), respectively (l6).
High-temperature phase equilibrium studies provided data for
the systems Ca3(P04)2-Al203-SiQ2 ( lj) and CaO-MgO-P205 (18-20).
2. Clay Minerals and Clays
a. Dehydration and Lattice Changes on Heating
In the dehydration of Na and Ca montmorillonites, molecular
water was essentially reversibly regained after mild heating,
and partial dehydroxylation was followed by some reconstitution.
Reconstitution of OH groups was about 60$ around 300°C. and
decreased to zero $ at about 850°C. Interparticle water was
"reversible" up to about 550°C. From about 500 to 800°C., all
individual layers were inactivated by dehydroxylation (21-23).
Li-saturated montmorillonite, however, exhibited pronounced
irreversiblility of hydration after heating to 190°C. (2*4-).
The isothermal decomposition of the clay minerals proceeded
according to the first-order kinetics law. The activation
energies for the Ca montmorillonite were lower than for Na
montmorillonite, and closer to the value for the kaolinite (28).
The upper limits of temperatures (°C.) at which the breakdown
of the colloidally dispersed minerals took place were montmoril-
lonite 725, illite 950, kaolinite 500, hydrogoethite 350, halloysite
50, and metahalloysite 500 (29).
b. Preparation and Characterization of Clay Minerals
Montmorillonite was synthesized from Si02 gel, MgO, Fe203, A1203,
KC1, and NaOH in 15 days at normal pressure, and temperatures
up to 80°C. (30).
- 97 -
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It was also synthesized from kaolinite and quartz by hydro-
thermal reaction with dolomite at 300°C. (31). Montmorillonite
was formed from illite by the removal of K with Na cobaltinitrite
or MgCl2 (32).
Hydrothermal treatment of montmorillonite into which Al-OH
polymers have been introduced readily generated kaolinite in
quantity (33).
Montmorillonite lost its capacity of fixing and exchanging cations
after prolonged grinding. A certain portion of the A1203, MgO,
and all the intercrystal OH ions were liberated as grinding was
continued. The A1203 and MgO thus liberated appeared to be
able to recombine partially and form a new compound which was
insoluble in acids
Free oxides such as AlgOs, FegOa, and SiOg in montmorillonite
can be determined based on the observation that when the sample
is decomposed by an acid, a linear change of the internal sur-
face area with the change in the amount of octahedral cations
takes place (35).
The second endothermal DTA effect at 700° C. in Na montmorillonite
results from the dehydroxylation of the octahedral structural
layer and from a partial dehydroxylation of the tetrahedral
layers. The third endothermal DTA effect, at 800-900°C., is
related to the destruction of the crystal lattice and also with
the final dehydroxylation (36).
The concentration of various montmorillonite types can be
determined by X-ray from the relative 001 diffraction intensities
of the glycerol complexes (38).
c. Acid Solubilities of Clays and Preheated Clays
Optimum conditions for the extraction of AlgOa from uncalcined
- 98 -
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and calcined clay minerals with acids, as stated in several
references, are also included in this section. In our case,
of course, we should try to avoid these conditions.
The Al atoms removed from montmorillonite crystals by hot acid
treatment are in octahedral coordination with 0 atoms held by
Si atoms. It is postulated that one of a pair of octahedral ly
coordinated Al atoms, together with two hydroxyl groups, are
removed • this leaves the remaining Al atom in tetrahedral
coordination (39).
In 50$ HC1 and exposure for 2 hr. at 80-85°C., the cation solu-
bility ($) of montmorillonite was 62, kaolinite 10, biotite
100, muscovite 5-32, and halloysite 6-15. The solubility of
montmorillonite depended more on the time of exposure than on
HC1 concentration. The solubility of aluminosilicate clay min-
erals in 25$ HC1 boiled for 2 min. was <10#, and the solubility
of Fe-Mg silicate clay minerals was >10#
HCl-insoluble residues of phosphate grains from the Atlantic
Coastal Plain, the Pacific Ocean, and other areas consist large-
ly of K feldspar and K mica in addition to quartz, organic matter,
and Fe compounds (^2).
Wavellite, crandallite, and millisite were completely dissolved
by boiling 0.33-g. samples for 20 min. with 20 ml. 1:1 HC1.
Only 1$ of the Al present in kaolinite was dissolved. This
method of decomposition is useful in differentiating the Al
present in wavellite, crandallite, and millisite from that in
kaolinite in samples from the Al phosphate zone of the Florida
pebble phosphate deposits (58).
The reaction between montmorillonite and H3P04 was rap-id but
incomplete. The reactions between kaolinite and H3P04 and that
between vermiculite and H3P04 were slow but continuous. The
reaction between chlorite and H3P04 was rapid and complete
- 99 -
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A nonuniform transfer of Al, Fe, and Mg ions in solution was
observed during the reaction of montmorillonite, kaolinite, and
actinolite with 10$ H2SQ4 solution. This was caused by changes
in composition and structure of the solid phase. Replacement
of bivalent Fe"1"1" and Mg'*"'" with H+ occurred during the initial
stage, and resulted in transfer of Fe"*^" and Mg"1^" into solution
and hydration of the minerals (Ml-).
On treating samples of montmorillonite, kaolinite, halloysite,
pyrophyllite, and zeolite with boiling solutions of 5-30$ H2S04,
the major change was the removal of A1203 from montmorillonite
and halloysite. IR absorption spectra show that the 0-H bands
near 3700 cm."1 and 900 cm.'1 weakened as A1203 was removed;
the Si-0 band in the 1000-1200 cm.'1 region changed from V-
to U-shape (V?).
Kaolinitic clay and hydromicaceous clay specimens, after
calcination in the 500-800°C. range for 1 hr., yielded 100
and 57$ of their A1203 contents, respectively, on extraction
with 5$ HC1. From a montmorillonite clay processed under the
same conditions, only an insignificant amount of A1203 was
extracted. This is because the Al hydrosilicate of the
montmorillonite is surrounded by two layers of silicic acid in
its 3-layer crystal lattice • in the case of kaolinite clays,
the 2-layer lattice consists of alternate layers of alumina
and silicic acid
The ratio of dissolved Si02 to A1203 in boiling HCl (0. 1 to
10. 5N, 30 min. ) seemed to be a constant for the same type of
clay. The absolute value of the dissolved material is a
measure of the amorphous material contained in the clay. If
the sample was first preheated to 750°C., the solubility of
Fe203 in HCl increased, whereas the solubility of Si02 and
A1203 did not change (59).
- 100 -
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A process for the extraction of A1203 from clay with HN03
involved calcining the ore at 750°C., followed by digestion
at 165° C. and 85 psig. with JOjG HN03 (60).
The optimum conditions for the production of A1203 from Egyptian
kaolin are: Grinding to 60 mesh, calcining at 750°C. for 1 hr.,
and boiling for 1 hr. with kcff> H2S04, 20$ HC1, or 32$ HN03.
The yields amount to 8k, 81.5, and 78$, respectively (61-63).
The exothermic reaction of kaolinite begins at 800°C. This is
related to the extraction of A1203 from kaolinite by HCl, which
attains its maximum recovery when the material is preheated to
750-800°C. This phenomenon may be attributed to an increasing
disorder of the lattice (64).
In an attempt to extract A1203 from kaolinite with H2S04,
unroasted ore produced only 38$ yield. The maximum yield (98$)
was obtained by heating the ore to 6-50-750°C. for 1 hr. prior
to the acid extraction. Higher and longer duration lowered the
yield because of spinel, Si3Al4Ol2, formation (65,66).
The rate of A1203 leaching from a calcined kaolin sample was
most rapid with HCl, slower with H2S04, and slowest with HN03.
The acid concentrations used were 5.9 and 8.6N, with reaction
temperatures of 95, 80, and 60°C. (67).
By using a melting-quenching-H2S04 leaching scheme, over 95$
of the A1203 was extracted from various silicates containing
30-^5$ A1203. The optimum conditions consisted of quenching
the melted material to a completely amorphous state and adjust-
ing the weight ratio of Si02/(CaOfNa20) in the quenched product
to 3.0-3.7. At higher ratios, recovery of A1203 decreased
(68,69).
The steep increase in A1203 solubility in acid after preheating
- 101 -
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a kaolinite clay specimen at 400-500°C. is explained by the
breakdown of the structure due to water release. This gives
a more open structure with easy access for the acid (70).
Preheating at 1000°C. did not increase the corrosion resistance
of halloysite as much as kaolinite in acids. Solubilities of
A1203 and Fe203 were 50-80 and 30-70$, respectively, for the
preheated halloysite. After preheating at lower temperatures
(<&00°C.), an even higher solubility of both A1203 (<90$) and
Fe203 (>90$) was obtained. The maximum solubility (~100$) was
obtained for a preheating temperature between 600 and 900°C.
The cause of the generally low corrosion resistance of halloy-
site are (a) higher stacking-fault disorders, (b) wide inter-
layer gaps because of the additional interlayer H20, and (c)
incomplete structural changes during the short-duration heat
treatment at 1000°C. The last point was verified by heating
halloysite for 15 hr. at 1000°C., which lead to only 10$ solu-
bility of A1203 in acid (71).
The firing of clay proceeded in two stages, during which the
properties of Si02, Al203,and alkali metal oxide compounds were
changed. In the first stage, decomposition of clayey minerals
occurred, accompanied by an increase in the solubility of com-
pounds in acid and in alkalies. In the second stage, formation
of new phases occurred, which was associated with a decrease in
the solubility of new compounds. In a reducing atmosphere, both
stages began at lower temperatures. When firing clay at temp-
eratures above 900°C. in an H2 current, the solubility of com-
pounds of A1203, K20, Li20, and other* in 5$ HC1 increased anew.
This increase is explained by the conversion of newly formed
compounds into other compounds which are more soluble in HC1.
In an H2 current at 600°C., and in an air current at 700°C.,
carbonates contained clay decomposed in 2 stages. Free MgO
was liberated in the first stage, and free CaO in the second
stage (72).
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Ceramics prepared from kaolinite-hydromiceous clay at 1000°C.
consisted of quartz, small amounts of mullite, and an amorphous
phase. They showed a low volume weight and a low acid resis-
tance. At 1000-1100°C., the content of mullite rose, while the
content of amorphous phase and quartz decreased somewhat. The
mechanical strength, volume weight, and acid resistance of
samples rose between 1100-1200°C. In this interval, the growth
of mullite crystals commences. Above 1200°C., all properties
studied increased only slightly. The ceramics prepared from
kaolinite-montmorillonite clay at 1000°C. consisted of cristo-
balite and mullite. The cristobalite content increased sharply
at 1050-1100°C. The ceramics prepared from kaolinite clays, at
temperatures up to 1100°C., consisted of amorphous products of
the decomposition of clayey mineral and quartz. The strong
crystallization of mullite and cristobalite, causing increase
of acid resistance, starts at 1100-1200°C. At 1J500°C., the
content of amorphous phases is practically zero. The acid
resistance of materials depends not only on the phase composi-
tion, but also on the amount of succession of formation of
phases (?3).
d. High-Temperature Chemistry of Clay Minerals
After deterioration of the lattice of montmorillonite at 900°C.,
amorphous SiOa, quartz, and some spinel were foundj at 1000°C.,
cristobalite, more quartz, spinel, anorthite, and less amorphous
SiOgj at 1100°C., more cristobalite, anorthite, spinel, less
quartz, and appearance of cordierite and mullitej at 1200°C.,
more mullite, anorthite, cordierite, and spinel
Gradual formation of Ca silicates occurred on prolonged heating
of clays with CaCOa. Feldspar formed on heating clays with KC1
or CaCl^, but NaCl and Na2S04 gave sodalite and noselite, respec-
tively. Addition of NaCl or KC1 caused the beginning formation
of mullite at 850°C., which otherwise begins only above 1000°C.
(55).
- 103 -
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The high-temperature crystal phases which develop on heating
of clay minerals are related both to structural inheritance
and to composition. Minor chemical variations and the presence
of trace impurities play a large role in phase development of
3- layer clay minerals. Nonclay components, such as feldspar
and mica, often react to alter 'the predicated firing response
of specific clay minerals in the mix. Alkali elements and Fe
are particularly effective in reducing phase minerals develop-
ment ( 56) .
The dehydrated kaolinite is purely amorphous in character, and
the exothermic reaction, which occurs at 960-1000°C., is the
sudden crystallization of y-AlaOs from the amorphous phase,
which is prevented at low temperature by the SiOg in intimate
contact with it ( 7^,75). The dehydration at 500-600° C. destroys
the octahedral layers and distorts the tetrahedral layers. One
half of the A13+ ions migrate to the previous position of the
lost OH groups (empty positions in the tetrahedral layers).
At 880-900°C., the atoms of the residual octahedral layers are
regrouped to f orm y-AlgOs (76). Fe, Mg, and Ca impurities
influence both the chemical and the phase changes. In the first
exothermic range, 920-1000°C., either y-Al^Oa or mullite forms,
depending on the impurities present. This influences the rate
of sintering and the origination of a second exothermic range,
1150-1300°C., corresponding to the formation of mullite (77-88).
The mineralogical sequences observed during the firing of impure
clays are as follows (89-93):
Kaolinite - > Metakaolinite -. ^ A1_gi Spinel
and Si02 8T°" 10^°° C' » Mullite and Cristobalite.
The solid-phase conversion of kaolinite to mullite follows a
first -order equation relative to the unreacted part in the
initial stages of the process. The mullite in the quickly cooled
specimens is more soluble in aqueous HF than in the slowly cooled
- 104 -
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specimens (9U). Mullite formation from kaolinite-type minerals
is affected by the firing atmosphere. The reaction is greatly
enhanced by H20 vapor and vacuum, and to a lesser extent by N2
and H2, but is retarded by 02 and C02. The crystallization
reaction of cristobalite from amorphous Si02 is enhanced by N2,
C02, H20, and vacuum, rather unaffected by 02 and air, and
retarded by H2 (95, 96). In the presence of a solid reducing
agent such as carbon, the rate increases. Thus, if under normal
conditions mullite crystallizes at 1250°C. or above, the presence
of carbon brings crystallization at or below 1200°C. (97).
In the sintering of kaolinite, the amount of mullite formed at
1200°C. increases with increasing Fe203 content. At higher
temperatures, it decreases if the Fe20s content exceeds 7. 7$
(98, 99). FeO also has a favorable effect on mullite formation
from kaolinite; it decreases the reaction temperature by 150-
200°C. In the kaolin-FeO system, hercynite forms first on heat-
ing, and contributes to the decomposition of metakaolin to quartz,
mullite, and amorphous Si02. Fayalite is formed only when the
Fe203 content is high (100).
High-temperature reaction studies on kaolinite-feldspar-quartz
mixtures indicate the amount of quartz in the fired materials
decreases with increasing temperature and increasing feldspar
content. No feldspar is unreacted in mixtures fired at 1200°C.
or above. Mullite develops very rapidly in the mixtures as the
temperature rises from 1100 to 1200°C. The amount of mullite
developed at 1200°C. is only slightly less than that found at
1300-1^00°C. The main hindrance to attainment of full equilibrium
at 1200°C. and above is the slow rate of dissolution or reaction
of the quartz (101-103).
e. Effect of Mineralizers on Mullite Formation
References which have some immediate bearing in our experimental
- 105 -
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work are the use of additives in the high-temperature conversion
of clay minerals to mullite. Very effective additives mentioned
include C, H20(vapor), FeO, MnO, NaCl, KC1, LiF, NH^F-HF, CaF2,
A1F3 and Na2SiF6. These additives, in general, either promote
mullite formation or lower the temperature required for mullite
formation, or both. In most cases, the amount of mullite formed
when small amounts of additive are used is greater than in the
case without additives. If the proportion of the additive ex-
ceeds the usually small optimum amount, however, mullite forma-
tion is reduced and eventually is less than in the control
sample. In addition, there exists an optimum temperature and an
optimum time of calcination with a given additive.
The phase transformations that occur in montmorillonite, illite,
kaolinite, and halloysite at temperatures up to 1^50°C. were in-
vestigated. Continuous high-temperature XRD is used to detect
changes that take place in the firing history of a clay in which
small amounts of chemical impurities or other mineralizing subs-
tances are present or have been added. Several chemical impuri-
ties were added to each of the clays to determine their ability
to either enhance or retard structural transition and new mineral
development upon firing. The effects which these additives have
on predicted structural changes are illustrated and are inter-
preted in lieu of chemical and structural requirements (105).
Clays heated for J hr. at 1100, 1200, and 1500°C. showed 31, 38,
and Vf$ mullite, while the theoretically possible maximum yield
is ^9-59$. With the addition of 1$ of MnS04, MgCl2, or CuCl2,
the temperature of the beginning of mullite formation was lowered
by 100-200°C. (10?).
Mullite formation was accelerated by the addition of mineralizers,
the most effective being CaF2 (108). The temperature of mullite
formation was reduced from 1300 to 600°C. by the addition of
5-20$ A1F3 (or A1C13) to the Al203-Si02 or clay-Al203 mixes.
At 1000°C., the product was more compact with better mechanical
-106 -
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strength, and was better crystallized (109). Mullite can be
formed in kaolin at temperatures considerably lower than normal
by introducing small amounts of fluorides (NasSiFg, NH^-HF,
BaF2, A1F3, SbF3). The dissolution rate of kaolin in molten
fluorides is very high. Very little F is detectable in the
fired kaolin. The mullite which forms is identical to the
mullite that is conventionally formed in kaolin at 1200°C. (llO).
Alkali and alkaline- earth fluorides promote the formation of
mullite from kaolin minerals, LiF being the most effective.
The dried materials were mixed with 2.5, 5, and 10$ LiF and
heated for 5 hr. at various temperatures. Mullite started to
form at 800°C. with 2.5$ LiF added to the kaolin, at TOO°C.
with 5$ LiF, and at 500°C. with 10$ LiF ( 111-113).
Generally, the greater the ionic charge and the smaller the
ionic radius, the more active is the ion in its mineralizing
effect. CaF2 is more active than CaCOs, while LiF is more active
than LiCl. In most cases, the amount of mullite formed when
small amounts of mineralizer are added is greater than in the
original mixture without any additions. If the proportion of
the mineralizer is increased above some quite-small optimum
amount, however, mullite formation is reduced and eventually
is less than in the original mixture. In addition, there exists
an optimum temperature and an optimum time of calcination with
a given mineralizer
If 2$ FegOs was added to kaolin, the crystallization of ^-
was considerably accelerated at 930°C., but mullite appeared
only in the range from 1160 to 1360°C. Three $ of MgO, CaO,
CaF2, MgF2 added to kaolin increased the effect at 930°C. and
reduced the exothermic reactions at 1050 to llU.O°C. The natural
contaminations of kaolins and clays by Fe203, MgO, CaO, etc.,
•Lave important effects on the mullite formation in ceramic
bodies (ll8). The addition of FeO to kaolin up to 10$ at 900-
1500°C. effected the phase composition, mullitization, and
morphology of mullite (119). The activity of mineralizers such
- 107 -
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as K20, MgO, CaO, Ti02, Fe203, MnO, PbO, and P205 Increased
with an increase in Si02 content, while their influence de-
creased with an increase in firing temperature (120). Among
the oxides Na20, K20, MgO, CaO, CuO, A1203, Fe203, Ti02, and
P205 best sintering additive was MgO. The use of combined
R(,0h+ P205 additions gave better results in kaolin sintering
than if either P205 or RjnOj, were used alone. The open porosity
of fireclay products without additions of oxides was about l.k—
2.9 times as high as that of- products with additions, or the
same porosity results at firing temperature of about 100-150°C.
lower (121). The additions of Na20, K20, MgO, or CaO acceler-
ated thermal transformations of pyrophyllite, the most effec-
tive being K20. In the mineral containing K20, mullite was
detected in samples ignited at 900°C. (122). The formation of
mullite from mixtures of 3:2. Al203-Si02 with different amounts
of NaF, B203, Fe203, or Ti02 at ll±00-l600°C. is related to the
capacity of these mineralizers in the mullite cell and to the
liquid phase formation of the system. The formation of sub-
stitutional solid solutions with FegOs and with Ti02 promoted
formation of mullite (123).
3- Aluminum Phosphate Minerals and Aluminum Phosphates
a. Synthesis of crandallite, variscite, and wavellite (125).
b. XRD and DTA data of crandallite, millisite, and wavellite (126-
129).
c. Preparation of ammonium phosphate fertilizer from Al-phosphate
ores and NH^F (130).
d. Preparation of phosphorus from Al-phosphate ores (l3l)«
e. Reaction of H3P04 with some forms of A1203 (132).
f. System A^Og-P^s-H^ at 25-90°C. (133-136).
g. System Al203-P205-Si02 (137-139)-
h. XRD and DTA data of A1P04 ( ito-U-3).
i. IR spectra of A1P04-2H20 (iMv) .
j. High-temperature chemistry of Al phosphates
- 108 -
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4. Aluminum Silicate Minerals and Aluminum Silicates
a. Composition, structure, and properties of staurolite ( 156-159)
b. Recovery of A1203 from staurolite concentrates ( l6p) .
c. Growth of mullite crystals in feldspathic glass ( l6l, 162).
d. Analyses and properties of feldspars ( 162-166).
e. High-temperature reactions between mullite and Na20, K20, MgO,
CaO, Fe203, or Ti02 (l6?-170).
f. Phase transformations in Al203-Si02 mixtures (lTl-17^).
g. Phase equilibrium for the system Al203-Si02 (175-178).
h. Stability of silicate materials in H2S04, H3P04, and HC1 ( 179-
I8o).
5. Aluminum Oxide
a. Phase transformations of A1203
b. Corrosion resistance of hydrous A1203 (182).
c. Corrosion resistance of Al203-base materials versus HC1, HN03,
and H2S04
6. Iron Oxide Minerals and Iron Oxides
a. Leaching of Goetfrifce with H2S04, HC1, HC104, or Mixtures of
these Three Acids.
A first-order dependence of leaching rate on H+ activity was
observed. The grain-to-particle-aize ratio of the oxide being
leached determined the shape of the leaching curve ( 185, 186) .
In 1:1 HsP04 at 100°C., only 10-20$ of the Fe in goethites was
soluble, while the limonites dissolved almost completely, with
the hydrogeethites taking an intermediate position (187). The
dehydration of limonite went through : the stages: Amorphous
Fe(0H)3, hydrogoethite, goethite, and hydrohematite (l88).
b. The Dissolution Rate of Fe203 in H2S04 Decreased with the Degree
of Crystallinity (l89).
The times required for 100 mg. Fe, in the form of Fe203, to
- 109 -
-------
dissolve completely at 60°C. were 28 hr. in 6.1% H2S04, 16 hr.
in k.&f> HC1, and 0.36 hr. in 2.5% HF. The corrosive effect of
acids was accelerated by the addition of HF (190). The dis-
solution of Fe oxides at 60°C. and at the boiling points in
H2S04 was about 30$ slower than in HC1. The addition of 5nM
HF to 0. 5M HC1 increased the dissolution rate of Fe304 by a
factor of 10, the addition of 20 nM HF by a factor of 100 (l9l).
7' Iron Phosphate Minerals and Iron Phosphates
a. Thermal decomposition of vivianite and its stability in the
system Fea(P04)2-H3P04-H20 (196,197).
b. Reactions in the Fe203-FeP04 system (198,199).
c. Phase equilibria in the system Fe203-H3P04-H20 at 25°C. (200,
201).
8. Magnesium Carbonate Minerals and Magnesium Oxide
a. Thermal Decomposition of Magnesite, Dolomite, and Ankerite
At l)-00-600°C., small MgO particles were formed by the decomposi-
tion of MgC03. Between 600 and 800°C., these particles grew
into large, porous secondary aggregates, and the porosity of
the unchanged MgCOs particles also increased. Sintering began
at 850°C., with greater adherence of the particles to each other,
and decreasing aggregation and porosity. Sintering was completed
at 1050°C., and sharply defined cubic crystals of MgO were
observed in large numbers. With natural magnesites containing
traces of Fe and Al oxides, the decomposition began at higher
temperatures than in pure MgC03, and the recrystallization
process also began at higher temperatures (202). The type of
process used for calcining magnesite and dolomite significantly
affects the recrystallization rate of MgO. Calcination at 800-
1250°C. in shaft and rotating kilns resulted in the growth of
MgO and CaO crystals. During the short-term firing of fine
fractions in a fluidized bed at 900-950°C., lime was obtained
- 110 -
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in which the MgO was converted into the active form (20k).
Dissociation products, MgO and calcite, appeared after the
dolomite was heated to iKX)-500°C. After calcining at 700°C.,
the dolomite crystals acquired a trizonal (unaltered dolomite,
MgO and calcite, calcite) structure. After calcining at 800°C.,
no unaltered dolomite remained. In the 1000-1100°C. range,
MgO recrystallized as periclase. MgO did not react with un-
ground silica sand, but reacted vigorously with ground sand,
forming Mg hydrated silicates, similar to serpentine in
composition (205, 206).
Alkali salts affect the decomposition of dolomite at the first
stage only. The decomposition temperature is lowered by about
150°C., which affects the MgO content, crystallite growth,
surface area, and porosity, leading to a higher reactivity of
the products. At higher temperatures, the additives decrease
the reactivity due to the lattice diffusion leading to the
structure ordering and the removal of defects (210). The pre-
sence of CaF2 increases the decomposition rate of magnesites
and dolomite. The activity of ignited materials depends on
the temperature of ignition and on the character and distribu-
tion of admixtures (Fe20a, A1203, Si02) or special additions
(CaF2). The higher the ignition temperature and/or the higher
the concentration of admixtures or additions, the lower the
reactivity of the product (212).
On heating a powdered ankerite sample at 600°C. for 6 hr., no
change in the X-ray powder pattern occurred. The 750°C. pattern
indicated a mixture of calcite with small amounts of MgO and
vaterite. At 950°C., a mixture of Ca2Fe205, MgO, and CaO was
formed (21^). Ankerite was not only thermally dissociated into
C02 and oxides, but also formed MgFe^O^.. It arose in the
presence of Ca2+ in a narrow temperature range near 700°C. At
higher temperatures it was transformed to CaFe204 (215).
- Ill -
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k* Dissolution of Calcite, Dolomite, and Magneslte in Acids
Magnesite and dolomite dissolved to a considerable extent in
0. IN solutions of HC1, H2S04, HN03, or H3P04 after 10 min. in
the cold, and almost completely after ko rain. Calcite in the
cold in 0. IN HC1 dissolved completely within 1 min. (216).
c. Reaction of Dolomite with NHSO^ Solution
CaS04 was formed faster from dolomites calcined at 100G°C.,
while MgS04 formation was faster from dolomites calcined at
850°C. (217, 218).
d. Sintering and the Rate of Hydration of MgO
CaO inhibits sintering to an extent that appears limited by
particle contact. TiOs promotes sintering as well as growth
of the periclase crystals. However, there is an optimum
concentration of TiOg, SiOg, and AlgOs beyond which sintering
is inhibited. The rate of hydration is controlled by the % of
open pores and crystal size of the periclase (219-221). Water
vapor pressure ( 10 3 to 5 nun. Hg) profoundly affects the nature
of thermal decomposition products such as MgO, CaO, and BeO in
relation to the crystal size and pore structure. On subsequent
sintering of the oxides, similar HgO vapor pressures may increase
the rate of crystal growth by >2 orders of magnitude (221, 222).
e- Infrared Absorption Spectra of Metal Oxides
The IR absorption spectra of 25 metal oxides such as Al, Fe,
Mg, Ca oxides, and silica over the range IkQO-kOO cm."1 are
given (223).
9. Magnes ium S i lie ate Minerals
Information on high- temperature chemistry of actinolite, anthopylite,
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deweylite, forsterite, saponite, sepiolite, and tremolite are given
(225-228).
10. Magnesium Phosphates
a. Phase equilibria in the system MgO-P205-H20 at 0 to 130°C.
(229, 250).
b. Interaction of MgO with H3P04 (231).
c. Thermal decomposition of Mg(H2P04)2- 2H2Q (2J2).
lls Bj-narV a"d Ternary Systems of A1203, Fe203, MgO, and Si02
a, The formation and subsequent decomposition of the spinel (FeO-
Ala03 •*• CO - •» Fe + A1203 + C02) occurred during the reduction
of Fe203 by CO in the presence of A1203 (233). Binary compounds
of the alum type, M2(S04}3' (NH4)2S04*nH20, resulted from the
sulfatization of A1203 and Fe203 with (NH4)2S04 at 300-^OG°C.
(235). When powder mixtures of M203 and Na2SiF6 were heated
to 75Q-80Q°C., the reaction 6Na2SiF6+ 2M2Oa - *
12NaF •*• 3SiF4 •*" 3Si02 reached the maximum rapidly with Fe203,
and after ^5-60 min. with A1203 (2J6).
b. When mixtures of A1203 and MgO were heated to between 800 and
1200°C., pure MgAl204 was formed at first, and the solid
solution rich in A1203 was formed gradually when an excess of
A1203 was present (237, 238). Spinel was produced by treating
compacted A1203 with MgO as the vapor carried by H2, or as a
MgO compound such as carbonate. The reaction was promoted by
heating at 1500-1900°C. (2Ul). A solid-solid reaction mechanism
is suggested, based on initial formation of spinel at the
contact surface, followed by dissolution of A1203 in the spinel
and by its penetration into it, to react further with MgO to
form more spinel (2^3). With the presence of MgCl2, MgO
dissolved in molten MgCl2 spread uniformly over the surface of
A1203 particles, then MgO was transported to the inner part of
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-------
A1203 particles and rapidly reacted with A1203 to form the
spinel layer through which the counter diffusion of Mg2+ and
A13+ occurred
c. The reaction MgO + Fe203 • MgFe204 occurred when a mixture
of MgO and Fe203 was heated at 850- 1000° C. (2^7-2^9) . The solu-
bility of MgO in HC1 was the highest when it was prepared by
firing Mg(OH)2 at 800°C. For MgFe204, MgO was preferentially
solubilized at the initial stage (25l).
d. During the reduction of Fe203 by CO in the presence of Si02, the
new solid phases that appeared successively were magnetite,
fayalite, and metallic Fe (252). When Fe203 and Si02 were
heated in 02, a light-red solid solution of Fe203 in cristoba-
lite was obtained above 900°C.(253).
e. The ternary system Al203-Fe203-Si02 was determined by the phases
appearing in the adjacent systems. A ternary combination of
oxides could not be observed
f. A critical review and discussion on the phase diagram of A1203-
MgO-Si02 is given (255, 256). Metastable solid solutions of
quartz structure along the composition line MgAl204-Si02 in the
range 14-1.3-73.2$ Si02 were obtained (257). Mixtures along the
mullite-spinel line of the Al203-MgO-Si02 system were synthesized
by firing the component oxides. At 900°C., highly defective fine
crystalline spinel was formed. At 1200-1300°C. , sapphirine and
cordierite appeared, and subsequently decomposed into spinel,
mullite, and a liquid phase. Above 1550°C., mullite decomposed
into corundum and a liquid. Sintering compressed mixtures for
15-30 min. at 1550- 1630° C. gave refractories stable in boiling
concentrated HCl and H2S04 (259, 260) .
12. Acid-Resistant Ceramics, Cements, and Enamels
One noteworthy reference (263) remarked that ceramics containing
anorthite gave good resistance to concentrated H2S04.
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-76-045
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
Elimination of Washer Slimes from the Production of
Phosphate Chemicals
5. REPORT DATE
March 1976
6. PERFORMING ORGANIZATION CODE
7 AUTHOR.S) R c cannon, R.S.Ribas, J.D. Nicker son,
and R. A. Weisback
8. PERFORMING ORGANIZATION REPORT NO,
9. PERFORMING ORSANIZATION NAME AND ADDRESS
USS Agri-Chemicals Division, U.S. Steel Corporation
685 DeKalb Industrial Way
Decatur, Georgia 30033
10. PROGRAM ELEMENT NO.
1BB036; ROAP 21AZR-007
11. CONTRACT/GRANT NO.
Grant S802684*
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final; 9/73-4/75
14. SPONSORING AGENCY CODE
EPA-ORD
15. SUPPLEMENTARY NOTES (*)Grantee was the State of Florida, Dept. of Environmental Regu-
lation, Tallahassee, FL 32301. EPA project officers are: R.R.Swank, Athens (GA)
Environmental Research Lab; and E.Lomasney, EPA Region IV (Atlanta).
16. ABSTRACT
report gives results of laboratory studies to determine the feasibility
of a new phosphoric acid process involving dry mining of the matrix, calcination,
and digestion with phosphoric/sulfuric acid mixtures (five types of Florida phosphate
matrices were used). Process steps included upgrading the matrix by dry methods ,
calcination in a static bed, and digestion comparable to commercial dihydrate pro-
cesses. The matrix samples were upgraded by removing clay by selective grinding
and air classification, and by separation of the sand fraction electrostatically. Typi-
cal clay removal values were 80-90% at a phosphate loss of 15-25%. Calcination
produced an acceptable phosphoric acid from good quality matrix, but failed to
reject metal impurities sufficiently to permit processing of poor-to-average matrix.
Calcination eliminated the interference of clay in the digestion and filtration steps.
Addition of mineralizers had only marginal effect on metal solubility.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Pollution Sulfuric Acid
Chemical Engineering Mining
Washers (Cleaners) Roasting
Slime
Digestion (Decomposition)
Phosphoric Acids
b.lDENTIFIERS/OPEN ENDED TERMS
Industrial Processes
Florida Phosphates
Washer Slimes
Dry Mining
c. COSATI Field/Group
13B
07A
08H
13H
07B
081
8. DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (ThisReport)
Unclass if ied
21. NO. OF PAGES
137
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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