EPA 560/2-77-006
CHEMICAL TECHNOLOGY AND
ECONOMICS IN
ENVIRONMENTAL PERSPECTIVES
TASK VI-CADMIUM IN PHOSPHATE FERTILIZER
PRODUCTION
ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF TOXIC SUBSTANCES
WASHINGTON, D.C. 20460
NOVEMBER 1977
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CHEMICAL TECHNOLOGY AND ECONOMICS IN
ENVIRONMENTAL PERSPECTIVES
Task VI - Cadmium in Phosphate Fertilizer Production
Contract No. 68-01-3201
MRI Project No. 4101-L
Project Officer
Charles Auer
Office of Toxic Substances
Environmental Protection Agency
Washington, D.C. 20460
Prepared for
Environmental Protection Agency
Office of Toxic Substances
Washington, D.C. 20460
November 1977
MIDWEST RESEARCH INSTITUTE 425 VOLKER BOULEVARD, KANSAS CITY, MISSOURI 64110 • 816753-7600
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DISCLAIMER
This report has been reviewed by the Office of Toxic Substances, Environ-
mental Protection Agency, and approved for publication. Approval does not
signify that the contents necessarily reflect the views and policies of the .
Environmental Protection Agency. Mention of trade names or commercial prod-
ucts is for purposes of clarity only and does not constitute endorsement or
recommendation for use.
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PREFACE
This report presents the results of Task VI of a project entitled "Chemi-
cal Technology and Economics in Environmental Perspectives," performed by Mid-
west Research Institute, under Contract No. 68-01-3201, for the Office of
Toxic Substances of the U.S. Environmental Protection Agency. Mr. Charles
Auer was project officer for the Environmental Protection Agency.
Task VI, "Cadmium in Phosphate Fertilizer Production," was conducted by
Mr. Charles Mumma, Ms. Kathryn Bohannon, and Mr. Fred Hopkins. Dr. Ivan C.
Smith served as an in-house consultant for this task. Dr. Thomas W. Lapp is
project leader for this contract. This report was prepared under the super-
vision of Dr. Edward W. Lawless, Head, Technology Assessment Section. This
program had MRI Project No. 4101-L.
Midwest Research Institute would like to express its sincere appreciation
to those companies who provided technical information for this report.
Approved for:
MIDWEST RESEARCH INSTITUTE
32->
L. JjJ Shannon, Director
Environmental and Materials
Sciences Division
November 1977
iii
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CONTENTS
Preface ill
Figures vi
Tables vii
1. Introduction 1
Objective 1
2. Summary and Conclusions 2
3. The Phosphate Fertilizer Industry 4
General history 4
Production and consumption of phosphate fertilizers .... 6
Fertilizer trends 6
References for Section 3 . 13
4. Current Data 14
Methodology 14
Manufacturing processes 15
Cadmium levels in phosphate ores and fertilizers 28
References for Section 4 36
5. Research Needs 39
Cadmium in phosphate rock 39
Mass balance studies 39
Cadmium removal 40
Smelter acid 40
Micronutrients 40
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FIGURES
Number Page
4-1 Generalized flow sheet of a phosphate rock mining and beneficia-
tion plant 13
4-2 Wet process phosphoric acid flow sheet 20
4-3 Normal superphosphate flow sheet 23
4-4 Flow sheet for granulated triple superphosphate production ... 24
4-5 Flow sheet for production of diammonium phosphate 26
VI
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TABLES
Number Page
3-1 Current U.S. Ammonium Phosphate Producers 7
3-2 Current U.S. Normal Superphosphate Producers 8
3-3 Current U.S. Triple Superphosphate Producers 9
3-4 U.S. Phosphate Consumption 10
4-1 Cadmium Concentrations in Phosphate Ores 29
4-2 Cadmium Concentrations in Phosphate Fertilizers 33
VII
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SECTION 1
INTRODUCTION
Cadmium has been known for many years to be a highly toxic element;
health problems attributed to cadmium exposure include proteinuria, pulmonary
emphysema, hypertension, and liver and kidney damage. The need for precautions
against human exposures in industrial operations involving cadmium or its com-
pounds has long been recognized. Not until comparatively recent times, how-
ever, has concern been expressed over the possible human health effects of
long-term exposure to low concentrations of cadmium, such as those that might
develop through environmental routes.
One of the potential environmental sources of cadmium is the use of agri-
cultural phosphate fertilizers, which may contain up to 100 ppm of cadmium.
The commercial phosphate fertilizer production process has the potential, in
fact, to increase the concentration of cadmium in the finished fertilizer
above that which had existed in the phosphate rock starting material.
OBJECTIVE
This brief task was initiated to study the levels of cadmium concentra-
tion as phosphate rock is processed into the finished commercial fertilizer.
The primary focus of this study was to determine if the concentration of cad-
mium in commercial, phosphate fertilizers represented an increase over the lev-
els initially contained in the phosphate rock and to identify specific points
of increase in the process. If the cadmium levels were, in fact, found to in-
crease as the phosphate rock is processed into fertilizer, the reasons for
such increases and the sources of the increases were to be ascertained.
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SECTION 2
SUMMARY AND CONCLUSIONS
The importance of phosphorus as a plant nutrient, essential for the
growth of higher plants, has been long recognized, and commercial phosphate
fertilizers have been produced for over 100 years. Essentially all phosphate
fertilizers are obtained from a single raw material source, a calcium mineral
known as apatite or phosphate rock. The phosphate rock is seldom used di-
rectly for fertilizer, and is normally chemically processed to one of several
other forms for fertilizer use. Prior to about 1955, most of the phosphate
fertilizer used domestically was in the form of normal superphosphate. Since
that time, the use of normal superphosphate has steadily declined as it has
been displaced by the more concentrated phosphate fertilizers, triple super-
phosphate (TSP) and the ammonium phosphates.
Cadmium occurs as a natural contaminant in the phosphate rock used in
fertilizer production, and may be present in a form which is readily avail-
able for uptake by edible fruits and plants. Concern has developed that pro-
duction methods may concentrate the cadmium in the finished fertilizer. This
brief project was initiated to study the levels of cadmium as phosphate rock
is processed into the commercial fertilizer and to determine if an increase
in cadmium levels occurs. In general, the results of this study have shown
that very little information is available on the levels and fate of cadmium
as the ore proceeds through the various manufacturing steps.
Raw ore is generally classified as eastern or western ore. The cadmium
levels in mined eastern ore average about 10 to 25 ppm, while in mined western
ore, levels range from about 50 to 150 ppm, depending upon the type of ore.
Some western ores have cadmium levels as high as 980 ppm; however, these ores
are not extensively mined at the present time. Nevertheless, because of the
tightening supply of high quality phosphate ores, domestic producers may be
forced to shift to the less desirable low grade ores. The movement towards
the use of lower grade ores may result in the future processing of raw phos-
phate rock containing a high cadmium content. Additional sources of potential
cadmium contamination during processing are sulfuric acid and the addition of
micronutrients. From the limited available data, it appears that by-product
sulfuric acid from zinc, lead, and copper smelters is used, where available,
in the processing of phosphate ore. Based on industry sources, an estimated
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107o of the sulfuric acid consumed in phosphate ore processing is smelter acid.
This is primarily true with the western ores. The cadmium content of the
by-product smelter acid is not well defined; the levels reported in the lit-
erature range from 1 ppb to 60 ppm by weight. High levels are normally as-
sociated with zinc smelter processes. Very few data are available concerning
the addition of micronutrients to phosphate fertilizers and any increase in
cadmium levels resulting from such additions.
Thus, it is not currently possible to establish material balances or draw
inferences about the concentrations of cadmium during the various stages of
manufacture of phosphate fertilizers. Existing data do not indicate that a
significant increase occurs in the cadmium to phosphorus ratio between raw
materials and finished product as a result of current manufacturing operations.
This conclusion is based on very limited data and must be considered tentative
until corroborated by additional evidence. Studies designed to resolve the
uncertainties of material balances and the question of possible enhancement of
cadmium in phosphate fertilizer manufacture are currently planned by the
Tennessee Valley Authority (TVA).
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SECTION 3
THE PHOSPHATE FERTILIZER INDUSTRY
GENERAL HISTORY
The importance of phosphorus as a plant nutrient, essential for the
growth of higher plants, has long been recognized and commercial production
of phosphate fertilizers has been practiced for over 100 years.—
Practically all of the phosphate fertilizers currently produced come from
a single raw material — a calcium phosphate mineral commonly known as apatite
(Ca^QCPO^^^) or phosphate rock^i' Organic materials were o.nce a major source
of phosphate, but their use has been discontinued as mined rock became more
available and less costly.
A general flow diagram for the production of various types of phosphate
fertilizers is shown below. Each of the steps in this diagram will be dis-
cussed later in Section 4.
ahoaahorlc icld
crlpjc «uo«fphosor.ac«
SHj
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Prior to approximately 1955, phosphate products (based on ?2®5^ were
major fertilizer nutrients consumed domestically. Since that time, nitrogen
consumption has become predominant, but phosphates are still used on a large
2/
s ca le .— '
During the past 20 years, there have been dramatic changes in phosphate
fertilizer production facilities, costs, and industry image.—' Prior to 1955,
most of the phosphate nutrient was in the form of normal superphosphate, which
3 /
contained about 16 to 20% P2C>5.— A low production cost and a single produc-
tion method resulted in the manufacture of normal superphosphate by a large
number of small plants located throughout the domestic market area. Since
1955, however, the market for normal superphosphate has steadily decreased,
and its former share of the market has been taken over by more concentrated
phosphate fertilizers. However, in order to manufacture the more concentrated
fertilizers, it was necessary to modify the process and to increase the domes-
tic production capacity of phosphoric acid, an essential intermediate. This
demanded the production of greater quantities of sulfuric acid, as well as
larger overall production facilities.—
Phosphoric acid is produced by two basic processes: (a) wet process,
and (b) the electric furnace process. Although acid produced by each process
is used in the fertilizer industry, the quantity of furnace process acid con-
sumed is relatively small. Most of the furnace process acid is used in non-
fertilizer applications. In contrast, almost all of the wet process phos-
phoric acid produced domestically is used in fertilizer processes.—
Triple superphosphate and ammonium phosphate facilities are generally
large, multipurpose complexes located at or near the mine site. Triple super-
phosphate (46 to 48%, ?2®5 content) contains approximately three times the
?20c content of normal superphosphate. Ammonium phosphates are combination
products which contain 46 to 61% ?2®5 P^us nitrogen values. Included are
monoammonium phosphate (MAP) and diammonium phosphate (DAP) which differ in
the degree of ammoniation attained during manufacture. The ammonium phos-
phates are currently the most widely used phosphate fertilizers in the
United States.
Until 1970, finely ground (< 0.074 mm) phosphate rock was used domesti-
cally in relatively small quantities as a fertilizer.— Since domestic fer-
tilizer prices are based on a citrate soluble ?2®5 standard, ground rock (low
in soluble ^2^5^ cannot compete with other products. However, there is still
a significant demand for ground rock in foreign markets.
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PRODUCTION AND CONSUMPTION OF PHOSPHATE FERTILIZERS
Current Producers
Tables 3-1, 3-2, and 3-3 show the top companies in each category in order
of production capacity. The three types of fertilizers represented—ammonium
phosphates, normal superphosphates, and triple superphosphates—account for
nearly 100% of the phosphatic fertilizers presently in use.—
From the tables, it can be seen that approximately 40% of all fertilizers
(i.e., normal superphosphates,triple superphosphates, and the ammonium phos-
phates) are produced in Florida. No other individual state produces more than
1070 of the total. If the production is considered on a regional basis, the
southeastern states of Florida, Georgia, Alabama, Tennessee, and North and
South Carolina combine to manufacture approximately 60 to 65% of the total
phosphate fertilizers.
Florida manufactures approximately 80% of all triple superphosphate. All
other individual states produce about 10% or less of the total quantity. For
normal superphosphate, three states (Florida, Georgia, and North Carolina)
produce approximately 50% of the total domestic quantity. Florida and
Louisiana combine to produce about 65% of all of the ammonium phosphates with
no other state contributing more than 107° of the total U.S. production quantity,
Domestic Phosphate Fertilizer Consumption
Data showing the U.S. consumption of phosphate fertilizers during the pe-
riod of 1970 to 1976 are presented in Table 3-4.
During the fiscal year periods from 1970 through 1976, domestic consump-
tion of normal superphosphate decreased by about 54% while the rate for con-
centrated superphosphate remained relatively constant. Over the same period,
the increases in the consumption rates for ammonium phosphates and for diam-
monium phosphates were about 24 and 43%, respectively.
FERTILIZER TRENDS
A brief discussion of processing trends in the industry and marketing
trends and projections is presented in this subsection.
Processing Trends
Until recent years, fertilizer producers had an adequate supply of pre-
mium quality phosphate rock for which the existing chemical processes were
designed.—'
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TABLE 3-1. CURRENT U.S. AMMONIUM PHOSPHATE PRODUCERS
Company—
The Williams Companies
Agrico Chemical Company, subsidiary
CF Industries, Inc.
Bartow Complex
Plant City Complex
Occidental Petroleum Corporation
Occidental Chemical Company, subsidiary
Florida operations
Jefferson Lake Sulfur Company, division
Western division
Beker Industrial Corporation
01 in Corporation
Agricultural Products Division
Farmland Industries, Inc.
Farmers Chemical Company, subsidiary
Mississippi Chemical Corporation
International Minerals and Chemicals
Corporation
Agricultural operations
IMC Chemical Corporation, subsidiary
Brews tar Phosphates
The Gardinier Companies
Gardinier, Inc.
U.S. Phosphoric Products
First Mississippi Corporation
FTRSTMISS, INC., subsidiary
V. R. Grace and Company
Agricultural Chemicals Group
Standard Oil of California
Ortho Division
United States Steel Corporation
USS Agri-Chemicals Division
Mobil Corporation
Mobil Chemical Company, division
Phosphorus Division
Simplot Company
Minerals and Chemical Division
Annual capacity
(103 tons)
Location
Donaldsonville, La.
Bartow, Fla.
Plant City, Fla.
White Springs, Fla.
Plainviev, Tex.
Lathrop, Calif.
Conda, Id.
Hahnville, La.
Marseilles, 111.
Pasadena, Tex.
Green Bay, Fla.
Joplln, Mo.
Pascagoula, Miss.
New Wales, Fla.
Mew Wales, Fla.
Geismar, La.
Luling, La.
Tampa, Fla.
Fort Madison, la.
Bartow, Fla.
Fort Madison, la.
Kennewick, Wash.
Richmond, Calif.
Cherokee, Ala.
Depue, 111.
Pocatello, Id.
Bv site
1,540
1,000
435
925
25
165
335
465
190
SOO
435
245
630
50
490
150
385
525
495
430
200
75
100
245
240
240
Total
1,540
1,435
1,115
990
300
680
630
540
535
525
495
430
375
245
240
240
Product
DAP
DAP
DAP
DAP
Mixtures
DAP
DAP
DAP
DAP and
mixtures
Mixtures
Mixtures
DAP and MAP
DAP and MAP
DAP and MAP
DAP and
mixtures
DAP and MAP
APN
APN
APN
DAP and
mixtures
DAP
DAP and MAP
a_/ These 16 companies produced 86% of the total annual ammonium phosphate production.
DAP = diammonium phosphate; HAP *" monoammonium phosphate; and APN n ammonium phosphate nitrates.
Source: Director;/ of Chemical Producers '- USA (1977).-
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TABI£ 3-2. CURRENT U.S. NORMAL SUPERPHOSPHATE PRODUCERS
Company^'
Kerr-McG«e Corporation
Kerr-McGee Chemical Corporation,
subsidiary
United States Steel Corporation
USS Agri-Chemicals Division
Esmark, Inc.
Swift Agricultural Chemicals Corporation
International Minerals and Chemicals
Corporation
Rainbow Division
Gold Kist, Inc.
Valley Nitrogen Producers, Inc.
AFC Company, subsidiary
Agriform of Imperial Valley, subsidiary
The Gardinier Companies
Gardlnier, Inc.
U.S. Phosphoric Products
Kaiser Aluminum and Chemicals Corporation
Kaiser Agricultural Chemicals Division
cloyster Company
American Plant Food
Indiana Farm Bureau Coop Associates, Inc.
Occidental Petroleum Corporation
Occidental Chemical Company, subsidiary
Western Division
Columbia Nitrogen Corporation
Stauffer Chemical Company
Fertilizer and Mining Division
The Williams Companies
Agrico Chemical Company, subsidiary
Dally capacity
(tons)
Location
Baltimore, Md.
Cottondale, Fla.
Jacksonville, Fla.
Philadelphia, Penn.
Albany, Ga.
Chicago Heights, 111.
Columbus, Ga.
Greensboro, N.C.
Nashville, Tenn.
Wilmington, N.C.
Bar tow, Fla.
Do than, Ala.
Savannah , Ga .
Wilmington, N.C.
Americus , Ga .
Florence, Ala.
Hartsville, S.C.
Spartanburg, S.C.
Clyo, Ga.
Cordele, Ga.
Bena, Calif.
Imperial, Calif.
Tampa, Fla.
Nashville, Tenn.
Omaha, Neb.
Riegelwood, N.C.
Athens, Ga.
Chesapeake, Va.
Galena Park, Tex.
Indianapolis, Ind.
Lathrop, Calif.
Moultrie, Ga.
Tacoma, Wash.
Saginaw, Mich.
By sice
500
500
500
500
175
500
200
200
400
400
300
700
190
500
230
400
400
400
400
400
300
400
600
Not available
Not available
600
150
300
> 400
400
395
395
300
300
Total
2,000
1,875
1,690
1,430
300
700
600
600
450
> 400
400
395
395
300
300
a/ These 15 companies produced 937. of the total daily normal superphosphate production.
Source: Directory of Chemical Producers - USA (1977).-'
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TABLE 3-3. CURRENT U.S. TRIPLE SUPERPHOSPHATE PRODUCERS
Company—
Annual capacity
(1Q3 tons)
Location
By site
Total
CF Industries, Inc.
Plant City Phosphate Complex
W. R. Grace and Company ""
Agricultural Chemicals Group
The Gardinier Companies
Gardinier, Inc.
U.S. Phosphoric Products
The Williams Companies
Agrico Chemical Company, subsidiary
Texasgulf
Agricultural Chemicals Division
Occidental Petroleum Corporation
Occidental Chemical Company, subsidiary
Florida operations
Beker Industrial Corporation
International Minerals and Chemicals
Corporation
Agricultural operations
United States Steel Corporation
USS Agri-Chemicals Division
Engelhard Minerals and Chemicals Corporation
Phillip Brothers Division
Plant City, Fla.
Bartow, Fla.
Joplin, Mo.
Tampa, Fla.
Bartow, Flu.
Aurora, N.C.
White Springs, Fla.
Conda, Id.
New Wales, Fla.
Ft. Meade, Fla.
930
665
100
745
675
600
460
340
300
295
930
765
745
675
600
460
340
300
295
Conservation Division
Farmland Industries, Inc.
Roy 9 tar Company
Simp lot Company
Minerals and Chemical Division
Bordon , Inc .
Bordon Chemical Division
Smith Douglas
Mississippi Chemical Corporation
Stauffer Chemical Company
Fertilizer and Mining Division
Nichols, Fla.
Green Bay, Fla.
Mulberry, Fla.
Pocatello, Id.
Piney Point, Fla.
Pascagoula, Miss.
Salt Lake City, Ut.
230
200
180
120
70
50
35
280
200
180
120
70
50
35
j/ These 16 companies accounted for 100% of the total annual production.
Source: Directory of Chemical Producers - USA (1977).-
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TABLE 3-4. U.S.
4/a/
PHOSPHATE CONSUMPTION--7
Fiscal
year
1970
1971
1972
1973
1974
1975
1976p.
Total
P2o5
consumption
4,573,750
4,803,443
4,863,738
5,085,162
5,098,625
4,510,979
5,215,246
P2o5
in
mixtures
3,709,062
3,943,372
3,997,280
4,237,591
4,271,429
3,717,825
4,422,380
Direct application
Superphosphate
Normal Concentrated
62,131 546,207
55,009 555,960
43,553 576,506
35,328 569,353
38,545 537,952
36,355 530,598
28,672 535,995
materials
Ammonium
phosphates
183,638
178,873
174,277
201,423
193,000
175,899
228,199
Di ammonium
phosphates
726,486
814,938
883,795
1,073,198
1,051,416
1,038,091
a/ Quantities in short tons of
This supply of phosphate rock was maintained by competition among mine pro-
ducers, and the processor had wide flexibility in selecting sources of this
raw material. This desirable situation appears to be rapidly fading.
Four factors are cited— as responsible for a recent worldwide trend to-
wards the use of lower quality phosphate rock for fertilizer production.
These factors are:
* A two-step price surge during 1973 and 1974 in the price of phosphate
rock.-t' The price increased from about $7 to $70 per ton.—
* A change in processes used for mining and beneficiation of phosphate
rock.
* An increase in exploitation pressure on phosphate ore reserves to
meet market demands.
* An extension of phosphate rock production to more diverse ore types.
The principal causes of variability in phosphate rock properties are the
diverse ore deposit characteristics.—' Although all commercial phosphate raw
materials are predominantly of the apatitic type, they differ with respect to
the composition of the apatitic mineral, the presence of mineral impurities,
the Po05 concentration, and physical properties.
Because of the tightening supply of high quality phosphate ores, many
domestic producers have abandoned their dependence on these ores. Instead,
the fertilizer manufacturers are striving for maximum ?205 recovery from in-
ferior ores because the greatly increased market value of phosphate fertili-
zers makes this economically more attractive. This trend is resulting in a
10
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gradual lowering of product quality because of phosphate rock blending, less
beneficiation to reduce ?205 waste, and the marketing of nonpremium grades (<
31% P20s)- This movement away from use of high quality raw materials appears
to be permanent .— '
Potential low-grade phosphate ore reserves include the Hawthorn Formation
of Florida and currently unmined portions of the Phosphoria Formation in the
western United States. However, new mining and processing techniques may have
to be developed to utilize these low-grade but potentially useful sites .2.'
Because of this development, fertilizer processors must now deal with a
complicated array of chemical and physical quality factors, which formerly
were of only minor concern.^.' Physical quality factors of concern include
phosphate rock texture, particle size, degree of crystallinity, and physical
alteration. Important chemical quality factors are ?2®5 levels, fluorine and
carbonate content, and the degree of contamination by organic matter, chlo-
rides, and inert mineral gangue (worthless material).
The presence of soluble iron and aluminum compounds, as well as the con-
centration of magnesium, can adversely affect both the processing and quality
of the products. These compounds affect the chemistry of fluorine distribu-
tion as well as intermediate precipitation processes, and are often reported
as insoluble phosphate compositions in the finished products.
Trace contaminants include heavy metals (i.e., cadmium, lead, zinc, mer-
cury, etc.) and toxic elements (i.e., arsenic, selenium, vanadium, chromium,
etc.) from minerals and acids, as well as radionuclides (i.e., uranium, tho-
rium, radium, and radon). The concentrations of radionuclide impurities are
generally too low to have any serious effect on processing or product grades.—
Following mining and beneficiation, western phosphate rock is almost al-
ways calcined to remove organic material prior to conversion to fertilizer.
As the movement to the utilization of lower grade ores continues, the use of
calcining techniques may become of increasing importance. However, calcina-
tion has the potential to volatilize cadmium and the volatilized cadmium is
generally lost to the atmosphere since pollution control techniques for cad-
mium emissions are not usually practiced. Volatilization losses of cadmium
are discussed in greater detail later in this report (see Section 4).
In the future, it appears that as the high quality weathered ore depos-
its of Florida, which have low cadmium content, are depleted, the lower grade
deposits will be exploited for fertilizer usage. The western ores and possi-
bly some of the lower grade ores of Florida and the Southeast will contain
higher cadmium levels than the currently-mined Florida deposits.
11
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Some experimental laboratory scale studies now under way at TVA are de-
signed to identify and resolve fertilizer processing problems caused by new or
increased impurities in phosphate rock raw materials.—' Exploratory work is
also under way toward improving the physical condition of phosphate rock that
may be used for direct application to the soil.— Interest in direct applica-
tion is reviving due to the development of a better understanding of methods
for characterization of phosphate rock. It is now relatively easy to identify
phosphate materials best suited for direct application. Recent studies have
shown that one promising method for convenient application of pulverized rock
is to suspend the rock in water, with or without added clay, and then apply
the suspension to soil with the use of spray equipment common to the fluid
fertilizer industry.
Marketing Trends and Projections
Total domestic phosphate fertilizer consumption was 5.2 million tons
^2^5 *n 1976.—' Mixed fertilizer products continue to dominate the phosphate
market and the use of diammonium phosphate has continued to expand. Produc-
tion of normal superphosphate continues to decline in favor of higher analysis
products. Concentrated superphosphates have remained at fairly stable produc-
tion levels in recent years (1974 to 1976).—' Projections described in the
literature^' indicate that domestic consumption of phosphate fertilizers will
grow at a compound rate of 3%/year from 1976 through 1980 and reach almost 6
million tons of P by 1980.
12
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REFERENCES FOR SECTION 3
1. Slack, A. V. Fertilizers. In Kirk-Othmer Encyclopedia of Chemical Tech-
nology, Volume 9. A. Standen, ed., Interscience Publishers, New York,
1966. pp. 81, 106.
2. Battelle Memorial Institute (Richland, Washington). Inorganic Fertilizer
and Phosphate Mining Industries - Water Pollution and Control. Prepared
for U.S. Environmental Protection Agency, Grant No. 12020 FPD, September
1971.
3. U.S. Environmental Protection Agency. Development Document for Effluent
Limitations Guidelines and New Source Performance Standards for the Basic
Fertilizer Chemicals Segment of the Fertilizer Manufacturing Point Source
Category. EPA 440/1-74-011-a, March 1974.
4. Tennessee Valley Authority, National Fertilizer Development Center. Fer-
tilizer Trends 1976. Bulletin, Y-lll, Muscle Shoals, Alabama, March 1977.
5. Stanford Research Institute. Directory of Chemical Producers - USA. 1977
Edition, Menlo Park, California, 1977.
6. Lehr, J. R. Phosphate Raw Materials and Fertilizers: A Look Ahead.
Tennessee Valley Authority Shortcourse in Modern Fertilizer Technology.
TVA National Fertilizer Development Center, Muscle Shoals, Alabama.
7. Gulbrandsen, R. A. Personal Communication. U.S. Department of the In-
terior, Geological Survey, Menlo Park, California, October 1977.
8. Lehr, J. R., Senior Scientist. Personal Communication. Fundamental Re-
search Branch, Division of Chemical Development, TVA National Fertilizer
Development Center, Muscle Shoals, Alabama, September 29, 1977.
9. Tennessee Valley Authority. National Fertilizer Development Center,
Bulletin Y-15, Situation 77, Muscle Shoals, Alabama, July 1977.
13
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SECTION 4
CURRENT DATA
METHODOLOGY
Midwest Research Institute (MRI) was provided with a preliminary litera-
ture survey by Radian Corporation. Data bases searched by computer included:
Agricola/Cain. 1970-; Compendex. 1970-; NTIS, 1964-; and Pollution Abstracts,
1970-. Manual and machine searches were made for Biological Abstracts, 1955-;
Chemical Abstracts. 1955-; Monthly Catalog. 1972-; and Soils and Fertilizers.
1974 to February 1977. Also reviewed were the Radian Library holdings, the
University of Texas at Austin holdings, and Books in Print. MRI conducted a
search of the Smithsonian Science Information Exchange, Inc. (SSIE) to iden-
tify ongoing research in the areas of interest.
Information was obtained from previous reports for the Environmental Pro-
tection Agency (EPA), National Science Foundation (NSF), Department of the In-
terior, and Energy Research and Development Administration (ERDA), as well as
many technical journals. Other periodicals surveyed were: Agrindex. Biore-
search Abstracts. Biological and Agricultural Index. Bibliography of Agricul-
ture, Phosphorus and Potassium, Phosphorus and the Related Group V Elements,
Phosphorus and Sulfur and the Related Elements, and Fertilizer Abstracts.
Information was obtained during a personal visit to TVA's National Fer-
tilizer Development Center at Muscle Shoals, Alabama. A large percentage of
the research and development effort on fertilizers is conducted at this site.
Fifteen companies and numerous individuals in the U.S. fertilizer indus-
try were contacted in order to obtain information concerning specific proce-
dures, materials, and chemical analyses. Among those companies were: Beker
Industries (Conda, Idaho), Valley Nitrogen Producers, Inc. (Helm, California),
Agrico Chemical Company, a subsidiary of The Williams Companies
(Donaldsonville, Louisiana), and Monsanto Industrial Chemicals Company (Soda
Springs, Idaho). Other companies contacted for information were located in
Florida, North Carolina, Idaho, Missouri, Kentucky, California, Louisiana,
and Utah.
14
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Contacts were also made with the Agronomy Department of Kansas State Uni-
versity, the Potash-Phosphate Institute, the Lawrence Livermore Laboratory at
the University of California, the Idaho Division of the Environment, The Fer-
tilizer Institute, and various offices of the Bureau of Mines, EPA, and the
Geological Survey.
MANUFACTURING PROCESSES
A discussion of phosphate ore mining, ore beneficiation, and commercial
fertilizer production processes is presented in this subsection to provide a
foundation for further discussions relative to the potential for the enhance-
ment of cadmium levels throughout the entire process.
Ore Mining
Phosphorus is mined in the United States almost entirely in the form of
phosphate rock from sedimentary deposits. About 80 to 90% of the domestically
mined phosphate rock is used in fertilizer for agricultural purposes. The re-
mainder is used to make phosphoric acid based chemicals, such as detergents,
water softeners, animal feed supplements, flame retardant compounds, and vari-
ous other compounds.
Domestic phosphate mining operations are conducted in the eastern states
of Florida, North Carolina, and Tennessee, and in the western states of Idaho,
Montana, Utah, and Wyoming. In 1976, the production distribution pattern was
84% from Florida and North Carolina, 4% from Tennessee, and 12% from the west-
ern states.— Of the percentage shown for Florida and North Carolina, essen-
tially all of this is from Florida. Thus, Florida is the major mining site
for phosphate ore.
Most phosphate rock is mined by open-pit methods, in which the overburden
is stripped with draglines and the phosphate rock removed.— The mined rock,
known as matrix, is then placed into a previously prepared sluice pit, and
high pressure water is used to break up the matrix to produce a slurry of ap-
proximately 40% solids. The matrix slurry is pumped through movable steel
pipelines for distances up to 6 miles to a beneficiation plant. At some mines
the matrix is loaded into trucks or railroad cars and hauled to beneficiation
plants.
In some western locations, phosphate rock is mined by underground tech-
niques; however, these operations account for only a minor part of total do-
mestic production.—
Commercial phosphate rock contains one or more phosphatic minerals such
as fluorapatite or tricalcium phosphate and numerous impurities. The phos-
phate deposits are usually mixed with clay and sand.— The Florida phosphate
15
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deposits are generally shallow and occur principally as a consolidated con-
glomerate mixed with sand and clay.— The Tennessee brown rock deposits are
a weathered phosphatic limestone, while the North Carolina deposits are found
in phosphatic clays, limestones, and sands. The western phosphates occur as
a folded and faulted shale member of the Permian Phosphoria Formation.
It is not possible to be explicit regarding specific associations of cad-
mium with phosphates because of the lack of published information on this sub-
ject. Cadmium may be associated with the apatite, suIfides, organic matter,
or any combination of these. Extensive anionic and cationic substitutions in
the apatite are possible.5:' Cadmium may substitute for calcium in the apatite
structure, but it can also occur with other heavy metals in sulfides (e.g.,
pyrite (FeS2) and troilite (FeS)), as well as inorganic matter.—' Pyrites are
commonly associated with marine phosphate deposits and demonstrate the impact
of weathering. Pyrite pseudomorphs found in phosphate pellets from shallow
deposits indicate a change from the sulfide of the original pyrite to the
oxide. More deeply buried deposits which have not undergone weathering, will
still contain pyrites.
Recent work by Martin et al. shows either that: (a) cadmium and phos-
o _
phorus (as PCv ) are taken up together by phytoplankton in an approximate
ratio of 1 rag phosphorus for each 1 ug of cadmium; and/or (b) cadmium is taken
up by adsorption. This relationship between phosphorus, a vital nutrient, and
cadmium could partially explain the presence of cadmium in phosphate deposits.—
Another factor in the differences in cadmium levels of eastern and western
ores may be attributed to their contrasting geological histories. Both the
eastern and western ores are due, at least in part, to marine deposits. How-
ever, a more dynamic environment in the West, including volcanic eruptions and
tectonic disturbances, could have resulted in lava, ash, and upward moving ore
solutions penetrating the western phosphate deposits. This would lead to west-
ern ores of generally lower quality and likely containing more cadmium. Ap-
parently due to high humidity and high rainfall, extensive water leaching of
the shallow Florida ores has resulted in lower cadmium levels,-^' By contrast,
the western ores existed in a dryer climate and occurred in deep deposits.
These factors resulted in minimum weathering of the ore and anaerobic condi-
tions in the deposits. Both sulfate reducing bacteria, which form the highly
insoluble cadmium sulfide, and the strong adsorption properties of the organic
matter combine to retain and stabilize the cadmium in the western deposits.—'
Ore Beneficiation
Methods of beneficiating phosphate rock differ to some extent with each
operating company.— Beneficiation is defined as the processing of ores for
the purpose of (a) regulating the size of the desired product, (b) removing
unwanted constituents, and (c) improving the quality, purity, or assay grade
16
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of a desired product. Factors which influence the type of beneficiation meth
ods used include: the matrix particle size and analysis; the ratio of phos-
phate, clay, and sand in the matrix; and the preference of the operator for
certain equipment. In general, the initial treatment consists of separating
coarse-sized phosphate rock from the clay, sand, and fine-sized phosphate.
This operation, conducted in a washer plant, separates the matrix into three
components: slimes, fine phosphate and sand, and coarse phosphate. A gener-
alized flow sheet is given in Figure 4-1.
The coarse phosphate separated from the washer is stockpiled for use in
all types of phosphate fertilizer plants.— Fine-sized material, consisting
of sands, clay, and phosphate, is generally deslimed to remove the clays and
then sent to a flotation plant where the fine phosphate is recovered by flo-
tation. Small quantities of sodium hydroxide, fatty acids, fuel oil, amines,
kerosine, and sulfuric acid are utilized in the flotation process. The re-
mainder of the material, referred to as sand tails, is then discarded in the
slime ponds. The slimes, containing about 4 to 6% solids, are generally
pumped to slime ponds constructed in mined out areas. These slimes, which
cannot be effectively beneficiated, can contain up to one- third of the
originally present in the mined ore^'
Following mining and beneficiation, western phosphate rock and some east-
ern ores are almost always calcined to remove organic material prior to con-
version to fertilizer. The average total weight loss from the beneficiated
ore due to ignition is reported to be about 10%.—
Calcining can also be effective against all three types of cadmium asso-
ciation in the phosphate rock, either by lattice decomposition or rearrange-
ment. The cadmium will be free to vaporize, but since total evolution of cad-
mium is not observed, it must be partially condensed and perhaps reprecipitated.
Calcining of the original apatite (~ 800 °C) to form fluorapatite involves a
complete recrystallization which will free any cadmium in the original ore.— '
At temperatures of 500 °C, cadmium in the organic matter will be released, and
any sulfides will decompose around 700 to 800 °C.
Calcination in the West is generally carried out at 900 to 1000 °C. These
temperatures can potentially remove (via volatilization) up to 67% of the cad-
mium. Some calcination is also performed in North Carolina; however, operat-
ing temperatures are generally in the range of 600 to 800 °C.
Calcination is generally conducted in rotary kilns similar to cement
kilns. The exhaust gases, containing volatilized cadmium probably in the form
of cadmium fluoride, are discharged from the kilns through a waste gas stack
(commonly 100 to 150 ft high) and vented to the atmosphere. Pollution control
17
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oo
Coarse Phosphate Rock
Clear Water
Mine
Ore
ll
I
Overburden
Fine Phosphate
Concentrate
I
Raw Material for All Types
of Phosphate Fertilizer Plants
Slimes
Fine Phosphate
and Sand
Flotation
*
Slime
Ponds
Sand Tails
Figure 4-1. Generalized flowsheet of a phosphate rock mining and beneficiation plant.
3/
-------
for cadmium emissions is not generally practiced in the United States during
calcination of phosphate rock; therefore, most of the evolved cadmium is ap-
parently discharged to the atmosphere.—'
The plant product sent to storage is analyzed for particle size, P20c
content, sodium, potassium, arsenic, and fluoride. Common shipping grades are
31 to 35% P205.i/
Wet Process Phosphoric Acid Production
This process is the principal source of fertilizer phosphoric acid in the
United States.— Beneficiated phosphate rock is reacted with a strong mineral
acid (normally sulfuric acid) to convert the tricalcium phosphate to ortho-
phosphoric acid (BLPO,) as shown in the reaction— :
Ca10(P04)6F2 + 10 H2S04 + 20 H20 > 10 CaSO^ • 2 H20 + 6 H-jPO^ + 2 HF
Depending on reaction conditions, the calcium sulfate can crystallize out as
an anhydrite (€3804), a hemihydrate (CaSO^ • 1/2 H20), or a dihydrate (CaSC>4 •
2 H20) commonly referred to as gypsum. Processes have been developed for each
of these three forms. In the United States, only the dihydrate process has
achieved any commercial significance, because this form is more easily fil-
tered, retains less P205, and is more economically attractive.—'
A flow sheet typical of the dihydrate processes showing the basic opera-
tions is given in Figure 4-2. Pulverized beneficiated phosphate rock, contain-
ing 30 to 35% P205» is continuously fed to a reaction system where it is mixed
with sulfuric acid and a recycle stream of dilute phosphoric acid. In most
plants, the concentration of the sulfuric acid used is between 77 and 98%.
In the digestion tank(s) the rock and acid react to form gypsum (dihydrate)
and phosphoric acid. To obtain complete reaction of the rock, the rock-gypsum-
acid slurry is rapidly circulated between the digestion tanks or the compart-
ments of a single tank at 75°C. Retention time in the digester is in the range
of 3 to 8 hr. The extraction of P^O,- from the refined ore normally exceeds 9670
and the strength of phosphoric acid produced is in the range of 30 to 327<, P20r.
The acid slurry flows from the digester to a filter system where gypsum is
removed.—' Operating conditions are normally controlled so that the gypsum is
easily filtered and retains a minimum of trapped P20r. Typically the filter
system yields two phosphoric acid streams: a 30 to 32% P20c product stream and
a stream containing about 20% P20 which recycles to the digester.
19
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Water
^ Vent to Atmosphere
Fluorine Scrubber
—»• Waste Water
Phosphate•
Rock
Recycle iFluoride i
Acid | Fumes
Water
1 fr Recycled
Wash Water
Gypsum Slurry
to Gypsum Pond
Water
» Vent to Atmosphere
Fluorine Scrubber
Waste Water
Figure 4-2. Wet process phosphoric acid flow sheet.—
3/
20
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The 30 to 32% Po^5 Pr°duct stream from the filter is evaporated to give a
phosphoric acid product containing about 54% P^^.—' After concentration, the
phosphoric acid becomes supersaturated with respect to impurities such as
iron and aluminum phosphates, soluble gypsum, and fluosilicates.— These im-
purities are present in amounts sufficient to create an accumulation problem
during acid storage. Thus, it is necessary to remove these precipitated im-
purities before the acid can be considered a marketable product. The removal
process involves holding the phosphoric acid product under controlled tempera-
ture conditions followed by physical separation of the impurities (e.g., cen-
trifugation). The separated solids are normally used as an additive in dry
fertilizer production, principally in diammonium phosphate and to a lesser ex-
tent in the manufacture of superphosphate products.—
The wet process phosphoric acid plant produces large tonnages of gypsum
(on the order of 4.5 tons of gypsum per ton of P2C>5 Product). It is the general
practice to store this gypsum in diked areas called gypsum ponds. These ponds
are entirely separate from the slime ponds used in phosphate rock mining and
beneficiation operations. The slurried gypsum from the filter is pumped to
these ponds where the gypsum settles to the bottom. The clarified water is
recycled back to the various parts of the process.—
Electric Furnace Phosphoric Acid
Phosphoric acid produced by the electric furnace process is of higher
purity than acid produced by the wet process, and, at the present time, finds
only limited use in the fertilizer industry.—'
While there are a number of companies which produce furnace grade phos-
phoric acid, the processes used by the various producers are quite similar.
Basically, the furnace processes involve the reaction of phosphate rock with
carbon and silica in an electric furnace to form elemental phosphorus.—' The
elemental phosphorus, which volatilizes from the furnace, is collected and
oxidized to P-^Oij.— The P20c *-s absorbed in water to give a concentrated
orthophosphoric acid with a 54% P20r content-
Normal Superphosphate Production
Basically, the production of normal superphosphate involves the reaction
of beneficiated phosphate rock with sulfuric acid to form monocalcium phos-
phate.— The overall reaction which occurs can be expressed as:
Ca1Q(P04)6F2 + 7 H2S04 +17 H20 > 7 GaS04 • 2 H20 + 3 Ca(H2P04)2 • H20 + 2 HF
The monocalcium phosphate is water soluble and the phosphate is available
for plant uptake from the soil solution. No attempt is made to separate the
calcium sulfate from the monocalcium phosphate.—
21
-------
Both batch and continuous processes have been developed for producing
normal superphosphate and a number of modifications of each process exists.—
Figure 4-3 shows a flow sheet which is typical of the continuous normal super-
phosphate process. Phosphate rock (98% < 0.147 mm) is fed at a controlled
rate to a mixer where it is thoroughly mixed with sulfuric acid which has been
diluted to about 75%. The rock-acid slurry discharges from the mixer to a pug
mill where additional mixing occurs and the reaction between the rock and acid
starts. From the mill, the slurry discharges to a slow moving conveyor where
the reaction continues and the slurry hardens to a plastic-like mass. As this
mass leaves the conveyor, it is cut into chunks and transferred to a storage
area for final curing. From the storage area, the normal superphosphate prod-
uct is fed to a pulverizer where it is crushed and screened. In some cases,
it is desired to produce a granular product. The superphosphate can be granu-
lated before or after curing, but granulation before curing is the preferred
route .1'
Triple Superphosphate Production
Triple superphosphate (TSP) contains about three times as much ?205 as
normal superphosphate, because no calcium sulfate is formed in the TSP. The
two principal types of TSP produced domestically are run-of-pile (ROP) and
granular triple superphosphate (GTSP).—' Most modernized and newly estab-
lished plants are of the GTSP type.
TSP is made by the reaction of beneficiated phosphate rock with phos-
Lc acid to g
be expressed as:
o/
phoric acid to give soluble monocalcium phosphate.—' The overall reaction can
2 HF
TSP can be manufactured by either batch or continuous processes, but
most commercial production is by the continuous process. Various modifica-
tions of the continuous process exist, but the basic operations are identical
in each case.—
A flow sheet typical of the production of GTSP by the continuous process
is presented in Figure 4-4. Beneficiated phosphate rock is ground (757o <
0.074 mm) and then mixed with phosphoric acid. The resultant slurry is fed
to a continuous belt where it solidifies. The discharge from the belt is
crushed and sent to a storage pile for curing. The cured product is then
ground and screened. The screened material is passed to a granulator where
it is mixed with water and steam. The resultant wet granules are discharged
to an air dryer where the water is evaporated to give a hard, dense, granu-
lar product.—
22
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Cone «^/V~—
• Ground Phosphate Rock
Sulfuric Acid.
Water-
Pug Mil!
Gas I
Containment j
Enclosure '
L Mixer
Cutter O-^
eyor Q
1
1
i
Exhaust Gas
1
1
11 ,
(J Conveyor ("} 1
I
Curing
Water
r-L
» Gas Dis
Exhaust Gas
0. 1
Building
Product
Figure 4-3. Normal superphosphate flow sheet.
3/
23
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Phosphoric Acid
Mixer
Water
Phosphate Rock
Gas
Containment 1
Enclosure j
I
I
Exhaust
Gas
Q i
Q Conveyor
ai
Conveyor
a
Exhaust Gas
Gas Scrubber
>• Wastewater
Water
Curing
Building
Exhaust Gas
Gas Scrubber
—^Wastewater
Product
Figure 4-4. Flow sheet for granulated triple superphosphate production.
3/
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Production of Ammonium Phosphates
The ammonium phosphates have become one of the two major sources of fer-
tilizer phosphate. The principal advantages which have led to their increas-
ing popularity include low production costs, good physical and chemical prop-
erties, and high nitrogen and phosphate content.—
Ammonium phosphates are normally prepared by neutralization of phosphoric
acid with ammonia.—' The product obtained depends on the ratio of phosphoric
acid and ammonia used, and may be raonoammonium phosphate (NH.H-PO,), diammo-
nium phosphate £(NHA)OHPOA]> or a mixture of the two. The ammonium phosphates
can be made from either furnace or wet process phosphoric acid; most ammonium
phosphates intended for fertilizer use are based on wet process acid.
Several processes can be used to produce ammonium phosphates.—' The am-
moniator process developed by TVA is typical of the processes used to prepare
diammonium phosphate. The flow sheet for the TVA process is shown in Figure
4-5. In this method, wet process phosphoric acid (about 40% Po^5^ *s *-ntro~
duced to the system through a gas scrubber where it serves as a scrubbing me-
dium for the off-gas from the process. The acid solution discharged from the
scrubber is partially neutralized in a reactor with anhydrous ammonia to form
a slurry. The slurry is pumped to an ammoniator-granulator where it is
sprayed over a bed of recycled fines. An excess of anhydrous ammonia is added
in the granulator until the product has a Nl^iPO^ ratio of 2:1. The solidi-
fied diammonium phosphate product flows from the granulator to a dryer, then
to screening, and finally is sent to storage. The common grades of diammonium
phosphate are 16% N, 48% P205, and 18% N, 46% P205.-/
Ammoniated Superphosphate Production
Ammoniated superphosphates are produced by reacting normal superphos-
phate or TSP with ammonia (usually in the form of an ammoniating solution).
The final product composition can be controlled by varying the ratio of feed
materials. In addition, it is possible to incorporate other fertilizer mate-
rials such as urea, ammonium nitrate, and potassium chloride into the produc-
3 /
tion scheme to make a wide range of fertilizer materials.—
The reactions involved in ammoniated superphosphate production are quite
complex.— The overall effect is to convert the monocalcium phosphate in the
superphosphate to dicalcium phosphate and the ammonia to monoammonium phos-
phate. Two secondary reactions can occur if calcium sulfate is present in the
superphosphate (as is the case with normal superphosphate): (a) production of
monocalcium phosphate, and (b) production of tricalcium phosphate. The reac-
tions are controlled to minimize the formation of the insoluble tricalcium
•5 /
phosphate.-^'
25
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fo
a*.
Phosphoric Acid
Ammonia
Other Mat Ms
(Optional)
Gas Disharged
Scrubber
Figure 4-5. Flow sheet for production of diaramonium phosphate.—
-------
2
Nitric Phosphate Production^1
Interest in nitric phosphate production has been limited in the United
States because of a preference for higher grade and more rapid acting fertil-
izers and for economic reasons.
These products are made by dissolving phosphate rock in nitric acid (or
nitric acid plus sulfuric or phosphoric acid), neutralizing the resulting
slurry with ammonia, and granulating. Part or all of the calcium present in
the phosphate rock remains in the product and may lead to complications in the
process chemistry.
The basic chemical reaction depends on the amount of nitric acid used.
If excess acid is required to provide the amount of nitrogen needed in the
product, the principal reaction products are calcium nitrate and phosphoric
acid. If excess acid is not required, and supplemental sulfuric or phosphoric
acid is not used, a HNO-jiCaO mole ratio of 1.8:1 is sufficient for good pro-
cess operation. In this case, the reaction produces monocalcium diphosphate,
calcium nitrate, and phosphoric acid. Neutralization with ammonia ideally
converts all phosphate to dicalcium phosphate and all of the calcium nitrate
to ammonium nitrate.
This mixture is acceptable agronomically, but the combination of calcium
nitrate with ammonium nitrate is too hygroscopic for practical fertilizer use.
Most of the variations in nitric phosphate production are concerned with re-
moval of the calcium nitrate or its conversion in situ to a less hygroscopic
compound.
Micronutrient Addition to Fertilizers
Zinc, copper, iron, and manganese are added to fertilizers used in re-
gions of the United States where soil deficiencies of these essential plant
nutrients exist. Cadmium is not commonly associated with salts of copper,
iron, or manganese; however, zinc may contain significant concentrations of
cadmium. From July 1, 1975, to June 30, 1976, 17,400 tons of zinc, as elemen-
tal zinc, were added to fertilizer.
Most micronutrients are field mixed today. Retail distributors purchase
bulk phosphate, nitrogen, potash, and micronutrients, and custom mix these ma-
terials for the farmer-user.
Although micronutrient-supplemented fertilizers may be used in any re-
gion where soil deficiencies exist, the majority of zinc-supplemented fertil-
izers are used on irrigated corn grown in the high plains area of eastern
Colorado, western Kansas, and Nebraska. Zinc is also typically added to fer-
tilizer used for rice production.
27
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Zinc application rates vary with need. The range of application rates
varies from 2 to 10 Ib of elemental zinc per acre and averages about 5 lb/
acre in the high plains area.
Micronutrient packages containing different ratios of the four micro-
nutrients are also marketed. Zinc is typically present in these micronutri-
ent packages as either zinc oxide or zinc sulfate.
Using the data on consumption of zinc for this purpose and assuming an
average zinc level of 2% in fertilizers, it can be calculated that about 5%
of all marketed fertilizer contains added zinc; this is the same level esti-
mated by TVA.—
CADMIUM LEVELS IN PHOSPHATE ORES AND FERTILIZERS
Cadmium levels in manufactured phosphate fertilizers can vary with the
ore source, with ore beneficiation processes, and with types of phosphate rock
and other raw materials used in the manufacturing process. Most of the data
available is for composite ore samples and for composited fertilizer samples.
In general, very little information exists on the levels and fate of cadmium
as the ore is carried through the various manufacturing steps.
Information on cadmium levels in phosphate ores and fertilizers was com-
piled by Swaine.— Other reviews that contain relevant analytical data in-
clude Athanassiadis,—' Fulkerson and Goeller,•=-!/ and Sargent and Metz.—'
More recent and extensive data can be found in Lee and Keeney,— Mortvedt
and Giordano,— unpublished data by EPA Region X,—' and Gulbrandsen in a
final Environmental Impact Statement.—'
Cadmium in Phosphate Ores
Most phosphate rock mined in the United States is classified either as
eastern (Florida, the Carolinas, and Tennessee) or western (Idaho, Montana,
Utah, California, and Wyoming). In general, cadmium concentrations in the
eastern ores are lower than those of the West. Florida ores range from 2 to
15 ppm, while western ores normally range from 50 to 150 ppm but can contain
up to 980 ppm. A brief discussion of the chemical and physical state of cad-
mium in phosphate ores and the differences between eastern and western ores
was presented earlier in this section.
Available data on cadmium levels found in different phosphate ore depos-
its are compiled in Table 4-1.
Some recent data on phosphate ores in southeastern Idaho have been com-
piled by Gulbrandsen of the U.S. Geological Survey (USGS) and reported, in
part, in an Environmental Impact Statement for that yog-inn 19,207
28
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TABLE 4-1. CADMIUM CONCENTRATIONS IN PHOSPHATE ORES
Origin
Eastern ores
Florida
North Carolina
South Carolina
Tennessee
Western ores
Southeastern Idaho
Meade Peak
Mud stone
Carbonate
Phosphoria Formations
Vanadiferous zone-
Unidentified site
Unidentified sites
Concentration (ppm)— '
8-15
2-10
10-25
13
0.1-2
60-340
50
40
90
470-980
60-100
2-50; 100
Reference
c/
17
14
17
17
19
19
19
19
19
c/
17
a/ Given as a range where possible, single values are averages.
b_/ These high cadmium deposits are not generally mined.
c/ Anonymous industrial sources.
29
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phosphate deposits surveyed contained significant amounts of several toxic
elements, such as cadmium, fluorine, uranium, vanadium, selenium, and the
rare earths. Cadmium averaged 90 ppm for all samples in the survey with a
maximum of 340 ppm in the Phosphoria Formation. In the vanadiferous zone,
cadmium levels as high as 980 ppm were found. The vanadiferous zone was orig-
inally named for a clearly defined area in Wyoming which contained vanadium
concentrations in excess of 1%. This definition has since broadened to denote
any area rich in vanadium content. One such zone in southeast Idaho
(Bloomington area) is presently being mined; however, the low grade phosphate
rock is actually a by-product rather than the ore of primary interest. As the
demand for phosphate rock and rare earth compounds continues, increased mining
of these areas may result. Because of the increased cadmium levels, new or
modified processing techniques may be required to reduce the impurity content.
The USGS is presently doing a similar survey of the Florida ores.
Sources of Cadmium in the Manufacturing Process
In addition to the raw phosphate ores, there are other potential sources
of cadmium that may contribute to the total level found in the end-product
fertilizer. The major sources identified include the acids used in fertili-
zer production and the micronutrients added to fertilizers.
Cadmium can substitute for calcium in phosphate rock and can stay with
the phosphate fraction during the beneficiation process and phosphoric acid
manufacture.—' Sargent and Metz— indicate that the solubility of cadmium
in mineral acid prevents any significant cadmium removal during the acid clar-
ification step. Fulkerson and Goeller,—' however, point out that while zinc
and cadmium are readily soluble in strong mineral acids, they are only slightly
soluble in phosphoric acid and most fertilizer solutions containing phosphates.
Nevertheless, cadmium and other impurities in the phosphate rock, once solubil-
ized during acidulation, generally stay in solution in the phosphoric acid.
At Beker's Conda, Idaho, plant, a filtered solution of a "gyp water" out-
fall to the gypsum pond contained 2.5 ppm of cadmium.—' In one of Beker's
beneficiation ponds, the cadmium level was 0.01 ppm which compares to the EPA
standard or recommended limit for drinking water of 0.01 ppm. Waste outfall
from Monsanto"s plant at Soda Springs, Idaho, contained cadmium at 0.002 ppm.
The variability of cadmium levels in process waters from various plants empha-
sizes the need to identify cadmium sources and to compile an accurate account-
ing of cadmium. In these cases, the cadmium levels in process waters indicate
that there is not a one-to-one transferral of cadmium from the ore to the acid
or fertilizer.
A survey of the fertilizer industry indicated that zinc, lead, and copper
smelter acids are used, where available, in fertilizer production. In most
cases, however, smelter acids are not available in sufficient quantity to meet
30
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the needs of a fertilizer production plant. Of the total U.S. production of
sulfuric acid, 10.9% is smelter acid with about 3% resulting from zinc roast-
ing.JJL' About 43% of the annual production of sulfuric acid is consumed in
PoOc production. Based on discussions with phosphate fertilizer producers,
we estimate that about 10% of the sulfuric acid used in fertilizer production
is a by-product smelter acid. This 10%, however, accounts for about 40% of
all smelter sulfuric acid.
Limited data are available regarding cadmium levels in by-product smelter
acid. Hedley et al..=l/ analyzed sulfuric acid produced by seven major lead,
zinc, and copper smelters. Cadmium levels (by weight) were detected at 1 and
5 ppb in sulfuric acid from two copper smelters; 2, 11, and 114 ppb in three
lead smelter acid samples; and 5. 5, 5, 10, and 17 ppb in five zinc smelter
samples. Fulkerson and Goeller—' report that zinc smelter acids may contain
20 to 60 ppm cadmium; however, no further information was provided regarding
specific sites. More and better data are needed on the cadmium content of smel-
ter sulfuric acid actually used in fertilizer production before the impact of
this source on the level of cadmium in end-products can be assessed.
The sulfuric acid used principally in the preparation of phosphate fer-
tilizers is manufactured from elemental sulfur. For this acid, elemental sul-
fur is mined by the Frasch process to yield a high purity (99.5-99.9%) prod-
uct, which is burned in air to yield sulfur dioxide. The sulfur dioxide is
then converted by the contact process to sulfur trioxide and reacted with wa-
22?
ter to yield high purity sulfuric acid.—' Because of the source of the sul-
fur and the production process, the resultant acid contains only very low lev-
els of heavy metal impurities including cadmium.—
Zinc is added as a micronutrient to fertilizers. Levels added are suffi-
cient to result in application rates of 2 to 10 Ib of elemental zinc per acre
with 5 Ib/acre being about average.
The source of zinc used by micronutrient packagers vary considerably de-
pending on availability and cost. One major source is the recovered skimmings
from the galvanizing industry. Slab zinc is used in galvanizing. The levels
of cadmium in slab zinc vary from 0.001% (10 ppm) to 1.0% (10,000 ppm). This
zinc may also contain 0.001 to 2.0% lead. Zinc used for galvanizing con-
tains an average of about 0.035% (350 ppm) cadmium.—' Another source of zinc
used for micronutrients is the baghouse dust from the brass industry. Zinc
used in brass production contains no more than 0.004% (40 ppm) cadmium.—'
However, because of the high volatility of cadmium, the concentrations of cad-
mium in baghouse dust is likely to be higher than that of the source zinc.
One industrial supplier of the zinc sulfate used by the micronutrient packag-
ers states that their zinc sulfate contains less than 10 ppm cadmium.
31
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Because of the variability of sources of zinc used as a micronutrient ,
the quantities of cadmium which might be introduced in fertilizers from this
source cannot be accurately estimated. However, the worst case would occur
where zinc from the galvanizing process, containing 17= cadmium, is added to
fertilizer at levels sufficient to result in an application rate of 10 Ib of
elemental zinc per acre. This application rate of high cadmium zinc material
would result in application of 0.1 Ib/acre cadmium. This compares to only
0.002 Ib/acre of cadmium that would result from the application of 200 Ib/
acre of phosphate fertilizer containing 100 ppm cadmium.
Cadmium in Phosphate Fertilizers
Cadmium levels in representative southeastern and western fertilizers,
reported by Wilson,.!^' Mortvedt and Giordano,—' Sargent and Metz, — and SCS
Engineers,— are shown in Table 4-2. In some cases, fertilizer concentra-
tions of cadmium correlate with the NPK guarantee.* However, one study by
Lee and Keeney— ' found no correla
level of the fertilizer guarantee.
Lee and Keeney— ' found no correlation between cadmium levels and the
•ye. I
Williams and David—' demonstrated a high correlation (r = 0.954) between
cadmium in a set of New South Wales phosphate fertilizers (ranging from 18 to
91 ppm cadmium) and the precursor phosphate rock. The authors suggested that
during processing, the cadmium in the phosphate rock is transferred to the
phosphoric acid with little, if any, gain or loss of cadmium during manufac-
ture (based on parts per million Cd/% P). This is the principal, if not only,
literature reference to a mass balance study. Acid used in these samples was
from a manufacturing process using elemental sulfur, rather than waste acid
from smelter flue gas absorbers, and therefore did not contribute to cadmium
contamination of the fertilizer. Williams and David^l' also cite a 1940 study
by Walkley, which concluded that cadmium in Australian superphosphates (50 to
170 ppm) was due to both the phosphate rock and the sulfuric acid used in fer-
tilizer manufacture. The highest cadmium concentration was from a process us-
ing acid from zinc concentrates.
A representative of the Beker Industries Corporation at Conda, Idaho, pro-
i the following breakdown of cadmium concent:
Lon of diammonium phosphate from western ore
necessarily representative of the Beker process.
vided the following breakdown of cadmium concentrations in the wet process pro-
duction of diammonium phosphate from western ore.— These figures are not
* NPK denotes the nitrogen-phosphorus-potash content.
32
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TABLE 4-2. CADMIUM CONCENTRATIONS IN PHOSPHATE FERTILIZERS
Concentration No. of
Origin (ppm) samples Reference
Eastern
Unidentified
TSP (0-45-0) 12-14 25
Diammonium phosphate (11-46-0) 6-14 25
Monoammonium phosphate (11-48-0) 6-7 25
Superphosphate mixture 5-7 . 25
North Carolina
Diammonium phosphate 30 17
(10-15-0) 17 17
Unidentified
TSP (0-46-0) 7.2 15
Diammonium phosphate (18-46-0) 9.0 15
Diammonium phosphate (16-48-0) 14.3 15
Monoammonium phosphate (13-52-0) 3.5 15
Western
Idaho
Diammonium phosphate 50 17
(10-15-0) 44 17
Unidentified
TSP (0-45-0) 41-174 14 18
Diammonium phosphate (18-46-0) 50-156 10 18
Monoammonium phosphate (11-48-0) 44-90 3 18
Ammonium phosphate/superphosphate
22-42 4 18
/16-20-OX
\0-18-0 /
33
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Process steps . % P2°5 PPm cd
1 Beneficiation feed (raw ore) 26 140 5.38
2 Beneficiation ore 32 140 4.38
3 Beneficiation tailings 15 130 8.67
4 Calcined ore 33 120 3.63
5 Gypsum by-product 0.5 60 120
6 Pond water (recycled) 0.8 2 2.5
7 30% Phosphoric acid 27 90 3.33
8 Diammonium phosphate (18-46-0) 46 140 3.04
The presence of cadmium in the pond water and the gypsum by-product is
evidence that cadmium does not stay totally with the phosphate, but becomes
distributed throughout the system. The trend (Cd/P20c column) from Steps
l-»2-»4-»7-»8 indicates a gradual decrease in the association of cadmium
with the phosphates as processing continues. The main transfer of cadmium is
apparent in the gypsum by-product, probably a result of acid solubilization.
An anonymous industry source also provided the following data.
Material ^2^5 content Cd analysis
analyzed (%) (ppm)
Calcined ore 33 100 3.3
Phosphoric acid 25 58 2.3
Phosphoric acid 44 109 2.5
Phosphoric acid 52 95-100 2.0
Superphosphoric acid 70 120 1.7
Monoammonium phosphate 48 83 1.7
Diammonium phosphate 46 90 2.0
Data from these two sources indicate that the Cd/P20c ratios are com-
parable for the fertilizers, phosphoric acids, and calcined ores. The second
manufacturer also indicated that some of their other data show that cadmium
precipitates in the gypsum and sludges (i.e., silicates, etc.) during the for-
mation and concentration of wet process phosphoric acid. This also is consis-
tent with the levels measured for gypsum by-product in the first set of data.
Based on the very limited available data, it appears that cadmium in the
phosphate ore is carried through the various stages of fertilizer production
with no evidence of major concentration or dilution.
34
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Additional data are necessary in order to trace cadmium contamination
and changes in concentration (Cd/P2C>5) through fertilizer manufacturing. The
bulk of data now available on fertilizers and ores cannot be directly compared
in an effort to complete a mass balance. A carefully designed program to es-
tablish the pathways of cadmium in the process steps will identify and quan-
tify cadmium emissions (air, ground, and water) as well as the introduction of
other sources of cadmium.
TVA is planning a program to study the fate of cadmium as phosphate rock
is processed into fertilizer products.—' These studies will determine the
ratio of cadmium to Po^5 ^n fertilizer products, raw materials, and inter-
mediates. This program is still in the early planning stages. TVA will work
with The Fertilizer Institute (Washington, D.C.) to obtain representative pro-
cessing samples from fertilizer manufacturers and will conduct chemical anal-
yses of these samples to determine the concentrations of cadmium, ?2®5' aru*
possibly other constituents.
Future Trends and Long-Term Effects
As the demand for phosphate fertilizers continues in the future, the
utilization of low grade phosphate rock will likely continue to increase. Im-
purities in these low grade ores consist not only of cadmium but organic mat-
ter, clays, heavy metals, etc. Cadmium levels will generally be higher as
the deeper deposits are mined. These deposits are less weathered and higher
in organic matter, conditions which facilitate the adsorption and retention
of cadmium.
A method to reduce cadmium contamination in phosphate ores was developed
in Australia by Walker and Tuffley.— The Australian method involves calcin-
ation to reduce cadmium levels to less than 20 ppm. The prime reason for this
work was legislation introduced in Japan to limit cadmium in imported phos-
phate rock to 20 ppm. Walker and Tuffley found a temperature of 1150°C and
an atmosphere of 0.5% oxygen provided the optimum conditions for single step
cadmium and organic carbon removal from the beneficiated ore. Cadmium removal
is enhanced by increasing the temperature in a Nn-COn atmosphere. Since oxy-
gen is required for the removal of carbon, the maintenance of a continual low
oxygen concentration of 0.570 in the No-CO? atmosphere at a temperature of
1150°C provided the desired conditions for effective cadmium removal from the
phosphate rock. The principal differences between this process and the one
currently used in the United States lie in the higher temperatures and the
different reaction atmosphere of the Australian process. Both of these fac-
tors lead to faster and more efficient cadmium removal from Australian phos-
phate ores.
35
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REFERENCES FOR SECTION 4
1. Commodity Data Summaries 1977. U.S. Department of the Interior, January
1977. pp. 124-125.
2. Slack, A. V. Fertilizers. In Kirk-Othmer Encyclopedia of Chemical Tech-
nology, Volume 9. A, Standen, ed., Interscience Publishers, New York,
1966. pp. 83, 133.
3. Battelle Memorial Institute. Inorganic Fertilizer and Phosphate Mining
Industries - Water Pollution Control. Prepared for the U.S. Environmen-
tal Protection Agency, Grant No. 12020 FPD, Richland, Washington,
September 1971.
4. Personal Communication with J. R. Lehr, Senior Scientist. Fundamental
Research Branch of Chemical Development, TVA National Fertilizer Develop-
ment Center, Muscle Shoals, Alabama, September and October, 1977.
5. Vlasov, K. A., ed. Geochemistry and Mineralogy of Rare Elements and
Genetic Types of Their Deposits. Israel Program for Scientific Transla-
tions, Jerusalem, 1966; translation of Geokhimiya, Mineralogiyai i
Geneticheskie Tipy Mostorozhdenii Redkikh Elementov, Publisher -
"Nauka," Moscow, 1964.
6. Martin, J. H., K. W. Bruland, and W. W. Broenkow. Cadmium Transport in
the California Current. In: Marine Pollutant Transfer, H. L. Windom
and R. A. Duce, eds. Lexington Books, D. C. Heath and Company,
Lexington, Massachusetts, Toronto, 1976.
7. Gulbrandsen, R. A. Personal Communication. U.S. Department of the In-
terior, Geological Survey, Menlo Park, California, October 1977.
8. U.S. Environmental Protection Agency. Development Document for Effluent
Limitation Guidelines and New Source Performance Standards for the Basic
Fertilizer Chemicals Segment of the Fertilizer Manufacturing Point Source
Category. EPA 440/1-74-011-a, March 1974.
9. Scott, W. C., Jr. Personal Communication. Chief, Process Engineering
Branch, Research and Engineering Office, Tennessee Valley Authority,
Muscle Shoals, Alabama, October 1977.
10. Considine, D. M. Chemical and Process Technology Encyclopedia. McGraw-
Hill Book Company, 1974. p. 474.
36
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11. Nelson, L. Personal Communication. Manager of Agricultural and Chemi-
cal Development, Tennessee Valley Authority, Muscle Shoals, Alabama,
October 1977.
12. Swaine, D. J. The Trace Element Content of Fertilizers. Technical Com-
munication No. 52, Commonwealth Bureau of Soils, Harpenden, Commonwealth
Agricultural Bureaux England, 1962. pp. 52-53.
13. Athanassiadis, Y. C. Air Pollution Aspects of Cadmium and Its Compounds.
Litton Systems, Inc. NTIS, No. 134, PB188 086, 1969.
14. Fulkerson, W., and H. E. Goeller, eds. Cadmium, the Dissipated Element.
Oak Ridge National Laboratory, NSF (RANN)-AAA-R-4-79, ORNL-NSF-EP-21,
January 1973.
15. Sargent, D. H., and J. R. Metz. Technical and Microeconomic Analysis of
Cadmium and Its Compounds. Versar, Inc. EPA 560/3-75-005, June 1975.
16. Lee, K. W., and D. R. Keeney. Cadmium and Zinc Additions to Wisconsin
Soils by Commercial Fertilizers and Wastewater Sludge Application. Water,
Air and Soil Pollution, 5:109-112, 1975.
17. Mortvedt, J. J., and P. M. Giordano. Crop Uptake of Heavy Metal Contami-
nants in Fertilizers. In: Proceedings of the 15th Hanford Biology Sym-
posium, Battelle Laboratories, Richland, Washington, September 29 to
October 1, 1975. pp. 402-416.
18. Wilson, C. B. Summary of Fertilizer/Cadmium Data. Unpublished Report by
Region X. Environmental Protection Agency, Surveillance and Analysis Di-
vision, 1977.
19. Development of Phosphate Resources in Southeastern Idaho. Final Environ-
mental Impact Statement, Volume I. Prepared Jointly by the U.S. Depart-
ment of the Interior and Agriculture, 1977.
20. Gulbrandsen, R. A. Analytical Data on the Phosphoria Formation Western
United States. U.S. Department of the Interior, Geological Survey, Open
File Report 75-554, 1975.
21. Hedley, W. H., et al. Determination of Hazardous Elements in Smelter
Produced Sulfuric Acid. Monsanto Research Corporation, NTIS, PB 240-343,
1974.
22. Lowenheim, F. A., and M. K. Moran. Industrial Chemicals. Fourth Edition,
Wiley Interscience Publication, New York, New York, 1975. pp. 795-800.
37
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23. Information from Anonymous Manufacturers of Phosphate Fertilizers.
September and October 1977. '
24. SCS Engineers. A Preliminary Assessment of Cadmium Additions to Agri-
cultural Lands Via Commercial Phosphate Fertilizers. Draft Final Report,
EPA, Office of Solid Waste, August 1977.
25. Williams, C. H., and D. J. David. The Effect of Superphosphate on the
Cadmium Content of Soils and Plants. Aust. J. Soil Research, 11:43-56,
August 1973.
26. Personal Communication with A. Kukla, Environmental Affairs Officer.
Beker Industries Corporation, Conda, Idaho, September 1977.
27. Personal Communication with C. H. Davis, Director of the Chemical Devel-
opment Division, National Fertilizer Development Center. Tennessee
Valley Authority, Muscle Shoals, Alabama, September 1977.
28. Walker, W. M., and J. R. Tuffley. Cadmium Volatilization from Phosphate
Rock. Proceedings of the National Chemical Engineering Conference,
Surfer's Paradise, Queensland, Australia, 1974.
38
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SECTION 5
RESEARCH NEEDS
This section briefly delineates the major areas in which new or addi-
tional data are required in order to resolve the questions regarding poten-
tial cadmium enrichment in the phosphate fertilizer manufacturing process.
Additional areas will be discussed which may not be directly applicable to
present manufacturing processes, but which may be important in assessing the
current and future impacts of phosphate fertilizers on cadmium levels in the
environment.
CADMIUM IN PHOSPHATE ROCK
Limited data are available concerning the geology and mineralogy of the
cadmium compounds in the raw, unbeneficiated phosphate rock. This is particu-
larly true for those raw ores from deep, unweathered deposits in which there
is an appreciable organic component as compared to the shallow, weathered de-
posits. Data are required for the mineral forms of cadmium (e.g., crystal
forms, host compounds, etc.) and the distribution between the apatite and
other components of the raw ore. This information would provide a more re-
fined view of the beneficiation process and the mechanism by which cadmium
is transported through this process. If cadmium removal becomes necessary in
the future, these data would provide the background for the determination of
the most technically and economically sound method of removal. The USGS is
currently conducting studies of the raw Florida phosphate ores.
MASS BALANCE STUDIES
From the information presented in this report, a detailed mass balance
study is obviously needed to ascertain the fate and levels of cadmium as the
raw ore is processed into a finished commercial fertilizer. At the present
time, data in this area are very limited and until such data are developed,
any conclusions concerning the changes in the level of cadmium during the
phosphate fertilizer production process must be considered tentative. The
TVA is currently in the very early planning stages of mass balance studies.
39
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CADMIUM REMOVAL
As deposits of high grade (low cadmium) ores are depleted and industry
turns to lower grade deposits, cadmium removal may become necessary. At the
present time, certain beneficiated phosphate ores in the United States are
calcined. Using data developed on the characterization of cadmium in the raw
phosphate ore, engineering studies can be performed to determine the effects
of calcining on the beneficiated ore, the most efficient calcination process,
and, if calcination is, in fact, the best method for the removal of cadmium.
In many other industrial processes, methods other than calcination are pres-
ently used to separate trace impurities from the host material.
As the cadmium levels in the phosphate rock increase, air emissions from
calcination processes may pose a serious localized air pollution problem. If
data are unavailable, studies should be conducted on the engineering aspects
(e.g., retention time, temperature, calcining atmosphere, etc.), pollution
control devices for emission control, and the fate of cadmium volatilized
during calcining.
SMELTER ACID
Additional data are needed to detail the actual quantities of by-product
smelter acid used in the manufacture of phosphate fertilizers, the geographi-
cal location of this consumption and its relationship to the source of the
raw ore, and the levels of cadmium present in this by-product acid. Current
reported data on cadmium levels in by-product smelter acid show a wide range
of values (approximately 1 ppb to 60 ppm) so that it is extremely difficult
to evaluate this material as a potential source of cadmium increase in the
manufacturing process.
MICRONUTRIENTS
Zinc micronutrients may be a significant source of cadmium addition to
the finished commercial phosphate fertilizer. Additional data are required
concerning the sources of zinc used as a micronutrient additive (e.g., slag
from galvanizing processes, bag dust from bronze manufacturing, etc.), the
quantities used from each source, and the cadmium levels present in the zinc
from each source. Currently, very limited data have been compiled concerning
this potential source of cadmium.
40
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BIBLIOGRAPHIC DATA
SHEET
1. Report No.
EPA 560/2-77-006
3. Recipient's Accession No.
4. Title and Subtitle
Cadmium in Phosphate Fertilizer Production
5. Report Date
November 1977
6.
7. Author(s)
Thomas W.
Lapp, Kathryn Bohannon, Charles E. Mumma, Fred Hopkins
8. Performing Organization Rept.
No.
9. Performing Organization Name and Address
Midwest Research Institute
425 Volker Boulevard
Kansas City, Missouri 64110
10. Project/Task/Work Unit No.
Task VI
11. Contract/Grant No.
Contract No.
68-01-3201
12. Sponsoring Organization Name and Address
Environmental Protection Agency
Office of Toxic Substances
Washington, D.C. 20460
13. Type of Report & Period
Covered
Final
14.
15. Supplementary Notes
16. Abstracts
The purpose of this task was to study the levels of cadmium as phosphate rock is
processed into commercial fertilizer and to determine if an increase in cadmium levels
occurs. In general, very little information is available on the levels and fate of cad-
mium as the ore proceeds through the various manufacturing steps. Cadmium levels in mined
raw ore range from about 10 to 150 ppm, depending upon the source of the ore. Additional
sources of potential cadmium contamination during processing are sulfuric acid and added
micronutrients. Approximately 10% of the sulfuric acid consumed in the manufacturing pro-
cess is by-product smelter acid; however, the cadmium content of this acid is not well
defined. Very few data are available concerning any increase in cadmium levels result-
ing from the addition of micronutrients. From the results of this study, it is not cur-
rently possible to establish material balances or draw inferences about the concentra-
tions of cadmium during the various stages of manufacture. Existing data do not indicate
that a significant increase occurs in the cadmium to phosphorus ratio between raw mate-
rials and the finished product. This conclusion is based on very limited data and must
be considered tentative until corroborated by additional evidence.
17. Key Words and Document Analysis. 17o. Descriptors
Cadmium
Phosphorus inorganic compounds
Manufacturing
Sulfuric acid
Trace elements
Micronutrients
Phosphate fertilizers
Plant nutrition
17b. Identifiers/Open-Ended Terms
Heavy metals
17c. COS ATI Field/Group
18. Availability Statement
Release unlimited
19.. Security Class (This
Report)
UNCLASSIFIED
20. Security Class (This
Page
UNCLASSIFIED
2i. No. of Pages
48
22. Price
FORM NTis-35 (REV. 10-731 ENDORSED BY ANSI AND UNESCO.
THIS FORM MAY BE REPRODUCED
USCOMM-DC 8Z8S-P74
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