TECHNICAL NOTE
ORP/CSD-75-3
RADIOACTIVITY DISTRIBUTION
IN PHOSPHATE PRODUCTS,
BY-PRODUCTS, EFFLUENTS,
AND WASTES
THE UNITED STATES
•NVIRONMENTAL PROTECTION AGENCY
OFFICE OF RADIATION PROGRAMS
AUGUST 1975
-------
ERRATA SHEET
Technical Mote ORP/CSD-75-3
Radioactivity Distribution in Phosphate Products,
By-Products, Effluents and Wastes
1. Page 1A, Figure 1, change B-|_ to Bi.
2. Page 1A, IB, 1C, Figures 1, 2, 3 - change all "S's" to "Y's".
3. Page 16, factor number "+, delete: "Information Circular 8501, U.S.
Department of the Interior, Bureau of Mines, 1971.
U. Page 17, Table 8, change "sodium flourosilicate" to sodium fluosilicate."
5. Page 19, Table 9, change "phospheric acid" to phosphoric acid.
6. Page 26, paragraph 1, line 22, change "tons" to pounds."
7. Reference number 11, add "Informtion Circular 8501, U.S. Department
of the Interior, Bureau of Mines, 1971.'
-------
Technical Note
ORP/CSD-75-3
RADIOACTIVITY DISTRIBUTION IN PHOSPHATE PRODUCTS,
BY-PRODUCTS, EFFLUENTS, AND WASTES
by
Richard J. Gulmond
Samuel T. Windham
August 1975
Criteria and Standards Division
Office of Radiation Programs
U.S. Environmental Protection Agency
401 M Street, S.W.
Washington, D.C. 20460
-------
PREFACE
The Office of Radiation Programs of the Environmental Protection
Agency carries out a national program designed to evaluate population
exposure to ionizing and non-ionizing radiation, and to promote
development of controls necessary to protect the public health and
safety. This report was prepared in order to determine the natural
radioactivity source terms associated with phosphate mining and milling
products, by-products, effluents, and wastes. Readers of this report are
encouraged to inform the Office of Radiation Programs of any omissions or
errors. Comments or requests for further information are also invited.
«J/l
William A. Mills, Ph.D.
Director
Criteria & Standards Division
Office of Radiation Programs (AW-460)
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TABLE OF CONTENTS
*
Page
INTRODUCTION 1
METHODOLOGY 3
PHOSPHATE ROCK MINING AND BENEFICIATION 4
WET-PROCESS PHOSPHORIC ACID PRODUCTION . 11
ELEMENTAL PHOSPHORUS PRODUCTION 22
POTENTIAL URANIUM RESOURCE 26
SUMMARY AND CONCLUSIONS 28
-------
LIST OF FIGURES
FIGURE 1 URANIUM-238 DECAY SERIES
FIGURE 2 THORIUM-232 DECAY SERIES
FIGURE 3 ACTINIUM DECAY SERIES
Page
la
Ib
Ic
LIST OF TABLES
TABLE 1 RADIUM-222, URANIUM AND THORIUM CONCENTRATIONS
IN FLORIDA PHOSPHATE MINE PRODUCTS AND WASTES
TABLE 2 ESTIMATED TOTAL RADIUM-226, URANIUM, AND THORIUM
ACTIVITIES IN FLORIDA PHOSPHATE MINE PRODUCTS
AND WASTE
TABLE 3 RADIUM-226 CONCENTRATIONS IN PHOSPHATE MINE
EFFLUENTS
TABLE 4 LABORATORY PROCESS WATER TREATMENT STUDY
TABLE 5 EFFECT OF LIME TREATMENT ON RADIOACTIVITY REMOVAL
FROM EFFLUENTS FROM A WET PROCESS PHOSPHORIC ACID
PLANT (PLANT A)
TABLE 6 EFFECT OF LIME TREATMENT ON RADIOACTIVITY REMOVAL
FROM EFFLUENTS FROM A WET PROCESS PHOSPHORIC ACID
(PLANT B)
Page
5
12
13
14
TABLE 7 EFFECT OF LIME TREATMENT ON RADIOACTIVITY REMOVAL
FROM EFFLUENTS FROM A WET PROCESS PHOSPHORIC ACID
PLANT (PLANT C)
14
TABLE 8 RADIUM-226, URANIUM, AND THORIUM CONCENTRATIONS IN 17
WET PROCESS PHOSPHORIC ACID PLANT PRODUCTS AND
-------
TABLE 9 ESTIMATED .TOTAL RADIUM-226, URANIUM, AND THORIUM 19
ACTIVITY IN PHOSPHATE FERTILIZER PRODUCTS AND
BY-PRODUCTS BASED ON 1973 PRODUCTION DATA
TABLE 10 RADIUM-226 CONCENTRATIONS IN ELEMENTAL PHOSPHORUS 23
PLANT RAW MATERIALS, PRODUCTS, AND BY-PRODUCTS
(AVERAGE OF TWO PLANTS USING FLORIDA ORE)
TABLE 11 RADIUM-226 CONCENTRATIONS IN ELEMENTAL PHOSPHORUS 24
PLANT RAW MATERIALS, PRODUCTS, AND BY-PRODUCTS
(ONE PLANT USING A BLEND OF TENNESSEE AND FLORIDA
ORES)
TABLE 12 COMPARISON OF QUANTITIES OF URANIUM AND RADIUM-226 27
EXTRACTED BY THE U.S. URANIUM AND PHOSPHATE MINING
INDUSTRIES
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ABSTRACT
Phosphate rock throughout the world contains uranium in
concentrations ranging from a few ppm to a few hundred ppm. In the
United States, phosphate rock normally contains between 100-150 ppm
uranium. Mining and processing of these ores redistributes much of the
uranium daughters among the various products, by-products, and wastes.
These materials are then widely dispersed throughout the environment.
This redistribution may lead to increased exposure of the public to these
naturally-occurring radionuclides. In determining the magnitude of the
population exposure caused by this redistribution and in developing
environmental standards and controls to prevent contamination of the
biosphere from these naturally-occurring radionuclides it is necessary to
determine the concentrations and total quantities of these radionuclides
in the products, by-products, effluents and wastes of phosphate mining
and manufacturing.
Samples of phosphate ores, products, by-products, effluents, and
wastes were obtained and analyzed for their radioactivity content.
Calculations were made to quantify the partitioning of _the radionuclides
in the processing steps from mining through the wet and thermal
production techniques. Laboratory studies were made to establish the
effectiveness of various treatments in controlling radioactivity in
liquid effluents. Field studies were conducted to verify the laboratory
results and assess liquid effluent control effectiveness in actual
facility operations. Quantities of radioactivity entering the
environment through various products, by-products, effluents, and wastes
were estimated.
Presented at the Session on Disposal and Utilization of Wastes from
Phosphate Fertilizer Production, 1975 American Chemical Society Annual
Meeting, Chicago, Illinois, August 24-29, 1975.
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INTRODUCTION
It has been recognized for several years that phosphate deposits
throughout the world contain appreciable concentrations of radioactive
material originating from the decay of uranium and thorium present in the
ores. Previous studies of the variability of concentrations of natural
uranium and thorium in the phosphate ores produced in the United States
indicate that they range from 8 to 399ppm (5.4 to 267 pCi per gram) and 2
to 19 ppm (0.4 to 4 pCi per gram), respectively (1). The highest
concentrations were reported in South Carolina phosphate and the lowest
were in Tennessee phosphate rocks.
Generally, the uranium daughters in the ores, at least through
radium-226, have been shown to be in secular equilibrium. This means
'• 1 A
that for each curie (3.7 x J10 disintegrations/sec) of the parent
V
radionuclide, such as uranium-238, there is one curie of each daughter
f
radionuclide also present. Figures 1, 2, and 3 illustrate the uranium,
9
actinium, and thorium decay series-. From the figures it is readily
\
observed that uranium-238, uranium-234, thorium-230, and radium-226 all
belong to the uranium series; uranium-235 and thorium-227 are in the
actinium series; and thorium-232 and thorium-228 are members of the
thorium series. Consequently, when in secular equilibrium, members of
the same series will display equal activity.
Mining and processing phosphate ores redistributes the uranium,
thorium, and their decay products among the various products, by-
products, and wastes. As a result of dispersal of the materials
throughout the environment, there may be increased exposure to the public
-------
FIGURE 1
. URANIUM - 233 DECAY SERIES
FIGURE 2
THORIUM - 232 DECAY SERIES
FIGURE 3
ACTINIUM (URANIUM-236) DECAY SERIES
238
92
4.5*
0°.
V
a
234
goTtl
24d>.
234
234
92"
2.8 « 10* yr
f
-------
from these naturally-occurring radlonuclides. Although some scientific
work has been performed regarding radioactivity in phosphate related
materials, the quantitative aspects have generally focused on determining
the concentration of uranium in the various phosphate formations. These
*r
efforts have primarily been undertaken from a geological perspective.
Little emphasis has been placed on the health physics or environmental
radioactivity perspectives of the various industry operations.
Therefore, in order to evaluate the population dose from phosphate
materials and thus determine the adequacy of present standards and
environmental controls, it was necessary to first quantitate the
radioactivity source terms from the individual operations. This was done
by analytically determining the concentrations in specific products, by-
products, effluents and wastes and estimating the total activity of the
various radionuclides that may a be entering the environment through
different materials. Establishing the concentrations in specific
products, process waters, wastes, and by-products enable the estimating
of local and regional impacts while estimates of total activity from
annual production data will enable evaluation of national impacts as well
as comparision with other industries that release natural radionuclides
to the environment.
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METHODOLOGY
Samples of phosphate ores, produ'cts, by-products, effluents, and
wastes were obtained from several mines, wet process phosphoric acid
plants, and electric furnace facilities throughout the southern United
States . and analyzed for their uranium, radium-226, and thorium content.
Laboratory studies were made to determine the effectiveness of various
neutralization treatments in controlling radioactivity in liquid
effluents from wet-process phosphoric acid plants. Field studies were
conducted at several wet-process phosphoric acid plants to verify the
results of the laboratory studies.
Radium-226 analyses were performed using the radon emanation method
as described in the American Public Health Association's Methods for the
Examination of_ Water and Waste Water (2). By this method, the radium was
*
chemically separated from the samples using a barium sulfate
precipitation. It was then dissolved in acid and stored in sealed glass
tubing for three weeks to allow ingrowth of radon-222, the gaseous
daughter of radium-226. The radon gas was then emanated into an
evacuated zinc coated chamber and counted for alpha activity.
Uranium and thorium were separated from solubilized samples using
liquid ion exchange procedures developed at the Environmental Protection
Agency's Eastern Environmental Radiation Facility in Montgomery, Alabama.
Samples were then coprecipitated and collected on a 0.2 micron pore
filter and counted by alpha spectroscopy using solid state surface
barrier detectors.
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PHOSPHATE ROCK MINING AND BENEFICIATION
Uranium was once thought to be very scarce, yet now It is considered
to be more plentiful than many other elements including mercury,
antimony, silver, and cadmium (3). It occurs in numerous minerals and
ores including pitchblende, uranite, caronite, autunite, uranophane,
lignite, monazite sands, and phosphate rock. Naturally-occurring uranium
contains 99.28% uranium-238, 0.71% uranium-235, and 0.0058% uranium-234
(4).
Thorium is believed to be more plentiful than uranium. It occurs
naturally as thorium-232. Natural thorium is frequently associated with
uranium in mineral deposits. Commercial production of thorium in the
United States has usually been from monazite sands.
Although uranium is present in most phosphate deposits, the higher
concentrations are associated with the marine phosphate deposits (5).
This is probably due to the dissolution of the uranium by the marine
«
environment and later redeposition (6). Marine deposits comprise all of
the phosphate materials presently extracted in the United States. In
Florida, uranium Is substituted for calcium in the extensive phosphate
deposits.
All. of the analytical results from the field studies have not been
obtained. Table 1 presents the results of the analytical determinations
for radium-226, uranium, and thorium concentrations in Florida phosphate
mine products and wastes. The^data indicates that in all of the mine
materials, the radionuclides of uranium and actinum decay series are in
equilibrium. The members of the thorium series are quite close to
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TABLE 1
RADIUM-226, URANIUM AND THORIUM CONCENTRATIONS IN FLORIDA
PHOSPHATE MINE PRODUCTS AND WASTES
MATERIAL
MARKETABLE
ROCK
SLIMES
SAND
TAILINGS
RADIUM - 226
(pCi/GRAM)
42
45
7.5
URANIUM (pCi/GRAM)
234
41
42
5.2
235
1.9
2.6
0.38
238
41
44
5.3
THORIUM (pCi/GRAM)
227
2.0
2.3
228
0.61
1.2
230
42.3
48
232
0.44
1.4
equilibrium. The low activity of the thorium-232 and thorium-228,
particularly in the marketable rock samples, cause an error term of about
+ 30 percent in the analyses so they may be in true equilibrium. These
findings both confirm previous examinations of phosphate rock and shows
that the primarily physical separations of beneficiation do not
V
significantly alter the states of equilibrium, although beneficiation
does produce a redistribution of the concentrations of the radionuclides
from the mine rock to the marketable rock, slimes, and sand tailings.
With respect to concentration, the marketable rock and slime contain
more radium-226, uranium and thorium than does the sand tailings. This
-------
Is expected because the radioactivity is directly associated with the
phosphate compound structure, and the marketable ore and slimes contain
most of phosphate. One-third of the phosphate originally contained in
the matrix remains in the slimes (7). The remainder is primarily in the
marketable rock.
In order to estimate the total annual radium-226, uranium, and
thorium activities extracted by phosphate mining, the production data
from 1973 was examined. In that year, 91% of the overall mine rock
production came from Florida, 3% from Tennessee, and the remainder from
the Western states of Idaho, Missouri, Montana, Utah, and Wyoming (8).
Eighty-two percent of the marketable rock produced was from Florida, 6%
was from Tennessee, and the remainder was from the Western states. Over
99.9% of the mine production in Florida was beneficiated, whereas, about
*
59% of the Western mine production was beneficiated. While estimates of
sand tailings and slime production indicate that they vary from mine to
mine, there are approximately 3250 pounds of sand tailings and 2110
pounds of slimes produced per ton of marketable rock (9). Clearly, with
1973 marketable rock production of 42.1 million tons, a sizable quantity
of slimes and sand tailings were produced.
Field investigations and sample analyses for Tennessee and Western
mine materials have not been completed. Therefore, estimates of the
total amounts of radium-226, uranium, and thorium extracted in phosphate
mining are only for Florida. It is believed that this probably
underestimates the total amounts of radioactivity extracted by about 10
to 15 percent since Tennessee rock should contain relatively low
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TABLE 2
ESTIMATED TOTAL RADIUM-226, URANIUM, AND THORIUM ACTIVITIES IN
FLORIDA PHOSPHATE MINE PRODUCTS AND WASTES
MATERIAL
MINE ROCK
MARKETABLE
ROCK
SLIMES1'1
SAND ,„,
TAILINGS
TOTAL
1973 PRODUCTION
1x10° TONS)
127.3
34.4
363
55.8
126.5
RADIUM - 226
(CURIES)
1300
1480
380
3160
URANIUM (CURIES)
234
•
1290
1390
264
2944
235
59
86
19
164
238
1290
1460
268
3020
THORIUM (CURIES)
227
82
74
228
19
39
230
1320
1570
232
14
46
M Bmd on 2110 pound* of
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Several slime ponds have discharges to the environment. The
discharge quantities depend upon the facility's degree of recycle,
overall water consumption and, local precipitation. Since most of the
radioactivity in the waste products of beneficiation is present in the
slimes, this could pose potential problems to receiving streams if the
radioactivity was not removed prior to discharge. To examine this
aspect, the concentration of radium-226 was determined for slime
discharges and effluent discharges from seven mine and beneficiation
plants. This data is illustrated in Table 3. The concentration of
dissolved radium-226 in slime discharges is less than 5.0 picocuries per
liter at all seven facilities. The concentration of radium-226 in the
undissolved fraction varies greatly and is highly dependent on the total
suspended solids in the slime discharge. The radium-226 concentrations
in picocuries per gram of the undissolved fraction at all seven
facilities are in the same order of magnitude emphasizing the importance
of the total suspended solids concentration in determining the total
concentration of radium-226 in picocuries per liter in the slime
discharge. Although no chemical process is used to treat the discharge
from the slime ponds, low dissolved radium-226 concentrations were
observed in the effluents. This is attributed to the generally low
dissolved radium-226 concentrations in the slime discharges.
The total concentration of radium-226 in every effluent discharge
sample analyzed was less than 3.0 picocuries per liter. Comparison of
the slime discharge and effluent discharge concentrations indicate that
no specific reduction in soluble radium-226 is predictable from the data
-------
TABLE 3
RADIUM-226 CONCENTRATIONS IN PHOSPHATE MINE EFFLUENTS
FACILITY
1
2
3
4
5
6
7
HEAVY SLIME DISCHARGE
DISSOLVED
pCi/LITER
0.82
4.8
2.0
0.6
2.2
1
0.95
UNDISSOLVED
pCi/LITER
10.2
1074
97.6
37.7
520
2248
725.6
pCi/gm
21.3
72.6
305
9.8
52.0
33.6.
15.0
DISCHARGE
POINT
A
B
C
A
A
A
-
-
A
EFFLUENT DISCHARGE
DISSOLVED
pCi/LITER
0.66
0.52
0.68
0.02
0.34
2.2
0.24
-
-
1.01
UNDISSOLVED
pCi/LITER
0.26
0.28
0.28
0.56
1.1
0.74
0.74
-
-
0.14
pCi/gm
17.3
21.5
18.7
31.1
52.4
38.9
28.5
-
-
7.0
obtained at the seven facilities. This is understandable since present
treatment of the slimes involves only settling of solids and consequently
no appreciable precipitation of soluble radium-226 would be expected.
The reduction of total radium-226 from the slime discharge to the
effluent discharge ranged from 92% to greater than 99.9% in the
facilities studied. This was primarily due to removal of suspended
solids containing large amounts of radium-226. Therefore, because of the
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10
significance of the contribution of the radium-226 contained in the
suspended solids to the total concentration of radium-226 observed in
either the slime or effluent discharge, great reductions in suspended
solids levels between the slime discharge and the effluent will result in
corresponding reductions in radium-226 concentrations.
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11
WET-PROCESS PHOSPHORIC ACID PRODUCTION
With 1973 production of 5.62 million tons ^2^5 of phosphoric acid,
that year about 20 million tons of marketable rock went to the
production of phosphoric acid by the wet process method. Under the
provisions of the Federal Water Pollution Control Act of 1972, as
amended, the Environmental Protection Agency is required to establish
effluent limitation guidelines for fertilizer and phosphate manufacturing
and to issue National Pollutant Discharge Elimination System (NPDES)
permits for individual fertilizer and manufacturing facilities. Because
of the need to expeditiously issue permits to such facilities, interim
guidelines for permits recommended a effluent limitation of 9 pCi per
liter total radium-226 pending results from additional studies (10) . To
provide a data base for subsequent guidelines and permits, laboratory
studies were conducted to investigate the reduction in radium-226 levels
after various treatments. Process pond water was obtained from a Florida
wet-process facility. Four bases, quick lime, limestone, hydrated lime,
and dolomite were added to 4 liters of process water in different amounts
to increase the pH. Other bases such as sodium hydroxide were not
studied because they did not appear to be economically viable treatment
alternatives if the bases studied proved satisfactory. After the bases
were added, they were vigorously agitated and allowed to settle until the.
pH stabilized. The resultant supernatant liquids were then filtered and
analyzed for their soluble radium-226 concentrations. No attempt was
made to examine the undissolved radium-226 concentrations because the
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12
TABLE 4
LABORATORY PROCESS WATER TREATMENT STUDY
TREATMENT
UNTREATED
PROCESS
WATER
CALCIUM OXIDE
(QUICK LIME)
LIMESTONE
ROCK
SLAKED LIME
(HYDRATED
LIME)
DOLOMITE
AMOUNT OF
BASE ADDED
(GRAMS)
-
70
500
50
500
RESULTANT
pH
2.0
7.9
4.6
8.0
4.0
DISSOLVED RADIUM - 226
pCi/LITER
75.8
(6.7 pCi/LITER UNDISSOLVED)
0.15
0.11
0.07
•
0.16
differences between laboratory settling and field settling of solids were
deemed to be significant enough to make the laboratory undissolved radium
fraction not representative of the field situation. The results of these-
studies are detailed in Table 4. In all treatment cases, soluble radium-
226 was reduced by more than 99.7%. This was true even though the
resultant pH of the treated wastes ranged from 4.0 to'8.0. This large
reduction is attributed to the readily available amount of sulfate ions
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13
TABLE 5
EFFECT OF LIME TREATMENT ON RADIOACTIVITY REMOVAL FROM EFFLUENTS
FROM A WET PROCESS PHOSPHORIC ACID PLANT
PLANT A - FIELD SURVEY NUMBER 1
SAMPLE 1.0.
UNTREATED
PROCESS WATER
OUTFALL (After
double timing)
SAMPLE I.D.
UNTREATED
PROCESS WATER
LIMED ONCE
PRIOR TO SECOND
LIMING
OUTFALL (After
second liming)
pH
2.0
9.1
pH
1.8
4.4
4.3
7.1
TOTAL RADIUM - 226
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14
TABLE 6
EFFECT OF LIME TREATMENT ON RADIOACTIVITY REMOVAL FROM EFFLUENTS FROM
A WET PROCESS PHOSPHORIC ACID PLANT/PLANT B - FIELD SURVEY NUMBER 1
SAMPLE 1.0.
UNTREATED
PROCESS
WATER
AFTER FIRST*
LIMING
PRIOR TO
SECOND
LIMING
OUTFALL
(Afar doubto-
linring)
UNTREATED
NON-PROCESS
WATER
NON-PROCESS
WATER AFTER
LIMING
NON-PROCESS
WATER OUT-
FALL
pH
2
4.5
«
8
TOTAL RADIUM - 226 (pCi/ll
88-2
74.0
0.90
0.45
1.38
2.6
0.88
TOTAL
234
1769
736
67.8
0.26
0.28
0.96
0.34
URANIUM (pCi/ll
23S
98.8
33.4
3.17
NO
NO
ND
NO
238
182S
734
68.1
0.33
0.39
0.75
0.42
TOTAL THORIUM (pCi/ll
228
3.92
6.15
NO
0.1
ND
0.13
NO
230
393
4.3
1.32
0.13
ND
0.79
1.32
232
6.33
7.5
ND
ND
NO
0.07
ND
•Tins* concentration! in high because of the large impaneled solids load of 23.5 grams par liter.
The dissolved conoantrations in pico curies par liter were:
.Radium -226-5.2
Uranium - 234 - 12.8
Uranium - 235 - 0.52
Uranium - 238 - 12.9
TABLE 7
EFFECT OF LIME TREATMENT ON RADIOACTIVITY REMOVAL
FROM EFFLUENTS FROM A WET PROCESS PHOSPHORIC ACID PLANT
PLANT C - FIELD SURVEY NUMBER 1
SAMPLE I.D.
PROCESS
WATER
OUTFALL
(After single
liming)
pH
1.9
6.6
TOTAL RADIUM - 228-fnCi/l)
56.2
%
2.55
TOTAL URANIUM (pCi/ll
234
676
.26
235
35.1
NO
238
661
. .28
TOTAL THORIUM (pCi/l)
228
0.86
NO'
230
8.6
NO
232
4.1
ND
rainy season. Field survey number 1 was conducted very early in the
rainy season, prior to the initiation of large scale effluent treatment.
Field survey number 2 was performed late in the rainy season after almost
continuous lime treatment for over two months.
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15
From Table 5, comparison of the process water from survey number 1
to survey number 2 shows a 32% decrease in radium-226 concentration
during the second survey. This is probably due to the combination of
dilution of the process water by the influx of surface rain runoff and
the removal of the radioactive material by treatment and discharge of
several million gallons of water per day.
The data indicate that the radionuclides are substantially out of
equilibrium. This is because the uranium, and thorium are dissolved
preferentially over radium-226 by the acidulation with sulfuric acid and
then enter the process water. In all four process water samples, the
uranium activity was a factor of 10 or more greater than the radium-226
activity. The thorium-230 activity varied greatly, ranging from .2 to
4.5 times the radium-226 activity.
/
• As evidenced by Tables 5, 6, and 7, treatment with /lime is highly
efficient in removing radium-226 from the discharged/process water. In
•
all four cases, the outfall samples exhibited radium-226 reduction of
greater than 94 percent. This data argrees very well with removal
efficiencies observed in laboratory experiments. Lime treatment also
proved to be extremely effective in removing uranium and thorium-230 from
treated process water. In addition, uranium and thorium-230 removal
between the process water and outfall were at least 96 and 99 percent,
respectively in the four cases noted.
Therefore, although primarily designed for pH, phosphorus and
flourides control and not for removal of radionuclides in the effluent,
treatment with lime was observed to be highly effective in removing
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16
radium-226, uranium, and thorium from the effluent discharge. These
results are attributed to the following factors:
1. Process water contains a large concentration of sulfate and
phosphate ions to enable ready compound formation.
2. Neutralization by an agent such as lime not only allows for the
reduction of solubility of several compounds but^ provides an ample supply
of calcium ions to enable the large-scale formation of calcium sulfate.
3. The relative insolubility of radium sulfate makes its readily
coprecipitate with calcium sulfate.
4. Uranium and thorium probably precipitate along with calcium
sulfate and other components through substitution for calcium in formed
compounds. .Information Circular 8501, U.S. Department of the Interior,
Bureau of Mines, 1971.
5. Settling provides the opportunity for*the precipitated compounds
to be removed from the effluent and not be discharged as suspended
solids.
Samples of normal superphosphate, diammonium phosphate (DAP)
monoammonium phosphate (MAP), triple superphosphate (TSP), phosphoric
acid, animal feed supplement, sodium fluosilicate, and gypsum were
obtained from several facilities using Florida phosphate rock. Radium-
226, uranium, and thorium data for these samples are shown in Table 8.
The uranium and thorium analyses for these samples are not all completed.
\
For the samples completed there is significant disequilibrium between
uranium-238, thorium-230, and radium-226. Although results are not
available, the normal superphosphate samples probably exhibit equilibrium
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•17
TABLE 8
•••
RADIUM-226. URANIUM, AND THORIUM CONCENTRATIONS IN WET PROCESS
PHOSPHORIC ACID PLANT PRODUCTS AND BYPRODUCTS*
MATERIAL
' GYPSUM
NORMAL SUPER-
PHOSPHATE
DIAMMONIUM
PHOSPHATE (DAP)
TRIPLE SUPER-
PHOSPHATE (TSP)
MONOAMMONIUM
PHOSPHATE (MAP)
SODIUM
FLOUROSILICATE
ANIMAL FEED
PHOSPHORIC ACID
RADIUM-226
(pCi/gm)
33
25 '
5.6
21
5.0
0.28
5.5
840pCi/l
te
URANIUM (pCi/gml
234
6.2
63
58
55
23S
0.32
3.0
2.8
2.9
238
6.0
63
58
55
THORIUM (pCi/gm)
227
0.97
1.6
1.2
228
1.4
0.8
0.9
230
13
65
48
232
0.27
0.4
1.3
•PLANTS USING FLORIDA PHOSPHATE ROCK
because the production of normal superphosphate does not require the
separation of gypsum from the reaction products.
\
Gross mass balancing of the input phosphate rock and the product
phosphoric acid and phosphogypsum indicates that approximately 1 percent
of the radium-226, 60 to 80 percent of the thorium-230, and 80 percent of
the uranium is dissolved during the acidulating by sulfuric acid. The
thorium-230 fraction appears to be the most variable. The numbers are
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18
quite similar to radium-226, uranium, and thorium dissolution by the acid
leach process of milling uranium ore (11). This is not surprising since
i
similar techniques and chemicals are used in both industrial processes.
Individual samples of phosphoric acid displayed a great variation of
radium-226 concentration ranging from a few hundred to greater than -one
thousand picocuries per liter. The variation was not observed to be a
function of solids content or ?2®5 concentration. The average of seven
samples was 840 pCi/liter as noted in the table. This translates to a
concentration of less than 1 pCi per gram of 52% phosphoric acid.
Ammonium phosphates (DAP and MAP) were observed to have
approximately .the same radium-226 concentrations. Uranium concentrations
were greater by a factor of about ten, although the DAP had slightly
higher uranium concentrations than the MAP. The relatively low radium-
226 concentration and much higher uranium concentration is attributed to
the fact that production of ammonium phosphates uses only ammonia and
phosphoric acid with no direct reaction with phosphate rock.
Consequently, the bulk of the radioactivity introduced to the reaction
comes from the phosphoric acid which is enriched with uranium and
deficient in radium-226 due to the partition by removal of the
phosphogypsum. Thorium-230 concentrations were about the same as the
uranium concentrations which is expected because of their similarity in
dissolution fractions.
Triple superphosphate (TSF) contained almost as much radium-226 as
normal superphosphate fertilizer and if we assume normal superphosphate
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19
TABLE 9
ESTIMATED TOTAL RADIUM.-226 URANIUM. AND THORIUM ACTIVITY IN PHOSPHATE
FERTILIZER PRODUCTS AND BYPRODUCTS BASED ON 1973 PRODUCTION DATA8
MATERIAL
NORMAL SUPER-
PHOSPHATE
TRIPLE SUPER-
PHOSPHATE
AMMONIUM
PHOSPHATES
PHOSPHERIC
ACIO
OYPSUM(b>
PRODUCTION
(« 10° TONS)
3.4
3.7
5.8
„(€)
2S.3
Ix 106TON PjOsI
0.62
1.72
2.87
5.62
-
RADIUM - 226
(CURIES)
77
69
30
5.E
760
URANIUM (CURIES)
234
190
330
140
236
9.4
18
7.3
238
190
330
140
THORIUM (CURIES)
227
4
8.4
• -
22
228
3.0
42
32
230
160
340
300
232
O
2.1
6.2
la) Wit Proora Production
(b) B«Md on 4.5 tons gyptum p«r ton PyQ^
(c) Aaumtog 50 pmant PjOg toA
fertilizer is in equilibrium, TSP probably contains more than twice the
concentration of uranium than normal superphosphate. These observations
are in accord with anticipated results because triple superphosphate is
produced by acidulating phosphate rock with phosphoric acid. Therefore,
the product triple superphosphate would be expected to display comprise
activities of radium-226, uranium, and thorium corresponding to the
activities in the reactants, phosphate rock and phosphoric acid, which
display markedly different radium-226, uranium, and thorium
concentrations.
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20
The other two product samples studied were animal feed supplement
which contained about the same radium-226 concentration as the ammonium
phosphate samples, and sodium fluosilicate which contained very little
radium-226. The low radium-226 in the sodium fluosilicate Infers that
by-product fluosilicic acid which is used to produce the sodium
fluosilicate also contains very little radium-226. Uranium and thorium
analyses have not yet been obtained for these two products.
In order to estimate the total activities of radium-226, uranium,
and thorium in the wet phosphoric acid plant products, 'and by-products,
1973 production data was obtained and used in conjunction with the
i
product radioactivity concentrations detailed in table 8 (12). The
[
resulting total activity estimates are illustrated in table 9. Blanks
i
reflect that no estimates were made because of Incomplete data. It
should be noted that because of the difficulty in separating production
• i
i
i
on the basis of Florida'rock versus Western rock, all .total estimates
\
assume that products made with Western rock exhibit approximately the
same radioactivity concentrations. Although this assumption may not be
completely valid, it is anticipated that the error introduced into the
estimates is within the error built into the production estimates and
product radioactivity concentrations.
Approximately 80% of the product radium-226 activity is contained in
the phosphogypsum. Although the radium-226 concentrations of normal
>
superphosphate and triple superphosphate are about 70% of the
phosphogypsum, the bulk magnitude of the amount of phosphogypsum
produced, about 4.5 tons per ton ?2® aci<*» is sufficient to outweigh the
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21
individual contributions of the other products (13). Phosphoric acid
contributes a major portion of the total uranium and thorium activity.
It is emphasized that the columns are not directly additive to determine
the total radioactivity in the products because some of the activity
reflected in the phosphoric acid is also accounted in the ammonium
phosphate and triple superphosphate estimates because phosphoric acid is
used to produce these products. Nevertheless, it is evident that a
sizable inventory of radioactivity is present In the phosphoric acid
plant products and by-products.
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22
ELEMENTAL PHOSPHORUS PRODUCTION
Three elemental phosphorus plants were studied, one using a blend of
Florida and Tennessee rock, and two others using only Florida rock. The
results of radium-226 analysis of the raw materials and products of these
facilities are shown in Tables 10 and 11.
Because of the hazards associated with handling elemental
phosphorus, special procedures had to be established to analyze it for
radioactivity. • Consequently, the early field trips omitted phosphorus
samples until appropriate analytical measures were established and
analytical results of their radium-226 content are not available.
However, elemental phosphorus samples have been obtained during
subsequent field trips* to the two facilities using only Florida rock. Of
all the raw materials used in the production of elemental phosphorus,
only the phosphate rock and particularly the Florida rock show
significantly elevated radium-226 concentrations. The slag exhibits the
greatest concentration of radioactivity of the solid products. In a mass
balance of radium-226 entering and leaving these elemental phosphorus
plants, almost all of it can be accounted for in the input phosphate rock
and in the output slag.
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23
TABLE 10
RADIUM-226 CONCENTRATIONS IN ELEMENTAL
PHOSPHORUS PLANT RAW MATERIALS.
PRODUCTS. AND BYPRODUCTS
AVERAGE OF TWO PLANTS USING FLORIDA ORE
MATERIAL
INPUT
FEED ORE
COKE
GRAVEL
OUTPUT
ELEMENTAL
PHOSPHORUS
SLAG
FERROPHOSPHORUS
(FEP)
RADIUM - 226 (pCi/gm)
60
1
0.5
56
1.2
Table 11 shows that the other major furnace products, elemental
phosphorus and ferrophosphorus contain very small concentrations of
radium-226 and since the production quantities of these materials are
>
small in comparison to slag, they account for only a very small fraction
of the total radium-226 in the products.
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24
TABLE 11
RADIUM-226 CONCENTRATION IN ELEMENTA
PHOSPHORUS PLANT RAW MATERIALS,
PRODUCTS, AND BYPRODUCTS
ONE PLANT USING A BLEND OF TENNESSEE AND FLORIDA ORES
MATERIAL
INPUT
TENNESSEE MATRIX
FLORIDA PEBBLE
COKE
SILICA
ELEMENTAL
PHOSPHORUS
SLAG
FERROPHOSPHORUS
(FEPJ
PHOSPHORIC ACID
MADE FROM SLUDGE
PHOSPHORIC ACID
MADE FROM CLEAN
PHOSPHORUS
RADIUM - 226 (pCi/GRAM)
3.6
65.2
*
0.28
0.36
0.63
17.6
0.24
440 pCi/LITER
101 pCi/LITER
The plant using the blend of Florida and Tennessee rock produced two
types of phosphoric acid, one from burning clean acid and another from
burning sludge. Analysis of these samples showed that the phosphoric
acid made from sludge contained 440 pCi/liter radium-226. Although this
.is not particularly high, its presence is probably due to the radium-226
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25
present In furnace particulates which were not removed by the furnace
precipitator and consequently were scrubbed and collected in the sludge
which was then burned to produce acid. It is the existence of
particulates missed by the precipitator that causes the sludge material.
The acid made from the clean phosphorus contained 101 pCi/liter radium-
226. This is probably due to the introduction of radium-226 from the
sludge acid since the "clean" acid was composed of 16% sludge acid.
Uranium and thorium analyses of these samples have not yet been
completed.
No estimates of total activities of radioactivity in elemental
phosphorus products and by-products were made because the elemental
phosphorus production from Florida rock is only a minor fraction of the
total U. S. production. The bulk of this production comes from the use
j
of Western rock. Although field studies have been initiated to examine
the concentrations in products and by-products using Western rock, they
are presently incomplete. . .
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26
POTENTIAL URANIUM RESOURCE
The radioactive constituents of the phosphate mining and
manufacturing products and wastes have the potential for becoming
environmental pollutants. However, the uranium also has the potential
for becoming an energy resource if concentrated from phosphate materials
and used to fuel, nuclear power reactors. Table 12 compares the tons of
ore extracted from the earth between the U.~S. uranium and phosphate
industries in 1973 and the estimated amounts of uranium and radium-226
contained in the ores. The phosphate industry extracted about 20 times
as much rock than did the uranium industry. The uranium industry
processed ore averaging about 0.2 percent uranium oxide (lUOg), whereas
the uranium content of phosphate rock averages about 0.014 per cent
uranium oxide (U^Og). The Atomic Energy Commission (now Energy Research
and Development Administration) reported that in 1973 the uranium
Industry extracted 13.8 thousand tons of tUOg. During that same period,
the UjOg content in Florida and Western mined phosphate rock was 18.9
thousand tons. The' uranium (U^Og) in the marketable phosphate rock
fraction was 6.2 thousand tons. Clearly, a substantial amount of uranium
comparable to that extracted by the U. S. uranium industry is mined
annually by the phosphate industry. Presently, the only technology being
developed to recover uranium from phosphate rock is the use of solvent
extraction methods to remove the uranium from phosphoric acid. While use
of this technology should enable recovery of several million tons of TJjOg
per year, the bulk of the uranium (about 70%) in the mined rock will
still be lost as a resource in the slime fraction and enter the
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27
TABLE 12
COMPARISON OF QUANTITIES OF URANIUM AND RADIUM-226 EXTRACTED BY
THE U.S. URANIUM AND PHOSPHATE MINING INDUSTRIES
(1973 PRODUCTION DATA)
INDUSTRY
URANIUM MINING
INDUSTRY
PHOSPHATE
MINING
INDUSTRY
MINE
ROCK
MARKET-
ABLE
ORE
TONS OF ORE
( x 10« )
6.77
139.7
42.1
TONS OF U3Oa
i
(a) Assuming equilibrium with uranium parent
(b) Assuming 120 ppm uranium in equilibrium with radium - 226
(c) No contribution was included for Temeaaa ore and Western rock was also assumed to contain 120 ppm uranium.
environment as a potential pollutant. In addition to the uranium
resources lost in the slimes, a substantial resource is also lost by not
recovering the uranium in the leach zone that comprises a portion of the
overburden in many of the Florida phosphate areas. The leach zone also
contains substantial concentrations of uranium (14).
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28
SUMMARY AND CONCLUSIONS
The mining and milling of phosphate rock annually extracts several
thousand curies of radium-226, uranium, and thorlum-230. Approximately
60% of the activity extracted in mining phosphate rock in Florida remains
as waste products of slime and sand tailings after beneficiation. Where
mined rock is used directly, the entire amount of radioactivty present in
the rock is transferred either to the electric furnace or wet-process
phosphoric acid plant. The radioactivity present in the mine rock,
marketable rock, slimes, and sand tailings exhibit equilibrium among
members of the same decay series.
The slimes contain most of the waste product after beneficiation.
Consequently, care must be taken to prevent unnecessary release of slime
material to streams and rivers either as suspended solids during normal
operations or through accidental slime releases. Studies at operating
mine and beneficiation facilities Indicate that routine releases of
radium-226 from slime ponds can easily be minimized by utilizing good
solids setting techniques.
Milling either by electric furnace or the wet-process phosphoric
acid process significantly alters the concentration of radium-226,
uranium and thorium in the resultant process streams, products and
wastes. In the wet-process system, most of the radium-226 is not
dissolved by acidilation with sulfuric acid and thus remains with the
phosphogypsum by-product. Whereas, most of the uranium and much of the
thorium does enter solution and is transferred to the phosphoric acid
product. The phosphate products reflect radium-226, uranium, and thorium
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29
concentrations characteristic of the phosphate material from which they
were derived. Where phosphoric acid is used as the sole source of
phosphorus, the products exhibit relatively low radium-226 concentrations
and substantially higher uranium and thorium concentrations. Where both
phosphate rock and phosphoric acid are used, the products exhibit both
higher radium-226 concentration characteristics of the phosphate rock,
and higher uranium and thorium concentrations characteristic of
:'
phosphoric acid. In the electric furnace, almost all of the radium-226
is retained by the calcium silicate slag by-product with very little
entering the other products. This concentration in the slag may not be
true for other radionuclides such as polonium-210, that may be
volitalized in the furnace.
Lime neutralization of wet-process effluents was observed to be
highly efficient in removing radium-226, uranium and thorium-230.
Removal rates of 94% or more for radium-226, uranium and thorium-230 were
*
observed when pH was increased to 6 or more in the field and even at
lower pH in the laboratory. Therefore, a properly operated liming system
should .be capable of minimizing radioactivity levels in wet-process
facility effluent streams.
Since a large fraction of the radioactivity that enters either the
electric furnace plant or the wet process facility is entrained in the
by-product slag and gypsum, respectively, increased emphasis on assessing
the potential impact of these materials is warranted. Existing as well
as potential future application of these materials such as soil
additives, aggregates, gravel and wallboard applications should be
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.30
thoroughly investigated to estimate the magnitude of their radiological
significance.
The radioactivity concentrations in raw materials, products, wastes,
by products and effluents as detailed in the paper should enable
individual phosphate processors to estimate the concentrations of
radioactivity in their materials. Since individual processors produce!
varying amounts of specific products, by-products, wastes, and effluents,
adaptation of this data to their own specific cases will allow them to
better characterize the redistribution of radioactivity in their
operations.
This paper is not intended to draw overall conclusions concerning
the environmental and public health significance of the data presented.
Rather, the existence of this data will enable additional work to model
*
the migration of the radioactivity through the environment to man via the
various pathways available and use these models to estimate the
individual and overall population impact. *
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REFERENCES
1. Menzel, R. G., Uranium, Radium, and Thorium Content in Phosphate
Rocks and Their Possible Radiation Hazard, J. Agr. Food Chem., Vol.
16, No. 2, pp. 231-234, 1968.
2. American Public Health Association, Methods for the Examination -f
Water and Wastewater.
3. Handbook of Chemistry and Physics. 46th Edition, Chemical Rubber
Company, pp. B-143, 1965.
4. Ibid, pp. 141.
5. Cathcart, J. B. and Gulbrandsen, R. A., Phosphate Deposit, U.S.
Mineral Resources, U.S. Geological Survey Professional Paper 820,
pp. 515-525.
6. Osburn, W. S., Primordial Radionucllde: Their Distribution, Movement
and Possible Effect Within Terrestial Ecosystems, Health Physic
Journal, Vol. 11, pp. 1275-1295, 1965.
7. Draft Environmental Impact Statement, Phosphate Leasing on the
Osceola National Forest, Florida, U.S. Department of the Interior,
Bureau of Land Management Eastern States Office, December 1973.
8. Stowasser,. W. F., Phosphate Rock, 1973 Mineral Yearbook, preprint,
Bureau of Mines, Department of the Interior.
9. Draft Development Document for Effluent Limitations Guidelines and
Standards of Performance, Mineral Mining and Processing Industry,
Vol. II, Mineral for the Chemical and Fertilizer Industries, January
1975.
10. Interim Radium-226 Effluent Guidelines for Phosphate Chemicals and
Phosphate Fertilizer Manufacturing, Statement of Considerations,
Office of Radiation Programs, Environmental Protection Agency,
August 1974.
11. Blanco, R. E., et. al., Correlation of Radioactive Waste Treatment
Costs and the Environmental Impact of Waste Effluents In the Nuclear
Fuel Cycle for Use in Establishing "As Low As Practicable" Guides,
Part 3, Milling of Uranium Ores, Revised Draft Report, Oak Ridge
National Laboratory, June 1974.
12. Fertilizer Trends-1973, National Fertilizer Development Center,
Tennessee Valley Authority, Muscle Shoals, Alabama, Bulletin Y-77,
June 1974.
-------
13. Slack, A. V., editor, Disposal or Use of Gypsum, Phosphoric Acid,
Vol. I, Part II, 1968.
3f
14. Bieniewski, C. L., et. al., Availability of Uranium at Various
Prices from Resources in the United States,
U.S. GOVERNMENT PRINTING OFFICE: 1975- 632-856/39
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