W62-12
          WASTE GUIDE
                   THE
URANIUM  MILTING  INDUSTRY
                                        -
                 U. S. DEPARTMENT OF HEALTH
                   EDUCATION, AND WELFARE
                        Public Health Service

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      WASTE  GUIDE
FOR   THE   URANIUM
 MILLING  INDUSTRY
                 by
            E. C. Tsivoglou
            R. L. 6'Connell
 U. S. Department of Health, Education, and Welfare
          Public Health Service
   Division of Water Supply and Pollution Control <
   Robert A. Taft Sanitary Engineerong Ce'riter
            Cincinnati, Ohio


                1962

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     CENTER  PUBLICATIONS
    The Robert A. Taft Sanitary Engineering Center is a
national laboratory of the Public Health Service for research.
training,  and technical consultation in problems of water and
waste treatment, milk and food safety,  air pollution control,
and radiological health.  Its technical reports and papers are
available without charge to professional users in government,
education, and industry.  Lists of publications in selected
fields may be obtained on request  to the Director, Robert A.
Taft Sanitary Engineering Center,  Public  Health Service,
Cincinnati 26.  Ohio.
                           11

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                     CONTENTS
                                                     Page
FOREWORD                                            v

INTRODUCTION                                         1
   Uranium Milling Industry                              2
   Raw Material - Uranium Ore                          4
   Radioactivity in Waste                                 5

MILL PROCESSES                                      9
   Ore Receiving,  Crushing, and Sampling                 9
   Grinding                                             9
   Uranium Extraction                                  10
   Liquid-Solid Separation                               H
   Uranium Recovery                                   12
      Ion Exchange (IX)                                 13
      Solvent Extraction (SX)                            14
   Upgrading                                          14

 PROCESS WASTES                                     21

   The Mill Balance                                    21
   Radium-226                                        26
      Acid Leach  - RIP                                 28
      Acid Leach  - Solvent Extraction                    29
      Alkaline Leach                                   30
      Summary                                        31
   Gross Alpha Radioactivity                            32
   Radium as Per Cent of Gross Alpha Radioactivity       35
   Thorium                                           36
   Uranium                                           37
   Waste Solids                                        38
   Water Usage                                        38
   Chemical  Characteristics                            40
      Alkaline Leach Process                           40
      Acid Leach Process                              41
      Ion-Exchange Recovery                           42
      Solvent Extraction Recovery                       44

 POLLUTIONAL EFFECTS OF WASTE                   45

   Radiological Pollutants                              45
                            iii

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     Radium                                           46
  Chemical Pollutants                                   50
     Effects on Stream Biota                            50
     Effects on Water Uses                              53
  Physical Pollutants                                   55

POLLUTION ABATEMENT METHODS                    57

  Tailings Ponds                                       58
  Chemical Treatment                                  63
     Waste Neutralization                               63
     Barite Treatment                                  64
     Raffinate Treatment                                65
  Deep-Weil Injection                                   67
  Solid Waste Disposal                                  68

SUMMARY AND CONCLUSIONS                           71
  Uranium Milling Industry                              71
  Process Wastes                                      72
  Pollutional Effects                                    72
  Mill Waste Treatment                                 73
  Conclusions                                          73

BIBLIOGRAPHY                                        75
                            IV

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                      FOREWORD
    Beginning in late 1957, the Public Health Service under-
took a series of in-plant surveys of uranium mills for the
purpose of developing detailed information regarding the char-
acteristics of wastes resulting from the extraction of uranium
from  its ores.  Although primary interest has been in the radio-
active wastes,  especially Radium-226, data regarding the
chemical characteristics and toxicity  of the wastes were also
obtained.  Field studies of the fate of  these wastes in the water
environment and their effects on water quality were also con-
ducted.  This waste guide is a compilation of the findings of
these  studies,  and has resulted from the efforts and generous
cooperation of many persons, companies,  and agencies.
    The studies referred to here were conducted  by the Radio-
logical Pollution Activities  Unit, Division of Water Supply and
Pollution Control,  Robert A.  Taft Sanitary Engineering Center.
They  were made possible by the participation and cooperation of
the Health Departments  and Water  Pollution  Control Agencies of
a number of States, the  companies that operate the uranium
mills, and other Federal agencies.  Especially, the studies
could  not have been completed without the cooperation and
assistance of the

           Arizona State Department of  Health
      Colorado  State Department of  Public Health
        New Mexico Department of Public Health
       South Dakota State Department of Health
            Utah State Department  of Health
       Wyoming State Department of Public  Health
and the
                Climax Uranium Company
                Gunnison Mining Company
             Homestake-New Mexico Partners
           Homestake-Sapin Partners Company
                Mines Development,  Inc.
              Uranium Reduction Company
           Vanadium Corporation of America

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and of the
          Grand Junction Operations Office of the
             U. S. Atomic Energy Commission
     This study was supported in part by funds made available
through the Environmental and Sanitary Engineering Branch,
Division of Reactor Development, U.  S.  Atomic Energy Com-
mission.
       Aerial view of a uranium mill in the Grants - Ambrosia Lake area of
       New Mexico. Its design capacity of 3,300 tons of ore per day is the
       largest of any United States mill. Approximately 350 acres of ponds
       are  used to receive liquid and solid mill wastes. (Photograph courtesy
       of Kermac Nuclear Fuels Corporation)
                                VI

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              WASTE   GUIDE
       FOR   THE    URANIUM
        MILLING  INDUSTRY


                 INTRODUCTION
    The relatively recent growth of uranium mining and mill-
ing to its present position as a major industry in the United
States has accentuated problems associated with disposal of its
waste materials.  In recognition of the importance of safe dis-
posal of the wastes from this industry the United States Public
Health  Service and the Atomic Energy Commission have
studied this matter extensively.  Since 1957 the Public Health
Service has examined in detail the various uranium extraction
processes in use and the effectiveness of waste  control mea-
sures in minimizing the discharge of harmful materials. 1-6  In
addition, the effects of uranium mill waste discharges on the
aquatic environment, the fate of these wastes in the stream,
and the resulting radiological hazards to downstream water
users have also received attention. '"" As a result of these
investigations as well as studies carried out by  others,  a
considerable body of information concerning uranium milling
wastes has been developed.  It is the purpose of this industrial
waste guide to gather together this material and present a
definitive analysis and characterization of the wastes which
can be  expected from uranium mills.  The guide is intended
primarily for the use of public health and water pollution con-
trol agencies, mill operators, and others in their efforts (1)
to evaluate the potential hazards associated with mill wastes,
(2) to determine the effectiveness of existing mill waste con-
trol practices, (3) to estimate the  effect of future mills on
their local stream environment and locate mill sites so as to
minimize such adverse  effects, and (4) to find more effective
methods of waste control and treatment.
                            1

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                                    URANIUM WASTE GUIDE
 URANIUM MILLING INDUSTRY
     The function of uranium mills is to extract uranium in
 concentrated form from ore deposits containing this element
 in quantities generally ranging from four to six pounds (as
 UsOs*) per ton of ore. Many such ore deposits are located
 in the Colorado Plateau area, and consequently, a number of
 the uranium mills are found in this area.  Other important
 uranium-producing areas more recently developed in the
 United States are in central Wyoming, Ambrosia Lake in
 New Mexico, the western Dakotas.  southern Oregon,  north-
 eastern Washington,  and south Texas. Figure 1 shows the
 location of the uranium mills and provides an indication of the
 major ore-producing areas  in the Western United States.

    Mining of  Colorado Plateau ores was started at the turn of
the century for radium values,  later for vanadium, and most
recently for uranium. Since the early 1940's uranium ore pro-
                   Figure I. Uranium mill locations.
    Uranium ore and mill product assays are conventionally
    expressed in terms of uranium oxide (UgOg) content. One
    pound of UgOg contains 0.85 pounds of uranium (U).

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  Introduction
 duction has climbed steadily,  and presently the United States
 is the world's largest producer of uranium ore and concentrate.
 In 1961 the United States produced 8 million dry tons of ore,
 more than twice the production four years earlier. ^  In spite
 of increasing production levels the Nation's undeveloped ore
 reserves remain high, the most recent estimate being 74
 million tons containing UsOg at an average concentration of
 0.25%.
     At  the end of 1961 there were 25 active uranium mills  (and
 two active concentrators) in the Western United States,  as
 listed in Table 1.  These mills, ranging in size from  200 to
 3300 tons per day. had an aggregate design processing capacity
 of 20, 800 tons per day.  One additional mill under construction
 has an estimated capacity of 200 tons per day.
Table 1. URANIUM PROCESSING MILLS - 1961*
Company
Anaconda Co.
Climax Uranium Co.
Cotter Corp.
Dawn Mining Co.
Federal-Radorock-Gas Hills Partners
Globe Mining Co,
Gunnison Mining Co.
Homestake-New Mexico Partners
Homestake-Sapin Partners^3
Kermac Nuclear Fuels Corp.
Kerr-McGee Oil Industries
Lakeview Mining Co. ^
Mines Development. Inc.
Petrotomics Co. c
Phillips Petroleum Co.
Rare Metals Corp. of America
Susquehanna-Western. Inc.
Susquehanna- Western. Inc.
Texas-Zinc Minerals Corp.
Trace Elements Cj.
Union Carbide Nuclear Co.
Union Carbide Nuclear Co.
Uranium Reduction Co.
Utah Construction and Mining Co.
Vanadium Corp. of America
Vitro Chemical Co.
Western Nuclear, Inc.
Location of mill
Grants. New Mexico
Grand Junction. Colo.
Canon Citv. Colo.
Ford, Washington
Fremont Co. . Wyoming
Natrona Co. . Wyoming
Gunnison. Colorado
Grants. New Mexico
Grants. New Mexico
Grants. New Mexico
Shiprock. New Mexico
Lakeview. Oregon
Edgemont. South Dakota
Carbon Co.. Wyoming
Grants. New Mexico
Tuba City. Arizona
falls City. Texas
Riverton, Wyoming
Mexican Hat. Utah
Maybell. Colorado
Rifle. Colorado
Uravan, Colorado
M:.ab. Utah
Fremont Co.. Wyoming
Durango. Colorado
Salt Lake City. Utah
Jeffrey City. Wyoming
Figure 1
code No.
1
2
3
4
5
S
7
8
9
10
11
12
13
14
15
16
17
18
19
21
21
22
23
24
25
25
27
Design ore.
capacity.
T/day'
3. COO
330
200
400
520
490
20o
750
1.500
3.300
300
210
400
200
1.725
300
200
500
l.CCO
330
1. 000
1.003
1.500
980
750
P--.I
645
Estimated
cost of
mill. S
19,358.000
3. CSS. 000
1.800. 000
3. ICO. 000
3. 370.000
3. luO.COO
2.025. 000
5. 325. COO
9. ceo. oco
16. 009.000
3. 161.000
2.610, 000
1.9oO.OOO
1. SCO. 000
9. 500. 000
3. 600.000
2. O'.O. 000
3. 500. 000
7. 000. COO
2, 2-.8.COO
8, 500. 000
S.OOo.OOO
tl. 172.000
6.9'jO.OOO
813, 030
5. 5jO,COO
4. 3:0,009
CONCENTRATORS
Wyoming Mining and Milling Co.c
Union Carb-.de Nuclear Co.b
Union Carbide Nuclear Co,b
Vanadium Corp. ut America
Vanadium Corp. of America

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 4                                    URANIUM WASTE GUIDE

     On the basis of design capacity, 46 percent of the total
 domestic ore produced is milled in the Grants, New Mexico,
 area.  The Colorado River Basin on the same basis accounts
 for 30 percent of the national total.  In 1961 United States
 mills produced 17, 399 tons of uranium oxide (UsOs)  in con-
 centrates which had an approximate gross industrial product
 value of $290 million dollars.

 RAW MATERIAL - URANIUM ORE

     Uranium-bearing ore, as it is delivered to the mills,
 may have a uranium content of from 0. 1 to 1 or 2 percent as
 UsOg, and generally averages about 0. 25 percent.  This
 uranium is present as uranium-238 and uranium-235, both of
 which are naturally occurring radioactive parents of long
 chains of radioactive daughter products.  Natural uranium
 contains about 99.28 percent uranium-238 and 0.71 percent
 uranium-235;^  hence,  the decay chain of uranium-238.
 known as the uranium-radium  family of elements,  is of pri-
 mary concern.  The decay scheme of this  chain is shown in
 Figure  2.  As presented in the figure,  the parent element
 uranium-238, which has a half-life of 4. 5  billion years, decays
 by  alpha emission to thorium-234.  which has a half-life of
 24.1 days and in turn decays by beta emission to protactin-
 ium-234; the decay chain continues until stable lead-206 is
 reached.  In all the series contains eight alpha emitters and
 six beta emitters.  Two minor branches occur in the chain.
 but are not shown since their  effect is negligible.

     The majority of ores contain this radioactive family of
 elements in secular equilibrium, i. e..  the daughter products
 are being formed at the same  rate at which they are decaying.
 with the amount of any member actually present remaining
 constant.  Roughly, one million years are required for pure
uranium to reach equilibrium.  Selective natural leaching from
 the  ore of certain members of the chain will  disrupt this equi-
librium,  and some ores are produced where  this has  occurred.
Most are in equilibrium, however,  and  where this is  the case
it is possible to estimate rather closely the amount of daughter
products present in the ore from knowledge of its uranium con-
tent.  E
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Introduction
239 	 ^ 234 	 ^ pa234
92 Alpha 90 Beta 91 Beta
4 S'lO9 yr 24 1 day I i min
V 226 222
Alpha 88 Alpha 86 Aip^a
80*iQ4 yr 1620 yr 38 day
V 2l4 ~ 2'4
Beta gj Beta 4 Alpha
268min 19 7 min i6iO"4sec
V 2I ,. 206
Beta 34 Alpha 33
50 day 140 day STABLE

234 	 ^230
92 Alpha 90 ~N
2 5I05 yr j
218 214
Po 	  Pb 	 .
84 Aipna 82 \
305mm j
210 210
Pt> 	 * 8>  x
82 Bta 83 A
22 y j

          Figure 2. Uranium-radium family - minor branches not shown.

total combined alpha and beta radioactivity of the ore is 2.1
millicuries (me) per pound of uranium.  The total radioactivity
of the ore delivered daily to the mills in 1960 may then be
estimated at approximately 200 curies, of which 115 curies
per day is alpha and 85 curies per day is beta activity.  Some
85 percent of this activity, or  170 curies daily, becomes mill
waste, the remainder being recovered in the uranium concen-
trate, l^ it is this large amount of radioactive waste material
which presents the  major disposal problem of the  uranium
milling industry.

 RADIOACTIVITY IN WASTE
     The gross radioactivity of the mill waste material is at-
 tributable to each member of  the uranium-radium series
 originally present  in the ore.  Though milling processes are
 designed to extract uranium from the ore.  some small por-
 tion (1 to 10%) of the total uranium remains in the waste
 liquors and spent ore solids.
     The relative degree of hazard presented by each of these
 isotopes covers a wide range.  Table 2 lists each of them in
 order of increasing maximum permissible concentrations in
 water. (MPCW values),  or decreasing degree of hazard.  The
 first isotope listed, radium-226.  is  the most hazardous with
 an MPCW of only 3.3 micromicrocuries per liter ( wc/1).  It

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 6                                    URANIUM WASTE GUIDE

 has, in fact, the lowest MPCW of any of the 264 isotopes  con-
 sidered by the National Committee on Radiation Protection
 (13) and the International Commission on Radiological Pro-
 tection. 14*
Table 2.  URANIUM-RADIUM FAMILY.
                                      j, VALUESa
Isotope
Ra22S
Pb210
Po210
Th230
Th234
U234
y238
Bi210
Pa234
Po218
Po214
Bi214
Pb214
Rn222
MPCW
MM/1
3.3
33
233
667
6.667
10.000
13.300
13.300
b
b
b
b
b
(gas)
Critical
organ
Bone
Kidney
Spleen
Bone
GI tract
GI tract
GI tract
GI tract
_
_
-
_
_
Lung
Half- life
1.620 yr
22 yr
140 day
8 x 104 yr
24. 1 days
2. 5 x 105 yr
4. 5 x 109 yr
5 days
1. 1 min
3.05 min
1.6 x 10'4 sec
19.7 min
26.8 min
3. 8 days
Emission
Alpha
Beta
Alpha
Alpha
Beta
Alpha
Alpha
Beta
Beta
Alpha
Alpha
Beta
Beta
Alpha
 aMPCw value is the maximum permissible concentration in water, for
  average member of the general population (I/30th HB69 value for con-
  tinuous occupational exposure). 13. 14
  No value given.

     The amount of radium-226 contained in the ore produced in
 1960 is estimated to  be about 5400 curies (or grams).  This is
 more than five times the estimated total United States inventory
 of purified  radium-226 for all medical and industrial uses. ^  By
 any measure, the amount of radium-226 contained  in the ore
 delivered to uranium mills is very large relative to what are
 considered  safe concentrations.  Essentially all of this radium
 will be contained in the mill wastes, and so major  waste con-
 trol efforts are concerned with this isotope.
     The isotope listed second in Table 2.  Pb210 (Lead-210),
is a relatively new addition to the list of hazardous  isotopes.
It was not listed in Handbook 5-2 (NCRP)1^, but did  appear  in
the  1960 revision of that document,  Handbook 69.  Thus, it
     More recently,  the Federal Radiation Council has also
     provided guidance  designed to limit radiation exposure
     of the population.   Their recommended exposure limits
     generally agree with those  of ICRP-NCRP.  They have as
     yet considered only four specific individual isotopes.

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Introduction
has received little attention to date as a contaminant in uranium
mill waste discharges.  A very few reported values ^ for
Colorado River waters show Pb^lO to be present, in one
instance,  significantly above background levels.  The extent
to which Pb^lO may be present in uranium mill waste dis-
charges has not been established,  however,  and future studies
should consider the actual degree  of hazard presented by this
isotope.
    The MFC values climb rapidly as one proceeds down the
list shown in Table 2.  For this reason, none of the other iso-
topes listed have been demonstrated to present a significant
hazard when radium-226 is also present.  For example, some
earlier doubt as to the relative hazard of thorium and radium
has been resolved^ with evidence  that the hazard due to thorium
was near negligible, as  compared to the radium-226 present.
The uranium MFC's given in T^ble  2 are based on the chemical
toxicity of uranium rather than on its radioactive properties.
Such levels of uranium in mill effluents are not normally en-
countered since they would represent a major economic loss
to the industry.  It is generally true, therefore, that effective
control of radium-226 pollution from uranium mill process
wastes precludes any dangerous contamination of receiving
waters by the other radioisotopes of the uranium-radium
family.

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                 MILL  PROCESSES
     The process of uranium extraction varies among the mills,
this variation being primarily due to the differences in the
characteristics of the ores being handled.  Process steps
which are basic to all mills, however, are crushing, grinding,
leaching wherein the uranium is dissolved from the crushed
ore, and recovery.  The latter step involves the selective re-
moval of the uranium from the leaching solution for prepara-
tion of the concentrated product.  The variety of actual pro-
cesses now  in use are generally described below. 1   *
ORE RECEIVING. CRUSHING. AND SAMPLING
     Uranium ore is usually transported from the mines to the
mill by truck, and at the mill is transferred to hopper bins
from which  it is fed to the process.  The first step is a crushing
operation which reduces the ore to  a uniform maximum size.
generally about 3/4 inch.  During the crushing operation a
precise repetitive sampling procedure is carried out to ob-
tain a representative  sample, usually  0.1 percent (2 pounds
per ton), of  the incoming ore.  This sample is assayed for its
uranium (^Og) content and is the basis  for  payment to the
mine.  The  crushed ore is  either stored for later blending or
fed directly  to the next processing step.  Blending is necessary
when the raw ore is delivered to the mill from different sources
and has significantly different compositions.  Adjusting the
feeding of these ores stabilizes the input to the mill process.
and fewer variations in  chemical feed rates  and other process
control procedures are  required.
GRINDING

     The crushed ore is conveyed to a ball or rod mill which is
usually followed by a spiral classifier, and in some cases a
cyclone  separator.  Water is usually added to the ore as it
enters the ball mill to form  a slurry, or a recycled mill solu-
tion may be  added  in place of water to  form  the slurry.  The
maximum particle size of solids in the effluent slurry from  the
ball  mill will vary depending upon the characteristics of the ore.

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10                                    URANIUM WASTE GUIDE

 and may be less than 65 mesh.  After classifying,  the ore solids
 are in a physical state suitable for dissolution of the uranium
 by a leaching process.  Thickening of these solids may be
 carried out just prior to leaching by passage  through sedimen-
 tation tanks.  The underflow from these tanks is fed to the
 leach circuit, thereby reducing the volume of slurry to be
 handled there.

     In  the case of carnotite ores which may contain valuable
 amounts of vanadium, the grinding process may be carried
 out dry following passage of the fine ore through a rotary dryer
 to reduce its moisture  content.  At one such mill? dry NaCl
 (5% of weight or ore) is added after grinding and the ore is
 then roasted (approximately 1 hour at 1500F).  The purpose
 of the roasting is to convert insoluble vanadium compounds
 in the ore to soluble sodium vanadates.  The  roasted ore is
 slurried in a quench tank with recycled leach  solution and is
 then delivered to the leach tanks for recovery of vanadium
 and uranium from the ore solids.

URANIUM EXTRACTION

    Uranium  is extracted from the ground ore slurry by leach-
ing with sulfuric acid at 21 of the mills listed in Table 2.  The
leaching circuit generally consists of a series of tanks to which
the ground ore slurry and sulfuric acid are added; pH is main-
tained near 1.0.  Agitation is provided and the total leaching
time generally exceeds 12 hours.  Heating of  the leach tank
contents is sometimes practiced to speed the  dissolution rate
of uranium and reduce leaching time.  Figure 3 presents a
flow diagram of  an acid leach mill.
    Alkaline carbonate leaching is practiced in six mills where
the ore has a high carbonate content (high lime ores) which
makes the acid requirements for leaching excessive. A typi-
cal carbonate leach circuit consists of a number of tanks or
autoclaves  in series,  each  having  a detention period of several
hours,  giving a total leaching period of from 10 to 72 hours.
Heat and often pressure are provided to maintain leaching
temperatures  up to 250F.   If uranium is to be dissolved, it
must be in the hexavalent form.   The leach tanks are aerated,
therefore, to oxidize the reduced uranium present.  Copper sul-
fate and ammonia, or other catalysts,  may be added to ac-
celerate the oxidation reaction.  An alkaline leach mill flow
diagram is shown in  Figure 4.

                                                 OPO B2S890-2

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                     SWIRLING  AND  CRUSHING
                                         GRINDING
                                           AND
                                         LEACHING
                        ORE   ACID               SOLUTION
                                                                                                                              SANDS-SLIMES  SEPARATION
                                                                                                                                                                                                         ANICN  ICN  EXCHANGE CIRCUIT
                                                                                                                                                                                                                                                                           ELUTING SOLUTION MAKE-UP
                                                                                                                                                                                                                                                                                 PRECIPITATION
                                                                                                                                                                                                         SLIME  TAILS  NEUTRALIZATION
                                                                                                                                                                                                  21!*  *  SC;,=  -  CalCHlji^; CaSOlj * 2H20
                                                                                                                                                                                                                                            AND
                                                                                                                                                                                                                                      TRYING CF PRCCUCT
                                                                                                                                                                                                                                            ELUTIKG SOLUTION
                                                                                                                                                                                       ! pH  KDICATOR
                                                                                                                                                                                       L_RE_COI!BEJ(__j
                                                                                                                                                                                      t>ISTRI3'JTO
                                                                                                                                                                                      (EACH SE!*T WILL
                                                                                                                                                                                       FEED A GIVEN SAKK)
                                                                                                                                                                                                                    6 / / HILL FEED AKY BAUK
                                                                                                                                                                                   f 3 T S .     .P J T S
                                                                                                                                                                                I SLIK THIS F3QM Ar 0E 3A  Ci(OH)2 __T  K95
LEGEND:
 IX -  lOlt EXCHAUSE
  P - PRE3KAHT LHUOR
  B - BAH);
  T - TAILS
  S - SUROE
  E - ELUTIKS SOLUTIOH
   - HES IK
FCY - FLOW COTBOL LYE
IP - E5I in PULP
    CRE SAMPLES
    FOB AHALTSIS
(C.IS OF MISIWL ME)
                                                                                                                                                                                        T SLI*S  PCW       Figure 3.  Flow diagram of acid-leach resin-in-pulp  process.
                                                                                                                                                       GFO  82589O3

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Mill Processes
11
            .	J. "p|LF I  *1 CffiiStf* J	L. SC^ENS
                            '
                                                      S?Ct-S3W-' ..,,
                                                      [ T'  " Fl-
                                                       TQ-P  :  sis
                TO TAILINGS PCD
               Figure 4, Flow diagram - alkaline leach process.

 LI QUID-SOLID SEPARATION
     The slurry (or pulp) flow as it leaves the leaching circuit
 carries the uranium dissolved in the leach liquor as well as a
 large quantity of  spent ore solids,  generally about 50 to 65
 percent by weight.  The first step  in the recovery of this dis-
 solved uranium is,  therefore,  the  separation of the spent solids
 from the liquid.  This is accomplished by sand-slime separa-
 tion, counter current decantation washing in classifiers and
 thickeners, or filtration.
     The separation method used is dependent to  a large extent
 upon whether acid or alkaline leaching is practiced.  The al-
 kaline leaches attack the ore solids less severely,  and fewer
 slimes or very fine solid particles are formed.  In order to
 permit recycling of the leach solution and thereby conserve
 their reagent values, alkaline leaches  are processed directly
 by multiple-stage filtration.  Prethickening may be employed,
 and  a synthetic polymer flocculant such as Separan is often
 used.  The resulting filter cake, or "tailings, " is a waste ma-
 terial which is discarded.   The filtrate,  or pregnant liquor.

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 12                                    URANIUM WASTE GUIDE

 may be further clarified by aeration-flotation for hydrocarbon
 removal prior to transfer to the pregnant liquor storage tank.

     Since acid leaching results in destruction of the excess
 acidity,  which cannot be regenerated, acid leach  pulps are
 clarified by more economical countercurrent decantation
 methods (see Figure 3).  The sands and slimes are handled
 separately, the sands being removed by classifiers and the
 slimes by flocculation and sedimentation in thickeners.   Floc-
 culant aids used include gums,  glues, starches, and synthetic
 polymers.  The washed sands and slimes are discarded as
 tailings,  and the clarified pregnant liquor is stored for sub-
 sequent uranium recovery steps.

 URANIUM RECOVERY
     Once the uranium content of the ore has been put in soluble
 form by the leaching process and the unwanted spent ore solids
 have been removed from the process flow, the next step is
 recovery of the dissolved uranium.  The simplest method is
 straight  chemical precipitation.  A relatively clear pregnant
 liquor containing few dissolved  impurities is  required.  Car-
 bonate leaching dissolves little  else from  the ore  other than
 the uranium, and as a result direct precipitation may be
 applied to  these leach liquors.   Sodium hydroxide is normally
 used to bring about the  precipitation of sodium diuranate at a
 pH  near  12.  The precipitated uranium is  removed as thickener
 tank underflow and filtered.  This filtrate and the tank overflow
 are then filtered, and the resulting barren liquor  is recarbon-
 ated and recycled for use as mill solution in the initial grind-
 ing step.   This procedure reduces the amount of make-up
 water and alkalinity  required (see Figure 4).  The filtered
 uranium precipitate  is heat-dried, ground, and packaged for
 shipment.  This final uranium concentrate is called "yellow-
 cake. "
    Acid leach liquors  contain dissolved impurities which would
 interfere with the simple chemical precipitation recovery meth-
 ods.  In order to produce a high-grade uranium concentrate
product from acid leach liquors, recovery processes utilizing
 ion-exchange or solvent-extraction principles are used.  These
processes  produce relatively pure and concentrated uranium
solutions which are suitable for recovery of uranium by chemi-
cal  precipitation methods.

-------
Mill Processes                                             13
 Ion Exchange (IX)

     Recovery of uranium by ionic-exchange methods (see
 Figure 3) is a relatively recent development which was found to
 be advantageous for use in processing ores containing  rela-
 tively low uranium concentrations.  The ion-exchange  process
 has the added advantages of providing a high uranium recovery
 and a final uranium product of high purity.

     The ion-exchange process utilizes the ability of certain
 anionic resins to selectively adsorb uranium from acid or al-
 kaline leach solutions.  When the resin becomes uranium
 saturated, it is  eluted,  the uranium being desorbed in  a highly
 concentrated and relatively pure eluate.  Alkaline precipitation
 of this solution removes the uranium and the precipitate, when
 filtered, yields  a high-grade yellowcake.

    The principle of ion exchange is applied in practice in two
 different ways.  These  are the column-ion-exchange and resin-
 in-pulp (RIP) processes.  In the former process, which is used
 at three mills, a clarified pregnant liquor solution is passed
 through fixed beds or solumns packed with the exchange resins.
 The uranium is  adsorbed by tne bed resins, and the barren
 effluent from the exchange unit is recycled for further  use or
 discharged as waste.  The RIP process which is used at eight
 mills, is  designed to extract uranium directly from the leach
 pulp without the necessity for first clarifying the pulp.  In this
 process pulp and resin  are contacted countercurrently  in a
 series of  tanks.  The resin may  be confined in screened bas-
 kets or it may be fed to the open tanks.  In the latter case.
 shaking screens are used to separate the resin between stages.

    After the resins have become saturated with uranium ions,
 they are eluted with acidified  solutions of nitrate or chloride
 salts.  Intricate piping  and valving systems are required for
 the entire cycle of operations, and because of the value of the
 eluting solutions, it is operated essentially as a closed circuit
 to minimize losses.  In addition,  the uranium values of flushing
 and back-washing waters dictate their conservation by  recycling.

    Following elution of the uranium from the resins,  the eluate
 is treated with NH3, MgO, or NaOH to bring about the  alkaline
precipitation of the dissolved uranium. The insoluble uranium
 precipitate  is recovered and filtered,  the filter cake being
 dried and packaged for  shipment as yellowcake.  The uranium

-------
14                                    URANIUM WASTE GUIDE

 recovery procedure for RIP eluates may require an additional
 step of clarification for slimes removal prior to uranium
 precipitation.  Clarification (usually by lime precipitation)
 followed by filtration produces a "whitecake" which is repulped
 and returned to the leach pulp feed to the RIP process.

 Solvent Extraction (SX)

     Uranium recovery by the solvent extraction process (see
 Figure 5) is used in 10 Western United States mills.  This pro-
 cess employs an organic solvent such as alkylated phosphoric
 acid or secondary or tertiary amines dispersed in a kerosene
 diluent which is mixed with clarified leach  liquors containing
 dissolved uranium.  The uranium transfers to the solvent, which
 is stripped  of its uranium content when brought in contact with
 a second aqueous solution which alters the form  of uranium so
 that it preferentially transfers back to the aqueous phase.
 Stripping agents used include sodium carbonate and acidic
 chloride or nitrate solutions, the selection of which is dictated
 by the  solvent extractant being used.  The stripped or barren
 solvent is recycled and may be used indefinitely  with periodic
 additions to make up losses.  Aqueous raffinate, which is the
 barren leach liquor, is discarded after the  entrained solvent
 has been scavenged and may be used  in pulping waste tailings.
 Scavenging of the entrained solvent is not complete and some
 amount of organic solvent leaves the mill in the raffinate waste
 effluent.
    As with ion-exchange eluates, uranium is recovered from
 solvent extraction strip liquors  by chemical precipitation and
filtration.  The chemicals used in this step are alkaline ma-
terials such as MgO, MaOH, or NH3  which raise the pH to the
point where insoluble uranium compounds are formed.

 UPGRADING
    Four  of the plants shown in Figure 1 are classified  as con-
centrators or upgraders.  At these plants a wet sand-slime
separation of the ground ore is carried out  in classifiers.  The
coarse sands, which constitute much of the ore bulk but con-
tain little of the uranium, may be acid-leached and washed be-
fore being discarded.  The uranium in the acid liquor is pre-
cipitated by neutralization with ammonia.  This precipitate,
called green sludge,  is combined with the unleached slimes and
filtered. The resulting filter cake is then dried and shipped
                                                    GPO 8258904

-------
                      '/  Sfj-Cs:;
                     Fl OBF_f|OH

                     CRU3HIIH} PLANT
O

 2
 G
               \
               *>'


Fe SLUDGE
(IHUMCimilT)
^ run. .2co,
EMjSOii
STFAM
HgO
niTr pfcip.
*" PlfSS  TAI  "

J

PRESS "I-*" FURMCF  (- - VELLtWCAKE
7 (j\ IPRODUCT1
J "'
                                                                                                                    Figure 5. Flow diagram  - solvent extraction process.
o
o
rt>
w
01
ft)
tn
                               Q-- SAHPLIHA fOIHTS

-------
16                                   URANIUM WASTE GUIDE

for use as feed material for a complete process mill.  The
neutralized leach liquor from which the uranium has been pre-
cipitated is used in pumping the leached sands to the tailings
pile.

    The  upgrading circuit reduces considerably the bulk of
material which must be shipped to the uranium mill.  This up-
grading process thereby permits the economic development of
ore bodies remote from the main mill which otherwise could
not be competitively developed.
    The  foregoing constitutes a general description of the
uranium  extraction processes in use.  For complete details
on circuits,  equipment, etc., in use,  the reader is referred
to the detailed process descriptions contained in the reports
of individual mills, 1~5 or to a detailed reference work. ^

-------
Uranium ore being delivered by truck to the mill. The ore is weighed
and moisture content determined. (Photograph courtesy  of  Mines
Development, Inc.)
The ore  is stored in separate piles according to uranium content.
The various grade ores are blended prior to  processing in  order to
stabilize the input to the mill. (Photograph courtesy  of Mines devel-
opment,  Inc.)

-------
After being crushed the ore is mixed with water or mill solution and
ground. A rod mill, as shown above, is often used. (Photograph cour-
tesy of The Anaconda Company)
The ground ore slurry is pumped to these tanks where the uranium
is leached from  the ore. (Photograph courtesy of The  Anaconda
Company)

-------
 The solids are removed from the leached ore slurry  in classifiers.  A
 rake classifier  is  shown.  {Photograph  courtesy  of  The  Anaconda
 Company)
Where the resin-in-pulp process is used, ion-exchange resins contain-
ed in metal baskets are used to extract the uranium from the  pulp
slurry. (Photograph courtesy of Mines Development Company)

-------
 The dissolved uranium is precipitated and filtered. A plat* and frame
 filter press is shown. (Photograph courtesy of The Anaconda Co.)
The filtered yellowcake is dried  and packaged for shipment in  55-
gallon drums. (Photograph courtesy of The Anaconda Company)

-------
                 PROCESS WASTES
THE MILL BALANCE

    The raw materials and the processing procedures pre-
viously described, make it clear that numerous opportunities
exist for the production of liquid-borne waste materials de-
trimental to the aquatic environment.  To determine the exact
quantitative and qualitative nature of the waste flows which
can be expected from the various ore refining processes des-
cribed, extensive field studies were carried out at a number of
mills  representative of each major  type of process.  The
objective of these studies was to establish a materials balance
for each mill, so that the important constituents of the raw ore
as well as materials added during processing could be accounted
for as  the ore passed through the individual processing steps.
With the information thus developed, it is possible to charac-
terize  the waste streams which could be expected from each
method of ore processing.  The findings of five such mill studies
have already  been reported. 1-5
    A balance of materials for the  mill processes described is
achieved by a combination of field and laboratory data. At the
mill,  slurry flows are sampled at enough stations to provide an
adequate description of the total process. Process flow charac-
teristics should be measured with sufficient frequency that fluc-
tuations arising from batch type operations  are incorporated
into the data.  Representative composite samples of the flow.
whether as a slurry or as solids, are necessary.  Analysis of
these  samples provides information on the physical and chemi-
cal characteristics of the process stream.  Radioactivity analy-
ses are also carried out for determination of radium-226 and
gross alpha and beta activity concentrations.

    Combining the flow data with the physical characteristics
of the process stream permits the calculation of average liquid.
dissolved solids,  and suspended solids flows passing each sam-
pling station.  With careful selection of sampling locations and
adequate frequency and duration of  sampling, a balanced solids-
liquids flow chart for the process can be established with

                            21

-------
 22                                    URANIUM WASTE GUIDE

 reasonable accuracy.  After a liquid solids-flow balance is
 achieved,  the suspended and dissolved radioactivity concen-
 trations can be applied to develop a balance for these materials
 as well.  The net result of these computations should present
 a clear picture of the changing composition of the process
 stream as it proceeds through the mill, and a quantitative
 and qualitative characterization of the waste flows leaving the
 mill.

     The materials balance obtained for an alkaline leach mill^
 illustrates the methods used.  At this mill process sampling
 was conducted during two consecutive sampling cycles of 72
 hours each.  At 11 of the 14 sampling stations a single repre-
 sentative sample was obtained for each cycle  by compositing
 volumes proportional to the flow every 2 hours for the duration
 of the cycle.  Each composite sample then was made up of 36
 portions.  Portions of the official mill sample of  the raw ore
 lots were obtained and composited according to the tonnage of
 each lot processed during the cycle.  In a similar manner,
 composite yellowcake samples representative of the ore pro-
 cessed during each cycle were collected. An automatic  sam-
 pling device was used to collect a representative sample from
 the waste slurry discharged to the tailings pond.  The mill
 balance was performed on each cycle, and average values
 were presented because of the close agreement obtained be-
 tween cycles.

     The results of laboratory analyses, as  shown in Table 3,
 and knowledge of the  ore tonnage made possible the calculation
 of a solids balance across each circuit in the mill process.
 A schematic process flow diagram is shown in Figure 6.
 Knowledge of the rate of raw ore feed (and its moisture content)
 at Station 1, the total weight of collected samples, and analy-
 tical information on specific gravities of the slurries and dry
 solids (Table 3) can be used to calculate solids, liquid, and
 slurry flows across the ball mill and classifier  circuit.  This
 is accomplished by preparing simultaneous equations based on
 the conservation of material.  For example, the slurry flow at
 Station 3 must be accounted for at Stations 1 and 2.  This applies
 to solids (suspended and dissolved) as well as  liquids.  Similarly
 the flows at Stations 4 and 5 should equal that at Station 3.
Other circuits within  the process are handled in the same
manner.  The flows shown on Figure  6 are the result of such
an analysis.  These calculated flows  may be checked against

-------
Process Wastes
                                                             23
                                             KEY:
                                                           1C gpm
                                                          ICC gpm
                                                          I 10 gpp
                                                             (I)
                          CTAILINGS POND
                          C
                         o  WELL WATER
                           MISC. WATER ~C
                                     75
            TO TAILINGS POND
        Figure 6. Schematic flow diagram, flow balance - alkaline leach mill.

 actual slurry flow measurements made at a number of points
 in the process.
     The slurry flows thus obtained may be used together with
 the dissolved and suspended solids concentrations (Table 3) to
 develop a solids balance for the mill as in Figure 7.  Here
 again the solids  flow entering a junction point in the process
 must equal that leaving.  For example,  the raw ore feed
 (Station 1) and mill solution (Station 2) have a combined  input
 to the classifier circuit of 2898 (1258 +  1640) tons per day as
 compared to the output of 29GO.  This 2900 tons per day is
 also the input to the primary thickeners whose combined out-

-------
 24                                      URANIUM WASTE GUIDE

 Table 3. PROCESS STREAM CHARACTERISTICS3- - ALKALINE LEACH MILL0
                  Slurry   Dry sus-    Specific    Dissolved     Suspended
      Station        specific  pended solids gravity of     solids,      solids (dry
                  gravity  by weight, % dry solids   mg/1 of slurry  weight).
1
2
3
4

5
6
7
8
9
10
11
12
13
14
Ore feed
Mill solution
Classifier overflow
Primary thickener
overflow
Feed to leach
Leach discharge
Filter feed
Pregnant liquor
Barren liquor
Yellowcake
Repulped tails
Tails pond water
Well water
Softened water

1.
1.
1.

1.
1.
1.
1.
1.

1.
1.
1.
1.
_
12
19
12

50
50
56
11
13
-
26e
01
00
00


_
d
13.9


51
50
54



d

.2
.2
.6
d
d
-
34. 6e



d
d
d


2.


2.
2.
2,



2.



_
-
.60
-

,46
.59
,50
-
-
-
40
-
-
-

138,
126.
137,

87,
94,
91,
159,
162.

12,
14.
1.
1.
c
000
000
000

900
500
300
000
000
c
200
.800
880
700


165,


765.
752,
854.



435,



c
850
000
780

000
000
000
145
50
c
000
198
8
56
 aAverage of Cycles I and II.
 ^Reference 4.
 cSolid sampie.
 ^Liquid sample (negligible solids).
 eBased on Cycle I only.
put was calculated to be 2896  (1067 +  1829) tons per day.  Al-
though the total solids  flow across the digesters should remain
constant (1829 in,  1824 out),  it is apparent that 15 to 20 tons of
the entering suspended solids left as dissolved solids.  Across
the entire process 1669 tons per day enter the mill. 1640 in the
raw ore at Station 1. 5. 8  tons in return water at Station 12, 5
tons in the well water at Station 13, and 18 tons in the form of
caustic soda at the precipitation tanks.  This  agrees with the
calculated total solids  leaving the process as  waste  to the tail-
ings pond (1666 tons per day.  Station  11) and in the yellowcake
product (2. 5 tons per day. Station 10).

     Once a satisfactory solids balance has been obtained for
the mill process, as in Figure 7,  a similar balance can be
attempted for the radioactivity contained in the solids.   Table
4 shows the radium-226 concentrations in the dissolved  and
suspended solids, as determined by laboratory analysis, for
the alkaline leach mill  shown  in Figures 6 and 7.
     These radium-226 concentrations, as well as the majority
of all others mentioned in this report, were determined by the
radon emanation technique.  The use  of this method precludes
obtaining radium-226 values which are too high because of  the
imperfect chemical separation required in other methods.  For
determination of dissolved radium-226.  care  was  also taken in
sample preparation to avoid high results.  Separation of sus-

-------
 Process Wastes
25
pended solids in the  sample was accomplished by filtration
through a membrane filter.  The necessary sample acidifica-
tion step was performed after solids separation to  avoid the
dissolution of radium-bear ing particulate matter.
                                          KEY:
                                          DISSOLVE" SOLI:-    ic TCNS'OAY
                                          SI'SPFNPFn SOLIDS - I.CC TQS'PAY
                                          TOTAL SOLID?    - IT TONS'DAY
   MILL
I2EC
 '
1 1 i'fS-
J
ORE
STORAGE

1
IALL MILLS
CLASSIFIERS
L
I ON
SGE SEPJRAN
4^ ivERFLCW
IC67
SEPARA
_ *
-r
CO
sL

wr
1666
-^
PR iMARY
THirxENFRS
ii-
I61C
I26C
I6UC
29CC .
_i
--

,w
a.
2C'4
1824
CVFRFLCW
I62C
179*




GUM
Q.
-
PPFGNANT
LPl'O*
STORAGE
--CD
TIOH TANKS
t
THirKFNFS
SAMPLING STATION NO
224
NsOH ~'


* 	 77T 	 7^
i-c (YELLOWr.AKF)
= ~i  _
Z u., , z g
ROTARY
,
r-:FR
.SOFTEXFP |
t-,'4T?r e O
n^ ^- r ^
~C '
~C BARREN SOLU-
TION STORAGE
~"^3 2.5
*%??

2.5
TWER
235


S 23
_j 1 SETU'N HATFR FROM I
A 5.8 T4ILINGS POND
FLL 5.8
MISC. WATER ~
C
~ RECAR3 V.l-


75
75
                                                           Q
            TO TAILIWS ONO

       Figure 7. Schematic flow diagram, solids balance - alkaline leach mill.

    Applying  the concentrations found at each station to the
solids flow at that station results in the radium-226 flow dia-
gram shown in Figure 8.  Here we see that the 739 milligrams
per day of radium-226 entejring the process agrees well for this
type of balance with the 766 milligrams leaving; 750 in the
waste effluent (Station 11) and  16 in the yellowcake product

-------
26
URANIUM WASTE GUIDE
  Table 4.  RADIUM-226 CONCENTRATIONS* -- ALKALINE LEACH MILLb
Station
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Radium-226
Dissolved
.
9.560
8.300C
8.790
5.160
6.620
5.280
18.900
59
-
34
35
5.4
4.2
.nugll of slurry
Suspended
_
1.220
83.900
d
328.000
370.000
380.000
286
5.4
-
222.000
d
d
d
Dry suspended
solids. A/ig/g
497
1.440
508
d
500C
492
445
1.970
107
7.190
510
d
d
d
  aAverage of Cycles I and II.
  ^Reference 4.
  cMost probable concentration.
  ''Not determined (negligible solids).
 (Station 10).  The balances around individual circuits in the
 mill process are in equally good agreement.  A balance such
 as jn Figure 8 is revealing as regards the fate  of the radium
 content of the entering raw ore.  It makes possible an under-
 standing of the portion of the radium which is dissolved from
 the ore. the point at which this dissolution occurs,  and the
 ultimate fate of the  dissolved radium.
     The results of such balances performed  for mills employ-
 ing various milling processes have been used in the succeeding
 sections to describe the flow of radioactivity, primarily rad-
 ium-226,  through the mills and to  characterize the various
 resulting  waste flows.

 RADIUM-226
    Raw ore as it enters the mill process contains  150 micro-
grams of radium-226 per pound of  uranium,  if secular equili-
brium  exists.  This  radium is entirely in solid or undissolved
form.  As  the ore passes through the various unit operations
within  the mill,  a small portion of  the radium is dissolved.
This dissolved radium may be partially precipitated to appear
in solid form in the yellowcake uranium concentrate, while
the remainder of the dissolved radium leaves the mill in the

-------
Process Wastes
                                                               27
                                          K E r:
                                         DISSOLVED RADIUM-226
                                         SUSPFNPFD RADIW-226
                                         TOTAL PAPIUM-226
- 1C mg/day
-ICC mq'day
 IIC ing.day
           ~0
          .isa
           75C
                     WELL WATER
                     MISC. WATER
           TO TAILINGS POND


    Figure 8. Schematic flow diagram, radium-226 balance - alkaline leach mill.
liquid waste effluents.  The radium  remaining undissolved
during passage through the mill,  which comprises all but a
small percentage of that entering, can be found in the solid
ore tailings which are discarded  by  the mill as waste.  The
amount of radium  which is  dissolved during milling, the
percentage precipitated in the concentrate, and the amount
to be found in the mill waste streams all vary within a small
range depending on the particular milling process being
employed.

-------
28
URANIUM WASTE GUIDE
 Acid Leach - RIP5
     A mill using this process was studied, and the radium
 balance shown in Figure 9 developed.  In this case, of the
 300 milligrams of radium entering the mill per day, 2
 milligrams  (Stations 3 and 4) were dissolved during acid
 leaching.  Of the total radium, 27 percent, including  60
 micrograms of the dissolved radium,  was discharged to waste
                               KEY.
                               DISSOLVED  RADIUM - 226   I0mg/day
                               SUSPENDED RADIUM-226  lOOmg/doy
                               TOTAL RADIUM-226       HOmg day

                               SAMPLING STATION NOS. 	O
                                                  ELUANT
                                                  MAKE-UP
                                                 o.ietesU
                                                 '
         Figure 9. Schematic flow diagram, radium-226 balance  acid
                leach-RIP mill

-------
Process Wastes                                            29

with the leached sands.  Of the dissolved radium remaining
in the process, 150 micrograms was extracted from the slimes
along with the uranium and became a part of the uranium con-
centrate product or yellowcake.  The slimes tails leaving
the ion-exchange banks contained 1.9 milligrams of dissolved
radium  and 223 milligrams  in an undissolved state.  Neutraliza-
tion of these slimes resulted in the precipitation of a substan-
tial fraction (85%)  of the dissolved radium present.
    Thus, in this process 0. 7 percent of the radium input was
dissolved  by acid leaching. 0. 05 percent appeared in the yellow-
cake,  and the difference, 0.65 percent, left the process in a
dissolved state.  Neutralization prior to discharge to the
slimes tailings pond,  however, reduced to G. 12 percent the
fraction of radium input  leaving the mill in the dissolved
state.
 Acid Leach - Solvent Extraction*
    Figure 10 illustrates the radium balance found for  a'mill
using this process.  Here 146 milligrams of radium-226 en-
tered the  mill per  day.  and  560 micrograms (sum of Stations
3, 4.  and 5) were dissolved in leaching.  The waste sands  con-
tained 26  milligrams,  whereas the wasted slimes  carried
considerably more radium,  or 116 milligrams per day.  Of
the radium dissolved during leaching. 90  micrograms left
the mill with the sands and slimes and the remaining 470
micrograms entered the solvent extraction step.   Of this
amount. 25 micrograms per day was extracted with the
uranium and could be found  in the yellowcake.  The dissolved
radium  remaining  in the raffinate or  barren acid liquor was
discharged to the tailings pond.
    At  this mill,  therefore,  about  0. 38 percent of the radium
entering in the ore was dissolved in the acid leach tanks.  A
very small portion. 0. 02 percent of the input,  was extracted
and precipitated with the uranium and left the mill in the
yellowcake.   The remaining dissolved radium. 0.36 percent
of the input, left the process in waste flows; 0. 06 percent and
0.30 percent of the input in the sand-slime wastes and  raffi-
nate.  respectively.  Part of the raffinate was used to repulp
the washed sand-slime mixture and as a result it  appears that
about 90 micrograms of radium was precipitated so that the
total dissolved radium discharged to tails was actually  only
0. 31 percent of the radium input.   The bulk of the radium

-------
30
          URANIUM WASTE GUIDE
DISSOLVED RADIUM-226   10. mg/day
SUSPENDED RADIUM-226  100. mg/doy
                       I 10 mg/day
                             TOTAL RADIUV 226
                             SAMPLING STATION NOS. - Q
                             0.47
                            PREGNAN
                             LIQUOR
                      0.14
                      0,04
                      0.18 RAFFINATE
                     .32 *
                     -09
                     .41
         Figure 10. Schematic flow diagram, radium-226 balance - acid
                 leach-SX mill.
input (99. 7^) remained undissolved.  18 percent of this con-
tained in the sands and 82 percent in the slimes.

Alkaline Leach^

     Significantly higher dissolution of  radium has been
encountered where the alkaline leach process is used.  As
shown by the radium balance found for  such a mill (Figure 8).
739 milligrams of radium-226 per  day  enters the mill in an
undissolved state.   The ore enters the  ball mill -  classifier
                                                     GPO exsaao-e

-------
 Process Wastes
31
 circuit, where recycled mill solution containing a high dis-
 solved radium content is added.  Radium dissolution begins
 at this step and continues through the thickening and leaching
 tanks.   The pregnant liquor that overflows from the secondary
 thickening step following leaching contains about 20 milligrams
 of dissolved radium per day.  All of  this radium is precipitated
 from solution along with the uranium and may be found in the
 yellowcake.  The underflow from the secondary thickeners
 contained  about 13 milligrams of dissolved radium as it
 entered the filtration circuit.  This filtrate which contains
 the dissolved radium is recycled back into the process,  and
 an essentially dry filter cake is produced.  Fresh  water  and/or
 return water from the tailings pond is used to repulp this filter
 cake to form a slurry which is discharged to  the tailings pond.

     For alkaline  leach mills, the,  it may be  expected that
 about 2 per cent of the radium-226 input will  be dissolved and
 that essentially all of this will subsequently be found in the
 uranium concentrate product. The process waste  is essentially
 a dry filter cake containing very small amounts of dissolved
 radium.

 Summary
     The alkaline  leach process  causes greater dissolution  of
 radium from the ore than does acid leaching;  however, virtually
 all of the dissolved raium in  the alkaline process leaves  the
 mill in the yellowcake (see Table 5).   In contrast,  the yellow-
 cake produced by acid mills contains very little radium,  about
 5  per cent of that dissolved during leaching.   That  dissolved
 radium  which does not appear in the yellowcake is  discharged
 to the tailings ponds.
Table 5.  DISSOLVED RADIUM-226  IN URANIUM MILL  PROCESS FLOWS


Process

Acid Leach
Solvent extraction3-
Raffinate
Sands and slimes

Resin-in-pulpb
Alkaline Leachc

<7C of Total Ra
dissolved by
leaching
0.4-0.7





1.5-2.2
%of
Dissolved Ra
leaving mill
in Tailings flow


(80)
(15)
95
93

in Yellowcake




5
7
100
Reference 1.
Reference 5.
cReferences 3 and 4.

-------
 32                                   URANIUM WASTE GUIDE

     It has been observed that the radium contained in the slimes
 fraction comprising about a third of the total waste solids re-
 presents a large portion (70 to 80cc) of the total radium origi-
 nally present in the ore. Analysis of a tailings sample from
 an acid leach mill showed that the minus-400-mesh particles
 have a radium concentration more than seven times that  found
 in the plus-200-mesh particles. 20 At the acid leach mills
 discussed above,  the radium concentration in the slimes  par-
 ticles was three times  that in the sands in one case, and  22
 times greater in the other.  It is  clear that the slimes repre-
 sent the major source of undissolved radium waste from  acid
 leach mills.

     Table 5  is a summary of findings pertaining to the content
 of dissolved  radium-226 in process flows.  The figures given
 there may be applied to a particular mill to provide an estimate
 of dissolved  radium discharged as waste.  For example,  an
 acid leach -  solvent extraction mill processing 1000 tons of
 "six pound ore" (0. 3;c l^Og) per  day would have a radium
 input of about 765 milligrams per day if secular  equilibrium
 exists in the ore  (857 U/U^On x 6 Ib  U/ton x 1000 ton/day x
                         O  O
 0. 150 mg Ra/lb U).  About  3 to 5. 5 milligrams per day would
 be dissolved during  leaching. 80 percent,  or 2.4 to 4.4
 milligrams per day,  would be discharged in the raffinate.
 15 percent or 450 to 800 micrograms  per day, with the sands
 and slimes,  and 5 percent or 150 to 300 micrograms per day.
 could be expected in the yellowcake.
     Others have reported 20 radium dissolution  during acid
 leaching up to an order of magnitude higher than  the values
 shown  in Table 5.  The reason for this lack of agreement is
 not known.  The methods used for radium  analyses differed
 in each case,  however,  and this may  represent a possible
 source of disagreement.  The radon emanation method of
 radium analysis as used herein is more selective for radium-
 226 and is recommended for use.

GROSS ALPHA RADIOACTIVITY

     At each of the mills discussed previously where a radium
balance was obtained through the process,  a similar balance
was attempted for  gross alpha activity.  The amount of gross
alpha activity entering the mill in  the ore can be  estimated from
knowledge of its uranium content.  Uranium-238  is the parent
isotope of a long chain of radioisotopes which includes eight

-------
Process Wastes                                             33

alpha emitters. If no selective leaching has occurred during
its geologic history, secular equilibrium can be expected in
the ore,  viz..  the daughter elements are being formed at the
same rate at which they are decaying.  The activity of  each of
the eight alpha emitters in the  chain, therefore, would be the
same. The total alpha  actvity  then should amount to about eight
times the acti\rity associated with a pound of uranium-238,  or
about 1200 microcuries per pound of uranium-238.
     The actual amount of alpha activity detected in a sample of
ground ore has generally been found to be somewhat less than
the theoretical amount  calculated above.  This is  due in part
to the assumption of secular equilibrium, which may not exist
because  of natural selective leaching of the ore vein.  This
leaching diminishes the content of one or more of the isotopes
in the chain.  The effect of this disruption of the decay chain
is to lower the gross alpha activity of the uranium ore. In
addition,  preparing the sample for analysis  (involving  such
steps as grinding and heating)  may permit some of the  radon-
222, a gas. to escape.   Unless special steps are taken in the
analytical procedure to permit the reformation of radon-222
in the sample, this loss of  radon, together with its short-lived
daughters, results in an apparent alpha activity somewhat
below the amount actually present in the undisturbed ore.   The
amount of gross alpha activity actually found by analysis in ores
as  they enter the mill process has varied from  80 to 96 percent
of the amount theoretically present  at secular equilibrium. 1- 3-5
A good average figure for use  is 90 percent. It is probable
that the major part of this discrepancy results in most cases
from losses of radon-222 and  daughters  during mining and
transport of the ore and that secular equilibrium  does  usually
occur, to quite close approximation, in the  undisturbed ore
body before mining.
     Proceeding into the mill process. Figure 11 illustrates
the disposition of the alpha activity as it  passes through a typ-
ical alkaline leach mill. It will be noted that a balance over
the mill has not been achieved  in that the gross alpha activity
leaving the mill is but three-fourths, approximately, of that
entering in the ore.  This phenomenon has been observed in
all types  of mills,  as shown in Table 6.  At these same mills
excellent radium balances were obtained (radium  output/input =
100 - 4'-c).

     This loss of alpha activity within the mill process  is attri-
buted primarily to the loss  of some  portion of the gaseous emit-

-------
34
URANIUM WASTE GUIDE
                                  KEY:
                                  DISSOLVED ALPHA RADIOACTIVITY  2000mc^o)T
                                  SUSPENDED ALPHA RADIOACTIVITY   500mc/day
                                  TOTAL ALPHA RADIOACTIVITY   2500mc/doy

                                  SAMPLING  STATION 	




| FILTRATE
17 1
7 
24
~ C

FILTERS

T WELL WATER
"I



1
         -0 I
                        TAILIN3S POND
                          WATER
          Figure 11. Schematic flow diagram, gross alpha radioactivity -
                 alkaline leach mill.
ter. radon-222, plus the same portion of at least two of its
short-lived daughters,  polonium-218 and polonium-214, at
those points in the process where crushing, grinding, heating.
and other ore-handling procedures are carried out.  In Figure
11, the observed losses in alpha activity appear  to occur pri-
marily during grinding of the ore and in multistage filtration
of the spent ore.  following alkaline leaching.  Approximately
13  percent of the entering gross alpha activity is solubilized
when brought into contact with the mill solution in the grinding
circuit and an additional 4 percent in the leach tanks.  About

-------
Process Wastes                                            35

    Table 6. GROSS ALPHA RADIOACTIVITY IN MILL OUTPUT


Mill process
Alkaline leach
Alkaline leach
Acid leach - SX
Acid leach - RIP
Average


Reference
(3)
(4)
(1)
(5)

Alpha activity

Yellowcake
11
15
15
14
14
as ~c of observed input
Waste
effluent
66
54
65
62
62
Total
output
77
69
80
76
76
    aUsing method of analysis described in Reference 9.


11 percent of the gross alpha input appears in the pregnant
liquor, and esssntially all of it is precipitated and can be found
in the yellowcake product.  The spent sands, which are pumped
to the tailings ponds,  contain some 66 percent of the gross
alpha mill input,  and  99. 4 percent of this activity is in undis-
solved form.   The percentage of alpha activity in waste streams
in dissolved form was found to be higher for  both the acid leach -
solvent extraction process  (2%) and for the acid leach - RIP pro-
cess (6.5%).
     Thus,  in general, the total alpha activity of mill wastes is
about 3. 3 millicuries per ton of ore processed (for a "six pound
ore"). A small amount of this activity (0. 5  to 6. 5%) is in dis-
solved form,  i.e., about 20 to 40 microcuries per ton for alka-
line leach mills and 100 to 200 microcuries  per ton for acid
leach mills.

RADIUM AS  PERCENT OF GROSS ALPHA RADIOACTIVITY
     The percentage of gross alpha activity in mill samples at-
tributable to radium-226 will usually vary within a small range
at a particular location in  a given mill,  depending upon the
source of the sample. It is often useful to establish a general
relationship  between radium content and gross alpha activity
for specific sampling points; this latter analysis can then be
used for certain routine monitoring purposes.  Since the gross
alpha analysis is a considerably simpler procedure,  an im-
provement in process control from the standpoint of radioactive
waste disposal can be obtained with little increase in analytical
costs.
     Table 7  lists radium - gross alpha relationships found in
some mills.   The range of values found for  some types of mill

-------
 36
URANIUM WASTE GUIDE
   Table 7.  RADIUM AS PERCENT OF GROSS ALPHA ACTIVITY IN MILL
          SAMPLES
Waste to tailings
Process
Alkaline leach
Alkaline leach
Acid leach - RIP
Acid leach - RIP

Acid leach - SX

Acid leach - SX

Input
16
16
17
18

11

19

Dissolved
1.8
0.4
3.7
7.1

1.0
1.3
7.0
0. 5ac
Suspended
23
31
15 (sands)
20 (sands
and slimes)
31 (sands)
19 (slimes)
18 (sands)
17 (slimes)
Yellowcake
2.1
2.3
0.06

0.07
0.01


0.01
Reference
(3)
(4)
(5)

(6)
(1)


(2)
 samples is small; for example, in raw ores where radium ac-
 counted for 11 to 19 percent of the gross alpha activity and in
 alkaline leach yellowcakes where the range was 2. 1 to 2. 3
 percent.  Radium in tailings solids \vas from 15 to 31 per-
 cent of the gross alpha, while that dissolved in mill discharges
 to tails varied from 0.4 to 7.1 percent.  The variability of this
 latter type of sample is dependent to some extent  upon whether
 or not recirculation of tailings pond water is practiced.

     Relationships such as those in Table 7 may be established
 for particular locations in a given mill.  So long as no major
 changes in process or ore sources occur, gross deviations from
 this relationship will indicate possible  errors in analysis.

 THORIUM
     There are two isotopes of thorium  in the uranium-radium
 decay chain shown in Figure 2.  These  are thorium-234,  which
 is a beta emitter, and thorium-230, which decays by alpha
 emission and is the parent of radium-226. In a typical uranium
 ore which is at secular equilibrium,  the activities due to these
 two isotopes will be approximately equal.  According to Table 2
 the long-lived alpha emitter, thorium-230, presents an internal
 human hazard 10 times greater than thorium-234,  which has a
 24.1-day half-life.  Actually the short-lived thorium-234 will
 decay out following its separation from  its parent, uranium-238.
 For  these reasons thorium-230 is the thorium isotope of pri-
 mary interest in mill wastes.
    It has been reported*^ that alkaline leaching does  not dis-
solve any thorium, since its compounds are insoluble at neutral

-------
Process Wastes                                             37
 or higher pH levels.  As a result,  essentially all of the thorium
 entering with the ore leaves the mill process in suspended form
 with the waste  tails and only negligible dissolved thorium  con-
 centrations can be  expected in liquid waste streams for alkaline
 mills.

     It is probable that acid leaching does, however,  cause the
 dissolution of some thorium-230 from the ore. 20 This isotope
 would then contribute to some extent to the higher dissolved
 alpha activity of acid leach effluents which were previously
 noted to contain from two to  ten times as much dissolved alpha
 activity as alkaline leach mill wastes.  It is not certain what
 portion of the dissolved  alpha activity is attributable to thorium-
 230, though concentrations higher than the MFC are possible;
 however, since this thorium precipitates at a neutral or higher
 pH.  it would not be expected in solution in most natural waters.

 URANIUM

     Uranium is one of the most toxic elements chemically,
 although it is absorbed into the body only with difficulty.   It
 is this toxic property rather than its radioactivity which has
 determined its  MFC value.   The MFC given for uranium-238
 in Table 2,  13. 300 micromicrocuries per liter,  corresponds to
 a concentration of 40  milligrams per liter (or ppm).

     During leaching,  solubilization of over 90 percent  of the
 uranium in the  ore is usually achieved.  Recovery of this
 soluble uranium during subsequent processing steps is very
 efficient,  reaching 99 percent in the ion-exchange and solvent-
 extraction processes.   The  unrecovered dissolved uranium
 appears in the  mill effluent and amounts  to 1 percent or more
 of that originally present in the ore.  Processing a "six pound
 ore, " at the rate of 500  tons per day. for example, would  re-
 sult in a dissolved uranium  waste flow of 30 pounds per day or
 more. At one mill using both alkaline and acid leaching it
 was  found that dissolved uranium losses could have been as
 much as 160 pounds per day from 514 tons of ore  processed
 daily. '  in this  exceptional case the uranium dissolved  in the
 waste flows was about 7. 5 percent of that entering in the ore.
Ordinarily,  it can be expected that  uranium losses will be
kept to a minimum  since its separation and recovery is the
objective of the milling process.  Dissolved uranium in waste
flows,  therefore, will usually be at least 15 to 50 grams per

-------
 38                                   URANIUM WASTE GUIDE

 ton of ore processed, depending upon the grade of the ore and
 the efficiency of the recovery step.

 WASTE SOLIDS
     Uranium ore enters the mill process as a solid, and for
 each ton of ore entering the mill 1 ton of solids, in either dis-
 solved or  suspended  form,  must leave the mill.  All of this solid
 material,  except-that incorporated in the final uranium concen-
 trate product, leaves the mill as waste.

     The extent to which the ore is dissolved during processing
 varies somewhat with the ore composition.  Generally 1 to 3 per-
 cent of the ore input is dissolved although even higher values
 may be encountered.   This means  that the ore would contribute
 20 to 60 pounds of dissolved solids per ton of ore processed to
 the liquid waste streams.  In addition to the dissolved ore
 solids, the large chemical additions during processing contri-
 bute to the final dissolved solids content of the mill waste.
     The solids leaving the mill as  yellowcake product are but
 0. 2 percent (four pounds per ton) of the raw ore solids entering
 the mill.  All but a small fraction of the ore solids input, then,
 can be expected to be discharged as suspended solids or tailings.
 Since these undissolved solids also contain the bulk of the ra-
 dium and other radioisotopes originally present in the ore,
 handling and disposal of the solid waste materials from uranium
 mills represent a very significant aspect of the total waste dis-
posal problem.

 WATER USAGE

     As indicated in the various process flow diagrams, fresh
 water enters the milling process at several points.  The amount
 of water used in the process affects the concentration of waste
 materials found in the mill effluents and also determines the
 magnitude  of the liquid waste disposal problem to be handled.

     The ore as it enters the mill brings with it a small amount
 of moisture, about 5 percent by weight, or 10 gallons per ton of
 ore.  In wet grinding  the ore in the alkaline leach process,
 recirculated mill solutions are used whereas in acid leach mills
 fresh water in large amounts is  usually added to the process
 stream at this point.   Fresh water may also enter the nrocess in
the feeding of reagents, in filter washing, filter cake repulping
counter-current washing of sands and slimes in classifiers and
thickeners,  in flushing and backwashing of ion-exchange columns

-------
  Process Wastes                                            09
 where this process is used, and in various other operations.
 Losses of water from the process are slight, being confined to
 evaporation from heated leach tanks and from the drying of  the
 yellowcake product.  Such losses are of the order of 5 gallons
 per ton of ore.

     The magnitude of liquid waste flows from uranium mills is
 greatly dependent upon the  milling process used and the extent
 to which solutions  are recirculated within the mill.   In some
 cases the  amount of water used is partially determined by the
 availability of water from local sources.  Table 8 gives water
 consumption values encountered in mill surveys. From these
 data, it is apparent that acid leach mills use considerably
 greater quantities  of water  than do alkaline leach mills.  It  has
 been reported elsewhere^*  that the alkaline and acid leach pro-
 cesses use 1 and 4 tons of water per ton of ore, respectively,
 or 240 and 960 gallons per  ton.  This generally agrees with  the
 figures in Table 8.  Even lower water use may  be encountered
 in alkaline mills where waste tails are repulped exclusively

   Table 8.  LIQUID WASTE VOLUMES
Process
Alkaline leach
Alkaline leach
Acid leach - RIP
Acid leach - RIP
Acid leach - SX
Acid leach - SX
Acid ieach - SX
Ore input.
tons/ day
1640
881
517
2320
330
560
515
Net flow to
tailings pond,
gpm
403
81
193
1950
219
222
361
Net
waste volumes.
gal/ ton
354
132
538
1210
955
572
1000
Reference
(4)
(3)
(5)
(6)
(1)
(2)
(8)
with recirculated tailings pond waters.  In one such case a net
\vater use of 67 gallons per ton of ore has been found. 22

    In general, it would appear that liquid flows to be expected
at alkaline leach mills average 250 gallons per ton of ore pro-
cessed, and may  range from 100 to 400 gallons  per ton.  Acid
leach mills produce larger flows, ranging from about  500
to 1200 gallons per ton and averaging about 850  gallons per  ton.
The higher water consumption for the acid process is  due pri-
marily to  the procedures used for liquid-solids  separation fol-
lowing leaching.  Alkaline pulps are filtered  directly after

-------
 40                                    URANIUM WASTE GUIDE

 leaching to conserve valuable leaching reagents, which are not
 irrevocably lost during contact with the ore.  In acid processes,
 however, the sulfuric acid is completely used up during leach-
 ing and the barren leach liquor has no further value.  In the
 latter case, the cheaper procedure of countercurrent decantation
 is employed to separate the spent ore solids from the pregnant
 liquor. As a  result, acid process waste flows are on the average
 three to four times greater than those from alkaline systems.

     As mentioned,  some mills recirculate tailings pond water
 to repulp the  separated sands,  forming a slurry which may then
 be transferred to the tailings pond.   Water requirements for
 this purpose are very high.  If the slurry formed is 20 percent
 solids, for example. 4 tons of water is required for each  ton of
 ore,  or about 1000 gallons per ton.   It can be seen, then,  that
 where tailings water recirculation is not practiced, net waste
 flows from the mill are greatly increased.

 CHEMICAL CHARACTERISTICS
 Alkaline Leach Process

    In the  alkaline leach process a pH slightly above 10. 0  is
 maintained in  the leach tanks by the addition of sodium carbonate
 and bicarbonate to the recycled barren mill solution as needed.
 Bicarbonate is necessary to prevent the pH from becoming too
 high and thereby allowing the uranium to precipitate during
 extraction.  Following extraction the spent ore solids are
 filtered from the pregnant liquor and are discharged as waste
 to the tailings area.  The moisture in the filter cake is highly
 alkaline and tends to raise the pH of the repulping water.

    The pregnant liquor filtrate is treated with caustic soda to
 achieve a pH of 12, at which point the uranium will precipitate.
 The resulting barren solution is recarbonated to  destroy excess
 alkalinity,  create carbonate and bicarbonate  ions, and reduce
 the solution pH to about 10. While this solution  is recycled, a
 small bleed-off is usually required to prevent build-up of
 interfering constituents. 23 As a consequence, the pH  of waste
 streams from  alkaline process mills is near 10. 0 though it may
 be reduced slightly below that figure by dilution  when fresh
 water is used to transport  waste tails.
    Another important chemical characteristic of alkaline  pro-
cess waste streams arises from the  use of oxidants  in the leach-
ing circuit.  In natural ores,  uranium is found in either the

-------
 Process Wastes                                            41

quadrivalent (uranous) or the hexavalent (uranyl) state.  For
dissolution of the uranium in the carbonate leach the uranous
form must first be oxidized to the uranyl form.   This is ac-
complished by bubbling air through  the ore slurry in the pre-
sence of catalysts or by adding chemical oxidants.  Catalysts
most often used with air  oxidation are copper sulfate and am-
monia.  Chemical oxidants include permanganate and cyanide
compounds.  Table 9 lists reported values of chemical usage
for these and other purposes in alkaline mills.

    Significant chemical constituents in waste flows are also
derived from the  raw ore itself.  Elements such as boron,
selenium, lead, fluorine, and arsenic may be present in some
uranium ores,  in addition to organic compounds.  These
materials, if present in the ore,  are leached out to some de-
gree during processing and  appear in the waste flows. The
actual concentrations encountered are specific for each ore

      Table 9. CHEMICAL USAGE IN ALKALINE LEACH MILLS1
Chemical
KMn04
NaCN (and Fe)
CuSO4
NH3
Separan
Guar (gum
NaCO3
NaOH
Purpose
Oxidant
Oxidant
Catalyst
Catalyst
Flocculant
Filter aid
Leaching
Precipitation
Usage. lb/ ton of ore
7.5
0.4
2-4
3.3 -6.5
0.023
0.052
2.65
17 - 31
      References 19.  3. and 4.

and process, however.  Table 10 shows waste stream concen-
trations which have been reported from alkaline mills.  These
waste analyses reflect the make-up of the particular raw ore
being processed and the chemicals added during processing.

Acid Leach Process

     The waste streams from these mills differ in composition
depending upon chemical usage and the uranium recovery pro-
cess used, i. e., ion exchange or solvent extraction.  Ail such
effluents,  however,  are highly acidic,  since the leaching cir-
cuit requires the maintenance of a pH near 1. 0 to 1. 5.  Sui-
furic acid is universally employed to provide the needed
acidity,  and hence,  all acid leach liquors can also be expected

-------
 42
URANIUM WASTE GUIDE
 Table 10.  CHEMICAL CHARACTERISTICS OF MILL EFFLUENTS AS DISCHARGED TO TAILS
                        (Concentrations in ppm}

                              	Acid leach mills
                                      Besin-i.i-pu.ip
                                                        Solvent extraction

Alkaline leach mills
Cl 353 275 256 Si
S04 Z46 - - 17t>
MS 10
N03 73
Cu .005
Be -
Fe .52 - - 0.1
Mn < . 1 5 -
Pb ....
As < .01 0. 20 0.49
B -
U 5.6
Na - 2953 - 3450
Ca - - - -=10
HC03 - - - 1100.
C03 ... 4613.
F 2.0 - - -
y ...
TDS 7530 - - 8270
Total
pH 10.0 9. 6 - 10.6
Reference (29) (3) (4) (24)

a
190
3:60 2210
535 42
1270 2630
I. 3 ^1. 3

42. 0.1
110.
0.65 G.04
0.21 -10.01
C.I 0.2
2.9 0.25
910
530 315
-

I. 2
-
-

3,3 7.7
(24) (24)
Sands
OfUV
240
21BO
120
0



7.
-

-
-

570

-





(5)
Slimes
onlv a
205
2330
75
2230


0. 14
-
_




730

-





(5)
Alkyl-
amine
1 10
2910
72
-
-

220
30


-

.
520

-
3.8

4370

2. 6
(24)

EHPA
235
11, 000


0. 2
2.2
67.
11.
_
14. 5
-
-
1055



13.
0,04
-

2. 1
(U
Amine
_ TBPb
3740
7500
-

3. 6
O.S
5. 4
9. 1

4. 9
-
34.
5400.

-

8.0
34.
19,300

2. 1-4. 1
(7) (3)
 *After neutralization.
 ^Effluents from tails, weighted average.
 to have high sulfate concentrations.  Other chemicals commonly
 used in acid leach mills are shown in Table 11.
           Table 11.  CHEMICAL USAGE IN ACID LEACH MILLSa
Chemical
H2S04
Fe (powder)
MnO2
NaClO3
MgO
NH3
NaOH
EHPA. Alkyl-
mine and others
Kerosene
NH4NO3
Na2CO3
NaCl
NH4NO3
NaCl
NaCl

Purpose
Leach
emf adjustment
Oxidant
Oxidant
U ppt (pH adj)
U ppt (pH adj)
U ppt (pH adj)

Solvent extraction
Solvent diluent
Solvent stripping
Solvent stripping
Solvent stripping
IX-eluant
IX-eluant
Roasting (vanadium
ores)
Usage,
Ib/ton of ore
30 - 500
variable
3 - 10
1 - 3
1-3
1 - 30
1-4

0.01-2.0
3.4
1.3
10-15
10-15
15-20
7

50-160
           aReferences 1.  5. 8. 10, 24. 25. and 26.

Ion-Exchange Recovery

     Following acid leaching,  the  sands and slimes are re-
moved from the pregnant liquor and discarded as waste.  In

-------
 Process Wastes                                             43

the case of the resin-in-pulp process only the sands are wasted
at this point.  Powdered iron may then be added for emf adjust-
ment if ferric iron (Fes) or vanadium (5) is present in the
leach solution. Vanadium in its oxidized pentavalent state
adsorbs on the resin but is not eluted,  resulting in a poisoning
of the resin.  By  proper adjustment of potential,  the vanadium
can be maintained in quadravalent form.
    The pregnant liquor (containing the slimes in the case of
the RIP process)  then enters the anionic ion-exchange circuit
where  one of the following reactions takes place, depending
upon whether chloride or nitrate is used in the elution cycle:

                         -4
    4RNO3 +  [UO2(SO4)3]    "	T R4UO2(SO4)3 + 4NOg

                             or

                         -4

    4 RC1 +  [UO2(SO4)3J    "7 R4UO2(SO4)3  + 4Cl"

    These reactions indicate that each uranium disuifate  anion
removed from the pregnant solution is replaced by two nitrate
or chloride anions.  As a result the barren liquor slimes stream,
as discharged to waste, contains a high concentration of one
or the other of these ions, depending upon which is used for
resin regeneration.
    After the uranium-bear ing resin is eluted with an acidic
 nitrate (or chloride) solution,  magnesium oxide, sodium hy-
 droxide, or ammonia are added to the pregnant eluate, pro-
 ducing an insoluble uranium precipitate.  This precipitate is
 filtered out to produce yellowcake, and the filtrate is adjusted
 with acid and nitrate (or chloride) to make fresh eluant.  Thus,
 elution is a recirculating circuit.   The only waste produced is
 a bleed-off, which is necessary to prevent a build-up of sul-
fate ions.  This waste flow, on the order of 3. 5 gallons per
 ton of ore, ^ has a near neutral pH and contains relatively
 high dissolved values of magnesium (or sodium or ammonia),
 nitrate (or chloride), calcium, and other mineral salts.

    Table 10  shows the chemical character of waste which can
be expected from a resin-in-pulp uranium mill.  This effluent
reflects the use of a nitrate elution cycle rather than a chloride
cycle.

-------
44                                    URANIUM WASTE GUIDE
 Solvent Extraction Recovery
     Wastes from  acid leach mills using the solvent extraction
 process for uranium recovery have chemical characteristics
 somewhat different from the wastes from mills using ion-
 exchange methods.  Following liquid-solids separation, the
 pregnant acid liquor enters the solvent extraction tanks where
 it is mixed with an organic solvent which preferentially picks
 up the dissolved uranium from the aqueous phase.  The loaded
 solvent and barren acid liquor, or raffinate,  are gravity sep-
 arated, and the raffinate is discharged to waste.   The loaded
 solvent may be stripped of its uranium content by an Na2CC>3
 (or acidified chloride or nitrate) solution; the barren organic
 is recirculated for reuse; and the loaded stripping solution is
 treated with sulfuric acid and MgO or  NHg for uranium recovery.

    Although the solvent is entirely recirculated some losses to
 the raffinate do take place.  These are estimated to be usually
 no greater than 1 to  2 pounds of solvent per ton of ore  treated.
 This amount may then be expected in the raffinate waste stream
 and a combined mill effluent concentration of about 150 to 330
 ppm would result.  24  The solvents primarily used include di-
 2ethylhexyl-phosphoric acid (EHPA) and alkylamines, with
kerosene commonly used as a diluent for the  solvents.  Tri-
 butyl phosphate (TBP) is sometimes added in minor amounts
as a supplement to improve the solvent characteristics.  The
use of Na2CO3 and H2SO4 during uranium recovery results in
high concentrations of sodium and sulfate ions in  the raffinate
waste stream.  Table 10 shows the reported concentration
ranges of these and other important chemical constituents of
wastes from acid leach - solvent extraction mills.  Reported
chemical usage is  shown in Table 11.

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            POLLUTIONAL EFFECTS
                      OF  WASTES
     The liquid wastes produced in uranium milling operations
 capable of producing significant adverse effects upon receiving
 stream waters if they are discharged without adequate treat-
 ment.  The  radioactivity in the waste sands and slimes and
 that dissolved in the waste streams are of greatest signifi-
 cance.  In addition, the chemical characteristics of these un-
 treated waste flows are such that, where adequate dilution by
 receiving streams cannot be provided, direct toxic effects on
 the aquatic biota and interference with the usefulness of the
 receiving water as a municipal or agricultural supply can re-
 sult.

 RADIOLOGICAL POLLUTANTS

    In order to properly evaluate actual or potential radio-
 logical contamination of the environment by uranium mill
 '.vastes. it is necessary to consider appropriate radiation
 protection criteria, which have been developed to assist  in
 controlling human exposure.  These criteria or standards have
 oeen promulgated primarily by three organizations:  the  Inter-
 national Commission on Radiological Protection  (ICRP),  the
 National Committee on Radiation (NCRP).  and most recently,
 the Federal  Radiation Council (FRC).  Publications of these
 organizations^. 14. 18 give limiting standards for human ex-
 posure to  all man-made sources of radiation.  The primary
 standards are in terms of radiation dose rate and are essen-
 tially the same for all three organizations.  Although they set
 permissible or acceptable levels of human exposure, each of
 these groups stresses the importance of minimizing to the
greatest feasible extent  the radiation dose received by the pub-
 lic, and urges that the actual radiation dose be kept as far be-
 low the permissible levels as possible.

    Direct measurement of the human dose resulting from in-
gestion of radioactive materials is not possible.   This dose can

                             45

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 46                                   URANIUM WASTE GUIDE

 be computed, however, if the amount and distribution of radio-
 active materials in the body are known.  The limiting dose,
 therefore, leads directly to a limiting "body burden" or amount
 of radioactive material retained in the body. Knowledge of rate
 of biological accumulation and elimination of a particular isotope
 by the body permits the further calculation of a limiting intake
 of radioactive material which corresponds to a limiting ex-
 posure.   For practical control measures,  the maximum per-
 missible  intake of radioisotopes is the parameter of greatest
 usefulness.  For convenience, these maximum permissible in-
 take levels have been converted to permissible concentrations
 in drinking water (or MPCW values) by dividing the intake level
 by  2. 2 liters per day,  the amount of water consumed by the
 "standard" man. By these procedures the ICRP and NCRP have
 selected MPCW values for over 250 radioisotopes.  These values
 are applicable to radiation workers and must be reduced by
 appropriate factors in  order to protect the general public ade-
 quately.   The MPCW values for members of the uranium-radium
 family shown in Table  2 are those given by ICRP  and NCRP.
 They are derived from occupational limits which must be re-
 duced by  a factor of 30 for application to the average member of
 the general public.

     To evaluate radiation exposure of the public due to radio-
 active waste discharges completely and adequately, it is neces-
 sary to determine the  total radioisotope intake  from all sources,
 which may include several environmental media,  i. e.,  food,
 milk, water, and air.  It  is useful, however, to utilize the MPC
 in water values as shown  in Table 2, for a general assessment
 of the degree of contamination of  receiving waters resulting
 from waste discharges.

 Radium
    Radium-226, with the lowest MPC of all radioisotopes, is
 the radiological contaminant of greatest concern in uranium
 mill waste discharges.  From the data in Table 5 it can be es-
 timated that for a typical ore approximately 3 to 5 micrograms
 of dissolved radium will be found in acid leach mill wastes for
 each ton of ore processed.  In order not to exceed the MPC for
 radium in the receiving stream, the untreated waste discharge
from a 1000 ton per day mill of this type,  for example,  would
have to be diluted by a  corresponding receiving stream flow of
about 400  to 600 cfs.

                                                     OPO 82389O-3

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Pollutional Effects of Wastes                                 47
     A potentially more important waste component is the radium
 which remains undissolved through the mill process.  The sus-
 pended radium which is contained in the waste ore tailings re-
 presents all but 1 or 2 percent of the radium originally present
 in the ore.  If tailings are permitted to enter the stream, these
 solids will be deposited and will accumulate  for long periods on
 the stream  bed within a short distance from  the discharge point.
 The undissolved radium will be leached from these solids to
 the overlying waters, increasing the dissolved radium content
 of the stream.  This has been observed to result,  in one in-
 stance. ^' in a dissolved radium content downstream from a
 uranium mill of 12 micromicrocuries per liter - about four
 times the MFC, and more than  20 times higher than would be
 expected on the basis of the dissolved radium discharged by
 the mill to the stream.  A brief series of laboratory experi-
 ments on  the leachability  of radium-bear ing  river  muds ob-
 tained from a stream bed below another mill indicated that
 from 0. 1  to 1.0 percent of the  radium in  such  mud may be
 leached out with only brief mixing. ^  The actual degree to which
 radium will leach out of stream bed muds depends upon the
 stream velocity,  degree of turbulence, and bottom agitation.

     Detailed laboratory studies have been conducted on the
 leaching of radium-226 from uranium mill waste solids and
 river sediments.  36  jne mm solids most thoroughly studied
 were sand and slime mixtures from mills utilizing the acid -
 leach solvent extraction process for uranium recovery.  These
 solids and the river sediments studied were  collected from
 representative locations in the Colorado Plateau area of the
 United States.  The leaching agents used on these  solids were
 distilled water, various inorganic reagents,  and natural river
 waters.

    These studies showed  that the most important  single para-
meter affecting the leaching of  radium was the liquid-to-solid
ration (ml/g).  The liquid-to-solid ratios studied ranged from
 10:1  to 10. 000:1;  the amount of radium leached from sands and
 slime mixtures ranged from 0. 10 to between 40 and 50 percent
of the total radium associated with the solids.  The effect of
liquid-to-solid ratio was greater on acid leach waste solids than
on river sediments and greater on acid leach waste solids than
on alkaline leach waste solids.

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 48                                    URANIUM WASTE GUIDE

      The studies also showed that time was not an important
 factor in the amount of radium leached,  an equilibrium amount
 being leached in about 10 to 15 minutes.   Natural river waters
 leached no greater amount of radium than distilled water,  and
 of the inorganic ions Na"1". K~ . Mg~ ~ .  Ca.  Si~ ~ .  and  Ra^ *
 only barium exerted a significant effect on radium leachability.

      The hydrology of western streams strongly affects the pat-
 tern of accumulation of radium-bearing solids on the stream
 bed.  These streams are typically unregulated,  and most of the
 total annual flow occurs  within a short period of  2 or 3 months
 during late spring.  Many of these streams run dry or nearly so
 in the late summer and fall months.   Discharged radium-bearing
 solids build up during such periods of low flow only to be scoured
 from the point where they were originally deposited by the high
 flows the following spring.  This flushing action can effectively
 cleanse a badly silted stream below  a uranium mill, but the
 solids which are removed are merely transferred to a down-
 stream location and eventually  come to rest in the major res-
 ervoirs of the river system. Recent examination of the  muds
 in Lake Mead, on whose  tributaries  are many of  the country's
 uranium mills, has shown them to have a radium content four
 times as high as the natural, or background, levels. 28  These
 findings may be used, together with  estimates of the volume of
 Lake Mead sediments involved, to arrive at a rough estimate  of
 the total amount of radium-226 added to this impoundment  by
 uranium milling operations over the  last 20 years.  Such cal-
 culations, together with a parallel computation based upon ore
 tonnage processed, earlier practices regarding discharge  of
 waste tails,  etc.. indicate that some 2500 curies of radium-226
 has accumulated in the sediments of  Lake Mead since 1940. In
 the case of a long-lasting contaminant such as radium-226.
 with its half-life of 1620 years, such an accumulation is  highly
 undesirable and dictates that the spent ore solids be retained
 indefinitely at their source as is presently the practice.

    Where the stream in  question is  used as a source of muni-
cipal  water supply, suspended radium-bearing solids may be
bound in the filter sand beds of  the water treatment plant.  They
remain there even after backwashing of the filters to slowly re-
lease radium into the treated water supply.  These effects  have
been demonstrated in studies of the pollution of the Animas Ri-
ver. 27

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 Pollutional Effects of Wastes                                49


    It can be concluded from the above that undissolved ore tail-
 ings, if released from uranium mills to streams,  represent a
 highly significant source of very long-term contamination of
 receiving waters.

     If the receiving stream is used as a source of municipal
 water supply, its dissolved radium  content,  of course, cannot be
 allowed to exceed generally recognized standards and should be
 kept as far below this level as possible.  If.  in addition,  the
 stream water is used as irrigation water,  consideration must
 be given to possible radium contamination of crops which are
 raised for human consumption. Radium ingestion  via contami-
 nated crops must be  included in estimating total intake by the
 general public in such cases.   Studies on the Animas River, a
 tributary of the Colorado, showed an average radium  content for
 edible crops from irrigated farms  below a uranium mill to be
 about double that of foods from farms above  the mill. ^ If cattle
 feed is grown on irrigated lands, it is possible that significant
 concentrations of radium may  be found in both meat and milk.

    In streams receiving radioactive wastes, an uptake of the
 activity by aquatic organisms can generally be observed.  These
 organisms provide a  good indication of past contamination, since
 they retain the activity taken up during prior periods.   Fish.
 being highly mobile,  present a relatively erratic pattern of con-
 tamination. Attached algae and aquatic insects, on the other
 hand, reflect contamination history at a specific place and.
 therefore, provide a  good picture of past contamination longi-
 tudinally along the stream.

    During a uranium mill survey,  samples  of attached filamen-
 tous algae,  bottom dwelling aquatic  insects,  and fish were col-
 lected and analyzed for gross'radioactivity and radium content.
An analysis of these data 30 indicates that the radium  content of
 either the attached algae or the aquatic insects reflects fairly
'.veil the dissolved radium content of the stream.   Because of
this fact  the more easily collected algae should be  useful as an
 indicator of radium-226 pollution.  This relationship is shown
in Figure 12.  The natural radium content of attached  algae  was
 found to range from 2.0  to 10 micromicrograms per gram of
 ashed weight, averaging 4. 5 micromicrograms per gram.
The average natural dissolved  radium content of the associated
flowing water was 0. 35 micromicrogram per liter.  In radium-
polluted waters the algal radium content was found to be much

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 50
                                        URANIUM WASTE GUIDE
X
1/1
     1,000
      800
     600
O
?    400
Q
z
<
Z
     200
               ALGAE, 1958
            a   INSECTS, 1958
            A   ALGAE, 1959
                    5          10          15
                      DISSOLVED Ra226 IN WATER,
           Figure 12. Radium-226 content of algae and fnsects versus
                   that of water - Animas river.
higher.  From Figure 12 it can be seen that, with a dissolved
radium concentration of  15 micromicrocuries per liter in the
stream, for example,  the insect and algal concentration could
be expected to lie in the  range  from 200 to 500 micromicro-
grams per gram.  This uptake of radioactivity by aquatic or-
ganisms, which serve as food for edible fish and shellfish,
provides another mode of entry for human intake of radioactive
materials which must be considered in evaluating total intake.

CHEMICAL POLLUTANTS

Effects on Stream Biota

    The Animas  River, receiving wastes from a 500-ton-per-
day mill using a combination alkaline leach and acid leach -

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Pollutional Effects of Wastes                                 51
 solvent extraction process with vanadium recovery was studied
 extensively in this regard.^ A census of bottom-dwelling or-
 ganisms above and below the mill discharge was conducted on
 this stream which,  at the time, had a flow of  300 cfs,  about  50
 percent higher than its annual  average minimum 30-day flow.
 Below the mill virtually complete elimination of bottom-dwell-
 ing aquatic insects was observed.  Partial recovery was indi-
 cated at a station 36 miles below the mill,  where the number of
 species of organisms present increased.  However, the total
 bottom fauna population did not approach normal proportions
 until the river had flowed for some 45 miles after receiving  the
 mill discharge.   Fish populations and types were greatly re-
 duced in these reaches.
     In conjuction with these stream investigations, bio-assay
 studies were performed on the various mill effluents.   These
 tests, in which local fish species are placed in various mixtures
 of waste effluent and unpolluted stream water, are designed  to
 measure waste toxicity in terms of the amount of dilution re-
 quired to prevent deaths in the local fish population.  Speci-
 fically, a median tolerance limit (TLm) is determined, i. e.,
 that waste concentration at which 50 percent of the test fish
 will survive a specified exposure period,  usually 72 or 96
 hours.  To permit all of the fish to survive indefinitely, a con-
 centration much lower than the TLm must be  maintained in the
 receiving stream.  The TLm is, therefore, reduced by an "ap-
 plication factor, " which may range from 3 to  10, depending upon
 the fish food organisms to be protected,  variability of the waste,
 temperature. pH, and chemical characteristics of the river
 water.

     The TLm values  observed for the waste effluents from this
 acid leach - solvent extraction mill are shown in Table 12.  At
 the minimal application factor  of 3, a stream  flow of 600 cfs
 would be required to protect the fishery resources of the stream.
 From these data it is apparent that at the normally expected
 annual minimum  30-day stream flow of 200 cfs large numbers
 of fish would die.  On the basis of the mill processing rate of
 500 tons per day, the required receiving stream flow for this
 particular stream would be from at least  1. 2  to as much as 4
 cfs per ton of ore processed per day by the acid leach - solvent
 extraction process, depending  upon the application factor se-
lected.

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 52
URANIUM WASTE GUIDE
   Table 12.  BIOLOGICAL TOXICITY OF EFFLUENTS DISCHARGED TO THE
           ANIMAS RIVER - 1958a
Waste stream
(a) Final tailings effluent
(b) Primary tails overflow
(c) Vanadium filter tray wash
(d) Raffinate
(e) Composite sample of (b). (c). and (d)
TLm range.
1.3 to 3.3
13 to 18
0.82 to 4.2
0.09 to 0.21
0. 31 to 7.6
Equivalent
dilution
flow. b
cfs
6 - 16
2.6 - 14
34 - 79
7 - 193
aReference 7.
bBased upon waste flow discharged.
     Subsequent changes in waste treatment and disposal carried
out by the mill reduced considerably the amount of suspended
solids and organic waste which entered the stream. 8  These
modifications resulted in marked improvements in the variety
of aquatic biota found in the stream below the mill.
     The most toxic single waste noted in Table 12 is the organic-
bearing raffinate which had a TLm of one-tenth the  next most
toxic waste.  For mills using a uranium recovery process other
than solvent extraction,  the over-all waste toxicity  and the re-
sulting dilution stream flow requirement would undoubtedly be
considerably less than those discussed above.   Because of the
variation in chemical content of streams and the importance of
this  factor of waste toxicity, generalization  in this regard is  not
appropriate and each stream that receives a mill waste discharge
must be evaluated as an  individual  case.  Such evaluations have
been conducted at a number of mills, 28 ancj  Table 13 summarizes
the results of these studies.
    Table 13.  URANIUM MILL EFFLUENT BIOASSAYSa
Mill location
Moab. Utah
Rifle. Colorado

Mexican Hat. Utah
Slick Rock. Colo.
Uravan. Colorado



Shiprock. New Mexico
Waste stream
Tailings pond effluent
Vanadium plant waste
Organic-bearing raffinate
Organic-bearing raffinate
Waste tails
Tailings seepage and ground water
Uranium-Vanadium effluent
Redcake (Vanadium) tails
Yellowcake filter pond
Organic-bearing raffinate
TLm. :c
32 - 42
2.4
0.25
0.20 - 0.39
1.5 - 2.4
100
0.42 - 0.75
4.2-8.0
2.4
0.41
    aReference 28.

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 Pollutional Effects of Wastes
53
     It is apparent from these results also that the organic-bear-
ing raffinate is the mill waste  component most toxic to fish.   The
TLm value of this raffinate varied between 0. 2 to 0.75 percent
meaning that these wastes, if  discharged to a stream, would  re-
quire a minimum dilution factor of 400 to  1500 (l/TLmx3) in  the
stream.  Wastes from vanadium processing circuits exhibited
about one-tenth the toxicity of the  organic-bearing raffinate.

Effects on Water Uses

     A comparison of the chemical content of  untreated or neu-
tralized mill effluents (Table 10) with commonly used drinking
water standards. 31 as shown in Talbe 14. indicates that sev-
eral  chemical components of the waste are present in relatively
high  concentrations.

  Table 14.  DILUTION REQUIREMENTS FOR CHEMICAL POLLUTANTS
Chemical constituent
Arsenic
Barium
Carbon chloroform extract
Chloride
Chromium (+ 6)
Copper
Cyanide
Fluoride^
Iron
Lead
Manganese
Nitrate
Suifate
Total dissolved solids
Uranium6
Limiting
concentration. a
mg/ 1.
0.01
1.0
0.2
250
0.05
1.0
0.01
2.0
0.3
0.05
0.05
45.0
250
500
40
Basis
for
limitb
P
P
A
A
P
A
P
P
A
P
A
P
A
A
P
Ratio of
required
stream flow
to waste flowc
1450
-
-
15
-
1.6
_
4.0
734
13
2200
60
45
39
0.9
  aPublic Health Service Drinking Water Standards. ISSljReference 31).
   P = Physiological effects; A = Aesthetic considerations.
  cUsing maximum waste concentrations in Table 10; assumes concentra-
   tion in dilution flow is zero.
  ^Varies from 1.4 to 2.4. depending upon average air temperature.
  e!CRP-NCRP Standard.
     The last column of Table 14 shows the ratio of diluting
stream flow to waste flow required to assure that the particular
chemical pollutant concentration will not exceed its limiting con-

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 54                                    URANIUM WASTE GUIDE
 centration in the receiving stream.  The pollutant concentration
 used in these calculations was the highest value reported in
 Table 10.  Thus,  all of these ratios do not apply to a single mill
 effluent, although one or more apply depending upon the process
 used.
     It is clear that manganese can be a major waste problem
 wherever it  is used as an oxidant in the mill process if liquid
 wastes are released  to a stream.  The dilution ratio shown in
 Table 14 for manganese indicates that for a particular acid mill
 waste a  ratio of receiving stream flow to waste flow of 2200.  or
 about 3000 cfs for a 1000-ton-per-day mill,  would be required
 if neutralization were not practiced.  Such a dependable flow
 is far in excess of that available at most mill sites.  A ratio of
 stream flow to waste flow of 1450 would be required to dilute
 wastes from the SX mill of Table 10 to prevent excessive ar-
 senic concentrations  in the receiving stream,  if wastes from
 that mill were released to the river.   (In practice, they are
 confined in the tailings pond.)  This element originates in
 certain uranium ores, and it is a potential problem only at
 mills using such ores.  Iron dissolved from  the ore or abraded
 from the grinding equipment, or metallic iron used for emf ad-
 justment will be found in  unneutralized acid mill effluents,  which
 require a high dilution stream flow.  However, simple neutral-
 ization of the waste reduces the soluble  iron content to negligible
 proportions,  as Table 10 shows.

     In mills using nitrate elution of ion-exchange resins, ni-
 trates can be expected in relatively high concentrations in
 waste streams. Where nitrate compounds are used for solvent
 stripping, somewhat lower, though still significant, concentra-
 tions of nitrate are produced.

     Of the potential chemical contaminants listed in Table 14
 the more serious involve  those which are capable of causing
 physiological damage to persons using the receiving stream for
 drinking  water.  These include elements such as arsenic.
 barium,  chromium, fluorine, and lead which may be contained
 in raw ores.   Compounds containing cyanide  and nitrate used
 in ore processing may be found in waste streams in significant
 concentrations.  The  limiting uranium concentration usually is
not approached in waste flows,  except possibly in some alkaline
mills where both water usage and uranium recovery efficiencies
are lower than those normally found.

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Pollutional Effects of Wastes                                55
     The remaining contaminants listed are objectional pri-
marily for aesthetic reasons: taste,  odor,  or appearance.
Some mill effluents contain excessive amounts of the hardness-
producing cations, calcium,  and magnesium.  The hardness
concentration of one mill effluent following lime neutralization
was computed to be near 4000 ppm (as CaCC^).  Drinking waters
with hardness levels exceeding about 250 ppm are usually con-
sidered "very hard" and undesirable  for domestic use.  Certain
mill effluent constituents,  such  as sodium,  boron,  chlorides.
and total dissolved solids, could cause degradation in the
stream's value for irrigation use.
     Discussion of the pollutional effects of mill effluents on
the aquatic environment has  been directed primarily to surface
waters, although much  of the foregoing applies equally well to
ground waters.  Mill wastes are commonly stored in tailings
ponds, and the opportunity thus  exists for contamination of
ground waters by seepage of the pond contents downward toward
water-bearing strata.   Pollution of this type where the ground
waters are used or are usable can be quite significant because
of the permanency of ground water contamination.  Once the dis-
charge of contaminants to surface waters ceases a fairly rapid
recovery of the stream to its former quality can be  expected:
this is not the case,  however, with ground waters.  Suspected
cases of ground water contamination  due  to seepage from mill
tailings ponds have been reported^, 4 where dissolved radium
concentrations significantly above background levels have been
found at test well depths to 95 feet.

     In another instance 35 nitrate pollution of ground waters by
seepage from tailings ponds  was demonstrated.  The 3. 9 tons
per day of nitrates (as N) contained in wastes from a resin-in-
pulp mill  caused observable contamination of shallow ground
waters at distances up to 6.3 miles from the mill.   It was  es-
timated that 87 percent of the waste volume discharged to a
70-acre tailings pond,  which had no surface overflow, was  lost
by seepage at the rate of 0.17 feet per day.  The possibility of
significant ground water pollution in  the vicinity of uranium mills
should not be overlooked.

PHYSICAL POLLUTANTS

     In addition to the radioactivity contributed to the stream
by discharged ore tailings, as discussed previously, these  spent

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56                                    URANIUM WASTE GUIDE
ore solids can smother the bottom organisms normally found on
the bed of an unpolluted stream.  The aquatic insects, algae.
and other organisms living on the river bottom are important
sources of food for fish life.   The depostition of ore solids in
the stream can cause a marked decrease in productivity of
bottom-dwelling fish food organisms by blanketing the stream
bottom, thus forming an undesirable physical environment that
inhibits their growth.  Such a reduction of bottom fauna brings
about a corresponding reduction of fish life in the stream.

    The discharge of very fine and not readily settleable ore
particles, or slimes, causes the receiving stream to become
turbid,  reducing its  suitability as a habitat for biological forms
and increasing the difficulty of water treatment for municipal
and some  industrial  uses.   Highly colored mill waste streams
create aesthetically  objectionable conditions in the receiving
stream.  In a  number of cases it has been observed that the
release of low pH effluents  (pH of 1. 0 to 2. 0) to the slightly
alkaline stream has  resulted in the formation  of a  fine floe
that may persist for miles and is most unsightly.

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                     POLLUTION

           ABATEMENT METHODS
     The preceding discussions of the pollutional capabilities of
uranium mill wastes clearly indicate the necessity for contain-
ment of certain wastes and treatment of others prior to dis-
charge to surface waters.  Treatment for reduction of radium,
both dissolved and suspended, is of primary importance to
minimize human internal radiation exposure.  Waste treatment
to protect the biological life of the receiving stream is necessary
and interference with legitimate uses of the down-stream waters,
such as municipal, industrial, or irrigation water supply,  must
be prevented.

     Waste treatment and control practices in the uranium in-
dustry have improved greatly during the past  5 years.  Direct
radium-226 pollution or the release  of undesirable chemical
wastes at significantly high levels occurs in only a few isolated
cases.  Other more  subtle problems such as the leachability of
radium-226 from tailings and refinement of waste treatment
practices are under  study.  It is now general  practice through-
out  the uranium industry to retain wastes in tailings ponds, or
lagoons, and this single measure is  of real value in preventing
many of the potential water damages discussed in  previous sec-
tions.  Under these conditions settieabie waste ore solids are
retained at the mills and the total amount of radium entering
the  country's rivers is kept to a low level, most certainly far
less than the estimate of 1000 curies per year which was made
recently. ^8 This is  readily apparent since all of the radium
dissolved by the milling industry amounts to less than fifty
curies each year and even  a large majority of this is not dis-
charged to surface waters.  Additional waste  treatment mea-
sures are often required,  however,  and these are discussed
in detail below.

     The Atomic Energy Commission,  under whose  licensing
authority the uranium mills operate,  has established limits
                             57

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 58                                    URANIUM WASTE GUIDE

 for the radioactivity content of liquid effluents discharged by
 the mills. 32 These limits, expressed as radioisotope concen-
 trations in the effluent before release, are one-tenth of the
 MFC values given in the National Bureau of Standards Hand-
 book 69 for continuous occupational exposure limits. 13 jn
 addition, the regulations provide for the possibility  of higher
 concentrations in the effluent at a particular mill if  it can be
 demonstrated that it is not likely that any individual will be
 exposed to radioisotope concentrations greater than the pre-
 scribed limits.  In the issuance or renewal of Source Material
 Licenses for uranium mills,  the Atomic  Energy Commission
 indicates what exceptions to the prescribed limits have been
 approved.  The license also contains additional specific dis-
 charge requirements.  These additional requirements now call
 for effluents to be substantially  free of settleable solid materials
 and may also limit volumes to be discharged.  Requirements for
 frequency of reporting on analysis of waste flows and receiving
 waters and maintenance of data  records are also usually stated
 in  the Atomic Energy Commission license.

     Thus,  the Atomic Energy Commission regulations provide
 guidelines for mill operators in  carrying out pollution abate-
 ment measures.   The ultimate test of the  success of such mea-
 sures,  however,  is the maintenance of receiving waters at a
 level which permits the full development of all legitimate  down-
 stream water uses. In addition, the total radiation exposure of
 downstream populations from ail man-made sources must re-
 main within prescribed limits and should be minimized to the
 greatest feasible extent.

 TAILINGS  PONDS

     A universal minimum treatment step for mill wastes  is the
 impoundment of liquid-borne wastes in ponds.   These ponds,
 which are used to retain solid ore residues (tails), are usually
 referred to as tailings ponds.   Because of the large amount of
solids or tailings to be handled,  the peripheral dikes of many
such ponds are in fact composed of the tails material itself.
These ponds gradually fill with solids and in this manner they
tend to "grow" in size and/or elevation.  The original dam or
dike behind which the slurried tailings are retained is often of
earthen construction.  The tailings solids which accumulate be-
hind this dike are then used to extend the  tickness and height of
the  earthen dam until ultimately  they become  its major consti-
tuent.  In practice, advantage is taken of the more readily sep-

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 Pollution Abatement Methods                                59

 arable coarse sands for use in covering the exterior surface of
 the dam.  thus leaving the slimes to settle out of the slurry and
 form the interior surface of the  dam wall.  Excessive use of
 uniformly sized tails in any one  portion of the dam wall leads
 to instability and should be avoided.

     The amount of overflow from the tailings ponds is a function
 of net liquid input and the evaporation and seepage which occur.
 It is not uncommon  for these ponds to produce no overflow for
 long periods of time, or  in some cases, indefinitely.   Where
 extensive land area is available,  advantage is taken of natural
 ground  contours to create ponds  or lagoons which may be as
 large as 300 acres.

     As a minimum  accomplishment, such ponds can success-
 fully remove  substantially all settleable solids.  In addition,
 they serve as reservoirs for water which may be recycled to
 the mill process,  thereby reducing the total water consumption
 and the quantity of liquid waste for disposal,  minimizing the
 required pond area.  Tailings pond water is commonly used to
 repulp the waste  tails filter cake that results from  the last
 stage of liquid-solids separation following alkaline  leaching.
 Although this procedure reduces significantly the net quantity
 of liquid to be disposed of,  the daily  quantity of dissolved radio-
 activity, as well  as  most other dissolved contaminants produced
 in the milling process,  remains  unchanged.   As a result the
 concentration of dissolved radium and other constituents tend
 to build up to higher levels  in tailings ponds where  recircula-
 tion  is practiced.

    At two alkaline  mills, 3. 4 for example, though  the dis-
 solved radium leaving the mill process was found to be negli-
 gible during the period  of the mill survey, the dissolved  ra-
 dium content of the tailings pond water was 35 micromicro-
 curies per liter in one case, and 160 in the other.   Dissolved
 radium  concentrations in tailings pond waters can  be expected
 to vary greatly, even among mills using the same process.  In
 addition to recirculation, this variation is brought about  by dif-
 ferences in the raw  ore,  size of  ponds, evaporation rates, mill
 solution bleedoff rates and other  factors, including coprecipita-
 tion  of radium.  Thus,  although  the daily quantity of dissolved
 radium wasted from a given milling process may be expected
to be in a relatively narrow range on a per ton basis,  the actual
 concentration in the  tailings pond discharge (overflow or  seep-
age)  may vary greatly among them.

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The waste ore slurry Is pumped to a  tailings pond where the solids
are separated and retained.
One of the industry's  most extensive tailings pond areas is  shown
above. In this case liquid is decanted from the  pond and injected
into a deep well for ultimate disposal. (Photograph courtesy of The
Anaconda Company)

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The  light-colored  tailings pile dominates this  scene.  Wind-blown
particles of waste  ore solids may be scattered over a wide area.
Waste tails are pictured next to an abandoned  uranium mill.  The
Colorado River flows by at the  right.  Permanent  retention of such
solids is a most important pollution control measure.

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 62                                    URANIUM WASTE GUIDE
     It may be noted at this point that the only liquid waste result-
 ing from the alkaline-filtration  process is the moisture con-
 tained in the final tails filter cake, which is usually about 80
 percent solids.  Instead  of repulping this relatively dry filter
 cake with additional water (fresh or recirculated), it could be
 disposed of as a solid  waste.  It appears probable that the
 slight moisture which  these solids contain would be lost rapidly
 through evaporation, thereby eliminating the liquid waste
 problem for this type of  mill.
     As noted previously, the amount of liquid overflow from
 tailings ponds is dependent upon the amount of inflow,  the net
 liquid loss or gain from  rainfall and evaporation,  and  losses
 from seepage.  Reduction in the amount of dissolved pollutants
 which may be discharged, however,  is  affected  primarily by
 seepage.  The output of dissolved radioactive isotopes  could
 actually increase if significant amounts are leached from the
 waste tails during the contact period in the pond.  Volume re-
 duction by seepage is desirable  except where ground water pol-
 lution is of significance.   In this event,  steps to prevent seepage,
 such as lining the pond bottom,  may be  required.

     Tailings ponds, then, are beneficial as a pollution abatement
 measure in several ways, including (1)  removal of settleable
 solids; (2) recovering water for  reuse;  (3) permitting evapora-
 tion; (4) providing opportunity for seepage,  thereby  reducing the
 amount of pollutants which reach the receiving stream; (5) re-
 taining wastes during dry periods of low stream flow for re-
 lease during high flow periods when greater dilution is  avail-
 able; and (6) retaining radioactive pollutants, temporarily per-
 mitting the decay of shorter-lived materials.

     Undesirable features of such ponds  are (1) the inherent por-
 osity of the tails,  permitting seepage laterally or vertically;
 (2) the prolonged contact  between the liquid and the tails, pro-
 viding the opportunity for continued leaching of radioactive con-
 taminants;  and (3) their observed tendency to fail structurally
 and release their contents,  if the walls are not properly con-
 structed or maintained.

    Where it is found necessary to minimize seepage,  mea-
sures to reduce the porosity of the pond bottom and sides is
required.  Minimization of contact between the liquid and the
waste solids  could be achieved  by providing two or more ponds

                                                      GPO 825890-7

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 Pollution Abatement Methods                                63

 in series. Removal of settleable solids could be accomplished
 in the first pond if a short liquid detention period is provided.
 The overflow from this pond could then be contained for further
 evaporation (and seepage if desirable) in a second, larger
 pond with dikes constructed of material other than  tails.

     The problem  of tailings pond dike failures is a most signi-
 ficant one.  Accidental releases of mill tailings pond contents
 to the environment by this means have occurred at several
 mill locations during the past 10 years. 28 jn a recent instance,
 a considerable volume of highly acid liquor with a high radium
 concentration spilled from a storage pond to an adjacent river
 over a period of a few hours.  It is estimated that as much as
 1 millicurie of dissolved radium-226 may have been released.
 Some portion of this dissolved radium probably precipitated as
 a result of neutralization of the waste by  the stream alkalinity.
 Evidences of an extensive fish kill due to chemical toxicity were
 observed downstream  of the mill immediately following the
 spill.  Although downstream river uses included municipal water
 supplies, it was concluded that significant human over-exposure
 to radiation did not occur because of the short duration of the
 release, the quantity of radium released,  and the available di-
 lution afforded by the prevailing river flow.   Considerably lower
 flows in this stream and others adjacent to uranium mills are
 common, however, so that dilution of the released material
 could have been much  less under other  circumstances.
     Such accidental releases present a distinct hazard to down-
 stream  aquatic populations and a potential hazard to humans.
 Accordingly, appropriate measures should be taken to preclude
 their occurrence.  A protective secondary dike surrounding the
 tailings pond area would, if properly designed and  constructed,
 contain  wastes accidentally released by tailings pond dike fail-
 ures and prevent their entrance into nearby surface waters.
 Such a dike would  also prevent the washing away of tails by
 excessive surface water runoff.  This or similarly reliable
 measures should be employed.

 CHEMICAL TREATMENT

 Waste Neutralization
     The relatively simple step of neutralization is quite effec-
 tive  in reducing the pollutional potential of acid leach mill
wastes.   In addition to eliminating the quite significant harm-

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 64                                   URANIUM WASTE GUIDE

 ful effects of excess acidity on the aquatic life of a receiving
 stream,  the solubility of certain radioactive and chemical
 pollutants is greatly reduced,  causing their precipitation and
 subsequent retention in the waste ponds.

     Of greatest significance is the removal of dissoU'ed radium
 in acid leach effluents by neutralization to a pH of 7. 0.  An 83
 percent reduction was observed at one mill^ and  slightly higher
 values to (90^) have been reported elsewhere. 20 jn addition,
 the dissolved thorium would be precipitated.  The concentra-
 tions of certain chemicals in solution, such as sulphate, phos-
 phate,  iron, copper,  cobalt, arsenic, uranium,  and vanadium.
 likewise are reduced by neutralization.   Lime is most commonly
 used as a neutralizing agent.
     The addition of sulfuric acid to alkaline mill wastes for pH
 reduction may also bring about some removal of  soluble radi-
 um. 20 The extent of  removal  observed in bench-scale labor-
 atory tests was variable, however.  The  observed removals
 probably resulted from the presence of finely divided solids
 and precipitates formed during neutralization, and the mech-
 anism of dissolved radium removal was adsorption onto solid
 particulate surfaces.  Because of this tendency of radium to
 be bound  to the finer solid particles, the  best sedimentation
 practice is required following  neutralization if maximum re-
 movals are to  be achieved.
     At a few mills both acid and alkaline leaching of ores is
 practiced.  At these mills combination of the respective acid
 and alkaline waste  streams is  an obvious and practical treat-
 ment step.

 Barite Treatment
     A reduction of dissolved radium in acid leach wastes by a
 factor of ten,  as obtained by neutralization,  is often insuf-
 ficient to  meet discharge requirements,  and further treatment
 steps may be required.  One procedure which has been found
 effective for dissolved radium  removal employs the crude min-
 eral  form of barium suifate. referred to  as barite.  This ma-
 terial has been tested on a pilot scale and is presently in use
 at several mills.

    Soluble radium  removals up to 90 percent and higher by
barite treatment have  been obtained in bench-scale tests of
neutralized acid and alkaline mill wastes. ^0 The amount of

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Pollution Abatement Methods                                 55

removal actually achieved was found to be dependent primarily
upon the mesh size of the barite, the intimacy and time of con-
tact, and the method of application.  The most efficient treat-
ment procedure is to percolate the waste through a column of
barite.  which results in a chemical consumption of about 300
milligrams of barite per liter of waste treated and results in
an apparent radium-226 removal in excess of 90 percent.
Treatment may also be carried out by percolation of the liquid
waste through a shallow bed of barite. or by batch treatment in
which the barite is added to the waste in agitated or quiescent
tanks.   The barite requirements for this latter mode of treat-
ment are higher for comparable radium removals and recycling
or series treatment may be necessary.  Thus the combination
of acid mill waste neutralization, which can  remove up to 90
percent of the dissolved radium, followed  by barite treatment
where an additional 90 percent removal may also be possible,
would result in an over-all removal of 99 percent or  a reduc-
tion in soluble  radium content by a factor of  100.

    Various methods of barite treatment are now being used by
several mills  to determine whether the laboratory findings  pre-
viously  described are as effective in full-scale applications.
There is some indication that a more refined form of barium.
i. e.,  barium carbonate or barium  chloride,  may be a more
effective treatment agent, with little or no increase in the cost
of treatment.   The total cost of chemicals for the neutralization-
barite treatment for acid mill wastes is estimated to be about
20 to 40 cents per ton of ore processed, 80 to 90 percent of
which represents the cost of neutralization.

    An  effective treatment for dissolved radium removal from
alkaline leach mill waste liquids has been  found in laboratory
tests with copperas (FeSC^Tf^O) as a flocculating agent together
with barite. 20  A two-step treatment, in which copperas  is added
in the first step followed by two-settling stages and barite is
added in the second step, yielded over-all removals of 97 per-
cent.  This level of removal would  ordinarily result in a treated
effluent which meets Atomic Energy Commission limits for  dis-
solved radium-226,  if it is as effective in  full-scale mill opera-
tions as in tests.

Raffinate Treatment

    In discussions of the pollutional effects of mill wastes,  the
organic-bearing raffinate from the  solvent extraction process

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66
URANIUM WASTE GUIDE
v tf*-.
       Organic-bearing raffinate is stored in ponds of this type. Because of
       its toxicity to aquatic life, this material should be disposed of by
       seepage or treated prior to discharge.
has been cited as the most toxic to aquatic life.  This waste
contains significant quantities of both the costly solvent and its
diluent, kerosene,  and is highly acidic.  Because of the nature
of the waste,  it may be impounded separately in retention ponds.
as has  been done in at least one case. & from which evaporation
or seepage may be sufficient to preclude its overflow. Prior
to entering the ponds  this waste usually is passed through a
holding tank  to permit any possible further recovery by skim-
ming.   An added treatment step for further entrained organic
removal which suggests itself at this point is the addition of
make-up kerosene.  The additional organic removed as a re-
sult could  be  recycled to the uranium extraction process with
attendant savings in solvent cost.  Such extra kerosene could
easily be added in a small flash mixer ahead of the holding
tank, and no loss of the diluent should result since the waste
is undoubtedly fully saturated and charged with kerosene on
leaving the extraction tank.   Even more thorough treatment
could be provided by vacuum or pressure flotation procedures.33
For  instance, air could be dissolved under pressure in the
raffinate by inserting  a pump and small pressure  tank ahead  of

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 Pollution Abatement Methods                                67

 the decantation tank.  Air and excess kerosene could be added
 at the suction side of the pump.  Upon reaching the decantation
 tank,  the dissolved air would come out oi" solution as minute
 bubbles which,  in rising to the surface, would tend to separate
 the immiscible kerosene and solvent present. These materials
 could be skimmed off for return to the uranium extraction pro-
 cess.  Any solvent dissolved in the raffinate rather than en-
 trained would be unaffected, however.
     Very  little dissolved radium is extracted by the solvent,  and
 the treated effluent from the decantation step would still contain
 substantial quantities (See Figure  10).   This effluent,  if treated
 as outlined above,  could then be impounded separately or added
 to the tailings pond contents for further treatment for dissolved
 radium removal.

 DEEP-WELL INJECTION

     The Anaconda Company at Grants.  New Mexico,  recently
 put into operation a deep-well injection system for disposal of
 tailing water from its acid-leach,  resin-in-puip mill.  The in-
 jection well was drilled to 2511 feet with an original diameter of
 slightly less than 8  inches.  The disposal zone extends down-
 ward from  950 feet for a distance  of almost 600  feet.
    The acidic waste waters are decanted from the tailings
pond, treated with copper sulphate (for slime control) and a
sequestering agent,  then passed through circular leaf filters
for turbidity removal.  The treated waste is  injected  into the
well  by gravity at a rate of 400 gallons per minute. The static
water level of 240 feet provides a natural hydrostatic  injection
pressure of about 100 pounds per square inch.

    Upon entry  of the waste water  into the underground forma-
tion,  neutralization, precipitation,  ion exchange, and dilution
by the ground waters take place.  Calculations of the porosity
and ion-exchange capacity of the sands in the disposal forma-
tions  indicate a  useful life expectancy of the system of more
than  10 years.

    Special care has been taken in casing the well to prevent
the possible contamination of the major potable water aquifer
at a higher  elevation.  A monitoring well has been located in
this aquifer some 300 feet away in  the direction of the hydraulic
gradient.  Weekly samples have indicated that no leakage is
taking place. A regional monitoring program of all fresh water

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 68                                    URANIUM WASTE GUIDE

 sources in a 20-square-mile area surrounding the well has
 also been instituted.

      The successful operation of this deep-well injection sys-
 tem  is most encouraging and points  the way toward what may be
 one of the most satisfactory available methods for disposal of
 liquid mill wastes.

 SOLID WASTE DISPOSAL

      The methods of waste treatment discussed above have as
 their objective the conversion of dissolved radioactivity,  speci-
 fically radium, to an insoluble form which can be precipitated
 from the waste solution prior  to discharge.  The radium thus
 removed from solution, together with the large amount of solid
 ore tailings,  is retained in ponds while  the treated liquid is
 disposed of by evaporation, seepage, and/or discharge to sur-
 face  waters.  These retained solids  contain a considerable quan-
 tity of radium, all but a minute fractional percentage of that or-
 iginally present in the raw ore.  Hence, the tailings  piles repre-
 sent a great reservoir of potential radium contamination of
 nearby surface and ground waters and must be controlled ac-
 cordingly.   The magnitude of this reservoir is indicated by the
 amount of tailing solids accumulated to date,  which is esti-
 mated to be 34 million tons. ^

    The radium contained in these solids  is known to be leach-
 able by contact with water.  This is especially true of the pre-
 cipitated solids from neutralization and  barite treatment pro-
 cesses. Therefore, these solids should not be permitted to
 enter natural bodies of  water.   Heavy rainfall, flooding of
 nearby streams,  and wind erosion of the dry tailings piles all
 present opportunities for the movement  of these materials into
 the aquatic environment.  Excessive  seepage from the base  of
 such  tailings piles provides an early  indication of potential
 structural failure  of the wall.   Whatever measures are needed
 at any particular mill site to prevent such movement, should be
 carried out.  These measures  may include,  for example,  the
 avoidance of flood plains, river banks, and dry wash areas as
 locations for tailings piles and the construction and maintenance
of pond dikes to preclude their rupture due to the  hydraulic head
 within the pond. Cementation of the exterior surfaces of aban-
doned tailings piles is worthy of consideration at some locations
to minimize wind-borne dust.   Abandoned  mines may make a

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Pollution Abatement Methods                                 69

suitable long-term repository for waste tailings solids, and
this method of disposal, as practiced elsewhere in the mining
industry, 34 may of necessity receive more attention in the
future.  Proposals have been made to use these tails as land-
fill material for highway and other construction projects.  A
thorough evaluation of possible hazards associated with this
means of disposal, which would be required in each case,  has
not been made to date.   This type of containment of waste  tails,
however, may merit further study.  The  indiscriminate use of
tailing sands by nearby residents in concrete,  mortar, or plas-
ter mixes,  for children's sand boxes or as a garden soil additive
should certainly be prevented, for obvious reasons.

    It must be emphasized strongly that any steps taken toward
reduction of the dissolved  radioactivity entering a stream  will
have been to no avail if the radioactive  solids are not perma-
nently controlled.   The half-life  of radium,  1620 years, clearly
indicates the importance of permanent retention and control of
this solid waste material.

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      SUMMARY AND  CONCLUSIONS
URANIUM MILLING INDUSTRY

    The extraction of uranium from its ores has become a
major industry in the United States since the end of World War
II.  The United States now ranks as the world's largest producer
of uranium ore,  and of uranium concentrate, the final product
of the milling process.  The location of major  ore deposits is
largely  centered in the Colorado Plateau and Ambrosia Lakes
areas and in Wyoming,  with the result that most of the indus-
try's milling capacity is located in the Colorado River Basin
and the  Grants,  New Mexico, area.

    The most significant waste materials from this industry are
the  radioactive daughter products of uranium-238,  each of which
is found in uranium ores at or near the same level of activity as
the  parent isotope.  The greatest human internal hazard of the
14 radioisotopes in the decay series is presented by radium-226,
a long-lived alpha  emitter.  Of the 264 radioisotopes considered
by the ICRP-NCRP.  the maximum permissible concentration in
water (MPCW) consumed by the general public  is lowest for
radium-226,  that is, 3. 3 micromicrocuries per liter.  The next
most hazardous isotope is lead-210,  which has an MPCW of 33. 3
micromicrocuries  per liter.  Thorium-230 and uranium-238,
whose MPCw's are 200 and 4, 000 times higher, respectively,
than radium,  have  also received attention as radioactive pollu-
tants having potential significance in  uranium mill wastes.

    Uranium mills employ acid or alkaline leaching to dissolve
the  uranium content of the ore following grinding. Once the
uranium has been put into  solution, it is recovered by chemical
precipitation,  which,  in some cases,  is preceded by a concentra-
tion step in which ion-exchange or solvent-extraction methods
are used.  The liquid and solid wastes from these operations
contain  potentially  hazardous amounts of radioactive materials,
as well  as chemical water pollutants  which are undesirable from
a toxicological. aesthetic, or economic standpoint.
                             71

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  72                                      Uranium Waste Guide
 PROCESS WASTES
     During acid leaching about 0. 5 percent of the radium-226
 content of the ore is usually dissolved and discharged in the
 mill waste streams.  Alkaline leaching has been found to dis-
 solve  a greater amount of radium-226 or about 2 percent of that
 present in the ore.  However, in this case, essentially all of
 that dissolved is precipitated together with the uranium and
 leaves the mill  in the final concentrate product.   The radium
 which is not dissolved during processing leaves  the mill as
 waste in the spent ore.

     Uranium and thorium have been shown to  be of  much less
 significance as  water pollutants than radium-226. Little is
 presently known of the possible significance of lead-210 as a
 radioactive pollutant in uranium mill waste discharges.

     Chemical constituents of mill wastes are of concern in
 some instances. Chlorides, nitrates,  sulfates,  hardness,  total
 dissolved solids, manganese,  iron, lead,  arsenic, fluoride,
 organics, and possibly other materials may be present at rela-
 tively  high levels in uranium mill wastes,  depending upon the
 particular raw ore composition,  the milling process, and the
 chemical reagents used during processing.

 POLLUTIONAL EFFECTS

     Where uranium mill wastes containing radioisotopes, es-
 pecially radium-226, are allowed to enter adjacent surface
 waters, a human internal radiation hazard is presented to down-
 stream water users.  This hazard arises from ingestion of
 radioactive materials in drinking water, and in crops irrigated
 with contaminated water,  and from ingestion by other routes
 involving animal feed crops such as hay and alfalfa.   The de-
 gree of hazard is directly related to the amount of both dis-
 solved and undissolved radium discharged to the stream.  Spent
 ore tailings contain virtually all of the radium  originally present
 in the ore and are important reservoirs of potential  contamina-
 tion. If discharged to streams, these solids settle to the bottom
 where  their radium content is gradually leached  into the overly-
 ing waters.

    Liquid mill  wastes, particularly the raffinate from solvent
 extraction mills, are capable of causing severe destruction of
the aquatic life in streams.  The excess acidity of certain mill

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Summary and Conclusions                                  73

wastes can produce similar effects.  The other chemical pollu-
tants mentioned above as being present in mill wastes are also
capable of impairing the stream's usefulness as a source of
municipal water supply.
     Many of the undesirable effects described  apply equally to
ground waters.  Vertical seepage of liquid mill wastes from
holding ponds to the ground water table has been demonstrated,
resulting in excessive chemical and radioisotope concentra-
tions in water drawn form nearby test wells.  The extent of
underground travel of  these pollutants has not been completely
established.

MILL WASTE TREATMENT
     Impoundment of mill wastes in tailings ponds is widely
practiced in the industry.  With proper operation and main-
tenance of such ponds,  it is possible to greatly restrict dis-
charges to nearby streams, depending upon the size of ponds
in relation to mill waste output and meteorological and soil
conditions.  These ponds,  in addition, are usually successful
in removing most settleable solids.  The dikes of many such
ponds  are made of uncompacted tailings solids,  resulting in
lateral seepage from the pond and occasional dike failure with
the loss of pond contents to the environment.

     Mill waste neutralization is an effective treatment step
which  can bring about  dissolved radium reductions of up to
90 percent.   Further treatment of neutralized wastes by the
addition of barium compounds makes additional reductions of
dissolved radium possible.

     Organic-bearing raffinate may be impounded separately to
allow for evaporation and vertical seepage into the ground. In
this way discharge to surface waters with attendant harmful
effects on the aquatic biota can be avoided.

CONCLUSIONS

     The uranium milling industry is a major potential  source
of radiological pollution of the aquatic environment.   The mag-
nitude of mill operations and the particular isotopes involved
present a very real potential threat of excessive human internal
radiation exposure.  It is only by employing the most careful
and deliberate waste control measures  that this potential threat
can be prevented from becoming an actuality.  Improvements in

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  74                                       Uranium Waste Guide


 presently available waste treatment and control procedures
 should continue to be pursued; however, existing methods,  if
 carefully applied, can provide a reasonably adequate degree of
 protection.

     During the past 5 years the uranium milling industry has
 made  substantial improvements in waste-handling and disposal
 procedures. As a result,  environmental contamination in the
 vicinity of many mills can be considered to be near a desirable
 minimum level.  Sound radiation protection philosophy dictates.
 however,  that wherever additional reductions in the amount of
 activity released to the environment can be obtained by reason-
 able means such reductions should be accomplished. In addition.
 continued study of the more subtle areas of possible or potential
 contamination is warranted.  Chemical or radiological pollution
 of ground waters by uranium mill wastes has been shown to oc-
 cur, for example, and continued investigation of this problem is
 desirable.  In addition, the importance of lead-210 as a mill
 waste  constituent should receive attention.

    The extremely long half-life of the major radioisotope  in-
 bolved, that is,  radium-226, whose half-life is 1620 years,
means that permanent control of ore residues is required.  Ac-
 ceptable methods of very long-term storage and retention,  there-
fore, need to be found.  Reliable measures to preclude the  acci-
dental  release of tailings pond contents and waste ore solids are
also needed.  Finally, continuous monitoring of the  environment
is necessary to ensure that waste treatment and confinement
methods are producing the  desired results.

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                 BIBLIOGRAPHY
     Shearer. S.  D. ,  Sponagle, C. E., Jones, J. D. ,  and
     Tsivoglou, E. C. ,  Waste Characteristics for the Acid-
     Leach Solvent Extraction Uranium Refining Process.  I.
     Gunnison Mining Company.  Technical Report W62-17,
                 Health Service, R. A. Taft San.  Engrg.
     Center, Cincinnati,  Ohio.  1962.

 2.   Cohen, J. B. ,  Sponagle, C. E. , Shaw.  R. M. , Jones,
     J.  K. .  and Shearer, S. D. ,  Waste Characteristics for
     the Acid- Leach Solvent Extraction Uranium Refining Pro-
     cess.   II.  Climax Uranium  Company, Technical Report
     W62-17,  U.  S. Public Health Service, R. A.  Taft San.
     Engrg. Center, Cincinnati,  Ohio.  1962.

3.   Cohen,  J.  B. ,  Pahren, H. R.,  Lammering,  M. W. ,
     Waste Characteristics for the Carbonate Leach Uranium
     Extraction Process.  I.  Homestake-New Mexico Partners
     Company.  Technical Report W62-17, Cincinnati, Ohio.
     1962.

4.   Pahren, H. R. , Lammering. M. W. ,  Hernandez, Waste
     Characteristics for the Carbonate Leach Uranium Ex-
     traction Process.  II.  Homestake-Sapin Company, Tech-
     nical Report W62-17, U. S.  Public Health Service, R. A.
     Taft San.  Engrg. Center,  Cincinnati, Ohio.  1962.

5.   Tsivoglou, E. C., Kalda, D. D. , Dearwater,  J. B. .
     Waste  Characteristics  for the Resin-in-Pulp Uranium Ex-
     traction Process, Second United Nations International
     Conference on the Peaceful Uses of Atomic Energy.  Paper
     No. 2359,  21 pp. June 1958.

6.   Shearer. S. D.  Jones, J. D. , Tsivoglou. E. C. , Survey
     of Uranium Reduction  Company Mill. Moab.  Utah.  U. S.
     Public Health Service, R. A. Taft San. Engrg. Center.
     Cincinnati, Ohio.  Unpublished report.

                            75

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 76                                       Uranium Waste Guide
  7.   Tsivoglou,  E. C., et al.,  Survey of Interstate Pollution of
      the Animas River (Colorado-New Mexico).  U.  S. Public
      Health Service, R. A. Taft San. Engrg. Center, Cincinna-
      ti, Ohio.  May 1959.

  8.   Tsivoglou,  E. C.. et al.,  Survey of Interstate Pollution
      of the Animas River  (Colorado-New Mexico). II.  1959
      Surveys.  U.  S. Public Health Service. R. A. Taft San.
      Engrg. Center, Cincinnati, Ohio.  Jan. 1960.

  9.   Tsivoglou.  E. C., et al.,  Effects of Uranium Ore Refinery
      Wastes on Receiving Waters.  Sew. and Ind.  Wastes,  30.
      p. 1012.1958.

10.   Data provided by Grand  Junction Operations  Office, Atomic
      Energy Commission.

11.   Halliday. D.. Introductory Nuclear Physics. John A.
      Wiley and Sons. Inc.  . New York.  N. Y.  1950.

12.   A Description of Uranium Mines and Mills and Radioac-
      tive Wastes. Working Group No. 6. Subcommittee N5. 2.
      ASA Sectional Comm. N5.  ASA.  (Draft) May 1962.

13.   Maximum Permissible Body Burdens and Maximum Per-
      missible Concentrations  of Radionuclides in Air and Water
      for Occupational Exposure. NCRP. Nat. Bur. of Stds.
      Handbook 69.  Wash. . D. C.  June 1959.

14.   International Commission on Radiological Protection,
      ICRP Part 2.  Report of Committee II  on Permissible
      Dose for Internal Radiation.  Pergamon Press.  London.
      1959.

15.   Terrill.  J.  G. .  Ingraham.  S.  C.. and Moeller.  D. W..
      Radium in the Healing Arts and Industry.  Public Health
      Reports.  69.  No.  3.  Mar.  1954.

16.   Maximum Permissible Amounts of Radioisotopes in the
      Human Body and Maximum Permissible Concentrations
      in Air and Water.  NCRP.  Nat. Bur. of Stds. Handbook
      52.  Wash.. D.  C.  1953.

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 Bibliography                                             77

 17.   Rama Minoru Korde and Goldberg. E.  C..  Lead 210 in
      Natural Waters.  Science.  Voi 134.  July 14. 1961.

 18.   Federal Radiation Council. Radiation Protection Guidance
      for Federal Agencies. Federal Register.  May  1960, and
      Sept.  1961.

 19.   Clegg and Foley. Uranium Ore Processing,  Addison-Wes-
      ley Publ. Co.. Inc..  Reading. Mass.  1958.

 20.   National Lead Co., An AEC Research and Development
      Report from Winchester Laboratory. Topical Report
      WIN-112,  Winchester, Mass.  Feb.  1960.

 21.   Hearings Before the Special Subcommittee on Radiation
      of the Joint Committee on Atomic Energy. Industrial
      Radioactive Waste Disposal, Vol. I,  pp. 37. 58.  U. S.
      Govt.  Printing Office.  1959.

 22.   DeSesa, M.  A.. Second Interim Report on Investigations
      into the Problem of Radioactive Pollution of Uranium Mill
      Effluents.  Nat.  Lead Co..  Inc..  Topical Report WIN-111,
      Winchester.  Mass.  April  1959.

 23.   Marvin. G.. et al.,  Recovery of Uranium from its Ores.
      Proc. UN Conf. on Peaceful Uses of Atomic Energy.  UN
      519, Geneva.  1955.

 24.   Whitman. A. and Porter, E.  C..  Chemical Stream  Pollu-
      tion from Uranium Mills. Nat. Lead Co..  Inc.  Topical
      Report WIN-99, Winchester.  Mass.  June 1958.

 25.   Whitman. A. and Beverly,  R.  G.,  Radium Balance in
      Monticello Acid RIP Uranium Mill.  Nat. Lead Co..  Inc.
      Topical Report WIN-113, Winchester.  Mass. Dec.  1958.

 26.   Hollis. R. F.. and McArthur, C. K..  The Resin-in-Pulp
      Process for Recoverv of Uranium. Proc.  UN Conf.  on
     Peaceful Uses of Atomic Energy.  UN526, Geneva.  1955.

27.   Tsivoglou. E. C.. et al.. Estimating Human Radiation
     Exposure on the Animas  River. Journ. AWWA,  52.  10,
     1271.  Oct.  1960.

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  78                                       Uranium Waste Guide

 28.   Transcript of Conference on Pollution of the Interstate
       Waters of the Colorado River and its Tributaries. Second
       Session.  Las Vegas,  Nev.  May  11, 1961.

 29.   Pahren. H.  R..  Sponagle,  C. E., and Anderson, J. B.,
       Stream Surveys in the Vicinity of Uranium Mills. II.
       Area of Moab. Utah - Aug.  1960.  Colo. R. Basin Water
       Quality Control Project, U. S. Public Health Service.
       Sept. 1961.

 30.   Anderson. J. B.  Tsivoglou, E. C., and Shearer. S.  D..
       Effects of Uranium Mill Wastes on Biological Fauna of
       the Animas River, Presented  at Symposium on Radioec-
       ology. Fort Collins. Colorado.  Sept.  11,  1961.

 31.   U.  S. Public Health Service Drinking Water Standards.
       Federal Register, 26 F. R. 6737.  July 27. 1961.

 32.   U.  S. Atomic Energy Commission. Standards for Pro-
       tection Against Radiation, Federal Register, 25 F.  R.
       8598.  Sept.  7, 1960.
 33.   Gurnham.  C. R., Principles of Industrial Waste Treat-
      ment. John A. Wiley and Sons. New York.  N. Y. 1955.

 34.   Harrison. A. C.. Ore Dressing Wastes and Mine Waters:
      The Problem of Their Disposal, in Disposal of Industrial
      Waste Materials,  Society of Chemical Industry,  London.
      MacMillan Co. , New York, N.  Y.  1957.

 35.   Report of  an Investigation  of Ground Water Pollution.
      Grants-Bluewater. New Mexico,  New Mexico Dept.  Pub-
      lic Health with U. S. Public Health Service.  Aug. 1957.
 36.   Shearer. S. D.. The Leachability of Radium-226 from
      Uranium Mill Waste Solids and River Sediments,  Ph.D.
      Dissertation, Univ.  of Wisconsin.  1962.

37.   West.  S. W.. Disposal of Uranium Mill Effluent Near
      Grants.  New Mexico. Paper No. 421. Geological Survey
      Research 1961, USGS Prof. Paper 424-D. U. S.  Govt.
      Printing Office. Wash.  D.  C.  1961.

38.   Calder. Ritchie.  Livi'hg  with the Atom,  p'.  78.  The Uni-
      versity of  Chicago Press,  Chicago,  111.  (1962).

                                                     GPO 8258906

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