Application of the electrolytic uranium recovery process to limestone ore from Grants, New Mexico, The

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"l:he Application of the Electrolytic U Recovery Proceso to Limestone

Ore from Grants, New Mexico" September 1953

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RAW MATERIALS DEVELOPMENT LABORATORY HOLTON STREET WINCHESTER, MASS. Dr. George G. Marvin T E L E P H O N E WINCHESTER 6-3820

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Assistant Director for Process Development Division of Raw Materials

U. S. Atomic Energy Commission Washington 25, D. C.

Dear Dr. Marvin:

Attached is a copy of Topical Report ACC0-29 entitled "The Application of the Electrolytic Uranium Recovery Process to Limestone Ore from Grants, New Mexico" by Galen W. Clevenger.

Very truly yours,

I

ACC0-29

1

-Metallurgy-Raw Materials

TOPICAL REPORT ACCQ-29

THE APPLICATION OF THE E1ECIROLX!IC URANIUM RECOVERY PROCESS TO LIMESTONE ORE FROM GRANTS, NEW NEXICO

By

Galen W. Clevenger

September 1, 1953

Contract AT(49-l)-533 Atomic Energy Division American Cyanamid Company Raw Materials Development Laboratory

Holton Street

TOPICAL REPORT ACC0-29

THE APPLICATION OF THE ELECTROLYTIC URANIUM RECOVERY PROCESS TO LIMESTONE ORE FROM GRANTS. NEW MEXICO

By

Galen W. Clevenger

ABSTRACT

The Electrolytic Uranium Process was operated for ninety days using one kilogram of Grants limestone ore as feed each day" The indicated overall recovery in a precipitate assaying 75

per cent

UJOS

was 91 per cent. Cost items of nine kilowatt

hours of electric power and five pounds of soda ash per pound of

UJOs

were consumed.

I. II. III. IV. Vo VI. VIIc TABLE OF QONTENT§ .ABSTRACT INTRODUCTION

SUMMARY AND CONCLUSIONS OBJECT OF INVESTIGATION DESCRIPTION OF PROCESS PRELIMINARY INVESTIGATIONS BENCH SCALE PILOT TEST

(A) Description of Apparatus

ACC0-29

4

-Metallurgy-Raw Materials ~ :3 5 6 6 7 9 10 10

(B) Flowsheet and Operating Technique 10

(C) Test Results 14

(1) Electrolyzing 14

(2) Leaching 14

FUTURE WORK 19

APPENDIX A Ai

I

ACC0-29

6

-ore from

0.49 cent UJ08· The test

pro-one kilogram of ore per day operating conditions and no assayed 0.04 per cent UJ08

indi-The uranium precipitate assayed

of carbonate and nine kilowatt

of UJ08 were consumed.

ammenaoility of the process.

IV. DESCRIPTION OF THE PROCESS

ACC0-29 7

-The process is based on two fundamental facts. -These are that uranium in a sodium carbonate solution can be precipitated (probably as a sodium uranate) with sodium hydroxide and that when an electric current is passed through such a solution sodium hydroxide is formed at the cathode and an equivalent amount of sodium bicarbonate at the anode. These principies are put to use as shown in Figure 1 below.

LEACH

+

RESIDUE ~--- FILTER

t

FILTRATE

+

CELL CATHODE

Cllo!P,TMENT

U PPT~---·FILTER CELL ANODE COMPARTMENT

Figure 1. Simplified Process Flowsheet

It is necessary to separate the cathode from the anode by a cloth mem-brane to prevent mixing of the two solutions surrounding the electrodes

prior to the r~moval of the precipitated uranium. The reaction taking

place in the ceal is as follows:

+ NaHC03

(anode)

Operation is continuous with feed of fresh solution to the cathode com-partment. This feed is regulated according to the current flowing to maintain the NaOH concentration in the compartment at an optimum value.

On the basis of the work done so far this seems to be between five and ten grams of NaOH per liter. The uranium precipitated in this compart-ment is continuously removed with the solution displaced by the feed solution. After recovery of the precipitate by filtration the NaOH en-riched solution is fed continously through the anode compartment where

the other direction:

+

thus making a continuous cyclic possible.

ACC0-29

8

-Sodium carbonate consumed by the ore.and an amount equivalent to the

caustic in the uranium precip~tate must be added, but otherwise no

rea-gents are required. Consumption of power depends largely on the grade of the solution fed to the precipitation cell. The work here reported indicates power consumption of about nine kilowatt hours per pound of UJOs recovered. Higher grade ores, or solution built up to greater strength by multiple leaching would tend to lower this power cost. Reasonably cheap power would be required in order for the process to

be more attractive than a direct chemical precipitation and

regenera-tion, but it should be kept in mind that the power consumed provides for both precipitation and regeneration of the leaching medium and that no chemicals are being added which might cause a harmful increase in salt strength of the leaching solutions.

Sodium bicarbonate is always present in the leaching solution due to the NaOH consumed by the uranium precipitation. This is beneficial to uranium extraction from some ores.

as

ACC0-29 9

-of two samples previously

~~~~== contained most of its uranium as

carnotite while ~~~~~ more uranophane and uranium in

asso-ciation

the composite feed

Minus 20 mesh ore mesh prior to

assay per cent further

extraction.

*

aomewhat more refractory. The assay of

Per Cent 0.49 0.27 92.7 4.2 0.42 0.29

0.33

was reduced in a rod mill to 60 - 70 per cent minus 200 in a residue assay about 0.02 than when the minus 20 mesh ore was leached without

amounts to a four per cent gain in leaching

Precipitation Tests on , Sept. 14, 1951, for

VI. BENCH SCALE PILOT TESTS

ACC0-29 10

-The electrolytic used is shown in Figure 2 on the following page. Feed to the cathode and anode compartments was from 2.5 liter bottles through The cell was constructed of 22 gauge sheet iron in the form of an top box three inches wide by four inches long by four and inches deep. Vertical guides were provided to hold the diaphragm which the box from top to bottom. Overflow laun-ders were fastened to each compartment one-half inch from the top of the cell. These were with baffles which went nearly to the cell bottom to minimize short circuiting of solution.

Total cell volume was 0.685 liters, one-half of this being in each com-were of sheet iron and with an area two by three which gave an electrode area of one-twelfth square foot.

A current of two an electrode current density of 24 to 48

amperes square foot depending on whether one or two sides of the electrode are assumed to be in use. The diaphragm was constructed of a finely woven orlon cloth (almost any kind of cloth will work) held in the metal cell by wooden Cell overflows were collected in

Leaching was by means of mechanical agitation in a beaker heated on an electric hot plate. Filtration and washing of residues and precipitates weredone on Buchner ftLnnels.

B. Flowsheet and Operating Technique

As far as the test was conducted as a full size operation. For the sake of simplification and because of the small scale of the test, some modifications were necessary. One of these was the shutting down of the cell overnight and on Sundays. For an hour or two after starting the ohmic cell was abnormally high due to temperatures below the normal The resulting higher voltage reflects a slightly than would be the case with normal continuous

Cathode cipitate lated in

and the cell was cleaned. be overcome

was not adequate to remove all of the pre-was made. Consequently precipitate accumu-was not recovered until the end of the run In a size operation this would probably the agitation entirely and removing the

pre-the cell. It is not thought that pre-the rela-of the precipitate in the results of the test.

ACC0-29

-ACC0-29 12

-Before the test~ a sufficient inventory of sodium carbonate leach

solution was provided so the operation could be carried on with a minimum

of The cell, cathode and anode feed bottles, and leaching

beaker were filled to the regular operating levels. This volume of

solu-tion was about three the daily feed. Consequently, about three

days were required to complete a solution cycle. The complete flowsheet is shown in Figure J on the following page.

The daily routine consisted of the following:

1. The power was turned on and the cell feed, which consisted of leach liquor from the previous day's leach, was started to the

cathode compartment and the previous day's cathode compartment over-flow (following removal of the uranium precipitate) was started to the anode compartment. For the first 40 days the current to the cell was held at 1.5 amperes and the feed at about two ml. per min-ute. This resulted in an average catholyte concentration of 8.8

grams NaOH per liter. The uranium depleted from solution was

3.6

grams UJ08 per liter.

For the next 50 days the current was increased to two amperes and the feed to about three ml.per minute. This resulted in a some-what lower NaOH concentration in the catholyte (7.5 grams NaOH per

liter) and also a lower depletion of uranium

(3.3

grams U308 per

liter), but the weight of uranium precipitated per unit of time was about 40 per cent greater. The retention time of solution in the cell at the two ml. per minute feed rate was about three hours. This was adequate as no additional precipitation was noticed from solutions which stood for as long as 48 hours.

2. The leach was started with the previous day's anode compartment overflow following fortification with fresh Na2C03 to give a

con-centration of 200 grams Na2C~ per liter. This addition amounted

to five pounds of Na2C03 for ~ach pound of U308 produced. Leaching

was for six' to eight hours at 95° to 100°0. following a grind of the ore in a portion of the leaching medium to 70 per cent solids minus 200 mesh.

Evaporation took place during the leaching in amounts more than adequate to maintain the inventory at the desired volume.

3.

Following the leach the residue was removed by filtration on

a 24 em. Buchner Four to five hundred ml. of wash water

was used. Each residue was dried, weighed, sampled and assayed

for UJOg. leach including the wash water, was set

aside to be used as the catholyte feed the following day.

current density following the forti-in the operatforti-ing procedure were

+

t

Makeup

200 g Na2C03/L Na2COJ

20 g NaHC0:3/L

-~·-~·-~----I

1. Electrolyzing

ACC0-29

14

-The operation was days during which time ninety

leaches were made of ore for each. This represents

about 25 solution days of operation the sheet iron

anode failed. This had beeri fabricated of 22 gauge stock and might have lasted longer had it been heavier. At this point 187 grams of UJOg had

been produced. The anode was about 25 grams, consequently

the indicated consumption was 0.1 to 0.2 pounds of sheet iron per pound" of UJ08 produced - of this at least one-half could be salvaged as scrap because the anode weight includes header bar, contact and other portions

of the electrode not in use the electrolyte. No noticeable corrosion

took place at the cathode.

The larger scale operation ~~·~u=

trode replacement, but at item.

will give more reliable data on elec-' it seems to be an insignificant cost

A condensed tabulation of the operating data is given in Table I on the

following page.

2. Leaching

Operating data for the leaching section is given in Table I I on page 16.

During the ~irst ten day period the residue assay, 0.057 per cent UJOg,

is high due to three days when the residue assay averaged over 0.1 per

cent due to the NaHCOJ* concentration of the leaching medium. After

the solutions had recycled from the electrolytic cell adequate

bicar-bonate concentration was established. This is inherent to the process because bicarbonate equiliviant to the caustic leaving the circuit with the uranium precipitate must appear in the anode compartment overflow. For the next forty days the residue assays were consistent and fairly low for this ore (O.OJ per cent UJOe). Then, for the next ten days the

aver-age doubled (0.06 cent UJOg). The reason for this is not known. The

increase followed replacement of the anode, but there is no obvious reason why this should have any effect. After this the average decreased until,

for the final ten day the average was down to 0.036 per cent UJ08

which is only slightly than initially.

For the most part, the

During the period when the

there were of the ten

While there are this was the

were harmful to the is

was maintained at about 100°C. averaged 0.06 per cent UJ08

temperature was 90°C or below. to definitely say that temperatures below 90°C

(Averaged For Ten Day Periods)

Cathode Com2artment Anode Com~artment

% KWH/Lb Feed Overflow Overflow

Hrs Amps Volts g Ppt. UJ08 g UJ08 U308 g U308/L g U308/L g NaOH/L g NaHC03/L g Na2COJ/L

-96.1 1.5 5.1 49.037 75.1 :36.836 9 5.0 1.8 8.7 14.8 155 97 1.5 5.1 45.775 73.4 :33.620 10 5.5 2.1 8.0 20.7 190 21-30 97.1 1.5 5.2 47.612 78.2 :37.215 9 5.9 1.9 8.1 22.4 179 31-40 97.4 1.5 5.1 5:3.977 7:3.:3 39.589 9 6.0 2.1 7.6 26.0 188 41-50 71.6 2.0 5.6 52.093 76.1 :39.619 9 6.2 2.4 6.:3 24.8 182 51-60 75.8 2.0 5.4 58.466 74.8 43.752 9 6.4 3.0 7.2 26.0 186 61-70 74.2 2.0 5.5 48.822 73.8 36.039 10 6.4 :3.2 8.2 17.4 183 71-8'0 72.0 2.0 5.4 49.132 74.0 36.341 10 6.2 3.1 7.9 14.2 :}.89 81-90 71._0 2.0

u

55.439

7.:h1

40.630

_...2....

1.t.1

7.7 _~ 184 or 752.4 1.7 5.3 471.082* 74.7*351.763* 9 p.O 2.5 7.7 20.7 182 Average

•>

₀

Includes material cleaned from anode feed bottle (10.729 grams 75.7% U308) 1-'0

\JIO

I I l\)

Leachi;gg Data Wash -5 94 5. .7 0.057 10 8 5.000 21. 9920 0.034

J.

8 5. 21.0

o.

0 6 103 5. 22.1 9909

o.

6 103 5.000 22.1 9909 0.034

3.

15 6 94 4.600 21.4 9915 0.059 5.836 190 15 6 94 4.000 20.6 9900 0.042 4.177 15 6 99 4.000 21.2 9916 0.047 4.642 15 __§_ 101 6:1000 21.1 2205 0.0:36 3.526 Total or 1745 99 41.600 21.2 89218 0.041 36.622 Average IIJ> 0 1-'0 0"0 I II\.) \.0

operating duce the

day shortened from ten from have a significant on the

to eight hours, it was necessary to re-to hours. This did not appear to results.

Initially, ore minutes (62 per cen~minus 200 mesh). This was increased to ten (72 percent, minus 200 mesh), then to

15 minutes. If the other possible variables are overlooked the grinding time had the

Time, Minutes

5

10

Residue Assay,

%

U308 0.036

0.034 0.031

After 56 days the volume of water used to wash the leach residue was re-duced from 0.500 to 0.400 liter. This was done to reduce the volume of cell feed inventory, which was increasing, and did not appear to re-sult in any increase assay. The salt strength of the solu-tions did not change extent. At the end of the second ten

I

day period the cell 21.1° Be. There were day to day fluc-tuations, but the final ten day period was also 21.1° B~. The precipitate assay was reasonably constant. The average assay for the first 40 days of was 75.0 per cent U30g and for the next 30 days 74.7 per cent U30g. is further evidence that impurities were not building up the circuit due to recycling of solutions. Table' III, below, shows the impurities in the uranium precipitate.

Table III

Impurities in Uranium Precipitate

V205 Si02 A120J P205 Fe Per Cent 4.62 3.91 3.43 0.20 0.11

The distribution and metal balance for a ninety day run is shown in Table IV on the

Table IV

Distribution and Metal Balance for Ninety Day Run Assay

Grams

%

UJ()S Grams

-Ore 90000 0.457* 411.10

471.08 74.7 351.76

Residue 89218 0.04 36.62

Samples (1. 0 liters) (4.5 g/L) 4.50

Inventory Adjustment (In process at start 14.48 g) 18.22

(In process at end 32.70 g)

Total Products 411.10 *Calculated

%

Dist. 1100.0 85.6 8.9 1.1 4.4 100.0 ill> 0 1-'0

<»?

I N

"'

VII 9 FUTURE WORK

ACC0-29 19

-The development of this process has reached the point where a larger operation is necessary in order to detect operation difficulties which might not be evident in the small scale bench tests.

A cell has been designed and constructed for continuous use in pre-cipitating uranium and regenerating the leaching solutions. Feed to the cathode chamber regulated according to the current flowing to give the desired NaOH concentration for precipitation. The catholyte overflows a weir into the anode chamber where the NaOH combines with the NaHCOJ made at the ano~e _{to regenerate the Na2co3 solution for}

leaching more ore. This solution overflows the anode compartment and is fortified;prior to leaching3to the desired strength with fresh Na2C03 to make up for that consumed by the ore etc. The electrodes are a single pair of hot rolled iron sheets, two feet by three feet by one-quarter inch, with an integral supporting header bar at th~ top. These are what would be full plant size, additional capacity being ob-tained by using multiple electrodes and cells.

This cell is to be tested in a pilot plant operation at Winchester using 1000 pounds of Grants limestone ore per day as feed.

ACC0-29 20

-Galen W. evenger

Atomic Energy Division

American Cyanamid Comp~y

Raw Materials Development Laboratory Holton Street

APPENDIX A

ACC0-29 Ai

-The following data are because they are thought to be of some

value although they do not apply specifically to the

appli-cation of the process to the Grants ore. Rather they are the result of some of the fundamental work conducted during the development of the pro-cess to its present form. All of the steps in the propro-cess are well es-tablished procedures, such as leaching, filtering, etc., except for the precipitation and solution regeneration section. Here electric power is

used to temporarily the leach solution into two components, one

enriched in alkali and one in acid. The alkali causes precipitation of uranium after which the two components are combined to regenerate the

original leaching Except for soda ash consumed in leaching the

ore, the major item of cost is for electric power. Consequently, the

early exploratory was by a desire to keep power consumption

at a minimum.

Figure A-1, on the following shows how the precipitation of uranium

proceeds when a tY,Pical leach liquor is made more alkaline by increasing

the time of shown here that precipitation did not

start until the NaOH concentration reached about six grams per liter. For this reason a concentration of between six and seven grams NaOH per liter was taken as the minimum at which it would be possible to operate. The actual operation showed the actual concentration for any given opera-tion would depend on a number of factors the most important being the amoun-t; of depletion of uranium desired in passing through th,e cell. The

power-consumed per volume of solution would increase with this

con-centration and unless sufficient additional precipitate were obtained the unit cost of precipitate would be higher.

Another factor affecting cost is the operating voltage of the cell. The

two tests shown in A-1 in which about the same depletion of

uranium occurred show a voltage 20 per cent lower using a current

den-sity of 25 amperes square foot than that obtained at 50 amperes per

square foot. Since the the product of the current and voltage

this means that the power is 20 per cent lower. It would, however,

re-quire the installation as much equipment and the extra capital

investment might not be justified.

Appreciable power can be realized by keeping electrode s~~~ing

as close as

voltages at various electrode

that a three inch

permit. Figure A-2 on page :·Aiii'::"shgws spacings. Here it may be seen, for example,

a inch spacing over JO per cent

Electrodes, however, should not be s~ac~~

4

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Figure A-2, Voltage at Various Electrode Spacings

50 Amps per Square Foot (No Diaphragm)

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