POLYMERIC LIGANDS Separation of Uranium f r o m Solutions and Ore Leaches with Salicylic Acid-Formaldehyde Polymers R . C. DEGEISO, L. G . D O N A R U M A , AND E. A. T O M I C Explosives Department, Experimental Station Laboratory, E. I. du Pont de Nemours & Co., Inc., Wilmington,Del.
Uranium is extracted as uranyl ion from solutions, using salicylic acid-formaldehyde polymers.
Use of the
technique described gave uranium of good purity in high yields.
HE preparation and characterization of a salicylic acidTformaldehyde polymer (SFP) and several polymeric chelates derived therefrom have been described (2). Subsequently, the ion exchange selectivity of the polymer for uranyl ions over all other metal ions above p H 3 was reported ( 7 ) . This publication describes the use of salicylic acidformaldehyde polymer (SFP) and resorcylic acid-formaldehyde polymer (RFP) as selective ion exchange reagents for the extraction of uranyl ion from uranium ore leach liquors.
Experimental
Polymers Used. T h e preparation of SFP has been reported (2). R F P was prepared by heating a mixture of resorcylic acid (2,4-dihydroxybenzoic acid) (15.4 grams), formaldehyde (10 grams. 36 to 37y0 aqueous), resorcinol (0.1 gram), oxalic acid (0.1 gram), and water (IO ml.) to reflux with good stirring. At the reflux temperature, 10 ml. of a 50 : 50 mixture of concentrated hydrochloric acid and water was added to the strongly foaming mixture. The reaction mixture immediately deposited solid polymer. Fifty milliliters of water was added and the mixture was refluxed one hour. At the end of this time, the polymer was heated overnight at 120' and 50-mm. pressure. The product was ground and extracted overnight with ethanol in a Soxhlet apparatus. The ethanol in the extractor was replaced with water and a water extraction was carried out for 24 hours. The polymer was dried, reground, and used without further modification. Equilibration of the product with a 10% aqueous solution of uranyl nitrate buffered to p H 4 with acetate ion showed that the polymer had a working capacity of 3.4 mmoles of uranium per gram. In addition, the screening procedure previously described ( 7 ) indicated a complete preference of uranyl ion over all others tried. Ores and Ore Leaches and Extraction Techniques. T h e uranium ores employed were either high-lime or highsilica ores from the Colorado plateau and were leached by conventional carbonate and sulfuric acid techniques. The following table shows some of the metals present (in addition
to alkali and alkaline earth metals) in both acid and carbonate leach liquors: Metal
u Fe Mg A1
Mn Ni Ti Zr Pb V Mo
\v
Si
Leach Employed, yo H2SO 4 NazCO3 0.01 0.8 2.0 0.05 1. o 0.02 0.5 ... 0.1 0.003 0.02 0.0005 0.2 0.5
:
0 005 0.02 0.005 ... 0.5
...
2.0
...
At the end of a leach, the p H of a sulfuric acid leach liquor was in the range 1.5 to 2 and the p H of a sodium carbonate leach liquor was in the range of 10 to 11. The sulfuric acid leach liquor was adjusted to p H 4 and the carbonate leach liquors were brought to either p H 3 or 4, boiled, and clarified before proceeding further. The resin was then introduced into the filtrate and the mixture stirred from 1 to 16 hours. During the resin equilibration, the p H was held constant by the addition of sodium hydroxide or ammonium hydroxide. The resin was removed by filtration (filtrate 1) and washed with a slight amount of water. The resin was placed in a beaker and eluted with concentrated hydrochloric acid or at p H 2 with dilute nitric acid. T h e resin was then removed again by filtration (filtrate 2) and both filtrates were analyzed for uranium by standard x-ray fluorescence techniques. T o get the samples into a constant matrix the metals in the filtrates were precipitated with ammonia and redissolved in 1.5M nitric acid. To determine uranium purity, aliquot portions of the filtrates were taken and the metals were precipitated with ammonia and ignited to the oxides. The uranium determined by x-ray analysis of the filtrates was taken as total uranium present; that determined by ignition of the precipitates from the aliquot portions included impurities. The difference VOL. 2
NO.
1
JANUARY 1 9 6 3
43
Table 1.
Type of Leach
Na2C03 HzS04
Recovery of Uranium from Ore leaches Using SFP yo Purity of ReProcess Grams covered Time, SFP p H of U from % Min. Used Chelation Filtrate 2 Recovery
960 960
25 10
3 3
90.0 92.5
96.4 97.1
90
10 20 10
4 4 2-4.
89.5
82.1 95.0
93.8 97.1 98.8
90
60
a Iron remooedfrom leachjirst by chelation at PH 1.5 to 2. Resin then eluted and uranium extracted with eluted resin at p H 4.
between these two numbers was the measure of the amount of impurity present. Checks on this gravimetric method of determining impurity with semiquantitative emission spectra data on impurities present in recovered uranium oxides gave good agreement. Table I shows the results obtained from uranium recoveries carried out in this manner using carbonate leach liquors. An alternative method for uranium recovery was devised for the sulfuric acid leach liquors which involved the initial removal of iron(II1) from the liquor by absorption into SFP. The liquor (pH 1.5 to 2.0) was clarified and contacted with fresh portions of resin until the resin no longer turned blue. The iron(II1)-free filtrate from this extraction was adjusted to p H 4 with standard sodium hydroxide and treated further with resin to recover the uranium in the manner described above. Prior removal of iron(II1) increased both the yield and purity of the product (see Table I) and reduced the consumption of base from 82 meq. to 13 to 15 per 100 ml. of leach liquor. Extraction of Uranyl Ion with MIBK Solutions of SFP. MIBK solutions of the polymer were prepared by dissolving SFP (15 grams) in the smallest possible quantity (100 ml.) of a 50:50 mixture of acetone and ethanol, followed by the addition of 200 ml. of MIBK. This solution was boiled in an open beaker until the volume was less than 200 ml., cooled to 25O, and diluted to 200 ml. with MIBK. Five-tenths gram of uranyl acetate dihydrate was dissolved in 100 ml. of water to yield a solution which contained 278 mg. of uranium. This solution was shaken with 100 ml. of the methyl isobutyl ketone solution of the resin. The yellow color disappeared from the aqueous layer and the methyl isobutyl ketone layer became red-brown. Analysis of the red-brown isobutyl ketone layer showed that all the uranium had been
44
!&EC
PROCESS DESIGN A N D DEVELOPMENT
Toble II.
Type of Leach H2S01
?;a?CO,
Recovery of Uranium from Carbonate and Sulfuric Acid leach liquors with RFP Process G. yo Purity p H of 70 U of ReTime, Polymer .Win. Used Elution Recowry covered U 20 5 0 91 91 2 90 97 20 5 960 10 0 96 62 960 10 0 92 65 20 5 0 85 80
extracted from the kvater. S o uranium was extracted when plain methyl isobutyl ketone was employed under identical conditions. Results and Discussion
Table I displays the results obtained by using SFP on carbonate and sulfuric acid ore leaches. Table I1 shows some of the results obtained when R F P was used to recover uranium in place of SFP. Table I shows that uranium recovery and product quality were good. Commercial ion exchange processes for the recoiery of uranium ordinarily yield a product of 70 to 80% purity at similar recovery values ( 4 ) . By elution of the uranium-loaded SFP p H 2 with dilute nitric acid rather than at p H 0 to 1 with strong hydrochloric acid, a somewhat purer product could be obtained, but the recovery \vas only about joyofor the same elution time. Removal of the iron from the leach liquor first gave a much purer product and a better recovery. The results obtained with R F P \vere similar, except that recoveries were lower at low contact time and increased contact time gave poor quality product. Hokvever, elution at p H 2 gave good recovery and good purity. This latter observation is probably due to the fact that the SFP is a stronger acid than R F P (3) and therefore uran!-l ion bound to SFP should be more stable at pH 2. literature Cited
(1) DeGeiso. R. C., Donaruma, L. G., Tomic. E. X.. .4nnl. Chem. 34, 845 (1962). (2) DeGeiso, R. C., Donaruma, L. G.. Tonic, E. .4.,J . Org. Chem. 27, 1424 (1962). ( 3 ) International Critical Tables, pp. 2’9-80. McGraw-Hill, New York, 1929. (4) Nachod, F. C., Schubert, J.; “Ion Exchange Technology,” p. 304, Academic Press, New York? 1956. RECEIVED for review January 8, 1962 A C C E P T E D July 2. 1962
