■/ '^^A^y'^kpp^'y?/ V ^ MDDC - 777 UNITED STATES ATOMIC ENERGY COMMISSION PURIFICATION OF URANIUM OXIDE by James I. Hoffman This document consists of 4 pages. Date of Manuscript: Unknown Date Declassified: March 18, 1947 This document is issued for official use. Its issuance does not constitute authority to declassify copies or versions of the same or similar content and title and by the same author (s). ■^i^s^sr Technical Information Division, Oak Ridge Directed Operations Oak Ridge, Tennessee PURIFICATION OF URANIUM OXIDE By James I. Hoffman INTRODUCTION In the early summer of 1941, Leo Szilard, (member of Power Production Subsection of the Uranium Committee), gave a sample of impure uranyl nitrate to the author and requested the the uranium be separaUd from everything else.' It was his desire to obtain the residue, after the re- moval of uranium, for measurements of neutron absorption. During the same period, samples of impure uranium oxide were sent to the Bureau of Standards for chemical analysis. For both purposes it was desirable to use some solvent that would dissolve the bulk of the uranium without dissolving any of the other substances. The solubility of uranyl nitrate in ethyl ether, first reported by E. Peligot,^ suggested its use for extraction of uranium as the nitrate, somewhat as ether is used in steel analysis for tne extraction of ferric chloride. This extraction had been successfully applied in 19.39 for separating uranyl nitrate from rhenium and certain rare earths in work on the determi- natiou of rhenium and molybdenum,' but, because of the conflicting statements concerning the sol- ubility of the rare earth nitrates in ether ,^ it was obvious that experimental work was necessary, especially since Szilard stated that certain members of the rare earth group are strong neutron absorbers. The work herein described is not intended to give the procedure finally used in large-scale pro- duction of uranium nor the methods used in the various laboratories of the Manhattan Area. Many improvements in procedure have bei made since this preliminary work was done. A procedure is given for the purification of uranium oxide by converting the oxide to the nitrate ■ and partitioning the nitrate between a large amount of ether and a relatively small amount of water. In modified form, the procedure was found to be applicable to pitchblende and carnotite ore concen- trates. EXPERIMENTAL WORK The bulk of the uranium was extracted with ether from 1.00 g of uranyl nitrate, UC^(N03)j.6HjO, to which had been added 5 ml of water and "rare earth" nitrates (equivalent to 0.0084 g of oxides) containing cerium, praseodymium, neodymium, erbium, gadolinium, terbium, dysprosium, holmium, erbium, ytterbium, lutecium, scandium, yttrium, lanthanum, and thorium. After removal of most of the urani\im, the combined "rare earths"were determined in the residual water solution by precipi- tating them as fluorides, converting the fluorides to sulfates, then precipitating as oxalates, and igniting the oxalates to "rare earth" oxides. The oxides weighed 0.0086 g. In this particular case the uranium extracted by the ether was not examined for impurities, but it was evident that extraction of uranyl nitrate with ether should be a good starting point for the purification of uranium. To obtain a quick answer to the possibility of using ether for the purification of uranium, the elements listed in mixture A* in nitric acid solution were evaporated as far as possible on the steam * Mixture A consisted of 2.5 g of uranium metal dissolved in an excess of nitric acid. To this was added as nitrates 2.5 mg each of copper, antimony, lead, aluminum, lithium, zirconium, indium, gal- lium, bismuth, potassium, dysprosium, cadmium, gadolinium, chromium, magnesium, holmium, cobalt, tin, calcium, and 10 mg of a mixture of "rare earths" known to contain cerium, lanthanum, scandium, praseodymium, thorium, and yttrium. MDDC - 777 . [1 2 ] MDDC - 777 bath. The residue was extracted with 100 ml of ether, the ether was washed twice with 5 drops of water, and then the uranium in the ether was converted to oxide. ^qualitative spectrochemical analysis showed that this oxide contained only calcium, magnesium, and silicon, besides uranium. These encouraging results prompted further experiments which formec the basis for the procedure given herewith. procb:dure used for the purification of uranium oxide Fifty grams of Vfig was tr:;nsferred to a 600-ml bealcer, 75 ml of diluted nitric acid (1 volume of concentr.'.ted nitric acid sp gr 1.42 diluted with 1 volume of water) was added, and the beaker was j>iac3d on the steambath until all action ceased. The insoluble matter was removed by filtration, and the residue was washed 4 or 5 times with diluted nitric acid (1 volume of nitric acid, sp gr 1.42. diluted with 20 volumes of water). The filtrate and washings containing the uranyl nitrate were evap- orated to dryness on the steambath. To the cooled and dried residue in the beaker, 5 ml of water and 100 ml of ethyl ether were added, and the beaker was swirled until the uranjl nitrate was dissolved. T\:e large quantities of impurities caused the aqueous phase in the bottom of the beaker to have the appearance of an emulsion, but this did not interfere in the separation because it was possible to pour the ether into a separatory funnel without mi.xing with the water layer. The ether was transferred to a separatory funnel, the beaker was washed 3 limes with 5-ml portions of ether which were likewise transferred to the separatory funnel. The funnel was stoppered and shaken vigorously for 1/2 to 1 minute. After allowing the liquid to stand 3 minutes, a few drops of water appeared in the bottom of the separatory funnel. This water was drained into the beaker which originally contained the ether solution. Five ml of water was now added to the solution in the separatory funnel, the mixture was shaken vigorously, and the solution was again allowed to stand until two layers formed. The aqueous phase was drained into the beaker which originally contained the ether solution. The washing with another 5-ml portion of water was repeated once more. To convert the purified uranyl nitrate to oxide, a little water was added to the ether, the ether was cautiously evaporated, and the residue wa.= ignited to U3O3 at 1000 °C. It was afterward found preferable to add 20 ml of water to the ether solution, shake vigorously for one minute, and allow the liquid to separate into 2 layers. The water layer was drained into a suitable dish, and the extraction with 20-ml portions of water was repeated until the ether above the water was colorless. Three or four such extractions were sufficient to remove the uranium. The combined water extracts were evaporated to dryness, and the uranyl nitrate in the residue was ignited to UjO, at 1000°C. The ether from which the uranyl nitrate had been removed was suitable for future extractions. The procedure was also applied to the extraction of uranium from pitchblende and carnotite ore concentrates by digesting the ore concentrate with nitric acid, evaporating to dryness, and extracting the residue with ether. The efficacy of this method of purification is shown in Table 1. The table shows that in many cases impurities that were not detected in the original oxide were concentrated and detected in the water extract. Note especially Ce, Co, Cr, Dy, Er, Eu, Gd, Ho, La, Lu, Nd, Pr, Sc, Sm, Tb, Tm, and Y. DISCUSSION It was evident that the purification of crude uranium oxide and the removal of uranium from ore concentrate:; by conversion of the uranium to uranyl nitrate and extraction with ether had possibil- ities because practically all impurities were removed in a single operation. Tests by L. F. Curtiss (Chief of Section on Radioactivity at the National Bureau of Standards) indicated that practically none of the radium in the original ore was extracted by the ether. Under stress of wartime conditions not all the possible confirmatory tests were made, but, as a check on removal of the rr.re earths, the purified oxides obtained from No. 155 and No. 181, Table 1, were put through a second purification by the same procedure. The water extracts in this case showed no rare earths. Tests by K. D. Fleischer indicated that if 0.5 mg of "rare earth" oxides had Table 1. Spectrochemical Analysis* of products obtained in the purification of uranium oxide or recovery of uranium from ore concentrates. ment ^ 0, No. 155 U,Ci No. 183 Carnotite ore * concentrate Pitcliblende concentrate oret Original Water Purified Original Water Purified Or'ginal ore UjO, Ob Original ore ",o. oxide extract oxide oxide extract oxide concentrate tained doncentrate obtained Ag T W T VW W T T T T T Al VW W VW VW W VW S S . As W M - W W - _ _ _ Au - T - VW VW T . _ B T VW - T w . T T _ Ba - - - - VS - M W . Be - - - - - VW _ Bi VW W _ VW w . _ W _ C Ca vs w - W M T VS T s _ Cb - _ - Cd - - - - - - - _ . Ce - w - - w Co - - - w M - w VW _ Cr - VW - VS - - T _ Cs - - - _ Cu VW M T w M T T T T T Dy s - - S - Er - M - - M - Eu - M - - M - Fe w M VW w M VW S M S _ Ga - - - Gd - M - - M - Ge - _ - _ _ _ _ _ _ Rf - - - _ _ _ Hg - - - - - - _ _ Ho - M - - M - - _ _ In - - - - VW _ . _ _ It - - - _ K T V - w M - La - T - T - ., _ Li - T . - VW - Lu - W.' - - VW - Mg w W T w W VW M T M T Mn VW W - w w - W W Mo w M W w M - - VW . Na w M T M S T Nd - W - W - Ni - VW - VW V. - - - - OS - - - - - - P Pb VW w - w M - VW M - Pd - - - - - Pr - w - . W - Pt - _ - _ w - - Ra Pb - - - - - - He - - - - _ . Rh Ru - - - - _ - Sb w M - w M - . - - Sc - w - - W - - Si M M WJ M W w S VW w VW Sm W . - W Sn - VW . - - - - VIS' - Sr - - - - VW - w VW - Ta - - - - - Tb _ M . - M - Te Th - - - - - - - Ti Tl Tm - - - - - S W . w _ »■ V VS VS VS \^ VS VS VS VS - - V VW W - VS VS VS VS W - - . w - Y - VS - VS w - Yb - M ' " M " M " The designations VS and S correspond to major constituents (greater than 1 per cent); M and W to minor constituents (1 to 0.01 per cent); and VW. T, and FT to trace constituents (less than 0.01 per cent). The absence of a designation indicates that a test was not madi for that element. • By B. F. Scribner and H. R. Mullin. t The water extracts contained rare earths, but no attempt was made to identfy them individually. 4 ] MDDC - 777 remained in the purified oxide, a positive test would have been obtained here. This showed that by this simple procedure the combined "rare earths" in the purified oxide were reduced to less than 5 parts per million. The spectrochemical tests showed that not more than 0.5 part of cadmium or boron per million remained in the purified material. SUMMARY A procedure is given for the purification of uranium oxide by converting the oxide to the nitrate and partitioning the nitrate between a large amount of ether and a relatively small amount of water. In modified form, the procedure was found to be applicable to pitchblende and carnotite ore concen- trater. REFERENCES 1. Smyth, Henry D., Atomic Energy, Princeton University Press, 1945. 2. Ann. Chim. Phys. (3) 5:5 (1842). 3. Hoffman, James I. and G. E. F. Lundell, J. Research NBS 23: 497 (1939). RP1248. 4. Wells, R. C, Wash. Acad. Sci. 20: 146 (1930); Soddy, F. and R. Pirret. Phil. Mag. (6) 20: 345 (1910); Hillebrand, W. F., U. S. Geol. Survey Bull. 78; 47 (1891); Davis, C. W., Am. J. Sci. (5) 11: 20(1926). UNIVERSITY OF FLORIDA 3 1262 08910 5521 a I,