Processes of producing uranium enriched with u235

摘要

Uranium values are recovered from deposits formed on parts of a calutron (see below) by washing with an aqueous solvent, converting the dissolved uranium to insoluble ammonium uranate, which is separated and dissolved in acid at a pH of 1.5; ammonium hyposulphite is added to reduce the impurities and the reduced solution is treated with formaldehyde to complex the sulphite formed; finally, ammonia is added to precipitate uranous hydroxide which is separated. The calutron is a device for separating isotopes described in Specification 816,772, wherein the ions of a vaporized compound are accelerated through an electromagnetic field which deflects the ions along curved paths, the radii of which are proportional to the square root of the masses of the ions. In such a calutron, uranium tetrachloride feed is split into three portions, one deposited in the first pocket of the collector of the calutron being enriched in U235; the second in the second pocket being impoverished in U235; and a third portion which deposits around the source region of the calutron. The calutrons are preferably employed in series, the enriched product from the first being converted to a suitable compound and fed to the second thereby obtaining double enrichment. The recovery of the uranium from the source of either calutron is effected by hot water scrubbing and washing as illustrated in Fig. 2, whereby the uranium tetrachloride together with copper, iron, chromium and nickel impurities as well as entrained solid carbon are taken up, after which the wash water is sieved to remove solid impurities and oxidized with hydrogen peroxide to convert the uranium values to uranyl ion and the metal impurities to their higher valent state. After filtering the solution is evaporated, if necessary, and the evaporated water is condensed and re-used as wash water. The solution is then treated with ammonium hydroxide or ammonia gas to precipitate ammonium diuranate together with the hydroxides of iron and chromium, leaving the copper and nickel in solution as complex amines. This precipitate is treated as described below. In a similar manner the uranium metal deposited on the collectors of the calutrons is taken up in nitric, hydrochloric or sulphuric acid solution which contains sufficient hydrogen peroxide to convert the uranium values to the uranyl state and to convert the metal impurities to their high valent state. The solutions obtained may be evaporated and the evaporated water condensed and re-cycled as before. The solution is then precipitated with ammonium hydroxide whereby a precipitate of ammonium diuranate containing the hydroxides of iron and chromium is obtained. A first composite precipitate is then obtained by mixing the precipitate recovered from the treatment of the source areas of the first stage calutron with that recovered from the second pocket of the collector of the second stage calutron, both these precipitates having a normal content of U235. A second composite precipitate is derived from the treatment of the source region parts of the second stage calutron mixed with that from the first pocket of the collector of the first calutron, these precipitates being singly enriched in U235; the precipitate obtained from the first pocket of the collector on the second stage calutron is doubly enriched with U235. Each of these precipitates is treated separately as illustrated in Fig. 4 by dissolving in a solvent such as hydrochloric acid and thereafter adjusting the pH to about 1.2. The solution is treated with ammonium hyposulphite as a reducing agent, preferably freshly prepared by the action of powdered zinc on an aqueous solution of ammonia and sulphur dioxide. The pH is not allowed to rise above 5 and the ammonium hyposulphite addition is gradual whereby the uranyl ion is reduced to the uranous ion, the ferric ion to the ferrous ion and the chromic iron remains unchanged. The reduction is complete when the pH of the solution is 3. The reduced solution is then treated with formaldehyde to form an aldehyde bisulphite addition compound. After the sulphite ion has been complexed ammonium hydroxide is added to bring the pH down to 4 to 4.8 whereupon the uranium is precipitated away from the iron and chromium ions as uranous hydroxide. Uranous hydroxide precipitate is then washed with an aqueous solution of ammonium hydroxide and calcined in a non-oxidizing atmosphere to produce UO2. The first and second composite precipitates above referred to yield UO2 normal and singly enriched in U235 respectively; both of these batches of UO2 are converted back to UCl4 for re-treatment in the first stage and second stage calutrons respectively, whilst the third batch of UO2, doubly enriched in U235 is the end product of the process. The conversion of the first and second batches of UO2 to UCl4 may be effected with carbon tetrachloride in the vapour phase at about 450 DEG C. and the crude uranium tetrachloride thus produced is then sublimed at about 600 DEG C. to produce a pure UCl4. The process may be modified to treat uranium compound other than UCl4 in either the first or second stage calutron, for example UCl6 or UBr4.