| 摘要 |
<p>Uranium ore concentrates which have been obtained by soda leaching of uranium ores are freed from vanadium and molybdenum impurities by treating the concentrate with aqueous nitric acid which selectively dissolves the uranium. On addition of nitric acid to such a concentrate, the pH initially falls to a minimum value after which it rises and finally falls again; the nitric acid addition should be such that the slurry has a pH between the above-mentioned initial minimum value and 0,5 thereabove. Uranium passes into solution whilst the impurities remain in the undissolved residue. The uranium-containing solution after separation from the residue may be treated with ammonium hydroxide to precipitate the uranium as ammonium uranate, this step preferably being effected at 25 DEG -70 DEG C. and at a final filtrate pH of 6-13. The initial concentrate may be obtained by leaching the uranium ore with sodium carbonate at 100 DEG C. under two atmospheres pressure of oxygen and precipitating the uranium as insoluble sodium uranate by adding sodium hydroxide to a pH of 11 or above; alternatively the carbonate solution may be neutralized with sulphuric acid, boiled to remove carbon dioxide and the uranium precipitated by neutralization with ammonia. The nitric acid attack on such concentrate is preferably effected at temperatures of 70-105 DEG C. with nitric acid of 5-36% strength. The purified uranium values finally obtained are particularly suitable for the production of uranium hexafluoride by gaseous reduction to the dioxide followed by hydrofluorination to the tetrafluoride and fluorination to the desired hexafluoride.</p> |
