The processing treatments for the production of uranium concentrates and the recovery of pure uranium compounds, as well as the conversion chemistry for producing uranium metal and the processes employed for preparing uranium alloys.
The procedures to recover uranium from its ores are numerous, because of the great variety in the nature of uranium minerals and associated materials and the wide range of concentration in the naturally occurring ores. Recovery of uranium requires chemical processing; however, preliminary treatment of the ore may involve a roasting operation, a physical or chemical concentration step, or a combination of these. In general, one of two leaching treatments—acid leaching and carbonate leaching—is used as the initial step in chemical concentration. The choice depends on the nature of the ore, which largely determines the efficiency and the cost of the process employed. See also Leaching.
The concentrate, whether obtained by chemical or physical means, is treated chemically to give a uranyl nitrate solution that can be further purified by solvent extraction. The impurities remain in the aqueous phase, while the uranium is extracted into the organic phase. See also Solvent extraction.
Uranium metal can be obtained from its halides by fused-salt electrolysis or by reduction with more reactive metals. The reaction of UO2 with calcium yields metal of fair quality. The largest tonnages of good-quality uranium have been produced by metallothermic reduction of finely divided UF4 with calcium or magnesium in steel bombs lined with fused dolomitic oxide (Ames process). The charge, consisting of an intimate mixture of UF4 with the reductant metal in granular form together with a suitable booster (usually calcium plus iodine), is placed into the reduction bomb, the lid is bolted down, and the bomb is heated to ignition temperature. The shape of the metal ingot (also referred to as a biscuit) depends on the shape of the reduction bomb.
Uranium alloys are prepared by fusing the components together. All procedures following conventional metallurgical techniques, however, may have to be carried out inside inert-gas glove boxes because many alloys are attacked by oxygen or moisture. See also Nuclear fuels; Nuclear fuels reprocessing; Uranium.
