Microbiological leaching of uranium ores

Microbiological leaching has been used as an alternative approach to conven tional hydrometallurgical methods of uranium extraction. In the microbiolog ical leaching process, iron-oxidizing bacteria oxidize pyritic phases to fe rric iron and sulfuric acid, and uranium is solubilized from the ore due to sulfuric acid attack. If uranium in the ore material is in the reduced, te travalent form (U-IV), a redox reaction is involved where by uranium is oxi dized to the hexavalent form (U-VI) upon dissolution, lit acid-leaching sys tems, the primary oxidant is ferric iron, which is reduced to ferrous iron by its chemical reaction with UN. The ferrous iron thus formed is reoxidize d to ferric iron by iron-oxidizing bacteria such as Thiobacillus ferrooxida ns and Leptospirillum ferrooxidans. Nutritional requirements and responses to environmental extremes of acidophilic iron-oxidizing bacteria are apprai sed The S-entity in Fe-sulfides is oxidized to sulfate by bacteria similar to Thiobacillus ferrooxidans and Thiobacillus thiooxidans. Pyrite and marca site oxidation is a sulfuric acid forming reaction. Heap, dump and in situ leach techniques are feasible as bacterial leaching systems.