Although atmospheric uranium leaching using sulfuric acid is the most common process for the recovery of uranium from its ores, alkaline leaching has also been used to extract uranium from high carbonate-bearing ore, particularly for calcrete deposits such as Langer Heinrich. For deposits which are high in acid consuming phases such as carbonates, alkaline leaching becomes, in most cases, the only viable option. The effect of varying leach parameters on uranium extraction and reagent consumption, and how these relate to the uranium and gangue mineralogy of an ore, has not been widely studied. ANSTO Minerals has performed an alkaline uranium atmospheric leaching fundamentals study, in order to better understand the effect of varying carbonate/bicarbonate concentration, oxidant type and dose, and temperature, on uranium extraction and reagent consumption for a uranium ore sample. As the rate of dissolution of uranium is reported to be controlled by the oxidation of U(IV) minerals, particular emphasis has been placed on understanding and enhancing the oxidation step with the aim of reducing retention time for atmospheric alkaline leaching.
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