Laboratory investigations on the leaching of precious and rare metals

Laboratory tests were carried out to assess whether depleted uranium-bearing ores from the Sugrali deposit can be used for secondary in-situ leaching of precious and rare metals. The study combined chemical and mineralogical analyses with particle-size, radiometric, and filtration measurements. XRD, XRF, ICP-MS, AAS, and column tests were used to characterize the ore and its response to leaching. On the basis of hydraulic conductivity and carbonate content, about 70% of the ore reserves were assigned to the group suitable for in-situ leaching. Sodium hypochlorite was used as the principal lixiviant in the column experiments. An L: S ratio of 3.5 gave a useful balance between extraction and reagent consumption, whereas extending leaching to an L:S ratio of 9.1 consumed more solution without a proportional gain. Additional active oxygen, supplied at about 0.1% of the ore mass, improved oxidation; recovery in strongly oxidized parts of the column reached 95%. The average recovery obtained under the selected chemical and filtration conditions was about 78%. These results support sodium hypochlorite as the reagent to be examined in subsequent pilot-scale work.

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