Bioleaching of uranium from low grade black schists by Acidithiobacillus ferrooxidans

The feasibility of bacterial recovery of uranium from the low grade black schists occurring in the Okcheon district, South Korea, was investigated. Following the introduction of Acidithiobacillus ferrooxidans, 80% of the uranium could be extracted from the schists, which contain 0.01% U₃O ₈ by weight, within 60 h at a pulp density of 100 g-ore/l. Only 18% of the uranium was extracted without microbial activity. The uranium-leaching efficiency was not greatly affected by the addition of Fe²⁺ in the range of 5-9 g/l, and the leaching efficiency of uranium from the schists by A. ferrooxidanscould be efficiently maintained at high pulp densities (up to 500 g-ore/l).