Removal of uranium(VI) under aerobic and anaerobic conditions using an indigenous mine consortium

Biological uranium removal was investigated using bacteria sourced from an uranium mine in Limpopo, South Africa. Background uranium concentration in the soil from the mine was determined to be 168 mg/kg using the ICP-OES calibrated against the uranium atomic absorption standard solution. Thus the bacteria isolated from the site were expected to be resistant to uranium-6 [U(VI)] toxicity. Preliminary studies using mixed cultures suggest that uranium reduction occurs under anaerobic conditions in most cases. U(VI) reduction by obligate aerobes isolated from the soil consortium was poor. The pure cultures namely; Pseudomonas sp., Pantoea sp. and Enterobacter sp. showed a high reduction rate at pH 5–6. The initial U(VI) reduction rate determined at 50% of added U(VI) was highest in the Pseudomonas sp. at 30 mg/L. Enterobacter sp. outperformed the other two species at 200 mg/L and 400 mg/L with a rate of 63 and 198 mg/L/h, respectively. Rapid reduction was observed in all cultures during the first 4–6 h of incubation with equilibrium conditions obtained only after incubation for 24 h. The results demonstrate the potential of microbial U(VI) reduction as an alternative technology to currently used physical/chemical processes for treatment and recovery of uranium in the nuclear industry.