Metals removal and sulfur production from uranium bearing effluents

The removal of dissolved uranium from aqueous phases is hampered by the formation of uranyl complexes such as uranyl-bicarbonate or nitrate. The chemical reduction of uranyl to insoluble uranite by a reductant such as sulfide does not take place at appreciable rates. However, bacteria can achieve this enzymatically. Lab tests showing that standard biomass from a full-scale sulfate reducing plant will remove uranium from a carbonate buffered solution to below 0.25 mg/l are presented. This paper also outlines a combination of uranium and heavy metals removal whilst sulfate is biologically reduced to elemental sulfur. The sulfur can be used to produce sulfuric acid while the production of gypsum is avoided and the effluent water complies with strict norms. A full-scale plant currently treating 400 m3/h of ground water in this manner is described. This biotechnology enables sulfur recycling and produces a compact uranite/metal sulfide residue instead of voluminous polluted gypsum. (author)