Galena bio-oxidation by moderate sulphur bacteria

Bioremediation is a simple and effective technology for metal extraction from low-grade contaminated soils and mineral concentrates. Metal remove from sulfide minerals is based on the activity of mesophilic and chemolithotrophic bacteria, mainly Acidithiobacillus ferrooxidans which convert insoluble metal sulfides into soluble metal sulfates. In this study bioremediation experiments carried out in 1 L Erlenmeyer flasks containing 300 ml basal medium of A. ferrooxidans and 5% (w/v) PbS with 45 and 75 meshes and also this condition repeated for Acidithiobacillus thiooxidans. The results showed that A. ferrooxidans had grown on the galena and obtained energy from it. Also, the galena was oxidized to form lead sulfate. The most important species for oxidizing galena concentrate showed A. ferrooxidans, because these species were more effective than A. thiooxidans in our bioremediation experiments. Anglesite (PbSO4) was the important product of the galena bacterial oxidation. In these experiments the highest quantity of dissolute lead was 34% approximately in A. ferrooxidans cultures. The low solubility of lead sulphate indicated that this process is not commercially feasible for the recovery of lead on mines. In view of these results, bioremediation appears to have some potential for remediation of Pb contaminated soils.