Abstract
Effect of silver ions on iron-oxidizing activity of Thiobacillus ferrooxidans was investigated in order to examine the application of T. ferrooxidans in the leaching of silver sulfide.The 6 strains of T. ferrooxidans used in this study were isolated from process waters of mine water treatment plants, a H2S gas treatment plant and a flue dust treatment plant utilizing T. ferrooxidans, and drainage waters of sulfide mineral mines in Japan.Silver ions inhibited iron-oxidizing activity of T. ferrooxidans. Oxidation rate decreased as silver concentration was increased. Critical silver concentrations at which each strain used could oxidize more than 90% of ferrous ions (initial concentration 4.0×10-2 mol/l) were from 0.10m/g to 0.28mg/l. Addition of copper ions revived iron-oxidizing activity of T. ferrooxidans that was inhibited by silver ions. A Copper tolerant strain cultured in the mediums with gradually increasing copper concentration up to 13g/l had higher silver tolerance. The strain oxidized more than 90% of ferrous ions at the silver concentration of 1.04mg/l. A nickel tolerant strain cultured in the mediums with gradually increasing nickel concentration up to 10 g/l had less silver tolerance.
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