Bioleaching of heavy metals from contaminated soil using Acidithiobacillus thiooxidans:: effect of sulfur/soil ratio

Bioleaching of heavy metals from contaminated soil was carried out using indigenous sulfur oxidizing bacterium Acidithiobacillus thiooxidans. Experiments were carried out by varying sulfur/soil ratio from 0.03 to 0.33 to evaluate the optimum ratio for efficient bioleaching of heavy metals from soil. The influence of sulfur/soil ratio on the bioleaching efficiency was assessed based on decrease in pH, increase in oxidation-reduction potential, sulfate production and solubilization of heavy metals from the soil. Decrease in pH, increase in oxidation-reduction potential and sulfate production was found to be better with the increase in sulfur/soil ratio. While the final pH of the system with different sulfur/soil ratio was in the range of 4.1-0.7, oxidation reduction potential varied from 230 to 629 mV; sulfate production was in the range of 2,786-8,872 mg/l. Solubilization of chromium, zinc, copper, lead and cadmium from the contaminated soil was in the range of 11-99%. Findings of the study will help to optimize the ratio of sulfur/soil to achieve effective bioleaching of heavy metals from contaminated soils.