Abstract
The effect of metabolites from the indigenous Acidithiobacillus thiooxidans and temperature on the bioleaching of cadmium from soil was investigated in the present study. Bioleaching was found to be more effective than chemical leaching of cadmium. The metabolite, mainly sulfuric acid, which was shown to be growthโassociated in the exponential phase, plays a major role in bioleaching. The maximum amount of cadmium leached was obtained after 8 days of precultivation when cells were directly involved in the leaching process. It indicates that cells in the exponential growth phase exhibit higher activity toward bioleaching. In contrast, the maximum amount of cadmium leached and the maximum initial rate for bioleaching were reached after 16 days of precultivation when only metabolites were involved in the bioleaching process. It implies that higher sulfuric acid concentration results in higher leaching efficiency. In addition, higher temperature leads to higher leaching efficiency. The optimal operation condition for bioleaching was determined to be a twoโstage process: The first stage involves the precultivation of the indigenous A. thiooxidans at 30ยฐC for 8 days followed by 20 minutes of centrifugation to discard cells. The second stage involves the bioleaching with the subsequent supernatant at 50ยฐC. ยฉ 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 83: 638โ645, 2003.