The presence of significant amounts of heavy metals in industrial sludge poses a severe threat to the environment and human health. In this study, bioleaching of heavy metals from electroplating industrial sludge was investigated using indigenous Acidithiobacillus ferrooxidans as the bacterial agent. The effect of sludge loading on the efficiency of heavy metal removal by bioleaching was studied. The efficiency of bioleaching was assessed based on media acidification, oxidation-reduction potential, and concentration of heavy metals in the aqueous solution. Experimental results showed that the sludge loading had great impact on the bioleaching process. At sludge loading of 1% (w/v), maximum removal of 96.31% and 84.4% was achieved for the heavy metals Zn and Ni, respectively. Bioleaching data were subjected to first-order-based kinetic studies for rate constant and further shrinking core model analysis was applied. It was found that the rate constants for Zn and Ni bioleaching were maximum at the treatment with lower sludge loading. The kinetic analysis using the shrinking core model revealed that chemical reaction step controls the overall rate of the bioleaching process. Such a kinetic study will be helpful in designing the sludge detoxification process by bioleaching.
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