RESUMO
The bioleaching process, including acidification and solubilization of heavy metals, is a promising method for removing heavy metals from industrial waste sludge. Solubilization of heavy metals in industrial waste sludge is governed by adding elemental sulfur. A sulfur concentration exceeding 0.5% (w/v) inhibits sulfate production and the activity of acidophilic bacteria. Sulfate production was described well by a substrate inhibition expression in Haldane's kinetics. After 15 days of bioleaching, 79 to 81% copper, 50 to 69% lead, and 49 to 69% nickel were solubilized from sludge with a sulfur concentration of 0.5 to 1.0% (w/v). Experimental results indicated that the optimal sulfur concentration for the maximum solubilization rate of copper and nickel was 0.5% (w/v) and 1.0% (w/v) for lead. The profiles of denaturing gradient gel electrophoresis confirmed that indigenous acidophilic Acidithiobacilli (A. thiooxidans and A. ferrooxidans) existed and were the dominant species in the bioleaching process.