Effect of sulfur concentration on microbial removal of arsenic and heavy metals from mine tailings using mixed culture of Acidithiobacillus spp.

The effects of elemental sulfur, an energy source for bacterial growth, on the removal of As and heavy metals from mine tailings collected from a flotation plant in the Philippines were investigated using a mixed culture of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. The fractionation of As and heavy metals in the mine tailings before and after bioleaching was also studied. Leaching tests were conducted in duplicate for 500 h, at 30 °C, and 200 rpm, with six sulfur concentrations (0%, 0.1%, 0.2%, 0.5%, 1%, and 2%, w/v). The laboratory results showed that 92.0% Mn, 45.0% Cu, 67.2% Zn, 42.4% As, and 47.7% Fe could be removed from mine tailings after 500 h at 0.5% elemental sulfur concentration. The results also indicated that 0.5% elemental sulfur concentration was the best for bacterial activities and metal removal from mine tailings under the chosen laboratory conditions. In sequential extraction results, it was observed that the bioleaching process also affected the changes of metal distribution in the final residue. Most of As and heavy metals was found to occur as stable forms in the residues after bioleaching.