Effects of pH, pulp density and particle size on solubilization of metals from a Pb/Zn smelting slag using indigenous moderate thermophilic bacteria

A series of bioleaching experiments were designed to elucidate the effect of pH, pulp density and particle size on solubilization of heavy metals, such as As, Fe, Cu, Zn, Pb and Mn, from a Pb/Zn smelting slag using indigenous moderate thermophilic bacteria, and the surface morphological characteristics of the residues were observed by SEM. The results showed that the solubilization of heavy metals from the slag was significantly influenced by pH and pulp density in bioleaching, however, it was slightly influenced by particle size of the slag when the particle size is less than 0.83 mm. Under the optimum condition (pH 1.5, pulp density 10%, and particle size of the slag less than 0.83 mm, respectively), about 86%–91% of As, 90%–93% of Cu, 90%–94% of Mn and 81%–87% of Zn from the slag have been bioleached after 6 days. The surface morphological characteristics of the residues after 6 days bioleaching analyzed by SEM showed that metal solubilization can be improved by acid leaching but significantly contributed to the activities of the ingenious bacteria. Consequently, metals in the slag can be extracted by bacteria according to the corrosive holes on the surface of the bioleached residues.