Biodissolution of metal values from complex sulfides using sulfur-oxidizing bacteria

Abstract

Bioleaching of a complex sulfide sample was carried out using an acidophilic microorganism namely sulfur-oxidizing bacteria (SOB). Various leaching parameters like initial pH, elemental sulfur, and pulp density were varied in order to evaluate their significance on the bioleaching process. The evaluation was based on the dissolution of elements like copper, zinc, iron, and sulfur present in the complex sulfide sample. All three leaching parameters significantly affected the biodissolution rate of the above elements. The SOB could able to leach 22.2, 33.9, 27.1 and 50.2 %(w/w) of copper, zinc, iron, and sulfur, respectively, at the optimum condition of elemental sulfur, 8 g/L; initial pH, 2.0; and pulp density, 10 %(w/v). The equilibrium contact time of the bioleaching was found to be 25 days. The biodissolution rate of zinc and sulfur was found to be more than that of copper and iron. The leaching rate increased with the increase of elemental sulfur addition and it decreased with the increase of pulp density. However, it increased with the increase of pH from 1.5 to 2.0 and decreased upon further increase of pH due to the maximum bacterial activity at pH 2.0.