Bioleaching of metals from tannery sludge in two stages: effect of pH

The present work assessed the effect of the pH in the bioleaching of Cr and other metals from tannery sludge with stage separation of biologic oxidation of elemental sulfur and leaching of solid waste. The concentration of elemental sulfur was 5 g L-1. The final bioleaching pH ranged from 3.0 to 1.0. The concentration of sludge solids was 100 g L-1 8 and the temperatures were 298.15 and 308.15 K. The leaching extractions of 100 g L-1 and increased at lower final pH and the leaching extraction of Ca decreased in this condition The maximum extraction of Cr was 70.11% at sludge solids concentration of 100 g L-1, final pH 1.0 and temperature of 298.15 K. The fraction of Cr bound to Fe and Mn oxides was more affected by changes at final pH than others fractions. The mass ratio of metals and Cr decreased at lower final pH. The concentration of Cr leached from the tannery sludge after the bioleaching at final pH of 1.0 was reduced to satisfactory values.