Acid Leaching of Cu and Zn from a Smelter Slag with a Bacterial Consortium

Abstract

This study was undertaken to determine the leaching of Cu and Zn from a smelter slag in acidic, sulfate-rich solutions with, and without, mesophilic Fe-and S-oxidizing bacteria. Cu in the slag was mostly distributed in fayalite, Fe-deficient Cu-sulfides and metallic Cu, and Zn was associated with fayalite, magnetite and glassy silicates. The test culture was enriched from acid mine water using mineral salt growth media supplemented with 4.5 g Fe2+ L-1 and 10 g S0 L-1. The bioleaching experiments were carried out in shake flasks at 27 °C and chemical controls were included. The slag sample was pre-leached for 24 h to partially satisfy the acid demand before the leaching experiments at 10% pulp density. In the bioleaching experiments, 69-83% Cu and 4.1-14% Zn were dissolved in 25 days at pH 2.0-2.2. The highest extent of bioleaching was with S0 as the substrate. The efficiency of the bioleaching depended on H2SO4 generation from the added S0. The activities of the bacteria were not adversely affected by the dissolved metals. The maximum yields of chemical leaching were 68% Cu and 3.7% Zn.