Leaching of copper and zinc from copper converter slag flotation tailings using H2SO4 and biologically generated Fe2(SO4)3

Leaching of converter slag flotation tailings from the Svyatogor copper smeltery (Sverdlovsk region, Russia) by sulfuric acid solutions containing ferric ions was investigated. The solutions were obtained using oxidation of ferrous sulfate by a consortium of moderately thermophilic acidophilic chemolithotrophic microorganisms, including Sulfobacillus species. Flotation tailings contained 0.56% Cu and 4.74% Zn. Copper was present mostly as digenite, bornite, and free metal. Zinc was present as a ferrite (franklinite) ZnFe2O4 and, to a lesser degree, as silicate. The effects of pH, pulp density, temperature, initial Fe3 + concentration, and the presence of oxygen in the leaching solution on the leaching dynamics of copper, zinc, and iron were investigated. Increasing Fe3 + concentrations was found to have an inhibitory effect on zinc and iron leaching, but not on copper leaching. Temperature had the most pronounced effect on the kinetics of copper and zinc leaching. Kinetic analysis was carried out, and the calculated activation energies for copper and zinc leaching were 51.3 and 53.8 kJ/mol, indicating control of this process by a chemical reaction on the particle surface. The recommended technological parameters for leaching of copper (the most important component) from converter slag flotation tailings are: pulp density of 30% (w/v), pH 1.5, temperature of 70 °C, initial Fe3 + concentration of 15.7 g/L, no aeration, leaching for 1.5 h. This process resulted in solubilization of 81.6% copper and 37.7% zinc with the relatively low iron recovery of 26.2%. Metal content in the leach residue was 0.13% Cu and 3.69% Zn.