Chalcopyrite concentrate leaching with biologically produced ferric sulphate

Biological ferric iron production was combined with ferric sulphate leaching of chalcopyrite concentrate and the effects of pH, Fe³⁺, temperature and solids concentration on the leaching were studied. The copper leaching rates were similar at pH of 1.0-1.8 and in the presence of 7-90 g L^-1 Fe³⁺ despite massive iron precipitation with 90 g L^-1 Fe³⁺. Increase of the leaching temperature from 50 °C to 86 °C and solids concentration from 1% to 10% increased the copper leaching rate. Increase in solids concentration from 1% to 10% decreased the copper yields from 80% to 40%. Stepwise addition of ferric iron did not improve the copper yields. CuFeS₂, Ag and Cu_1.96S potentials indicated the formation of a passivating layer, which consisted of jarosite and sulphur precipitates and which was responsible for the decreased leaching rates.