Chemical metathesis of chalcopyrite in acidic solutions

The chemical metathesis of chalcopyrite in the presence of cupric ions was studied in sulphuric acid solutions. The effects of stirring, Cu(II) concentration, temperature and annealing were investigated by leaching and kinetic experiments. The primary reaction involved in the chemical metathesis leads to the formation of covellite, which is followed by an oxidation–reduction couple, with digenite production. This second step was found to be very slow requiring sub-sieve size particles for extensive reaction. The reaction was insensitive to the copper ion concentrations, and practically insensitive to stirring speed. The strain induced by stirred ball milling enhanced the reaction rate markedly due to the recrystallisation process which provides easy paths for diffusion along dislocation and grain boundaries. The kinetics were well correlated with a two-stage product layer diffusion model, with apparent activation energies less than 30 kJ mol− 1, and ferrous ion was found to be the rate determining diffusion species through the covellite phase (first stage) and covellite and digenite phase (second stage).