Kinetics and mineralogical analysis of copper dissolution from a bornite/chalcopyrite composite sample in ferric-chloride and methanesulfonic-acid solutions

Ore samples contain a variety of copper-bearing and gangue minerals that affect the leach kinetics. The kinetic behaviour of a natural ore sample (that contained 48.7% bomite and 15.8% chalcopyrite) in a solution of methanesulfonic acid and ferric chloride was studied. The dependence of the reaction kinetics on the acid and oxidant concentration, temperature and particle size was investigated. The reaction activation energy was calculated using two methods, by empirical kinetic equations and by the 'time-to-a-given-fraction' method. The shrinking-core-model was fitted according to diffusion through a product layer, and an average apparent activation energy of 79.3 kJ mol(-1) was obtained. Three apparent activation energies were obtained by the 'time-to-a-given-fraction' method; that for a copper extraction below 20% was 15.6 kJ mol(-1) for copper intermediate formation, that between 20% and 50% copper extraction was 42.3 kJ mol(-1) associated with sulfur formation and that for dissolution above 50% was 76.5 kJ mol(-1) for the final stage when the sulfur layer is covering the entire particle surface. The presence of chalcopyrite in the sample increased the average activation energy by 69% compared with a pure bornite sample. The leach products had different textures; the sulfur formed from chalcopyrite showed a more porous texture than that formed from bomite. These differences in texture are expected to affect the lixiviant access.