Hydrothermal purification and enrichment of Chilean copper concentrates: Part 1: The behavior of bornite, covellite and pyrite

The nature and basic kinetics of the hydrothermal reactions of bornite, covellite and pyrite with copper sulfate solutions were investigated, as a previous study on the behavior of the bulk Chilean copper concentrates. The reaction of bornite produced digenite at < 160 °C and djurleite above this temperature. The reaction products formed a continuous, non porous layer. The rates were of zero order with respect [Cu2+](aq), and the activation energy was ∼ 100 kJ/mol. Covellite was transformed to digenite at < 200 °C and to chalcocite (Q and M) at > 200 °C. The reaction was characterized for an irregular nucleation and growth of the products, which were non-protective. The order with respect the [Cu2+](aq) was 0.6 and the activation energy ∼ 110 kJ/mol. The pyrite reaction was significant at > 200 °C and extensive at 240 °C. It produced a mixture of digenite/chalcocite-Q, with small amounts of djurleite. The transformation has a high Philling–Betworth ratio (∼ 1.6), causing the break of the product layers. The reaction order and the activation energy were also 0.6 and ∼ 110 kJ/mol, respectively. The rate of the bornite reaction should be controlled by solid-state ionic diffusion, whereas for covellite and pyrite the rates should be limited by electrochemical processes. Towards the hydrothermal transformation, the reactivity of the main phases present in Chuquicamata-type concentrates was: bornite > chalcopyrite > covellite > sphalerite > pyrite.