Chalcopyrite leaching in alcoholic acid media

In recent years, the kinetics and mechanism of chalcopyrite dissolution in different media have been the focus of much investigation since a fundamental understanding of the phenomena would help to resolve the problems that challenge the implementation of a hydrometallurgical processing alternative. The addition of polar organic solvents has been found to have a beneficial effect by depassivating the chalcopyrite surface. The present article describes chalcopyrite leaching in the presence of alcohols, such as 2-propanol and methanol, in an acid solution at different temperatures with distinct oxidants (H₂O₂, CuSO₄ and O₃). For both alcohols, the temperature was found to be a very important variable in the process. For 2-propanol, copper dissolution by hydrogen peroxide fits the shrinking core model controlled by chemical reaction in the temperature range up to 40 °C with an activation energy of 42 kJ mol^-1. At higher temperatures, the peroxide rapidly decomposed and the copper extraction ceased. In contrast to the straightforward kinetics in peroxide, the dissolution behavior using cupric ion and ozone as oxidants displayed a complex mechanism, initiating with the solid phase transformation upon reaction with the cupric ion to form an iron-free phase, which later was oxidized by the ozone. A reaction scheme is proposed according to the different phases formed during the leaching process, identified using ultraviolet and atomic absorption spectroscopies, as well as X-ray diffraction. Methanol was found to stabilize the cuprous ion and allow the formation of roxbyite (Cu₂S₂-6Cu₂S), which is essential to achieve high copper extractions.