Chalcopyrite leaching in alcoholic acid media

• Chalcopyrite leaching in acidic solutions with 2-propanol or methanol was studied.
• Alcohols stabilized the cuprous ion, promoting the formation of a copper-rich phase.
• Different oxidants showed distinct reaction mechanisms.
• Cupric/ozone in acidic methanol solution proved to be the most effective combination.

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.