Abstract
The suitability of methanesulfonic acid as a copper lixiviant with ferric chloride as an oxidant was studied by analysing the leaching kinetics and by characterising solid residues from leach tests on a chalcopyrite-rich ore sample. The effects of temperature, initial acidity, ferric-ion concentration and particle size were determined. The leach kinetics were dependent on the temperature and particle size, whereas the acid and ferric concentrations had a minimal impact on the leaching rate within the ranges studied. Although a sulfur layer formed on the solid residue, the reaction mechanism could be modeled with the shrinking-core model with surface chemical-reaction control, which implies that lixiviant flow through the sulfur layer did not control the reaction rate. The apparent activation energy was 101 kJ mol−1 as calculated by the Arrhenius and 'time-to-a-given-fraction' methods. The activation parameters of the reaction were an enthalpy (ΔH++) of 99.4 kJ mol−1, and an entropy (ΔS++) of −197 J mol−1 K−1 as calculated by using transition state theory and the Eyring equation.
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