Iron-Speciation Control of Chalcopyrite Dissolution from a Carbonatite Derived Concentrate with Acidic Ferric Sulphate Media

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Abstract
The mechanisms involved in the dissolution of chalcopyrite from a carbonatite concentrate in a ferric sulphate solution at pH 1.0, 1.5 and 1.8, and temperatures 25 °C and 50 °C were investigated. Contrary to expectations and thermodynamic predictions according to which low pH would favour high Cu dissolution, the opposite was observed. The dissolution was also highly correlated to the temperature. CuFeS2 phase dissolution produced intermediate Cu rich phases: CuS, Cu2S and Cu5FeS4, which appeared to envelop CuFeS2. Thermodynamic prediction revealed CuS to be refractory and could hinder dissolution. CuFeS2 phase solid-state dissolution process was further discussed. Free Fe3+ and its complexes (Fe(HSO4)2+, Fe(SO4)2– and FeSO4+ were responsible for Cu dissolution, which increased with increasing pH and temperature. The dissolution improved at pH 1.8 rather than 1.0 due to the increase of (Fe(HSO4)2+, Fe(SO4)2– and FeSO4+, which were also the predominating species at a higher temperature. The fast and linear first dissolution stage was attributed to the combined effect of Fe3+ and its complex (Fe(HSO4)2+, while Fe(SO4)2– was the main species for the second Cu dissolution stage characterised by a slow rate.

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