Formation of Phase Transition During the Dissolution of Silicate and Carbonate Chalcopyrite in Acidic Ferric Sulfate

In this investigation, two ore bodies (silicate and carbonate), carefully sized, containing chalcopyrite (CuFeS 2 ) were assessed for their Cu dissolution in acidic ferric sulfate (H 2 SO 4 -Fe 2 (SO 4 ) 3 ) at various pH (1.0, 1.5 and 1.8) and temperature (25 and 50 °C) under atmospheric pressure. Experiments were conducted with a size fraction of 53 + 38 for 12 h at a constant pulp density of 10% solids. The maximum Cu recovery of 70 and 58% was obtained in less than 2 h at pH 1.8 and 50 °C from silicate and carbonate chalcopyrite, respectively. The XRD analyses results of the residues indicated that copper dissolution from its CuFeS 2 mineral proceeded through the formation of transient phases, dependent upon the media pH value. Cu 2 S was the major intermediate phase at pH1.0, while Cu 5 FeS 4 was the major phase at both pH 1.5 and 1.8. It was further observed that mineralogical composition plays a vital role during Cu dissolution. The thermodynamic modeling predicted the sequential formation of CuFeS 2 → Cu 5 FeS 4 → Cu 2 S → CuS in which soluble intermediates were Cu 5 FeS 4 and Cu 2 S, while CuS was identified as the end-transitory metastable, and main thermodynamically refractory phase, supporting its cumulating behavior throughout the dissolution. The obtained results suggest that the formation of CuS and excessive gypsum could contribute to the passive film formed during CuFeS 2 leaching.