pH-dependent leaching mechanism of carbonatitic chalcopyrite in ferric sulfate solution

Abstract The dissolution of a carbonatitic chalcopyrite (CuFeS2) was studied in H2SO4−Fe2(SO4)3−FeSO4−H2O at varying pH values (0.5−2.5) and 25 °C for 12 h. Experiments were conducted with a size fraction of 53−75 µm. Low Cu recoveries, below 15%, were observed in all pH regimes. The results from the XRD, SEM−EDS, and optical microscopic (OM) analyses of the residues indicated that the dissolution proceeded through the formation of transient phases. Cu3.39Fe0.61S4 and Cu2S were the intermediate phases at pH 0.5 and 1.0, respectively, whereas Cu5FeS4 was the major mineral at pH 1.5 and 1.8. The thermodynamic modelling predicted the sequential formation of CuFeS2→ Cu5FeS4→Cu2S→CuS. The soluble intermediates were Cu5FeS4 and Cu2S, whilst, CuS and Cu3.39Fe0.61S4 were the refractory phases, supporting their cumulating behaviour throughout the dissolution. The obtained results suggest that the formation of CuS and Cu3.39Fe0.61S4 could contribute to the passive film formed during CuFeS2 leaching.