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. Cu_3.39Fe_0.61S₄ 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 Cu_3.39Fe_0.61S₄ were the refractory phases, supporting their cumulating behaviour throughout the dissolution. The obtained results suggest that the formation of CuS and Cu_3.39Fe_0.61S₄ could contribute to the passive film formed during CuFeS₂ leaching.

Key words: chalcopyrite; carbonatite; chemical leaching; leaching mechanism; intermediate phase; thermodynamic behavior