Bioleaching residue-introduced thermal activation-leaching of refractory chalcopyrite

Currently, about 10% − 20% of the world's copper production comes from bioleaching processes. On the one hand, the bioleaching residues accumulated over the years require harmless treatment. On the other hand, the gradual depletion of secondary copper sulphide ores has made refractory chalcopyrite the most important copper resource, but bioleaching of chalcopyrite has not yet achieved commercial success, and more efficient and cost-effective technologies need to be developed. To this end, the bioleaching residue-introduced thermal activation-leaching of chalcopyrite was investigated for the first time in this work. As the main or typical components of bioleaching residues, elemental sulphur, jarosite and covellite were selected as additives to chalcopyrite, which were thermally activated at 375 °C, 475 °C and 575 °C. The solubility of the activated products was evaluated using three leaching media including deionised water, dilute H2SO4 (pH 1.85) and 10 wt% H2SO4, with a solid/liquid ratio of 0.5 g/10 mL. The leaching results showed that the highest Cu recoveries of the different groups were 96.10% (with jarosite added), 93.10% (with all three components added), 90.30% (with elemental sulphur added), 88.40% (chalcopyrite alone) and 88.00% (with covellite added). An improved Cu recovery of 5.32% with a significantly reduced iron leaching rate of 71.24% was obtained when all three additives were present. Combining the results of XRD, SEM, EDS, TG-DSC and predominance area diagram analysis, the sulphation mechanism of chalcopyrite induced by the thermal decomposition intermediates KFe(SO4)2 and K2SO4 was proposed and the favourable sulphation atmosphere attributed to the formation of SO2 and SO3 was discussed. In addition, high-purity hematite was shown to be the main phase of the final solid product, achieving the simultaneous valuable and harmless transformation of the bioleaching residue.