Recovery of copper from bioleaching residues containing chalcopyrite through calcination-leaching: Emphasis on the presence of pyrite

The industrial application of bioleaching of copper ore has been developed for decades. As the easily soluble copper ore is gradually depleted, the refractory chalcopyrite becomes an increasing proportion of the original ore. Partially undissolved chalcopyrite, along with its associated pyrite, bioleaching intermediates, and microorganisms, are deposited in tailings. These tailings represent a significant environmental hazard but also a potential copper-bearing resource. In this regard, a synergistic calcination-leaching treatment method for bulk flotation was proposed, and calcination-leaching research was carried out on the bioleaching residues of pure chalcopyrite and mixed chalcopyrite-pyrite ore and control groups (chalcopyrite, pyrite and mixed chalcopyrite-pyrite ore) in this work. Calcination was carried out at 275 °C, 375 °C, 475 °C, 575 °C and 675 °C. The calcined products were then leached with 10 wt% H2SO4 at a solid/liquid ratio of 0.5 g/10 mL. The results indicated that the thermal activation of the mixed chalcopyrite-pyrite ore bioleaching residues occurred at 575 °C, and the presence of pyrite and the bioleaching intermediate elemental sulfur promoted copper recovery from the bioleaching residue up to 94.9 % with only 0.41 % iron leached. Combining the results of the leaching experiments, solid characterization, and thermal decomposition analysis, the underlying thermal decomposition mechanism was discussed in terms of competitive O2 consumption, SO2 partial pressure, temperature, and the formation of intermediate sulfation products. Furthermore, the final solid product consisted mainly of high-purity hematite with a multivoid framework structure, demonstrating the achievement of valuable and benign transformation of the bioleaching residue.