Leaching Mechanism for Chalcopyrite in Electrochemically Regenerated Vanadium(II)

Vanadium(II) sulfate was utilized as an electrochemical reagent to reductively leach and convert chalcopyrite into less refractory mineral phases for subsequent copper extraction. During leaching, iron was selectively extracted into the solution. Fast leaching kinetics under various pulp densities and temperatures were observed, with ∼90% iron being leached within 60 min under all conditions tested. The phase composition and particle morphology of the solid product were analyzed by using X-ray diffraction (XRD), automated mineral identification characterization systems (AMICS), and scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM-EDS). The results showed that djurleite (Cu1.94S) emerged as the predominant product after V2+ leaching. The conversion of chalcopyrite to djurleite was accompanied by a significant morphological transformation from ∼30 μm mineral particles to ∼200 nm nanoparticles. To provide insight into the phase conversion, the initial stage of the reaction between chalcopyrite and V2+ solution was examined, revealing crack formation within the inner particle and nucleation of the product phase at the leached particle surface. Along the cracks and at the particle surface, chalcopyrite was replaced by an iron-depleted and copper-rich phase. In an unstirred system, the leached particles were found to preserve the original external shape while attaining a highly porous structure. Based on the texture observations, a dissolution–precipitation mechanism was proposed. And the precipitation chemistry was hypothesized to be a reaction between hydrogen sulfide and dissolved copper intermediate. In addition, copper metal was successfully obtained as the primary product of V2+ leaching when a sufficient reactant was present.