Leaching characteristics of chalcocite in NH3·H2O-NH4+–O2-H2O system

Abstract

To address the unclear leaching behavior of chalcocite in the NH₃·H₂O-NH₄⁺–O₂-H₂O system and the scarcity of selective hydrometallurgical approaches for this mineral, this study systematically investigated the leaching characteristics and reaction mechanisms of chalcocite in the aforementioned system using multiple characterization techniques, including inductively coupled plasma atomic emission spectrometry (ICP-OES), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and X-ray diffraction (XRD). The results revealed that the NH₃·H₂O-NH₄⁺–O₂-H₂O system enabled highly selective leaching of copper from chalcocite. Under optimized leaching conditions of 5 mol/L NH₃·H₂O, 2 mol/L NH₄Cl, 55 °C (328.15 K), a liquid-to-solid ratio of 5:1, and a reaction duration of 3 h, the copper extraction efficiency reached 98.52 %, with impurity concentrations (Fe, Al, Ca, Mg) in the leachate consistently maintained below 5 mg/L. Notably, ammonium chloride exhibited significantly higher leaching efficiency than ammonium sulfate under identical conditions. Kinetic analysis indicated that the leaching process of chalcocite in this system was well-described by the solid-film diffusion control model, with an apparent activation energy (E_a) of 38.54 kJ/mol. This value closely matches the experimental observations, confirming that interfacial mass transfer serves as the rate-limiting step in the leaching mechanism.