Transformation of sphalerite particles into copper sulfide particles by hydrothermal treatment with Cu(II) ions

The nature of the hydrothermal reaction between sphalerite and copper solutions was investigated in the range 160–225 °C. Digenite (Cu1.8S) was the main reaction product at 160–212 °C, and chalcocite (Cu2S) at 225 °C. The reaction was characterized by the formation of a compact layer of copper sulfide around the sphalerite nuclei. Final particles retained the size and shape of the original ZnS. Reaction rate followed a parabolic kinetic law. No significant effect of aqueous copper concentration was observed in the range 1–10 g/L. An activation energy of 147 kJ/mol was obtained, indicating kinetic control by solid-state counter diffusion of Cu+ and Zn2+ ions through the copper sulfide layer. A possible electrochemical mechanism is discussed. The removal of zinc from digenite or chalcocite bearing copper concentrates is effective at ∼225 °C, in which a high sphalerite conversion can be achieved in times allowing autoclave processing (∼1 h).