Abstract

The nature of the hydrothermal reaction between sphalerite and copper solutions was investigated in the range 160-225°C. Digenite (Cu 1.8S) 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). © 2004 Elsevier B.V. All rights reserved.