Kinetics of chalcocite leaching in oxygenated alkaline glycine solutions

Naturally occurring chalcocite (Cu2S) was leached with oxygenated alkaline glycine solutions. The influence of glycine concentration, stirring speed, particle size, dissolved oxygen concentration and temperature on the copper dissolution rate were evaluated. Under all conditions, the copper leach rate was very rapid in the first 6 h of leaching after which significant slower rates were recorded. The influence of fine grinding P100-20 μm was remarkable with up to 78% Cu extracted over 6 h of leaching as compared to just 40% for 38-53 μm size fraction under the same conditions. SEM-EDS and XPS analysis of the leach residue confirmed the presence of covellite (CuS) on the particle surfaces. It appears that chalcocite leaching in oxygenated alkaline glycine solution occurs in two stages. The first stage is fast and involves the conversion of chalcocite into cupric ions and covellite while in the second stage, the formed covellite slowly converts to cupric ions and sulfate ions. Kinetic analysis using the shrinking core model of both the first and second stages indicates that the reactions appear to be controlled by diffusion through the product layer with calculated apparent activation energies being 25.kJ/mol (1st stage) and 108 kJ/mol (2nd stage).