Leaching kinetics of digenite concentrate in oxygenated chloride media at ambient pressure

The leaching of digenite concentrate in CuCl₂-HCl-NaCl oxygenated solutions is very rapid. From the effect of variables on the leaching rate and measurements of the concentrations of cuprous and cupric species in the solution as a function of time, it was concluded that the leaching in O₂ atmosphere proceeds by the attack of cupric ions on the copper sulfides to produce cuprous ions which are subsequently oxidized to cupric by the O₂ present in the system. The kinetic study showed that the leaching proceeds in two sequential stages. In the first stage, the digenite is transformed to covellite, and in the second stage, the covellite is dissolved to copper and elemental sulfur. In the first stage, the fraction of copper extracted varied linearly with time according to α=k _l t, whereas in the second stage, the dissolution of covellite was well represented by a shrinking core model controlled by diffusion through a porous product layer kinetic equation: 1−2/3α _cv−(1−α _cv)^2/3=k _cv t. The calculated activation energies were 15.8 and 80.0 kJ/mol for the first and second stages, respectively. These results were explained by an electrochemical mechanism of digenite dissolution.