A new reaction model for the catalytic effect of silver ions on chalcopyrite leaching in sulfuric acid solutions

Chalcopyrite leaching in sulfuric acid solutions depends on the redox potential determined by the concentration ratio of ferric to ferrous ions, and the leaching rate is higher at redox potentials below a critical value. Previously, the authors have proposed a reaction model to interpret this phenomenon. The present study applied the model to interpret the catalytic effect of silver ions on chalcopyrite leaching. The model assumes that at lower potentials, chalcopyrite leaching proceeds in two steps: first, chalcopyrite is reduced by ferrous ions to form Cu₂S that is more rapidly leached; next, the intermediate Cu₂S is oxidized by ferric and/or dissolved oxygen to release cupric ions. During the chalcopyrite reduction, hydrogen sulfide is released to the liquid phase. Silver ions react with the hydrogen sulfide to form silver sulfide precipitate and decrease the concentration of hydrogen sulfide in the liquid phase, causing a rise in the critical potential of Cu₂S formation and broadening of the potential range where rapid copper extraction takes place. To confirm the model, the redox potential dependence of chalcopyrite leaching was investigated in the presence of various concentrations of silver ions with 0.1 kmol m^-3 sulfuric acid containing known concentrations of ferrous and ferric ions at 298 K in air. The critical potential increased with increasing concentrations of silver ions. This agrees with the model proposed here but cannot be explained by the conventional model proposed by Miller et al.