Batch leaching behavior of ground chalcopyrite (median particle diameter 6 μ mm) was investigated anaerobically by a shaking flask method. The experiments used 0.1 mol dm-3 sulfuric acid solutions containing 0.25 mol dm-3 ferric ions and known concentrations of ferrous and cupric ions at 303 K. The initial pulp density of the chalcopyrite was 10 kg m-3.
When 1.00 mol dm-3 of ferrous ions were added, copper extraction proceeded in three steps: (1) an induction period, (2) a leaching period, and (3) a stationary period. This extraction behavior can be interpreted by the following reaction model: in the induction period, copper is extracted slowly by the direct oxidation of chalcopyrite with ferric ions and the redox potential of the solution decreases due to the consumption of oxidant ferric ions. When the solution potential becomes lower than a critical potential, a leaching period, intermediate Cu2S that is oxidized faster than chalcopyrite is formed by the reduction of chalcopyrite and copper extraction rate becomes high. When the solution potential decreases further, a stationary period, Cu2S oxidation and copper extraction stop.
Based on this reaction model, the effects of the initial pulp density and the initial concentrations of ferric, ferrous, and cupric ions on the leaching behavior were simulated numerically. As a result, it was predicted that the induction period could be eliminated by adding more than a critical amount of cupric ions with ferrous ions and that the stationary period can be eliminated by solution potential regulation during the leaching.
The simulation agreed with the experimental results. When 1.00 mol dm-3 ferrous ions and 0.05 mol dm-3 cupric ions were added together, 56 % copper extraction was obtained after 9 days without an induction period, then extraction stopped. Further when the solution potential was regulated by the addition of ferric ions, 80 % of copper was extracted in two weeks. On the other hand, without the ferrous and cupric addition and the potential regulation, copper extraction was only 11 % even after 27 days.
