Redox potential-dependent chalcopyrite leaching in acidic ferric chloride solutions: Leaching experiments

Abstract

The redox potential dependence of chalcopyrite leaching was investigated in acidic ferric chloride solutions using a specially designed batch leaching experimental setup that accurately determined and monitored changes of solution redox potential with time. The concentration ratio of ferric (Fe3+) to ferrous (Fe2+) ions and leaching rate-redox potential relationship were then determined from measured redox potential data assuming chalcopyrite oxidation with Fe3+ occurred stoichiometrically. A distinct peak was observed in the leaching rate vs. redox potential plot; that is, the leaching rate increased with increasing redox potential, reaching a (local) maximum (i.e., the peak rate) at a certain redox potential (i.e., the peak redox potential) followed by the gradual decrease in leaching rate at higher redox potentials. For example, in the experiment performed at [Cu2+] = [Fe2+] = 0.01 kmol m−3 in HCl (0.1 kmol m−3) at 343 K, the rate continuously increased with increasing redox potential, reaching the fastest rate of 9.7 × 10−8 mol s−1 g−1 (peak rate) at 0.442 V (peak redox potential). After passing this redox potential peak, the rate started to decrease, slowing down to 2.9 × 10−8 mol s−1 g−1 at 0.487 V. Using this setup, the effects of temperature and solution composition (Cu2+, Fe3+ and HCl concentrations) on the peak rate and peak redox potential were investigated. The results showed that the peak rate increased with increasing temperature, decreased with increasing HCl and Fe3+ concentrations but was not strongly affected by Cu2+ concentration. In comparison, the peak redox potential was less dependent on the temperature and concentrations of HCl and Fe3+. Although the role of Cu2+ was apparently not crucial in the occurrence of the peak rate, it exerted a relatively strong influence on the peak redox potential; that is, the peak redox potential increased with increasing Cu2+ concentration. Based on these results, an empirical equation for the relationship between peak redox potential and Cu2+ concentration was derived.