The effect of chloride ions on the electrochemical dissolution of chalcopyrite in sulfuric acid solutions

The dissolution of chalcopyrite in 0.2 M sulfuric acid solutions with different sodium chloride concentrations was investigated. Different anodic potentials were applied, and the behavior of the electrode was observed using potentiodynamic, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) techniques. The results showed that the chalcopyrite open circuit potential (OCP, approximately 245 mV vs. SCE) decreased as the NaCl concentration increased. Four different surface conditions emerged on the chalcopyrite surface as the anodic potentials increased: (1) a Cu1−xFe1−yS2 passive layer formed at OCP-500 mV; (2) a second passive layer (Cu1−x-zS2) formed at 500-700 mV (electrolyte without NaCl) or 500-800 mV (electrolyte with NaCl); and (3) chalcopyrite was in an active area at 700-800 mV (electrolyte without NaCl) or 800-900 mV (electrolyte with NaCl), and all the previous passive layers disappeared. In this case, SO42− or S2O32− and S4O62− for the electrolyte without NaCl or with NaCl, respectively, are the oxidized forms of sulfide sulfur; (4) when the potential is above 800 mV (for the electrolyte without NaCl) or 900 mV (for the electrolyte with NaCl), pseudo-passive CuS is formed. Subsequently, the sulfur of CuS was oxidized to SO42−, and Cu2+ changed into CuCl+ with a NaCl concentration of 0 mol/L and 0.5 mol/L, respectively. However, a new passive layer(s) of Cu2(OH)3Cl formed with NaCl concentrations above 0.5 mol/L. Overall, the results revealed that Cl− ions are advantageous for chalcopyrite dissolution. However, the oxidation of chalcopyrite generated chloride and cupric ions that can form the cuprous complexes CuCl0, CuCl2− or CuCl32−, which dramatically inhibit the on-going dissolution of chalcopyrite. EIS data confirmed that a high concentration of Cl− ions was not essential for chalcopyrite dissolution under the present conditions. Moreover, the critical Cl− ion concentrations were different for the four distinct potential areas outlined above, namely, 1.0 mol/L, 1.25 mol/L, 1.25 mol/L and 0.5 mol/L, respectively.