Open circuit potential and leaching rate of pyrite in cupric chloride solution

As a refractory gold mineral, pyrite needs to be oxidised prior to gold leaching. In this study, the effect of [Cl⁻] concentration (40.6–149.8 g/L), [Cu²⁺] concentration (0.8–31.6 g/L), pH (1.5–2.5) and temperature (25–90 –C) on the pyrite leaching rate was investigated. In addition, the open circuit potential (OCP) values of pyrite in cupric chloride solution were investigated. A linear regression model was constructed to predict pyrite dissolution rate i.e. corrosion current density. It was shown that the temperature had a significant positive effect on pyrite dissolution, while increased cupric ion concentration was also shown to provide some dissolution enhancement. According to the regression analysis, pH had no effect on the corrosion current density at OCP. Dissolution rates of pyrite varied between 0.05 and 2.9 µm/h. The activation energy values varied from 20 to 90 kJ/mol, indicated that the pyrite dissolution reaction rate was controlled by the chemical reaction or mixed mechanism rather than diffusion alone. The simultaneous increase in corrosion potential and corrosion current density indicated that the anodic pyrite dissolution reaction was rate determining at OCP.