Abstract

In the leaching of copper sulfide ores or refractory gold ores in chloride solutions, the regeneration of oxidative agents such as Cu (II) and Fe (III) is a key aspect for a sustainable process over time. This regeneration is carried out from the oxidation of Cu (I) and Fe (II) with O2, which helps to maintain a conveniently high oxidative potential in solution and a high leaching efficiency. In this context, Cu (I) and Fe (II) oxidation are affected by the accumulation of Cu or Fe species resulting from sulfide dissolution during the process. Therefore, a good understanding of the interaction mechanism of O2 with Cu (I), Cu (II), Fe (II), and Fe (III) species is necessary to describe the oxidation kinetics in this complex environment. The present work reports a study of the Cu (I) and Fe (II) oxidation at 75 °C in solutions containing 4.0 M NaCl and 0.1 M HCl. The solutions used in the experiments contained different initial concentrations of Cu (I), Cu (II), Fe (II), and Fe (III) with values in the range of 0.0001 – 0.1 M. Experiments were conducted in a thermostatized reactor containing 0.5 L solution agitated with a magnetic stirrer at 450 rpm, while oxygenated by air bubbling at 3.5 L/min. The evolution of the concentration of Cu (I), Cu (II), Fe (II), and Fe (III) during oxidation was determined by an electrochemical method, which was mainly based on Eh measurements of solution over time. A reaction mechanism was proposed for the oxidation of Cu (I) and Fe (II) with O2 in the presence of Cu and Fe species, which described very well the results obtained in the oxidation experiments under various conditions. Based on the proposed mechanism, a kinetic model was developed that could predict the concentration of Fe (II), Fe (III), Cu (I), Cu (II), O2, HO2–, H2O2, OH– and H+ in acid aerated chloride solutions satisfactorily. These proved to be a valuable tool to approach the modeling of chloride-leaching reactors.