The leaching of sintered CuS disks with ferric chlorides

A comparative study of chemical and electrochemical leaching of a sintered disk of CuS was carried out at 343 to elucidate the leaching mechanism of CuS with FeCl₃. The leaching,rate of CuS exhibited a half order dependence on the FeCl₃ concentration, but the addition of FeCl₂ slightly reduced the leaching rate. The mixed potential of CuS exhibited a 53 mV decade^-1 dependence upon the FeCl₃ concentration; no significant effect on the mixed potential was observed by the addition of FeCl₂. Based on these observations, an electrochemical mechanism is proposed which involves the oxidation of CuS and the reduction of FeCl₂ ⁺ . The activation energy in chemical leaching of CuS was 46.7 kJ mol^-1, while in electrochemical leaching, it was 50.4 kJ mol^-1. By converting the leaching rate to electric current density,i, a 110 mV decade^-1 dependence of mixed potential, E, against log i is obtained. This dependence of the mixed potential during chemical leaching of CuS on FeCl₃ concentration agrees with the value theoretically expected from the electrochemical model of the leaching process. These findings strongly support an electrochemical mechanism for the FeCl₃ leaching of CuS. HIROSHI HIAI, formerly Graduate Student with Kyoto University