Selective separation of metallic phases from chalcopyrite
Owing to the environmental problems associated with copper extraction alternative processes are sought. The carbothermic reduction of natural chalcopyrite concentrates, from Ghatsila mines in Bihar, India, in the presence of lime, was studied across the temperature range 850-1250°C. Studies have been completed previously in synthetic chalcopyrite. This study stresses the need to investigate the reduction of natural chalcopyrite. The reduction of chalcopyrite proceeds in two steps, initially with the direct reduction by carbon. This is followed by indirect reduction by the carbon monoxide evolved from the first stage of reduction. Both stages of the reduction were investigated to determine the reaction mechanism. Metallic copper and iron are produced from the reduction of chalcopyrite. The oxysulphide phase, Cm, also produced from the reduction of chalcopyrite, was not previously categorised. X-ray diffraction analysis and scanning electron microscopy were utilised to evaluate the structure of Cm. Silver is an important by-product of copper extraction therefore it was necessary to study its path during the reduction of chalcopyrite. This was achieved by additions of Ag and Ag2S prior to reduction. Silver will preferentially segregate out with the copper phase hence providing a valuable metallic product from the reduction reaction. The addition of Ag to the reduction mixtures facilitates metallic phase separation of copper and iron. Arsenic and antimony are deleterious elements present in naturally occurring chalcopyrite. The addition of calcium sulphate and silica to chalcopyrite, heat treated under partially reducing conditions, will produce a calcium silicate slag phase that will entrain impurities such as arsenic and antimony, thus providing a method of control of those elements. An initial investigation into the possible control and elimination of impurities during extraction of copper has been conducted with favourable results.