Recovery of Cobalt, Copper and Zinc from Kure-Kastamonu Historical Copper Slag by High Pressure Oxidative Acid Leaching

Copper slags are solid by-products formed during the copper production process by pyrometallurgical method from sulfide copper ores. These slags usually contain significant quantities of valuable metals, such as cobalt, nickel, zinc and copper, in different forms. Extraction characteristics of Cu, Co, Zn, and Fe from Kure historical copper slag (KHS) by oxidative pressure leaching were investigated with sulfuric acid lixivant in this study. The phase composition of the studied slag was identified by the use of a combination of methods, including a mineral liberation analyzer (MLA), a scanning electron microscope coupled with an energy-dispersive spectrometer (SEM-EDS), and X-ray powder diffraction (XRD). Bornite, chalcopyrite, cuprospinel, brochantite, chalcocite, and metallic Cu are identified as copper-containing minerals. The samples used in leach tests contained averages of 0.84% Cu, 0.34% Co, 0.23% Zn, 2.90% Al, 0.70% Ca, 1.30% S, and 42.80% Fe. The factors affecting the performance and efficiency of the pressure leaching process, such as acid concentration, leaching time, solid/liquid ratio, oxygen partial pressure, particle size, and temperature, were investigated separately. It was found that metal extraction increased with temperature and sulfuric acid concentration. However, high acid concentrations led to gel formation that caused filtration problems. Under optimum conditions, the extraction efficiencies of cobalt, copper, and zinc from KHS were 96.82, 92.85, and 93.44%, respectively, while the extraction of iron was only 0.3%.