Carbothermic Reduction of Copper Slag in the Presence of Borax

Abstract

ABSTRACT The low temperature carbothermic reduction of copper slag with charcoal in the presence of borax followed by leaching with H2SO4 was investigated in this study. The copper slag sample was characterized using the XRD. Thermogravimetry was used to study the thermal degradation processes of copper slag. The standard Gibbs free energy at each reaction temperature was calculated using the HSC Chemistry® software. In the reduction experiments, the effects of charcoal and borax, as well as the reduction temperature and time, were investigated in order to identify the mechanism of enhanced reduction. The degree of metal dissolution was investigated in the leaching experiments in relation to leaching time and acid concentration. According to the results of the mineralogical analysis, the primary phases in the copper slag were fayalite, and magnetite. The HSC Chemistry results on equilibrium phase composition show that the carbothermic reduction of magnetite at various temperatures proceeded stepwise as Fe3O4 → FeO → Fe. Meanwhile, fayalite was first catalyzed at low temperature of 300°C before being reduced to metallic phase at 545oC. Thermochemical calculations, phase characterization and experimental results demonstrate that using borax in carbothermic reduction can accelerate phase transformation, lower the temperature of fayalite reduction, and improve the extraction of Co, Cu, and Fe at 850°C.