Contribution to the Metal-Slag Equilibrium Study During Carbothermic Reduction of Copper Slag for Cobalt Recovery

Abstract

In today's mining industry, the growing demand for high-tech materials and the diminishing primary cobalt resources have compelled the industry to turn to recycling slag as a secondary source of cobalt. Cobalt has been discovered in copper slag originating from the water-jacket furnace in the Katanga Province of the Democratic Republic of Congo. This study aimed to optimize cobalt content and investigate whether the system reached equilibrium during the carbothermic reduction of the slag. The primary fayalitic slag was analysed using XRD, XRF, and SEM. To influence the cobalt activity, lime was added to adjust the basicity to unity, affecting the activities of other oxides. The smelting process was conducted at 1400°C, with coke serving as the reductant, and carbon monoxide was blown into the furnace to create strong reducing conditions. The sample spent two hours in the furnace, which was deemed sufficient to reach full equilibrium if possible. The outcomes included a secondary slag and an alloy, which were analysed using XRD, XRF, and SEM. The results indicated that the metallic phase contained copper, cobalt, iron, and minor traces of zinc, while the secondary slag phase consisted of SiO2, CaO, and some FeO. The recovery of cobalt fell short of the calculated equilibrium amount, suggesting that the system did not reach full equilibrium but was very close to it.