Pyrometallurgical Extraction of Technology and Base Metals from Copper Smelting Slags

Copper (Cu) smelting slags are considered secondary reserves of technology metals (TMs) and base metals (BMs), which are crucial for the transition to renewable energy and mechatronic applications. In this study, thermochemical and experimental analyses were conducted to investigate the pyrometallurgical extraction of TMs and BMs from Cu smelting slag. FactSage thermochemical simulations and smelting experiments were carried out at temperatures from 1300 to 1600 °C and with carbon (reductant) additions of 2% to 10% relative to the mass of the feed slag. The results showed that during smelting, gallium (Ga), germanium (Ge), cobalt (Co), and copper (Cu) deported into the iron-based alloy product. Zinc (Zn) and lead (Pb) oxidised to ZnO and PbO, respectively, which were subsequently collected as fumes. The produced alloy mass was more sensitive to carbon addition than to smelting temperature variation. The TM and BM contents in the alloy decreased with increasing carbon addition in the feed; this was attributed to dilution by Fe, Si, and C from the increasing reduction of iron and silicon oxides in the feed slag and dissolution of C in the alloy. High recovery degrees of TMs and BMs in the alloy stream—over 90% for Co and Cu, over 50% for Ga, and over 70% for Ge—were achieved when smelting at 1500 °C with 4% carbon addition. The final alloy comprised 70.5% Fe, 6.6% Co, 23.6% Cu, 0.11% Ga, and 0.13% Ge. The fumes primarily comprised ZnO and, to a lesser extent, PbO, with recovery degrees over 90% for Zn and Pb. These alloy and fume products would be processed following conventional hydrometallurgical separation and purification processes to produce high-purity metals. The pyrometallurgical extraction of TMs and BMs presents an opportunity for the valorisation of Cu smelting slag dumps, especially in Southern Africa, aiming to attain zero-waste industrial processes.