Phase equilibria and precious or high-tech metal distributions in copper smelting systems

Abstract

Metals have historically played an important role in modern societies and the industrial revolution. Nowadays, however, they are mainly derived from primary ore resources and secondary materials, such as waste electrical and electronic equipment (WEEE). WEEE contains a variety of products that no longer serve their initial purpose and their metal concentrations are significantly higher than that in primary ores. In the face of a strong demand for a circular economy model, the recovery of metal values from WEEE has attracted increasing attention. Base metals like copper, lead, and nickel are good collector metals for precious/high-tech metals. Therefore, the smelting technologies of base metals are potential and effective methods for recycling metals from secondary materials. To have a better understanding of the favorable conditions for the recoveries of valuable metals from secondary materials through copper smelting, it is critical to determine the behavior of various metals in copper smelting systems. In this study, the phase equilibria of matte/copper and silica/spinel/wüstite-saturated iron silicate slags as well as the distribution equilibria of precious (Au, Ag, Pt, and Pd) and high-tech (Ni, Co, and Sn) metals in the equilibrium systems were investigated using an advanced high-temperature isothermal equilibration/quenching technique, followed by direct phase composition analyses using electron probe X-ray microanalysis (EPMA) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The experimental parameters and conditions were selected to simulate primary and secondary copper smelting processes. An investigation was made of the effects of pSO2, the slag modifiers Al2O3 and CaO, the temperature, and the saturation phase on the equilibrium phase relations of copper/matte and slag, as well as on the equilibrium distributions of the aforementioned precious/high-tech metals. The equilibrium compositions of matte/metal, slag, and spinel/wüstite were displayed as a function of matte grade or oxygen partial pressure. The distribution coefficients of precious/high-tech metals between matte/metal and spinel/wüstite/slag were calculated based on experimentally determined metal concentrations in matte, slag, and spinel/wüstite. The novel experimental data obtained in this study provide insights for improving the performance of copper smelters and increasing the recovery of valuable metals from primary and secondary materials by adjusting the temperature and oxygen partial pressure, and by adding fluxes like Al2O3 and CaO. Moreover, the present results are useful for thermodynamic database development and for the modeling of the phase relations of major components and precious/high-tech metals distributions in copper smelting systems.