Breaking the Fe₃O₄-wrapped copper microstructure to enhance copper–slag separation

The precipitation of Fe₃O₄ particles and the accompanied formation of Fe₃O₄-wrapped copper structure are the main obstacles to copper recovery from the molten slag during the pyrometallurgical smelting of copper concentrates. Herein, the commercial powdery pyrite or anthracite is replaced with pyrite–anthracite pellets as the reductants to remove a large amount of Fe₃O₄ particles in the molten slag, resulting in a deep fracture in the Fe₃O₄-wrapped copper microstructure and the full exposure of the copper matte cores. When 1wt% composite pellet is used as the reductant, the copper matte droplets are enlarged greatly from 25 μm to a size observable by the naked eye, with the copper content being enriched remarkably from 1.2wt% to 4.5wt%. Density functional theory calculation results imply that the formation of the Fe₃O₄-wrapped copper structure is due to the preferential adhesion of Cu₂S on the Fe₃O₄ particles. X-ray photoelectron spectroscopy, Fourier transform infrared spectrometer (FTIR), and Raman spectroscopy results all reveal that the high-efficiency conversion of Fe₃O₄ to FeO can decrease the volume fraction of the solid phase and promote the depolymerization of silicate network structure. As a consequence, the settling of copper matte droplets is enhanced due to the lowered slag viscosity, contributing to the high efficiency of copper–slag separation for copper recovery. The results provide new insights into the enhanced in-situ enrichment of copper from molten slag.