Polarization Effects on Cu Migration at the Interface between Cu-Containing Molten Fe and Molten Slag

In the steelmaking industry, using electric arc furnaces with scrap as raw material is the most promising method to significantly reduce CO₂ emissions. However, Cu in molten iron is a major contaminant that causes metallurgical and mechanical issues in steel. In this study, we experimentally explored the feasibility of separating Cu from molten Cu-containing iron by constant-voltage electrolysis at 1823 K using molten slag from actual processes. With industrial molten slag containing 25.5 wt % FeO and 0.05 wt % S, the decopperization rate decreased with increasing voltage under anode polarization, whereas it increased under cathodic polarization. The Cu concentration in the metal phase dropped from 0.501 to 0.379 wt % at −10 V in an Ar-5 vol % O₂ atmosphere. Molecular dynamics simulations revealed a Cu-rich phase at the slag–metal interface, with Cu being more energetically stable than Fe at this boundary. Cu in the metal tended to be negatively charged owing to its high electron affinity, attracting Cu atoms in the slag to the interface under excess charge. Thus, anodic polarization is ineffective for decoppering in industrial slag electrorefining, whereas cathodic polarization increases Cu concentration at the interface. The Cu concentration can be controlled by applying a potential, which is useful in processes leading to the final product.