Potential-dependent removal of Cu, Sn, Ni, and Cr from molten Fe in contact with FeS-containing slag

Abstract

Abstract The accumulation of tramp elements in scrap-derived steel is a major obstacle to high-grade steel recycling. In this study, first-principles molecular dynamics (MD) calculations and a series of constant-potential screening experiments were used to examine interfacial sulfur behavior and changes in the metal-phase concentrations of Cu, Sn, Ni, and Cr in contact with an FeS-containing oxysulfide slag. The calculations showed that sulfur is preferentially stabilized near the molten metal–slag interface, and that its valence state is strongly influenced by local Fe coordination, suggesting that sulfur-bearing species can actively participate in interfacial electrochemical reactions. Electrolysis experiments revealed strong element-dependent removal behavior. Sn was preferentially removed under a wide range of conditions with an apparent removal ratio of 95.0%, whereas Ni removal was negligible. Although Cr was also removed, its migration is expected to be affected by Sn coexistence and the applied potential. Cu exhibited limited depletion under the present multicomponent conditions. Application of + 1 V did not enhance depletion in the single-element tests, and the charge passed varied substantially with alloy composition and operating condition. The results therefore provide a comparative screening data set and define the measurements required for a mass-balanced electrochemical refining.