Selective elemental concentration during the solidification of stainless steel slags for increased Cr recovery with MnO addition

The study investigated the effect of MnO on the viscosity and the equilibrium crystallization behavior of CaO-SiO₂-Al₂O₃-Cr₂O₃-MnO stainless steel slags to understand the selective concentration behavior of Cr during slag solidification. The apparent viscosity gradually decreases with higher MnO content, which act as a network modifier, resulting in simpler [SiO₄]-structural units. Due to the formation of MnCr₂O₄ spinel crystals, the tendency of decreasing viscosity is impeded. The equilibrium crystal phase with higher MnO content changes from the Cr₂O₃ phase to the MnCr₂O₄ spinel phase during the crystallization process. Distinct separation between Cr-enriched phases with the amorphous phase can be observed and analysis of as-quenched slags after thermochemical equilibrium experiments shows that the overall Cr content in the amorphous phase gradually decreases with higher MnO content and lower temperature, indicating Cr can be selectively enriched in a corresponding Cr-containing crystalline phase. The sizes of the primary Cr-enriched phases are < 20 μm. With a higher MnO content, the volume of the Cr₂O₃ phase decreases, and the corresponding volume of the MnCr₂O₄ spinel phase increases. Understanding the distribution characteristics of the Cr-enriched phase and the gradually enriched Cr content can provide a new approach for the increased retrieval of stainless steel slags.