Thermodynamic calculation of precipitation behavior of chromium spinel in the CaO-SiO₂-MgO-Al₂O₃-FeO-Cr₂O₃ slag system

Chromium existing as a spinel phase in stainless steel slag can prevent the leaching of Cr⁶⁺ into the environment. Chromium in stainless steel is selectively enriched and stabilized, which is beneficial to improve the comprehensive utilization rate of stainless steel slag. Based on slag non-equilibrium solidification theory, the effects of basicity, MgO and FeO contents on the precipitation temperature, precipitation amount and chemical composition of the spinel phase during the solidification process of the CaO-SiO₂-MgO-Al₂O₃-FeO-Cr₂O₃ stainless steel slag system were studied, respectively. The results show that the precipitated phases of CaO-SiO₂-MgO-Al₂O₃-FeO-Cr₂O₃ are mainly Ca₂SiO₄, Ca₂MgSi₂O₇, Ca₂Al₂SiO₇ and spinel phase. The precipitation amount of MgCr₂O₄ spinel gradually increases with increasing basicity, which can inhibite FeCr₂O₄ precipitation. When the temperature is reduced to 1 000 ℃ and MgO content ranges from 8% to 12%, the precipitation amount of MgCr₂O₄ is maximum. The precipitation amount of FeCr₂O₄ spinel decreases with the increase of MgO. With the increase of FeO content, the precipitation amount of MgCr₂O₄ spinel decreases and the amount of FeCr₂O₄ spinel increases. FeO is not conducive to the enrichment of chromium in MgCr₂O₄ spinel phase. The experimental results of chromium spinel phase precipitation in stainless steel slag have verified the thermodynamic calculation results. At a basicity of 1.5, the enrichment rate of chromium in the spinel phase of the stainless steel slag is approximately 93%.