Effects of oxygen atmosphere, FeOx and basicity on mineralogical phases of CaO–SiO2–MgO–Al2O3–FetO–P2O5 steelmaking slag

Abstract

ABSTRACTThe mineralogical phase of slag after crystallisation is essential to utilisation of steelmaking slag. The mineralogical phases of cooled multicomponent CaO–SiO2–MgO–Al2O3–FetO–P2O5 slag with different iron oxide contents and basicities (defined as the ratio of mass percentage of CaO to mass percentage of SiO2 (w(CaO)/w(SiO2))) in different atmospheres were investigated in the present work by scanning electronic microscopy and energy dispersed spectroscopy analysis and X-ray diffraction. The mineralogical phases in steelmaking slag cooled in argon are mainly nCa2SiO4-Ca3(PO4)2 (thereafter nC2S-C3P) solid solution, (Fe, Mn, Mg)O (RO) phase. Some CaMgSiO4 phases could be found in slag with lower basicity. The mineralogical phases in steelmaking slag cooled in air are mainly nC2S-C3P solid solution, spinel phase. The overall crystallisation of slag cooled in both argon and air was enhanced with increasing basicity. However, the crystal sizes become smaller in sample with high basicity. The Fe-enriched phases were transformed from non-faceted RO phase in sample cooled in argon to faceted spinel phases in sample cooled in air. The crystallisation of slag cooled in both argon and air was promoted with increasing FeOx content. The phosphorus content in solid solution was elevated with decreasing basicity and increasing FeOx content. It was implied by the present work that appropriate basicity and air oxidation would be beneficial to magnetic separation and phosphorus utilisation.