Effect of Alumina on the Behavior of V-Rich Spinel Phase in CaO-SiO2-FeOt-MgO-Al2O3-V2O3-P2O5 Slags at 1573 K (1300 °C)

To ascertain the thermodynamic conditions for the enrichment of vanadium in V-bearing steelmaking slag and V-bearing black shale, the effects of alumina content and basicity on the formation of phases and distribution of vanadium in CaO-SiO2-FeOt-MgO-Al2O3-V2O3-P2O5 slag system at 1573 K (1300 °C) were investigated by adopting the high-temperature quenching method. The phases formed in the samples were characterized by X-ray diffractometry and scanning electron microscopy combined with energy dispersive spectroscopy. For slags with a basicity of 1.7, it was found that nearly all of the vanadium were concentrated in the (Fe, Mg)O·(Al, Fe, V)2O3 spinel. For slags with basicities of 1.5 and 1.3, vanadium was almost not found in the supercooled glass phase when the alumina content was less than 6 mass pct. However, some vanadium was present in the supercooled glass phase when the alumina content was more than 6 mass pct. For slags with a basicity of 1.0, vanadium migrated between the V-rich spinel and the supercooled glass phase. With an increase in the alumina content from 2 to 10 mass pct, the vanadium content in the spinel phase decreased from 28 to 33 mass pct to approximately 10 mass pct. From these results, it can be concluded that the increase in alumina content and decrease in basicity of the slag are unfavorable for the enrichment of vanadium present in the spinel.