Experimental Study on the Formation of V-Rich Spinel Phase in CaO-SiO₂-MgO-FeO_t-Al₂O₃-V₂O₃-P₂O₅ Slags at 1573 K (1300 °C)

To concentrate vanadium dissolved in steelmaking slag and to separate the obtained vanadium (V)-concentrating phase by a magnetic method, the mineral phases in a CaO-SiO₂-MgO-FeO_t-Al₂O₃-V₂O₃-P₂O₅ system at 1573 K (1300 °C) were characterized by scanning-electron microscopy-energy-dispersive spectroscopy and X-ray diffractometry. When the samples were equilibrated in a pure iron crucible and argon atmosphere, four phases were identified, namely, orthosilicate, V-bearing spinel, wüstite, and a glass phase. The orthosilicate, V-bearing spinel, and glass phase occurred in all samples, whereas wüstite appeared only in samples with a higher basicity or high FeO_t content. The results indicate that the V-bearing spinel phase, which is analogous to Fe₃O₄, is a thermodynamically stable phase that is suitable for the enrichment of vanadium dissolved in slags. Further analysis reveals that the increases in contents of FeO_t and MgO in slag favor spinel-phase formation. When the slags are saturated by the wüstite phase, almost all dissolved vanadium can be concentrated in the spinel phase.