Phase Diagrams of “FeO”-SiO₂-CaO-V₂O₃-TiO₂ System and Phase Transformation of Vanadium-enriched Phases

Abstract

Achieving phase transformation from spinel to the vanadium-enriched phase with higher chemical activity of vanadium oxide is essential for the efficient extraction of vanadium resources in vanadium slag. However, there is a severe lack of thermodynamic data for the relevant systems, which hampers our understanding for phase relations of vanadium-enriched phases. In this study, the phase equilibria of the "FeO"-SiO₂-CaO-V₂O₃-TiO₂ system were investigated at 1400 °C and 1200 °C, and the corresponding phase diagrams were constructed. It was found from these phase diagrams that the vanadium-rich phase (V,Ti,Fe)₂O₃ with a higher chemical activity of vanadium oxide than Fe(V,Ti,Fe)₂O₄ was identified, but the decrease in temperature was detrimental to the crystallization of (V,Ti,Fe)₂O₃. On these bases, the phase transformation from Fe(V,Ti,Fe)₂O₄ to (V,Ti,Fe)₂O₃ was further investigated at 1400 °C. It was found that the phase transformation occurred in three stages: the Fe(V,Ti,Fe)₂O₄ stage, the coexistence stage of Fe(V,Ti,Fe)₂O₄ and (V,Ti,Fe)₂O₃, and the (V,Ti,Fe)₂O₃ stage, and the phase transformation from Fe(V,Ti,Fe)₂O₄ to (V,Ti,Fe)₂O₃ was fully completed when the w("FeO")/w(SiO₂) ratio was lower than 0.8. In this study, the essential thermodynamic data of the relevant system are complemented, while the phase transformation results of vanadium-enriched phases provide theoretical guidance for the efficient extraction of vanadium resources from vanadium slag.