Phase Diagrams of “FeO”–SiO<sub>2</sub>–CaO–V<sub>2</sub>O<sub>3</sub>–TiO<sub>2</sub> System and Phase Transformation of Vanadium-enriched Phases

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.