Influence of CaO on Existence form of Vanadium-containing Phase in Vanadium Slag

Abstract

A novel de-Phosphorisation & V-extraction process (de-P & V-extraction) is proposed in which lime is added during the production of vanadium slag. This is expected to promote both phosphorus removal and environment-friendly vanadium extraction from the vanadium-containing hot metal simultaneously. The influence of CaO addition on the chemical components and mineralogical morphology of vanadium-containing phase in vanadium slags has been investigated by XRD and SEM/EDS. Results show that the increase in CaO contents changes both species of vanadium-containing phase and the morphologies of vanadium-containing spinels in vanadium slags. Vanadium concentrates as (Mn,Fe,Mg)V₂O₄ in the spinel phase in vanadium slag with CaO content less than 10 mass%. When CaO content is higher than 12.89 mass%, vanadium exists both as (Mn,Fe,Mg)V₂O₄ in dendritic-like spinel and as Ca₃V₂(SiO₄)₃ in goldmanite in the matrix. Precipitation of perovskite results in the dendritic-like shape of spinels while V³⁺ diffusing away from spinel lattice leads to the formation of goldmanite Ca₃V₂(SiO₄)₃. Thermodynamic calculation of phase equilibrium has been conducted to understand the phase evolution. This work demonstrates the influence of CaO addition on the existence form of vanadium-containing phase in vanadium slag and thus provides the theoretical foundation for the proposed novel de-P & V-extraction process.