Process Optimization of Slag Composition for Improved Vanadium Recovery and Slag–Iron Separation in V–Ti Magnetite Smelting

Abstract

South African vanadium–titanium magnetite is predominantly composed of lump ore and is characterized by relatively high Fe, V, and Ti contents, indicating its potential advantages for comprehensive utilization and value-added processing. However, its utilization is challenged by issues such as viscous slag, iron entrainment, and slag foaming during smelting. In this study, a combination of thermodynamic calculations and experimental investigations was employed to analyze the phase assemblage and phase equilibrium relationships under various slag compositions, with the aim of identifying a slag system with relatively low melting point and low viscosity, high vanadium recovery, and good slag–metal separation. Thermodynamic results indicate that, to maintain the slag phases predominantly within the pseudobrookite stability region while keeping the liquidus temperature low, the optimal composition was determined to be TiO₂: 48–52 wt.%, SiO₂: 14–18 wt.%, Al₂O₃: 10–14 wt.%, CaO: 10–14 wt.%, and MgO: 8–12 wt.%. Investigation of vanadium–titanium partitioning between slag and metal revealed that vanadium precipitates as Ca₂V₂O₇ only when the smelting temperature is below 900°C. Experimental results show that, for a slag system with low melting temperature, low viscosity, and high vanadium–titanium partition ratios between slag and metal, the smelting temperature should be controlled at 1550°C with a holding time of 60 min, yielding an average vanadium recovery of 82.4% and an average TiO₂ content of 46.25% in the slag. This study proposes an optimized slag formulation, elucidates the vanadium–titanium partitioning mechanism, and provides a sound theoretical basis for slag system optimization in the electric furnace smelting of South African vanadium–titanium magnetite.