The Effect of Al2O3, CaO and SiO2 on the Phase Relationship in FeO–SiO2 Based Slag with 20 Mass% Vanadium

An innovative and sustainable way for production of vanadium (V) is to co-process V titanomagnetite ores with V-bearing steel slag, via reduction. V-slag produced from highly enriched Fe–V melt contains as high as 20 mass% V. The phase relationship in FeO–SiO2 based slag with V fixed at 20.4 mass% was investigated experimentally at 1673 K. The compositions covered the normal production range, viz. Al2O3 from 0 to 6 mass%, CaO from 1 to 5 mass% and SiO2 from 10 to 17 mass%. The content of MnO was fixed at 5.5 mass%. Samples quenched at 1673 K were found to be solid–liquid mixtures, either in a 2-phase region consisting of liquid and a solid spinel phase, or in 3-phase region consisting of liquid, spinel phase and silica phase. Free silica was only found in samples with a composition of 0 mass% Al2O3, 1 mass% CaO and 17 mass% SiO2. Formation of free silica was prohibited in samples with 1 mass% CaO and up to 17 mass% SiO2 by adding 5 mass% Al2O3. Addition of 4 mass% Al2O3 was also sufficient to prevent the presence of free silica in samples with 3 mass% CaO and 13.5 mass% SiO2. Most of the V was kept in the spinel phase, while the solubility of V in the liquid was generally less than 1 mass% as V2O3. Fe, Mn and Al coexisted in both liquid phase and spinel phase. On the other hand, Si and Ca only distributed in the liquid phase. The fraction of solid phase, viz. spinel was found to decrease with increasing SiO2 content.