Influence of slag composition and oxygen potential on thermodynamic behavior of vanadium in FeO-TiO2-MgO-SiO2-Al2O3 smelting slag and molten iron

The influence of slag composition of FeO/TiO2 (=F/T) ratio, Al2O3/(SiO2+Al2O3) (=A/(S+A)) ratio and oxygen partial pressure ( p O 2 = 10 − 10 t o 10 − 9 a t m ) on the thermodynamic behavior of vanadium oxide in molten ilmenite smelting slag, i.e., FetO-TiO2-MgO-Al2O3-SiO2 system, was investigated at 1550 °C. The distribution ratio of vanadium (= L V ) between molten iron and FetO-TiO2-MgO-Al2O3-SiO2 slag increases with increasing F/T ratio, while it decreases with increasing A/(S+A) ratio. In addition, l o g L V generally increases with increasing theoretical optical basicity of the slag (= Λ s l a g ). Vanadium oxide (VOx) is expected to behave as an acidic component in the present system. Vanadium in ilmenite smelting slags primarily consist of V3+, V4+, and V5+ ions, as determined by Gaussian deconvolution of X-ray photoelectron spectra. A linear relationship between l o g ( w t % V 4 + / w t % V 3 + ) and l o g p O 2 is confirmed. Both (wt% V3+) and (wt% V5+) ions increase with increasing F/T ratio, whereas (wt% V4+) ions show the opposite behavior with increasing F/T ratio, irrespective of A/(S+A) ratio. Meanwhile, (wt% V3+) increase while (wt% V4+) and (wt% V5+) decrease with increasing A/(S+A) ratio. The linear relationship between l o g ( w t % V 3 + / w t % V 5 + ) and l o g ( w t % V 4 + ) has a slope of 1.8, which is good agreement with the theoretical slope of 2.0, which indicates that multi-valent vanadium ion species, i.e., V3+, V4+, and V5+, are thermodynamically balanced based on redox equilibria.