Mechanism on the Separation of Vanadium and Titanium from Vanadium Slag by Roasting with Ammonium Sulfate

The technology of simultaneously recovering V and Ti from vanadium slag via ammonium salt roasting has proven to be an efficient route. However, due to the phase stability and complex chemical composition of vanadium slag, intermediate materials containing Fe, V, Ti and Mn are difficult to be characterized critically. This work aims to investigate the decomposition and transformation of vanadium slag during ammonium salt roasting, using a combination of FT-IR, XRD, XPS and SEM techniques. It was found that the lattice structure of Fe-contained spinel would be transformed from FeV2O4 to Fe2+VnFe2−nO4 (0 < n < 2) during directly roasting in the air. However, there is no obvious change for Ti-contained and Mn-contained spinel. Using NH4HSO4 (ABS) as an additive and roasting the slag in the N2 atmosphere, those spinels would be decomposed into various sulfate salts. Meanwhile, when the slag was roasted with NH4HSO4 in the air, a part of Fe(II) in (NH4)2Fe(SO4)2 would be transferred into Fe(III), but V(III), Ti(IV) and Mn(II) from those salts would remain the same valance state. Ultimately, about 88% V and 81% Ti were recovered, when vanadium slag was roasted at 663.15 K with a 1:5 ratio of slag-to-NH4HSO4 and followed by 8 vol.% H2SO4 leaching.