In the V₂O₅ production process, purification of vanadium-bearing solution plays an important role in determining the quality of the final product. The choice of purification method depends on the vanadium species, aqueous media, and associated impurities. In this review, the recent research results for the separation and recovery of vanadium from leaching solution with solvent extraction, ion exchange, and chemical precipitation separation are presented. The effects of the main operational parameters on the efficiency of purification with these three methods are compared and discussed respectively, and several problems existing in these processes are proposed.

The isothermal and non-isothermal oxidation kinetics of a converter vanadium slag in the presence of calcium oxide was studied using thermal analysis. The isothermal experimental data for the whole oxidation process are described in terms of the equation [1− (1−α)^2/3] = kt with E_a = 20.42 kJ mol^–1 at lower temperatures of 400-500 °C, and described by [(1−α)^–1/3−1]² = kt with E_a = 227.66 kJ mol^–1 at temperature higher than 500 °C. In the nonisothermal oxidation study, heating rate greatly affects the oxidation process. Using a heating rate of 3 °C min^–1 results in overlapping oxidations of vanadium spinel and augite over temperature range of 608-959 °C, which is described by the 3/2 order reaction. Increasing the heating rate to 5 °C min^–1 or 10 °C min^–1, only oxidation of vanadium spinel takes place in temperature range of 657-914 °C and 691-954 °C respectively, both described by the third order chemical reaction. As the slag particle decreases from 250 µm to 48 µm, the kinetic equation for describing the overlapping oxidation process changes from the Anti–Zhuravlev equation with internal diffusion controlling to reaction limiting equations.

Converter vanadium slag is a byproduct of the iron making process when the vanadium titanomagnetite is used as iron raw material. A cleaner process including calcified roasting, dilute acid leaching, precipitation purification, vanadium precipitation with ammonium salt, followed by thermal decomposition was proposed to extract vanadium resource from this slag. And then vanadium pentoxide with purity over 98% was prepared, which can be used as additives for high strength low alloy steel production. A total vanadium recovery beyond 80% was achieved in this whole process. Since no sodium and potassium salt was introduced, wastewater generated was closed-circulating after removing the enriched impurities of P, Si, Ti and Cr with adding powder CaO. The content of V₂O₅ in residues after vanadium extraction was lower than 1.2 wt.%, while other valuable metals like Fe, Mn, Cr and Ti were concentrated. With no alkaline metal salts added in this process, the metal resources of Fe, Mn, Cr and Ti in the residues were more feasible to be recovered with pyrometallurgy processes.