Study of Reductive Leaching of Vanadium from Spent Vanadium Catalysts

The development of efficient technologies for processing secondary technogenic raw materials represents a promising approach to replenishing vanadium resources. This study investigates the processes of sulfuric acid reductive leaching of vanadium from spent vanadium catalysts using oxalic acid and metallic iron as reducing agents. It was established that oxalic acid provides vanadium extraction of up to 95.2%, whereas the use of metallic iron (2–3 wt.% of the catalyst mass) enables a vanadium recovery rate of 91–92% at a solid-to-liquid ratio of 1:7 and pH 1.3–1.5, offering a more cost-effective alternative. Thermodynamic modeling of the V–Fe–P–SO4–C2O4–H2O system was performed using the Medusa software package over a pH range of 0–3. The results showed that vanadium(IV) predominantly exists as the VOSO4 complex in sulfuric acid solutions, whereas the formation of oxalate and phosphate complexes is thermodynamically insignificant. Iron(III) was found to exhibit a strong affinity toward phosphate ions, promoting their selective precipitation as an iron phosphate phase while maintaining vanadium in solution. The obtained results provide a scientific basis for the efficient preliminary separation of iron and vanadium and for improving the selectivity of subsequent vanadium sorption.