Selective vanadium extraction by reductive acid leaching from ultra-low vanadium spent V2O5-WO3/TiO2 catalysts

Spent V₂O₅-WO₃/TiO₂ catalyst is a harmful but valuable secondary resources. Efficient recovery of vanadium from spent V₂O₅-WO₃/TiO₂ catalyst is still a great challenge. Here, a selective leaching and enrichment route of vanadium from ultra-low vanadium spent V₂O₅-WO₃/TiO₂ catalyst is proposed by reductive acid leaching using clean oxalic acid and iron salt precipitation. The composition, structure and element valence of spent V₂O₅-WO₃/TiO₂ catalyst are firstly characterized. Thermodynamic calculations of V-H₂SO₄-H₂O system are carried out to determine the existence form of vanadium and reaction feasibility between vanadium oxides and acid. It is found that oxalic acid is more efficient reducing agent in acidic solution for the conversion of V(5+) to V(4+). According to potential-pH diagram of V-H₂SO₄-H₂O system, high temperature and low pH bring about high reducing potentials of V(5+) to V(4+). The effects of temperature, liquid-to-solid ratio, H₂SO₄ concentration and leaching time on the leaching rate of V are investigated. At optimal conditions, the leaching rate of V from ultra-low vanadium spent V₂O₅-WO₃/TiO₂ catalyst reaches 90.13 %, and vanadium concentration in the leach solution is 1.23 g/L. By the iron salt precipitation, vanadium-rich slag with vanadium content of 25.08 wt% is obtained and a high-quality raw material for further vanadium extraction.