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 ultralow 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.