Preparation of V2O5 using Pb5(VO4)3OH recovered from Bayer vanadium sludge through H2SO4 pre-treatment, H2O2 leaching, V5O12∙6H2O and V10O24∙12H2O precipitation and oxidative roasting at 400 °C

Bayer vanadium sludge (BVS), discharged during the Bayer alumina production, is a promising secondary resource for the supply of vanadium. Previous vanadium extraction process involving Pb₅(VO₄)₃OH precipitation by PbSO₄, H₂SO₄ and (NH₄)₂SO₃ leaching, (NH₄)₂S₂O₈ oxidation followed by ammonium vanadate precipitation, suffered from large amounts of reagent consumption and discharge of ammonia-containing waste. In this study, a cleaner and cost-efficient process based on H₂SO₄ pre-treatment, H₂O₂ leaching, hydrolytic precipitation, and preparation of V₂O₅ through oxidative roasting was proposed to reduce reagent consumption and waste. Results show that the maximum vanadium leaching efficiency reached 99.7 % under the most suitable conditions of H₂SO₄ pre-treatment with H₂SO₄/Pb₅(VO₄)₃OH molar ratio of 6.5, pulp density of 250 g/L at 90 °C for 4 h followed by H₂O₂ leaching with H₂O₂/V molar ratio of 3.0 at 15 °C for 10 min. Furthermore, 96.5 % of vanadium was precipitated in the forms of V₅O₁₂∙6H₂O and V₁₀O₂₄∙12H₂O by heating the leach liquors to 100 °C for 60 min, followed by the oxidative roasting at 400 °C for 2 h to prepare V₂O₅ product with a purity of 99.2 %, with only H₂O as a by-product. This research provides new insights into vanadium extraction in a cleaner, cost-efficient, and sustainable industrial process which saves 147.4 $/t Pb₅(VO₄)₃OH.