Vanadium Recovery from Spent SCR Denitration Catalyst by Reductive Acid Leaching and Ammonium Precipitation

The selective catalytic reduction catalyst commonly used in denitration in industry will be transformed into non-renewable spent SCR denitration catalyst (SSDC) after long-term use and deactivation. The SSDC is considered a potential secondary resource for recovering rare metal vanadium. Because trivalent/tetravalent vanadium has a higher solubility than pentavalent vanadium in an acidic solution, reductive acid leaching is more conducive to recovering vanadium from SSDC than direct acid leaching. The study of “reductive acid leaching-circulating leaching and oxidation-ammonium precipitation” was systematically carried out for the efficient recovery of vanadium from SSDC. First, the thermodynamics, leaching behaviors, and kinetics of the vanadium reductive leaching process were studied in the H₂SO₄-Na₂SO₃ system. The effects of leaching parameters on the vanadium leaching behaviors were explored. The vanadium leaching efficiency reaches 88.26% under the best experimental conditions. The leaching process of vanadium matches the Johnson-Mehl-Avrami dynamic model, and the Avrami index is 0.133, which indicates this process belongs to internal diffusion control. After circulating leaching and oxidation, vanadium was precipitated by adding (NH₄)₂SO₄, and the vanadium precipitation efficiency reached 84.87% under the optimal conditions. The purity of V₂O₅ product prepared by high-temperature calcination of ammonium polyvanadate can reach 99.96%.