Green and Efficient Recovery of Tungsten from Spent SCR Denitration Catalyst by Na2S Alkali Leaching and Calcium Precipitation

Selective catalytic reduction (SCR) catalyst of V₂O₅-WO₃/TiO₂ type is widely used in industrial denitration process. Deactivated spent SCR denitration catalyst can be used for tungsten recovery. In the existing hydrometallurgical recovery processes, NaOH leaching and Na₂CO₃ leaching need high temperature and high pressure to obtain high leaching efficiency of tungsten, and they have the disadvantages of large reagent consumption, high impurity leaching efficiency, and high equipment requirements. In this paper, tungsten is recovered from the reductive leaching residue of spent SCR denitration catalyst (LRDC) using Na₂S as leaching agent after vanadium recovery is achieved, and it can achieve higher tungsten leaching efficiency, lower impurity leaching efficiency, and lower energy consumption under the low alkalinity condition. The thermodynamics, leaching behaviors, and kinetics of tungsten alkali leaching process are investigated respectively, and the leaching efficiency of tungsten reaches 82.03% under the optimum conditions. After circulating leaching, oxidation, and neutralizing precipitation, tungsten is precipitated by adding CaCl₂, and the precipitation efficiency of tungsten can reach 94.45% under the optimum conditions. The chemical composition of CaWO₄ product meets the requirements of GB5192-85 for impurity content of II-class synthetic scheelite.