Tungsten Recovery from Spent SCR Catalyst Using Alkaline Leaching and Ion Exchange

The recovery of tungsten (W) from a honeycomb-type spent selective catalytic reduction (SCR) catalyst using an alkaline leaching-ion exchange method was investigated. Spent SCR catalyst mainly consists of TiO2 and other oxides (6.37% W, 1.57% vanadium (V), and 2.81% silicon (Si), etc.). The ground catalyst was leached at the optimal conditions, as follows: NaOH concentration of 0.3 kg/kg of catalyst, pulp density of 3%, leaching temperature of 70 degrees C, particle size of -74 mu m, and leaching time of 30 min. In this study, the leaching rate values of V and W under the above conditions were 87 wt %, and 91 wt %, respectively. The pregnant solution was then passed through a strong base anion exchange resin (Amberlite IRA900). At high pH conditions, the use of strong base anion exchange resin led to selective loading of divalent WO42- from the solution, because the fraction of two adjacent positively-charged sites on the IRA900 resin was higher and separate from the coexisting VO43-. The adsorbed W could then be eluted with 1 M NaCl + 0.5 M NaOH. The final concentrated W solution had 8.4 g/L of W with 98% purity. The application of this process in industry is expected to have an important impact on the recovery of W from secondary sources of these metals.