Differential adsorption of vanadium(V) and tungsten(W) on ion exchange resins: A novel approach for separation and recovery of spent catalyst leachate

Vanadium (V) and tungsten (W) are essential metals for various industries, but separating them is challenging due to the molecular similarity of the two metal ions. A highly concentrated mixed solution of V and W is obtained from spent selective catalytic reduction (SCR) catalysts, but their complete recycling is impeded by the difficulty of separating V and W. In this study, we investigate the ion exchange resin (IXR) technique's effectiveness for separating V and W from the leaching solution of spent catalysts. We evaluated the performance of three IXRs: Lewatit MP800 (strong basic), MP62WS (medium basic), and TP260 (weak acidic) for the separation of V and W ions in the solution. Among these IXRs, MP800 exhibits V and W ion separation behavior at pH 14. It selectively adsorbs W ions, while V ions demonstrate low affinity for adsorption on MP800. The primary mechanism for the adsorption of V and W ions appears to be an ion exchange reaction on the quaternary ammonium group of MP800. Conversely, MP62WS, which adsorbs V and W ions through both ion exchange and chelation mechanisms, does not separate V and W ions effectively when the solution's pH is controlled. The adsorbed W ions on MP800 can be completely regenerated with 2 M NaCl solution through re-ion exchange. We also conducted dynamic column operations using a simulated spent catalyst leaching solution (V = 600 mg/L, W = 4000 mg/L) with MP800 at pH 14. The successful separation of V and W was achieved for up to 15 bed volumes (BV). Finally, we performed V and W separation using an actual spent catalyst leaching solution. MP800 displayed a notably high separation factor (αVW) of 19.59, highlighting its effectiveness in separating V and W.