Recovery of tungsten compounds from spent tungstophosphate catalyst using leaching, solvent extraction with phosphonium-based ionic liquids and precipitation

A novel hydrometallurgical process involving leaching, precipitation, solvent extraction (SX) using phosphonium-based ionic liquids (ILs), and crystallization stripping was developed in this study. First, the spent catalyst was completely leached in distilled water at 343 K for 24 h. The leaching percentage of W(VI) was > 99.9% according to ICP/SEM/EDX analysis. After leaching, the phosphate ions were separated by precipitation using Fe(NO3)(3)& BULL;9H(2)O as the precipitating agent. The separation percentage of phosphate was 90.8% at pH 8.11 according to ion-chromatography (IC) analysis. After the removal of phosphate, Alamine 336 and triethyl-n- pentyl phosphonium bis(trifluoromethylaulfonyl)amide ([P-2225][NTf2]) were used as the extractant and diluent, respectively, for SX. The extraction percentage (E) of W(VI) reached 94.6% at pH 1.03, and the separation factor, W/P, was 101. The extraction mechanism of W(VI) was based on the ion association reaction related to the extracted complex, [(R3NH)(n)HxWyOz](IL), where x, y, z, and n are pH-dependent stoichiometric coefficients. After SX, the stripping percentage of W(VI) reached 100% at pH 8. Finally, crystallization proceeded at pH & AP;4.5, and the obtained precipitate was identified to be ammonium paratungstate (NH4)(10)(H2W12O42)& BULL;4H(2)O by XRD analysis. A series of novel hydrometallurgical processes using ILs led us to conclude that W(VI) was efficiently recovered from the spent tungstophosphate catalyst.