Separation of tungsten and molybdenum with solvent extraction using functionalized ionic liquid tricaprylmethylammonium bis(2,4,4-trimethylpentyl)phosphinate

Functionalized ionic liquids (FILs) as extractants were employed for the separation of tungsten and molybdenum from a sulfate solution for the first time. The effects of initial pH, extractant concentration, metal concentrations in the feed were comprehensively investigated. The results showed that tricaprylmethylammonium bis(2,4,4-trimethylpentyl)phosphinate (A336Cyanex272) could selectively extract W over Mo at an initial pH value of 5.5; the best separation factor β_W/Mo of 25.61 was obtained for a solution with low metal concentrations (WO₃: 2.49 g/L, Mo: 1.04 g/L). The A336Cyanex272 system performed effectively for solutions of different W/Mo molar ratios and different metal ion concentrations in the feed. The chemical reaction between A336Cyanex272 and W followed the ion association mechanism, which was further proved by the Fourier-transform infrared (FTIR) spectra of loaded A336Cyanex272 and the free extractant. The stripping experiments indicated that 95.48% W and 100.00% Mo were stripped using a 0.20 mol/L sodium hydroxide solution. Finally, the selective extractions of W and Mo from two synthetic solutions of different high metal concentrations were obtained; the separation factor β_W/Mo reached 23.24 and 17.59 for the first and second solutions, respectively. The results suggest the feasibility of A336Cyanex272 as an extractant for the separation of tungsten and molybdenum.