Complete removal of trace vanadium from ammonium tungstate solutions by solvent extraction

The complete removal of trace vanadium from ammonium tungstate solutions by solvent extraction using a quaternary ammonium salt with bicarbonate type as extractant was investigated. The effects of organic composition, equilibrium pH and A/O ratio on the extraction and stripping were studied. The metal extraction and stripping isotherms were plotted and the simulation multi-stage counter current extraction and stripping tests were conducted. The results showed that the vanadium can be more easily extracted over tungsten from ammonium tungstate solutions, dropping vanadium to 0.004 g/L with tungsten loss below 5% after six-stage counter current extraction with an organic solvent consisting of 1% (v/v) Aliquat336 and 5% (ν/ν) 2-octanol and a feed containing 100.0 g/L W(VI) and 0.42 g/L V(V) with an A/O ratio of 1/1.25 at pH 8.74 and 25 °C for 10 min. The extracted vanadium(V) species of V2W4O194− in loaded organic solution was identified by the combination of thermodynamic analysis and saturation methods, and FTIR spectral analysis. The vanadium(V) in loaded organic was easily stripped and enriched using 2 mol/L NaOH solution with an A/O ratio of 1/15 in a four-stage counter current stripping, and the stripped organic could also be recycled to extraction after regeneration with ammonium bicarbonate solution.