Selective extraction of vanadium from chromium by pure [C8mim][PF6]: An anion exchange process

Separations among vanadium(V) and chromium(VI) remain challenging. The extraction behaviors of V(V) along with Cr(VI) by a few of pure imidazolium-based hydrophobic ionic liquids have been investigated. Among these hydrophobic ionic liquids, [C(8)mim][PF6] exhibits a special extraction for V(V) while a weak extraction for Cr(VI). The extraction behavior of V(V) by [C(8)mim][PF6] was particularly studied. The extraction of V(V) is strongly dependent on the acidity of the aqueous phase, and the maximum separation factor between V and Cr (beta(V/Cr)) was calculated to be 100.6 in case of pH 3.5. The most probable extraction mechanism of V(V) has been proposed to be the anion exchange between the main species HV10O273- and PF6-. Furthermore, V(V) in IL phase can be quantitatively stripped by KPF6 solution under the basic condition (C-OH(-) = 1 mol/l). Recycle test indicates that the extraction capacity shows no apparent decline until the 9th continuous extraction-stripping cycle. The result also provides a new approach for the preparation of a novel ionic liquid with metal oxo-anions as counter anion. (C) 2014 Elsevier B.V. All rights reserved.