Efficient and selective transport of rhodium(III) across a polymer
inclusion membrane (PIM) from a 0.1 mol dm–3 HCl
feed solution, also containing iron(III), to a receiving solution
containing 0.1 mol dm–3 HCl and 4.9 mol dm–3 NH4Cl was achieved using a phosphonium-type ionic liquid,
trioctyl(dodecyl)phosphonium chloride (P88812Cl), as the
metal ion carrier. The optimum PIM composition for the Rh(III) transport
was 50 wt % poly(vinylidene-co-hexafluoropropylene) (PVDF-HFP), 30
wt % P88812Cl, and 20 wt % plasticizer 2-nitrophenyl octyl
ether (2NPOE). The driving force for the Rh(III) transport was suggested
to be the concentration difference of the chloride ion between the
feed and the receiving solutions. More than 70% rhodium(III) could
be recovered from the receiving solution, and no transport of iron(III)
was observed; however, the two metal ions cannot be separated by liquid–liquid
extraction. This is the first report of selective transport of rhodium(III)
across a polymer inclusion membrane.