Technique of supported liquid membranes (SLMs) for the facilitated transport of vanadium ions (VO 2+) : Parameters and mechanism on the transport process

Abstract

Two supported liquid membranes (SLMs) containing two different carriers but formed by the same polymer support polyvinylidene difluoride ( PVDF ) and the same organic phase (xylene), were used to realize the facilitated transport of vanadium ions (VO 2 +) from the concentrated acid solutions. The SLM support was a micro porous PVDF polymer film of thickness 100 µm with pore size 0.45 µm which has been impregnated with a solution of xylene containing 0.01 M of one of the carriers, the Di-(2-ethylhexyl) phosphoric acid ( D2EHPA ) or the Trioctylphosphine oxide ( TOPO ). The permeabilities P and the initial fluxes J 0 for the transport of the VO 2 + ions were calculated from the proposed kinetic model for the two SLMs used. These two macroscopic parameters depend on both the concentration of the carrier ( T) and that of the substrate ( S) to be transported. The proposed mechanism indicates the formation of a complex (1/1) carrier–substrate (TS), and the migration of this complex through the organic phase of the SLM, is the rate-determining step in the transport mechanism. The initial flux J 0 is related to the initial substrate concentration C 0 in the feed phase by a saturation law, which allowed the determination of the apparent diffusion coefficients D* and the association constants K ass of the complexes (TS), formed in the organic phase of the two studied SLMs. These results clearly indicate that the values of these two microscopic parameters ( D* and K ass), depend certainly on the acidity of the medium and probably the concentration of co-ions NO 3 −.