Technique of supported liquid membranes (SLMs) for the facilitated transport of vanadium ions (VO2+): Parameters and mechanism on the transport process

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 (VO2+) 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 J0 for the transport of the VO2+ 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 J0 is related to the initial substrate concentration C0 in the feed phase by a saturation law, which allowed the determination of the apparent diffusion coefficients D* and the association constants Kass 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 Kass), depend certainly on the acidity of the medium and probably the concentration of co-ions NO3−.