Kinetic modelling of the facilitated transport of cadmium (II) using Cyanex 923 as ionophore

The facilitated transport of cadmium (II) from chloride through a flat-sheet supported liquid membrane is studied, using Cyanex 923 (phosphine oxides mixture) as ionophore, as a function of various experimental variables: hydrodynamic conditions, concentration of cadmium (II) (0.01–0.08 g l−1) and HCl (0.1–5 M) in the feed phase, carrier concentration (2.5–40%, v/v) and diluent in the membrane phase. A model is derived that describes the transport mechanism, consisting of diffusion through a feed aqueous diffusion layer, a fast interfacial chemical reaction, and diffusion of carrier and the metal complexes through the organic membrane. The organic membrane diffusional resistance (Δorg) and aqueous diffusional resistance (Δaq) were calculated from the model, and their values were 196145 and 260 s cm−1, respectively, whereas the values of the bulk diffusion coefficient (Dorg,b) and diffusion coefficient (Dorg) also calculated from the model were 2.4 × 10−7 and 6.4 × 10−8 cm2 s−1. The separation of Cd(II) against Zn(II), Fe(III), Co(II) and Cu(II) is evaluated.