On cadmium (II) membrane-based extraction using Cyanex 923 as carrier

The facilitated transport of cadmium (II) from HCl medium by Emulsion Pertraction Technique (EPERT), using Cyanex 923 (phosphine oxides mixture) as ionophore, is investigated as a function of various experimental variables: hydrodynamic conditions, concentration of cadmium (II) (5 - 100 mg L(-1)) and HCl (0.2-5 M) in the source phase, carrier concentration (5-40% v/v) and diluent in the organic phase. A model that describes the transport mechanism is derived, consisting of diffusion through a source aqueous diffusion layer, a fast interfacial chemical reaction, and diffusion of the carrier and the metal complexes through the membrane. The thickness of the source phase boundary layer was calculated as 2.2 x 10(-3) cm. The organic membrane diffusional resistance (Delta(org)) and aqueous diffusional resistance (Delta(aq)) were calculated from the model, and their values were 1.0 x 10(7) s cm(-1) and 347 s cm(-1), respectively, whereas the values of the bulk diffusion coefficient (D(org,b)) and diffusion coefficient (D(org)) also calculated from the model were 4.8 x 10(-9) cm(2) s(-1) and 1.3 x 10(-9) cm(2) s(-1). The separation of Cd(II) against Zn(II), Fe(III), Cr(VI) and Cu(II) and also the performance of the system in relation with other extractants were evaluated.