Kinetic modelling of the active transport of copper(II) across liquid membranes using thiourea derivatives immobilized on microporous hydrophobic supports

Abstract

The facilitated transport of CuII from chloride media through a flat-sheet supported liquid membrane (FSSLM) is investigated, using thiourea derivatives as ionophores, as a function of hydrodynamic conditions, concentration of copper (1–3×10-7 mol cm-3) and H+ (pH 0.1–2.5) in the feed solution, structure of carrier, carrier concentration (0.7–3×10-5 mol cm-3) in the membrane, strippant in receiving phase and support characteristics. A model is presented that describes the transport mechanism, consisting of diffusion through a feed aqueous diffusion layer, a fast interfacial chemical reaction, and diffusion of carrier and its metal complex through the organic membrane. The organic membrane diffusional resistance (Δo) and aqueous diffusional resistance (Δa) were calculated from the proposed model, and their values were 107×102 s cm-1 and 625 s cm-1, respectively. It was observed that the CuII flux across the membrane tends to reach a plateau at a high concentration of CuII or a low concentration of H+ owing to carrier saturation within the membrane, leading to a diffusion-controlled process. The values of the apparent diffusion coefficient (Doa) and limiting metal flux Jlim were calculated from the limiting conditions and found to be 2.9×10-6 cm2 s-1 and 1.4×10-9 mol cm-2 s-1, respectively. The values of the bulk diffusion coefficient (Do,b) and diffusion coefficient (Do) calculated from the model were 2.6×10-6 cm2 s-1 and 1.2×10-6 cm2 s-1. The polymeric microporous solid support, Durapure, was selected throughout the study as it gave the best performance.