Micellar-enhanced electrodialysis: Influence of surfactants on the transport properties of ion-exchange membranes

Thin layers of ionic surfactants were formed on the surfaces of ion-exchange membranes by adsorption with electrostatic interactions and were conformed by FTIR spectra. The effect of the adsorption on the transmission characteristics were investigated by membrane resistance and permselectivity studies, and it was found that adsorption of cationic surfactant onto the cation-exchange membrane and anionic surfactant onto the anion-exchange membrane associated with the increase in membrane resistance while decrease in membrane permselectivity, which became limiting beyond the critical micelle concentration of respective surfactant. Based on the studies schematic model for the orientations of surfactant molecules on the membranes surfaces under the electrodialytic conditions was presented. Improvement in the electrodialysis (ED) process efficiencies was observed due to the adsorption of the ion-exchange membranes surfaces because of the reduction in the concentration gradient between dilute and concentrated compartments of the ED unit, and thus back diffusion. This phenomenon is also schematically presented by the concentration profiles across the ion-exchange membranes under the electrical gradient in the polarized conditions. Based on the experimental results so called micellar-enhanced electrodialysis has been proposed for the efficient electrolyte separation up to very low concentration (with high purity) with reduced energy consumption, concentration polarization and improved limiting current density.