Kinetic aspects of Donnan dialysis through Nafion-117 membrane

The transport rate of ions across Nafion-117 ion-exchange membrane in a Donnan dialysis process has been measured for mono–monovalent (Na+–Cs+) and mono–bivalent (Na+–Ba2+, Na+–Mg2+) ion-exchange process. This has been carried out for different salt concentrations (0.01 M, 0.1 M and 0.5 M). The transport rate has also been calculated using appropriate form of Nernst–Planck equation. The self-diffusion coefficients of the ions and the ion-exchange capacity of the membrane have been given as input parameters in the calculations. The concentration of ions at the solution/membrane interface has been obtained from solution concentrations by the use of Donnan relation. The calculated time profile has been found to match with the experimental time profile at 0.1 M and 0.5 M salt concentrations. At 0.01 M concentration, there is significant deviation between the two profiles, probably showing the change in selectivity of the membrane with decrease in salt concentration. The experimental and the NP calculations have been compared with the calculations based on mass balance approach as given by Miyoshi (1996, 1997, 1998) . The NP calculations coupled with the experimental time profile, have been used to obtain the self-diffusion coefficient of Mg2+ ion in Nafion-117 membrane.