This study investigates ion partitioning and transport mechanisms within ionexchange membranes (IEMs) and their influence on electrodialysis (ED) permselectivity.Time-dependent partitioning measurements of monovalent cations into the membrane enabled the determination of partitioning rate constants (ki) and diffusion coefficients in the membrane (Di mem ) for H, Li, Na, K, and NH.A simulation model incorporating ion partitioning at the membrane surface and ion diffusion within the membrane was developed to analyze these processes.The obtained Di mem values exhibited an order (Li > NH > Na > K) that differs from the diffusion coefficients of the corresponding ions in aqueous solution (K = NH > Na > Li).The ED permselectivity showed a qualitative correlation with the ratio of ki but only a weak dependence on Di mem .This discrepancy is interpreted as distinct ion-transport directions and steric interactions in partitioning versus ED conditions.These findings demonstrate that time-dependent ion partitioning provides a powerful approach for quantifying membrane ion-transport parameters and for advancing mechanistic understanding of ion selectivity in ED.
Yu Sugimoto (Thu,) studied this question.