Prediction of ion concentrations in ion exchange membranes in multivalent, multicomponent ion systems

Ion exchange membranes (IEMs) play an important role in membrane separation processes such as electrodialysis and reverse electrodialysis. In these processes, seawater is often used as the feed solution; however, the analysis of ion selectivity in multivalent, multicomponent systems such as seawater is complex, and the current understanding remains insufficient. As a result, variability in reported values and a lack of comprehensive discussion have become significant issues. In this study, focusing on partition selectivity, a simulation model for ion concentrations within membranes applicable to multivalent, multicomponent systems was developed. This model describes ion behavior within the membrane based on Donnan equilibrium theory and the condition of electroneutrality, using membrane-specific values representing the affinity and the ion activity coefficient between the membrane and ions, as well as the fixed charge density. Here, membrane-specific values for each ion were determined from partition experiments. Using the values, simulations of the relationship between ion concentrations within an IEM and those in the external solution for different mixed ion systems quantitatively reproduced the experimental results. • Membrane ion concentrations were predicted using membrane-specific parameter Qi values • Calculated values using Qi showed quantitative agreement with experimental values • Optimization of partition experiments enabled accurate measurement of ion concentration. • Higher affinity of K+ than Na+ was confirmed in commercial CEM. • Higher affinity of NO3- than Cl- was confirmed in commercial AEM.