Prediction of ion concentrations in ion exchange membranes in multivalent, multicomponent ion systemsPrediction 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 Qi values representing the affinity between the membrane and ions, as well as the fixed charge density. Here, membrane-specific Qi values for each ion were determined from partition experiments. Using the Qi 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.