Selective removal of specific anions using composite carbon electrodes coated with an anion-exchange resin powder

The selective removal of specific ions was explored by using a capacitive deionization (CDI) system with a selective composite carbon electrode (SCCE). An SCCE was manufactured by coating a carbon electrode with anion-exchange resin (AER) powders. The correlation between the characteristics of the AERs and ion selectivity was analyzed, and the ion selectivity of the SCCE was verified through CDI experiments with a mixed solution of chloride, nitrate, and sulfate ions. The adsorption equilibrium results of the AERs showed that the ion selectivity of an AER was greatly influenced by its ion-exchange capacity (IEC). The higher the IEC value was, the higher the selectivity for the divalent sulfate ion, whereas the smaller the IEC was, the higher the selectivity for the nitrate ion. The CDI experimental results show that the equivalent fraction of ions adsorbed to the SCCE was consistent with the result of the adsorption equilibrium test. Therefore, the ion selectivity of the SCCE was governed by the ion selectivity of the AER coated on the electrode surface. Notably, as the current density applied to the cell increased, the AER could not maintain an adsorption equilibrium state, which resulted in a decrease in the ion selectivity of the SCCE.