Regeneration Mechanism of Ion Exchange Materials in Electrodeionization System

The regeneration mechanism of an ion exchange fabric inserted between the ion exchange membranes in the electrodeionizer has been investigated. The ion exchange fabric comprising cation- and anion-exchange fibers was introduced into the diluting compartment of a five-compartment electrodialysis cell. A significant pH change occurred in the adjacent concentrating compartments when a voltage was applied, probably due to migration of H+ and OH− ions generated by water dissociation in the diluting compartment filled with the ion-exchange fabric. By observing the color change in the ion-exchange fabric adsorbed with phenolphthalein, the water dissociation was found to occur at the boundary between the ion-exchange fabric and an ion-exchange membrane. These findings suggest that water molecules dissociate drastically under a strong electric field at the electrical double layer on the surface of ion-exchange membrane, and the H+ and OH− ions thus formed regenerate the ion-exchange material.