Ion Transport through Diffusion Layer Controlled by Charge Mosaic Membrane

The kinetic transport behaviors in near interface of the membranes were studied using commercial anion and cation exchange membrane and charge mosaic membrane. Current-voltage curve gave the limiting current density that indicates the ceiling of conventional flux. From chronopotentiometry above the limiting current density, the transition time was estimated. The thickness of boundary layer was derived with conjunction with the conventional limiting current density and the transition time from steady state flux. On the other hand, the charge mosaic membrane was introduced in order to examine the ion transport on the membrane surface in detail. The concentration profile was discussed by the kinetic transport number with regard to the water dissociation (splitting) on the membrane surface. 1. Introduction It is well known that electrodialysis using ion exchange membrane makes drinking water or table salt from sea water.In Japan especially it is popular to use this electrodialysis in various fields such as food, medical pharmacy and ultrapure water [1–3]. However, the more efficient and improved electrodialysis have been required for pure water production because conventional system costs much of electric power at present. One of the main problems originates from the limiting current density that restricts the direct current for supplying through the system and depends on the thickness of diffusion layers. In this study, the way to see the thickness of the depleted solution layer was examined in order to improve the efficiency on the electrodialysis from fundamental standpoint. As mentioned above, the aim will be focused on the ionic behavior of ion transport from bulk solution to membrane surface. In addition, so far developed charge mosaic membrane [4–6] is introduced into electrodialysis model system and the ion transport mechanism is investigated. As experimental strategies, electrical methods were mainly adopted, and 4 kinds of membrane systems were selected to study: cation exchange membrane system (CMV), anion exchange membrane system (AMV), charge mosaic membrane and cation exchange membrane system (MM？+？CMV), and anion exchange membrane and charge mosaic membrane system (AMV？+？MM). The potentiometry was also used on the same membrane systems to elucidate the diffusion layer. The chronopotentiometry has been carried out to obtain the transition time [7–9]. The technique was adopted for 4 membrane arrangements to examine the contribution to the boundary layer of the charge mosaic membrane. The kinetic parameter about the boundary layer was noticed