Abstract
Electrodialytic equipments with ion exchange membranes have been mainly used for separating and refining operations of brackish water; that is, concentrating or desalting. When these electrodialytic equipments are operated under the conditions which are more than the limiting current density, it is well known that the, excessive electric current deteriorates the properties of the ion exchange membranes.
From this reason, many studies have so far been made to predict the limiting current density. One is the approach made by Rosenberg et al. and Cowan et al. without spacers in the electrodialytic stack, and another is the approach by Kitamoto et al. with spacers. However, it seems that an agreed view has not given yet about the limiting current density.
In this paper, as an approach to predict the limiting current density, the concentration distribution within the ion exchange stack without spacers was estimated for the case that the ion exchange liquid flows in laminar under the steady state in the electrodialytic equipment with ion exchange membranes, and the estimating equation for the limiting current density was proposed.
On the limiting current density, the effects of ion exchange membranes, electrolytes, concentration of feed solution and flow rates were checked under various conditions.
It was found that both Eq.(26) of present work and Eq.(27) of Rosenberg et al. agreed approximately with experimental data in laminar region and that they may be applied to the estimation of the limiting current density.
