Effect of Electric Field in the Treatment Giving Low Permeability for Bivalent Ions to Cation Exchange Membrane

Studies on the Treatment Giving Low Permeability for Bivalent Ions in Electrodialytic Concentration Using Ion Exchange Membrane (Part 6)

Abstract

Mixed solution of aqueous 0.25 N NaCl and aqueous 0.25 N CaCl₂was electrodialyzed using a small electrodialyzer. Cation exchange membranes were treated by a reagent of organic electrolyte with applied current or without applied current.
When the membranes were treated with applied current, permselectivity coefficientT^Ca_Nadecreased remarkably, but dissociation of water occured readily on the membrane surfaces. Treatment without applied current showed a few decreases inT^Ca_Na, but dissociation of water scarcely occured. Electric resistance of the treated membrane increased with the increase of the ratio of bivalent ions in the solution. This phenomenon was considered to depend on the increase of the electric resistance of the membrane and the reagent layer formed on the membrane surface. In order to evaluate the effects of electric field in the treatment, Nernst-Planck equation was applied and transport of reagent ions across a diffusion layer in desalted side of the membrane was examined. Consequently, it was understood that the concentration of the reagent in the reagent layer increased with the increase in current density, so that electric field enhanced the effects of the treatment.