Modification of the ionic composition of salt solutions by electrodialysis

The present work investigated the separation properties through monovalent-ion-permselective membranes (Neosepta CMX-S, ACS) in electrodialysis. An experimental study for desalting single electrolytes, binary and ternary mixtures, was carried out. Results showed that divalent-ion rejection takes place simultaneously with a number of different transport mechanisms. Electrostatic effects between solutes and the membrane were examined in desalting experiments involving single electrolytes. The trends observed in mixed-salt-solution experiments were interpreted in terms of physicochemical properties of ions and characteristics of the ion-exchange membranes used.

The aim of this work was to contribute to the identification of ion mechanism transfer in electrodialysis on monovalent ion permselective membranes. The experimental study done on single salt solutions showed that permselectivity of divalent anions through ACS membranes is mainly governed by hydration energy of anions. For CMX-S membranes having an oppositely charged layer on their surface, permselectivity is due to electrostatic repulsion force more strongly opposed to divalent cations than the monovalent ones. Besides membrane properties and ion hydration energy, experiments carried out on mixtures of electrolytes showed that low mobilities of divalent ions in the membrane phase and the Donnan effect play a determining role in ion extraction.