Chapter 6 Ion-exchange and electrodialysis ALISTAIR S. GRANDISON, Department of Food Science and Technology, The University of Reading, Reading RG6 6AP, UK Ion-exchange and electrodialysis are distinct methods of separation, but can conveniently be treated together, as the basic criterion for separation in both cases is the molecular electrostatic charge. While ion-exchange involves retention of ionised solutes on a solid support material, electrodialysis permits the separation of ions using selective ion exchange membranes 6.1 ION-EXCHANGE Ion-exchange methods can potentially be used for separations of many types of molecules such as metal ions, proteins, amino acids or sugars. The technology is utilised in many sensitive analytical chromatography procedures, frequently on a very small scale. On the other hand industrial-scale production operations, such as demineralisation or protein recovery, are possible. This chapter will consider only the larger-scale applications which have current or potential use for production in the food and biotechnology industries 6.1.1 Theory, materials and equipment a brief summary of the theory of ion-exchange will be given here. More detailed ac- counts can be found elsewhere(e. g. Vermeulen et al., 1984: Walton, 1983; Helfferich, Solute/ion-exchanger interactions Ion-exchange could be defined as the selective removal of a single, or group of, charged pecies from one liquid phase followed by transfer to a second liquid phase by means of a solid ion-exchange material. In practice this involves the process of adsorption - the transfer of specific solute(s) from a heterogeneous feed solution on to the solid ion exchanger. The mechanism of adsorption is electrostatic, involving opposite charges on the solute(s) and the ion- exchanger. The feed solution is washed off, and this is followedChapter 6 Ion-exchange and electrodialysis ALISTAIR S. GRANDISON, Department of Food Science and Technology, The University of Reading, Reading RG6 6AP, UK Ion-exchange and electrodialysis are distinct methods of separation, but can conveniently be treated together, as the basic criterion for separation in both cases is the molecular electrostatic charge. While ion-exchange involves retention of ionised solutes on a solid support material, electrodialysis permits the separation of ions using selective ion￾exchange membranes. 6.1 ION-EXCHANGE Ion-exchange methods can potentially be used for separations of many types of molecules such as metal ions, proteins, amino acids or sugars. The technology is utilised in many sensitive analytical chromatography procedures, frequently on a very small scale. On the other hand industrial-scale production operations, such as demineralisation or protein recovery, are possible. This chapter will consider only the larger-scale applications which have current or potential use for production in the food and biotechnology industries. 6.1.1 Theory, materials and equipment A brief summary of the theory of ion-exchange will be given here. More detailed ac￾counts can be found elsewhere (e.g. Vermeulen et al., 1984; Walton, 1983; Helfferich, 1962). Solutelion-exchanger interactions Ion-exchange could be defined as the selective removal of a single, or group of, charged species from one liquid phase followed by transfer to a second liquid phase by means of a solid ion-exchange material. In practice this involves the process of adsorption - the transfer of specific solute(s) from a heterogeneous feed solution on to the solid ion￾exchanger. The mechanism of adsorption is electrostatic, involving opposite charges on the solute(s) and the ion-exchanger. The feed solution is washed off, and this is followed