The electrolyte and membranes are subjected to an electric field, and a transport of current by ionic conduction is induced. In the membrane this is dominated by migration, whereas in the electrolyte solutions this transport is complemented by diffusion and convection processes. A unit cell from an electrodialysis stack is shown in Figure 1. An anion selective membrane is placed facing the anode, while the cation selective membrane faces the cathode. The respective ions are forced through the membrane by the imposed electric field.
Desalination takes place in the channel centre where electroneutrality is present.
The membrane works through the principle of electroneutrality. In the membrane, charged ionic groups are attached at regular intervals along the polymer chains, which form the skeleton of the membranes. These groups are positively charge in anion selective membranes, which promote content with a high concentration of anions, while repelling cations. In addition, the structure and distribution of ionic groups can be engineered to allow higher concentrations of mono-ionic species, as opposed to species with greater charges. In this case this results in the selective transport of chloride, from a chloride and sulphate-containing electrolyte.