Introduction and Definitions

The history of electrodialysis began with the work of Ostwald (1890). He investigated the properties of semipermeable membranes and was the first to discover that a membrane is impermeable for any electrolyte if it is impermeable either for its cation or its anion. To illustrate this, he postulated the existence of the so-called “membrane potential” at the boundary between the membrane and the solution as a consequence of the difference of concentration. Later, Donnan (1911) confirmed this postulate for the boundary of an ion-exchange membrane and its surrounding solution. Simultaneously, he developed a mathematical equation describing the concentration equilibrium, which resulted in the so-called “Donnan exclusion potential.”