Polarisation in electrodialysis. Rotating-disc studies

Abstract

Polarisation in an electrodialysis stack is difficult to examine because of the complex flow of the fluids through the stack. A rotating-disc apparatus has been built, for which the fluid mechanics are both well-known and convenient. Using anion-exchange membranes, the current against voltage plots at high voltages show considerable “water-splitting”, with large fluxes of H+ and OH– ions. The results correlate well with the treatments of Levich and of Cowan, and the enhancement of the anion fluxes by the water-splitting can be explained. Using cation-exchange membranes there is much less water-splitting, with anomalously high cation flux enhancement. Though these characteristics are desirable in practice, they are not explicable by the same approach as seems successful with anion membranes.