HYDRODYNAMIC MODEL OF ELECTRODIALYSIS WITH ION-EXCHANGE MEMBRANES OF DIFFERENT SELECTIVITY

An analytical solution to the problem of steady-state convective diffu sion under laminar hydrodynamic conditions is obtained for continuous direct-flow electrodialysis with alternating cation- and anion-exchang e membranes. The difference in their selectivity, and the transport nu mbers of cations and anions in solution, as well as the concentration polarization in all sections of the electrodialysis apparatus, before and after overlapping of the diffusion boundary layers, are taken into consideration. The solution obtained is more general than those in th e literature. It makes it possible to obtain express calculations of t he process of electrodialytic desalination both by the voltage preset at the electrodes (for multisection apparatuses) and by the average cu rrent density along the channel lengths in the general case. It reliab ly agrees with the published data obtained by the method of laser inte rferometry.