Influence of Electrolyte Сoncentration in the Electrodialyzer Concentrate Chamber on the Intensity of Electroconvection

Increasing the mass transfer rate in electrodialysis allows for a reduction in the area of expensive membranes and, in some cases, lowers the cost of the final product. It has been experimentally established that an increase in the concentration of a KCl solution (from 0.02 to 0.75 M) in the concentrate chamber of a flow-through electrodialysis cell (cc) leads to a significant growth in the limiting current density (ilim) through the MA-41P anion-exchange membrane, provided that the desalination chamber contains a solution with a constant concentration (0.02 M KCl). This growth (36% at cc = 0.5 M) significantly exceeds the value (4%) that could be expected due to the increase in diffusion and electromigration transport of co-ions through the membrane caused by the increase in cc. As the experiment shows, an increase in cc leads, on the contrary, to a decrease in the rate of H+ and OH– ion generation at the solution/membrane boundaries, which could also contribute to an increase in the limiting and overlimiting current density. Using voltammetry, chronopotentiometry, and pH-metry, it is shown that the observed growth in ilim may be associated with the emergence of unstable equilibrium electroconvection, the possibility of which was theoretically predicted in the works of Rubinstein and Zaltzman.