Towards optimized cation-exchange membranes for overlimiting current electrodialysis: Correlation between size of resin particles in membranes and mechanism of ion transport through them

•The influence of resin particle size on the ion transport through the membrane is studied.•Ion-exchanger size affects the contribution of various ion transport mechanisms in membrane systems.•Reducing the resin particle size increases the electroconvection contribution to the mass transfer.•The contribution of water splitting reaction products falls with decreasing resin particle size. Experimental heterogeneous membranes with different particle sizes of cation-exchange resin KU-2–8 (the diameter of resin particles varied from 20 to 71 μm) were manufactured under the production conditions of LLC “IE “Shchekinoazot”. It is established that at currents higher than the limiting current the main mechanisms of electrolyte ion transport are classical electrodiffusion and electroconvection. It is shown for the first time that at the same degree of membrane polarization i/ilim the fraction of electroconvection contribution increases, and the fraction of contribution of water splitting reaction products decreases with decreasing size of resin particles in membranes. The theoretical evaluation of the influence of the size of resin particles in the membrane on the internal parameters of electromembrane systems MK-40/0.01M NaCl solution has shown that the crucial role in the development of electroconvection is played not by the field effect, but by the peculiarities of electrical heterogeneity of the membrane surface.