INFLUENCE OF THE LAYER FIXED CHARGE-DISTRIBUTION ON THE PERFORMANCE OF AN ION-EXCHANGE MEMBRANE

The effect of different fixed charge distributions on the current efficiency and electric resistance of an ion-exchange membrane has been investigated on the basis of the Donnan model of a membrane including the polarization layers. It has been found that the studied quantities always depend on the current density. For adequately high current densities the current efficiency exceeds that for the uniform distribution. The efficiency decreases with the number of distribution units in the membrane and even falls below that for homogeneous distribution. The relation between the efficiency and the sorption does not depend on the type of fixed charge distribution when the bulk concentrations are the same. A comparison of two methods for determining the transport number of counter-ions has led to the conclusion that the potentiometric (zero-current) method in comparison to the real current conditions could give false results for macroheterogeneous membranes.