On the role of gravitational convection in the transfer enhancement of salt ions in the course of dilute solution electrodialysis

The gravitational convection contribution to the increment of salt ion transfer through ion-exchange membranes at overlimiting currents is estimated by measuring total and partial current voltage characteristics of membrane desalination channels. The experiments were carried out by means of the technique enabling one to maintain the solution composition constant. The gravitational convection contribution is shown to increase with the growth of the distance between the membranes, with the decrease of the solution flow rate, as well as with the increase of the solution concentration. However, during the diluted solution electrodialysis in the channels with a small intermembrane distance (0.5 to 0.8 mm) the gravitational convection contribution is insignificant. High current densities of salt ions with a 2-4-fold excess of their ''limiting'' values are accounted for by the influence of the ''exaltation effect'' and electroconvection.