Diagnostics of the Structural and Transport Properties of an Anion-Exchange Membrane MA-40 after Use in Electrodialysis of Mineralized Natural Waters

Abstract

Changes in the structural and transport characteristics of MA-40 anion-exchange membranes after operation in industrial electrodialysis apparatuses have been assessed. Causes for the deterioration of operational properties by the action of various factors in the process of demineralization and concentration of natural waters have been revealed. Samples of the anion-exchange membrane after long-term operation in the working stack of an electrodialysis concentrator, as well as samples taken out from the electrode compartment of the electrodialysis reversal apparatus, have been studied. The most significant change in the structure of the membrane taken out from the electrodialyzer concentrator is an increase in macroporosity, which is the main reason for the growth in the electrical conductivity and water content against the background of a loss of ion-exchange capacity and selectivity. The formation of poorly soluble carbonates and hydroxides both on the surface and in the bulk of a membrane from the electrode compartment of the reversal electrodialyzer leads to the blocking of the functional groups and transport channels, decrease in electrical conductivity, and complication of transport processes.