Physicochemical and selective properties of heterogeneous ion-exchange membranes MK-40 and MA-40 after electrodialysis of natural water

Abstract

The method of electrodialysis is quite effective and environmentally appropriate, a known limitation of the applicability of which is the rapid decrease in the electrochemical activity of membranes under the influence of polarization and temperature effects, as well as sedimentation during the process. The purpose of this work was to study the changes in the physicochemical and selective properties of heterogeneous ionexchange membranes during long-term operation in electrodialysis equipment during desalting and concentration of mineralized natural waters.
Structural changes of the heterogeneous membranes after continuous operation in the electrodialyzers of different types were evaluated by the scanning electron microscopy. Information on the chemical composition of the membrane surface or cross section was obtained by mapping the elemental composition using an energy dispersive spectrometer. The physicochemical characteristics of membranes were identified by the standard procedures.
The influence of structural changes and the formation of precipitation after electrodialysis of natural water on the equilibrium and selective properties of heterogeneous ion-exchange membranes MK-40 and MA-40 was established. The formation of poorly soluble precipitates on the surface and in the bulk of the membranes extracted from the electrode section of the reversal electrodialyzer leads to blocking of the functional groups and transport channels, reduction of the exchange capacity, water content and transport numbers of counter ions, preventing the transfer processes. An increase in macroporosity was revealed for themembrane from the electrodialyzer-concentrator, which is the main cause of the growth of water content against the background of loss of exchange capacity and selectivity.