Changes in the microstructure and operational characteristics of the MK-40 sulfocation-exchange membrane during the electrodialysis of natural waters

Abstract

Structural changes in MK-40 sulfocation-exchange membrane material are estimated after the electrodialysis of natural waters. The reasons for a deterioration of its operational properties under the influence of various factors are revealed. Differences in the surface and bulk microstructures of membrane samples, which arise after long-term operation in electrodialysis apparatuses of various types, are visualized via scanning electron microscopy. The membrane extracted from an electrodialyzer-desalinator is characterized by an increase in macroporosity. The membrane from the near-electrode section of a reverse electrodialysis unit is distinguished by the fact that slightly soluble compounds are formed both on the membrane surface and in its bulk (salt contamination). It is established that morphological changes and sedimentation caused by the electrodialysis of natural waters affect the electrochemical and physical-chemical properties of the MK-40 sulfocation-exchange membrane. The growth in membrane macroporosity in the case of the longterm desalination of natural waters is the primary reason for an increase both in the electroconductivity against the background of losses in the exchange capacity and selectivity and in the water content and diffusion permeability. It is ascertained that the membrane transport properties deteriorate due to sedimentation which affects not only the membrane surface but also its bulk.