Diagnosis of surface and bulk microstructure changes of the MK-40 sulfocation exchange membrane at electrodialysis of highly mineralized natural waters

Abstract

An important limitation which worsens efficiency of electrodialysis during natural waters demineralization
is to reduce of the membrane electrochemical activity under the influence of polarization and temperature
effects as well as salt fouling. The purpose of this work is the detection of the relationship between
the structural and transport properties of MK-40 sulfocation exchange membrane after prolonged use in the
reverse electrodialysis stack during desalination of natural waters.
Structural changes of the MK-40 cation exchange membrane material after continuous operation in
the reverse electrodialysis stack are evaluated by the scanning electron microscopy. The physicochemical
characteristics of membranes were identified by the standard procedures. The conductivity was measured by
the contact–difference method. The diffusion properties of membranes were determined by estimating the
amount of electrolyte, which was transported through the membrane to the water.
The influence of the morphological changes and scaling after electrodialysis of natural waters on the
electrochemical and physicochemical properties of the MK-40 cation exchange membrane is established.
Possible reasons of deterioration of membrane operational properties at the process of demineralization of
natural water by electrodialysis are revealed. The degradation of the membrane transport properties as a result
of scaling, affecting not only the surface but also the bulk of the membrane, is established. Formation of
slightly soluble compounds leads to blocking of functional groups and transport channels of the membrane,
decreasing of selectivity and electrical conductivity, and hindering of the diffusion processes.