MINERAL FOULING ON THE MA-40 ANION EXCHANGE MEMBRANE WITH THE AT ELECTRODIALYSIS OF STRONGLY MINERALIZED NATURAL WATERS

Abstract

Mineral fouling of ion exchange membranes is one of the major problems during electrodialysis operation. The purpose of this work is the detection of the relationship between the structural and transport properties of the MA-40 anion exchange membrane after prolonged use desalinating and concentrating natural waters. Structural changes of the MA-40 anion exchange membrane after continuous operation in electrodialysis stacks of various types are evaluated by scanning electron microscopy. The physicochemical characteristics of membranes were identifi ed by the standard procedures. The conductivity was measured by the contact–difference method. The diffusion properties of the membranes were determined by estimating the amount of electrolyte, which was transported through the membrane to the water. The infl uence of structural changes in the MA-40 anion-exchange membrane after the electrodialysis of natural waters on the physical-chemical and electrochemical characteristics were estimated. The possible mechanisms of decreasing the operational characteristics of MA-40 membranes, which arise due to the demineralization and concentrating of natural waters, were revealed via the electrodialysis method. The main cause of reduction of the transport properties of membranes from near-electrode sections from the reverse electrodialysis stack during demineralization of natural waters from the Aral region is precipitation occurring both on the membrane surface and in its bulk. If on the membrane surface Mg insoluble compounds are preferably formed, then in the membrane phase on both sides of the surface the formation of CaCO3 is established. The main reason for the deterioration of the operational characteristics of the MA-40 anion-exchange membrane after electrodialysis concentration of natural waters is the destruction of ionogenic groups of the membranes, which causes a decrease in the total exchange capacity. The increase in surface macroporosity was accompanied by a slight mineral scaling of a carbonate nature.

Keywords

• anion-exchange membrane
• reverse electrodialysis stack
• electrodialyzer-concentrator
• natural waters
• mineral fouling.