(299g) Selectivity Comparison for Two Cation Exchange Membranes in the Electrodialysis Process

Electrodialysis is a membrane based separation in which charged species can be removed due to applied electrical potential. Although electrodialysis has been applied in very diverse industrial fields such as brackish and sea water desalination, salt production by concentering sea water or using brine discharged from a reverse osmosis seawater desalination plant, heavy metal recovery from waste water, recovering reverse osmosis concentrate stream, and citric acid separation, its high capability in brackish water desalination has been demonstrated. It is more applicable than reverse osmosis process for removing the impurities from saline water with high amount of silica. Saline water with high content of silica causes scaling problem in RO membranes, while ED is robust against scaling problems occurred due to silica content.

 Depending on saline water resources, its composition can be very different and the levels of some ions can be more than the others. Therefore, they should be critically removed in order to reach the standard drinking water levels. Focusing on preferential ion removal in the ED operation makes it more purposeful to reduce the cost. Preferential separation of ions can lead to remove specific ions at appropriate rate and control the process cost. ED process is affected by several parameters; however, the ion exchange membranes have the most significant role in selective removal of ions in ED process. In fact, ion exchange membranes have significant role in selective removal of ions in this process. Various ion exchange membranes with diverse characteristics have different preference toward removing the charged species.

In this study the different operation of cation exchange membranes for CR67 and coated CR67 with Polyethyleneimine (PEI) were investigated. Their behavior toward preferential removal of different cations was verified. The experiments were done using a lab-scale ED equipped to a complete data acquisition which gives a significant level of confidence that both membranes were examined at same conditions. The water samples were analyzed using ion chromatography, IC 5000. The studied ion exchange membranes showed different behavior at toward different charged species. Sodium ion removal was considered as a reference ion in this study.