Ion Exchange Mixed Bed Industrial Ultra-Pure Water EDI Module

Ion Exchange Mixed Bed Industrial Ultra-Pure WaterEDIModule

An EDI membrane stack consists of a certain number of pairs of units sandwiched between two electrodes. Within each unit, there are two different types of chambers: the fresh water chamber to be desalinated and the concentrated water chamber that collects the removed impurity ions. The fresh water chamber is filled with uniformly mixed cation and anion exchange resins, which are located between two membranes: the cation exchange membrane that only allows cations to pass through and the anion exchange membrane that only allows anions to pass through.
The resin bed is continuously regenerated using direct current applied across the ends of the chamber. The voltage decomposes water molecules in the influent into H⁺ and OH⁻. These ions in the water are attracted to their respective electrodes and migrate through the cation and anion exchange resins toward the corresponding membranes. When these ions pass through the exchange membranes and enter the concentrated chamber, H⁺ and OH⁻ combine to form water. The generation and migration of these H⁺ and OH⁻ ions are precisely the mechanism by which the resin achieves continuous regeneration.
When impurity ions such as Na⁺ and Cl⁻ in the influent adsorb onto the corresponding ion exchange resins, these impurity ions undergo ion exchange reactions similar to those in a conventional mixed bed, correspondingly displacing H⁺ and OH⁻. Once the impurity ions within the ion exchange resins also join the migration of H⁺ and OH⁻ toward the exchange membranes, these ions will continuously pass through the resin until they penetrate the exchange membranes and enter the concentrated water chamber. Due to the blocking effect of the adjacent compartment's exchange membranes, these impurity ions cannot further migrate toward the corresponding electrodes. Therefore, the impurity ions are concentrated in the concentrated water chamber, and this concentrated water containing impurity ions can then be discharged from the membrane stack.