How does electrodeionization work

Type your search. Home Electrodeionization EDI. Back to Technologies. Electrodeionization EDI. Last Updated. Relevant Impurities. Technology Notes. What is Electrodeionization? What does Electrodeionization remove from water? Keeping high purity water flowing and operating costs down. Learn about more benefits of Electrodeionization by visiting our blog.

The cleaner the water is when it reaches the EDI system, the longer the life span to expect. What is Electrodeionization? How Does Electrodeionization Work? When flow enters the resin filled diluiting compartment, several processes are set in motion. Strong ions are scavenged out of the feed stream by the mixed bed resins.

Under the influence of the strong direct current field applied across the stack of components, charged ions are pulled off the resin and drawn towards the respective, oppositely-charged electrodes.

In this way these charged strong-ion species are continuously removed and transferred in to the adiacent concentrating compartments. As the ions go towards the membrane, they can pass through the concentration chamber see figure but they cannot reach the electrode.

They are blocked by the contiguous membrane, that contains a resin with the same charge. As the strong ions are removed from the process stream, the conductivity of the stream becomes quite low. The strong, applied electrical potential splits water at the surface of the resin beads, producing hydrogen and hydroxyl ions. These act as continuous regenerating agents of the ion-exchange resin. These regenerated resins allow ionization of neutral or weakly-ionized aqueous species such as carbon dioxide or silica.

Ionization is followed by removal through the direct current and the ion exchange membranes. Only cations will be able to pass through to the other side. When we insert another ion exchange membrane made of anion selectively resins, it will block the flow of cations and water molecules. Only anions will be able to pass through to the other side. This configuration membranes and electrodes forms the framework of an EDI module.

This process is limited however by the slow speed at which ions move through water. In effect, the low conductivity of water impedes ion removal. In other word, as the product compartment water becomes more and more pure, the electrical resistance of this water increases. EDI technology solves this problem by sandwiching a mixture of cation and anion selective resins between the two membranes. The large surface area now offered by the resin beads effectively eliminates the ion diffusion resistance and allows the ions to move freely.

Even in ultrapure water solution, the surface of the resin beads acts as a conductive path, effective acting as a bridge for the ions to move quicker toward the membrane surface faster than they were in water alone. Take a step back to look how an EDI module is constructed, we can see that if we move the electrodes farther apart and continue to add resin beads sandwiched between the cation and anion selectively membranes, we create a series of water purification compartments alternating with compartments where the ions are concentrated.

As feed water is pumped into the system, it is diverted into separate compartments, namely the concentrating compartment and the purification or dilute compartment.