EDI & Ion Exchange Resin

Overview

An EDI module stacks dilute-water, concentrate and electrode-water compartments between anion- and cation-exchange membranes, with ion-exchange resin packed in the dilute compartments and electrodes at both ends. Feed water runs through the dilute compartments and comes out desalinated. Salt ions that leave the dilute compartments cross the membranes into the concentrate compartments and are drained as concentrate water. The electrode compartments host the electrode reactions and discharge electrode water separately.

• The resin is regenerated in place by the H⁺ and OH⁻ ions that water itself produces when it splits under the DC field. No hydrochloric acid, no caustic soda, and no acid-alkali waste to dispose of.
• Highly automated and simple to operate. The unit runs unattended around the clock and can be integrated into a DCS automatic control system.
• Small footprint. Compared with a conventional mixed-bed system, the acid-alkali storage tanks, regeneration water tanks and neutralization tanks are eliminated, which reduces the civil-engineering floor area.
• Low operating cost. No chemical purchasing; the unit mainly consumes a small amount of electric power, concentrate water and electrode water.
• Stable ultrapure water output at 15–18.2 MΩ·cm, with better removal of weak electrolytes such as silica and CO₂ than a single-stage RO.