How does EDI equipment achieve continuous electrochemical regeneration of ion exchange resins without the need for acid-base chemical regeneration?
Publish Time: 2026-02-12
Electrodeionization (EDI) technology, as one of the core processes in modern ultrapure water production, is widely used in electronics, power, pharmaceuticals, and laboratories due to its advantages such as no need for chemical regeneration, continuous and stable water production, and environmental friendliness and efficiency. Unlike traditional ion exchange resins that require periodic chemical regeneration with acids and alkalis, EDI equipment can achieve "self-regeneration" of the resin during operation—that is, continuously restoring its exchange capacity through electrochemical action. This mechanism not only simplifies the operation process but also avoids the generation of waste acid and alkali.1. Basic Structure and Working Environment of EDIThe EDI membrane stack consists of multiple functional units stacked alternately, mainly including a desalination chamber, a concentrate chamber, a cation exchange membrane, an anion exchange membrane, a mixed ion exchange resin, and an electrode system. The desalination chamber is filled with a mixed bed of ion exchange resin, through which the feed water flows; driven by a DC electric field, the residual cations and anions in the water begin to migrate directionally. It is within this microenvironment, jointly constructed by the electric field, ion exchange resin, and selective ion exchange membrane, that the electrochemical regeneration of the resin is achieved.2. Synergistic Effect of Ion Migration and Water ElectrolysisWhen a DC electric field is applied across the EDI module, ions also participate in migration. Under high electric field strength, water molecules near the resin-membrane interface become polarized and electrolyzed. This process is particularly crucial: the generated H⁺ displaces cations adsorbed on the resin, releasing them into the water flow and continuing their migration towards the cathode; similarly, OH⁻ displaces anions. The displaced ions pass through the corresponding selective ion exchange membrane, enter the concentrate chamber, and are discharged from the system. The newly generated H⁺ and OH⁻ are then reloaded onto the resin, restoring it to its H- and OH- forms—this is the "regenerated" state of the ion exchange resin.3. Continuous Cycle of the "In-Situ Regeneration" MechanismTraditional mixed-bed resins must be shut down after saturation and flushed with strong acids and alkalis to restore function. Regeneration in EDI is not centralized or intermittent, but rather distributed throughout the entire freshwater chamber, occurring in real-time alongside the product water process. As long as the DC power supply remains continuous, water molecules can continuously electrolyze in localized areas. This "in-situ, continuous" regeneration method keeps the resin in a highly active state, thus maintaining stable desalination efficiency and ultrapure water quality.4. Precise Coordination of Electric Field, Water Flow, and Membrane StructureThe self-regeneration capability of EDI relies on a precise balance of multiple factors. First, the feed water must be sufficiently pure to avoid a large ion load causing a "short circuit" in the electric field or uncontrolled concentration polarization. Second, the water flow rate must be moderate, ensuring sufficient contact with the resin while avoiding excessive residence time that could lead to drastic local pH changes. Third, the selective permeability of the ion exchange membrane must be good, ensuring that only target ions migrate to the concentrate chamber, preventing cross-contamination. Furthermore, a reasonable current density is crucial for triggering water electrolysis without causing excessive heating or gas evolution.5. The Root of Environmental and Operational AdvantagesBy achieving electrochemical regeneration, the EDI system completely eliminates its dependence on chemicals such as hydrochloric acid and sodium hydroxide. This not only reduces operating costs but also eliminates the problem of chemical waste treatment, aligning with green manufacturing principles. Furthermore, since there is no need to switch regeneration cycles, the system can continuously produce high-purity water 24 hours a day, exhibiting a high degree of automation and minimal human intervention.In summary, EDI equipment cleverly utilizes a DC electric field to induce water molecule electrolysis, generating a regenerant in situ within the desalination chamber, allowing the ion exchange resin to self-renew while in operation. This process integrates the three principles of electrodialysis, ion exchange, and electrochemical regeneration, forming the core of modern ultrapure water technology—efficient, clean, and intelligent.
