Features and working principle of EDI (Elcctrodeionization) equipment

EDI (Elcctrodeionization) is a pure water manufacturing technology that combines ion exchange technology, ion exchange membrane technology and ion electromigration technology. It cleverly combines electrodialysis and ion exchange technology, uses the high voltage of electrodes at both ends to move charged ions in water, and cooperates with ion exchange resin and selective resin membrane to accelerate ion movement and removal, so as to achieve the purpose of water purification. In the EDI desalination process, ions are removed through the ion exchange membrane under the action of an electric field. At the same time, the water molecules generate hydrogen ions and hydroxide ions under the action of an electric field, and these ions continuously regenerate the ion exchange resin to keep the ion exchange resin in its best condition. The salt removal rate of EDI facilities can be as high as 99% or more. If the reverse osmosis equipment is used to preliminarily demineralize the water before EDI, then ultrapure water with a resistivity of 15M.cm or more can be produced by EDI demineralization.

EDI (Elcctrodeionization) is a pure water manufacturing technology that combines ion exchange technology, ion exchange membrane technology and ion electromigration technology. It cleverly combines electrodialysis and ion exchange technology, uses the high voltage of electrodes at both ends to move charged ions in water, and cooperates with ion exchange resin and selective resin membrane to accelerate ion movement and removal, so as to achieve the purpose of water purification. In the EDI desalination process, ions are removed through the ion exchange membrane under the action of an electric field. At the same time, the water molecules generate hydrogen ions and hydroxide ions under the action of an electric field, and these ions continuously regenerate the ion exchange resin to keep the ion exchange resin in its best condition. The salt removal rate of EDI facilities can be as high as 99% or more. If the reverse osmosis equipment is used to preliminarily demineralize the water before EDI, then ultrapure water with a resistivity of 15M.cm or more can be produced by EDI demineralization.

The resin bed is continuously regenerated by the direct current applied to both ends of the chamber. The voltage decomposes the water molecules in the water into H+ and OH-. These ions in the water are attracted by the corresponding electrodes and pass through the cation and anion exchange resins to the corresponding membranes. When these ions enter the concentration chamber through the exchange membrane, H+ and OH- combine to form water. This generation and migration of H+ and OH- is the mechanism by which the resin can be continuously regenerated.

When the impurity ions such as Na+ and CI- in the feed water are absorbed on the corresponding ion exchange resin, these impurity ions will undergo the same ion exchange reaction as in the ordinary mixed bed, and correspondingly replace H+ and OH-. Once the impurity ions in the ion exchange resin are also added to the migration of H+ and OH- towards the exchange membrane, these ions will continuously pass through the resin until they penetrate the exchange membrane and enter the concentrated water chamber. These impurity ions cannot migrate further in the direction of the corresponding electrode due to the blocking effect of the adjacent compartment exchange membrane, so the impurity ions can be concentrated in the concentrated water chamber, and then the concentrated water containing impurity ions can be discharged from the membrane stack.

For decades, the preparation of pure water has been at the expense of consuming a large amount of acid and alkali. During the process of production, transportation, storage and use of acid and alkali, it will inevitably cause environmental pollution, corrosion of equipment, and potential for human Injuries and maintenance costs remain high. The use of reverse osmosis greatly reduces the amount of acid and alkali, but it still leaves a tail. The widespread use of reverse osmosis and electric desalination will bring an industrial revolution to the production of pure water.

System Features

  • High and stable water quality.
  • Continuous water production, no shutdown due to regeneration.
  • No need for chemical regeneration.
  • Thoughtful stacking design, small footprint.
  • Simple and safe operation.
  • Low operating costs and maintenance costs.
  • No acid-base storage and transportation costs.
  • Fully automatic operation without special care

The development of pure water treatment technology mainly experienced the stages of anion and cation exchanger + mixed ion exchanger; reverse osmosis + mixed ion exchanger; reverse osmosis + electrodeionization device. The complete desalination system of pretreatment + reverse osmosis + electrodeionization has the unparalleled advantages of other treatment systems and is being widely used in the preparation of pure water and high purity water.

Application field

  • Chemical water treatment in power plants
  • Ultra pure water in electronics, semiconductor and precision machinery industries
  • Process water for pharmaceutical industry
  • Preparation of food, beverage and drinking water
  • Desalination of sea water and brackish water
  • Water for fine chemicals and sophisticated subjects
  • Preparation of high purity water required by other industries

How EDI works

Tap water often contains dissolved salts such as sodium, calcium, magnesium, chlorine, nitrate, and silicon. These salts are composed of negatively charged ions (negative ions) and positively charged ions (positive ions). Reverse osmosis can remove more than 99% of the ions. Tap water also contains trace metals, dissolved gases (such as CO2), and other weakly ionized compounds (such as silicon and boron) that must be removed in industrial processing.

RO outlet water (EDI inlet water) is generally 40μ/cm (conductivity), according to different needs, the general resistance of ultrapure water or deionized water is 28.2MΩ.

The exchange reaction is carried out in the pure chemical chamber of the module, where the anion exchange resin exchanges the anion in the dissolved salt (such as the chloride ion C1) with their hydrogen and oxygen according to the ion (OH). Correspondingly, cation exchange resins use their hydrogen ions (H) to exchange cations (such as Na) in dissolved salts.

A DC electric field is applied between the anode (+) and the cathode at both ends of the module. The electric potential causes the ions exchanged on the resin to migrate along the surface of the resin particles and enter the concentrated water chamber through the membrane. The anode attracts negatively charged ions (such as OH, CI) through the anion membrane and enters the adjacent concentrated water flow, but is blocked by the cation selective membrane and stays in the concentrated water flow. The cathode attracts cations (such as H, Na) in the pure water stream. These ions pass through the cation selective membrane, enter the adjacent concentrated water stream but are blocked by the anion membrane, and stay in the concentrated water stream. When water flows through these two parallel chambers, the ions are removed in the pure water chamber and accumulate in the adjacent concentrated water stream, and then the concentrated water stream takes them away from the module. The use of ion exchange resins in pure water and concentrated water is the key to ElectropupreEDI technology and technology. An important phenomenon occurs in the ion exchange resin in the pure water compartment. In the local area where the potential difference is high, the water decomposed by the electrochemical reaction produces a large amount of H and OH. The local generation of H and OH in the mixed-bed ion exchange resin allows the resin and membrane to be continuously regenerated without adding chemicals.

The basic requirement for EDI to be in the best working condition without failure is to properly pre-process the EDI inlet water requirements. The impurities in the incoming water have a great influence on the deionization module. It may also shorten the life of the module.

EDI system water treatment

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