What Is an Ion Exchange?
Ion exchange is the action or phenomenon in which ions in a solution exchange with ions on an ion exchanger. It is based on the exchange of ions in a solid ion exchanger with ions in a dilute solution to achieve the purpose of extracting or removing certain ions in the solution. It is a unit operation that belongs to the mass transfer separation process. Ion exchange is a reversible equivalent exchange reaction. The ion exchange resin is sandwiched between anion and cation exchange membranes to form a single processing unit, and constitutes a fresh water chamber. The ion exchange rate decreases with the degree of resin crosslinking and increases with the particle size. Ion exchange is a liquid-solid phase reaction process, which necessarily involves the diffusion of substances in the liquid and solid phases.
- Some cations in the aqueous solution enter the counter ion layer, and the cations originally in the counter ion layer enter the aqueous solution. This kind of homogeneous ion exchange between the counter ion layer and the aqueous solution at normal concentration is called ion exchange. Ion exchange mainly occurs between the diffusion layer and normal aqueous solution. Because the surface of clay particles is usually negatively charged, cation exchange is mainly cation exchange, so it is also called cation exchange. Ion exchange strictly obeys the law of equivalents, that is, the equivalent of the cations entering the counter-ion layer and the cations replaced by the counter-ion layer are equal.
- The ion exchange phenomenon when the soil absorbed ammonium salts was discovered as early as 1850, but as a modern separation method, ion exchange resin was artificially synthesized in the 1940s. Processes and equipment for ion exchange operations, with
- Ion exchange is mainly used for water treatment (softening and purification); refining and decoloring of solutions (such as sugar liquid); extracting uranium and rare metals from mineral leachate; extracting antibiotics from fermentation broth; and recovering precious metals from industrial wastewater. [2]
- The main types are:
- Stirring tank, suitable for handling viscous liquids. When single-level switching fails, multiple levels can be used to form a cascade.
- Fixed-bed ion exchangers, also called ion exchange columns, are used for ion exchange.
EDI How ion exchange EDI works
- EDI (Electro-de-ionization) is a pure water manufacturing technology that combines ion exchange technology, ion exchange membrane technology and ion electromigration technology (electrodialysis technology). This technology uses ion exchange energy to deeply desalinate to overcome the electrodialysis polarization and incomplete desalination, and uses electrodialysis polarization to generate water and ionization to generate H and OH ions to achieve self-regeneration of the resin to overcome the defect of regeneration by chemical agents after resin failure Is a new technology that has gradually emerged since the 1980s. After more than ten years of development, EDI technology has occupied a considerable part of the ultrapure water market in North America and Europe.
- EDI device includes anion / cation exchange membrane, ion exchange resin, DC power supply and other equipment. Among them, the anion exchange membrane allows only anions to pass through, and does not allow cations to pass, while the cation exchange membrane allows only cations to pass through, and does not allow anions to pass. The ion exchange resin is sandwiched between anion and cation exchange membranes to form a single processing unit, and constitutes a fresh water chamber. The unit and the unit are separated by a mesh to form a concentrated water chamber. The positive and negative electrodes of the DC power supply at both ends of the cell group form an electric field. The tap water flows through the fresh water chamber, and the anions and cations in the water are removed by the anion and cation exchange membrane under the action of the electric field and enter the concentrated water chamber. The ion exchange resin filled between the ion exchange membranes greatly increases the speed at which ions are removed. At the same time, water molecules generate hydrogen ions and hydroxide ions under the action of an electric field. These ions continuously regenerate the ion exchange resin to keep the ion exchange resin in an optimal state. The EDI device divides the feed water into three separate streams: pure water, concentrated water, and polar water. Pure water (90% -95%) is the final water, concentrated water (5% -10%) can be recycled, and polar water (1%) is discharged.
- The EDI device belongs to a refined water treatment system. Generally, it is used in conjunction with reverse osmosis (RO) to form an ultrapure water treatment system for pretreatment, reverse osmosis, and EDI devices, replacing the mixed ion exchange equipment of traditional water treatment processes. The water inlet requirement of the EDI device is 0.025-0.5M · cm, and the reverse osmosis device can fully meet the requirements. The EDI device can produce ultra-pure water with a resistivity of up to 15M · cm or more.
EDI Application of ion exchange EDI technology
- EDI technology has been widely used in foreign countries for more than ten years, most of which are used in the pharmaceutical industry, microelectronics industry, power generation industry and laboratories. It is also widely used in surface cleaning, surface coating, electrolytic industry and chemical industry. The application time in China is only 2-3 years. It is mainly used for the treatment of ultrapure water in the pharmaceutical and microelectronics industries, and the application in the chemical water treatment system of the power generation industry has just emerged.
Ion exchange conclusion
- EDI device belongs to water treatment equipment, which has the advantages of continuous water production, high water quality, easy control, less land occupation, no need for acid and alkali, and environmental protection. With the improvement of equipment and technology and optimization for different industries, the initial investment cost will be greatly reduced. It is believed that in the near future, it will completely replace the mixing in the traditional water treatment process.