Two common ion exchange methods are hard water softening and deionization. Hard water softening is mainly used in reverse osmosis (RO) treatment to reduce the hardness of the water before a pre-treatment process. The spherical resin in the softener softens the water by exchanging two sodium ions with one calcium ion or magnesium ion.
The ion exchange method uses a spherical resin (ion exchange resin) to filter the raw water, and the ions in the water are exchanged with the ions fixed on the resin.
Ion exchange resins use hydrogen ions to exchange cations, and hydroxide ions to exchange anions; cation exchange resins made of sulfonate-containing styrene and divinylbenzene exchange various cations (such as Na+, Ca2+, Al3+). Similarly, an anion exchange resin made of styrene containing quaternary ammonium salt will exchange various anions (such as Cl-) that it encounters with hydroxide ions. The hydrogen ions released from the cation exchange resin are combined with the hydroxide ions released from the anion exchange resin to produce pure water.
Anion and cation exchange resins can be packaged in different ion exchange beds, and divided into so-called anion exchange beds and cation exchange beds. It is also possible to mix the cation exchange resin and anion exchange resin together and place them in the same ion exchange bed. Regardless of the form, when the resin and the charged impurities in the water have exchanged the hydrogen ions and (or) hydroxide ions on the resin, it must be “regenerated”. The regeneration procedure is just the opposite of the purification procedure. It uses hydrogen ions and hydroxide ions to regenerate and exchange impurities attached to the ion exchange resin.
If the ion exchange method is combined with other water purification methods (such as reverse osmosis, filtration, and activated carbon adsorption), the ion exchange method will play a very important part in the entire purification system. The ion exchange method can effectively remove ions, but it cannot effectively remove most of the organic matter or microorganisms. The microorganisms can be attached to the resin, and the resin is used as the culture medium, so that the microorganisms can grow quickly and generate heat. Therefore, it needs to be designed and used in conjunction with other purification methods.