The ion exchange method uses spherical resin (ion exchange resin) to filter raw water. The ions in the water will exchange with the ions fixed on the resin. Two common ion exchange methods are hard water softening and deionization. Hard water softening is mainly used as a pre-treatment procedure to reduce water hardness before reverse osmosis (RO) treatment. The spherical resin inside the softener softens water by exchanging two sodium ions for one calcium or magnesium ion.
Ion exchange resin uses hydrogen ions to exchange cations and hydroxyl ions to exchange anions; cation exchange resins made of styrene and divinylbenzene containing sulfonate groups will use hydrogen ions to exchange the ions encountered. Various cations (such as Na, Ca2, Al3). Likewise, anion exchange resins made from styrene containing quaternary ammonium salts will exchange various anions encountered (such as Cl-) with hydroxyl ions. The hydrogen ions released from the cation exchange resin combine 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 respectively, divided into so-called anion exchange beds and cation exchange beds. Cation exchange resin and anion exchange resin can also be mixed together and placed in the same ion exchange bed. No matter which form it is, when the hydrogen ions and/or hydroxide ions on the resin have been exchanged between the resin and the charged impurities in the water, "regeneration" must be performed. The regeneration procedure is just the opposite of the purification procedure. Hydrogen ions and hydroxide ions are used for regeneration to exchange impurities attached to the ion exchange resin.