Ion exchange resins are synthetic materials, usually spheres of 0.5-1 mm of diameter, designed for industrial wastewater treatment. These are formed by a polymer matrix to which have been attached a large amount of radicals of cation or anion, acid or base. When water passes through, the resin retains the water ions (sodium, chlorine, calcium, magnesium, etc.) and gives back an equal amount of protons or hydroxyls.

Ion exchange resins can be of the following type:

  • Strong acid cation resins: they remove cations exchanging sodiums or protons.
  • Weak acid cation resins: they remove cations related to bicarbonates.
  • Strong base anion resins: they remove all anions. Used to eliminate carbonates and silicates.
  • Weak base anion resins: they eliminate strong acid anoins (sulfates, nitrates and chlorides) with high efficiency.

When an ion exchange resin exhausts its ability to exchange ions, it can fully recover its original exchange ability by means of a regenerating solution. The column regeneration is achieved by making a solution of the original ion pass through the resin. The ion bonds with the resin radicals and displaces the captured ions during normal operation. Common salt, hydrochloric or sulfuric acid, or caustic soda are usually used for resin regeneration based on the column type.