What is ion exchange resin?
Ion exchange resin or ion exchange polymer is the types of resins molecules or polymers that are capable of exchanging ions. Depending on the types of ions, resins are termed cation exchange and anion exchange resin.
Usually, they are white or yellow fabricated organic compounds or polymers that are insoluble in common solvents. Ion exchange resins are widely used for the purification or separation of protein or amino acids, water softening, and separation of metal.
The discovery of ion exchange resin is accidental. England agricultural chemist, Thompson and way notice the exchange properties of soil samples by adding fertilizer like ammonium sulfate. The exchange of sodium and calcium in soil indicates the phenomenon of ion exchange.
Types of ion exchange resin
All the resins have reactive OH, COOH, and HSO3 groups in exchange sites. The labile ion is a hydrogen ion in cation exchangers and a suitable anion in anion exchange resins. Resins with sulfonic groups or quaternary amine groups are highly ionized, insoluble, and reactive.
Depending upon the type of labile ions exchanged by the resins, they have been classified into two types,
- Cation exchange resin
- Anion exchange resin
Cation exchange resin
A common synthetic cation exchange resin is obtained by polymerization of styrene and a small amount of divinylbenzene followed by sulfonation. Sodium polystyrene sulfonate, sodium zirconium cyclosilicate are examples of cation exchange resin.
Normally, the H+ is the exchangeable cation in this type of resin. When we treat it with Na+ ions, the H+ ion is replaced by Na+ ions.
Cation exchanger → (Resin anion−)H+
(Resin anion−)H+ + Na+ → (Resin anion−)Na+ + H+
For the water softening, we used natural or artificial zeolites as synthetic cation exchange resin because they are regenerated many more times.
Anion exchange resins
An anion exchange resin is a polymer having amines or quaternary ammonium groups in a polymeric network.
In this resin, the chloride ion is the exchangeable ion and the rest is the non-exchangeable bulky polymeric cation.
Anion exchanger → (Resin anion+)Cl−
(Resin anion+)Cl− + OH− → (Resin anion+)OH− + Cl−
A significant application of both cation and anion exchange resin is softening or deionization of water. Depending upon the labile groups, ion exchange resins are broadly classified into four groups.
Strong acid cation exchange resin
Such types of cation exchange resin contain acidic groups such as HSO3. Sodium polystyrene sulfonate and sodium zirconium cyclosilicate are examples of strongly acidic cation exchange resin.
Weak acid cation exchange resin
Usually, weakly acidic cation exchange resin contains the carboxylic acid group. Wofatote C and Amberlite 45 C belong to this class of resin.
Strong base anion exchange resin
Strongly basic anion exchange resin containing quaternary or tertiary amine groups in their exchange site. Dowex IX8, Dowex 21K, and Amberlite IRA 400 are examples of strongly basic anion exchange resins.
Weak base anion exchange resin
Weakly basic anion exchange resin containing an OH group in their exchange site. Dowex 3 and Amberlite IR 4B are examples of weak base anion exchange resin.
Application of ion exchange resin
The idea of ion exchange resin first comes from the agricultural investigation. This time, the process is used widely for the analysis of micronutrients in soils.
- Presently, it is used mainly in water softening, purification, and separation of metal.
- Ion exchange resin chromatography is also used in different fields like medicine, agriculture, pharmaceutical, mining, and petrochemical industries.
- It is used for the analysis of sugar and amino acids.
- In the petrochemical industry, it is used for the determination of sulfur compounds.
- In mining, for analysis of inorganic anions of heavy metals, we used ion exchange chromatography.
A significant application of ion exchange resin is softening or deionization of water. Temporary hardness caused by calcium or magnesium bicarbonate can be easily removed by boiling or the addition of lime water.
Commonly, we used ion exchange method for softening hard water by removal of sulfates and chlorides of calcium or magnesium. We used the hydrogen form of cation exchange resin and the hydroxyl form of anion exchange resin for the deionization of water. The principal merit of deionization is that it is not time-consuming like distillation.
For the purification of domestic water, we used activated charcoal mixed with resin. It can be removed chloride ions and organic impurities from water.
Ion exchange resin in metal separation
Some examples of ion exchange resins and their applications are given below the table,
|Dowex 50W X12
|Used for separation of cobalt (Co)
|Dowex 50W X8
|Used for separation of titanium (Ti), scandium (Sc), and manganese (Mn)
|Used for separation of indium (In), thallium (Th), and Gallium (Ga)
The cation exchange chromatographic method is used for the separation of magnesium, calcium, strontium, and barium by Dowex 50 with ammonium lactate buffer at pH scale 7.
For the purification and manufacturing of pharmaceuticals, we used widely ion exchange resin. Resins like sodium polystyrene sulfonate, colestipol, and cholestyramine are used widely in pharmaceutical industries.