what is ion exchange in water treatment
Ion Exchange Process / Demineralization Process: In this process, a reversible exchange of ions occurs between the stationary ion exchange phase and the external liquid mobile phase.
Ion-exchange resins are insoluble, cross-linked, long-chain high molecular weight organic polymers their microporous which are permeable due to structure, and the functional groups attached to the chains are involved in the ion - exchanging properties.
The purely synthetic organic exchanger are made of Polycondensation and Polymerisation.
→ The functional groups are then introduced into the cross-linked resin network. It is these functional groups that decide the nature of the resin exchanger i.e. cationic or anionic.
→ The ion - exchange resins on the basis of their acidity or basicity are classified as follows :
Cation exchange resins ( RH2 ) ( RH + )
→ Resins containing acidic functional groups ( -COOH , - SO₂ H , etc ) exchange their H + ions with other cations , which come in their contact are known as cation exchange resins . These are represent as RH + or RH2 .
→ These resins are capable of exchanging rapidly cations like Ca² + and Mg2 + by hydrogen ions .
For example: Divingl benzene copolymer, formaldehyde resins etc. are some of the commercially available cation exchange resins.
Their exchange reactions with cations (Ca² + and Mg2+) are as follows :
RH₂ + Ca + →→→→ Rca + 2H +
RH₂ + Mg² + →→ R Mg + 2H ±
(2).Anion exchange resins ( R ' COH ) )
The resin containing basic functional groups ( eg - NK₂ , = NH , etc. ) exchange their anions with other anions , which come in their contact . They are known as anion exchange resin.
These resins are capable of exchanging rapidly ( a-, so4²-. )by OH-ions.
They are represented as R + and OH- where R + represents the insoluble matrix.
→ For example amino-formaldehyde resin, copolymer of styrene and divingl benzene. Amberlite 400 , Zeolite -FF etc.Their exchange reactions with anions ( SO4₂-, C03²- " etc. ) are as follows :
Types of ion - exchange
1).Cation - exchangers
a)Strongly acidi-----SO3H
b)Weakly acidic-----COOH or OH
2).Anion - exchangers
a)Strongly basic-------NR3+,CH3 = P * etc.
b)Weakly basic - -NH₂ - ( C₂H4 ) X , ( NH)y-
In other words , water collected from cation exchanger is free from all cations , but is acidic.
→ After this , the acidic hard water is passed through an anion exchange bed which removes all the anions like Son Cl- etc. present in the water, and equivalent amount of OH ions are released from it to water.
H+ and OH- ions are released from cation exchange and anion exchange bed respectively which combine to produce water molecule , as