Ion Exchange resins used in demineralization process of water - Fame Agidife @fameAfrice

Positively charged ions are called cations(Ca+2,Mg+2 etc.) & negatively charged ions(Cl-,SO4-2  etc.) are called anions.

Demineralization or Deionization is the process of removal of ions from water using ion exchange resin. Ions are electrically charged molecules found in water that has either a positive charge or negative charge.


There are major two types of Ion Exchange resins called cation & anion used for demineralization process of water. As the name implies cation resin removes cations & anion resin removes anions from the water.

Cation exchange resin is divided into two subcategories called Weak Acid Cation (WAC) & Strong Acid Cation(SAC).

Anion resin divided into two subcategories called Weak Base Anion(WBA) & Strong Base Anion(SBA) from which SBA resin further split into two categories Type-1 & Type-2.

Ion exchange resin structure is either gel or macroporous. Gel resins are translucent while macroporous are opaque. Typically gel based resin is the best choice for conventional water treatment plant because of their higher capacity & better regeneration efficiency.

Types of ion exchange resin chart

Weak Acid Cation Resin(WAC)

Weak Acid Cation(WAC) ion exchange resins have a carboxylic acid functional group (-COOH) exchange site.

These resins remove cations associated with alkalinity only.It is the best choice where hardness to alkalinity ratio of water is >1.

They are used very effectively with SAC resins operating in hydrogen form, in this case, water first contacts with WAC here all cations associated with alkalinity removed.SAC resins remove the remaining cations.

WAC resin regenerated with the waste acid of SAC unit.This process is called thoroughfare regeneration.

Strong Acid Cation Resin(SAC)

Strong Acid Cation(SAC) ion exchange resins have a sulfonic acid group (SO3-H+)as the exchange site. This resin works well within all pH range.

These resins used in two forms hydrogen(H+) and Sodium(Na+) from which hydrogen form resin removes all cations from water & sodium form resin used only for removal of water hardness softening process.

Hydrogen form resin regenerated with hydrochloric acid or sulphuric acid while sodium form resin regenerated with sodium chloride solution called brine.



Weak Base Anion Resin(WBA)

Weak Base Anion(WBA) ion exchange resins have polyamine exchange sites.

This resin removes strong acids or Free mineral acidity(FMA) from the cation effluent stream.It is the best choice where water is having high chloride and sulfate levels or removal of alkalinity and silica are not required.

WBA resins regenerated with the waste base from SBA unit. This process is called thoroughfare regeneration.

Strong Base Anion Resin(SBA)

Strong Base Anion(SBA) ion exchange resins have quaternary amine exchange sites. These resins are Type-1 & Type-2 depending on the type of amine used during the chemical activation process.

Type-1 resin has a three methyl groups & Type-2 resin one ethanol group replaces one of the three methyl group.

A Type-1 resin is suitable for anion removal in all waters. They are more resistant to high temperature and should use in high silica & high alkalinity water.

Type-2 resin has also removed all anion but less efficient in removing silica. This resin is the best choice for small plant & where CO2 & SiO2 <30% of total feed anions.

SBA resins regenerated with sodium hydroxide (NaOH) solution.