Ion-exchange resins are widely used in different separation, purification, and decontamination processes. The most common examples are water softening and water purification. In many cases ion-exchange resins were introduced in such processes as a more flexible alternative to the use of natural or artificial zeolites. Also, ion exchange resins are highly effective in the biodiesel filtration process.

Anion resins may be either strongly or weakly basic . Strongly basic anion resins maintain their positive charge across a wide pH range, whereas weakly basic anion resins are neutralized at higher pHs.[3] Weakly basic resins do not maintain their charge at a high pH because they undergo deprotonation.They do, however, offer excellent mechanical and chemical stability. This, combined with a high rate of ion exchange, make weakly base anion resins well suited for the organic salts.
For anion resins, regeneration typically involves treatment of the resin with a strongly basic solution, e.g. aqueous sodium hydroxide. During regeneration, the regenerant chemical is passed through the resin and trapped negative ions are flushed out, renewing the resins’ exchange capacity.
 

The following ions are widely found in raw waters:

Ion exchanges can be unselective or have binding preferences for certain ions or classes of ions, depending on their chemical structure. This can be dependent on the size of the ions, their charge, or their structure. Typical examples of ions that can bind to ion exchangers are:

H+ (proton) and OH− (hydroxide)
Single-charged monatomic ions like Na+, K+, and Cl−
Double-charged monatomic ions like Ca2+ and Mg2+
Polyatomic inorganic ions like SO42− and PO43−
Organic bases, usually molecules containing the amine functional group -NR2H+
Organic acids, often molecules containing -COO− (carboxylic acid) functional groups
Biomolecules that can be ionized: amino acids, peptides, proteins, etc.
Along with absorption and adsorption, ion exchange is a form of sorption.

Ion exchange is a reversible process and the ion exchanger can be regenerated or loaded with desirable ions by washing with an excess of these ions.

Reverse osmosis system ion exchanger water treatment machine