An ion-exchange resin or ion-exchange polymer is a resin or polymer that acts as a medium for ion exchange. It is an insoluble matrix (or support structure) normally in the form of small microbeads, usually white or yellowish, fabricated from an organic polymer substrate. The beads are typically porous, providing a large surface area on and inside them the trapping of ions occurs along with the accompanying release of other ions, and thus the process is called ion exchange. There are multiple types of ion-exchange resin. Most commercial resins are made of polystyrene sulphonate.

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.

TYPES OF ION EXCHANGE RESINS

  • Cation-exchange resin
  • Anion-exchange resin

Ion exchange resins contain electrically charged functional groups that are either sulfonic or carboxylic acid salts or quaternary ammonium salts. Based on their charges, the ion exchange materials are classified into two main groups: cation exchange resin and anion exchange resins.

CATION EXCHANGE RESINS

Cation Exchange Resins contain negatively charged functional groups, which attract positively charged ions in solution. One of its applications is separating positive ions from contaminated water.

Cation Exchange Resins are also further classified into two sub-groups:

  • Strong acid cation (SAC) resins: They are made of polystyrene with a sulfonate functional group (SO3-) that is either charged with hydrogen ions (H+) or sodium ions (Na2+).
  • Weak acid cation (WAC) resins:They are composed of acrylic polymer with carboxylic acid groups as functional groups and have a high affinity for hydrogen ions. These are commonly used to remove alkalinity-associated cations.

ANION EXCHANGE RESINS

Anion Exchange Resins contain positively charged functional groups, which attract negatively charged ions in solution. They contain amine as a functional group in their matrix.

These also are used to purify water as well, by removing negatively charged contaminants. The two subcategories of anion resins are:

  • Strong base anion (SBA) resins:These resins consist of a polystyrene matrix that has been chloromethylated and then aminated with dimethylamine. They either yield chloride ions or hydroxide ions during the exchange reaction.
  • Weak base anion (WBA) resins: They are also composed of a polystyrene matrix. Their degree of ionization is regulated or controlled by the pH of the solution. Additionally, since they lack exchangeable ions, they act as acid absorbers for removing ions from strong mineral acids.