Ion-exchange resin

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, fabricated from an organic polymer substrate. 

The beads are typically porous.

The beads provide a large surface area on and inside them where the trapping of ions occurs along with the accompanying release of other ions, and thus the process is called ion exchange. 

Most commercial resins are made of polystyrene sulfonate.

Ion-exchange resins are widely used in different separation, purification, and decontamination processes: water softening and water purification. 

Most ion-exchange resins are based on crosslinked polystyrene. 

Ion-exchanging sites are introduced after polymerisation. 

Crosslinking decreases ion-exchange capacity of the resin and prolongs the time needed to accomplish the ion-exchange processes.

Crosslinking improves the robustness of the resin. 

Smaller bead particles have larger outer surface.

Besides being made as bead-shaped materials, ion-exchange resins are also produced as membranes, that allow passage of ions, but not of water, are used for electrodialysis.

Four main types of ion-exchange resins differ in their functional groups:

strongly acidic, 

Strongly basic

weakly acidic,

weakly basic,

Specialised ion-exchange resins are also known such as chelating resins.

While anion resins attract negatively charged ions, cation resins attract positively charged ions.

For anion resins, regeneration typically involves treatment of the resin with a strongly basic solution, and during regeneration, the regenerant chemical is passed through the resin, and trapped negative ions are flushed out, renewing the resin exchange capacity.

In water softening ion-exchange resins are used to replace the magnesium and calcium ions found in hard water with sodium ions. 

Ion-exchange resins are used to remove poisonous and hazardous metal (e.g. ions from water, replacing them with more innocuous ions, such as sodium and potassium.

Water of highest purity is required for electronics, scientific experiments, production of superconductors, and nuclear industry, and such water is produced using ion-exchange processes or combinations of membrane and ion-exchange methods.

Yellowcake Ion-exchange processes are used to separate and purify metals, including separating uranium from plutonium and other actinides, including thorium; and lanthanum, neodymium, ytterbium, samarium, and lutetium.

Through an ion-exchange process, resin beads attract uranium.

The ion-exchange process is also used to separate zirconium and hafnium, which incidentally is also very important for the nuclear industry.

Ion exchange resins are used in organic synthesis for esterification and hydrolysis. 

Being high surface area and insoluble, they are suitable for vapor-phase and liquid-phase reactions. 

Ion-exchange resins are used in the manufacture of fruit juices to remove bitter-tasting components and so improve the flavor. 

Ion-exchange resins are used to help convert one type of sugar into another type of sugar, and to decolorize and purify sugar syrups.

Ion-exchange resins are used in the manufacturing of pharmaceuticals.

Ion-exchange resins are used for catalyzing certain reactions, isolating and purifying pharmaceutical active ingredients. 

Three ion-exchange resins, sodium polystyrene sulfonate, colestipol, and cholestyramine, are used as active ingredients. 

These anion-exchange resins are nonabsorbed

They are highly positively charged substances that bind bile acids, which are negatively charged anions, and 

relieve itching caused by excess bile acids in circulation by binding bile acids in the gut and facilitating elimination. 

Bloating or constipation may occur with anion-exchange resins.

Sodium polystyrene sulfonate is a strongly acidic ion-exchange resin and is used to treat hyperkalemia. 

Colestipol is a weakly basic ion-exchange resin and is used to treat hypercholesterolemia. 

Cholestyramine is a strongly basic ion-exchange resin and is also used to treat hypercholesterolemia. 

Colestipol and cholestyramine are known as bile acid sequestrants.

Ion-exchange resins are used as excipients in pharmaceutical formulations such as tablets, capsules, gums, and suspensions: taste-masking, extended release, tablet disintegration, increased bioavailability, and improving the chemical stability of the active ingredients.

Selective polymeric chelators used for maintenance therapy of some pathologies, where chronic ion accumulation occurs, such as Wilson disease where copper accumulation occurs or hereditary hemochromatosis where iron accumulation occurs.

Anion exchange resins readily absorb CO2 when dry and release it again when exposed to moisture, and is a promising material for direct carbon capture from ambient air.