Ion exchange is widely used in the food and beverage industry, hydrometallurgy, metals finishing, chemical, petrochemical, pharmaceutical technology, sugar and sweetener production, ground- and potable-water treatment, nuclear, softening, industrial water treatment, semiconductor, power, and many other industries. A typical example of application is preparation of high-purity water for
power engineering, electronic and nuclear industries; i.e.
polymeric or
inorganic
insoluble ion exchangers are widely used for
water softening,
water purification, water
decontamination, etc. Ion exchange is a method widely used in household filters to produce
soft water for the benefit of laundry detergents, soaps, and water heaters. This is accomplished by exchanging divalent cations (such as
calcium Ca2+ and
magnesium Mg2+) with highly soluble monovalent cations (e.g., Na+ or H+) (see
water softening). Another application for ion exchange in domestic water treatment is the removal of
nitrate and
natural organic matter. In domestic filtration systems ion exchange is one of the alternatives for water softening in households along with reverse osmosis (RO) membranes. Compared to RO membranes, ion exchange requires repetitive regeneration when inlet water is hard (has high mineral content). Industrial and analytical
ion-exchange chromatography is another area to be mentioned. Ion-exchange chromatography is a
chromatographical method that is widely used for chemical analysis and separation of ions. For example, in
biochemistry it is widely used to separate charged molecules such as
proteins. An important area of the application is extraction and purification of biologically produced substances such as proteins (
amino acids) and
DNA/
RNA. Ion-exchange processes are used to separate and purify
metals, including separating
uranium from
plutonium and the other
actinides, including
thorium,
neptunium, and
americium. This process is also used to separate the
lanthanides, such as
lanthanum,
cerium,
neodymium,
praseodymium,
europium, and
ytterbium, from each other. The separation of neodymium and praseodymium was a particularly difficult one, and those were formerly thought to be just one element
didymium – but that is an alloy of the two. There are two series of
rare-earth metals, the lanthanides and the actinides, both of whose families all have very similar chemical and physical properties. Using methods developed by
Frank Spedding in the 1940s, ion-exchange processes were formerly the only practical way to separate them in large quantities, until the development of the "solvent extraction" techniques that can be scaled up enormously. A very important case of ion-exchange is the plutonium-uranium extraction process (
PUREX), which is used to separate the plutonium (mainly ) and the
uranium (in that case known as
reprocessed uranium) contained in
spent fuel from
americium,
curium,
neptunium (the
minor actinides), and the
fission products that come from
nuclear reactors. Thus the waste products can be separated out for disposal. Next, the plutonium and uranium are available for making nuclear-energy materials, such as new reactor fuel (
MOX-fuel) and (plutonium-based)
nuclear weapons. Historically some fission products such as
Strontium-90 or
Caesium-137 were likewise separated for use as
radionuclides employed in industry or medicine. The ion-exchange process is also used to separate other sets of very similar chemical elements, such as
zirconium and
hafnium, which is also very important for the nuclear industry. Physically, zirconium is practically transparent to free neutrons, used in building nuclear reactors, but hafnium is a very strong absorber of neutrons, used in reactor
control rods. Thus, ion-exchange is used in
nuclear reprocessing and the treatment of
radioactive waste. Ion-exchange resins in the form of thin
membranes are also used in
chloralkali process,
fuel cells, and
vanadium redox batteries. Ion exchange can also be used to remove hardness from water by exchanging calcium and magnesium ions for sodium ions in an ion-exchange column. Liquid-phase (aqueous) ion-exchange
desalination has been demonstrated. In this technique anions and cations in salt water are exchanged for carbonate anions and calcium cations respectively using
electrophoresis. Calcium and carbonate ions then react to form
calcium carbonate, which then precipitates, leaving behind fresh water. The desalination occurs at ambient temperature and pressure and requires no membranes or solid ion exchangers. The theoretical energy efficiency of this method is on par with
electrodialysis and
reverse osmosis.
Other applications • In
soil science,
cation-exchange capacity is the ion-exchange capacity of
soil for positively charged ions. Soils can be considered as natural weak cation exchangers. • In pollution remediation and
geotechnical engineering, ion-exchange capacity determines the swelling capacity of swelling or
expansive clay such as
montmorillonite, which can be used to "capture" pollutants and charged ions. • In planar
waveguide manufacturing, ion exchange is used to create the guiding layer of higher
index of refraction. •
Dealkalization, removal of alkali ions from a
glass surface. •
Chemically strengthened glass, produced by exchanging K+ for Na+ in
soda glass surfaces using KNO3 melts. == Advantages and limitations ==