Ion exchange is an exchange of ions between two electrolytes or
between an electrolyte solution and a complex. In most cases the term
is used to denote the processes of purification, separation, and
decontamination of aqueous and other ion-containing solutions with
solid polymeric or mineralic "ion exchangers".
Typical ion exchangers are ion-exchange resins (functionalized porous
or gel polymer), zeolites, montmorillonite, clay, and soil humus. Ion
exchangers are either cation exchangers, which exchange positively
charged ions (cations), or anion exchangers, which exchange negatively
charged ions (anions). There are also amphoteric exchangers that are
able to exchange both cations and anions simultaneously. However, the
simultaneous exchange of cations and anions can be more efficiently
performed in mixed beds, which contain a mixture of anion- and
cation-exchange resins, or passing the treated solution through
several different ion-exchange materials.
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).
Singly charged monatomic ions like Na+, K+, and Cl−.
Doubly charged monatomic ions like Ca2+ and Mg2+.
Polyatomic inorganic ions like SO42− and PO43−.
Organic bases, usually molecules containing the amine functional group
Organic acids, often molecules containing −COO− (carboxylic acid)
Biomolecules that can be ionized: amino acids, peptides, proteins,
Along with absorption and adsorption, ion exchange is a form of
Ion exchange is a reversible process, and the ion exchanger can be
regenerated or loaded with desirable ions by washing with an excess of
1.1 Other applications
2 Regenerating wasted water
3 See also
5 External links
Ion exchange is widely used in the food and beverage industry,
hydrometallurgy, metals finishing, chemical, petrochemical and
pharmaceutical technology, sugar and sweetener production, ground- and
potable-water treatment, nuclear, softening and industrial water
treatment, semiconductor, power, and a host of other industries.
A typical example of application is preparation of high-purity water
for power engineering, electronic and nuclear industries; i.e.
polymeric or mineralic insoluble ion exchangers are widely used for
water softening, water purification, water decontamination, etc.
Ion exchange is a method widely used in household (laundry detergents
and water filters) to produce soft water. This is accomplished by
exchanging calcium Ca2+ and magnesium Mg2+ cations against Na+ or H+
cations (see water softening). Another application for ion exchange in
domestic water treatment is the removal of nitrate and natural organic
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 other actinides,
including thorium, and lanthanum, neodymium, ytterbium, samarium,
lutetium, from each other and the other lanthanides. 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 used to be the only practical way to separate them in
large quantities, until the advent of solvent extraction techniques
that can be scaled up enormously.
A very important case is the
PUREX process (plutonium-uranium
extraction process), which is used to separate the plutonium and the
uranium from the spent fuel products from a nuclear reactor, and to be
able to dispose of the waste products. Then, the plutonium and uranium
are available for making nuclear-energy materials, such as new reactor
fuel and nuclear weapons.
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.
Zirconium is practically
transparent to free neutrons, used in building reactors, but hafnium
is a very strong absorber of neutrons, used in reactor control rods.
Ion exchangers are used in nuclear reprocessing and the treatment of
Ion-exchange resins in the form of thin membranes are used in
chloralkali process, fuel cells and vanadium redox batteries.
Large cation/anion ion exchangers used in water purification of boiler
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.
Theoretical energy efficiency of this method is on par with
electrodialysis and reverse osmosis.
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.
Regenerating wasted water
Most ion-exchange systems contain containers of ion-exchange resin
that are operated on a cyclic basis.
During the filtration process, water flows through the resin container
until the resin is considered exhausted. That happened only when water
leaving the exchanger contains more than the desired maximal
concentration of the ions being removed.
Resin is then regenerated by
sequentially backwashing the resin bed to remove accumulated solids,
flushing removed ions from the resin with a concentrated solution of
replacement ions, and rinsing the flushing solution from the resin.
Production of backwash, flushing, and rinsing wastewater during
regeneration of ion-exchange media limits the usefulness of ion
exchange for wastewater treatment.
Water softeners are usually regenerated with brine containing 10%
sodium chloride. Aside from the soluble chloride salts of divalent
cations removed from the softened water, softener regeneration
wastewater contains the unused 50 – 70% of the sodium chloride
regeneration flushing brine required to reverse ion-exchange resin
equilibria. Deionizing resin regeneration with sulfuric acid and
sodium hydroxide is approximately 20–40% efficient. Neutralized
deionizer regeneration wastewater contains all of the removed ions
plus 2.5–5 times their equivalent concentration as sodium
Alkali anion exchange membrane
^ Mischissin, Stephen G. (7 February 2012). "University of Rochester -
Investigation of Steam Turbine Extraction Line Failures" (PDF).
Arlington, VA. pp. 25–26. Archived from the original (PDF) on
23 September 2015. Retrieved 23 February 2015.
^ Shkolnikov, Viktor; Bahga, Supreet S.; Santiago, Juan G. (August 28,
Desalination and hydrogen, chlorine, and sodium hydroxide
production via electrophoretic ion exchange and precipitation" (PDF).
14 (32). Phys. Chem. Chem Phys.
^ Kemmer, pp. 12–17, 12 – 25.
^ Betz, p. 59.
^ Kemmer, p. 12 – 18.
Betz Laboratories (1976). Handbook of Industrial Water Conditioning
(7th Edition). Betz Laboratories.
Ion Exchangers (K. Dorfner, ed.), Walter de Gruyter, Berlin, 1991.
C. E. Harland,
Ion exchange: Theory and Practice, The Royal Society of
Chemistry, Cambridge, 1994.
Friedrich G. Helfferich (1962).
Ion Exchange. Courier Dover
Publications. ISBN 978-0-486-68784-1.
Kemmer, Frank N. (1979). The NALCO Water Handbook. McGraw-Hill.
Ion exchange (D. Muraviev, V. Gorshkov, A. Warshawsky), M. Dekker, New
A. A. Zagorodni,
Ion Exchange Materials: Properties and Applications,
Elsevier, Amsterdam, 2006.
Illustrated and well defined chemistry lab practical on ion exchange
from Dartmouth College
Some applets illustrating ion exchange processes
A simple explanation of deionization
Ion exchange, BioMineWiki
Acid mine drainage
Adsorbable organic halides
Biochemical oxygen demand
Chemical oxygen demand
Total dissolved solids
Total suspended solids
Agricultural wastewater treatment
API oil-water separator
Decentralized wastewater system
Fecal sludge management
Industrial wastewater treatment
Rotating biological contactor
Sewage sludge treatment
Ultraviolet germicidal irradiation
Wastewater treatment plant
Septic drain field