Zeolites are a group of several
microporous, crystalline
aluminosilicate minerals commonly used as commercial
adsorbents and
catalyst
Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...
s. They mainly consist of
silicon
Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...
,
aluminium
Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...
,
oxygen
Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
, and have the general formula ・y where is either a metal ion or H
+.
The term was originally coined in 1756 by
Swedish mineralogist
Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical mineralogy, optical) properties of minerals and mineralized artifact (archaeology), artifacts. Specific s ...
Axel Fredrik Cronstedt
Baron Axel Fredrik Cronstedt (''/kroonstet/'' 23 December 1722 – 19 August 1765) was a Sweden, Swedish Mineralogy, mineralogist and chemist who discovered the Chemical element, element nickel in 1751 as a mining expert with the Bureau of Mines. ...
, who observed that rapidly heating a material, believed to have been
stilbite, produced large amounts of steam from water that had been
adsorbed by the material. Based on this, he called the material ''zeolite'', from the
Greek , meaning "to boil" and , meaning "stone".
Zeolites occur naturally, but are also produced industrially on a large scale. , 253 unique zeolite frameworks have been identified, and over 40 naturally occurring zeolite frameworks are known.
Every new zeolite structure that is obtained is examined by the International Zeolite Association Structure Commission (IZA-SC) and receives a three-letter designation.
Characteristics
Properties

Zeolites are white solids with ordinary handling properties, like many routine
aluminosilicate minerals, e.g.
feldspar
Feldspar ( ; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagiocl ...
. They have the general formula where M
+ is usually H
+ and Na
+. The Si/Al ratio is variable, which provides a means to tune the properties. Zeolites with a Si/Al ratios higher than about 3 are classified as high-silica zeolites, which tend to be more hydrophobic. The H
+ and Na
+ can be replaced by diverse cations, because zeolites have
ion exchange properties. The nature of the cations influences the porosity of zeolites.
Zeolites have microporous structures with a typical diameter of 0.3–0.8 nm. Like most aluminosilicates, the framework is formed by linking of aluminum and silicon atoms by oxides. This linking leads to a 3-dimensional network of Si-O-Al, Si-O-Si, and Al-O-Al linkages. The aluminum centers are negatively charged, which requires an accompanying cation. These cations are hydrated during the formation of the materials. The hydrated cations interrupt the otherwise dense network of Si-O-Al, Si-O-Si, and Al-O-Al linkage, leading to regular water-filled cavities. Because of the porosity of the zeolite, the water can exit the material through channels. Because of the rigidity of the zeolite framework, the loss of water does not result in collapse of the cavities and channels. This aspect – the ability to generate voids within the solid material – underpins the ability of zeolites to function as catalysts. They possess high physical and chemical stability due to the large covalent bonding contribution. They have excellent hydrophobicity and are suited for adsorption of bulky, hydrophobic molecules such as hydrocarbons. In addition to that, high-silica zeolites are exchangeable, unlike natural zeolites, and are used as
solid acid catalysts. The acidity is strong enough to protonate hydrocarbons and high-silica zeolites are used in acid catalysis processes such as
fluid catalytic cracking in petrochemical industry.
Framework structure

The structures of hundreds of zeolites have been determined. Most do not occur naturally. For each structure, the International Zeolite Association (IZA) gives a three-letter code called framework type code (FTC).
For example, the major molecular sieves, 3A, 4A and 5A, are all LTA (Linde Type A). Most commercially available natural zeolites are of the MOR, HEU or ANA-types.
An example of the notation of the ring structure of zeolite and other silicate materials is shown in the upper right figure. The middle figure shows a common notation using
structural formula. The left figure emphasizes the SiO tetrahedral structure. Connecting oxygen atoms together creates a four-membered ring of oxygen (blue bold line). In fact, such a ring substructure is called four membered ring or simply four-ring. The figure on the right shows a 4-ring with Si atoms connected to each other, which is the most common way to express the topology of the framework.
The figure on the right compares the typical framework structures of
LTA (left) and
FAU (right). Both zeolites share the
truncated octahedral structure (
sodalite cage) (purple line). However, the way they are connected (yellow line) is different: in LTA, the four-membered rings of the cage are connected to each other to form a skeleton, while in FAU, the six-membered rings are connected to each other. As a result, the pore entrance of LTA is an 8-ring (0.41 nm
) and belongs to the small pore zeolite, while the pore entrance of FAU is a 12-ring (0.74 nm
) and belongs to the large pore zeolite, respectively. Materials with a 10-ring are called medium pore zeolites, a typical example being
ZSM-5 (MFI).
Although more than 200 types of zeolites are known, only about 100 types of aluminosilicate are available. In addition, there are only a few types that can be synthesized in industrially feasible way and have sufficient thermal stability to meet the requirements for industrial use. In particular, the FAU (faujasite, USY),
*BEA (beta), MOR (high-silica mordenite), MFI (ZSM-5), and FER (high-silica ferrierite) types are called the big five of high silica zeolites, and industrial production methods have been established.
Porosity
The term
molecular sieve refers to a particular property of these materials, i.e., the ability to selectively sort molecules based primarily on a size exclusion process. This is due to a very regular pore structure of molecular dimensions. The maximum size of the molecular or ionic species that can enter the pores of a zeolite is controlled by the dimensions of the channels. These are conventionally defined by the ring size of the aperture, where, for example, the term "eight-ring" refers to a closed-loop that is built from eight tetrahedrally coordinated silicon (or aluminium) atoms and eight oxygen atoms. These rings are not always perfectly symmetrical due to a variety of causes, including strain induced by the bonding between units that are needed to produce the overall structure or coordination of some of the oxygen atoms of the rings to cations within the structure. Therefore, the pores in many zeolites are not cylindrical.
Isomorphous substitution
Isomorphous substitution of Si in zeolites can be possible for some heteroatoms such as
titanium
Titanium is a chemical element; it has symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...
,
[}] zinc
Zinc is a chemical element; it has symbol Zn and atomic number 30. It is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodic tabl ...
and
germanium
Germanium is a chemical element; it has Symbol (chemistry), symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid or a nonmetal in the carbon group that is chemically ...
.
Al atoms in zeolites can be also structurally replaced with
boron
Boron is a chemical element; it has symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the boron group it has three ...
and
gallium
Gallium is a chemical element; it has Chemical symbol, symbol Ga and atomic number 31. Discovered by the French chemist Paul-Émile Lecoq de Boisbaudran in 1875,
elemental gallium is a soft, silvery metal at standard temperature and pressure. ...
.
The
silicoaluminophosphate type (AlPO molecular sieve),
in which Si is isomorphous with Al and P and Al is isomorphous with Si, and the gallogermanate
and others are known.
Natural occurrence

Some of the more common mineral zeolites are
analcime
Analcime (; ) or analcite is a white, gray, or colorless tectosilicate mineral. Analcime consists of hydrated sodium aluminium silicate in cubic crystalline form. Its chemical formula is NaAlSi2O6 · H2O. Minor amounts of potassium and calcium ...
,
chabazite,
clinoptilolite,
heulandite,
natrolite,
phillipsite, and
stilbite. An example of the mineral formula of a zeolite is: ·2H
2O, the formula for
natrolite.
Natural zeolites form where
volcanic
A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
On Earth, volcanoes are most often fo ...
rocks and
ash layers react with
alkaline
In chemistry, an alkali (; from the Arabic word , ) is a basic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The ...
groundwater. Zeolites also crystallize in post-depositional environments over periods ranging from thousands to millions of years in shallow marine basins. Naturally occurring zeolites are rarely pure and are contaminated to varying degrees by other minerals, metals,
quartz
Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...
, or other zeolites. For this reason, naturally occurring zeolites are excluded from many important commercial applications where uniformity and purity are essential.
Zeolites transform to other minerals under
weathering
Weathering is the deterioration of rocks, soils and minerals (as well as wood and artificial materials) through contact with water, atmospheric gases, sunlight, and biological organisms. It occurs '' in situ'' (on-site, with little or no move ...
,
hydrothermal alteration
Metasomatism (from the Greek μετά ''metá'' "change" and σῶμα ''sôma'' "body") is the chemical alteration of a Rock (geology), rock by hydrothermal and other fluids. It is traditionally defined as metamorphism which involves a change in t ...
or
metamorphic conditions. Some examples:
* The sequence of
silica
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant f ...
-rich
volcanic rock
Volcanic rocks (often shortened to volcanics in scientific contexts) are rocks formed from lava erupted from a volcano. Like all rock types, the concept of volcanic rock is artificial, and in nature volcanic rocks grade into hypabyssal and me ...
s commonly progresses from:
**
Clay
Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...
→ quartz →
mordenite–
heulandite →
epistilbite →
stilbite →
thomsonite →
mesolite →
scolecite →
chabazite →
calcite
Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
.
* The sequence of silica-poor volcanic rocks commonly progresses from:
**
Cowlesite →
levyne →
offretite →
analcime
Analcime (; ) or analcite is a white, gray, or colorless tectosilicate mineral. Analcime consists of hydrated sodium aluminium silicate in cubic crystalline form. Its chemical formula is NaAlSi2O6 · H2O. Minor amounts of potassium and calcium ...
→
thomsonite →
mesolite →
scolecite →
chabazite →
calcite
Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...
.
Gemstones
Thomsonites, one of the rarer zeolite minerals, have been collected as
gemstone
A gemstone (also called a fine gem, jewel, precious stone, semiprecious stone, or simply gem) is a piece of mineral crystal which, when cut or polished, is used to make jewellery, jewelry or other adornments. Certain Rock (geology), rocks (such ...
s from a series of
lava
Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...
flows along
Lake Superior
Lake Superior is the largest freshwater lake in the world by surface areaThe Caspian Sea is the largest lake, but is saline, not freshwater. Lake Michigan–Huron has a larger combined surface area than Superior, but is normally considered tw ...
in
Minnesota
Minnesota ( ) is a U.S. state, state in the Upper Midwestern region of the United States. It is bordered by the Canadian provinces of Manitoba and Ontario to the north and east and by the U.S. states of Wisconsin to the east, Iowa to the so ...
and, to a lesser degree, in
Michigan
Michigan ( ) is a peninsular U.S. state, state in the Great Lakes region, Great Lakes region of the Upper Midwest, Upper Midwestern United States. It shares water and land boundaries with Minnesota to the northwest, Wisconsin to the west, ...
. Thomsonite nodules from these areas have
eroded
Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust and then transports it to another location where it is deposited. Erosion is disti ...
from
basalt
Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...
lava flows and are collected on beaches and by scuba divers in Lake Superior.
These thomsonite nodules have concentric rings in combinations of colors: black, white, orange, pink, purple, red, and many shades of green. Some nodules have copper inclusions and rarely will be found with
copper
Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...
"eyes". When polished by a
lapidary
Lapidary () is the practice of shaping rock (geology), stone, minerals, or gemstones into decorative items such as cabochons, engraved gems (including cameo (carving), cameos), and faceted designs. A person who practices lapidary techniques of ...
, the thomsonites sometimes displays a "cat's eye" effect (
chatoyancy).
Production
The first synthetic structure was reported by
Richard Barrer. Industrially important zeolites are produced synthetically. Typical procedures entail heating aqueous solutions of
alumina
Aluminium oxide (or aluminium(III) oxide) is a chemical compound of aluminium and oxygen with the chemical formula . It is the most commonly occurring of several aluminium oxides, and specifically identified as aluminium oxide. It is commonly ...
and
silica
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant f ...
with
sodium hydroxide
Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula . It is a white solid ionic compound consisting of sodium cations and hydroxide anions .
Sodium hydroxide is a highly corrosive base (chemistry), ...
. Equivalent reagents include
sodium aluminate and
sodium silicate. Further variations include the use of structure directing agents (SDA) such as
quaternary ammonium cation
In organic chemistry, quaternary ammonium cations, also known as quats, are positively-charged polyatomic ions of the structure , where R is an alkyl group, an aryl group or organyl group. Unlike the ammonium ion () and the primary, secondary, ...
s.
Synthetic zeolites hold some key advantages over their natural analogs. The synthetic materials are manufactured in a uniform, phase-pure state. It is also possible to produce zeolite structures that do not appear in nature. Zeolite A is a well-known example. Since the principal raw materials used to manufacture zeolites are silica and alumina, which are among the most abundant mineral components on earth, the potential to supply zeolites is virtually unlimited.
Ore mining
, the world's annual production of natural zeolite approximates 3 million
tonne
The tonne ( or ; symbol: t) is a unit of mass equal to 1,000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton in the United States to distinguish it from the non-metric units of the s ...
s. Major producers in 2010 included
China
China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
(2 million tonnes),
South Korea
South Korea, officially the Republic of Korea (ROK), is a country in East Asia. It constitutes the southern half of the Korea, Korean Peninsula and borders North Korea along the Korean Demilitarized Zone, with the Yellow Sea to the west and t ...
(210,000 t),
Japan
Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...
(150,000 t),
Jordan
Jordan, officially the Hashemite Kingdom of Jordan, is a country in the Southern Levant region of West Asia. Jordan is bordered by Syria to the north, Iraq to the east, Saudi Arabia to the south, and Israel and the occupied Palestinian ter ...
(140,000 t),
Turkey
Turkey, officially the Republic of Türkiye, is a country mainly located in Anatolia in West Asia, with a relatively small part called East Thrace in Southeast Europe. It borders the Black Sea to the north; Georgia (country), Georgia, Armen ...
(100,000 t)
Slovakia
Slovakia, officially the Slovak Republic, is a landlocked country in Central Europe. It is bordered by Poland to the north, Ukraine to the east, Hungary to the south, Austria to the west, and the Czech Republic to the northwest. Slovakia's m ...
(85,000 t) and the
United States
The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
(59,000 t). The ready availability of zeolite-rich rock at low cost and the shortage of competing minerals and rocks are probably the most important factors for its large-scale use. According to the
United States Geological Survey
The United States Geological Survey (USGS), founded as the Geological Survey, is an agency of the U.S. Department of the Interior whose work spans the disciplines of biology, geography, geology, and hydrology. The agency was founded on Mar ...
, it is likely that a significant percentage of the material sold as zeolites in some countries is ground or sawn volcanic
tuff that contains only a small amount of zeolites. These materials are used for construction, e.g.
dimension stone
Dimension stone is natural stone or Rock (geology), rock that has been selected and finished (e.g., trimmed, cut, drilled or ground) to specific sizes or shapes. Color, Texture (geology), texture and pattern, and surface finish of the stone are ...
(as an altered volcanic tuff), lightweight
aggregate,
pozzolanic cement, and
soil conditioners.
Synthesis

Over 200 synthetic zeolites have been reported. Most zeolites have aluminosilicate frameworks but some incorporate germanium, iron, gallium, boron, zinc, tin, and titanium. Zeolite synthesis involves
sol-gel-like processes. The product properties depend on reaction mixture composition, pH of the system,
operating temperature
An operating temperature is the allowable temperature range of the local ambient environment at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the de ...
, pre-reaction 'seeding' time, reaction time as well as the templates used. In the sol-gel process, other elements (metals, metal oxides) can be easily incorporated.
Applications
Zeolites are widely used as catalysts and
sorbents. In chemistry, zeolites are used as
membranes to separate
molecule
A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...
s (only molecules of certain sizes and shapes can pass through), and as traps for molecules so they can be analyzed.
Research into and development of the many
biochemical
Biochemistry, or biological chemistry, is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology, ...
and
biomedical
Biomedicine (also referred to as Western medicine, mainstream medicine or conventional medicine) applications of zeolites, particularly the naturally occurring species
heulandite,
clinoptilolite, and
chabazite has been ongoing.
Ion-exchange, water purification and softening
Zeolites are widely used as
ion-exchange beds in domestic and commercial
water purification
Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids, and gases from water. The goal is to produce water that is fit for specific purposes. Most water is purified and disinfected for hu ...
,
softening, and other applications.
Evidence for the oldest known zeolite water purification filtration system occurs in the undisturbed sediments of the Corriental reservoir at the Maya city of
Tikal
Tikal (; ''Tik'al'' in modern Mayan orthography) is the ruin of an ancient city, which was likely to have been called Yax Mutal, found in a rainforest in Guatemala. It is one of the largest archaeological sites and urban centers of the Pre-Col ...
, in northern Guatemala.
Earlier, polyphosphates were used to soften hard water. The polyphosphates forms complex with metal ions like Ca
2+ and Mg
2+ to bind them up so that they could not interfere in cleaning process. However, when this phosphate rich water goes in main stream water, it results in
eutrophication
Eutrophication is a general term describing a process in which nutrients accumulate in a body of water, resulting in an increased growth of organisms that may deplete the oxygen in the water; ie. the process of too many plants growing on the s ...
of water bodies and hence use of polyphosphate was replaced with use of a synthetic zeolite.
The largest single use for zeolite is the global laundry
detergent
A detergent is a surfactant or a mixture of surfactants with Cleanliness, cleansing properties when in Concentration, dilute Solution (chemistry), solutions. There are a large variety of detergents. A common family is the alkylbenzene sulfonate ...
market. Zeolites are used in laundry detergent as water softeners, removing Ca
2+ and Mg
2+ ions which would otherwise precipitate from the solution. The ions are retained by the zeolites which releases Na
+ ions into the solution, allowing the laundry detergent to be effective in areas with hard water.
Catalysis
Synthetic zeolites, like other mesoporous materials (e.g.,
MCM-41), are widely used as
catalyst
Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quick ...
s in the
petrochemical industry
file:Jampilen Petrochemical Co. 02.jpg, 300px, Jampilen Petrochemical co., Asaluyeh, Iran
The petrochemical industry is concerned with the production and trade of petrochemicals. A major part is constituted by the plastics industry, plastics (poly ...
, such as in fluid catalytic
cracking and
hydrocracking. Zeolites confine molecules into small spaces, which causes changes in their structure and reactivity. The acidic forms of zeolites prepared are often powerful solid-state
solid acids, facilitating a host of acid-catalyzed reactions, such as
isomerization,
alkylation Alkylation is a chemical reaction that entails transfer of an alkyl group. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion, or a carbene (or their equivalents). Alkylating agents are reagents for effecting al ...
, and cracking.
Catalytic cracking uses a reactor and a regenerator. Feed is injected onto a hot, fluidized catalyst where large
gasoil molecules are broken into smaller gasoline molecules and
olefins
In organic chemistry, an alkene, or olefin, is a hydrocarbon containing a carbon–carbon double bond. The double bond may be internal or at the terminal position. Terminal alkenes are also known as α-olefins.
The International Union of P ...
. The vapor-phase products are separated from the catalyst and distilled into various products. The catalyst is circulated to a regenerator, where the air is used to burn coke off the surface of the catalyst that was formed as a byproduct in the cracking process. The hot, regenerated catalyst is then circulated back to the reactor to complete its cycle.
Zeolites containing cobalt
nanoparticle
A nanoparticle or ultrafine particle is a particle of matter 1 to 100 nanometres (nm) in diameter. The term is sometimes used for larger particles, up to 500 nm, or fibers and tubes that are less than 100 nm in only two directions. At ...
s have applications in the recycling industry as a catalyst to break down
polyethylene
Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes and containers including bott ...
and
polypropylene
Polypropylene (PP), also known as polypropene, is a thermoplastic polymer used in a wide variety of applications. It is produced via chain-growth polymerization from the monomer Propene, propylene.
Polypropylene belongs to the group of polyolefin ...
, two widely used plastics, into
propane
Propane () is a three-carbon chain alkane with the molecular formula . It is a gas at standard temperature and pressure, but becomes liquid when compressed for transportation and storage. A by-product of natural gas processing and petroleum ref ...
.
Nuclear waste reprocessing
Zeolites have been used in advanced
nuclear reprocessing
Nuclear reprocessing is the chemical separation of fission products and actinides from spent nuclear fuel. Originally, reprocessing was used solely to extract plutonium for producing nuclear weapons. With commercialization of nuclear power, the ...
methods, where their micro-porous ability to capture some ions while allowing others to pass freely allows many
fission products to be efficiently removed from the waste and permanently trapped. Equally important are the mineral properties of zeolites. Their alumino-silicate construction is extremely durable and resistant to radiation, even in porous form. Additionally, once they are loaded with trapped fission products, the zeolite-waste combination can be hot-pressed into an extremely durable ceramic form, closing the pores and trapping the waste in a solid stone block. This is a waste form factor that greatly reduces its hazard, compared to conventional reprocessing systems. Zeolites are also used in the management of leaks of radioactive materials. For example, in the aftermath of the
Fukushima Daiichi nuclear disaster
The Fukushima nuclear accident was a major nuclear accident at the Fukushima Daiichi Nuclear Power Plant in Ōkuma, Fukushima, Japan, which began on 11 March 2011. The cause of the accident was the 2011 Tōhoku earthquake and tsunami, which r ...
, sandbags of zeolite were dropped into the seawater near the power plant to adsorb the radioactive
cesium-137 that was present in high levels.
Gas separation and storage
Zeolites have the potential of providing precise and specific separation of gases, including the removal of H
2O, CO
2, and SO
2 from low-grade
natural gas
Natural gas (also fossil gas, methane gas, and gas) is a naturally occurring compound of gaseous hydrocarbons, primarily methane (95%), small amounts of higher alkanes, and traces of carbon dioxide and nitrogen, hydrogen sulfide and helium ...
streams. Other separations include
noble gases
The noble gases (historically the inert gases, sometimes referred to as aerogens) are the members of group 18 of the periodic table: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn) and, in some cases, oganesson (Og) ...
, N
2, O
2,
freon
Freon ( ) is a registered trademark of the Chemours Company and generic descriptor for a number of halocarbon products. They are stable, nonflammable, low toxicity gases or liquids which have generally been used as refrigerants and as aerosol p ...
, and
formaldehyde
Formaldehyde ( , ) (systematic name methanal) is an organic compound with the chemical formula and structure , more precisely . The compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde. It is stored as ...
.
On-board oxygen generating systems (OBOGS) and
oxygen concentrators use zeolites in conjunction with
pressure swing adsorption to remove nitrogen from compressed air to supply oxygen for aircrews at high altitudes, as well as home and portable oxygen supplies.
Zeolite-based
oxygen concentrator systems are widely used to produce medical-grade oxygen. The zeolite is used as a
molecular sieve to create purified oxygen from air using its ability to trap impurities, in a process involving the adsorption of nitrogen, leaving highly purified oxygen and up to 5% argon.
The German group
Fraunhofer e.V. announced that they had developed a zeolite substance for use in the
biogas
Biogas is a gaseous renewable energy source produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste, Wastewater treatment, wastewater, and food waste. Biogas is produced by anaerobic ...
industry for long-term storage of energy at a density four times greater than water. Ultimately, the goal is to store heat both in industrial installations and in small combined heat and power plants such as those used in larger residential buildings.
Debbie Meyer Green Bags, a produce storage and preservation product, uses a form of zeolite as its active ingredient. The bags are lined with zeolite to adsorb
ethylene
Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon–carbon bond, carbon–carbon doub ...
, which is intended to slow the ripening process and extend the shelf life of produce stored in the bags.
Clinoptilolite has also been added to chicken food: the absorption of water and ammonia by the zeolite made the birds' droppings drier and less odoriferous, hence easier to handle.
Zeolites are also used as a
molecular sieve in
cryosorption style
vacuum pump
A vacuum pump is a type of pump device that draws gas particles from a sealed volume in order to leave behind a partial vacuum. The first vacuum pump was invented in 1650 by Otto von Guericke, and was preceded by the suction pump, which dates to ...
s.
Solar energy storage and use
Zeolites can be used to thermochemically store solar heat harvested from
solar thermal collectors as first demonstrated by Guerra in 1978 and for
adsorption refrigeration, as first demonstrated by Tchernev in 1974. In these applications, their high heat of
adsorption
Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the ''adsorbate'' on the surface of the ''adsorbent''. This process differs from absorption, in which a ...
and ability to
hydrate
In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understo ...
and dehydrate while maintaining structural stability is exploited. This
hygroscopic
Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption (chemistry), absorption or adsorption from the surrounding Natural environment, environment, which is usually at normal or room temperature. If water mol ...
property coupled with an inherent
exothermic (energy releasing) reaction when transitioning from a dehydrated form to a hydrated form make natural zeolites useful in harvesting waste heat and solar heat energy.
Building materials
Synthetic zeolites are used as an additive in the production process of warm mix
asphalt concrete
Asphalt concrete (commonly called asphalt, blacktop, or pavement in North America, and Tarmacadam, tarmac or bitumen macadam in the United Kingdom and the Republic of Ireland) is a composite material commonly used to surface road surface, roads ...
. The development of this application started in Germany in the 1990s. They help by decreasing the temperature level during manufacture and laying of asphalt concrete, resulting in lower consumption of fossil fuels, thus releasing less
carbon dioxide
Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...
, aerosols, and vapors. The use of synthetic zeolites in hot mixed asphalt leads to easier compaction and, to a certain degree, allows cold weather paving and longer hauls.
When added to
Portland cement
Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar (masonry), mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in th ...
as a
pozzolan, they can reduce chloride permeability and improve workability. They reduce weight and help moderate water content while allowing for slower drying, which improves break strength. When added to
lime mortar
Lime mortar or torching is a masonry mortar (masonry), mortar composed of lime (material), lime and an construction aggregate, aggregate such as sand, mixed with water. It is one of the oldest known types of mortar, used in ancient Rome and anci ...
s and lime-metakaolin mortars, synthetic zeolite pellets can act simultaneously as a pozzolanic material and a water reservoir.
Cat litter
Non-clumping
cat litter is often made of zeolite (or
diatomite), one form of which, invented at
MIT
The Massachusetts Institute of Technology (MIT) is a private research university in Cambridge, Massachusetts, United States. Established in 1861, MIT has played a significant role in the development of many areas of modern technology and sc ...
, can sequester the
greenhouse gas
Greenhouse gases (GHGs) are the gases in the atmosphere that raise the surface temperature of planets such as the Earth. Unlike other gases, greenhouse gases absorb the radiations that a planet emits, resulting in the greenhouse effect. T ...
methane
Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...
from the atmosphere.
Hemostatic agent
The original formulation of
QuikClot brand
hemostatic agent, which is used to stop severe bleeding, contained zeolite granules. When in contact with blood, the granules would rapidly absorb water from the blood plasma, creating an exothermic reaction which generated heat. The absorption of water would also concentrate clotting factors present within the blood, causing the clot formation process to occur much faster than under normal circumstances, as shown
in vitro
''In vitro'' (meaning ''in glass'', or ''in the glass'') Research, studies are performed with Cell (biology), cells or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", these studies in ...
.
The 2022 formulation of QuikClot uses a nonwoven material impregnated with
kaolin
Kaolinite ( ; also called kaolin) is a clay mineral, with the chemical composition Al2 Si2 O5( OH)4. It is a layered silicate mineral, with one tetrahedral sheet of silica () linked through oxygen atoms to one octahedral sheet of alumina (). ...
, an inorganic mineral activating
Factor XII, in turn accelerating natural clotting. Unlike the original zeolite formulation,
kaolin
Kaolinite ( ; also called kaolin) is a clay mineral, with the chemical composition Al2 Si2 O5( OH)4. It is a layered silicate mineral, with one tetrahedral sheet of silica () linked through oxygen atoms to one octahedral sheet of alumina (). ...
does not exhibit any thermogenic properties.
Soil treatment
In agriculture,
clinoptilolite (a naturally occurring zeolite) is used as a soil treatment. It provides a source of slowly released
potassium
Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...
. If previously loaded with
ammonium
Ammonium is a modified form of ammonia that has an extra hydrogen atom. It is a positively charged (cationic) polyatomic ion, molecular ion with the chemical formula or . It is formed by the protonation, addition of a proton (a hydrogen nucleu ...
, the zeolite can serve a similar function in the slow release of
nitrogen
Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...
.
Zeolites can also act as water moderators, in which they will absorb up to 55% of their weight in water and slowly release it under the plant's demand. This property can prevent root rot and moderate drought cycles.
Aquaria
Pet stores market zeolites for use as filter additives in
aquaria,
where they can be used to adsorb
ammonia
Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...
and other nitrogenous compounds. Due to the high affinity of some zeolites for calcium, they may be less effective in hard water and may deplete calcium. Zeolite filtration is also used in some marine aquaria to keep nutrient concentrations low for the benefit of corals adapted to nutrient-depleted waters.
Where and how the zeolite was formed is an important consideration for aquarium applications. Most Northern hemisphere, natural zeolites were formed when molten lava came into contact with sea water, thereby "loading" the zeolite with Na (sodium) sacrificial ions. The mechanism is well known to chemists as
ion exchange. These sodium ions can be replaced by other ions in solution, thus the take-up of nitrogen in ammonia, with the release of the sodium. A deposit near
Bear River in southern
Idaho
Idaho ( ) is a landlocked U.S. state, state in the Pacific Northwest and Mountain states, Mountain West subregions of the Western United States. It borders Montana and Wyoming to the east, Nevada and Utah to the south, and Washington (state), ...
is a fresh water variety (Na < 0.05%). Southern hemisphere zeolites are typically formed in freshwater and have a high calcium content.
Veterinary and human use
Zeolites have some veterinary applications, with
clinoptilolite approved in the EU as an additive for cattle feed. It acts primarily as a detoxifying agent in the gut, where is can absorb undesirable species via ion-exchange before being excreted. For instance, nitrate fertilisers are water soluble and prolonged exposure by dairy cattle is known to impair protein metabolism and glucose utilization. Clinoptilolite adsorbs nitrate ions with good selectivity, allowing it to reduce these ill effects.
Zeolites have been studied for human medical applications, particularly for bowel conditions. There are no approved medical uses for zeolites as of 2024. Regardless, they are widely marketed as
dietary supplements
A dietary supplement is a manufactured product intended to supplement a person's diet by taking a pill, capsule, tablet, powder, or liquid. A supplement can provide nutrients either extracted from food sources, or that are synthetic ...
.
Mineral species

The zeolite structural group (
Nickel-Strunz classification) includes:
* 09.GA. – Zeolites with T
5O
10 units (T = combined Si and Al): the fibrous zeolites
** Natrolite framework (NAT):
gonnardite,
natrolite,
mesolite,
paranatrolite,
scolecite,
tetranatrolite
** Edingtonite framework (EDI):
edingtonite,
kalborsite
** Thomsonite framework (THO):
thomsonite-series
* 09.GB. – Chains of single connected 4-membered rings
** Analcime framework (ANA):
analcime
Analcime (; ) or analcite is a white, gray, or colorless tectosilicate mineral. Analcime consists of hydrated sodium aluminium silicate in cubic crystalline form. Its chemical formula is NaAlSi2O6 · H2O. Minor amounts of potassium and calcium ...
,
leucite (
topologically a zeolite despite being
anhydrous; chemically a
feldspathoid
The feldspathoids are a group of tectosilicate minerals which resemble feldspar
Feldspar ( ; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, pota ...
),
pollucite,
wairakite
**
Laumontite (LAU),
yugawaralite (YUG),
goosecreekite (GOO),
montesommaite (MON)
* 09.GC. – Chains of doubly connected 4-membered rings
** Phillipsite framework (PHI):
harmotome,
phillipsite-series
** Gismondine framework (GIS):
amicite,
gismondine,
garronite,
gobbinsite
**
Boggsite (BOG),
merlinoite (MER),
mazzite-series (MAZ),
paulingite-series (PAU),
perlialite (Linde type L framework, zeolite L, LTL)
* 09.GD. – Chains of 6-membered rings: tabular zeolites
** Chabazite framework (CHA):
chabazite-series,
herschelite,
willhendersonite and
SSZ-13
** Faujasite framework (FAU):
faujasite-series, Linde type X (zeolite X, X zeolites), Linde type Y (zeolite Y, Y zeolites)
** Mordenite framework (MOR):
maricopaite,
mordenite
** Offretite–wenkite subgroup 09.GD.25 (Nickel–Strunz, 10 ed):
offretite (OFF), wenkite (WEN)
** Bellbergite (TMA-E, Aiello and Barrer; framework type EAB), bikitaite (BIK), erionite-series (ERI), ferrierite (FER), gmelinite (GME),
levyne-series (LEV), dachiardite-series (DAC),
epistilbite (EPI)
* 09.GE. – Chains of T
10O
20 tetrahedra (T = combined Si and Al)
** Heulandite framework (HEU):
clinoptilolite,
heulandite-series
** Stilbite framework (STI): barrerite, stellerite,
stilbite-series
** Brewsterite framework (BRE): brewsterite-series
* Others
**
Cowlesite, pentasil (also known as
ZSM-5, framework type MFI), tschernichite (beta polymorph A, disordered framework, BEA), Linde type A framework (zeolite A, LTA)
Computational study
Computer calculations have predicted that millions of hypothetical zeolite structures are possible. However, only 232 of these structures have been discovered and synthesized so far, so many zeolite scientists question why only this small fraction of possibilities are observed. This problem is often referred to as "the bottleneck problem". Currently, several theories attempt to explain the reasoning behind this question.
# Zeolite synthesis research has primarily concentrated on hydrothermal methods; however, new zeolites may be synthesized using alternative methods. Synthesis methods that have started to gain use include microwave-assisted, post-synthetic modification, and steam.
# Geometric computer simulations have shown that the discovered zeolite frameworks possess a behavior known as "the flexibility window". This shows that there is a range in which the zeolite structure is "flexible" and can be compressed but retains the framework structure. It is suggested that if a framework does not possess this property then it cannot be feasibly synthesized.
# As zeolites are metastable, certain frameworks may be inaccessible as nucleation cannot occur because more stable and energetically favorable zeolites will form. Post-synthetic modification has been used to combat this issue with the ADOR method, whereby frameworks can be cut apart into layers and bonded back together by either removing silica bonds or including them.
# Based on dense crystal model systems, the theory of crystallization via solute pre-nucleation clusters was developed. Investigation of zeolite crystallization in hydrated silicate ionic liquids (HSIL) has shown that zeolites can nucleate via the condensation of ion-paired pre-nucleation clusters. This line of research identified several connections between the synthesis medium liquid chemistry and important properties of zeolite crystals, such as the role of inorganic structure-directing agents in zeolite framework selection, the role of ion-pairing on the zeolite molecular composition and topology, and the role of liquid cation mobility on the zeolite crystal size and morphology. Consequently, complex relations exist between the properties of zeolite synthesis media and the crystallizing zeolite, potentially explaining why only a small fraction of the hypothetical zeolite frameworks can be synthesized. While these relations are not yet fully understood, HSIL zeolite synthesis is an exceptional model system for zeolite science, providing opportunities to advance current understanding of the zeolite conundrum.
See also
*
*
*
*
*
*
References
Further reading
* The classic reference for the field has been Breck's book ''Zeolite Molecular Sieves: Structure, Chemistry, And Use''.
*
*
*
* American Solar Energy Society, American Solar Energy Society meeting. 1 Jun 1983. Minneapolis, MN, USA
*
*
*
External links
International Zeolite AssociationDatabase of zeolite pore characterizations
The Synthesis Commission of the International Zeolite AssociationFederation of European Zeolite AssociationsBritish Zeolite AssociationDatabase of Zeolite Structures
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Zeolites
Tectosilicates
Antihemorrhagics
Conservation and restoration materials
Porous media
Industrial minerals
Catalysts
Acid catalysts