Zeolites are
microporous
A microporous material is a material containing pores with diameters less than 2 nm. Examples of microporous materials include zeolites and metal-organic frameworks.
Porous materials are classified into several kinds by their size. The recom ...
, crystalline
aluminosilicate
Aluminosilicate minerals ( IMA symbol: Als) are minerals composed of aluminium, silicon, and oxygen, plus countercations. They are a major component of kaolin and other clay minerals.
Andalusite, kyanite, and sillimanite are naturally occurr ...
materials commonly used as commercial
adsorbents
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
catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
s. They mainly consist of silicon, aluminium, oxygen, and have the general formula ・y where is either a metal ion or H
+. These positive ions can be exchanged for others in a contacting
electrolyte
An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon dis ...
solution. exchanged zeolites are particularly useful as solid
acid catalysts
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
.
The term ''zeolite'' was originally coined in 1756 by
Swedish
Swedish or ' may refer to:
Anything from or related to Sweden, a country in Northern Europe. Or, specifically:
* Swedish language, a North Germanic language spoken primarily in Sweden and Finland
** Swedish alphabet, the official alphabet used by ...
mineralogist
Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical) properties of minerals and mineralized artifacts. Specific studies within mineralogy include the proces ...
Axel Fredrik Cronstedt
Baron Axel Fredrik Cronstedt (''/kroonstet/'' 23 December 1722 – 19 August 1765) was a Swedish mineralogist and chemist who discovered the element nickel in 1751 as a mining expert with the Bureau of Mines.
Cronstedt is considered a founder of ...
, who observed that rapidly heating a material, believed to have been
stilbite
Stilbite is the name of a series of tectosilicate minerals of the zeolite group. Prior to 1997, stilbite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a series nam ...
, produced large amounts of steam from water that had been
adsorbed
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 ...
by the material. Based on this, he called the material ''zeolite'', from the
Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
, 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 and receives a three letter designation.
Characteristics
Properties
![Zeolite structure as an assembly of tetrahedra](https://upload.wikimedia.org/wikipedia/commons/a/a3/Zeolite_structure_as_an_assembly_of_tetrahedra.png)
Zeolites are the
aluminosilicate
Aluminosilicate minerals ( IMA symbol: Als) are minerals composed of aluminium, silicon, and oxygen, plus countercations. They are a major component of kaolin and other clay minerals.
Andalusite, kyanite, and sillimanite are naturally occurr ...
members of the family of
microporous material
A microporous material is a material containing pores with diameters less than 2 nm. Examples of microporous materials include zeolites and metal-organic frameworks.
Porous materials are classified into several kinds by their size. The recom ...
s, and mainly consist of silicon, aluminium, oxygen, and have the general formula ・y where is either a metal ion or H
+. The value of x (Si/Al molar ratio) is greater than 1 and y is the number of water molecules in the formula unit. Zeolites have microporous structures with a typical diameter of 0.3–0.8 nm and accommodate a wide variety of
cations
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
, such as Na
+, K
+, Ca
2+, Mg
2+ and others. These positive ions are often loosely held and can readily be exchanged for others in a contacting
electrolyte
An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon dis ...
solution. Cation exchanged zeolites possess different acidity and catalyze different reactions.. The Si/Al ratio is greater than 1 because zeolites have no Al-O-Al bond (Löwenstein rule).
They are formed by the linking of the corner oxygen atoms of AlO
4 and SiO
4 tetrahedra to form covalent network structures.
The general formula of zeolite, , where the part is
ionic bond
Ionic bonding is a type of chemical bonding that involves the electrostatic attraction between oppositely charged ions, or between two atoms with sharply different electronegativities, and is the primary interaction occurring in ionic compounds. ...
-like and the part is
covalent bond
A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atoms ...
-like. Zeolites therefore have both
ionic crystal
In chemistry, an ionic crystal is a crystalline form of an ionic compound. They are solids consisting of ions bound together by their electrostatic attraction into a regular lattice. Examples of such crystals are the alkali halides, including ...
and
covalent crystal
A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atom ...
properties, and the balance of these properties depends on the Si/Al ratio (x).
Si/Al ratios below about 3 correspond to natural zeolites and some synthetic zeolites such as A-type and X-type zeolites. They are useful as ion-exchange agents because of their high ion-exchange capacity. Commercially available
molecular sieve
A molecular sieve is a material with pores (very small holes) of uniform size. These pore diameters are similar in size to small molecules, and thus large molecules cannot enter or be adsorbed, while smaller molecules can. As a mixture of molecu ...
adsorbents often belong to this group.
Zeolites with a Si/Al ratios higher about 3 are classified as high-silica zeolites, which are rarely found in nature and are synthesized industrially. They possess high physical and chemical stability due to the large colvalent bonding contribution. They have excellent hydrophobicity and are suited for adsorption of builky, hydrophobic molecules such as hydrocarbons. In addition to that, high-silica zeolites are exchangeable, unlike natural zeolites, and are used as
solid acid catalyst
In acid catalysis and base catalysis, a chemical reaction is catalyzed by an acid or a base. By Brønsted–Lowry acid–base theory, the acid is the proton (hydrogen ion, H+) donor and the base is the proton acceptor. Typical reactions catalyze ...
s. The acidity is strong enough to protonate hydrocarbons and high-silica zeolites are used in acid catalysis processes such as
fluid catalytic cracking
Fluid Catalytic Cracking (FCC) is the conversion process used in petroleum refineries to convert the high-boiling point, high-molecular weight hydrocarbon fractions of petroleum (crude oils) into gasoline, olefinic gases, and other petroleum prod ...
in petrochemical industry.
![Zeolite Mordenite (with Al substitution)](https://upload.wikimedia.org/wikipedia/commons/3/3f/Zeolite_Mordenite_%28with_Al_substitution%29.png)
Apart from the adsorption, catalytic, and other properties of zeolites, it also shows several interesting properties, e.g. window effect, single-file diffusion, and Levitation Effect.
The Levitation Effect is an anomalous diffusion phenomenon observed in all systems with van der Waals interactions.
Framework structure
![FAU and LTA](https://upload.wikimedia.org/wikipedia/commons/8/8f/FAU_and_LTA.png)
As of December 2018, the framework structures of 253 different zeolites or their analogues are known, nearly 200 of which can only be synthesized artificially. 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 structural formula of a chemical compound is a graphic representation of the molecular structure (determined by structural chemistry methods), showing how the atoms are possibly arranged in the real three-dimensional space. The chemical bondi ...
. 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
Sodalite ( ) is a tectosilicate mineral with the formula , with royal blue varieties widely used as an wikt:ornamental, ornamental gemstone. Although massive sodalite samples are opaque, crystals are usually transparent to translucent. Sodalite i ...
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
ZSM-5, Zeolite Socony Mobil–5 (framework type MFI from ZSM-5 (five)), is an aluminosilicate zeolite belonging to the pentasil family of zeolites. Its chemical formula is NanAlnSi96–nO192·16H2O (0 (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
A molecular sieve is a material with pores (very small holes) of uniform size. These pore diameters are similar in size to small molecules, and thus large molecules cannot enter or be adsorbed, while smaller molecules can. As a mixture of molecu ...
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
In mathematics, an isomorphism is a structure-preserving mapping between two structures of the same type that can be reversed by an inverse mapping. Two mathematical structures are isomorphic if an isomorphism exists between them. The word i ...
of Si in zeolites can be possible for some heteroatoms such as
titanium
Titanium is a chemical element with the 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 with the symbol Zn and atomic number 30. Zinc 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 periodi ...
and
germanium
Germanium is a chemical element with the symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid in the carbon group that is chemically similar to its group neighbors s ...
.
Al atoms in zeolites can be also structurally replaced with
boron
Boron is a chemical element with the 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 th ...
and
gallium
Gallium is a chemical element with the symbol Ga and atomic number 31. Discovered by French chemist Paul-Émile Lecoq de Boisbaudran in 1875, Gallium is in group 13 of the periodic table and is similar to the other metals of the group (aluminiu ...
.
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
![Thomsonite-61017](https://upload.wikimedia.org/wikipedia/commons/0/06/Thomsonite-61017.jpg)
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 Na Al Si2 O6· H2O. Minor amounts of potassium and calci ...
,
chabazite
Chabazite ()The New Oxford Dictionary of English (1998) - p. 300 "chabazite /'kabəzʌɪt/ noun "A colourless, pink or yellow zeolite mineral, typically occurring as rhombohedral crystals.". is a tectosilicate mineral of the zeolite group, clos ...
,
clinoptilolite
Clinoptilolite is a natural zeolite composed of a microporous arrangement of silica and alumina tetrahedra. It has the complex formula . It forms as white, green to reddish tabular monoclinic tectosilicate crystals with a Mohs hardness of 3.5 to ...
,
heulandite
Heulandite is the name of a series of tecto-silicate minerals of the zeolite group. Prior to 1997, heulandite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a ser ...
,
natrolite
Natrolite is a tectosilicate mineral species belonging to the zeolite group. It is a hydrated sodium and aluminium silicate with the formula . The type locality is Hohentwiel, Hegau, Germany.
It was named natrolite by Martin Heinrich Klapro ...
,
phillipsite
Phillipsite is a mineral series of the zeolite group; a hydrated potassium, calcium and aluminium silicate, approximating to . The members of the series are phillipsite-K, phillipsite-Na and phillipsite-Ca. The crystals are monoclinic, but only c ...
, and
stilbite
Stilbite is the name of a series of tectosilicate minerals of the zeolite group. Prior to 1997, stilbite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a series nam ...
. An example of the mineral formula of a zeolite is: ·2H
2O, the formula for
natrolite
Natrolite is a tectosilicate mineral species belonging to the zeolite group. It is a hydrated sodium and aluminium silicate with the formula . The type locality is Hohentwiel, Hegau, Germany.
It was named natrolite by Martin Heinrich Klapro ...
.
Natural zeolites form where
volcanic
A volcano is a rupture 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 found where tectonic plates a ...
rocks and
ash
Ash or ashes are the solid remnants of fires. Specifically, ''ash'' refers to all non-aqueous, non- gaseous residues that remain after something burns. In analytical chemistry, to analyse the mineral and metal content of chemical samples, ash ...
layers react with
alkaline
In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a base (chemistry), basic, ionic compound, ionic salt (chemistry), salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as ...
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 atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...
, 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, and biological organisms. Weathering occurs ''in situ'' (on site, with little or no movement), ...
,
hydrothermal alteration
Metasomatism (from the Greek μετά ''metá'' "change" and σῶμα ''sôma'' "body") is the chemical alteration of a rock by hydrothermal and other fluids. It is the replacement of one rock by another of different mineralogical and chemical com ...
or
metamorphic
Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causin ...
conditions. Some examples:
* The sequence of
silica
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...
-rich
volcanic rock
Volcanic rock (often shortened to volcanics in scientific contexts) is a rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcanic r ...
s commonly progresses from:
**
Clay
Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4).
Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...
→ quartz →
mordenite
Mordenite is a zeolite mineral with the chemical formula, ( Ca, Na2, K2) Al2 Si10 O24·7 H2O. and it is one of the six most abundant zeolites and is used commercially.
It was first described in 1864 by Henry How. He named it after the small co ...
–
heulandite
Heulandite is the name of a series of tecto-silicate minerals of the zeolite group. Prior to 1997, heulandite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a ser ...
→
epistilbite
Zeolites are microporous, crystalline aluminosilicate materials commonly used as commercial adsorbents and catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ・y where is either a metal ion or H+. These pos ...
→
stilbite
Stilbite is the name of a series of tectosilicate minerals of the zeolite group. Prior to 1997, stilbite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a series nam ...
→
thomsonite
Thomsonite is the name of a series of tecto-silicate minerals of the zeolite group. Prior to 1997, thomsonite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a ser ...
→
mesolite
Mesolite is a tectosilicate mineral with formula Na2 Ca2( Al2 Si3 O10)3·8 H2O. It is a member of the zeolite group and is closely related to natrolite which it also resembles in appearance.
Mesolite crystallizes in the orthorhombic system and t ...
→
scolecite
Scolecite is a tectosilicate mineral belonging to the zeolite group; it is a hydrated calcium silicate, Ca Al2 Si3 O10· 3H2O. Only minor amounts of sodium and traces of potassium substitute for calcium. There is an absence of barium, strontium, ...
→
chabazite
Chabazite ()The New Oxford Dictionary of English (1998) - p. 300 "chabazite /'kabəzʌɪt/ noun "A colourless, pink or yellow zeolite mineral, typically occurring as rhombohedral crystals.". is a tectosilicate mineral of the zeolite group, clos ...
→
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
Cowlesite is a mineral named after American mineralogist John Cowles. It was first described by W.S. Wise and Rudy W. Tschernich in material from roadcuts along Neer Road, Goble, Oregon, United States. The description also incorporated data fr ...
→
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 Na Al Si2 O6· H2O. Minor amounts of potassium and calci ...
→
thomsonite
Thomsonite is the name of a series of tecto-silicate minerals of the zeolite group. Prior to 1997, thomsonite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a ser ...
→
mesolite
Mesolite is a tectosilicate mineral with formula Na2 Ca2( Al2 Si3 O10)3·8 H2O. It is a member of the zeolite group and is closely related to natrolite which it also resembles in appearance.
Mesolite crystallizes in the orthorhombic system and t ...
→
scolecite
Scolecite is a tectosilicate mineral belonging to the zeolite group; it is a hydrated calcium silicate, Ca Al2 Si3 O10· 3H2O. Only minor amounts of sodium and traces of potassium substitute for calcium. There is an absence of barium, strontium, ...
→
chabazite
Chabazite ()The New Oxford Dictionary of English (1998) - p. 300 "chabazite /'kabəzʌɪt/ noun "A colourless, pink or yellow zeolite mineral, typically occurring as rhombohedral crystals.". is a tectosilicate mineral of the zeolite group, clos ...
→
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
Thomsonite
Thomsonite is the name of a series of tecto-silicate minerals of the zeolite group. Prior to 1997, thomsonite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a ser ...
s, one of the rarer zeolite minerals, have been collected as
gemstone
A gemstone (also called a fine gem, jewel, precious stone, or semiprecious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewelry or other adornments. However, certain rocks (such as lapis lazuli, opal, ...
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 moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...
flows along
Lake Superior
Lake Superior in central North America is the largest freshwater lake in the world by surface areaThe Caspian Sea is the largest lake, but is saline, not freshwater. and the third-largest by volume, holding 10% of the world's surface fresh wa ...
in
Minnesota
Minnesota () is a state in the upper midwestern region of the United States. It is the 12th largest U.S. state in area and the 22nd most populous, with over 5.75 million residents. Minnesota is home to western prairies, now given over to ...
and, to a lesser degree, in
Michigan
Michigan () is a state in the Great Lakes region of the upper Midwestern United States. With a population of nearly 10.12 million and an area of nearly , Michigan is the 10th-largest state by population, the 11th-largest by area, and the ...
. Thomsonite nodules from these areas have
eroded
Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust, and then sediment transport, tra ...
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 with the symbol Cu (from la, cuprum) 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 pinkis ...
"eyes". When polished by a
lapidary
Lapidary (from the Latin ) is the practice of shaping stone, minerals, or gemstones into decorative items such as cabochons, engraved gems (including cameos), and faceted designs. A person who practices lapidary is known as a lapidarist. A la ...
, the thomsonites sometimes displays a "cat's eye" effect (
chatoyancy
In gemology, chatoyancy ( ), or chatoyance or cat's eye effect, is an optical reflectance effect seen in certain gemstones, woods, and carbon fibre. Coined from the French "œil de chat", meaning "cat's eye", chatoyancy arises either from the ...
).
Production
Industrially important zeolites are produced synthetically. Typical procedures entail heating aqueous solutions of
alumina and
silica
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...
with
sodium hydroxide
Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions .
Sodium hydroxide is a highly caustic base and alkali ...
. Equivalent reagents include
sodium aluminate
Sodium aluminate is an inorganic chemical that is used as an effective source of aluminium hydroxide for many industrial and technical applications. Pure sodium aluminate (anhydrous) is a white crystalline solid having a formula variously given as ...
and
sodium silicate
Sodium silicate is a generic name for chemical compounds with the formula or ·, such as sodium metasilicate , sodium orthosilicate , and sodium pyrosilicate . The anions are often polymeric. These compounds are generally colorless transparent ...
. Further variations include the use of structure directing agents (SDA) such as
quaternary ammonium cation
In chemistry, quaternary ammonium cations, also known as quats, are positively charged polyatomic ions of the structure , R being an alkyl group or an aryl group. Unlike the ammonium ion () and the primary, secondary, or tertiary ammonium cations ...
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
![Natrolit, Gracza 2Polska](https://upload.wikimedia.org/wikipedia/commons/9/9a/Natrolit%2C_Gracza_2Polska.jpg)
Conventional
open-pit mining
Open-pit mining, also known as open-cast or open-cut mining and in larger contexts mega-mining, is a surface mining technique of extracting rock or minerals from the earth from an open-air pit, sometimes known as a borrow.
This form of mining ...
techniques are used to mine natural zeolites. The overburden is removed to allow access to the ore. The ore may be blasted or stripped for processing by using tractors equipped with ripper blades and front-end loaders. In processing, the ore is crushed, dried, and milled. The milled ore may be air-classified as to particle size and shipped in bags or bulk. The crushed product may be
screened to remove fine material when a granular product is required, and some pelletized products are produced from fine material.
, the world's annual production of natural zeolite approximates 3 million
tonne
The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton ( United State ...
s. Major producers in 2010 included
China
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
(2 million tonnes),
South Korea
South Korea, officially the Republic of Korea (ROK), is a country in East Asia, constituting the southern part of the Korea, Korean Peninsula and sharing a Korean Demilitarized Zone, land border with North Korea. Its western border is formed ...
(210,000 t),
Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
(150,000 t),
Jordan
Jordan ( ar, الأردن; tr. ' ), officially the Hashemite Kingdom of Jordan,; tr. ' is a country in Western Asia. It is situated at the crossroads of Asia, Africa, and Europe, within the Levant region, on the East Bank of the Jordan Rive ...
(140,000 t),
Turkey
Turkey ( tr, Türkiye ), officially the Republic of Türkiye ( tr, Türkiye Cumhuriyeti, links=no ), is a list of transcontinental countries, transcontinental country located mainly on the Anatolia, Anatolian Peninsula in Western Asia, with ...
(100,000 t)
Slovakia
Slovakia (; sk, Slovensko ), officially the Slovak Republic ( sk, Slovenská republika, links=no ), 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 s ...
(85,000 t) and the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
(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), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...
, it is likely that a significant percentage of the material sold as zeolites in some countries is ground or sawn volcanic
tuff
Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock cont ...
that contains only a small amount of zeolites. Some examples of such usage include
dimension stone
Dimension stone is natural stone or rock that has been selected and finished (e.g., trimmed, cut, drilled, ground, or other) to specific sizes or shapes. Color, texture and pattern, and surface finish of the stone are also normal requirements. A ...
(as an altered volcanic tuff), lightweight
aggregate,
pozzolanic cement, and
soil conditioner
A soil conditioner is a product which is added to soil to improve the soil’s physical qualities, usually its fertility (ability to provide nutrition for plants) and sometimes its mechanics. In general usage, the term "soil conditioner" is often ...
s.
Synthesis
![Ceolite nax](https://upload.wikimedia.org/wikipedia/commons/d/d9/Ceolite_nax.JPG)
There are over 200 synthetic zeolites that have been synthesized by a process of slow
crystal
A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...
lization of a
silica
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...
-
alumina gel in the presence of alkalis and organic templates. Many more such structures could theoretically be made. In addition to variations in structures, zeolites can also be made with a variety of other atoms in them to make them chemically interesting and active. Some examples of the so-called heteroatoms that have been incorporated include germanium, iron, gallium, boron, zinc, tin, and titanium. One of the important processes used to carry out zeolite synthesis is
sol-gel processing. 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. The
silicalite sol formed by the
hydrothermal
Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...
method is very stable. The ease of scaling up this process makes it a favored route for zeolite synthesis.
Applications
Zeolites are widely used as catalysts and sorbents. Their well-defined pore structure and adjustable acidity make them highly active in a large variety of reactions.
In chemistry, zeolites are used to separate
molecule
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...
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 an ...
and
biomedical
Biomedicine (also referred to as Western medicine, mainstream medicine or conventional medicine) applications of zeolites, particularly the naturally occurring species
heulandite
Heulandite is the name of a series of tecto-silicate minerals of the zeolite group. Prior to 1997, heulandite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a ser ...
,
clinoptilolite
Clinoptilolite is a natural zeolite composed of a microporous arrangement of silica and alumina tetrahedra. It has the complex formula . It forms as white, green to reddish tabular monoclinic tectosilicate crystals with a Mohs hardness of 3.5 to ...
, and
chabazite
Chabazite ()The New Oxford Dictionary of English (1998) - p. 300 "chabazite /'kabəzʌɪt/ noun "A colourless, pink or yellow zeolite mineral, typically occurring as rhombohedral crystals.". is a tectosilicate mineral of the zeolite group, clos ...
has been ongoing.
In organic synthesis
In synthetic chemistry, homogeneous catalysts are preferred because of availability, low cost, and excellent catalytic activity as all the catalytic sites are readily available. But these homogeneous catalysts have several disadvantageous, such as being non-reusable, and require more than the stoichiometric amount. Also, some other drawbacks in its use include the potential dangers in handling, toxicity, corrosive nature, difficulty in separation and recovery, and disposal problems due to the acidic effluent. In addition to that, hydrolysis and purification of the resultant complex results in corrosive by-products. So, the basic idea is to find alternative heterogeneous solid catalysts which are stable, reusable, and nature-friendly, and there has been much attention to finding new ones which will also allow a better work up of reaction products. Among these different solid catalysts, zeolites were found to be superior due to their shape selectivity, thermal stability, and reusability .
Freidel-Crafts alkylation and acylations using zeolites as catalyst are common in organic synthesis.
Ion exchange and softeners
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.
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 the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phytopla ...
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 cleansing properties when in dilute solutions. There are a large variety of detergents, a common family being the alkylbenzene sulfonates, which are soap-like compounds that are more ...
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
MCM-41 (Mobil Composition of Matter No. 41) is a mesoporous material with a hierarchical structure from a family of silicate and alumosilicate solids that were first developed by researchers at Mobil Oil Corporation and that can be used as cat ...
), are widely used as
catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
s in the
petrochemical industry
The petrochemical industry is concerned with the production and trade of petrochemicals. A major part is constituted by the plastics (polymer) industry. It directly interfaces with the petroleum industry, especially the downstream sector.
Compan ...
, such as in fluid catalytic
cracking and
hydrocracking
In petrochemistry, petroleum geology and organic chemistry, cracking is the process whereby complex organic molecules such as kerogens or long-chain hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of ...
. 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 acid
Solid is one of the four fundamental states of matter (the others being liquid, gas, and plasma). The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structural ...
s, facilitating a host of acid-catalyzed reactions, such as
isomerization
In chemistry, isomerization or isomerisation is the process in which a molecule, polyatomic ion or molecular fragment is transformed into an isomer with a different chemical structure. Enolization is an example of isomerization, as is tautomeriz ...
,
alkylation
Alkylation is the transfer of an alkyl group from one molecule to another. 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 ...
, and cracking.
Catalytic cracking
Fluid Catalytic Cracking (FCC) is the conversion process used in petroleum refineries to convert the high-boiling point, high-molecular weight hydrocarbon fractions of petroleum (crude oils) into gasoline, olefinic gases, and other petroleum prod ...
uses a reactor and a regenerator. Feed is injected onto a hot, fluidized catalyst where large
gasoil
Fuel oil is any of various fractions obtained from the distillation of petroleum (crude oil). Such oils include distillates (the lighter fractions) and residues (the heavier fractions). Fuel oils include heavy fuel oil, marine fuel oil (MFO), bun ...
molecules are broken into smaller gasoline molecules and
olefins. 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.
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 product
Nuclear fission products are the atomic fragments left after a large atomic nucleus undergoes nuclear fission. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons, the release ...
s 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 was a nuclear accident in 2011 at the Fukushima Daiichi Nuclear Power Plant in Ōkuma, Fukushima, Japan. The proximate cause of the disaster was the 2011 Tōhoku earthquake and tsunami, which occurred on the afternoon of 11 March 2011 and ...
, sandbags of zeolite were dropped into the seawater near the power plant to adsorb the radioactive
cesium-137
Caesium-137 (), cesium-137 (US), or radiocaesium, is a radioactive isotope of caesium that is formed as one of the more common fission products by the nuclear fission of uranium-235 and other fissionable isotopes in nuclear reactors and nuclea ...
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 called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
streams. Other separations include
noble gases
The noble gases (historically also the inert gases; sometimes referred to as aerogens) make up a class of chemical elements with similar properties; under standard conditions, they are all odorless, colorless, monatomic gases with very low chemi ...
, 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 prop ...
, and
formaldehyde
Formaldehyde ( , ) (systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section F ...
.
On-board oxygen generating systems (OBOGS) and
oxygen concentrator
An oxygen concentrator is a device that concentrates the oxygen from a gas supply (typically ambient air) by selectively removing nitrogen to supply an oxygen-enriched product gas stream. They are used industrially and as medical devices for oxy ...
s use zeolites in conjunction with
pressure swing adsorption
Pressure swing adsorption (PSA) is a technique used to separate some gas species from a mixture of gases (typically air) under pressure according to the species' molecular characteristics and affinity for an adsorbent material. It operates at nea ...
to remove nitrogen from compressed air to supply oxygen for aircrews at high altitudes, as well as home and portable oxygen supplies.
![pressure swing adsorption principle](https://upload.wikimedia.org/wikipedia/commons/7/76/Pressure_swing_adsorption_principle.svg)
Zeolite-based
oxygen concentrator
An oxygen concentrator is a device that concentrates the oxygen from a gas supply (typically ambient air) by selectively removing nitrogen to supply an oxygen-enriched product gas stream. They are used industrially and as medical devices for oxy ...
systems are widely used to produce medical-grade oxygen. The zeolite is used as a
molecular sieve
A molecular sieve is a material with pores (very small holes) of uniform size. These pore diameters are similar in size to small molecules, and thus large molecules cannot enter or be adsorbed, while smaller molecules can. As a mixture of molecu ...
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 mixture of gases, primarily consisting of methane, carbon dioxide and hydrogen sulphide, produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste and food waste. It is a ...
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
The Debbie Meyer Green Bag are food storage bags sold and licensed by Housewares America, Inc.
Independent laboratory results (Nova Biologicals, Inc - Conroe, Texas) and television commercials for the product claim it will keep fruits and vegetabl ...
, 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 double bonds).
Ethylene i ...
, 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
A molecular sieve is a material with pores (very small holes) of uniform size. These pore diameters are similar in size to small molecules, and thus large molecules cannot enter or be adsorbed, while smaller molecules can. As a mixture of molecu ...
in
cryosorption style
vacuum pump
A vacuum pump is a device that draws gas molecules from a sealed volume in order to leave behind a partial vacuum. The job of a vacuum pump is to generate a relative vacuum within a capacity. The first vacuum pump was invented in 1650 by Otto v ...
s.
Solar energy storage and use
Zeolites can be used to thermochemically store solar heat harvested from
solar thermal collector
A solar thermal collector collects heat by absorbing sunlight. The term "solar collector" commonly refers to a device for solar hot water heating, but may refer to large power generating installations such as solar parabolic troughs and sola ...
s 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 f ...
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 or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules become suspended among the substance ...
property coupled with an inherent
exothermic
In thermodynamics, an exothermic process () is a thermodynamic process or reaction that releases energy from the system to its surroundings, usually in the form of heat, but also in a form of light (e.g. a spark, flame, or flash), electricity (e ...
(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.
Light emission
Zeolites were discovered to help
silver
Silver is a chemical element with the Symbol (chemistry), symbol Ag (from the Latin ', derived from the Proto-Indo-European wikt:Reconstruction:Proto-Indo-European/h₂erǵ-, ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, whi ...
naturally emit light, which may compete with fluorescent lights or
LED
A light-emitting diode (LED) is a semiconductor Electronics, device that Light#Light sources, emits light when Electric current, current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy i ...
s.
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 tarmac, bitumen macadam, or rolled asphalt in the United Kingdom and the Republic of Ireland) is a composite material commonly used to surface roads, parkin ...
. 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 (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
, 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, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in the early 19th c ...
as a
pozzolan
Pozzolans are a broad class of Silicon_dioxide, siliceous and aluminium oxide, aluminous materials which, in themselves, possess little or no cementitious value but which will, in finely divided form and in the presence of water, react chemically ...
, 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 composed of lime and an aggregate such as sand, mixed with water. The ancient Egyptians were the first to use lime mortars, which they used to plaster their temples. In addition, the Egyptians also incorporated various ...
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
A litter box, also known as a sandbox, cat box, litter tray, cat pan, potty, pot or litter pan, is an indoor feces and urine collection box for cats, as well as rabbits, ferrets, miniature pigs, small dogs, and other pets that instinctively or ...
is often made of zeolite (or
diatomite
Diatomaceous earth (), diatomite (), or kieselgur/kieselguhr is a naturally occurring, soft, siliceous sedimentary rock that can be crumbled into a fine white to off-white powder. It has a particle size ranging from more than 3 μm to le ...
), one form of which, invented at
MIT
The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the m ...
, can sequester the
greenhouse gas
A greenhouse gas (GHG or GhG) is a gas that Absorption (electromagnetic radiation), absorbs and Emission (electromagnetic radiation), emits radiant energy within the thermal infrared range, causing the greenhouse effect. The primary greenhouse ...
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 relative abundance of methane on Eart ...
from the atmosphere.
Hemostatic agent
QuikClot
QuikClot is a brand of hemostatic wound dressing, that contains an agent that promotes blood clotting. It is primarily used by militaries and law enforcement to treat hemorrhaging from trauma.
History
Using zeolite as a clotting agent was ...
brand
hemostatic agent
An antihemorrhagic (antihæmorrhagic) agent is a substance that promotes hemostasis (stops bleeding). It may also be known as a hemostatic (also spelled haemostatic) agent.
Antihemorrhagic agents used in medicine have various mechanisms of action: ...
, which is used to stop severe bleeding, contains a calcium-loaded form of zeolite found in
kaolin
Kaolinite ( ) is a clay mineral, with the chemical composition Al2 Si2 O5( OH)4. It is an important industrial mineral. It is a layered silicate mineral, with one tetrahedral sheet of silica () linked through oxygen atoms to one octahedral ...
clay.
Soil treatment
In agriculture,
clinoptilolite
Clinoptilolite is a natural zeolite composed of a microporous arrangement of silica and alumina tetrahedra. It has the complex formula . It forms as white, green to reddish tabular monoclinic tectosilicate crystals with a Mohs hardness of 3.5 to ...
(a naturally occurring zeolite) is used as a soil treatment. It provides a source of slowly released
potassium
Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...
. If previously loaded with
ammonium
The ammonium cation is a positively-charged polyatomic ion with the chemical formula or . It is formed by the protonation of ammonia (). Ammonium is also a general name for positively charged or protonated substituted amines and quaternary a ...
, the zeolite can serve a similar function in the slow release of
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
.
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 compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...
and other nitrogenous compounds. They must be used with some care, especially with delicate tropical corals that are sensitive to water chemistry and temperature. 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
Ion exchange is a reversible interchange of one kind of ion present in an insoluble solid with another of like charge present in a solution surrounding the solid with the reaction being used especially for softening or making water demineralised, ...
. 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 state in the Pacific Northwest region of the Western United States. To the north, it shares a small portion of the Canada–United States border with the province of British Columbia. It borders the states of Montana and Wyom ...
is a fresh water variety (Na < 0.05%). Southern hemisphere zeolites are typically formed in freshwater and have a high calcium content.
Zeolite mineral species
![Stilbite-Ca-Natrolite-Laumontite-247898](https://upload.wikimedia.org/wikipedia/commons/2/2d/Stilbite-Ca-Natrolite-Laumontite-247898.jpg)
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
Natrolite is a tectosilicate mineral species belonging to the zeolite group. It is a hydrated sodium and aluminium silicate with the formula . The type locality is Hohentwiel, Hegau, Germany.
It was named natrolite by Martin Heinrich Klapro ...
,
mesolite
Mesolite is a tectosilicate mineral with formula Na2 Ca2( Al2 Si3 O10)3·8 H2O. It is a member of the zeolite group and is closely related to natrolite which it also resembles in appearance.
Mesolite crystallizes in the orthorhombic system and t ...
,
paranatrolite,
scolecite
Scolecite is a tectosilicate mineral belonging to the zeolite group; it is a hydrated calcium silicate, Ca Al2 Si3 O10· 3H2O. Only minor amounts of sodium and traces of potassium substitute for calcium. There is an absence of barium, strontium, ...
,
tetranatrolite
** Edingtonite framework (EDI):
edingtonite,
kalborsite
** Thomsonite framework (THO):
thomsonite
Thomsonite is the name of a series of tecto-silicate minerals of the zeolite group. Prior to 1997, thomsonite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a ser ...
-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 Na Al Si2 O6· H2O. Minor amounts of potassium and calci ...
,
leucite
Leucite is a rock-forming mineral of the feldspathoid group, silica-undersaturated and composed of potassium and aluminium tectosilicate KAlSi2O6. Crystals have the form of cubic icositetrahedra but, as first observed by Sir David Brewster in 18 ...
,
pollucite
Pollucite is a zeolite mineral with the formula with iron, calcium, rubidium and potassium as common substituting elements. It is important as a significant ore of caesium and sometimes rubidium. It forms a solid solution series with analcime. I ...
,
wairakite
**
Laumontite
Laumontite is a mineral, one of the zeolite group. Its molecular formula is , a hydrated calcium-aluminium silicate. Potassium or sodium may substitute for the calcium but only in very small amounts.
It is monoclinic, space group C2/m. It forms ...
(LAU),
yugawaralite (YUG),
goosecreekite
Zeolites are microporous, crystalline aluminosilicate materials commonly used as commercial adsorbents and catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ・y where is either a metal ion or H+. These po ...
(GOO),
montesommaite (MON)
* 09.GC. - Chains of doubly connected 4-membered rings
** Phillipsite framework (PHI):
harmotome
Harmotome is a mineral, one of the rarer zeolites; a hydrated barium silicate with formula: ( Ba0.5, Ca0.5, Na, K)5 Al5, Si11 O32·12( H2O). It forms vitreous white well defined monoclinic crystals, often associated with calcite and other zeolite ...
,
phillipsite
Phillipsite is a mineral series of the zeolite group; a hydrated potassium, calcium and aluminium silicate, approximating to . The members of the series are phillipsite-K, phillipsite-Na and phillipsite-Ca. The crystals are monoclinic, but only c ...
-series
** Gismondine framework (GIS):
amicite
Amicite is a silicate mineral of the zeolite family. It has a general formula of K2Na2Al4Si4O16·5(H2O). Amicite was described in 1979 from specimens obtained at the Höwenegg quarry in Immendingen, Hegau, in the German state of Baden-Württembe ...
,
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
Chabazite ()The New Oxford Dictionary of English (1998) - p. 300 "chabazite /'kabəzʌɪt/ noun "A colourless, pink or yellow zeolite mineral, typically occurring as rhombohedral crystals.". is a tectosilicate mineral of the zeolite group, clos ...
-series,
herschelite,
willhendersonite and
SSZ-13
** Faujasite framework (FAU):
faujasite
Faujasite (FAU-type zeolite) is a mineral group in the zeolite family of silicate minerals. The group consists of faujasite-Na, faujasite-Mg and faujasite-Ca. They all share the same basic formula by varying the amounts of sodium, magnesium and ...
-series, Linde type X (zeolite X, X zeolites), Linde type Y (zeolite Y, Y zeolites)
** Mordenite framework (MOR):
maricopaite,
mordenite
Mordenite is a zeolite mineral with the chemical formula, ( Ca, Na2, K2) Al2 Si10 O24·7 H2O. and it is one of the six most abundant zeolites and is used commercially.
It was first described in 1864 by Henry How. He named it after the small co ...
** 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
Erionite is a naturally occurring fibrous mineral that belongs to a group of minerals called zeolites. It usually is found in volcanic ash that has been altered by weathering and ground water. Erionite forms brittle, wool-like fibrous masses in t ...
-series (ERI),
ferrierite
The ferrierite group of zeolite minerals (the FER structure) consists of three very similar species: ferrierite- Mg, ferrierite- Na, and ferrierite- K, based on the dominant cation in the A location. ferrierite-Mg and ferrierite-K are orthorhombic ...
(FER),
gmelinite
Gmelinite-Na is one of the rarer zeolites but the most common member of the gmelinite series, gmelinite-Ca, gmelinite-K and gmelinite-Na. It is closely related to the very similar mineral chabazite. Gmelinite was named as a single species in 182 ...
(GME),
levyne-series (LEV),
dachiardite
Zeolites are microporous, crystalline aluminosilicate materials commonly used as commercial adsorbents and catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ・y where is either a metal ion or H+. These pos ...
-series (DAC),
epistilbite
Zeolites are microporous, crystalline aluminosilicate materials commonly used as commercial adsorbents and catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ・y where is either a metal ion or H+. These pos ...
(EPI)
* 09.GE. - Chains of T
10O
20 tetrahedra (T = combined Si and Al)
** Heulandite framework (HEU):
clinoptilolite
Clinoptilolite is a natural zeolite composed of a microporous arrangement of silica and alumina tetrahedra. It has the complex formula . It forms as white, green to reddish tabular monoclinic tectosilicate crystals with a Mohs hardness of 3.5 to ...
,
heulandite
Heulandite is the name of a series of tecto-silicate minerals of the zeolite group. Prior to 1997, heulandite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a ser ...
-series
** Stilbite framework (STI):
barrerite,
stellerite,
stilbite
Stilbite is the name of a series of tectosilicate minerals of the zeolite group. Prior to 1997, stilbite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a series nam ...
-series
** Brewsterite framework (BRE):
brewsterite
Brewsterite is the name of a series of tectosilicate minerals of the zeolite group. Prior to 1997, brewsterite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a ser ...
-series
* Others
**
Cowlesite
Cowlesite is a mineral named after American mineralogist John Cowles. It was first described by W.S. Wise and Rudy W. Tschernich in material from roadcuts along Neer Road, Goble, Oregon, United States. The description also incorporated data fr ...
,
pentasil (also known as
ZSM-5
ZSM-5, Zeolite Socony Mobil–5 (framework type MFI from ZSM-5 (five)), is an aluminosilicate zeolite belonging to the pentasil family of zeolites. Its chemical formula is NanAlnSi96–nO192·16H2O (0 , 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
* , the amorphous alumino-silicate equivalent of zeolite
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References
*
Further reading
* The classic reference for the field has been Breck's book ''Zeolite Molecular Sieves: Structure, Chemistry, And Use''.
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External links
International Zeolite AssociationDatabase of zeolite pore characterizations
The Synthesis Commission of the International Zeolite AssociationFederation of European Zeolite AssociationsBritish Zeolite AssociationBulk ZeoliteDatabase of Zeolite Structures
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Zeolites
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