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Bentonite (volcanic ash) from Wyoming Volcanic Tuff of Green River Formation in Wyoming.jpg
Bentonite (volcanic ash) from Wyoming

Bentonite ( /ˈbɛntənʌɪt/ ) [1] is an absorbent aluminium phyllosilicate clay consisting mostly of montmorillonite. It was named by Wilbur C. Knight in 1898 after the Cretaceous Benton Shale near Rock River, Wyoming. [2] [3]

Absorption (chemistry) chemical process

In chemistry, absorption is a physical or chemical phenomenon or a process in which atoms, molecules or ions enter some bulk phase – liquid or solid material. This is a different process from adsorption, since molecules undergoing absorption are taken up by the volume, not by the surface. A more general term is sorption, which covers absorption, adsorption, and ion exchange. Absorption is a condition in which something takes in another substance.

Aluminium Chemical element with atomic number 13

Aluminium is a chemical element with the symbol Al and atomic number 13. It is a silvery-white, soft, non-magnetic and ductile metal in the boron group. By mass, aluminium makes up about 8% of the Earth's crust; it is the third most abundant element after oxygen and silicon and the most abundant metal in the crust, though it is less common in the mantle below. The chief ore of aluminium is bauxite. Aluminium metal is so chemically reactive that native specimens are rare and limited to extreme reducing environments. Instead, it is found combined in over 270 different minerals.

Clay A finely-grained natural rock or soil containing mainly clay minerals

Clay is a finely-grained natural rock or soil material that combines one or more clay minerals with possible traces of quartz (SiO2), metal oxides (Al2O3, MgO etc.) and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure. Clays are plastic due to particle size and geometry as well as water content, and become hard, brittle and non–plastic upon drying or firing. Depending on the soil's content in which it is found, clay can appear in various colours from white to dull grey or brown to deep orange-red.


The different types of bentonite are each named after the respective dominant element, such as potassium (K), sodium (Na), calcium (Ca), and aluminium (Al). Experts debate a number of nomenclatorial problems with the classification of bentonite clays. Bentonite usually forms from weathering of volcanic ash, most often in the presence of water. However, the term bentonite, as well as a similar clay called tonstein, has been used to describe clay beds of uncertain origin. For industrial purposes, two main classes of bentonite exist: sodium and calcium bentonite. In stratigraphy and tephrochronology, completely devitrified (weathered volcanic glass) ash-fall beds are commonly referred to as K-bentonites when the dominant clay species is illite. In addition to montmorillonite and illite another common clay species that is sometimes dominant is kaolinite. Kaolinite-dominated clays are commonly referred to as tonsteins and are typically associated with coal.

Chemical element a species of atoms having the same number of protons in the atomic nucleus

A chemical element is a species of atom having the same number of protons in their atomic nuclei. For example, the atomic number of oxygen is 8, so the element oxygen consists of all atoms which have 8 protons.

Potassium Chemical element with atomic number 19

Potassium is a chemical element with the symbol K and atomic number 19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmospheric oxygen to form flaky white potassium peroxide in only seconds of exposure. It was first isolated from potash, the ashes of plants, from which its name derives. In the periodic table, potassium is one of the alkali metals, all of which have a single valence electron in the outer electron shell, that is easily removed to create an ion with a positive charge – a cation, that combines with anions to form salts. Potassium in nature occurs only in ionic salts. Elemental potassium reacts vigorously with water, generating sufficient heat to ignite hydrogen emitted in the reaction, and burning with a lilac-colored flame. It is found dissolved in sea water, and occurs in many minerals such as orthoclase, a common constituent of granites and other igneous rocks.

Sodium Chemical element with atomic number 11

Sodium is a chemical element with the symbol Na (from Latin natrium) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table, because it has a single electron in its outer shell, which it readily donates, creating a positively charged ion—the Na+ cation. Its only stable isotope is 23Na. The free metal does not occur in nature, and must be prepared from compounds. Sodium is the sixth most abundant element in the Earth's crust and exists in numerous minerals such as feldspars, sodalite, and rock salt (NaCl). Many salts of sodium are highly water-soluble: sodium ions have been leached by the action of water from the Earth's minerals over eons, and thus sodium and chlorine are the most common dissolved elements by weight in the oceans.


Sodium bentonite

Sodium bentonite expands when wet, absorbing as much as several times its dry mass in water. Because of its excellent colloidal properties, [4] it is often used in drilling mud for oil and gas wells and boreholes for geotechnical and environmental investigations. [3] The property of swelling also makes sodium bentonite useful as a sealant, since it provides a self-sealing, low permeability barrier. It is used to line the base of landfills, for example. Various surface modifications to sodium bentonite improve some rheological or sealing performance in geoenvironmental applications, for example, the addition of polymers. [5]

Mass Quantity of matter

Mass is both a property of a physical body and a measure of its resistance to acceleration when a net force is applied. An object's mass also determines the strength of its gravitational attraction to other bodies.

Colloid A mixture of an insoluble substance microscopically dispersed throughout another substance

In chemistry, a colloid is a mixture in which one substance of microscopically dispersed insoluble particles is suspended throughout another substance. Sometimes the dispersed substance alone is called the colloid; the term colloidal suspension refers unambiguously to the overall mixture. Unlike a solution, whose solute and solvent constitute only one phase, a colloid has a dispersed phase and a continuous phase that arise by phase separation. To qualify as a colloid, the mixture must be one that does not settle or would take a very long time to settle appreciably.

An oil is any nonpolar chemical substance that is a viscous liquid at ambient temperatures and is both hydrophobic and lipophilic. Oils have a high carbon and hydrogen content and are usually flammable and surface active.

Calcium bentonite

Calcium bentonite is a useful adsorbent of ions in solution, [6] as well as fats and oils. It is the main active ingredient of fuller's earth, probably one of the earliest industrial cleaning agents. [7]

Adsorption Adhesion of atoms, ions, or molecules from a substance to a surface

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 fluid is dissolved by or permeates a liquid or solid, respectively. Adsorption is a surface phenomenon, while absorption involves the whole volume of the material. The term sorption encompasses both processes, while desorption is the reverse of it.

Fullers earth soil type

Fuller's earth is any clay material that has the capability to decolorize oil or other liquids without the use of harsh chemical treatment. Fuller's earth typically consists of palygorskite (attapulgite) or bentonite.

Calcium bentonite may be converted to sodium bentonite (termed sodium beneficiation or sodium activation) to exhibit many of sodium bentonite's properties by an ion exchange process. In common usage, this means adding 5–10% of a soluble sodium salt such as sodium carbonate to wet bentonite, mixing well, and allowing time for the ion exchange to take place and water to remove the exchanged calcium.[ citation needed ] Some properties, such as viscosity and fluid loss of suspensions, of sodium-beneficiated calcium bentonite (or sodium-activated bentonite) may not be fully equivalent to those of natural sodium bentonite. [4] For example, residual calcium carbonates (formed if exchanged cations are insufficiently removed) may result in inferior performance of the bentonite in geosynthetic liners. [8]

Ion exchange

Ion exchange is an exchange of ions between two electrolytes or between an electrolyte solution and a complex. In most cases the term is used to denote the processes of purification, separation, and decontamination of aqueous and other ion-containing solutions with solid polymeric or mineralic "ion exchangers".

Sodium carbonate chemical compound

Sodium carbonate, Na2CO3, (also known as washing soda, soda ash and soda crystals) is the inorganic compound with the formula Na2CO3 and its various hydrates. All forms are white, water-soluble salts. All forms have a strongly alkaline taste and give moderately alkaline solutions in water. Historically it was extracted from the ashes of plants growing in sodium-rich soils. Because the ashes of these sodium-rich plants were noticeably different from ashes of wood (once used to produce potash), sodium carbonate became known as "soda ash". It is produced in large quantities from sodium chloride and limestone by the Solvay process.

Potassium bentonite

Also known as potash bentonite or K-bentonite, potassium bentonite is a potassium-rich illitic clay formed from alteration of volcanic ash. [9]



Bentonites are used for decolorizing various mineral, vegetable, and animal oils. They are also used for clarifying wine, liquor, cider, beer, mead, and vinegar. [3]

Creating a bentonite slurry for fining after wine pressing Creating a bentonite slurry for fining after wine pressing.jpg
Creating a bentonite slurry for fining after wine pressing

The main uses of bentonite are for drilling mud, binder (e.g. foundry-sand bond, iron ore pelletizer), purifier, absorbent (e.g. pet litter), and as a groundwater barrier. [3] As of around 1990, almost half of the US production of bentonite was used for drilling mud. [3]

Drilling mud

Bentonite is used in drilling fluids to lubricate and cool the cutting tools, to remove cuttings, and to help prevent blowouts. [3] Much of bentonite's usefulness in the drilling and geotechnical engineering industry comes from its unique rheological properties. Relatively small quantities of bentonite suspended in water form a viscous, shear-thinning material. Most often, bentonite suspensions are also thixotropic, although rare cases of rheopectic behavior have also been reported. At high enough concentrations (about 60 grams of bentonite per litre of suspension), bentonite suspensions begin to take on the characteristics of a gel (a fluid with a minimum yield strength required to make it move). So, it is a common component of drilling mud used to curtail drilling fluid invasion by its propensity for aiding in the formation of mud cake.


Bentonite has been widely used as a foundry-sand bond in iron and steel foundries. Sodium bentonite is most commonly used for large castings that use dry molds, while calcium bentonite is more commonly used for smaller castings that use "green" or wet molds. [3] Bentonite is also used as a binding agent in the manufacture of iron ore (taconite) pellets as used in the steelmaking industry. Bentonite, in small percentages, is used as an ingredient in commercial and homemade clay bodies and ceramic glazes. It greatly increases the plasticity of clay bodies and decreases settling in glazes, making both easier to work with for most applications.

The ionic surface of bentonite has a useful property in making a sticky coating on sand grains. When a small proportion of finely ground bentonite clay is added to hard sand and wetted, the clay binds the sand particles into a moldable aggregate known as green sand used for making molds in sand casting. Some river deltas naturally deposit just such a blend of clay silt and sand, creating a natural source of excellent molding sand that was critical to ancient metalworking technology. Modern chemical processes to modify the ionic surface of bentonite greatly intensify this stickiness, resulting in remarkably dough-like yet strong casting sand mixes that stand up to molten metal temperatures.

The same effluvial deposition of bentonite clay onto beaches accounts for the variety of plasticity of sand from place to place for building sand castles. Beach sand consisting of only silica and shell grains does not mold well compared to grains coated with bentonite clay. This is why some beaches are much better for building sand castles than others.

The self-stickiness of bentonite allows high-pressure ramming or pressing of the clay in molds to produce hard, refractory shapes, such as model rocket nozzles.

Bentonite has the property of adsorbing relatively large amounts of protein molecules from aqueous solutions. Consequently, bentonite is uniquely useful in the process of winemaking, where it is used to remove excessive amounts of protein from white wines. Were it not for this use of bentonite, many or most white wines would precipitate undesirable flocculent clouds or hazes upon exposure to warm temperatures, as these proteins denature. It also has the incidental use of inducing more rapid clarification of both red and white wines.


Bentonite is used in a variety of pet care items such as cat litter to absorb the odor and surround the feces. It is also used to absorb oils and grease.

Groundwater barrier

The property of swelling on contact with water makes sodium bentonite useful as a sealant, since it provides a self-sealing, low-permeability barrier. It is used to line the base of landfills to prevent migration of leachate, for quarantining metal pollutants of groundwater, and for the sealing of subsurface disposal systems for spent nuclear fuel. [10] Similar uses include making slurry walls, waterproofing of below-grade walls, and forming other impermeable barriers, e.g., to seal off the annulus of a water well, to plug old wells.

Bentonite can also be "sandwiched" between synthetic materials to create geosynthetic clay liners (GCLs) for the aforementioned purposes. This technique allows for more convenient transport and installation, and it greatly reduces the volume of bentonite required. It is also used to form a barrier around newly planted trees to constrain root growth so as to prevent damage to nearby pipes, footpaths and other infrastructure. Farmers use bentonite to seal retention ponds and line canals.


Bentonite has been prescribed as a bulk laxative, and it is also used as a base for many dermatologic formulas. [11] Granular bentonite is being studied for use in battlefield wound dressings. [12] Bentonite is also sold online and in retail outlets for a variety of indications. [13]

Bentoquatam is a bentonate-based topical medication intended to act as a shield against exposure to urushiol, the oil found in plants such as poison ivy or poison oak. [14]

Bentonite can also be used as a desiccant due to its adsorption properties. Bentonite desiccants have been successfully used to protect pharmaceutical, nutraceutical, and diagnostic products from moisture degradation and extend shelf life. In fact, in the most common package environments, bentonite desiccants offer a higher adsorption capacity than silica gel desiccants. Bentonite complies with the FDA for contact with food and drugs. [15]

In Thai farming

The application of clay technology by farmers in northeast Thailand, using bentonite clay, has dramatically reversed soil degradation and resulted in greater economic returns, with higher yields and higher output prices. Studies carried out by The International Water Management Institute and partners in 2002–2003 focused on the application of locally sourced bentonite clays to degraded soils in the region. These applications were carried out in structured field trials. Applying bentonite clays effectively improved yields of forage sorghum grown under rain-fed conditions. [16] [17]

Bentonite application also influenced the prices that farmers received for their crops. Production costs are higher, but due to more production and the quality of the food, clay farmers could afford to invest and grow more and better food, compared to nonclay-using farmers. [18] [19]

Bentonite slurry walls in modern construction

Bentonite slurry walls (also known as diaphragm walls [20] ) are used in construction, where the slurry wall is a trench filled with a thick colloidal mixture of bentonite and water. [21] A trench that would collapse due to the hydraulic pressure in the surrounding soil does not collapse as the slurry balances the hydraulic pressure. Forms for concrete, and rebar, can be assembled in a slurry-filled trench, and then have concrete poured into the form. The liquid concrete being denser displaces the less-dense bentonite slurry and causes the latter to overflow from the trench. This displaced bentonite slurry is then channelled to a recycling unit from which it can subsequently be reused in a new trench elsewhere on the construction site.

In addition, because the colloid is relatively impervious to water, a slurry wall can prevent the seepage of groundwater, which is useful in preventing the further spread of groundwater that has been contaminated by toxic material such as industrial waste. [21]


The clay from which pottery is made is described as "plastic" if it can be stretched without cracking, or "short" or non-plastic if it tends to break up when formed. A small amount of bentonite is often added to make a clay mixture more plastic. This makes the clay more easily formed, by methods such as throwing on a potter's wheel and various hand building techniques. Short clay, such as a porcelain mixture consisting only of kaolinite and feldspar, can be formed only by a limited set of methods such as pressing and molding, that do not put the clay under tension. One problem with adding bentonite is that it typically contains minerals that affect the color of the mix.

Ceramic glazes often contain bentonite. The bentonite is added to slow or prevent the settling of the glazes. It can also improve the consistency of application of glazes on porous biscuit-fired ware. Once a certain amount of glaze water has been absorbed by the biscuit the bentonite effectively clogs the pores and resists the absorption of further water resulting in a more evenly thick coat.

Emergency use

Bentonite is used in industry and emergency response as a chemical absorbent and container sealant.

History and natural occurrence

In 2011, the U.S. was the top producer of bentonite, with almost an one-third share of the world's production, followed by China and Greece. [22]

Most high-grade natural sodium bentonite is produced from the western United States in an area between the Black Hills of South Dakota and the Bighorn Basin of Wyoming, and the Tokat Resadiye region of Turkey. [3] Mixed sodium/calcium bentonite is mined in Greece, Australia, India, Russia, and Ukraine.

In the United States, calcium bentonite is mined primarily in Mississippi and Alabama. [3] Other major locations producing calcium bentonite include New Zealand, Germany, Greece, Turkey, India, and China.

See also

Related Research Articles

Adobe Building material made from earth and organic materials

Adobe is a building material made from earth and organic materials. Adobe is Spanish for mudbrick, but in some English-speaking regions of Spanish heritage, the term is used to refer to any kind of earth construction. Most adobe buildings are similar in appearance to cob and rammed earth buildings. Adobe is among the earliest building materials, and is used throughout the world.

Slurry wall technique used to build reinforced concrete walls in areas of soft earth close to open water or with a high ground water table

A slurry wall is a civil engineering technique used to build reinforced concrete walls in areas of soft earth close to open water, or with a high groundwater table. This technique is typically used to build diaphragm (water-blocking) walls surrounding tunnels and open cuts, and to lay foundations.

Earth materials

Earth materials include minerals, rocks, soil and water. These are the naturally occurring materials found on Earth that constitute the raw materials upon which our global society exists. Earth materials are vital resources that provide the basic components for life, agriculture and industry. Earth materials can also include metals and precious rocks.

Plaster general term for a broad range of building materials

Plaster is a building material used for the protective or decorative coating of walls and ceilings and for moulding and casting decorative elements. In English "plaster" usually means a material used for the interiors of buildings, while "render" commonly refers to external applications. Another imprecise term used for the material is stucco, which is also often used for plasterwork that is worked in some way to produce relief decoration, rather than flat surfaces.

Clay minerals group of minerals

Clay minerals are hydrous aluminium phyllosilicates, sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces.

Montmorillonite smectite, phyllosilicate mineral

Montmorillonite is a very soft phyllosilicate group of minerals that form when they precipitate from water solution as microscopic crystals, known as clay. It is named after Montmorillon in France. Montmorillonite, a member of the smectite group, is a 2:1 clay, meaning that it has two tetrahedral sheets of silica sandwiching a central octahedral sheet of alumina. The particles are plate-shaped with an average diameter around 1 μm and a thickness of 0.96 nm; magnification of about 25,000 times, using an electron microscope, is required to "see" individual clay particles. Members of this group include saponite.

Palygorskite phyllosilicate mineral

Palygorskite or attapulgite is a magnesium aluminium phyllosilicate with formula (Mg,Al)2Si4O10(OH)·4(H2O) that occurs in a type of clay soil common to the Southeastern United States. It is one of the types of fuller's earth. Some smaller deposits of this mineral can be found in Mexico, where its use is tied to the manufacture of Maya blue in pre-Columbian times.

Geosynthetics synthetic material used to stabilize terrain

Geosynthetics are synthetic products used to stabilize terrain. They are generally polymeric products used to solve civil engineering problems. This includes eight main product categories: geotextiles, geogrids, geonets, geomembranes, geosynthetic clay liners, geofoam, geocells and geocomposites. The polymeric nature of the products makes them suitable for use in the ground where high levels of durability are required. They can also be used in exposed applications. Geosynthetics are available in a wide range of forms and materials. These products have a wide range of applications and are currently used in many civil, geotechnical, transportation, geoenvironmental, hydraulic, and private development applications including roads, airfields, railroads, embankments, retaining structures, reservoirs, canals, dams, erosion control, sediment control, landfill liners, landfill covers, mining, aquaculture and agriculture.

Drilling fluid Aid for drilling boreholes into the ground

In geotechnical engineering, drilling fluid, also called drilling mud, is used to aid the drilling of boreholes into the earth. Often used while drilling oil and natural gas wells and on exploration drilling rigs, drilling fluids are also used for much simpler boreholes, such as water wells. One of the functions of drilling mud is to carry cuttings out of the hole.

Metakaolin is the anhydrous calcined form of the clay mineral kaolinite. Minerals that are rich in kaolinite are known as china clay or kaolin, traditionally used in the manufacture of porcelain. The particle size of metakaolin is smaller than cement particles, but not as fine as silica fume.

Geosynthetic clay liner

Geosynthetic clay liners (GCLs) are factory manufactured hydraulic barriers consisting of a layer of bentonite or other very low-permeability material supported by geotextiles and/or geomembranes, mechanically held together by needling, stitching, or chemical adhesives. Due to environmental laws, any seepage from landfills must be collected and properly disposed of, otherwise contamination of the surrounding ground water could cause major environmental and/or ecological problems. The lower the hydraulic conductivity the more effective the GCL will be at retaining seepage inside of the landfill. Bentonite composed predominantly (>70%) of montmorillonite or other expansive clays, are preferred and most commonly used in GCLs. A general GCL construction would consist of two layers of geosynthetics stitched together enclosing a layer of natural or processed sodium bentonite. Typically, woven and/or non-woven textile geosynthetics are used, however polyethylene or geomembrane layers or geogrid geotextiles materials have also been incorporated into the design or in place of a textile layer to increase strength. GCLs are produced by several large companies in North America, Europe, and Asia. The United States Environmental Protection Agency currently regulates landfill construction and design in the US through several legislations.

Deep foundation type of building foundation

A deep foundation is a type of foundation that transfers building loads to the earth farther down from the surface than a shallow foundation does to a subsurface layer or a range of depths. A pile or piling is a vertical structural element of a deep foundation, driven or drilled deep into the ground at the building site.

Alkali soil soil type

Alkali, or Alkaline, soils are clay soils with high pH, a poor soil structure and a low infiltration capacity. Often they have a hard calcareous layer at 0.5 to 1 metre depth. Alkali soils owe their unfavorable physico-chemical properties mainly to the dominating presence of sodium carbonate, which causes the soil to swell and difficult to clarify/settle. They derive their name from the alkali metal group of elements, to which sodium belongs, and which can induce basicity. Sometimes these soils are also referred to as alkaline sodic soils.
Alkaline soils are basic, but not all basic soils are alkaline.

Tonstein is a hard, compact sedimentary rock that is composed mainly of kaolinite or, less commonly, other clay minerals such as montmorillonite and illite. The clays often are cemented by iron oxide minerals, carbonaceous matter, or chlorite. Tonsteins form from volcanic ash deposited in swamps.

Medicinal clay

The use of medicinal clay in folk medicine goes back to prehistoric times. Indigenous peoples around the world still use clay widely, which is related to geophagy. The first recorded use of medicinal clay goes back to ancient Mesopotamia.


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