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The term bentonite refers to clays or clay rock (very fine grained sediments or sedimentary rock), which primarily consists of the expandable mineral montmorillonite.
Bentonite is a clay mineral with incredibly small particle sizes.
This, in combination with the active chemistry on the surface of the particles (that makes them hold onto water), makes Bentonite the most plastic and impermeable common clay material used in ceramics.
CAS Number: 1302-78-9
EC Number: 215-108-5,
Bentonite is a type of clay that is the primary constituent of drilling fluid.
Bentonite properties make Bentonite suitable for keeping ground cuttings in suspension so that they can be pumped to the surface.
Bentonite is also used to lubricate the cutting head, thus, reducing wear and lubricating the tunnel walls, making Bentonite easier for pipes to be installed.
Bentonite is a clay mineral with incredibly small particle sizes.
This, in combination with the active chemistry on the surface of the particles (that makes them hold onto water), makes Bentonite the most plastic and impermeable common clay material used in ceramics.
Bentonite contribution to working properties in glazes and clay bodies is balanced by the undesirable properties that are also imparted.
Thus anyone who uses this material should have their eyes open to Bentonite advantages and disadvantages.
There is a huge variation in the chemistries of bentonites, Bentonite is impossible to specify an average (bentonite is not employed in ceramics for Bentonite chemistry).
Any generic chemical analysis is thus only an attempt to represent the amounts you might find in a common variety.
Because of the high iron content, bentonite is considered a dirty material and thus the tug-of-war between the valuable working properties Bentonite imparts and the need for whiteness or pure color that Bentonite impedes.
Bentonite is defined as a naturally occurring material that is composed predominantly of the clay mineral smectite.
Most bentonites are formed by the alteration of volcanic ash in marine environments and occur as layers sandwiched between other types of rocks.
The smectite in most bentonites is the mineral montmorillonite, which is a dioctahedral smectite but occasionally other types of smectite may be present.
Bentonite is the presence of smectite which imparts the desirable properties to bentonites, although associated factors such as the nature of the exchangeable cations in the interlayer also affect properties.
For example naturally occurring bentonites with Na+ as the interlayer cation can have very different properties to bentonites where the interlayer cation is Ca++.
Most commercial bentonites contain more that 80% smectite, however, a wide variety of other minerals may occur as impurities.
The image on this page shows a geosynthetic liner with bentonite granules as fill.
Bentonite is rock that consists mainly of montmorillonite, a clay mineral, and contains impurities such as quartz, feldspar, and other minerals.
Bentonite is believed that deposits of bentonite were formed by reaction of volcanic ash accumulated following volcanic eruptions several million years or several hundred million years ago under certain temperature or pressure conditions or with hydrothermal solutions.
Bentonite deposits exist in the U.S., Europe, China, Japan, and other areas around the world.
Montmorillonite, which is the main component of bentonite, has the characteristic property of swelling to many times Bentonite original volume when it absorbs water.
This property is called a swelling property.
Bentonite becomes viscous when dispersed in water, and has the ability to well adsorb various kinds of cations.
Thus, Bentonite has various properties.
Because of these properties, bentonite is used in a wide range of industrial fields.
For example, Bentonite is used in the fields of castings, civil engineering and construction, toilet sand for pets, chemical products, and many other products.
Bentonite is listed in the Japanese Pharmacopoeia and the Food Sanitation Act, and is also used in cosmetics, pharmaceuticals, or food additives.
This is why bentonite is known as clay with 1,000 uses.
Recently, Bentonite has been studied as a candidate barrier material used in geological disposal of radioactive waste, widening the range of Bentonite use.
Bentonite is a natural mineral mostly composed of hydrous aluminum silicates (their formula being something like Al2H2O12Si4, which means there is a basic content of Aluminum, Hydrogen and Silica).
Bentonite’s usually negatively charged.
Therefore, Bentonite attracts cations, like Sodium, Calcium, Iron, and Magnesium.
The two most common cations that attracted are sodium and calcium, making sodium and calcium bentonite the two predominant bentonite types on the planet.
Although they are similar, the different cation provides them with other properties.
While they both have absorbent properties, the materials they absorb are not the same.
Bentonite is the commercial name of a whole range of natural clays with a high water absorption capacity causing Bentonite to expand and swell.
Bentonite predominantly consists of montmorillonite: a clay mineral belonging to a class of phyllosilicates called smectites.
Bentonites may contain a variety of accessory minerals in addition to montmorillonite.
These may include lesser amounts of other clay minerals such as kaolin, mica, illite, as well as non-clay minerals like quartz, feldspar, calcite, and gypsum.
Bentonite quality, and, consequently, Bentonites applications, depend on whether it contains any of these other minerals.
Bentonite density when dry varies depending on the quality, and may range from 2.2 to 2.8 g/cm3.
Bentonite apparent density, when quarried and piled under natural moisture conditions, ranges from 1.5 to 1.8 g/cm3.
The apparent density of milled bentonite products varies depending on mill fineness, ranging from 0.7 to 0.9 g/cm3.
Bentonite is clay formed by the alteration of minute glass particles derived from volcanic ash.
Bentonite was named for Fort Benton, Mont., near which Bentonite was discovered.
The formation of bentonite involves the alteration of volcanic glass to clay minerals; this requires hydration (taking up or combination with water) and a loss of alkalies, bases, and possibly silica, with the preservation of the textures of the original volcanic glass.
Bentonite consists chiefly of crystalline clay minerals belonging to the smectite group, which are hydrous aluminum silicates containing iron and magnesium as well as either sodium or calcium.
Two types of bentonite are recognized, and the uses of each depend on specific physical properties.
Sodium bentonites absorb large quantities of water, swelling to many times their original volume, and give rise to permanent suspensions of gellike masses.
These have been used to seal dams; in bonding foundry sands, asbestos, and mineral wool; as drilling muds; in portland cements and concrete, ceramics, emulsions, insecticides, soaps, pharmaceuticals, and paints; in the manufacture of paper; for clarifying water, juices, and liquors; and as a water softener to remove calcium from hard water.
Calcium bentonites are nonswelling and break down to a finely granular aggregate that is widely used as an absorbent clay sometimes called fuller’s earth.
Bentonite occurs in rocks that were deposited in the Ordovician to Neogene periods (about 488.3 to 2.6 million years ago).
In the United States the principal producers are Wyoming, Montana, California, Arizona, and Colorado.
Important world producers are Greece, Japan, Italy, Brazil, Romania, Germany, Mexico, Argentina, Spain, India, Hungary, Poland, Canada, Turkey, and Cyprus.
Bentonite (/ˈbɛntənaɪt/ is an absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite.
Na-montmorillonite has a considerably greater swelling capacity than Ca-montmorillonite.
Bentonite usually forms from the weathering of volcanic ash in seawater, or by hydrothermal circulation through the porosity of volcanic ash beds, which converts (devitrification) the volcanic glass (obsidian, rhyolite, dacite) present in the ash into clay minerals.
In the mineral alteration process, a large fraction (up to 40-50 wt.%) of amorphous silica is dissolved and leached away, leaving the bentonite deposit in place.
Bentonite beds are white or pale blue or green (traces of reduced Fe2+) in fresh exposures, turning to a cream color and then yellow, red, or brown (traces of oxidized Fe3+) as the exposure is weathered further.
As a swelling clay, bentonite has the ability to absorb large quantities of water, which increases Bentonite volume by up to a factor of eight.
This makes bentonite beds unsuitable for building and road construction.
However, the swelling property is used to advantage in drilling mud and groundwater sealants.
The montmorillonite / smectite making up bentonite is an aluminium phyllosilicate mineral, which takes the form of microscopic platy grains.
These give the clay a very large total surface area, making bentonite a valuable adsorbent.
The plates also adhere to each other when wet.
This gives the clay a cohesiveness that makes Bentonite useful as a binder and as an additive to improve the plasticity of kaolinite clay used for pottery.
One of the first findings of bentonite was in the Cretaceous Benton Shale near Rock River, Wyoming.
The Fort Benton Group, along with others in stratigraphic succession, was named after Fort Benton, Montana, in the mid-19th century by Fielding Bradford Meek and F. V. Hayden of the U.S. Geological Survey.
Bentonite has since been found in many other locations, including China and Greece (bentonite deposit of the Milos volcanic island in the Aegean Sea).
The total worldwide production of bentonite in 2018 was 20,400,000 metric tons.
Bentonite has a high cation exchange capacity.
That means clay, which has a negative charge, can attract positively charged ions.
Those are minerals like magnesium, sodium, and potassium.
Bentonite also has aluminum and silica.
Bentonite may also attract positively charged toxins in your gut.
Bentonites are ash falls that have undergone extensive devitrification to dioctahedral smectite (usually montmorillonite).
Because they have a very simple mineralogical assemblage (most mudrocks contain not only more than one clay type, but a mixture of smectites and illite–smectites), and are often almost monomineralic, ancient bentonites have been extensively used to study the process of illitization of smectite.
Comparison of different bentonites, or single bentonites which have undergone variable heating during burial, shows that Si4+, Ca2+, and Na+ are lost from the bed and K+ is gained as the smectite is illitized.
Bentonite should be noted that the supply of K+ is the rate-limiting step in the illitization of most bentonites because they are K+ deficient.
Thus, the most potassic (illitized) portions of many bentonite beds are frequently the margins.
Where the enclosing sediment is limestone, illitization will be restricted to any K+ present within the bentonite bed.
Bentonite dispersions are used in many civil engineering applications.
Most impressive is the diaphragm-walling technique.
A thixotropic bentonite dispersion is used as an intermediate supporting material, obviating the need for revetting (retaining wall) when the trench is excavated.
In addition, the plastering effect is important.
The slurry penetrates only to some extent into the trench sides and forms an impermeable filter cake of clay mineral layers on the walls so that excessive loss of fluid to the surrounding formation is prevented.
In the next step, the bentonite dispersion is displaced by the concrete.
Concrete walls about 100 m deep and 0.8–1.5 m thick are built up by this technique. (Bentonite is interesting to note that the stabilizing effect of bentonite dispersions was observed in the middle of the nineteenth century.
The first patent was issued in 1912 but the technique was only widely applied since about 1950.)
Bentonite is a clay consisting mainly of smectite minerals, commonly formed by decomposition of volcanic ash or tuff, or sometimes from other igneous or sedimentary rocks.
Bentonite is a very plastic clay that shrinks (or swells) markedly in response to the removal (or addition) of water.
There are three main types of bentonite:
High swelling (sodium)
Low swelling (calcium)
Moderate swelling (intermediate sodium-calcium) bentonite.
The sodium bentonites are the most useful because of their greater swelling capacity.
They are used mainly as bonding clay in foundries, in drilling mud, in animal feed pellets, and for civil engineering applications
Historically the majority of bentonite production in Victoria has been from the Greenwald deposit.
The deposit consists of a layer of up to six metres thickness of calcium-rich bentonite that rests on limestone and is overlain by sandy clay and basalt.
Most of the bentonite has been used in animal feed pellets.
The only other significant bentonite deposit is at Gellibrand, where there are a few impure bentonite seams interlayered with feldspathic sandstone, mudstone and shale.
There are minor bentonite occurrences at Soapy Rocks near Anglesea, at Poowong in South Gippsland, and near Coleraine.
There is potential for bentonite discoveries in the Murray Basin in northwestern Victoria.
The host rocks are equivalent to those of the Arumpo deposit in southwest NSW.
Bentonite is a very old clay that has been used as a remedy for many things.
The fine powder forms when volcanic ash ages.
Bentonite’s named after Fort Benton, WY, which has a lot of Bentonite.
But Bentonite’s found all over the world.
Bentonite’s also known as Montmorillonite clay after a region in France with a large deposit.
And you may hear Bentonite called calcium bentonite clay.
People have eaten bentonite clay or put Bentonite on their skin for thousands of years.
Bentonite’s been used to:
Clean or protect skin
Heal skin infections or acne
Treat stomach gas
Ease diarrhea
Today, bentonite is used to make medicine and makeup.
You can buy Bentonite in powders and pills, too.
Bentonite’s sometimes used in:
Shampoo
Lotion
Face masks
Toothpaste
Dietary supplements
Types of Bentonite:
In geology, the term bentonite is applied to a type of claystone (a clay rock, not a clay mineral) composed mostly of montmorillonite (a clay mineral from the smectite group).
Bentonite forms by devitrification of volcanic ash or tuff, typically in a marine environment.
This results in a very soft, porous rock that may contain residual crystals of more resistant minerals, and which feels soapy or greasy to the touch.
However, in commercial and industrial applications, the term bentonite is used more generally to refer to any swelling clay composed mostly of smectite clay minerals, which includes montmorillonite.
The undifferentiated reference to the weathered volcanic rock for the geologist or to the industrial mixture of swelling clays can be a source of confusion.
The montmorillonite making up bentonite is an aluminium phyllosilicate mineral whose crystal structure is described as low-charge TOT.
This means that a crystal of montmorillonite consists of layers, each of which is made up of two T sheets bonded to either side of an O sheet.
The T sheets are so called because each aluminium or silicon ion in the sheet is surrounded by four oxygen ions arranged as a tetrahedron.
The O sheets are so called because each aluminium ion is surrounded by six oxygen or hydroxyl ions arranged as an octahedron.
The complete TOT layer has a weak negative electrical charge, and this is neutralized by calcium or sodium cations that bind adjacent layers together, with a distance between layers of about 1 nanometer.
Because the negative charge is weak, only a fraction of the possible cation sites on the surface of a TOT layer actually contain calcium or sodium.
Water molecules can easily infiltrate between sheets and fill the remaining sites.
This accounts for the swelling property of montmorillonite and other smectite clay minerals.
The different types of bentonite are each named after the respective dominant cation.
For industrial purposes, two main classes of bentonite are recognized: sodium and calcium bentonite.
Sodium bentonite is the more valuable but calcium bentonite is more common.
In stratigraphy and tephrochronology, completely devitrified (weathered volcanic glass) ash-fall beds are sometimes also referred to as "K-bentonites" (the illitized clay rock) when the dominant clay species is illite (a non-swelling clay).
However, in pure clay mineralogy, the term illite is more appropriate than "K-bentonite" (the "altered K-rock") because Bentonite is a distinct type of non-swelling clay while the commercial term bentonite implicitly refers to a swelling clay, a smectite (in the European and UK terminology), or a montmorillonite (in the US terminology).
Sodium bentonite:
Sodium bentonite expands when wet, absorbing as much as several times Sodium bentonite dry mass in water.
Because of Sodium bentonite excellent colloidal properties, Sodium bentonite is often used in drilling mud for oil and gas wells and boreholes for geotechnical and environmental investigations.
The property of swelling also makes sodium bentonite useful as a sealant, since Sodium bentonite provides a self-sealing, low permeability barrier.
Sodium bentonite is used to line the base of landfills, for example.
Bentonite is also part of the backfill material used at the Waste Isolation Pilot Project.
Various surface modifications to sodium bentonite improve some rheological or sealing performance in geoenvironmental applications, for example, the addition of polymers.
Sodium bentonite can be combined with elemental sulfur as fertilizer prills.
These permit slow oxidation of the sulfur to sulfate, a plant nutrient needed for some crops like onions or garlic synthesizing a lot of organo-sulfur compounds, and maintain sulfate levels in rainfall-leached soil longer than either pure powdered sulfur or gypsum.
Sulfur/bentonite pads with added organic fertilizers have been used for organic farming.
Calcium bentonite:
Calcium bentonite is a useful adsorbent of ions in solution, as well as fats and oils.
Calcium bentonite is the main active ingredient of fuller's earth, probably one of the earliest industrial cleaning agents.
Calcium bentonite has significantly less swelling capacity than sodium 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.
As commonly practiced, 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.
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.
For example, residual calcium carbonates (formed if exchanged cations are insufficiently removed) may result in inferior performance of the bentonite in geosynthetic liners.
Illitisation of smectite clays by potassium ions and K-bentonite rock:
Illite is the main clay constituent of potash bentonite (a rock type also known as K-bentonite or potassium bentonite).
K-bentonite is a term reserved to volcanic stratigraphy and tephrochronology and is related to the weathered clay rock type only.
Illite, the clay mineral, is a potassium-rich phyllosilicate formed from the alteration of smectic clay in contact with groundwater rich in K+ ions.
Illite is a high-charge TOT clay mineral, in which sheets are bound relatively strongly by more numerous potassium ions, and so Bentonite is no longer a swelling clay and has few industrial uses.
In contrast to the highly hydrated Na+ ions which act as "swellers" or "expanders" ions, poorly hydrated K+ ions behave as "collapsers" when exchanging with Na+ ions accessible in the interlayers space present between two TOT layers.
Dehydrated K+ ions are preferentially located in between two face-to-face hexagonal cavities formed by six joined silica tetrahedra present at the surface of the basal plane of a TOT layer (see the corresponding figure showing an elementary TOT layer).
Because dehydrated, these K+ ions are sometimes said to form inner-sphere bonds with the surrounding oxygen atoms present in the hexagonal cavity hosting them.
Bentonite means there is no water molecule in between the K+ ion and the oxygen atoms attached to the silica tetrahedra (T).
Applications of Bentonite:
The main uses of bentonite are in drilling mud and as a binder, purifier, absorbent, and carrier for fertilizers or pesticides.
As of around 1990, almost half of the US production of bentonite was used as drilling mud.
Minor uses include filler, sealant, and catalyst in petroleum refining.
Calcium bentonite is sometimes marketed as fuller's earth, whose uses overlap with those of other forms of bentonite.
Drilling mud:
Bentonite is used in drilling mud to lubricate and cool the cutting tools (drill bit), to remove cuttings, to stabilize the borehole walls, and to help prevent blowouts (by maintaining a sufficient hydraulic pressure in the well).
Bentonite also curtails drilling fluid invasion by Bentonite propensity for aiding in the formation of mud cake.
Much of bentonite's usefulness in the drilling and geotechnical engineering industry comes from Bentonite 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, ~6wt.%), bentonite suspensions begin to take on the characteristics of a gel (a fluid with a minimum yield strength required to make Bentonite move).
Binder:
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.
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.
Bentonite 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 sandcastles 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.
Purification:
Bentonites are used for decolorizing various mineral, vegetable, and animal oils.
They are also used for clarifying wine, liquor, cider, beer, mead, and vinegar.
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 Bentonite 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.
Bentonite also has the incidental use of inducing more rapid clarification of both red and white wines.
Bentonite is also considered an effective low-cost adsorbent for the removal of chromium(VI) ions from aqueous solutions (contaminated wastewater).
Absorbent:
Bentonite is used in a variety of pet care items such as cat litter to absorb pet waste.
Bentonite is also used to absorb oils and grease.
Carrier:
Bentonite is used as an inert carrier for pesticides, fertilizers, and fire retardants.
Bentonite helps ensure that the active agent is uniformly dispersed and that pesticides and fertilizers are retained on the plants.
Filler:
Bentonite is used as a filler in a wide variety of products, including adhesives, cosmetics, paint, rubber, and soaps.
Bentonite also acts as a stabilizer and extender in these products.
Sealant:
The property of swelling on contact with water makes sodium bentonite useful as a sealant since Bentonite provides a self-sealing, low-permeability barrier.
Bentonite is used to line the base of landfills to prevent migration of leachate, for confining metal pollutants of groundwater, and for the sealing of subsurface disposal systems for spent nuclear fuel.
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 Bentonite greatly reduces the volume of bentonite required.
Bentonite 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.
Catalyst:
High-purity calcium bentonite is treated with acid for use as a catalyst in cracking heavy petroleum fractions.
Medicine:
Bentonite has been prescribed as a bulk laxative, and Bentonite is also used as a base for many dermatologic formulas.
Granular bentonite is being studied for use in battlefield wound dressings.
Bentonite is also sold online and in retail outlets for a variety of indications.
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.
Bentonite can also be used as a desiccant due to Bentonite adsorption properties.
Bentonite desiccants have been successfully used to protect pharmaceutical, nutraceutical, and diagnostic products from moisture degradation and extend shelf life.
In most common package environments, bentonite desiccants offer a higher water adsorption capacity than silica gel desiccants.
Bentonite complies with the FDA for contact with food and drugs.
Farming in Thailand:
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.
Bentonite application also influenced the prices that farmers received for their crops.
Production costs are higher, but due to higher production and the quality of the food, clay farmers could afford to invest and grow more and better food, compared to nonclay-using farmers.
Bentonite slurry walls in modern construction:
Bentonite slurry walls (also known as diaphragm walls) are used in construction, where the slurry wall is a trench filled with a thick colloidal mixture of bentonite and water.
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 channeled to a recycling unit from which Bentonite 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.
Ceramics:
Plasticity is the property of clay that allows Bentonite to be manipulated and retain its shape without cracking after the shaping force has been removed; clays with low plasticity are known as or short or non-plastic.
A small amount of bentonite added to clay can increase Bentonite plasticity, and hence ease forming of articles by some shaping techniques.
However, bentonite typically contains minerals that affect the fired color of the mix, and Bentonite swelling properties can make such a mix prone to significant shrinkage and potential cracking as Bentonite dries.
Ceramic glazes often contain bentonite.
The bentonite is added to slow or prevent the settling of the glazes.
Bentonite 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.
Uses of Bentonite Clay:
Bentonite’s used in many ways, but some show more promise than others.
Skin:
Bentonite clay works like a sponge on your skin.
Bentonite absorbs dirt and oil, like sebum.
Too much sebum can lead to acne.
The antibacterial and anti-inflammatory properties may help your skin heal.
Fields of Application:
The main application domains and use of bentonite range from pet hygiene and pet food to foundries, oil drilling industry, agriculture, cosmetics industry.
Studies show bentonite clay may help with:
Allergic reactions to poison ivy and poison oak
Hand dermatitis
Diaper rash
Skin infections or ulcers
Sunscreen protection
Talk to your doctor before using the clay if you have acne or dermatitis (eczema).
They can help you figure out the best way to treat Bentonite.
Hair:
Some people use bentonite clay as a hair mask.
There are no studies to show whether Bentonite’s a good way to clean or soften human hair.
Digestion:
Some animal studies show bentonite might boost good bacteria in the gut.
This may help with taking in nutrients.
In humans, bentonite is sometimes used to treat occasional or ongoing diarrhea.
One study showed bentonite helped with constipation from irritable bowel syndrome (IBS).
More research is needed.
Teeth:
Natural toothpaste makers say the minerals in bentonite clay are good for teeth and gums.
Some say brushing with clay can “purify, detoxify, and alkalize” your mouth.
There are no scientific studies to back up these claims.
Researchers are also studying the effects of bentonite clay on:
Cancer
Blood clotting
Immune system response
Kidney health
Aflatoxin exposure in children
Benefits of Bentonite:
Fine particle size:
Bentonite is colloidal (particles are so small the action of water molecules is enough to keep them in suspension).
Bentonite is typically 10 times finer than ball clay.
Bentonite can have a surface area of almost 1000 square meters per gram (50 times that of kaolin, 5000 times that of silica flour).
Plasticity:
Because of their active electrolytic behavior and fine particle size, bentonites exhibit extremely high plasticity (and associated high shrinkage).
In pottery and porcelain clay bodies additions of only 2% can produce marked improvements in workability and dry strength without much effect on fired color.
The use of up to 5% is common, especially where high plasticity is needed in a white burning body.
However the need for higher additions than this may indicate a lack of other clean or adequately clays in the recipe.
Also, high amounts of bentonite will dramatically slow down the drying rate.
In certain applications Bentonite is practical to use bentonite as the only plasticizer in a mix (in larger percentages).
The plasticity-producing effects of bentonite depend on the shapes, sizes, surfaces and electrolytics of the particles Bentonite is interacting with.
Equal additions of bentonite to two different host bodies may have considerably different effects on the plasticities.
Drying performance:
Bentonite makes bodies more plastic and dry harder but this comes at a cost, they shrink more during drying and thus potentially crack more.
Bentonite is far too plastic to prepare test specimens (e.g. for drying, strength and shrinkage evaluation).
However, a mix of 20-30% virgin material with calcined material can be extruded and formed (test specimens will still shrink to a very small size).
Permeability:
Most bentonites are impermeable to water.
To demonstrate this fill a tall glass cylinder with bentonite to near the top and then carefully pour water on top.
The water will penetrate down into the clay only a few millimeters and no matter how long you leave Bentonite will not penetrate further.
This occurs because the powder swells as the water penetrates and adjacent particles 'hang onto' the water between them.
The water thus becomes a glue that holds the mass together and prevents more from entering or passing through.
This phenomenon accounts for why glazes and bodies of high bentonite content dry slower.
As an example, if you pour a slurry of silty clay onto a plaster surface the water is often pulled out in seconds.
However a bentonite slurry may require days or weeks to pull the water out evenly.
Swelling:
Most bentonites expand (as much as 15 times) when added to water.
This characteristic is valuable in thickening liquids and slurries and is another contributing factor to maintaining suspensions.
Bentonite is used in large quantities in the gas and oil drilling industries to suspend high specific gravity slurries which are used as a medium to float out the chunks of rock cut by the drill bit.
Suspension:
Bentonite is used to keep particulates in suspension in all sorts of consumer and industrial products, and in glazes in ceramics.
The mechanism is charge attraction, that is, opposite electrolytic charges develop on the surfaces and edges of dispersed particles and give rise to a stable 'house-of-cards" structure that can be disrupted by shear stress.
However when the stress is removed, the structure re-establishes itself.
The amazing thing is that large amounts of other types of particles can be tolerated within this structure, they are kept in suspension as well.
Thus maximum suspending benefit can be achieved by blunging bentonite with the water before adding the other dry materials (to insure that every particle is whetted on all sides).
However, this cannot be done without a powerful high-speed propeller mixer.
Thus Bentonite is normal to blend dry ingredients including bentonite first and then add them to the water.
However beware of too much bentonite in glazes, they will dry too slowly and will shrink too much during drying causing cracks that later turn into crawling during firing.
Thixotropy:
This is a tendency of a suspension to gel after sitting for a time and then re-liquify when Bentonite is agitated.
Clay bodies also exhibit this behavior, stiffening on aging but then re-softening when worked.
Thixotropy is valuable in clay slurries for this reason, they gel when not being used and thus do not settle out.
While typical industrial thixotropic agents employ various mechanisms bentonite works by charge attraction (see above).
Chemically inert, Inorganic, Non-irritating:
Formulations that are not fired are not altered chemically by bentonite additions.
Bentonite does not support organic growth.
Thus Bentonite is suitable as a carrier for personal care products like hand cream and cosmetics.
Binder:
Bentonite binds particles together in ceramic bodies to make them stronger in the green or dry state.
Bentonite minute particles fill voids between others to produce a more dense mass with more points of contact.
Adding bentonite to glazes also imparts better dry strength and a harder and more durable surface.
To fully appreciate how plastic, hard and strong bentonite can be, try mixing 25:75 with silica and preparing plastic test bars.
Firing:
Standard grades typically vitrify (around Orton cone 6-10) from grey to deep red coloration.
However soluble salts can be so high that they form a glaze on pure test specimens.
Utility grades often contain granular iron material that causes specking in clay bodies, even materials rated at 325 mesh can contain significant speck-causing particles.
For good reason, bentonite is considered a very dirty material.
However commercial micro-fine grades (100% minus 325 mesh) are available (these are very expensive however).
Barium carbonate can be added to bodies to precipitate the solubles bentonite brings.
Thus the iron content is the only firing issue associated with visual character.
Contrary to what many think, a white body can often tolerate a up to 5% bentonite without firing significantly darker.
Normal microfine bentonite or raw bentonite even at 5% does not darken the color of the porcelain as much as you might think.
Examining recipes often shows that the kaolin and ball clay are contributing more iron than the bentonite.
Even white plasticizers often have up to 0.5% iron also 5% bentonite increases the iron content of the body by 25% without considering the factors above.
Considering them Bentonite might cut it to half that.
Use only 2.5% bentonite and it is not really an issue.
Firing cracks, explosions:
Bentonite slows down water penetration.
Not only does a bentonite-containing clay body dry slower but Bentonite does not dry as completely.
Although ware might look dry Bentonite likely is not, several percent tightly-bound water remains.
If ware is not temperature-dried before being fired there is a risk that water will not be able to escape fast enough during firing and ware will crack, fracture under steam pressure.
Health Benefits:
Bentonite clay is antibacterial and anti-inflammatory.
Bentonite also has trace minerals like calcium, iron, copper, and zinc.
Some people eat Bentonite to get these nutrients.
That’s called geophagy.
But the foods people typically eat already have these minerals.
Most of the research on bentonite clay involves animals.
Studies show Bentonite may lower the amount of certain toxins in the body, like aflatoxins.
They’re made by certain molds and can hurt your liver.
Some research shows Bentonite may remove pesticides and help treat metal poisoning.
But more human studies are needed.
You don’t usually need help to clean out your body.
Your kidneys and liver already do that.
The fiber from fruits and vegetables also helps.
Properties of Bentonite:
Bentonite exceptional properties – e.g. capability of expansion, absorption – are defined by the clay material montmorillonite.
Due to Bentonite crystal structure (montmorillonite is a so-called layer silicate with expandable layers in the crystal), montemorillonite has the capability to absorb or deposit substances in Bentonite crystal grid, to partially exchange or fix them.
Bentonite is capable to expand its volume by 6 times by water absorption and to form stable gels (gelatinous substance).
Formation of Bentonite:
Montmorrillonite-rich clays have formed by weathering and metamorphose of volcanic ashes, tuff and basic rock (e.g. basalts).
The term bentonite is derived from the first archaeological site near Fort Benton, Wyoming (USA), where plastic clays were found and described for the first time.
There are numerous bentonite formations differentiated acc. to montmorillonite type, kind and location of formation and mineralogical composition.
History and Natural Occurrence of Bentonite:
In 2018, China was the top producer of bentonite, with almost a one-quarter share of the world's production, followed by the United States and India.
Total worldwide production was 24,400,000 metric tons of bentonite and 3,400,000 metric tons of fuller's earth.
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.
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.
Other major locations producing calcium bentonite include New Zealand, Germany, Greece, Turkey, India, and China.
Identifiers of Bentonite:
EC No.: 215-108-5
CAS No.: 1302-78-9m
