Bentonite is an absorbent aluminium phyllosilicate clay consisting principally of montmorillonite. It was named by Wilbur C. Knight in 1898 after the Cretaceous Benton Shale near Rock River, Wyoming.

The completely different types of bentonite are each named after the respective dominant factor, reminiscent of potassium (K), sodium (Na), calcium (Ca), and aluminium (Al). Specialists debate a number of nomenclatorial problems with the classification of bentonite clays. Bentonite often forms from weathering of volcanic ash, most frequently in the presence of water. Nevertheless, the term bentonite, as well as an identical clay called tonstein, has been used to describe clay beds of uncertain origin. For industrial purposes, two foremost lessons of bentonite exist: sodium and calcium bentonite. In stratigraphy and tephrochronology, fully 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 one other common clay species that’s generally dominant is kaolinite. Kaolinite-dominated clays are commonly referred to as tonsteins and are typically related with coal.

The principle makes use of of bentonite are for drilling mud, binder (e.g. foundry-sand bond, iron ore pelletizer), air purifier, absorbent (e.g. pet litter), and as a groundwater barrier. As of around 1990, nearly half of the US production of bentonite was used for drilling mud.

Drilling mud

Bentonite is utilized in drilling fluids to lubricate and funky the cutting instruments, to remove cuttings, and to assist prevent blowouts. Much of bentonite’s usefulness in the drilling and geotechnical engineering industry comes from its distinctive rheological properties. Comparatively small quantities of bentonite suspended in water form a viscous, shear-thinning material. Most often, bentonite suspensions are also thixotropic, though uncommon cases of rheopectic habits have additionally been reported. At high enough concentrations (about 60 grams of bentonite per litre of suspension), bentonite suspensions begin to take on the traits of a gel (a fluid with a minimum yield power required to make it move). So, it is a standard part of drilling mud used to curtail drilling fluid invasion by its propensity for aiding in the formation of mud cake.

Binder

Bentonite has been widely used as a foundry-sand bond in iron and steel foundries. Sodium bentonite is most commonly used for big castings that use dry molds, while calcium bentonite is more commonly used for smaller castings that use «green» or wet molds. Bentonite can be 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 commercially designed clay bodies and ceramic glazes. Bentonite clay is also used in pyrotechnics to make finish plugs and rocket engine nozzles.

The ionic surface of bentonite has a helpful 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 right into a moldable mixture 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 drastically intensify this stickiness, resulting in remarkably dough-like yet sturdy 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 position for building sand castles. Beach sand consisting of only silica and shell grains doesn’t mold well compared to grains coated with bentonite clay. This is why some beaches are a lot better for building sand castles than others.

The self-stickiness of bentonite allows high-pressure ramming or urgent of the clay in molds to produce hard, refractory shapes, comparable to model rocket nozzles. To test whether or not a particular brand of cat litter is bentonite, simply ram a sample with a hammer right into a sturdy tube with a close-fitting rod; bentonite will form a very hard, consolidated plug that is not easily crumbled.

Purification

Bentonites are used for decolorizing numerous mineral, vegetable, and animal oils. They are additionally used for clarifying wine, liquor, sandmat cider, beer, and vinegar.

Bentonite has the property of adsorbing comparatively massive quantities of protein molecules from aqueous solutions. Consequently, bentonite is uniquely useful in the process of winemaking, the place it is used to remove extreme quantities of protein from white wines. Have been it not for this use of bentonite, many or most white wines would precipitate undesirable flocculent clouds or hazes upon publicity to warm temperatures, as these proteins denature. It also has the incidental use of inducing more rapid clarification of each red and white wines.

Absorbent

Bentonite is utilized in quite a lot of pet care items comparable to cat litter to soak up the odor and surround the feces. Additionally it is 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 bottom of landfills to stop migration of leachate, for quarantining metal pollutants of groundwater, and for the sealing of subsurface disposal systems for spent nuclear fuel. Similar makes use of embrace making slurry walls, waterproofing of under-grade walls, and forming other impermeable limitations, e.g., to seal off the annulus of a water well, to plug old wells.

Bentonite can also be «sandwiched» between artificial supplies to create geosynthetic clay liners (GCLs) for the aforementioned purposes. This approach allows for more convenient transport and installation, and it significantly reduces the volume of bentonite required. It is usually used to form a barrier around newly planted bushes to constrain root progress in order to stop damage to close by pipes, footpaths and other infrastructure. Farmers use bentonite to seal retention ponds.