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

The totally different types of bentonite are every 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 normally forms from weathering of volcanic ash, most often in the presence of water. Nonetheless, the term bentonite, as well as a similar clay called tonstein, has been used to describe clay beds of unsure origin. For industrial functions, predominant courses 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 frequent 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 uses 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, almost half of the US production of bentonite liner was used for drilling mud.

Drilling mud

Bentonite is utilized in drilling fluids to lubricate and cool the chopping tools, to remove cuttings, and to assist prevent blowouts. Much of bentonite’s usefulness in the drilling and geotechnical engineering industry comes from its unique rheological properties. Comparatively small quantities of bentonite suspended in water form a viscous, shear-thinning material. Most frequently, bentonite suspensions are also thixotropic, although rare 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 characteristics of a gel (a fluid with a minimal yield power required to make it move). So, it is a typical 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 metal foundries. Sodium bentonite is most commonly used for giant 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 within the steelmaking industry. Bentonite, in small percentages, is used as an ingredient in commercially designed clay bodies and ceramic glazes. Bentonite clay can be used in pyrotechnics to make finish plugs and rocket engine nozzles.

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 right 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 historic metalworking technology. Modern chemical processes to switch the ionic surface of bentonite greatly intensify this stickiness, resulting in remarkably dough-like yet sturdy casting sand mixes that stand as much as molten metal temperatures.

The same effluvial deposition of bentonite clay onto beaches accounts for the number of plasticity of sand from place to put 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 much better for building sand castles than others.

The self-stickiness of bentonite permits high-pressure ramming or pressing of the clay in molds to produce hard, refractory shapes, reminiscent of 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 an in depth-fitting rod; bentonite will form a very hard, consolidated plug that is not easily crumbled.

Purification

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

Bentonite has the property of adsorbing relatively massive amounts of protein molecules from aqueous solutions. Consequently, bentonite is uniquely helpful in the process of winemaking, where it is used to remove excessive 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 fast clarification of both red and white wines.

Absorbent

Bentonite is utilized in a variety of pet care items corresponding 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 helpful as a sealant, since it provides a self-sealing, low-permeability barrier. It’s used to line the bottom of landfills to prevent migration of leachate, for quarantining metal pollution of groundwater, and for the sealing of subsurface disposal systems for spent nuclear fuel. Similar uses embody making slurry walls, waterproofing of under-grade partitions, and forming different impermeable obstacles, e.g., to seal off the annulus of a water well, to plug old wells.

Bentonite can be «sandwiched» between synthetic supplies to create geosynthetic clay liners (GCLs) for the aforementioned purposes. This method allows for more convenient transport and installation, and it tremendously reduces the volume of bentonite required. Additionally it is used to form a barrier around newly planted timber to constrain root progress in order to forestall damage to nearby pipes, footpaths and other infrastructure. Farmers use bentonite to seal retention ponds.