Bentonite is an absorbent aluminium phyllosilicate clay consisting principally of montmorillonite. It was named by Wilbur C. Knight time in 1898 after the Cretaceous Benton Shale near Rock River, Wyoming.
The completely different types of bentonite are each named after the respective dominant element, akin to potassium (K), sodium (Na), calcium (Ca), and aluminium (Al). Consultants 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. Nonetheless, the term bentonite, as well as the same clay called tonstein, has been used to explain clay beds of unsure origin. For industrial purposes, major courses of bentonite exist: sodium and calcium bentonite. In stratigraphy and tephrochronology, utterly 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 widespread clay species that is typically dominant is kaolinite. Kaolinite-dominated clays are commonly referred to as tonsteins and are typically associated 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 round 1990, virtually half of the US production of bentonite was used for drilling mud.
Bentonite is utilized in drilling fluids to lubricate and cool the slicing instruments, to remove cuttings, and to assist forestall blowouts. Much of bentonite’s usefulness within the drilling and geotechnical engineering trade 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 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 minimal yield strength required to make it move). So, it is a common part 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 metal foundries. Sodium bentonite liner 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 is also used as a binding agent within 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 also be used in pyrotechnics to make end 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 into a moldable aggregate known as green sand used for making molds in sand casting. Some river deltas naturally deposit just such a mix of clay silt and sand, making a natural supply of excellent molding sand that was critical to ancient metalworking technology. Modern chemical processes to switch 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 number 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 pressing of the clay in molds to produce hard, refractory shapes, equivalent to model rocket nozzles. To test whether a particular model of cat litter is bentonite, merely ram a sample with a hammer into a sturdy tube with an in depth-fitting rod; bentonite will form a very hard, consolidated plug that is not easily crumbled.
Bentonites are used for decolorizing various 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. Had 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 additionally has the incidental use of inducing more fast clarification of both red and white wines.
Bentonite is utilized in a variety of pet care items reminiscent of cat litter to absorb the odor and surround the feces. It’s also used to soak up oils and grease.
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’s used to line the base of landfills to stop migration of leachate, for quarantining metal pollution of groundwater, and for the sealing of subsurface disposal systems for spent nuclear fuel. Similar uses include making slurry partitions, waterproofing of below-grade partitions, and forming different impermeable obstacles, e.g., to seal off the annulus of a water well, to plug old wells.
Bentonite will also be “sandwiched” between artificial supplies to create geosynthetic clay liners (GCLs) for the aforementioned purposes. This method permits for more convenient transport and set up, and it significantly reduces the amount of bentonite required. It is usually used to form a barrier round newly planted trees to constrain root development in order to prevent damage to close by pipes, footpaths and other infrastructure. Farmers use bentonite to seal retention ponds.