Bentonite is an absorbent aluminium phyllosilicate clay consisting largely of montmorillonite. It was named by Wilbur C. Kevening in 1898 after the Cretaceous Benton Shale near Rock River, Wyoming.
The totally different types of bentonite are every named after the respective dominant component, comparable to 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 frequently in the presence of water. Nevertheless, the time period bentonite, as well as an analogous clay called tonstein, has been used to describe clay beds of uncertain origin. For industrial purposes, principal lessons 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 widespread clay species that is generally dominant is kaolinite. Kaolinite-dominated clays are commonly referred to as tonsteins and are typically associated with coal.
The primary 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, virtually half of the US production of bentonite was used for drilling mud.
Bentonite is utilized in drilling fluids to lubricate and funky the reducing instruments, to remove cuttings, and to assist prevent blowouts. A lot of bentonite’s usefulness in 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 frequently, bentonite suspensions are also thixotropic, although uncommon cases of rheopectic conduct have also been reported. At high sufficient concentrations (about 60 grams of bentonite per litre of suspension), bentonite suspensions start to take on the characteristics of a gel (a fluid with a minimal yield power required to make it move). So, it is a common element 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 giant castings that use dry molds, while calcium bentonite is more commonly used for smaller castings that use “green” or wet molds. Bentonite can also 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 our 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 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, making a natural source of fantastic 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 but strong casting sand mixes that stand as much as molten metal temperatures.
The identical effluvial deposition of bentonite clay onto beaches accounts for the variety 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 significantly better for building sand castles than others.
The self-stickiness of bentonite permits high-pressure ramming or urgent of the clay in molds to produce hard, refractory shapes, akin to model rocket nozzles. To test whether a particular model of cat litter is bentonite, simply ram a sample with a hammer into a sturdy tube with a close-fitting rod; bentonite will form a very hard, consolidated plug that is not simply crumbled.
Bentonites are used for decolorizing numerous mineral, vegetable, and animal oils. They are also used for clarifying wine, liquor, cider, beer, and vinegar.
Bentonite has the property of adsorbing relatively large quantities of protein molecules from aqueous solutions. Consequently, bentonite is uniquely useful in the process of winemaking, the place 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 also has the incidental use of inducing more fast clarification of each red and white wines.
Bentonite is utilized in a variety of pet care items similar to cat litter to soak up the odor and surround the feces. It’s also used to absorb 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 bottom of landfills to forestall migration of leachate, for quarantining metal pollution of groundwater, and for the sealing of subsurface disposal systems for spent nuclear fuel. Related uses include making slurry walls, waterproofing of under-grade walls, and forming other impermeable obstacles, e.g., to seal off the annulus of a water well, to plug old wells.
Bentonite can be “sandwiched” between artificial materials to create geosynthetic clay liners (GCLs) for the aforementioned purposes. This technique permits for more convenient transport and installation, and it greatly reduces the volume of bentonite required. Additionally it is used to form a barrier round newly planted timber to constrain root progress so as to forestall damage to close by pipes, footpaths and other infrastructure. Farmers use bentonite to seal retention ponds.
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