Bentonite is an absorbent aluminium phyllosilicate clay consisting mostly of montmorillonite. It was named by Wilbur C. Knight in 1898 after the Cretaceous Benton Shale near Rock River, Wyoming.
The totally different types of bentonite are every named after the respective dominant factor, corresponding to potassium (K), sodium (Na), calcium (Ca), and aluminium (Al). Consultants debate a number of nomenclatorial problems with the classification of bentonite clays. Bentonite normally forms from weathering of volcanic ash, most frequently within the presence of water. However, the term bentonite, as well as an analogous clay called tonstein, has been used to explain clay beds of unsure origin. For industrial functions, two essential 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 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 round 1990, nearly half of the US production of bentonite was used for drilling mud.
Drilling mud
Bentonite is used in drilling fluids to lubricate and funky the cutting instruments, to remove cuttings, and to assist forestall blowouts. A lot of bentonite’s usefulness within the drilling and geotechnical engineering trade comes from its unique rheological properties. Comparatively small quantities of bentonite suspended in water form a viscous, shear-thinning material. Most often, bentonite suspensions are also thixotropic, though rare cases of rheopectic behavior have also been reported. At high sufficient 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 minimum yield energy required to make it move). So, it is a typical element of drilling mud used to curtail drilling fluid invasion by its propensity for aiding within 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 also be 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 our bodies and ceramic glazes. Bentonite clay can also be utilized in pyrotechnics to make end 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 mix of clay silt and sand, creating a natural supply of fantastic molding sand that was critical to historical metalworking technology. Modern chemical processes to modify the ionic surface of bentonite tremendously intensify this stickiness, leading to 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 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, akin to model rocket nozzles. To test whether a particular model of cat litter is bentonite, merely ram a pattern with a hammer right into a sturdy tube with an in depth-fitting rod; bentonite will form a very hard, consolidated plug that isn’t easily crumbled.
Purification
Bentonites are used for decolorizing varied mineral, vegetable, and animal oils. They are additionally used for clarifying wine, liquor, cider, beer, and vinegar.
Bentonite has the property of adsorbing relatively large amounts of protein molecules from aqueous solutions. Consequently, bentonite is uniquely useful within 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 exposure to warm temperatures, as these proteins denature. It additionally has the incidental use of inducing more speedy clarification of each red and white wines.
Absorbent
Bentonite is used in quite a lot of pet care items similar 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 prevent migration of leachate, for quarantining metal pollution of groundwater, and for the sealing of subsurface disposal systems for spent nuclear fuel. Related makes use of embrace making slurry partitions, waterproofing of below-grade partitions, and forming different impermeable boundaries, 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 method permits for more handy transport and set up, and it enormously reduces the volume of bentonite required. Additionally it is used to form a barrier round newly planted bushes to constrain root development in order to forestall damage to nearby pipes, footpaths and other infrastructure. Farmers use bentonite to seal retention ponds.
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