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 near Rock River, Wyoming.
The different types of bentonite are every named after the respective dominant ingredient, equivalent 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 often within the presence of water. However, the time period bentonite, as well as an identical clay called tonstein, has been used to explain clay beds of unsure origin. For industrial functions, fundamental classes 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 widespread clay species that is sometimes dominant is kaolinite. Kaolinite-dominated clays are commonly referred to as tonsteins and are typically related 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, almost half of the US production of bentonite was used for drilling mud.
Drilling mud
Bentonite is used in drilling fluids to lubricate and cool the reducing tools, to remove cuttings, and to assist stop blowouts. A lot of bentonite’s usefulness within the drilling and geotechnical engineering business 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, although uncommon cases of rheopectic conduct have additionally 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 minimum yield energy required to make it move). So, it is a common component 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 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 within 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 can be 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 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 source of fantastic molding sand that was critical to historical metalworking technology. Modern chemical processes to switch the ionic surface of bentonite drastically intensify this stickiness, leading to remarkably dough-like yet strong casting sand mixes that stand up to molten metal temperatures.
The identical effluvial deposition of bentonite clay onto beaches accounts for the number of plasticity of sand from place to place 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, such as model rocket nozzles. To test whether a particular model of cat litter is bentonite, simply ram a pattern with a hammer right into a sturdy tube with a detailed-fitting rod; bentonite will form a very hard, consolidated plug that is not easily crumbled.
Purification
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 comparatively massive amounts of protein molecules from aqueous solutions. Consequently, bentonite is uniquely useful in the process of winemaking, where it is used to remove excessive quantities of protein from white wines. Were 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 speedy clarification of each red and white wines.
Absorbent
Bentonite is used in a wide range of pet care items comparable to cat litter to soak up the odor and surround the feces. It’s also used to soak up 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 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. Related makes use of embody making slurry walls, waterproofing of under-grade partitions, and forming different impermeable barriers, e.g., to seal off the annulus of a water well, to plug old wells.
Bentonite will also be “sandwiched” between synthetic materials to create geosynthetic clay liners (GCLs) for the aforementioned purposes. This technique allows for more convenient transport and set up, and it significantly reduces the volume of bentonite required. It is also used to form a barrier around newly planted timber to constrain root progress in order to stop damage to close by pipes, footpaths and different infrastructure. Farmers use bentonite to seal retention ponds.
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