Bentonite is an absorbent aluminium phyllosilicate clay consisting largely 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 component, 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 normally forms from weathering of volcanic ash, most frequently within the presence of water. Nonetheless, the time period bentonite, as well as an identical clay called tonstein, has been used to describe clay beds of uncertain origin. For industrial functions, predominant classes 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 one other common clay species that is generally dominant is kaolinite. Kaolinite-dominated clays are commonly referred to as tonsteins and are typically related with coal.
The principle makes use of of bentonite are for drilling mud, binder (e.g. foundry-sand bond, iron ore pelletizer), 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 utilized in drilling fluids to lubricate and funky the reducing instruments, to remove cuttings, and to assist forestall blowouts. Much 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 additionally thixotropic, although rare cases of rheopectic habits have also been reported. At high enough concentrations (about 60 grams of bentonite per litre of suspension), bentonite suspensions start to take on the traits of a gel (a fluid with a minimum 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.
Binder
Bentonite has been widely used as a foundry-sand bond in iron and steel foundries. Sodium bentonite is most commonly used for large 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 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, creating a natural supply of excellent molding sand that was critical to historical metalworking technology. Modern chemical processes to modify the ionic surface of bentonite vastly intensify this stickiness, leading to remarkably dough-like yet robust 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 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 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 or not a particular model of cat litter is bentonite, merely ram a sample with a hammer right into a sturdy tube with a detailed-fitting rod; bentonite will form a really hard, consolidated plug that isn’t 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 relatively massive amounts of protein molecules from aqueous solutions. Consequently, bentonite is uniquely useful within the process of winemaking, where it is used to remove excessive amounts 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 additionally has the incidental use of inducing more rapid clarification of each red and white wines.
Absorbent
Bentonite is used in a wide range of pet care items akin to cat litter to soak up the odor and surround the feces. Additionally it is 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 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. Similar uses embrace making slurry partitions, waterproofing of under-grade walls, and forming other impermeable boundaries, e.g., to seal off the annulus of a water well, to plug old wells.
Bentonite may also be “sandwiched” between artificial supplies to create geosynthetic clay liners (GCLs) for the aforementioned purposes. This approach permits for more convenient transport and set up, and it significantly reduces the amount of bentonite required. It is also used to form a barrier round newly planted bushes to constrain root growth in order to forestall damage to close by pipes, footpaths and different infrastructure. Farmers use bentonite to seal retention ponds.
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