Bentonite

Bentonite is an absorbent swelling clay consisting mostly of montmorillonite (a type of smectite).

Bentonite usually forms from the weathering of volcanic ash in seawater, or by hydrothermal circulation through the porosity of volcanic ash beds, which converts (devitrification) the volcanic glass (obsidian, rhyolite, dacite) present in the ash into clay minerals. As a swelling clay, bentonite has the ability to absorb large quantities of water, which increases its volume by up to a factor of eight. This makes bentonite beds unsuitable for building and road construction. However, the swelling property is used to advantage in drilling mud and groundwater sealants. Bentonite is used in industry and emergency response as a chemical absorbent and container sealant.

Types of Bentonite         

Sodium Bentonite

Sodium bentonite expands when wet, absorbing as much as several times its dry mass in water. Because of its excellent colloidal properties, it is often used in drilling mud for oil and gas wells and boreholes for geotechnical and environmental investigations.

Calcium Bentonite   

Calcium bentonite is a useful adsorbent of ions in solution, as well as fats and oils. It is the main active ingredient of fuller's earth, probably one of the earliest industrial cleaning agents. It has significantly less swelling capacity than sodium bentonite

Applications

•    Drilling Mud
Bentonite is used in drilling mud to lubricate and cool the cutting tools (drill bit), to remove cuttings, to stabilize the borehole walls, and to help prevent blowouts (by maintaining a sufficient hydraulic pressure in the well). Bentonite also curtails 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 is also used as a binding agent in the manufacture of iron ore (taconite) pellets as used in the steelmaking industry
•    Purification
Bentonites are used for decolorizing various mineral, vegetable, and animal oils. They are also used for clarifying wine, liquor, cider, beer, mead, and vinegar
•    Absorbent
Bentonite is used in a variety of pet care items such as cat litter to absorb pet waste. It is also used to absorb oils and grease
•    Carrier
Bentonite is used as an inert carrier. It helps ensure that the active agent is uniformly dispersed and that pesticides and fertilizers are retained on the plants.
•    Filler
Bentonite is used as a filler in a wide variety of products.It also acts as a stabilizer and extender in these products
•    Sealant
The property of swelling on contact with water makes sodium bentonite useful as a sealant since it provides a self-sealing, low-permeability barrier.
•    Catalyst
High-purity calcium bentonite is treated with acid for use as a catalyst in cracking heavy petroleum fractions
•    Medicine
Bentonite has been prescribed as a bulk laxative, and it is also used as a base for many dermatologic formulas.[33] Granular bentonite is being studied for use in battlefield wound dressings
•    Ceramics
Plasticity is the property of clay that allows it to be manipulated and retain its shape without cracking after the shaping force has been removed; clays with low plasticity are known as or short or non-plastic. A small amount of bentonite added to clay can increase its plasticity, and hence ease forming of articles by some shaping techniques
History and Natural Occurrence
In 2018, China was the top producer of bentonite, with almost a one-quarter share of the world's production, followed by the United States and India. Total worldwide production was 24,400,000 metric tons of bentonite and 3,400,000 metric tons of fuller's earth.
Most high-grade natural sodium bentonite is produced from the western United States in an area between the Black Hills of South Dakota and the Bighorn Basin of Wyoming, and the Tokat Resadiye region of Turkey. Mixed sodium/calcium bentonite is mined in Greece, Australia, India, Russia, and Ukraine.

Reference: Google