BENTONITE

Bentonite is an absorbent aluminum phyllosilicate generally impure clay consisting mostly of montmorillinite, (Na,Ca)0.33(AI,Mg)2Si4O10(H2O)n. Two types exist: swelling bentonite which is also called sodium bentonite and non-swelling bentonite or calcium bentonite. It forms from weathering of volcanic ash, most often in the presence of water.

Bentonite is a rock that comprises claylike minerals. The most common clay minerals in bentonite are members of the smectite group (MOSTLY MONTMORILLINITE); other components of bentonite include biotite, feldspars, illite, kaolinite, quartz, and volcanic glass. There are two types of bentonite-swelling bentonite, which is also called sodium or western bentonite, and non-swelling bentonite, which is also called calcium, or southern, bentonite. Both types formed through the alteration of volcanic ash that was deposited in the marine environment. Bentonite is mined mainly in the Western United States and Greece. Most of the bentonite mined in the United States is used in oil and gas well drilling.

SODUIM BENTONITE

Sodium bentonite expands when wet – it can absorb several times its dry weight in water. It is mostly used in drilling mud in the oil and gas well drilling industries.

The property of swelling also makes sodium bentonite useful as a sealant, especially targeted for the sealing of subsurface disposal systems for spent nuclear fuel and for quarantining metal pollutants of groundwater. Similar uses include making slurry walls, waterproofing of below grade walls and forming other impermeable barriers (e.g. to plug old wells or as a liner in the base of landfills to prevent migration of leachate into the soil).

CALCIUM BENTONITE

The non-swelling calcium bentonite is sold within the alternative health market for its purported cleansing properties. It is usually combined with water and ingested as part of a detox diet, in a practice known as geophagy. It is claimed that the microscopic structure of the bentonite draws impurities into it from the digestive system, which are then excreted along with the bentonite, It is also claimed that native tribes in South America, Africa and Australia have long used bentonite clay for this purpose.

Pascalite is another commercial name for the calcium bentonite clay.

USES FOR BOTH TYPES

Much of bentonites usefulness in the drilling and geotechnical engineering industry comes form its unique rheological properties. Relatively small quantities of bentonite suspended in water form a viscous, shear thinning material. Most often, bentonite suspensions are also thixotropic, although rare cases of rheopectic behavior have also been reported. At high enough concentrations, bentonite suspensions begin to take on the characteristics of a gel (a material with finite yield strength).

Bentonite can be used in cement, adhesives, ceramic bodies, cosmetics and cat litter. Fuller’s earth, an ancient dry cleaning substance is finely ground bentonite, typically used for purifying transformer oil. Bentonite, in small percentages, is used as an ingredient in commercially designed clay bodies and ceramic glazes. Bentonite clay is also used in pyrotechnics to make end plugs and rocket nozzles, and can also be used as a therapeutic face pack for the treatment of acne/oily skin.

HISTORY

The absorbent clay was given the name bentonite by an American geologist sometime after its discovery in about 1890 – after the Benton Formation (a geological stratum, at one time Fort Benton) in eastern Wyoming’s Rock Creek area. Other modern discoveries include Montmorillinite discovered in 1847 in Montmorillon in the Vienne prefecture of France, in Poitou-Charentes, South of the Loire Valley and Pascalite discovered in about 1830 by French-Canadian fur trapper Emile Pascal atop the 8600-foot high Big Horn Mountains in Wyoming, USA.

Most high-grade commercial sodium bentonite mined in the United States comes from the area between the Black Hills of South Dakota and the Big Horn Basin of Montana. Sodium bentonite is also mined in the southwestern United States, in Greece and in other regions of the world. Calcium bentonite is mined in the Great Plains, Central Mountains and southeastern regions of the United States. Supposedly the world’s largest current source of bentonite is Chongzuo in China’s Guangxi province.

REFERENCES

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