Bentonite is an absorbent aluminium Phyllosilicate, essentially impure clay consisting mostly of Montmorillonite. There are different types of Bentonite, each named after the respective dominant element, such as potassium (K), sodium (Na), calcium (Ca), and aluminium (Al). Experts debate a number of nomenclatorial problems with the classification of Bentonite clays. Bentonite usually forms from weathering of volcanic ash, most often in the presence of water.
However, the term Bentonite, as well as a similar clay called Tonstein, has been used to describe clay beds of uncertain origin. For industrial purposes, two main 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.
Physical Properties :
|Viscosity @ 600 rpm||:||> 60 by FANN Viscometer|
|Free Swelling 2gm/100ml||:||> 28|
|Moisture||:||< 12 %|
|Residue greater than 75 mic||:||< 3|
|pH||:||8 ~ 9|
|Plat Water Absorption||:||725 ~ 760|
|MB Value||:||425 ~ 450|
|Colour||:||Brown, light red, greenish|
|Montmorllonite content||:||> 75|
Chemical Properties :
|SiO2||:||48 ~ 52|
|Al2O3||:||16 ~ 17|
|Fe2O3||:||11 ~ 14|
|CaO||:||1 ~ 2|
|MgO||:||2 ~ 2.5|
|Na2O||:||3 ~ 4|
|L O I||:||3 ~ 14|
Bentonite expands when wet, absorbing as much as several times its dry mass in water. Hence, care needs to be taken that Bentonite does not come in contact with water before using it for the desired application.
1. Because of its excellent colloidal properties, it is often used in drilling mud for oil and gas wells and for geotechnical and environmental investigations.
2. The property of swelling also makes sodium Bentonite useful as a sealant, since it provides a self-sealing, low permeability barrier.
3. It is used to line the base of landfills to prevent migration of Leachate, for quarantining metal pollutants of groundwater, and for the sealing of subsurface disposal systems for spent nuclear fuel. Similar uses include making slurry walls, waterproofing of below-grade walls, and forming other impermeable barriers, e.g., to seal off the annulus of a water well, to plug old wells.
4. It is also used to form a barrier around newly planted trees to constrain root growth so as to prevent damage to nearby pipes, footpaths and other infrastructure.
5. 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 into a moldable aggregate known as green sand used for making molds in sand casting.
6. The self-stickiness of Bentonite allows high-pressure ramming or pressing of the clay in moulds to produce hard, refractory shapes, such as model rocket nozzles.
7. Bentonite also has the interesting property of adsorbing relatively large amounts of protein molecules from aqueous solutions. Therefore, it is uniquely useful in the process of winemaking, where it is used to remove excessive amounts of protein from white wines.