Clay consisting at least 70% montmorillonite is commonly referred to as bentonite. Montmorillonite is a high-dispersity layered aluminosilicate in which, due to nonstoichiometric substitution of cations in crystal lattice, an excess negative charge occurs that compensates exchange cations in the interlayer space.
This responds to hydrophilic properties of bentonite. When bentonite is mixed with water, the water penetrates in interlayer space of montmorillonite, hydrates its surface and exchange cations which results in the mineral swelling. By limiting the free space for swelling, a stress is caused in the bentonite structure, which ensures low permeability. And with further dilution with water, bentonite forms a stable viscous suspension with well-defined thixotropic properties. If space available for swelling is limited, there is a stress state in bentonite structure and this provides a low permeability. And on further dilution with water bentonite forms stable viscous thixotropic suspension.
Due to the above properties bentonite became widely used as visco-gel-forming agent and fluid loss reducer in drilling fluids preparation for wells and crossing drilling, as a binding agent in moulding sand mixture and iron-ore pellets, and as waterproofing and adsorption material. In agriculture bentonite is effective for mixed feed production, as bedding for animals, for soil improvement and for clarification of wine and juice. Bentonite is also widely used for best quality clumping cat litters production. More than 200 fields of bentonite application are known.
Bentonite possesses best processing properties when montmorillonite contains mostly sodium exchangeable cations. Deposits of natural sodium bentonite are located in the South Caucasus. In Russia frequently occur clay deposits with content of montmorillonite 30-60% which are mistakenly referred to bentonite. In fact, all Russian bentonites are Ca-Mg type. After activation with soda ash consumer properties of such bentonites with at least 70% of montmorillonite, may be close to the properties of natural sodium bentonites.
