NON-TRADITIONAL AMELIORANTS - Fertilizers: Components, Uses in Agriculture and Environmental Impacts - page 200

It belongs to a class of layered aluminosilicates having high dispersibility (crystal size
less than 1 micron) and therefore having a very large specific surface. The largest number of
montmorillonite contained in bentonite clays - more than 70% of the rock mass. The name of
bentonite clay or bentonite due to its large deposit near Fort Benton in the US.
Beside montmorillonite in bentonite composition includes other less common minerals of
smektite groups: beidellite, nontronite, saponite, volkonskoite, and others. Of the non-clay
minerals presents detrital quartz, amorphous silica, glauconite, iron hydroxides in the form of
films and subtle inclusions, sometimes zeolite and ilmenite (Goryushkin, 2006).
The crystal lattice of all smectite consists of three layers that make up the package: the
extreme upper and lower layers of the package consist of tetrahedron and AlSiO 4 called
tetrahedral. Between the tetrahedral layers there is a layer composed of octahedrons Al and Fe,
called octahedral. Three-layer packet has a negative charge due to the substitution of trivalent
elements (Al, Fe) in the octahedron layer by divalent elements (Mg, Fe) or tetravalent Si to
trivalent Al in the tetrahedral layer (Gradusov, 1976).
Owing to the negative charge on the surface of the package are situated the positive one-,
two-and trivalent cations. It mainly, Na, K, Ca, Mg and Fe. Features of crystal-chemical
structure of montmorillonite and presence on its surface of the ion-exchange cationsgives it a
number of unique features:

1 High dispersion. Cause to the very small size of the crystals of the mineral, which

ensures a large specific surface.

2 Hydrophilicity and swellability. This is due to the presence of mobile, able to expand

the crystal lattice. Depending on the chemical composition of the mineral when
hydration it increases in volume by 2-20 times. The most significant swelling mont-
morillonite containing an increased amount of exchangeable sodium.

3 The high absorption capacity. The cation exchange capacity of montmorillonite is

one of the highest among the other minerals and is equal to 80-120 mmol-100 g -1 of
minerals.

4 The high binding capacity. Is a good soil-aggregate stabilizer. In conjunction with

humic acids it forms in soil water-resistant aggregates.

5 Nontoxicity and chemical resistance. This property makes it indispensable in manu-

facturing, construction and many other fields.

Chemical composition of bentonite clay is one of the most important characteristics. It
gives considerable information on the nature of rock, its adsorption properties and the ability
to swell. Chemical composition of bentonite is directly related to the mineral composition and
by the presence of inclusions which accompanying with clay rocks.
Furthermore, the chemical composition of the montmorillonite has fluctuated signify-
cantly: SiO 2 -53.5-73.5%; Al 2 O 3 -3.5-27.8%; Fe 2 O 3 -2.2-32.0%; CaO-0.2-2.6%; MgO-1.5-
6.2 %; K 2 O-0.2-0.6%; Na 2 O-0.1-1.9% (Gorbunov, 1978).
According to the chemical composition there are two types of bentonite clays:

Ⓩ alkaline - with a predominance of exchangeable sodium (most valuable to the

industry);

Ⓩ alkaline-earth - with a predominance of exchangeable calcium.