Characteristics

Montmorillonite, like other clay minerals, is hydrous aluminium silicate. The primary elements of its composition are silicon, aluminium, oxygen or the hydroxyl group. The molecular structure of montmorillonite consists of a unit cell described as a Si-Al-Si structure. The changes in the geometry of the layers create ion exchange properties in the montmorillonites, which contribute towards their fundamental physical properties, and are responsible for the three characteristics of bleaching earth.

There are three main characteristics of bleaching earth that make it commercially useful. These include thixotropy, swelling, and adsorption.

Thixotropy

Thixotropy is the property by which bleaching earth-water slurries under certain temperature, and ionic concentrations become very viscous, gel-like, but lose some of the viscosity under shear stress.

Swelling

Bleaching earth swells in water. Water collects between the flakes to form additional molecular layers, forcing the flakes apart and causing the mass to swell. In addition, this water binds the layers together with increasing force. When the water is removed, the mass contracts by the flakes reassuming their original spacing like an accordion. Organic matter can also be absorbed in mono-molecular layers in between adjacent silicon-oxygen sheets.

Adsorption

The adsorption of exchangeable metallic ions in the clay lattice determines some of the properties of the clay. Bentonite is very unusual in the fact that once it becomes hydrated, the electrical and molecular components of the clay rapidly change and produce an "electrical charge". Its highest power lies in the ability to absorb toxins, impurities, heavy metals and other internal contaminants. Bleaching earth's structure assists it in attracting and soaking up poisons on its exterior wall and then slowly draws them into the interior centre of the clay where it is held in a sort of repository. When bleaching earth is mixed with water, it rapidly swells open like a highly porous sponge. From here the toxins are drawn into the sponge through electrical attraction and once there, they are bound.