Bentonite is a kind of clay rock, also called montmorillonite clay rock. It often contains a small amount of illite, kaolinite, indianite, chlorite, zeolite, quartz, feldspar and calcite, etc. Generally, it is white and light yellow. For the iron content changing, the bentonite is light gray, light green, pink, auburnish red, brick red and ash black. It has a waxy, soil, or oil sheen.
Bentonite features with high hygroscopicity which can adsorb the water for 8 to 20 times of their own volume to expansion to 30 times. In aqueous media, the bentonite can disperse colloidal suspension and features with definite stickiness, thixotropy and lubricity. The bentonite also has plasticity and cohesiveness and the things such as silt mixture also have these features. It also features with high cation exchange capacity and adsorptive capacity.
Bentonite is known as the all-powerful clay for its good physical and chemical properties. The bentonite can be cementing agent, suspending agent, thixotropic agent, stabilizing agent, purification decoloring agents, fillingmaterial, feedstuff and catalytic agent. The bentonite is widely used for a lot of areas, such as oil exploitation, directional undercrossing, steel casting, metallurgy pellets, coatings, compound fertilizer, sizing, rubber, plastic, papermaking, purified water, dehumidizer and pesticide.
Bentonite is surface mined through a process called backcasting where reclamation is performed by filling the mining pits with soils from subsequent pits while the mine is in production. Typically the topsoil layer is about 30 inches deep, which is removed using heavy equipment.
Once the bentonite is removed, it is cleaned and then tested to confirm the grade. It is then dried in the field before being taken to the plant for processing and stockpiled on-site or transferred to a processing facility.
Bentonite has been called the mineral of 1,000 uses, which includes absorbents, animal feed, drilling fluids, foundry, iron ore pelletizing, and sealants. Wyoming bentonite is particularly in demand for pet litter because of it’s ability to absorb many times its volume in water and control odors. Among other uses, bentonite is found in crayons, medication, and cosmetic such as shampoos, lotions, face creams, and lipstick.
Originally, Wyoming bentonite was used by local Indians as a bleaching clay and a washing agent. Pioneers used it as a substitute for axle grease to cure inflamed horses hoofs and to waterproof roofs.
Today bentonite is used in a variety of industries including the metal casting industry where it is used as a bonding material for molding processes. When mixed with certain types of molding sands, a bond is formed that can withstand very high temperatures.
Bentonite is also used in the ceramic and building industries where it is mixed with clay and sand to form adhesive which is effective in sealing against water.