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What is Wyoming Bentonite Clay?

Wyoming Means Quality

Bentonite clay in Wyoming formed naturally from the chemical weathering of volcanic materials such as tuff or glass, volcanic ash, other igneous and sedimentary rocks. First mined and developed during the 1880's, demand and value of Wyoming bentonite clay increased, and bentonite clay deposits were soon discovered in other parts of Wyoming during the 1920's. The first bentonite processing plant was built shortly after this, followed by many other competitive plants built to process Wyoming bentonite. The largest deposits of commercial sodium bentonite are found in Wyoming, Montana and South Dakota.

Wyoming bentonite is composed essentially of montmorillonite clay, also known as hyrdous silicate of alumina. In laymans terms, Wyoming bentonite is formed much like a deck of cards sandwiched together. When exposed to water, these cards or clay platelets shift apart. Attracting water to its negative face, bentonite holds the water in place similar to iron to a magnet. Because of this unique characteristic, this unique material is capable of adsorbing 7 to 10 times its own weight in water, and swelling up to 18 times its dry volume. Over the years, the area has become famous as the location unique to this high quality material, resulting in the states' name being synonymous with the quality.

Montmorillonite and Adsorption

Montmorillonite has a crystalline structure. It results in a "flake" particle shape that resembles a corn flake. These flakes are extremely small, ranging in long dimension from 10 micrometers to 0.01 micrometers. Hundreds of such flakes aggregate to form a thin particle. One gram of montmorillonite has a surface area of 750 m2/gram, nearly as much as the best activated carbon grains. Twelve grams have a surface area that covers an entire football field. This variance in thickness is related to the adsorption of water and other polar molecules.

The material is always electrically unbalanced by substitutions, such as magnesium, iron, or calcium replacing aluminum. This results in a charge deficiency that must be balanced externally by cations, which in turn are exchangeable. The quantity of cations required to create a net charge balance is called "the exchangeable cation capacity." The internal charge deficiency inside it results in a net negative charge of the particle, which in turn is compensated for by exchangeable cations positioned but weakly held near the tetrahedral layers. The most prominent cations are sodium, calcium, magnesium, and potassium, respectively.

The exchangeability of these cations allows this material to remove heavy metals from water, an important consideration for wastewater treatment. Simultaneously, it removes cationic organics by ion exchange, resulting in an interaction with polymers. Its large swelling capacity, combined with ion exchange capacity, allows the material to form a floc with suspended solids that can be precipitated out of the water.

The combination of the relative purity, its unusual geochemistry and structure is why the material is unique to this area of the world is an extremely high quality material. Purity is defined by the amount of sodium montmorillonite as compared to the other minerals present. A typical sample contains up to 90% montmorillonite while other similar materials produced around the world have only 70-80% montmorillonite.

The color of the material can range from white to light olive green, cream, yellow, earthy red, brown and sometimes sky blue when fresh but yellowing rapidly with exposure to air. When wet it is highly plastic and slippery, often appearing greasy or waxy.