bentonites

Bentonite is a highly plastic clay formed from the alteration of volcanic ash and dominated by the clay mineral montmorillonite, a 2:1 phyllosilicate. It consists of tiny platelets capable of exchanging cations such as sodium or calcium. The dominant interlayer cation controls swelling and gel formation: sodium bentonite swells substantially when hydrated, creating a viscous, gel-like suspension, while calcium bentonite swells more modestly and tends to produce lower-viscosity suspensions.

Formation and naming: Bentonite originates when volcanic ash deposits alter in water-rich environments and undergo diagenesis. The name derives from Fort Benton, Montana, where early deposits were studied; major commercial sources include Wyoming and Montana in the United States, as well as Greece, Turkey, China, and India.

Properties and uses: Bentonite is fine-grained with a high surface area and high cation exchange capacity. It becomes plastic when wet and forms low-permeability barriers when compacted, making it useful as a sealant. Practical applications include drilling muds for oil and gas exploration, foundry sands as a binder, iron ore pelletization, and liners or barriers for landfills and groundwater containment. It is also used as a purifier and adsorbent, and in consumer products such as cat litter.

Environmental and safety notes: Bentonite is generally inert, but processed materials can generate dust that may irritate the respiratory tract. Its performance depends on mineralogy, particle size, water chemistry, and temperature, which influence swelling, viscosity, and sealing capability.