bentonita

Bentonite, also known as bentonita, is a group of clay minerals dominated by montmorillonite, a hydrated aluminum–silicate formed from the alteration of volcanic ash. It belongs to the smectite family and is prized for its swelling, plastic, and adsorptive properties. The name derives from Fort Benton, Wyoming, where large deposits were first described.

Bentonite consists of layered 2:1 silicate sheets with exchangeable cations between the layers. Its high cation exchange capacity and surface area allow it to absorb water and many dissolved substances. When dispersed in water, it can swell markedly, forming gels. Sodium-rich bentonites typically exhibit greater swelling than calcium-rich varieties. Wet bentonite is plastic and cohesive, while dried material can become brittle.

Commercial bentonite is mined from volcanic ash beds and weathered tuffs. Major deposits are found in the United States (notably Wyoming) and in several other countries, including China, India, Greece, Turkey, and France. The ore is processed to meet end‑use requirements, which may involve drying, refining, bleaching, or milling.

Applications are diverse. The most important use is as an additive in drilling muds for oil and gas exploration, where its rheological and filtration properties stabilize boreholes. It also serves as a binder in foundry sands, a sealant and barrier material in civil engineering, and an adsorbent in water treatment and purification (including wine and juice clarification). Bentonite is used in cosmetics, pharmaceuticals, building materials, and as cat litter.

Safety and environmental notes: bentonite is generally non-toxic, but fine dust can irritate the eyes, skin, and lungs. Quality and grade vary by deposit and intended use, with food-grade and pharmaceutical-grade products subject to regulatory standards.