Bentonite: Properties and Applications

Bentonite is a special type of hydrous aluminum silicate clay mineral, primarily composed of montmorillonite. Its name derives from the discovery of this clay in the Benton Shale of Wyoming, USA, in 1898. Montmorillonite has a chemical formula of (Al₂,Mg₃)Si₄O₁₁₄OH₂•nH₂O. This mineral has a layered structure composed of silicon-oxygen tetrahedra and aluminum-oxygen octahedra.

Characteristics of Bentonite

(I) Physical and Chemical Properties

Swelling: Bentonite swells into a paste upon contact with water, with its volume expanding by several to 30 times.

Adsorption: Bentonite has a strong adsorption capacity for various gases, liquids, and organic substances, with a maximum adsorption capacity of up to 5 times its own weight.

Thixotropy: Bentonite can disperse into a gelled or suspended state in aqueous media, exhibiting certain viscosity and thixotropy.

Suspension Stability: Bentonite forms a stable suspension in water.

Specific Surface Area: Natural bentonite has a specific surface area of up to 63 m²/g. 

(II) Chemical Stability

Bentonite loses the water adsorbed between silicate sheets at relatively low temperatures (100-200°C), with the loss of structural water (i.e., hydroxyl groups) beginning at 450-500°C. It is an inorganic, non-toxic, and non-irritating substance.

Applications of Bentonite

(I) Industrial

Drilling mud: Used in oil and water well drilling to seal well walls, remove drill cuttings, and lubricate cutting heads.

Foundry: Mixed with sand for use in casting molds to improve their strength and stability.

Papermaking: Used as a filler and coating to enhance the strength and printing properties of paper.

Rubber and plastics: Used as a filler and modifier to improve material properties.

(II) Environmental Protection

Wastewater treatment: Absorbs pollutants from water, such as heavy metal ions and organic matter.

Waste disposal: Mixed with sand as a lining material for use in waste disposal sites.

(III) Agricultural

Soil improvement: Improves soil structure and enhances soil water retention and fertility. (IV) Food and Pharmaceutical Fields

Food additives: used as thickeners, stabilizers, and clarifiers.

Pharmaceuticals: used in the preparation of ointments and creams, and as suspending agents.

Modification Methods

Acid modification: Improves the adsorption properties of bentonite through acid reaction.

Organic modification: Treats bentonite with organic matter to produce organobentonite for specific applications.

Bentonite is widely used in various fields due to its unique physical and chemical properties. Its modification methods further expand its application range. With technological development, the application prospects of bentonite will be even broader.

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