Bentonite

BENTONITE

Introduction

Bentonite is the common name for a group of water-absorbing aluminum phyllosilicate clays, whose principal mineral component is Montmorillonite (typically ≥ 70%).
This clay mineral has a unique layered structure, allowing alkali and alkaline-earth metal cations (such as Na⁺ and Ca²⁺) to be hydrated and intercalated between the layers. As a result, Bentonite exhibits strong swelling capacity, high viscosity, and excellent ion-exchange and adsorption properties.

Bentonite is mainly classified into Sodium Bentonite (high swelling capacity) and Calcium Bentonite (high adsorption capacity).

1. Classification and Composition

1.1. Classification by Exchangeable Cations

• Sodium Bentonite
  Exhibits very strong swelling behavior (several times its original dry volume) upon contact with water, generating high viscosity and pronounced thixotropic properties.
  Commonly used in drilling fluids, casting, and molding applications.
• Calcium Bentonite
  Displays lower swelling capacity but higher adsorption performance.
  Often used for activation to produce activated clay (bleaching earth) for oil refining and environmental treatment.

1.2. Main Chemical Composition

Component	Formula	Notes
Primary mineral	Montmorillonite	(Na,Ca)₀.₃(Al,Mg)₂Si₄O₁₀(OH)₂·nH₂O
Silicon Dioxide	SiO₂	Present in high proportion
Aluminum Oxide	Al₂O₃	Significant content
Exchangeable cations	Na⁺, Ca²⁺, Mg²⁺, K⁺	Influence swelling behavior
Accessory minerals	Quartz, Illite, Kaolinite, etc.	Minor constituents

2. Physical & Mechanical Properties

Parameter	Characteristics
Appearance	Fine powder, odorless; gray, cream-white, or yellow-brown
Viscosity	Very high (especially Sodium Bentonite), exhibiting strong thixotropy
Swelling capacity	High (Sodium Bentonite can swell >10 times its dry volume)
Adsorption capacity	Large specific surface area; excellent adsorption of liquids, ions, and contaminants
Thermal resistance	Good thermal stability; non-melting material

3. Key Applications in Industry and Ceramics

Bentonite is a highly versatile material with widespread industrial applications.

3.1. Applications in the Ceramic Industry

Bentonite is used as an important additive, even at very low dosages:

• Plasticizer (Body Additive)
  When added to ceramic body formulations (porcelain, ceramic tiles), Bentonite enhances plasticity and inter-particle bonding, improving formability and green mechanical strength (unfired strength).
  Note: Dosage must be carefully controlled (typically 0.25% – 1.0%) as excessive Bentonite may increase drying shrinkage.
• Glaze Suspender
  Bentonite acts as a suspending agent in ceramic glazes, keeping glaze particles uniformly dispersed in water, preventing settling at the bottom of storage tanks, and ensuring smooth, even glaze coverage on the product surface.

3.2. Applications in Other Industries

• Drilling Industry (Oil & Gas, Piling Works)
  Bentonite slurry (drilling mud) is essential for lubricating drill bits, reducing torque, and most importantly stabilizing borehole walls by forming a protective mud cake, thanks to its swelling and viscosity properties.
• Metal Casting Industry
  Used as a binder in sand molds for iron and steel casting, providing mold strength, plasticity, and thermal resistance.
• Oil Refining and Chemical Processing
  Activated Calcium Bentonite (Activated Bleaching Earth) is used to adsorb pigments and impurities, decolorizing vegetable oils and mineral oils.
• Construction and Environmental Applications
  • Used as a waterproofing and sealing material (liners for reservoirs, landfills, dams) due to its swelling-induced impermeability
  • Applied in soil improvement to enhance water retention and cation exchange capacity (nutrient retention)
• Animal Feed / Pharmaceutical Applications
  Used as a pellet binder, filler, and mycotoxin adsorbent in animal feed formulations.