Bentonite is a type of volcanic mineral and soil primarily composed of clay. When exposed to water, it swells and expands. Its structure mainly consists of the mineral montmorillonite, which originates from the Cretaceous geological period and was one of the first discoveries in the study of shale bentonite. Bentonite comes in various types, classified based on the predominant elements in its composition. This classification is similar to the categorization of mineral clays, which can have adverse respiratory effects. This article provides concise information about this material and its applications, helping us better understand it.
What is Bentonite?
Bentonite is defined as a clay mineral derived from volcanic ash alterations. Its primary minerals are smectite and montmorillonite. Other minerals in the smectite group include hectorite, saponite, beidellite, and nontronite. Smectites are clay minerals composed of single crystallites about 2 micrometers in size. The structure of smectite crystals comprises three-layered clay minerals, including one octahedral layer and two tetrahedral layers.
The negative charges within silicate-containing layers are neutralized by exchangeable ions located in the inter-crystallite regions. This charge is low, allowing the material to absorb cations like divalent magnesium, divalent calcium, and monovalent sodium. Hydration induces swelling between the crystals. Other minerals, such as quartz, feldspar, calcite, and gypsum, can be found in bentonites depending on their formation and origin.
Properties of the Tetrahedral and Octahedral Units in Bentonite
Silica serves as the tetrahedral unit and is common to all clay minerals, positioned centrally and surrounded by four oxygen atoms. These units connect continuously, forming a sheet layer through bonds between base oxygens in the silicate layers. A hexagonal structure results from planar connection among tetrahedral units, creating cavities suitable for stabilizing interlayer ions if the surface charge on the oxygen is sufficiently strong.
In bentonite, six hydroxyl groups surround each octahedral unit. Planar bonding between octahedral units forms octahedral layers. The tetrahedral and octahedral sheets interconnect through shared oxygen atoms at the tetrahedron’s apex. Aluminum serves as the central element in the octahedral unit.
Properties of Bentonite
Weak van der Waals bonds exist between the layers of this material, enabling their easy sliding and giving it a greasy feel when touched. This characteristic allows bentonite particles to absorb moisture up to 7–20 times their volume. Surface layers hydrate by exchanging cations, absorbing water, and separating via repulsive forces like osmotic pressure. As a result, bentonite swells, especially faster in warm water. Its ability to repeatedly swell and dry is noteworthy. The surface area of bentonite ranges from 600 to 800 square meters.
History of Bentonite
Around 5000 BCE, calcium bentonites were used in Cyprus to increase the thickness of wool fabrics and for washing purposes. In the last century, it became effective in removing colors and bleaching vegetable, animal, and petroleum oils. The term “bentonite” was first used in 1890 near Fort Benton, Montana. By the 20th century, bentonite’s usage became widespread. Below are its diverse applications.
Production of Bentonite
Bentonite is mined from rock deposits using extraction methods. The extracted material remains solid even with 30% moisture. During production, the material is crushed, and soda ash (sodium carbonate) may be added for activation. The solid material is dried using air drying or instant drying methods, reducing moisture to 15%.
Based on its intended use, bentonite is sieved and processed into granules or finely milled into micronized powder. It may also be treated with acids or organic substances to meet specific standards.
Types of Bentonite
Bentonite can be classified into two main categories: sodium (sodic) and calcium, based on structure and impurities.
Sodium Bentonite
Contains primarily sodium impurities and is highly absorbent.
Swells upon water absorption, holding several times its dry weight in water.
Its excellent colloidal properties make it suitable for drilling mud in oil and gas wells and geotechnical and environmental studies.
Used as a sealant to prevent water intrusion into cracks and gaps.
Typically cream, white, or pink.
Calcium Bentonite
Acts as an ion absorber in solutions and absorbs fats and oils in environments.
Considered a key ingredient in industrial cleaning agents.
Can be converted into sodium bentonite through ion exchange by adding sodium carbonate to wet calcium bentonite.
Usually cream, white, or green and is used in cosmetics and personal care products.
Potassium Bentonite
Also known as potassic bentonite, rich in potassium, and formed from altered volcanic ash.
Applications of Bentonite
Bentonite is widely used in drilling mud for oil and gas exploration due to its ability to stabilize boreholes. It also serves as a sealant in construction, a binder in foundries, a clarifier in winemaking, and a soil conditioner in agriculture.
In Earthing Systems
Used as a low-resistance grout around earthing electrodes.
Fills gaps around ground rods, reducing resistance and retaining moisture.
In Agriculture
Sodium bentonite’s water retention properties make it ideal for agriculture.
Reduces irrigation frequency and enhances crop quality and productivity.
In Pelletizing
Combines with crushed iron ore to form pellets called “pellets,” which are baked for hardness and durability.
In Foundry Casting
Sodium bentonite enhances mold quality, improving casting results.
In Food and Feed
Used in animal feed to improve digestion and reduce intestinal contamination.
In Cosmetics and Personal Care
Acts as an emulsifier in products like creams, sunscreens, and lotions.
In Water Treatment
High absorbency makes it effective in wastewater treatment and landfill sealing to protect groundwater from pollutants.
In Paper Production and Catalysts
Enhances paper quality and is modified for use as a catalyst in various reactions.
Drilling Bentonite
Drilling bentonite is a high-performance clay used extensively in the oil and gas industry, particularly for drilling mud. This naturally occurring clay has exceptional swelling, viscosity, and thixotropic properties, making it ideal for creating a stable and efficient drilling fluid. The primary component of drilling bentonite is sodium montmorillonite, which allows it to absorb water and swell up to several times its dry volume.
The primary function of drilling bentonite is to lubricate and cool the drill bit, remove drill cuttings, and stabilize the borehole walls. Its thixotropic nature helps maintain the fluid’s consistency, preventing sedimentation of solid particles during drilling. Furthermore, it acts as a sealant, reducing fluid loss to surrounding formations.
Drilling bentonite is widely used in geotechnical projects, water well drilling, and horizontal directional drilling (HDD) due to its cost-effectiveness and environmentally friendly characteristics. Its ability to suspend heavy materials ensures efficiency during operations. The product is processed to meet industry standards, ensuring optimal performance in different drilling conditions.
Mineral Bentonite
Mineral bentonite is a versatile clay formed from volcanic ash that has undergone natural aging. Its unique properties arise from its main constituent, montmorillonite, a layered silicate mineral with excellent absorption and swelling capacities. Depending on its dominant ions, bentonite is categorized into sodium and calcium types, each with specific applications.
Sodium bentonite is known for its superior swelling properties and water retention capabilities. It is widely used in sealing ponds, constructing landfills, and manufacturing drilling fluids. This type creates a low-permeability barrier, making it ideal for environmental applications.
On the other hand, calcium bentonite is valued for its higher adsorption capacity and is commonly utilized in industries like cosmetics, animal feed, and pharmaceuticals. It serves as a detoxifying agent, binding impurities and toxins due to its negatively charged surface.
Both types of mineral bentonite find applications in foundry sand binding, pelletizing iron ore, and wastewater treatment. Additionally, its use in agriculture enhances soil quality by improving water retention and nutrient availability.
With its natural abundance, eco-friendly nature, and exceptional functionality, mineral bentonite remains an indispensable material across a wide range of industries.
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