0 to 100 Chemical and physical properties of bentonite

Before discussing the chemical and physical properties of bentonite, it should be said that bentonite is one of the most important minerals with wide applications in various industries. It is a type of clay that is used in many fields due to its special properties (see the article What is bentonite?). This mineral is mainly composed of smectite group minerals and has attracted a lot of attention due to its unique chemical and physical properties.

Chemical composition of bentonite

Bentonite is mainly composed of montmorillonite, a type of mineral in the smectite family. Its chemical structure consists of aluminum silicate with variable amounts of cations such as sodium, calcium, magnesium, and iron. The chemical formula of montmorillonite is generally represented as follows:

(Al, Mg)2Si4O10(OH)2·nH2O

This composition indicates the presence of tetrahedral silicate units combined with octahedral aluminum layers. Replacing some aluminum ions with magnesium or iron creates a negative charge in the structure, which is compensated by the adsorption of mobile cations (such as Na+ or Ca2+).

This cationic property is very important in the industrial applications of bentonite, especially in processes that require ion exchange.

Types of Bentonite

Based on the type of dominant cation, bentonite is divided into two main categories:

Sodium bentonite:
Has a high water absorption and expansion capacity.
Forms a viscous gel in water.
It is mostly used in drilling oil and gas wells and as a material in the foundry industry.

Calcium bentonite:
Has a lower expansion and water absorption capacity.
It is mostly used in applications such as animal absorbents and the production of food granules.

(Refer to the article Types of Bentonite and Their Differences)

Physical Properties of Bentonite

Water Absorption Capacity:

Water absorption capacity is one of the most prominent features of bentonite, especially in its sodium type, which can absorb water several times its own weight. This phenomenon is due to the layered structure of montmorillonite, where the spaces between its layers allow water to penetrate. This property causes the bentonite to swell and increase in volume, which has many applications in various industries, such as drilling and soil engineering.

Gelling properties:

Bentonite forms a stable and viscous gel in contact with water. This process is due to the distribution of clay particles in water and the formation of a network of particles that prevents the free flow of liquid. Its gelling property is very useful in drilling oil and gas wells, where there is a need to stabilize the well wall and transport particles to the surface. This gelling property is also used in the production of cosmetics such as face masks.

Viscosity:

The viscosity or stickiness of a bentonite solution in water changes under the influence of concentration, temperature and type of dominant cation (sodium or calcium). Sodium bentonite usually produces a highly viscous solution that is used in drilling applications as well as in the manufacture of adhesives and industrial lubricants. This property is also important in the production of paints and coatings.

Color and Appearance:

The color of bentonite depends on the type of mineral impurities present in it; for example, the presence of iron in the structure can change its color from white or light cream to yellow or green. Bentonite is usually supplied as a powder or fine granules with a soft texture, the fine-grained texture being due to the small size of the montmorillonite particles.

Density:

The true density of bentonite is in the range of 2 to 2.8 g/cm3. However, the bulk density of bentonite packaged as a powder can be much lower, around 0.7 to 1 g/cm3. This property is important in determining the weight of packages and in engineering calculations. Its density can vary depending on humidity and degree of compaction.

Chemical Properties of Bentonite

Cation Exchange Capacity (CEC):

Cation Exchange Capacity is a key characteristic of bentonite, which is related to the layered structure of montmorillonite. In this structure, the natural negative charge caused by the replacement of aluminum ions with magnesium or iron causes mobile cations such as sodium, calcium, potassium and magnesium to be located in the interlayers. These cations can easily be exchanged with other ions in solution.

This property is of great importance in removing harmful ions from water such as heavy metals (such as lead and cadmium) and in improving the quality of agricultural soils. The cation exchange capacity of bentonite is usually between 80 and 150 milliequivalents per 100 grams, which varies depending on the type and source of bentonite.

Chemical Stability:

Bentonite has high chemical stability (chemical behavior of bentonite under different environmental conditions) in neutral and slightly acidic environments. This material remains stable in environments with a pH between 6 and 9 and maintains its properties. However, in very acidic environments (pH less than 4) or very alkaline (pH greater than 10), the montmorillonite structure may be destroyed.

In particular, in acidic conditions, silicate layers may be decomposed due to the dissolution of alumina or silica, so this property is very important in industrial applications that deal with different environmental conditions, such as water treatment or the oil and gas industry.

Adsorption properties:

Bentonite has a high ability to adsorb organic and inorganic molecules, and this property is due to its high surface area (up to 800 m2 / g) and its layered structure, which allows the adsorption of a variety of substances. Bentonite can absorb oils, fats, heavy metals, and even complex organic compounds.

This adsorption property is very effective in environmental applications, such as industrial wastewater treatment and the removal of pollutants from water. In the pharmaceutical industry, bentonite is also used as an adsorbent for toxins and harmful substances in the digestive system, and in the cosmetic industry, it is also used to absorb skin oil and regulate surface oil.

Acidity:

The acidity or pH of bentonite (the intrinsic pH of bentonite and how it affects applications) depends on its source and type, usually varying between 6 and 9. That is, sodium bentonite often has a higher pH and is stable in alkaline environments, while calcium bentonite may have a lower pH. This characteristic determines the specific applications of bentonite in different industries.

For example, in water treatment, bentonite with a neutral or alkaline pH is usually used to remove acid ions and adjust pH. Also, in agriculture, modifying the pH of acidic soils using bentonite increases soil productivity and improves plant growth.

Chemical and physical properties of bentonite in industrial applications

Oil and gas drilling: Bentonite is used as a material to prepare drilling mud, which stabilizes the well wall, cools the drill and transports cuttings to the surface.

Foundry: In the casting process, bentonite is used as a binder in the preparation of sand molds.

Water purification: Bentonite can absorb and remove contaminants in water. This feature is due to its cation exchange capacity and absorption properties.

Agricultural industry: Bentonite is used to improve soil quality, increase water retention and correct soil acidity.

Pharmaceutical and cosmetic industries: Bentonite is used as an absorbent and stabilizing material in the production of tablets, creams and face masks.

Livestock and poultry feed: Bentonite is used as an absorbent of fungal toxins in livestock and poultry feed.

Environmental Properties

Bentonite is a natural, non-toxic material that does not have any harmful environmental effects. It is easily biodegradable and can help improve soil quality.

Summary

Bentonite is a very valuable material in various industries due to its unique chemical and physical properties. Its ability to absorb water, exchange cations, and form gels has made it one of the most important minerals. These properties, along with its non-toxicity and chemical stability, have provided bentonite with a variety of applications.