Uses and Applications of Bentonites

Bentonite is a rock composed of more than one type of mineral, although smectites and their essential constituents give Bentonite its characteristic properties.

 

It was discovered and classified in 1888 in Fort Benton, Wyoming, USA, thereby receiving the name "Bentonite". Bentonite has very special properties, particularly its expansion in water which gives it a voluminous and gelatinous mass.

 

Bentonites are also called "activated clay" because of their affinity in certain chemical reactions that are caused by excessive negative charge.

 

Commercial Bentonites products are broadly classified as:

 

Montmorillonites: Clays with a smectic layer structure. The aluminum ion predominates in the structure but can be replaced by another metal ion to form a large variety of minerals.

 

Bentonite: Generally composed essentially of montmorillonite clay.

 

Sodium Bentonite: Montmorillonite found naturally that contains a high level of sodium ions. It expands when mixed with water. Also known as "Wyoming Bentonite" or "Western Bentonite".

 

Calcium Bentonite: Montmorillonite in which the predominant exchangeable cation is calcium. It does not exhibit the expansion capacity of sodium Bentonite, but has absorbent properties. It is also called "Southern, Texas or Mississippi Bentonite."

 

Fuller's Earth: Used for the processing of oils. Fuller's Earth clays have a different mineralogical composition. The most common are composed of calcium smectite and / or palygorskite and, less frequently, sepiolite. However, Fuller’s Earth has also been marketed with opal as the most abundant constituent, accompanied by montmorillonite, halloysite and kaolinite as clay minerals.

Bentonites have very ample and attractive properties which gives them a wide and diverse range of uses.

 

Industrial applications include:

Bentonite is still used in the manufacture of molds for casting, even though the industry has begun using other technologies and has been replacing the Bentonite by other products.

 

The process known as smelting is one in which a molten metal is poured into a mold having the shape of the article to be produced, which is obtained after the metal cools and solidifies.

 

Molding sands are composed of sand and clay, usually Bentonite, which provides cohesion and plasticity to the mix. This makes it easier to mold once the molten material has been poured and gives sufficient strength to retain the shape when the mold is being removed.

 

The proportion of Bentonite in the mixture varies between 5 and 10%; it can contain as much sodium as calcium, depending on its intended use as a mold. Sodium Bentonite is used instead of the calcium variety in foundries for higher temperatures. Sodium Bentonite is typically used for cast iron, malleable and ductile iron, and less so for the range of non-ferrous metals. On the other hand, calcium Bentonite facilitates the production of complex molds with more detail and is used mainly in non-ferrous metal smelting.

 

The specifications developed by industry associations for foundry Bentonites include properties such as moisture content, expansion index, pH values and liquid limits, among others.

Despite the many changes that have taken place in the formulations of drilling mud, Bentonite is still used in many ways.

 

Drilling mud is pumped and circulated through a well while it is being drilled. Its composition is adjusted as requirements change, according to the depth of drilling and the presence of other found materials.

 

The functions performed by drilling mud are:

 

- Control pressure during the formation and stabilization of the walls

- Cool the drilling tool

- Seal or form a thin impermeable coating on the wall of the well that prevents water from affecting the geological formation.

- Enable the addition of weighting agents

- Produce hydrostatic pressure sufficient to stabilize the wall and trap the geological formation fluids.

- Remove debris from the bottom of the pit and transport it to the surface.

- Support the weight of the drill

- Transmit hydraulic power to the drill

 

A wide variety of industrial minerals and chemicals are used in drilling mud, but the most important ingredient is always Bentonite. Its use is based on increasing the viscosity of the mud, which ensures the effective removal of surface debris.

For over fifty years Bentonite has been used as a binder in the production of pellets of material previously pulverized during separation and concentration tasks.

 

Although there are no standard specifications for this use, natural or activated sodium Bentonites are used since they are the only ones that form good pellets with the green and dry strength required, as well as the high mechanical strength required after calcification.

The high specific surface of Bentonite gives it a large capacity for both absorption and adsorption. Therefore, it is used in the bleaching and clarification of oils, wines, ciders, beers, etc. Bentonites are importance in industrial processes for purifying water that contains different types of industrial oils and organic contaminants.

 

Bentonites are also used as a carrier for chemicals such as herbicides, pesticides and insecticides, allowing a homogeneous distribution of toxic products.