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What
is Bentonite?
The Industrial
Minerals Association
The term Bentonite
was first used for a clay found in about 1890 in upper cretaceous tuff near
Fort Benton, Wyoming.
The main constituent,
which is the determinant factor in the clay's properties, is the clay mineral
montmorillonite.
This in turn, derives
its name from a deposit at Montmorillon, in Southern France.
Bentonite is a clay
generated frequently from the alteration of volcanic ash, consisting
predominantly of smectite minerals, usually montmorillonite.
Other smectite group
minerals include hectorite, saponite, beidelite and nontronite.
Smectites are clay
minerals, i.e. they consist of individual crystallites the majority of which
are <2µm in largest dimension.
Smectite crystallites
themselves are three-layer clay minerals. They consist of two tetrahedral
layers and one octahedral layer.
In montmorillonite
tetrahedral layers consisting of [SiO4] - tetrahedrons enclose the
[M(O5,OH)]-octahedron layer (M = and mainly Al, Mg, but Fe is also often
found).
The silicate layers
have a slight negative charge that is compensated by exchangeable ions in the
intercrystallite region.
The charge is so weak
that the cations (in natural form, predominantly Ca2+, Mg2+ or Na+ ions) can be
adsorbed in this region with their hydrate shell.
The extent of
hydration produces intercrystalline swelling. Depending on the nature of their
genesis, bentonites contain a variety of accessory minerals in addition to
montmorillonite.
These minerals may
include quartz, feldspar, calcite and gypsum.
The presence of these
minerals can impact the industrial value of a deposit, reducing or increasing
its value depending on the application.
Bentonite presents
strong colloidal properties and its volume increases several times when coming
into contact with water, creating a gelatinous and viscous fluid.
The special
properties of bentonite (hydration, swelling, water absorption, viscosity,
thixotropy) make it a valuable material for a wide range of uses and
applications.
Bentonite deposits
are normally exploited by quarrying. Extracted bentonite is distinctly solid,
even with a moisture content of approximately 30%.
The material is
initially crushed and, if necessary, activated with the addition of soda ash
(Na2CO3).
Bentonite is
subsequently dried (air and/or forced drying) to reach a moisture content of
approximately 15%.
According to the
final application, bentonite is either sieved (granular form) or milled (into
powder and super fine powder form).
For special applications,
bentonite is purified by removing the associated gangue minerals, or treated
with acids to produce acid-activated bentonite (bleaching earths), or treated
with organics to produce organoclays.
Foundry: Bentonite is used as a bonding material in the preparation
of molding sand for the production of iron, steel and non-ferrous casting.
The unique properties of
bentonite yield green sand moulds with good flowability, compactability and
thermal stability for the production of high quality castings.
Cat Litter: Bentonite is used for cat litter, due to its advantage
of absorbing refuse by forming clumps (which can be easily removed) leaving the
remaining product intact for further use.
Pelletizing: Bentonite is used as a binding agent in the production
of iron ore pellets. Through this process, iron ore fines are converted into
spherical pellets, suitable as feed material in blast furnaces for pig iron
production, or in the production of direct reduction iron (DRI).
Construction and Civil Engineering: Bentonite in civil
engineering applications is used traditionally as a thixotropic, support and
lubricant agent in diaphragm walls and foundations, in tunnelling, in
horizontal directional drilling and pipe jacking. Bentonite, due to its
viscosity and plasticity, also is used in Portland cement and mortars.
Environmental Markets: Bentonite's adsorption/absorption
properties are very useful for wastewater purification.
Common environmental
directives recommend low permeability soils, which naturally should contain
bentonite, as a sealing material in the construction and rehabilitation of
landfills to ensure the protection of groundwater from the pollutants.
Bentonite is the active protective layer of geosynthetic clay liners.
Drilling: Another conventional use of bentonite
is as a mud constituent for oil and water well drilling. Its roles are mainly
to seal the borehole walls, to remove drill cuttings and to lubricate the
cutting head.
Oils/Food Markets: Bentonite is utilized in the removal of
impurities in oils where its adsorptive properties are crucial in the
processing of edible oils and fats (Soya/palm/canola oil). In drinks such as
beer, wine and mineral water, and in products like sugar or honey, bentonite is
used as a clarification agent.
Agriculture: Bentonite is used as an animal feed supplement, as a
pelletizing aid in the production of animal feed pellets, as well as a
flowability aid for unconsolidated feed ingredients such as soy meal.
It also is used as an ion
exchanger for improvement and conditioning of the soil. When thermally treated,
it can be used as a porous ceramic carrier for various herbicides and
pesticides.
Pharmaceuticals: Cosmetics and Medical Markets:
Bentonite is used as filler in pharmaceuticals, and due to its
absorption/adsorption functions, it allows paste formation.
Such applications include
industrial protective creams, calamine lotion, wet compresses, and anti-irritants
for eczema.
In medicine, bentonite is
used as an antidote in heavy metal poisoning. Personal care products such as
mud packs, sunburn paint, baby and facepowders, and face creams may all contain
bentonite.
Detergents: Laundry detergents and liquid hand
cleansers/soaps rely on the inclusion of bentonite, in order to remove the
impurities in solvents and to soften the fabrics.
Paints: Dyes and Polishes: Due to its thixotropic properties,
bentonite and organoclays function as a thickening and/or suspension agent in
varnishes, and in water and solvent paints.
Its adsorption properties
are appreciated for the finishing of indigo dying cloth, and in dyes (lacquers
for paints & wallpapers).
Paper: Bentonite is crucial to paper making, where it is used in
pitch control, i.e. absorption of wood resins that tend to obstruct the
machines and to improve the efficiency of conversion of pulp into paper as well
as to improve the quality of the paper.
Bentonite also offers
useful de-inking properties for paper recycling. In addition, acid-activated
bentonite is used as the active component in the manufacture of carbonless copy
paper.
Catalyst: Chemically-modified clay catalysts find application in
a diverse range of duties where acid catalysis is a key mechanism. Most
particularly, they are employed in the alkylation processes to produce fuel
additives.
The
Industrial Minerals Association - North America (IMA-NA) is the
representative voice of companies which extract and process a vital and
beneficial group of raw materials known as industrial minerals. Industrial
minerals are the ingredients for many of the products used in everyday life,
and our companies and the people they employ are proud of their industry and
the socially responsible methods they use to deliver these beneficial
resources.
IMA-NA represents ball clay, barite, bentonite, borates, calcium carbonate, diatomite, feldspar, industrial sand, kaolin, magnesia, soda ash, talc and wollastonite.
Industrial minerals . . . Your world is made of them!
IMA-NA represents ball clay, barite, bentonite, borates, calcium carbonate, diatomite, feldspar, industrial sand, kaolin, magnesia, soda ash, talc and wollastonite.
Industrial minerals . . . Your world is made of them!
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