Attapulgite
Attapulgite is a term that is synonymous with the more commonly
used palygorskite. While palygorskite is the formal name used
in the mineral nomenclature, attapulgite is still recognized
commercially in the many products made from it. Attapulgite’s
structure is commonly called a “chain-layer” or
“ribbon-layer” silicate due to its unique mineral
structure that manifests ribbons of alumino-silicate layers
to be joined at their edges. Unlike bentonite (or montmorillonite),
attapulgite crystals are needle shaped (acicular) rather than
flat or flake-like. The result is a mineralogical version
of organized Swiss cheese where the voids in the structure
can be filled with liquids of all types. This structure produces
a magnesium aluminum silicate clay of very fine particle size,
or a micro-sponge that is naturally designed to absorb liquids.
Attapulgites disperse well and exhibit excellent thickening,
suspending and gelling properties without flocculation problems.
Attapulgite is also known as Fullers Earth and is closely
related to sepiolite minerals. It has been mined in Georgia
and Florida since the 1930s. These deposits are known around
the world for their light tan to white color, high sorption
capability, and very strong particle integrity. Attapulgite
is used mainly in oil and grease absorbents, pet litter, soil
amendments, and as a component of drilling muds.
Bentonite
Bentonite is an industrial ore that is mined throughout the
world. It is formed from the alteration of siliceous, glass-rich
volcanic rocks such as tuffs and ash deposits. The major mineral
in bentonite is montmorillonite, a hydrated sodium, calcium,
magnesium, aluminum silicate. Bentonite is known as “swelling”
or “plastic” clay that effectively sorbs and retains
relatively high amounts of water.
Bentonite has been mined for centuries, but for over 75 years
the most famous deposits have been mined commercially in the
United States. There are two types of bentonite produced in
the U.S.: “Wyoming” or “western” bentonites
are mined from sodium bentonite deposits in Wyoming, South
Dakota and Montana; “southern” bentonites are
mined from calcium bentonite deposits in the Gulf Coast states
of Mississippi and Alabama.
Bentonite possesses strong colloidal properties and its volume
increases several times when it comes in contact with water.
These unique swelling and adhesive properties make bentonite
ideal for use in an extensive range of applications.
Bentonite is used as a binding agent in the production of
iron ore pellets; as a flow control agent in paints, dyes
and polishes; as the clumping agent in clumping cat litter;
as a sealant and lubricant in oil and water-well drilling;
and in various pharmaceutical and cosmetic products.
Montmorillonite
Montmorillonite is a layered silicate belonging to the smectite
group of phyllosilicate minerals. It is formed primarily by
the alteration of extrusive volcanic rocks such as volcanic
ash falls and ash fall tuffs. Commonly these minerals are
products of geological weathering or hydrothermal alteration
of silicate minerals and silica phases in these igneous rocks.
Montmorillonite occurs naturally as a sequence of stacked
layers 1.0 to 1.5 nanometers thick. These layers are the fundamental
building blocks of montmorillonite and are strongly two-dimensional.
These layers are frequently described as “stacks of
cards” or “layers of cards” to better describe
their unique structure and form. As a result of its unique
structure, montmorillonite possesses the ability to absorb
large amounts of water and other liquids. The liquid is sorbed
onto, or hydrates, the layers at the interlayer cation site,
causing swelling. The result is a mineral that can absorb
in 2-10 times its weight of liquid.
It is the absorption and swelling characteristics that makes
montmorillonite so useful in industrial and commercial applications.
Montmorillonite is used in cat litters, industrial oil absorbents,
filtration media, animal feeds, soil amendments and agricultural
applications.
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