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Attapulgite

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Attapulgite

Palygorskite
A sample of Palygorskite
General
Category Phyllosilicate
Formula
(repeating unit)
(Mg,Al)2Si4O10(OH)·4(H2O)
Strunz classification 09.EE.20
Crystal symmetry 2/m - Prismatic
Unit cell

a = 12.78Å, b = 17.86Å, c = 5.24Å

β = 95.78°
Identification
Color White, grayish, yellowish, gray-green
Cleavage Distinct/Good, Good on {110}
Mohs scale hardness 2 - 2½
Luster Waxy, earthy
Diaphaneity Translucent
Specific gravity 1 - 2.6
References [1][2][3]

Palygorskite or attapulgite is a magnesium aluminium phyllosilicate with formula (Mg,Al)2Si4O10(OH)·4(H2O) that occurs in a type of clay soil common to the Southeastern United States. It is one of the types of fuller's earth. Some smaller deposits of this mineral can be found in Mexico, where its use is tied to the manufacture of Maya Blue in pre-Columbian times.

Name

The name attapulgite is derived from the U.S. town of Attapulgus, Georgia, in the extreme southwest corner of the state, where the mineral is abundant. It is surface-mined in the area, dry-ground and air-separated into precise particle sizes, and transported in covered hopper cars via the railroad, and is also shipped in 50 pounds (23 kg) paper bags and bulk bags by truck.

The name palygorskite is given after the place in the Ural Mountains where it was discovered.

Prehistoric use

Palygorskite is known to have been a key constituent of the pigment called "Maya Blue", which was used notably by the pre-Columbian Maya civilization of Mesoamerica on ceramics, sculptures, murals, and (most probably) Maya textiles. The clay mineral was also used by the Maya as a curative for certain illnesses, and there is evidence to show it was also added to pottery temper.

A Maya region source for palygorskite was unknown until the 1960s, when one was found at a cenote on the Yucatán Peninsula near the modern township of Sacalum, Yucatán. A second possible site was more recently (2005) identified, near Ticul, Yucatán.[4]

The Maya Blue synthetic pigment was also manufactured in other Mesoamerican regions and used by other Mesoamerican cultures, such as the Aztecs of central Mexico. The blue coloration seen on Maya and Aztec codices, and early colonial-era manuscripts and maps, is largely produced by the organic-inorganic mixture of añil leaves and palygorskite, with smaller amounts of other mineral additives.[5] Human sacrificial victims in Postclassic Mesoamerica were frequently daubed with this blue pigmentation.[6]

Extraction

Two companies are involved in the industrial extraction and processing of gellant-grade attapulgite clay within the same Attapulgus deposit: Active Minerals International, LLC, and BASF Corp. In 2008, BASF acquired the assets of Zemex Attapulgite leaving only 2 gellant-grade producers. Active Minerals operates a dedicated factory to produce the patented product Actigel 208 and built a new state-of-the-art production process in early 2009 involving portable plant processing at the mine site.

Properties

Attapulgite clays are a composite of smectite and palygorskite. Smectites are expanding lattice clays, of which bentonite is a commonly known generic name for smectite clays. The palygorskite component is an acicular bristle-like crystalline form that does not swell or expand. Attapulgite forms gel structures in fresh and salt water by establishing a lattice structure of particles connected through hydrogen bonds.

Attapulgite, unlike bentonite, will form gel structures in salt water and is used in special salt-water drilling mud for drilling formations contaminated with salt. Palygorskite particles can be considered as charged particles with zones of + and - charges. It is the bonding of these alternating charges that allow them to form gel suspensions in salt and fresh water.

Attapulgite clays found in the Meigs-Quincy district are bundles of palygorskite clay particles between 2 and 3 micrometres long and below 3 nanometres in diameter. The bundles are surrounded by a matrix of smectite clays that are slightly swellable. Dry-process grades contain up to 25% non-attapulgite material in the form of carbonates and other mineral inclusions. Processing of the clays consist of drying and grinding the crude clay to specific particle size distributions with specific ranges of gel viscosity measured by a variety of means depending on the end use.

Gel-grade, dry-processed attapulgites are used in a very wide range of applications for suspension, reinforcement and binding properties. Paints, sealants, adhesives, tape-joint compound, catalysts, suspension fertilizers, wild-fire suppressants, foundry coatings, animal feed suspensions, and molecular sieve binders are just a few uses of dry process attapulgite.

Seven to ten percent attapulgite clay mixed with the eutectic salt, sodium sulfate decahydrate (Glaubers salt), will keep anhydrous crystals suspended in the solution, where they will hydrate during phase transition and hence contribute to the heat absorbed and released when Glaubers salt are used for heat storage.

Medical use

Attapulgite is used widely in medicine. Taken by mouth, it physically binds to acids and toxic substances in the stomach and digestive tract. Also, as an anti-diarrheal, it was believed to work by adsorbing the bacteria or germ that may be causing the diarrhea. For this reason, it has been used in several anti-diarrheal medications, including Diar-Aid, Diarrest, Diasorb, Diatabs, Diatrol, Donnagel, Kaopek, K-Pek, Parepectolin, and Rheaban. [7] It has been used for decades to treat diarrhea.

Until 2003, Kaopectate marketed in the US also contained attapulgite. However, at that time, the U.S. Food and Drug Administration retroactively rejected medical studies showing its efficacy, calling them insufficient.[8][9] Kaopectate's U.S. formula was changed to bismuth subsalicylate (pink bismuth). The next year (2004), an additional change in labelling was made; from then on, Kaopectate was no longer recommended for children under 12 years old.[10] Nevertheless, Kaopectate with attapulgite is still available in Canada and elsewhere. Until the early 1990s, Kaopectate used the similar clay product kaolinite with pectin (hence the name).

Construction

Palygorskite can be added to lime mortar with metakaolin for restoration of cultural heritage. [11]

Notes

References

External links

  • International Chemical Safety Card 1321
  • attapulgite clay patent
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