Palygorskite

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A sample of Palygorskite

Palygorskite (also known as attapulgite) is a magnesium aluminium phyllosilicate with formula (Mg,Al)₂Si₄O₁₀(OH)·4(H₂O) which occurs in a type of clay soil common to the Southeastern United States. It is one of the types of fuller's earth. When used in medicine, it physically binds to acids and toxic substances in the stomach and digestive tract. For that reason, it has often been used in antidiarrheal medications. Until 2003, it was the active ingredient used in Kaopectate, before that product was reformulated with bismuth subsalicylate. Like bismuth, it is not absorbed into the body, however the two work differently.

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, mixed with water into a slurry, and transported in covered hopper cars via railroad.

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 change and hence contribute to the heat absorbed and released when Glaubers salt are used for heat storage.

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.^[1]

The Maya Blue pigment synthetic 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 manuscipts and maps, is largely produced by the organic-inorganic mixture of añil leaves and palygorskite, with smaller amounts of other mineral additives.^[2]

Human sacrificial victims in Postclassic Mesoamerica were frequently daubed with this blue pigmentation.^[3]

Three companies are involved in the industrial extraction and processing of attapulgite clay on the same Attapulgus deposit - Active Minerals, Englehart, and Zemex Corp. Active Minerals and Englehard shared some production but Active Minerals operate a dedicated factory to produce the patented product Actigel 208.

Attapulgite clays are swellable clays like bentonites, although more asicular (or needle like). Like many clays, they can be considered as charged particles with zones of + and - charges. Standard attapulgite clays are agglomorated bundles of clay particles between 20 and 100 microns long and below 1 micron in diameter. Most grades contain up to 25% non-attapulgite material in the form of carbonates and other inclusions. Despite this, they are a beneficial ingredient of cementicious tile adhesives in competition with polyacrylates and starch ethers. The advantage of attapulgites is that their performance is not temperature sensitive and they have lower water demand. They must have free ions ion in an aqueous system to work.

Actigel 208 is a patented exfoliated attapulgite where the clay has been chemically and mechanically purified into discrete particles 20 angstroms diameter. This material has special viscosity modification properties with high solid aqueous systems that cannot be matched with any other ingredients

[edit] Notes

^ See abstract of Arnold (2005).
^ Haude (1997).
^ Arnold and Bohor (1975), as cited in Haude (1997).

[edit] References

Arnold, Dean E. (2005). "Maya Blue and Palygorskite:A second possible pre-Columbian source". Ancient Mesoamerica 16: pp.51–62. doi:10.1017/S0956536105050078.