Sepiolite and Palygorskite Occurrence In Arid and Semi-Arid Environments and Their Use In Nanotechnology.

Palygorskite and sepiolite are magnesium-rich hydrous silicates having fibrous or acicular morphology.  These “nanorods” are formed by ribbons of a 2:1 phyllosilicate structure that are linked to tetrahedra chains that create structural blocks with cavities in between.  The tunnels and channels that comprise the cavities contain zeolitic water molecules and exchangeable cations.  While the cation exchange capacity of these minerals is low, the specific surface area is high and provides many potential sorption sites for a variety of compounds.  Applications of these minerals in industry and nanotechnology are well-known, but environmental and agricultural uses are of increasing importance.  Both the morphology and chemistry of these minerals affect their stability and usefulness in the environment.  Sepiolite contains more magnesium and less aluminum than palygorskite; it also has wider channels.  Soils containing sepiolite and/or palygorskite are generally found in arid to semi-arid regions such as the southwestern U.S. including west Texas where B.L. Allen conducted research.  His work demonstrated that these minerals are more common in soil environments than previously thought.  Various sorptive, catalytic, nutritive, and other applications of these important nanoporous minerals will be described both in the context of monomineralic deposits as well as their occurrence in soils.