Hydrotalcite

Hydrotalcite is a layered double hydroxide (LDH) of general formula [Mg6Al2(OH)16]CO3·4H2O. It is a naturally occurring mineral that is a member of the brucite group of minerals. Hydrotalcite is named after its high water content and its resemblance to talc.

History

Hydrotalcite was first described in 1842 for an occurrence in Snarum, Buskerud, Norway. It was named by Carl Christian Hochstetter, a German mineralogist, for its water content (from the Greek "hydro") and its resemblance to talc.

Structure and properties

Hydrotalcite is a layered double hydroxide (LDH) with a brucite-like structure. The layers are positively charged due to the substitution of divalent magnesium ions by trivalent aluminium ions. The charge is balanced by interlayer carbonate anions and water molecules.

Hydrotalcite has a white to apple-green colour and a pearly lustre. It is transparent to translucent and has a hardness of 2 on the Mohs scale. It has a specific gravity of 2.12.

Occurrence and production

Hydrotalcite occurs in serpentine or chlorite, in hydrothermally altered dolomite and ultramafic rocks, and in zeolite veins in basalt. It is often associated with minerals such as artinite, brucite, magnesite, and dypingite.

Hydrotalcite can also be synthesized in the laboratory by co-precipitation or by hydrothermal methods. The synthetic form of hydrotalcite is used in a variety of applications, including as a flame retardant, an anion exchanger, and a catalyst.

Applications

Hydrotalcite is used in a variety of industrial applications. It is used as a flame retardant in PVC and other polymers, as an anion exchanger in water treatment, and as a catalyst in the synthesis of polymers and other chemicals. It is also used in medicine as an antacid and antipeptic.

See also

• List of minerals
• Layered double hydroxides
• Brucite
• Talc