Hydrotalcite


Hydrotalcite is a layered double hydroxide of general formula
·), whose name is derived from its resemblance with talc and its high water content. The layers of the structure stack in multiple ways, to produce a 3-layer rhombohedral structure, or a 2-layer hexagonal structure formerly known as manasseite. The two polytypes are often intergrown. The carbonate anions that lie between the structural layers are weakly bound, so hydrotalcite has anion exchange capabilities.
It was first described in 1842 for an occurrence in a serpentine - magnesite deposit in Snarum, Modum, Buskerud, Norway. It occurs as an alteration mineral in serpentinite in association with serpentine, dolomite and hematite.

Applications

Nuclear fuel reprocessing

Hydrotalcite has been studied as potential getter for iodide in order to scavenge the long-lived 129I and also other fission products such as 79Se and 99Tc, present in spent nuclear fuel to be disposed under oxidising conditions in volcanic tuff at the Yucca Mountain nuclear waste repository. Carbonate easily replaces iodide in its interlayer. Another difficulty arising in the quest of an iodide getter for radioactive waste is the long-term stability of the sequestrant that must survive over geological time scales.

Anion exchange

are well known for their anion exchange properties.

Medical

Hydrotalcite is also used as an antacid.

Wastewater treatment

Treating mining and other wastewater by creating hydrotalcites often produces substantially less sludge than lime. In one test, final sludge reductions reached up to 90 percent. This alters the concentration of magnesium and aluminum and raises the pH of the water. As the crystals form, they trap other waste substances including radium, rare earths, anions and transition metals. The resulting mixture can be removed via settling, centrifuge, or other mechanical means.