Hydrotalcite

Structure and discovery

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. The layers of the structure stack in multiple ways, to produce a 3-layer rhombohedral structure (3R polytype), or a 2-layer hexagonal structure (2H polytype) formerly known as manasseite. The two polytypes are often intergrown.

Applications

Anion exchange

Layered double hydroxides (LDH) are well known for their anion exchange properties.

Wastewater treatment

Treating mining and other wastewater by producing hydrotalcite 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 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, centrifuging, or other mechanical means.

Anion getter for nuclear waste disposal

Hydrotalcite has been studied as potential getter for iodide to scavenge the long-lived 129I (T1/2 = 15.7 million years) and also other fission products such as 79Se (T1/2 = 327,000 years) and 99Tc, (T1/2 = 211,000 years) present in spent nuclear fuel to be disposed under oxidising conditions in volcanic tuff at the Yucca Mountain nuclear waste repository. However, carbonate anions easily replace iodide anions in its interlayer and therefore the selectivity coefficient for the anion exchange is not favorable. Another difficulty arising in the quest for an iodide getter for radioactive waste is the long-term stability of the sequestrant that must survive over geological time scales.

Medical

Hydrotalcite is also used as an antacid, such as Maalox (magnesium-aluminium oxide).

References

• Douglas, G., Shackleton, M. and Woods, P. (2014). Hydrotalcite formation facilitates effective contaminant and radionuclide removal from acidic uranium mine barren lixiviant. Applied Geochemistry, 42, 27–37.
• Douglas, G.B. (2014). Contaminant removal from Baal Gammon acidic mine pit water via in situ hydrotalcite formation. Applied Geochemistry, 51, 15–22.

References

1. Warr, L.N.. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine.
2. [http://www.mindat.org/min-1987.html, Mindat.org]
3. [http://rruff.geo.arizona.edu/doclib/hom/hydrotalcite.pdf Handbook of Mineralogy]
4. [http://www.webmineral.com/data/Hydrotalcite.shtml Webmineral data ]
5. "IMA Nomenclature Report".
6. Rammelsberg, C.. (1856-05-01). "On völknerite or hydrotalkite, and the so-called steatite of Snarum". The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science.
7. Hoopes, Heidi. (June 12, 2014). "Wastewater that cleans itself results in more water, less sludge".
8. Krumhansl, James L., Pless, Jason D., Chwirka, J. Benjamin, Holt, Kathleen C. (July 2006). Yucca Mountain Project getter program. Results (Year 1): I-129 and other anions of concern. SANDIA Report SAND2006-3869. 55 pp. https://www.osti.gov/servlets/purl/893147#page=1.00&gsr=0
9. (July 2021). "Hydrotalcite – Drugs.com".