Hydrotalcite
Hydrotalcite is a layered double hydroxide of general formula
Mg
6Al
2CO
3(OH)
16·4(H
2O), 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 (3R Polytype), or a 2-layer hexagonal structure (2H polytype) formerly known as manasseite. The two polytypes are often intergrown.[1][2][4] The carbonate anions that lie between the structural layers are weakly bound, so hydrotalcite has anion exchange capabilities.
| Hydrotalcite | |
|---|---|
 | |
| General | |
| Category | Carbonate mineral |
| Formula (repeating unit) | Mg6Al2CO3(OH)16·4(H2O) |
| Strunz classification | 5.DA.50 |
| Crystal system | 3R polytype: Trigonal 2H polytype: Hexagonal |
| Crystal class | 3R polytype: Hexagonal scalenohedral (3m) H-M symbol: (3 2/m) 2H polytype: Dihexagonal dipyramidal (6/mmm) |
| Space group | R3m |
| Unit cell | a = 3.065 Å, c = 23.07 Å; Z = 3 |
| Identification | |
| Color | White with possible brownish tint |
| Crystal habit | Subhedral platey crystals, lamellar-fibrous, rarely euhedral prismatic; commonly foliated, massive |
| Cleavage | {0001}, perfect |
| Tenacity | Flexible, not elastic |
| Mohs scale hardness | 2 |
| Luster | Satiny to greasy or waxy |
| Streak | White |
| Diaphaneity | Transparent |
| Specific gravity | 2.03 - 2.09 |
| Optical properties | Uniaxial (-) |
| Refractive index | nω = 1.511 - 1.531 nε = 1.495 - 1.529 |
| Birefringence | δ = 0.016 |
| Other characteristics | Greasy feel |
| References | [1][2][3] [4] |
It was first described in 1842 for an occurrence in a serpentine - magnesite deposit in Snarum, Modum, Buskerud, Norway.[1] It occurs as an alteration mineral in serpentinite in association with serpentine, dolomite and hematite.[2]
Applications
Nuclear fuel reprocessing
Hydrotalcite has been studied as potential getter for iodide in order to scavenge the long-lived 129I (T1/2 = 15.7 million years) and also other fission products such as 79Se (T1/2 = 295 000 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. 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
Layered double hydroxides 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.[5]
See also
- Brucite, Mg(OH)
2 - Fougerite
- Layered double hydroxide
- Magnesium hydroxide
References
- Mindat.org
- Handbook of Mineralogy
- Webmineral data
- IMA Nomenclature Report
- Hoopes, Heidi (June 12, 2014). "Wastewater that cleans itself results in more water, less sludge". www.gizmag.com. Retrieved 2016-06-11.
- 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.
Further reading
- Jow, H. N.; R. C. Moore; K. B. Helean; S. Mattigod; M. Hochella; A. R. Felmy; J. Liu; K. Rosso; G. Fryxell; J. Krumhansl (2005). Yucca Mountain Project-Science & Technology Radionuclide Absorbers Development Program Overview. Yucca Mountain Project, Las Vegas, Nevada (US).
- Jow, H. N.; R. C. Moore; K. B. Helean; J. Liu; J. Krumhansl; Y. Wang; S. Mattigod; A. R. Felmy; K. Rosso; G. Fryxell. "Radionuclide absorbers development program overview Office of Civilian Radioactive Waste Management (OCRWM), Science and Technology Program". Cite journal requires
|journal=(help)
- Kaufhold, S.; M. Pohlmann-Lortz; R. Dohrmann; R. Nüesch (2007). "About the possible upgrade of bentonite with respect to iodide retention capacity". Applied Clay Science. 35 (1–2): 39–46. doi:10.1016/j.clay.2006.08.001.
- Krumhansl, J. L.; P. Zhang; H. R. Westrich; C. R. Bryan; M. A. Molecke (2000). "Technetium getters in the near surface environment". Migration Conference. 99.
- Krumhansl, J. L.; J. D. Pless; J. B. Chwirka; K. C. Holt (2006). Yucca Mountain Project getter program results (Year 1) I-I29 and other anions of concern. SAND2006-3869, Yucca Mountain Project, Las Vegas, Nevada.
- Mattigod, S. V.; G. E. Fryxell; R. J. Serne; K. E. Parker (2003). "Evaluation of novel getters for adsorption of radioiodine from groundwater and waste glass leachates". Radiochimica Acta. 91 (9): 539–546. doi:10.1524/ract.91.9.539.20001.
- Mattigod, S. V.; R. J. Serne; G. E. Fryxell (2003). Selection and testing of getters for adsorption of iodine-129 and technetium-99: a review. PNNL-14208, Pacific Northwest National Lab., Richland, WA (US).
- Moore, R. C.; W. W. Lukens (2006). Workshop on development of radionuclide getters for the Yucca Mountain waste repository: proceedings. SAND2006-0947, Sandia National Laboratories.
- Pless, J. D.; J. Benjamin Chwirka; J. L. Krumhansl (2007). "Iodine sequestration using delafossites and layered hydroxides". Environmental Chemistry Letters. 5 (2): 85–89. doi:10.1007/s10311-006-0084-8.
- Stucky, G.; H. M. Jennings; S. K. Hodson (1992). Engineered cementitious contaminant barriers and their method of manufacture. Google Patents.