Chemistry:Hydrotalcite
| Hydrotalcite | |
|---|---|
 Hydrotalcite with serpentine, Snarum, Modum, Buskerud, Norway . Size: 8.4 × 5.2 × 4.1 cm | |
| General | |
| Category | Carbonate mineral |
| Formula (repeating unit) | Mg 6Al 2CO 3(OH) 16 · 4H2O |
| 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 |
| |re|er}} | 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] |
Hydrotalcite, or formerly also völknerite,[6] is a layered double hydroxide (LDH) of general formula Mg6Al2CO3(OH)16·4H2O, whose name is derived from its resemblance with talc and its high water content. Multiple structures containing loosely bound carbonate ions exist. The easily exchanged carbonates allow for applications of the mineral in wastewater treatment and nuclear fuel reprocessing.
Structure and discovery
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] 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]
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 = 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 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 (LDH) are well known for their anion exchange properties.[citation needed]
Medical
Hydrotalcite is also used as an antacid, such as Maalox (magnesium-aluminium oxide).[7]
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 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.[8]
See also
- Barbertonite
- Brucite, Mg(OH)2
- Fougerite
- Layered double hydroxide (LDH)
- Magnesium hydroxide
- Stichtite
References
- ↑ 1.0 1.1 1.2 Mindat.org
- ↑ 2.0 2.1 2.2 Handbook of Mineralogy
- ↑ Webmineral data
- ↑ 4.0 4.1 "IMA Nomenclature Report". http://pubsites.uws.edu.au/ima-cnmnc/Mills%20et%20al%202012%20hydrotalcite%20nomenclature.pdf.
- ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine 85 (3): 291–320. doi:10.1180/mgm.2021.43. Bibcode: 2021MinM...85..291W.
- ↑ 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 11 (73): 405–407. doi:10.1080/14786445608642090. ISSN 1941-5982. https://doi.org/10.1080/14786445608642090.
- ↑ "Hydrotalcite – Drugs.com". July 2021. https://www.drugs.com/international/hydrotalcite.html.
- ↑ Hoopes, Heidi (June 12, 2014). "Wastewater that cleans itself results in more water, less sludge". http://www.gizmag.com/wastewater-cleans-self-hydrotalicites-sludge/32521/.
- 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 et al. (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 et al. (February 2005). Radionuclide absorbers development program overview Office of Civilian Radioactive Waste Management (OCRWM), Science and Technology Program. pp. 13ofviewgrahs. https://inis.iaea.org/search/searchsinglerecord.aspx?recordsFor=SingleRecord&RN=40073831.
- 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. https://digital.library.unt.edu/ark:/67531/metadc708946/.
- 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. https://digital.library.unt.edu/ark:/67531/metadc889478/.
- Stucky, G.; H. M. Jennings; S. K. Hodson (1992). Engineered cementitious contaminant barriers and their method of manufacture. Google Patents.
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