Hydrotalcite

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Hydrotalcite
Hydrotalcite-200667.jpg
Hydrotalcite from Snarum, Modum, Buskerud, Norway (size: 8.4 × 5.2 × 4.1 cm)
General and classification
chemical formula Mg 6 Al 2 [(OH) 16 | CO 3 ] • 4H 2 O
Mineral class
(and possibly department) 		Carbonates and Nitrates (8th Edition: Carbonates, Nitrates and Borates)
System no. to Strunz
and to Dana 		5.DA.50 ( 8th edition : V / E.03)
16b.06.02.01
Crystallographic Data
Crystal system trigonal
Crystal class ; symbol ditrigonal-scalenohedral; 3 2 / m
Room group (no.) R 3 m (No. 166)
Lattice parameters a  = 3.05  Å ; c  = 22.81 Å
Formula units Z  = 3/8
Physical Properties
Mohs hardness 2
Density (g / cm 3 ) 2.03 to 2.09
Cleavage completely after {0001}
Break ; Tenacity pliable but not elastic
colour colorless, white, brownish
Line color White
transparency transparent
shine Silk gloss to wax gloss, pearlescent gloss
Crystal optics
Refractive indices n ω  = 1.511 to 1.531
n ε  = 1.495 to 1.529
Birefringence δ = 0.016
Optical character uniaxial negative

Hydrotalkite ( international non-proprietary name : hydrotalcite ), formerly also Völknerite , is a rarely occurring mineral from the mineral class of " carbonates (and relatives)" (see classification ). It crystallizes in the trigonal crystal system with the chemical composition Mg 6 Al 2 [(OH) 16 | CO 3 ] · 4H 2 O and develops mostly transparent, hypidiomorphic to idiomorphic , tabular crystals up to about 4 mm in size with silky to wax shiny crystal surfaces . Leafy to fibrous mineral aggregates are also found.

Special properties

Hydrotalcite has the ability to bind acids through gradual release of aluminum hydroxide and is therefore used in many different ways in industry and as a drug.

Etymology and history

Hydrotalkite was first found in 1842 in the "Solvverkets Pyrite Mine" near Snarum in the Norwegian municipality of Modum and described by Carl Christian Hochstetter , who named the mineral after its talc- like appearance and its water content ( ancient Greek ὕδωρ hýdor , "water").

The substance group of hydrotalcites includes not only the natural and the synthetic varieties of the basic double salt hydrotalcite. The first comprehensive work on this mineral group was done by Frondel (1941) with his classification of the pyroaurite and sjögrenite groups , and Feitknecht and Gerber (1942) with their work on magnesium-aluminum double hydroxide.

classification

In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the hydrotalcite still belonged to the common mineral class of "carbonates, nitrates and borates " and there to the department of "hydrous carbonates with foreign anions", where it is named as the mineral "Hydrotalkitgruppe" with the other members Comblainit , Desautelsit , Pyroaurit , Reevesit , Sergeevit , Stichtit and takovite formed.

Since the complete revision of Strunz's mineral systematics in the 9th edition (2001), the mineral class of carbonates (and relatives) has been redistributed and the borates form a class of their own. The hydrotalcite is therefore now in the mineral class of "carbonates and nitrates" and there in the department of "carbonates with additional anions; with H 2 O ”. However, this is now more precisely subdivided according to the size of the cations involved and the mineral is sorted according to its composition in the sub-section “With medium-sized cations”. The "hydrotalcite group" that still exists there was reduced by the sergeevite and received the system no. 5.DA.50 .

In the Dana system of minerals used in the English-speaking world , the carbonates, nitrates and borates form a common mineral class as in the outdated Strunz system. However, the hydrotalcite can be found there in the section of " carbonates with hydroxyl or halogen ", where it forms a total of three groups together with the sjögrenite . According to its crystal system, hydrotalcite is found together with stichtite, pyroaurite and desautelsite in the rhombohedral ( rhombohedral ) oriented "hydrotalcite subgroup" with the system no. 16b.06.02 .

The representatives of the group only differ from one another in part by the different stacking sequences of the octahedron layers. This results in either a hexagonal (2H) or a rhombohedral (3R) crystal lattice .

Modifications and varieties

The compound Mg 6 Al 2 [(OH) 16 | CO 3 ] · 4H 2 O is dimorphic and, in addition to the trigonal hydrotalcite, can also occur in nature as hexagonally crystallizing manassite .

Education and Locations

Hydrotalcite is mainly formed hydrothermally through the secondary decomposition of serpentinite . Besides serpentinite, accompanying minerals include manassite , dolomite and hematite .

So far (as of 2010), hydrotalcite has been found at around 60 sites worldwide, including in Australia , Germany , France , Greece , Israel , Italy , Canada , Norway , Austria , Poland , Romania , Russia , Sweden , South Africa , Tajikistan , Czech Republic , Turkey , Hungary , the United Kingdom (Great Britain) and the United States of America (USA).

Crystal structure

Hydrotalcite crystallizes trigonal in the space group R 3 m (space group no. 166) with the lattice parameters a  = 3.05  Å and c  = 22.81 Å and 3/8 formula units per unit cell .

In addition to the natural representatives of the hydrotalcite family, which contain exclusively CO 3 2− anions and OH groups as interlayer anions, hydrotalcites with other interlayer anions can also be synthesized. Thus Allmann describes (1968) has a slightly distorted Ca 2 Al (OH) 6 ½SO 4 · 3H 2 O hydrotalcite. A Mg / Zn mixed hydrotalcite with sulfate anions was synthesized by Kooli, Kosuge, Hibino and Tsunashima (1993). Kooli, Kosuge and Tsunashima (1995a) also synthesized and investigated hydrotalcites with mixed Me 3+ positions (Ni-Al / Cr-CO 3 and Ni-Al / Fe-CO 3 ). The Ni hydrotalcites in particular are the subject of research [z. B. Faure, Borthomieu, Delmas (1991), Clause, M. Gazzano, Trifiro, Vaccari, ZatorskiI (1991), Ehlsissen, Delahaye-Vidal, Genin, Figlarz, Willmann (1993)], especially because of their importance as electrode material in modern energy storage cells .

use

Hydrotalcite is mainly used in medicine as an antacid for over-acidification of the stomach ( hyperacidity ) to neutralize stomach acid . Well-known trade names include Talcid ® ( Bayer AG , Wiechert 1976) or Altacit ® (Roussel Lab., Playle 1974)

In applied chemistry, hydrotalcite serves as a catalyst to produce various organic compounds or to bind organic solutions or waste containing heavy metals.

Synthetically produced hydrotalcites are also used as stabilizers in PVC production. In doing so, they react with the HCl that is formed when PVC ages .

See also

literature

  • Paul Ramdohr , Hugo Strunz : Klockmann's textbook of mineralogy . 16th edition. Ferdinand Enke Verlag, 1978, ISBN 3-432-82986-8 , pp. 583 .
  • Petr Korbel, Milan Novák: Encyclopedia of Minerals . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 127 .
  • C. Frondel: Constitution and polymorphism of the pyroaurite and sjögrenite groups. American Mineralogist, 26 (5). 1941, 295-315
  • W. Feitknecht, M. Gerber: To the knowledge of the double hydroxides and basic double salts III: about magnesium-aluminum double hydroxide. Helvetica Chimica Acta, 25. 1942, 131-137
  • C. Hochstetter: Investigation into the composition of some minerals. Journal of Practical Chemistry, 27. 1842, 375-378
  • R. Allmann: The double-layer structure of the platelet-shaped calcium aluminum hydroxide salts using the example of 3CaO * Al 2 O 3 * CaSO 4 * 12H 2 O. New year book for mineralogy, monthly books , 1968, 140-144
  • F. Kooli, K. Kosuge, T. Hibinos, A. Tsunashima: Synthesis and Properties of Mg-Zn-Al-SO 4 hydrotalcite-like compounds. Journal of Materials Science, 28. 1993, 2769-2773
  • F. Kooli, K. Kosuge, A. Tsunishima: New Ni-Al-Cr and Ni-Al-Fe Carbonate Hydrotalcite-like Compounds: Synthesis and Characterization. In: Journal of Solid State Chemistry , 118.1995 285-291
  • C. Faure, Y. Borthomieua, C. Delmas: Infrared characterization of turbostratic á- and well crystallized á * -cobalted nickel hydroxides. In: Journal of Power Sources , 36.1991 , 113-125, doi : 10.1016 / 0378-7753 (91) 80008-L
  • O. Clause, M. Gazzano, F. Trifiro, A. Vaccar, L. Zatorski: Preparation and thermal reactivity of nickel / chromium and nickel / aluminum hydrotalcite-like precursors. Applied Catalysis, 73.1991, 217-236
  • TK Ehlissen, A. Delahaye-Vidal, P. Genin, M. Figlarz, P. Willmann: Preparation and Characterization of Turbostratic Ni / Al Layered Double Hydroxides for Nickel Hydroxide Electrode Applications. Journal of Materials Chemistry, 3 (8). 1993, 883-888
  • AC Playle: The in vitro antacid and anti-pepsin activity of hydrotalcite. Pharmaceutica Acta Helvetica, 49. 1974, 298-302
  • E. Wiecher: Talcid, a new antacid. Report on an open 'Clinical Test'. Med. Welt, 27. 1976, 2489-2491
  • Giulini Chemie GmbH: Fine chemicals catalog. 1989
  • W. Hofmeister, H. von Platen: Crystal Chemistry and Atomic Order in Brucite-Related Double-Layer Structures. Crystallography Reviews, 3. 1992, 3-29
  • F. Rennemann: Investigation of the proton mobility in synthetic hydrotalcites ( Memento of October 8, 2007 in the Internet Archive ). (PDF; 11.4 MB) Dissertation, University of Mainz 1997, DNB 953522385

Web links

Commons : Hydrotalcite  - collection of images, videos, and audio files

Individual evidence

  1. ↑ a b c d e Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 314 .
  2. ↑ a b c Mindat - Hydrotalcite (English).
  3. ↑ C. Rammelsberg: About the Völknerite (hydrotalcite) from Snarum. In: Annals of Physics and Chemistry. 173, 1856, p. 296, doi : 10.1002 / andp.18561730209 .
  4. ↑ From practice: Antacids - variety in hydrotalcid by Gode Meyer-Chlond ( Memento from December 2, 2012 in the Internet Archive ) (PDF; 282 kB).
  5. ^ Johannes Karl Fink: A Concise Introduction to Additives for Thermoplastic Polymers , John Wiley & Sons, Salem, Massachusetts 2010, ISBN 0-470-60955-9 .