Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10636911 | Solid State Sciences | 2005 | 28 Pages |
Abstract
A green rust has been recognised as a new mineral (IMA 2003-057) and given the name fougerite. Its chemical counterpart is FeII-III hydroxycarbonate GR1(CO32â) compound, which is partially deprotonated since formed by reduction of ferric oxyhydroxides through the activity of dissimilatory iron-reducing bacteria (DIRB) in anaerobic gley soils. Preparation of GR1(CO32â) by co-precipitation of FeII and FeIII cations in carbonated medium shows by using Mössbauer spectroscopy that the domain of existence of GR1(CO32â) lies within [0.25,0.33] for x={[FeIII]/[Fetotal]} with ordered upper limit [FeII4FeIII2(OH)12]2+â
[CO3â
â¼3H2O]2â. GR1(CO32â) gets oxidised into ferrihydrite evolving to goethite by aerial oxidation, or into ferric green rust GR1(CO32â)â, [FeIII6(OH)4(OOH)4]2+â
[CO3â
â¼3H2O]2â by OHâ deprotonation. A mass balance of iron ox(yhydrox)ides is drawn accordingly in the carbonated medium. Mössbauer spectra measured at 12 K show quite different magnetic properties and the three quadrupole doublets, comprising 2 ferrous and 1 ferric in GR1(CO32â), become 3 magnetically split ferric sextets in GR1(CO32â)â. Structures of ordered GR1(CO32â), GR1(CO32â)â and GR1(Clâ) hydroxychloride are drawn. Extension to other hydrotalcite-like compounds is proposed whereas occurrences of fougerite mixed with clay minerals are presented. Fougerite is FeII6(1âx)FeIII6x(OH)4(4â3x)(OOH)2(3xâ1)CO3, the partially deprotonated green rust where 1/3⩽x<2/3. Substitution of Fe cations by MgII or AlIII may occur but the proposal advocating a ferrosic hydroxide Fe(OH)(2+x) is discarded.
Related Topics
Physical Sciences and Engineering
Materials Science
Ceramics and Composites
Authors
Jean-Marie R. Génin, Rabha Aïssa, Antoine Géhin, Mustapha Abdelmoula, Omar Benali, Vibeke Ernstsen, Georges Ona-Nguema, Chandan Upadhyay, Christian Ruby,