Fougerite and FeII–III hydroxycarbonate green rust; ordering, deprotonation and/or cation substitution; structure of hydrotalcite-like compounds and mythic ferrosic hydroxide

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 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 by co-precipitation of FeII and FeIII cations in carbonated medium shows by using Mössbauer spectroscopy that the domain of existence of lies within for with ordered upper limit . gets oxidised into ferrihydrite evolving to goethite by aerial oxidation, or into ferric green rust , by OH− 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 , become 3 magnetically split ferric sextets in . Structures of ordered , and GR1(Cl−) hydroxychloride are drawn. Extension to other hydrotalcite-like compounds is proposed whereas occurrences of fougerite mixed with clay minerals are presented. Fougerite is , the partially deprotonated green rust where . Substitution of Fe cations by MgII or AlIII may occur but the proposal advocating a ferrosic hydroxide is discarded.
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Submitted on : Wednesday, December 12, 2018 - 4:53:27 PM
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Jean-Marie Génin, Rabha Aissa, Antoine Géhin, Mustapha Abdelmoula, Omar Benali, et al.. Fougerite and FeII–III hydroxycarbonate green rust; ordering, deprotonation and/or cation substitution; structure of hydrotalcite-like compounds and mythic ferrosic hydroxide. Solid State Sciences, Elsevier, 2005, 7 (5), pp.545-572. ⟨10.1016/j.solidstatesciences.2005.02.001⟩. ⟨hal-01953218⟩

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