Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (20) Citing Articles via Google Scholar Google Scholar Articles by Drits, V.A. Articles by Manceau, A. Search for Related Content GeoRef GeoRef Citation

A MODEL FOR THE MECHANISM OF Fe³⁺ TO Fe²⁺ REDUCTION IN DIOCTAHEDRAL SMECTITES

¹ Environmental Geochemistry Group, LGIT-IRIGM, University Joseph Fourier and CNRS, 38041 Grenoble Cedex 9, France
² Geological Institute of the Russian Academy of Sciences, 7 Pyzhevsky Street, 109017 Moscow, Russia

E-mail of corresponding author: manceau{at}ujf-grenoble.fr

A model to compensate the 2:1 layer having excess negative charge owing to the reduction of Fe³⁺ to Fe²⁺ by sodium dithionite buffered with citrate-bicarbonate in nontronite, beidellite, and montmorillonite is proposed. This model is based on reassessing published experimental data for Fe-containing smectites and on a recently published structural model for reduced Garfield nontronite. In the reduced state, Fe²⁺ cations remain six-fold coordinated, and increases of negative charge in the 2:1 layer are compensated by the sorption of Na⁺ and H⁺ from solution. Some of the incorporated protons react with structural OH groups to cause dehydroxylation. Also, some protons bond with undersaturated oxygen atoms of the octahedral sheet. The amount of Na⁺ (p) and H⁺ (n_i) cations incorporated in the structure as a function of the amount of Fe reduction can be described quantitatively by two equations: p = m/(1 + K₀m_rel) and n_i = K₀mm_rel/(1 + K₀m_rel); with K₀ = CEC (9.32 – 1.06m_tot + 0.02m_tot²), where m_tot is the total Fe content in the smectite, m is the Fe²⁺ content, m_rel is the reduction level (m/m_tot), CEC is the cation-exchange capacity, and K₀ is a constant specific to the smectite. The model can predict, from the chemical composition of a smectite, the modifications of its properties as a function of reduction level. Based on this model, the structural mechanism of Fe³⁺ reduction in montmorillonite differs from that determined in nontronite and beidellite owing to differences in the distribution of cations over trans- and cis-octahedral sites.

Key Words: CMS Source Clay SWa-1 • Dioctahedral Smectite • Iron Reduction • Structural Formula

This article has been cited by other articles:

				B. R. Bzdek and M. M. McGuire POLARIZED ATR-FTIR INVESTIGATION OF Fe REDUCTION IN THE ULEY NONTRONITES Clays and Clay Minerals, April 1, 2009; 57(2): 227 - 233. [Abstract] [Full Text] [PDF]

				G. E. Christidis Do bentonites have contradictory characteristics? An attempt to answer unanswered questions Clay Minerals, December 1, 2008; 43(4): 515 - 529. [Abstract] [Full Text] [PDF]

				W. P. Gates CATION MASS-VALENCE SUM (CM-VS) APPROACH TO ASSIGNING OH-BENDING BANDS IN DIOCTAHEDRAL SMECTITES Clays and Clay Minerals, February 1, 2008; 56(1): 10 - 22. [Abstract] [Full Text] [PDF]

				F. Favre, J. W. Stucki, and P. Boivin REDOX PROPERTIES OF STRUCTURAL Fe IN FERRUGINOUS SMECTITE. A DISCUSSION OF THE STANDARD POTENTIAL AND ITS ENVIRONMENTAL IMPLICATIONS Clays and Clay Minerals, August 1, 2006; 54(4): 466 - 472. [Abstract] [Full Text] [PDF]

				J.-w. Kim, J.-w. Kim, Y. Furukawa, T. L. Daulton, D. Lavoie, and S. W. Newell CHARACTERIZATION OF MICROBIALLY Fe(III)-REDUCED NONTRONITE: ENVIRONMENTAL CELL-TRANSMISSION ELECTRON MICROSCOPY STUDY Clays and Clay Minerals, August 1, 2003; 51(4): 382 - 389. [Abstract] [Full Text] [PDF]

				C.-I. Fialips, C.-I. Fialips, D. Huo, L. Yan, J. Wu, and J. W. Stucki INFRARED STUDY OF REDUCED AND REDUCED-REOXIDIZED FERRUGINOUS SMECTITE Clays and Clay Minerals, August 1, 2002; 50(4): 455 - 469. [Abstract] [Full Text] [PDF]

				C.-I. Fialips, D. Huo, L. Yan, J. Wu, and J. W. Stucki Effect of Fe oxidation state on the IR spectra of Garfield nontronite American Mineralogist, May 1, 2002; 87(5-6): 630 - 641. [Abstract] [Full Text] [PDF]

				G. E. Brown Jr. and N. C. Sturchio An Overview of Synchrotron Radiation Applications to Low Temperature Geochemistry and Environmental Science Reviews in Mineralogy and Geochemistry, January 1, 2002; 49(1): 1 - 115. [Full Text] [PDF]