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 Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Wolters, F. Articles by Emmerich, K. Search for Related Content

A COMPREHENSIVE CHARACTERIZATION OF DIOCTAHEDRAL SMECTITES

Felicitas Wolters^1,*,, Gerhard Lagaly², Guenter Kahr³, Rolf Nueesch and Katja Emmerich^1,4

¹ Institute for Technical Chemistry, Water and Geotechnology Division, Forschungszentrum Karlsruhe GmbH, P.O. Box 3640, 76021 Karlsruhe, Germany
² Institute of Inorganic Chemistry, University of Kiel, D-24098 Kiel, Germany
³ ETH Zurich, Institute for Geotechnical Engineering, Schafmattstr. 6, 8093 Zürich, Switzerland
⁴ Competence Center for Material Moisture, University of Karlsruhe, c/o Forschungszentrum Karlsruhe, ITC-WGT, P.O. Box 3640, 76021 Karlsruhe, Germany

^* E-mail address of corresponding author: feli-h{at}gmx.de

The term ‘montmorillonite’ encompasses a wide range of chemical compositions and structures. Comprehensive and reliable characterization is essential for unambiguous classification. Twenty eight purified, Na-exchanged smectites (<0.2 µm) were characterized by layer-charge measurement using the alkylammonium method, by cation exchange capacity (CEC) measurement with Cu-triethylenetetramine, by determination of the chemical composition using X-ray fluorescence analysis, by calculation of the structural formula following determination of the octahedral structure (trans-vacant vs. cis-vacant) by simultaneous thermal analysis, and by X-ray diffraction analysis. Mössbauer spectroscopy was applied to determine the oxidation state and coordination of Fe and changes thereof during purification of the source materials.

The charge derived from chemical composition was considerably greater (by up to 30%) than the measured layer charge. The independently measured layer charge was used to calculate the structural formula. The measured CEC values, comprising the permanent charges and the pH-dependent edge charges, were consistent with measured layer charge but not with layer charge derived from the chemical composition. Therefore, the structural formula of smectites should be calculated using the measured layer charge.

The dehydroxylation temperature, which conveys information about the structure of the octahedral sheet, was correlated to the amount of Mg and Fe³⁺ and the location of charges. No relationship was found among the dehydroxylation temperature and the mean layer charge or the Mg content. In contrast, a clear relationship was observed between the Fe content and the dehydroxylation temperature. Montmorillonites with an Fe content <0.3/f.u. are cis-vacant and those containing Fe³⁺ > 0.3 mol/f.u. are trans-vacant, mostly with additional cis-vacancies. Tetrahedral substitution also appeared to be a function of the number of trans-vacancies.

The parameters analyzed provide the basis for a new descriptive classification system.

Key Words: CEC • Chemical Composition • Cis-vacant • Dehydroxylation • Fe content • Layer Charge • Montmorillonite • Octahedral Charge • Simultaneous Thermal Analysis • Structural Formula • Tetrahedral Charge • Trans-vacant

This article has been cited by other articles:

				K. Emmerich, F. Wolters, G. Kahr, and G. Lagaly CLAY PROFILING: THE CLASSIFICATION OF MONTMORILLONITES Clays and Clay Minerals, February 1, 2009; 57(1): 104 - 114. [Abstract] [Full Text] [PDF]