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Effects of iron oxidation state and organic cations on dioctahedral smectite hydration

Joseph W. Stucki, Jun Wu, Huamin Gan, Peter Komadel and Amos Banin
Effects of iron oxidation state and organic cations on dioctahedral smectite hydration
Clays and Clay Minerals (April 2000) 48 (2): 290-298


Reduction of structural Fe in Na-exchanged dioctahedral smectites decreases swellability in water, but because clay interlayers also collapse in the process the concomitant effect on surface hydration energy is uncertain. This study examined the hydration behavior of oxidized and reduced dioctahedral smectite clays exchanged with polar (Na) and weakly-polar (organic) cations to determine the nature of the surface before and after Fe reduction, and to determine if clay surfaces are hydrophilic or hydrophobic. The H (sub 2) O content in various dioctahedral smectites decreased if Na was replaced by tetramethylammonium (TMA), trimethylphenylammonium (TMPA), or hexadecyltrimethylammonium (HDTMA). Among the organo-clays, H (sub 2) O adsorption decreased with increasing complexity of the cation. For oxidized smectites, those exchanged with TMPA retained less H (sub 2) O than those exchanged with Na at all pressures. The extent of this difference depended on the clay and decreased with increasing applied pressure. Reduction of Fe(III) to Fe(II) in the octahedral sheets decreased the swelling of Na-saturated smectites, apparently causing some previously swelling interlayers to collapse. If the Na interlayer cation was exchanged to alkylammonium after reduction, but prior to swelling-pressure measurements, the swelling increased or remained near constant, suggesting that the organo-cation disrupted the collapse process of the interlayers associated with the reduced smectite layers. Reduced TMPA-saturated smectite surfaces are more strongly hydrated if the octahedral sheet is reduced than if oxidized. Thus, reduction of structural Fe increases the hydration energy of smectite basal surfaces, but swellability could decrease or increase depending on the extent of interlayer collapse occurring with different exchangeable cations.

ISSN: 0009-8604
Serial Title: Clays and Clay Minerals
Serial Volume: 48
Serial Issue: 2
Title: Effects of iron oxidation state and organic cations on dioctahedral smectite hydration
Affiliation: University of Illinois, Department of Natural Resources and Environmental Sciences, Urbana, IL, United States
Pages: 290-298
Published: 200004
Text Language: English
Publisher: Clay Minerals Society, Clarkson, NY, United States
References: 43
Accession Number: 2000-042099
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
Secondary Affiliation: Slovak Academy of Sciences, SVK, SlovakiaHebrew University, ISR, Israel
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland
Update Code: 200014
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