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Effects of Exchanged Cation on the Microporosity of Montmorillonite

Published online by Cambridge University Press:  28 February 2024

David W. Rutherford ,
Cary T. Chiou  and
Dennis D. Eberl
David W. Rutherford
Affiliation:
US Geological Survey, Box 25046, MS 408, Denver Federal Center, Denver, Colorado 80225
Cary T. Chiou
Affiliation:
US Geological Survey, Box 25046, MS 408, Denver Federal Center, Denver, Colorado 80225
Dennis D. Eberl
Affiliation:
US Geological Survey, 3215 Marine Street, Boulder, Colorado 80303
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Abstract

The micropore volumes of 2 montmorillonites (SAz-1 and SWy-1), each exchanged with Ca, Na, K, Cs and tetramethylammonium (TMA) ions, were calculated from the measured vapor adsorption data of N2 and neo-hexane by use of t- and αs-plots. The corresponding surface areas of the exchanged clays were determined from Brunauer-Emmett-Teller (BET) plots of N2 adsorption data. Micropore volumes and surface areas of the samples increased with the size of exchanged cation: TMA > Cs > K > Ca > Na. The SAz-1 exchanged clays showed generally greater micropore volumes and surface areas than the corresponding SWy-1 clays. The vapor adsorption data and d(001) measurements for dry clay samples were used together to evaluate the likely locations and accessibility of clay micropores, especially the relative accessibility of their interlayer spacing. For both source clays exchanged with Na, Ca and K ions, the interlayer spacing appeared to be too small to admit nonpolar gases and the accessible micropores appeared to have dimensions greater than 5.0 Å, the limiting molecular dimension of neo-hexane. In these systems, there was a good consistency of micropore volumes detected by N2 and neo-hexane. When the clays were intercalated with relatively large cations (TMA and possibly Cs), the large layer expansion created additional microporosity, which was more readily accessible to small N2 than to relatively large neo-hexane. Hence, the micropore volume as detected by N2 was greater than that detected by neo-hexane. The micropore volumes with pore dimensions greater than 5 Å determined for clays exchanged with Na, Ca and K likely resulted from the pores on particle edges and void created by overlap regions of layers. The increase in micropore volumes with pore dimensions less than 5 Å determined for clays exchanged with TMA and possibly Cs could be caused by opening of the interlayer region by the intercalation of these large cations.

Keywords

Exchanged CationInterlayer AccessibilityMicroporosityMontmorilloniteSurface Area
Type
Research Article
Information
Clays and Clay Minerals , Volume 45 , Issue 4 , August 1997 , pp. 534 - 543
Copyright
Copyright © 1997, The Clay Minerals Society

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