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Effect of extensive drying on the cation exchange capacity of bentonites

Published online by Cambridge University Press:  09 July 2018

S. Kaufhold  and
R. Dohrmann
S. Kaufhold*
Affiliation:
BGR, Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, D-30655 Hannover, Germany
R. Dohrmann
Affiliation:
BGR, Bundesanstalt für Geowissenschaften und Rohstoffe, Stilleweg 2, D-30655 Hannover, Germany LBEG, Landesamt für Bergbau, Energie und Geologie, Stilleweg 2, D-30655 Hannover, Germany
*
*E-mail: s.kaufhold@bgr.de
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Abstract

Extensive drying of smectites can cause the interlayer space to break down (collapse). This can affect the properties of bentonites as geotechnical barriers of HLRW (highly radioactive waste) repositories. If and to what extent the collapse occurs depends strongly on the type of interlayer cation. In particular K is known to lead to ready dehydration, in contrast to Ca and Mg. In the present study, various bentonites and one illite/smectite clay were dried/heated at 90ºC for 1.5 a and in a different experiment at 120ºC for 4.5 a and investigated with respect to mineralogical and geochemical changes of the smectite.

Smectite alteration after extensive drying was restricted to changes of the exchangeable cations. The CEC decreased by 9% (90ºC test) and 14% (120ºC test). A slight decrease of exchangeable Na+ was observed following the 90ºC test. No significant further decrease was observed after the 120ºC test. In contrast, the larger cation exchange capacity (CEC) decrease after the 120ºC test could be explained by increased Ca/Mg fixation. A possible mechanism for the observations is presented.

Keywords

bentonitedryingheatingcation exchange capacitygeotechnical barriergeochemical barrierreactive chemical barrierHLRW repository
Type
Research Article
Information
Clay Minerals , Volume 45 , Issue 4 , December 2010 , pp. 441 - 448
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2010

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