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Bentonite pore distribution based on SAXS, chloride exclusion and NMR studies

Published online by Cambridge University Press:  09 July 2018

A. Muurinen ,
T. Carlsson  and
A. Root
A. Muurinen*
Affiliation:
VTT Technical Research Centre of Finland. P.O. Box 1000, FI-02044 VTT, Finland
T. Carlsson
Affiliation:
VTT Technical Research Centre of Finland. P.O. Box 1000, FI-02044 VTT, Finland
A. Root
Affiliation:
MagSol, Tuhkanummenkuja 2, 00970 Helsinki, Finland
*
*E-mail: arto.muurinen@vtt.fi
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Abstract

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Water-saturated bentonite is planned to be used in many countries as an important barrier component in high-level nuclear waste (HLW) repositories. Knowledge about the microstructure of the bentonite and the distribution of water between interlayer (IL) and non-interlayer (non-IL) pores is important for modelling of long-term processes. In this work the microstructure of water-saturated samples prepared from MX-80 bentonite was studied with nuclear magnetic resonance (NMR) and small-angle X-ray scattering spectroscopy (SAXS) coupled with chloride exclusion modelling. The sample dry densities ranged between 0.7 and 1.6 g/cm3. The NMR technique was used to get information about the relative amounts of different water types. Water in smaller volume domains has a shorter relaxation time than that in larger domains due to the average closer proximity of the water to the paramagnetic Fe at the layer surfaces. The results were obtained using 1H NMR T 1ρ relaxation time measurements with the short inter-pulse CPMG method. The interpretation of the NMR results was made by fitting a sum of discrete exponentials to the observed decay curves. The SAXS measurement on bentonite samples was used to get information about the size distribution of the IL distance of montmorillonite. The chloride porosity measurements and Donnan exclusion calculations were used together with the SAXS results to evaluate the bentonite microstructure. In the model, the montmorillonite layers were organized in stacks having IL water between the layers and non-IL water between the stacks. In the modelling, the number of layers in the stacks was used as fitting parameters which determined the IL and non-IL surface areas. The fitting parameters were adjusted so that the modelled chloride concentration was equal to the measured one. The NMR studies and SAXS studies coupled with the Cl porosity measurements provided very similar pictures of how the porewater is divided in two phases in bentonite.

Keywords

high-level nuclear waste (HLW) repositoriesbentonite buffermicrostructurepore distributionNMRSAXSexclusion

Information

Type
Research Article
Information
Clay Minerals , Volume 48 , Issue 2 , May 2013 , pp. 251 - 266
Creative Commons
Creative Common License - CCCreative Common License - BY
Copyright © The Mineralogical Society of Great Britain and Ireland 2013 This is an Open Access article, distributed under the terms of the Creative Commons Attribution license. (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2013

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