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NMR Study of Interlayer and Non-interlayer Porewater in Water-saturated Bentonite and Montmorillonite

Published online by Cambridge University Press:  25 January 2013

Torbjörn Carlsson ,
Arto Muurinen  and
Andrew Root
Torbjörn Carlsson
Affiliation:
VTT Technical Research Centre of Finland, Espoo, P.O. Box 1000, FI-02044 VTT, Finland.
Arto Muurinen
Affiliation:
VTT Technical Research Centre of Finland, Espoo, P.O. Box 1000, FI-02044 VTT, Finland.
Andrew Root
Affiliation:
MagSol, Tuhkanummenkuja 2, 00970 Helsinki, Finland.
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Abstract

Bentonite is planned to be used in many countries as an important barrier in high-level waste repositories. Assessment of the barrier with regard to, inter alia, its ability to hinder transport of dissolved radionuclides leaking from a damaged canister containing spent nuclear fuel, requires quantitative data about the pore structure inside bentonite. The present NMR study was made in order to determine the number of distinguishable porewater phases in compacted water-saturated samples of MX-80 bentonite and Na-montmorillonite. The samples were compacted to dry densities in the interval 0.7-1.6 g/cm3 and subsequently saturated with Milli-Q water or 0.1 M NaCl solution in equilibrium cells. The NMR measurements were performed with a high-field 270 MHz NMR spectrometer using a short inter-pulse CPMG method to study proton T1ρ relaxation. The measured relaxation curves were found to consist of one faster and one slower proton relaxation. Subsequent analysis of the data indicated that the faster relaxation was associated with interlayer (IL) water between montmorillonite unit layers, while the slower one was associated with non-interlayer (non-IL) water located outside the interlayer spaces. The results indicate for compacted samples with a dry density of ≥ 1.0 g/cm3, that Na montmorillonite contains a larger relative volume of non-IL water than the corresponding MX-80 bentonite. This in turn, suggests that the stacking number in Na-montmorillonite is smaller than in MX-80 bentonite. Changing the porewater chemistry seemed to have some effect on the non-IL water content in the Na montmorillonite but not in the MX-80 bentonite.

Keywords

microstructurenuclear magnetic resonance (NMR)waste management
Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 1518: Symposium LL – Scientific Basis for Nuclear Waste Management XXXVI , 2012 , pp. 167 - 172
Copyright
Copyright © Materials Research Society 2013 

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