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Buffering of pH conditions in sodium bentonite

Published online by Cambridge University Press:  27 March 2012

Veli-Matti S. Pulkkanen ,
Aku P. Itälä  and
Arto K. Muurinen
Veli-Matti S. Pulkkanen
Affiliation:
VTT Technical Research Centre of Finland, Otakaari 3 K, Espoo, P.O. Box 1000, FI-02044 VTT, Finland
Aku P. Itälä
Affiliation:
VTT Technical Research Centre of Finland, Otakaari 3 K, Espoo, P.O. Box 1000, FI-02044 VTT, Finland
Arto K. Muurinen
Affiliation:
VTT Technical Research Centre of Finland, Otakaari 3 K, Espoo, P.O. Box 1000, FI-02044 VTT, Finland
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Abstract

A bentonite buffer is a part of the engineering barrier system of the geological disposal concept for spent nuclear fuel in Finland. The chemical conditions in the bentonite porewater determine the solubility, speciation and diffusion/sorption behaviour of the radionuclides in the bentonite. The OH-groups on the edge sites of the montmorillonite, the main component of bentonite, can buffer the pH conditions especially in the case that the buffering capacity of the accessory minerals is small. In this work, the pH conditions created by the interaction of sodium montmorillonite and an acetate buffer solution were studied experimentally in batch experiments and in compacted sodium montmorillonite. In the experiment with the compacted sample, the ends of an 18.4 mm long cylinder were exposed to an external solution of 0.3 M NaCl and 0.1 M acetate adjusted to pH 5 with NaOH. The effects were monitored by measuring the pH in the montmorillonite sample at 5 mm and 9.2 mm from the solution-montmorillonite interface as a function of time. The batch experiment was modelled considering the surface reactions of montmorillonite and the dissolution reactions of calcite and the added constituents to explain the observed phenomena.

Type
Articles
Information
MRS Online Proceedings Library (OPL) , Volume 1475: Symposium NW – Scientific Basis for Nuclear Waste Management XXXV , 2012 , imrc11-1475-nw35-p32
Copyright
Copyright © Materials Research Society 2012

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References

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