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Water - Compacted Na-Bentonite Interaction in Simulated Nuclear Fuel Disposal Conditions: the Role of Accessory Minerals

Published online by Cambridge University Press:  25 February 2011

A. Melamed  and
P. Pitkänen
A. Melamed
Affiliation:
Technical Research Centre of Finland, P.O.Box 108, FIN-02151 Espoo, Finland
P. Pitkänen
Affiliation:
Technical Research Centre of Finland, P.O.Box 108, FIN-02151 Espoo, Finland
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Abstract

In an earlier laboratory study1, ion exchange processes and smectite alteration were investigated through the interaction between compacted Na-bentonite (Volclay MX-80) and simulated granitic groundwater solutions. The change of montmorillonite from Na- to Ca-rich was found to be the major alteration process in the bentonite. In the water, a concentration decrease in Ca, Mg and K, and an increase in Na, HCO3 and SO4 were recorded. The total amount of Ca available in the water, however, was found insufficient to account for the recorded formation of Ca-smectite, and it is therefore assumed that the accessory Ca-bearing minerals in the bentonite provide the fundamental source of these cations.

X-ray powder diffraction analyses and microscope observations of the bentonite samples were re-conducted. Quartz, feldspars, pyrite, calcite and traces of gypsum were revealed as the primary accessories. In reacted samples, goethite and siderite are found as the secondary mineral products in association with corroded pyrite grains, while calcite and gypsum tend to disappear. From these results it is assumed that the oxygen present in the water and bentonite pore space promotes the oxidation of pyrite (dissolved) and the precipitation of goethite. The pore water pH decreases and calcite is partly dissolved. Through the dissolution, the bulk amount of Ca ions in addition to those arising by diffusion from the water is provided. Some of the reaction-released bicarbonate and Fe2+ re-precipitate in the bentonite as siderite, while the rest (as also SO4 ions) diffuse into the water.

Though the relative oxygen content in the experiment may be considered higher than that of the repository concept for nuclear fuel disposal (interaction in a semi-closed system with high water/bentonite ratio), the near field geochemistry predictions imply limited oxidizing conditions, which will be characterized by the above-described processes in sulphide-bearing bentonite and occur for some time after the sealing of the repository.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 333: Symposium V – Scientific Basis for Nuclear Waste Management XVII , 1993 , 919
Copyright
Copyright © Materials Research Society 1994

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References

REFERENCES

1 Melamed, A., Pitkänen, P., Olin, M., Muurinen, A., and Snellman, M. in Scientific Basis for Nuclear Waste Management XV. edited by Sombert, C.G. (Mater. Res. Soc. Proc. 257, Pittsburgh, PA, 1992) pp. 557–566.Google Scholar
2 Borchardt, G., , G., in Minerals in Soil Environments, edited by Dixon, J. B. and Weed, S. B. (Soil Science Society of America, Madison, Wisconsin, USA, 1989).Google Scholar
3 Pusch, R., KBS TR 74, 1978.Google Scholar
4 D. M. Anderson, (ed.), KBS TR 84–11, 1983.CrossRefGoogle Scholar
5 Güven, N., Eng. Geol., 28, 233 (1990).CrossRefGoogle Scholar
6 Velde, B. and Brusewitz, A.M., Geochim. et Cosmochim. Acta, 46, 447 (1982).CrossRefGoogle Scholar
7 Pusch, R. and Karnland, O., SKB TR 88–26, 1988.Google Scholar
8 Inoue, A., Utada, M. and Wakita, K., Applied Clay Science, 7, 131 (1992).CrossRefGoogle Scholar
9 Pusch, R. and Karnland, O., SKB TR 90–44, (1990).Google Scholar
10 Bruno, G., Decarreau, A., Proust, D. and Lajudie, A., Applied Clay Science, 7, 169 (1992).CrossRefGoogle Scholar
11 Cuevas, J., Medina, J.A. and Leguey, S., Applied Clay Science, 7, 185 (1992).CrossRefGoogle Scholar
12 Witney, G., Applied Clay Science, 7, 97 (1992).CrossRefGoogle Scholar
13 Wanner, H., Wersin, P. and Sierro, N., SKB TR 92–37, 1992.Google Scholar
14 Pusch, R., Karnland, O. and Muurinen, A., 1990. Nuclear Waste Commission of Finnish Power Companies, Report YJT 90–06, 1990.Google Scholar
15 Hall, P.L., in A Handbook of Determinative Methods in Clay Mineralogy, edited by Wilson, M. J. (Chapman and Hall Publishers, New York, 1987), p. 308.Google Scholar
16 Pusch, R. and Güven, N., Eng. Geol., 28, 303 (1990).CrossRefGoogle Scholar
17 Brandberg, F., Grudfelt, B., Höglund, L.O., Karlsson, F., Skagius, K. and Smellie, J., Nuclear Waste Commission of Finnish Power Companies, Report YJT 93–07, 1993.Google Scholar