J. Phys. IV France 104 (2003) 413
DOI: 10.1051/jp4:20030111

Natural organic matter (NOM)-clay association and impact on Callovo-Oxfordian clay stability in high alkaline solution: Spectromicroscopic evidence

T. Schäfer¹, F. Claret^{1, 2}, A. Bauer¹, L. Griffault², E. Ferrage³ and B. Lanson<sup>3

1</sup>  Forschungszentrum Karlsruhe, Institut für Nukleare Entsorgung, INE, P.O. Box 3640, 76021 Karlsruhe, Germany
²  ANDRA, Parc de Croix Blanche, 1-7 rue Jean Monnet, 92298 Châtenay-Malabry cedex, France
³  Environmental Geochemistry Group, LGIT, Maison des Géosciences, Université J. Fourier, CNRS, BP. 53, 38041 Grenoble cedex 9, France

Abstract
The understanding of chemical association between natural organic matter (NOM) and clay minerals is of paramount importance to predict the long term stability of host rock formations for deep geological nuclear waste repositories. Synchrotron-based soft X-ray spectromicroscopy demonstrates a strong association between K-rich clay phases (illite) and NOM in the Callovo-Oxfordian argillite (Meuse-Haute Marne, or MHM site, France) and a weaker association in the Opalinus clay (Benken, Switzerland). C(1s) spectra show no significant depth dependent variation in the MHM site (447-516m). Alteration experiments under oxidizing conditions and high pH of the Callovo-Oxfordian clay indicate a passivation of chemically reactive sites by NOM that is responsible for the kinetic hindered clay dissolution/transformation. These experiments lead to a significant release of humic/fulvic acid colloids in the alkaline solution with time dependent variation in size and functional group content.

© EDP Sciences 2003