Characterization of the organic matter of argilite from the Callovo-Oxfordian

Geologic disposal of radioactive waste is under consideration at a number of different geological settings. One site under consideration in France is in the eastern part of the Paris Basin (Departments Meuse and Haute Marne), where the French nuclear agency (Andra) is currently setting up an underground laboratory. The sedimentary host formation is the approximately 130 m thick clay-rich Callovo-Oxfordian formation at approximately 350 - 550 m depth below ground surface in the selected area. The maximum burial temperature recorded for the Callovo-Oxfordian formation did not exceeded 40 C. Under these burial temperatures the part of the immature organic material has decreased, but was not fully degraded. Furthermore, some humic-like substances can be generated via oxidative conversion of clay organic matter. Substantial generation of hydrophilic dissolved organic carbon from hydrophobic clay organic matter has also been observed by alkaline extended treatment of clay. Moreover, organic matter present in natural groundwater can play a major role in the migration of radionuclide in natural aquifer systems, carboxylic functional groups generally dominating the metal ion complexation behavior. The objectives of this study are: 1) to isolate the organic matter fractions from the mineral matrix of the Callovo-Oxfordian argilites, 2) to characterize the organic fractions at the molecular level, 3) to quantify the functional groups (i.e. carboxylic and hydroxylic groups) by titrations. (authors)