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Experimental study of the transformation of smectite at 80 and 300°C in the presence of Fe oxides

¹ Géologie et Gestion des Ressources Minérales et Energétiques (G2R), UMR 7566 CNRS-CREGU-INPL-UHP, Université Henri Poincaré, BP 239, 54506 Vanduvre-lès-Nancy, ² Laboratoire Environnement et Minéralurgie (LEM), UMR 7569 CNRS-INPL, Ecole Nationale Supérieure de Géologie, BP 40, 54501 Vanduvre-lès-Nancy, ³ Laboratoire de Chimie Physique et Microbiologie pour l’Environnement (LCPME), UMR 7564 CNRS-UHP, Université Henri Poincaré, 405 rue de Vanduvre, 54600 Villers-lès-Nancy, ⁴ Agence nationale pour la gestion des déchets radioactifs (ANDRA), Direction Scientifique/Service Matériaux, Parc de la Croix Blanche, 1/7 rue Jean Monnet, 92298 Châtenay-Malabry, France

View larger version (31K): [in a new window]   FIG. 1. XRD powder patterns of the Mt-Hm starting sample, 1 month, 3 months and 9 months ‘Mt-Hm 300’ run samples, and 9 months ‘Bentonite 300’ run sample. Reflection values in Å.

View larger version (135K): [in a new window]   FIG. 2. Evolution of the morphology of primary minerals as seen by SEM: (a) hematite powder used in the Mt-Hm starting sample; (b) hematite and magnetite crystals observed in the 9 months ‘Mt-Hm 80’ run sample; (c) overgrowth of quartz in the 3 months ‘Mt-Hm 80’ run sample; (d) overgrowth of albite in the 9 months ‘Bentonite 300’ run sample; (e) framboidal pyrite in the starting bentonite, (f) partly dissolved pyrite in the 9 months ‘Bentonite 300’ run sample.

View larger version (17K): [in a new window]   FIG. 3. XRD patterns of the Mt-Hm starting-sample, 1 month, 3 months and 9 months ‘Mt-Hm 300’ run samples, and 9 months ‘Bentonite 300’ run sample. (a, c, e, g, i) oriented air-dried; (b, d, f, h, j) EG-saturated. Reflection values in Å.

View larger version (16K): [in a new window]   FIG. 4. XRD patterns of the Mt-Hm starting sample, 3 months and 9 months ‘Mt-Hm 300’ run samples, and 9 months ‘Bentonite 300’ run sample, after Greene-Kelly test. Reflection values in Å.

View larger version (4K): [in a new window]   FIG. 5. Evolution of the Fe3+/Fetot ratio in the clay phase of the run samples measured by TMS vs. experimental duration. Dark diamonds: ‘Mt-Hm 300’ experiments; dark triangle: ‘Mt-Hm 80’ experiment; open circle: comparison with the Fe3+/Fetot ratio in the starting montmorillonite (Guillaume et al., 2001b).

View larger version (30K): [in a new window]   FIG. 6. Chemistry of the clay phase of the starting sample (open square), 1 month (filled triangles), 3 months (open diamonds) and 9 months (filled squares) run samples. Si vs. interlayer cations (I.C. = Na+2Ca+K), from structural formulae calculated on the basis of 11 oxygens. Reference minerals are reported: low-charge and high-charge smectite (LC-Sm, HC-Sm), low-charge and high-charge beidellite (LC-Bei, HC-Bei), Muscovite (Mu).

View larger version (20K): [in a new window]   FIG. 7. Chemistry of the clay phase of the starting sample (open square), 1 month (filled triangles), 3 months (open diamonds) and 9 months (filled squares) run samples. Fe total vs. Mg, from structural formulae calculated on the basis of 11 oxygens.

View larger version (31K): [in a new window]   FIG. 8. Chemistry of the clay phase of the starting sample (open square), 1 month (filled triangles), 3 months (open diamonds) and 9 months (filled squares) run samples. (Fe3+,AlVI) vs. (Fe2+,Mg), from structural formulae calculated on the basis of 11 Oxygens.

View larger version (11K): [in a new window]   FIG. 9. Chemistry of the run solutions: (a–b) evolution of pH vs. time for ‘Bentonite’- and ‘Mt-Hm’-type experiments, respectively. (c–d) Evolution of Eh vs. time for ‘Bentonite’- and ‘Mt-Hm’-type experiments, respectively.

View larger version (40K): [in a new window]   FIG. 10. Chemistry of the run solutions. Evolution with time of the solution composition (ppm scale) for different cations (Si, Al, Fe, Mg, K, Ca, Na and Cl) and the four different experimental conditions. 1d = 1 day, 1w = 1 week, 1m = 1 month, 3m = 3 months, 9m = 9 months.