Hydration and swelling of synthetic Na-saponites: Inß uence of layer charge.

Laurent J. Michot (1) , Isabelle Bihannic (1) , Manuel Pelletier (1) , Emmanuel Rinnert (2, 3) , Jean-Louis Robert (4)

1 LEM - Laboratoire Environnement et Minéralurgie
2 LCPME - Laboratoire de Chimie Physique et Microbiologie pour l'Environnement
3 ANDRA - Agence Nationale pour la Gestion des Déchets Radioactifs
4 ISTO - Institut des Sciences de la Terre d'Orléans

This paper concerns the hydration and swelling behavior of four synthetic sodium saponite samples with general formula Nax(Si4–x,Alx)(Mg3)O10(OH)2, where x = 0.4, 0.5, 0.6, and 0.7. The combination of gravimetric water adsorption measurements and X-ray diffraction experiments under controlled water pressure allows us to analyze the inß uence of layer charge on swelling mechanisms. When the layer charge increases, swelling occurs for lower values of the chemical potential, i.e., at lower relative pressure. In parallel, as the cohesion between layers increases with increasing layer charge, a greater amount of water is needed to initiate swelling for higher-charged samples. In this last case, due to the proximity of interlayer cations, the transition between the one layer and two-layer hydrate occurs before the sodium cations are surrounded by a complete hydration sphere. This study also shows that the “one-layer” or “two-layer” hydrates cannot be considered as deÞ ned states as they appear to be modiÞ ed with both layer charge and relative pressure.

Domains: Geochemistry

Laurent J. Michot, Isabelle Bihannic, Manuel Pelletier, Emmanuel Rinnert, Jean-Louis Robert. Hydration and swelling of synthetic Na-saponites: Inß uence of layer charge.. American Mineralogist, 2005, 90, pp.166-172. ⟨10.2138/am.2005.1600⟩. ⟨hal-00023484⟩