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Influence of Tetrahedral Layer Charge on the Fixation of Cesium in Synthetic Smectite Liva Dzene, Heloïse Verron, Alfred Delville, Laurent J. Michot, JeanLouis Robert, Emmanuel Tertre, Fabien Hubert, and Eric Ferrage J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b06308 • Publication Date (Web): 29 Sep 2017 Downloaded from http://pubs.acs.org on October 6, 2017
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The Journal of Physical Chemistry
Influence of Tetrahedral Layer Charge on the Fixation of Cesium in Synthetic Smectite Liva Dzene*,a,†, Heloïse Verrona,††, Alfred Delvilleb, Laurent J. Michotc, Jean-Louis Robertd, Emmanuel Tertrea, Fabien Huberta and Eric Ferragea a
Université de Poitiers/CNRS, UMR 7285 IC2MP, Equipe HydrASA, 5 rue Albert Turpain, Bât.
B8, TSA - 51106, 86073 Poitiers cedex 9, France b
Interfaces, Confinement, Matériaux et Nanostructures - ICMN CNRS, UMR 7374, Université
d'Orléans, 45071 Orléans Cedex 2, France c
Phenix CNRS-UPMC-Sorbonne Université UMR 8234, 4 place Jussieu case courrier 51, 75005
Paris, France d
IMPMC, Sorbonne Universités, UMR 7590, UPMC, CNRS, MNHN, IRD, 4 Place Jussieu,
75252 Paris Cedex 05, France
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ABSTRACT
After radionuclides pollution of soils by nuclear power plant accidents, Cs+ strongly interacts with swelling clay minerals, which in turn control the fixation or the migration of this pollutant in the natural media. Little is known, however, about the role played by the amount of layer charge and the two-dimensional confinement on Cs+ fixation. In this study a series of tetrahedrally charged smectites with structural formula inter[M+x]oct[Mg6]tet[Si8−xAlx]O20(OH)4 and with a layer charge (x) varying from 0.8 to 2.0 and with Na+ or Cs+ as interlayer cation M+ were used. While Na+ remains fully exchangeable over the entire range of layer charges investigated, the fraction of exchangeable Cs+ decreased gradually for samples with x ≥1.4/O20(OH)4. Structure analysis of Cs+-samples in water-saturated or at 80% relative humidity conditions showed a gradual decrease of the layer-to-layer distance. The results were found to qualitatively agree with analysis of the thermodynamics of the clay/water interfaces derived from molecular simulations. Quantitative structure analysis by modeling of 00ℓ reflections on experimental Xray diffraction patterns suggested that exchangeable Cs+ can be correlated with the amount of hydrated interlayers, whereas fixed Cs+ in these conditions corresponds to the amount of collapsed layers. To describe the coexistence of both exchangeable and fixed Cs+, a toy-model accounting for the presence of heterogeneous charge distribution was used, in agreement with experimental data obtained on these samples. This model successfully interprets the overall reactivity of Cs+ towards smectite over a large range of layer charge values and may contribute to an improved description of Cs+ mobility in contaminated soil environments.
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The Journal of Physical Chemistry
INTRODUCTION Swelling clays such as smectites are lamellar silicates that are one of the main components of soils. The structure of these colloidal ( 40 Å) the diffuse layer theory46–49 perfectly reproduces the swelling behavior of the clay/water interface by neglecting the molecular structure of the solvent in the framework of the Primitive Model.50 By contrast, at small layer-to-layer distances (i.e.,
