FIRST PRINCIPLES MOLECULAR DYNAMICS STUDY OF INTERLAYER WATER AND CATIONS IN VERMICULITE

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  • IKEDA TAKASHI
    Condensed Matter Science Unit, Quantum Beam Science Center, Japan Atomic Energy Agency (JAEA)

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Description

To clarify possible origins of irreversible adsorption/desorption of cesium on clay minerals, we performed first principles molecular dynamics simulations for vermiculite including water molecules along with Mg^<2+>, K^+, and Cs^+ in its interlayers. Our close examination on the structural and dynamical properties of interlayer water included in vermiculite together with the cations shows that Mg^<2+> and Cs^+ form respectively outer- and inner-sphere surface complexes in the interlayers, while K^+ forms both types of complexes. The structure of electrical double layers formed in the interlayers is found to depend significantly on the types of surface complexes of the interlayer cations. The reorientational motions of H_2O molecules are suggested to be enhanced by Cs^+ in contrast to a minor influence of Mg^<2+> and K^+. Our observed enhanced diffusion of interlayer H_2O molecules along with their rapid reorientation indicates that Cs^+ ions work as structure-breaking ions even in confined 2-dimensional space of the interlayers.

Journal

  • Clay Science

    Clay Science 18 (2), 23-31, 2014

    The Clay Science Society of Japan

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