Anisotropy and Effect of Salinity in Diffusion and Activation Energy of Cs<SUP>+</SUP> Ions in Compacted Smectite

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Abstract

In-diffusion experiments for Cs+ ions in compacted Na-smectite were performed in the directions parallel and perpendicular to the orientation of the smectite particles as a function of smectite dry density (between 0.9 and 1.4Mg/m3), salinity ([NaCl] =0.01 and 0.51M) and temperature (295-333K).<BR>The apparent diffusion coefficient (Da) tended to be higher in the direction parallel than in the direction perpendicular to the orientation of the smectite particles. Higher salinity leads to an increase of the Da-values for all conditions. The activation energies (ΔEa) are independent of the orientation of the smectite particles. Higher dry densities correspond to higher ΔEa-values. For a dry density of 1.0Mg/m3, the corresponding ΔEa-value agrees well to a predicted value ΔEa-value=24.66±0.96kJ/mol. This value is obtained as the difference of the activation energy for diffusion of cesium in pure water (16.47kJ/mol) and the Cs/Na ion exchange enthalpy ΔH0 (-11.10kJ/mol). For a dry density of 1.4Mg/m3, ΔEa is 35.20±0.83kJ/mol. The higher ΔEa-values found at higher dry densities are attributed to complex effects of ΔH0 and the lowering of porewater activity at high-dry densities.

Journal

  • Clay Science

    Clay Science 12 (Supplement2), 160-165, 2006

    The Clay Science Society of Japan

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