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Uptake characteristics of alginate microcapsules containing bis(2,4,4-trimethylpentyl)monothiophosphinic acid for adsorption of Ag(I) ions were examined using batch methods. Under a definite initial Ag+ concentration (C b), at equilibrium, all the Ag(I) ions are adsorbed by extractant, while above C b, ion exchange by the alginate matrix becomes the dominating mechanism. The kinetic mechanism varies depending on the presence of coexisting ions (CI). If the concentration of CI is low, the kinetics is controlled by a combination of slow adsorption of Ag(I) ions by Cyanex 302 (HA) microdroplets and shielding of inner microdroplets by the outer reacting ones (physical−chemical shielding mechanism). At higher concentrations of CI, intrapore diffusion controls the kinetics. Different types of the shrinking core model remarkably fitted the kinetics experiments. The microcapsules were able to selectively adsorbed 90% of the Ag(I) ions from a 10 ppm Ag(I) + 3 mol·dm-3 Na+ solution. In addition, the uptake percentage was constantly high in wide range of pH values and Ag+ concentrations.

Abstract. Tracer response experiments were carried out using a packed bed of glass beads, where fluid flowed as either a single phase (water) or two phases (water and gas) under steady unsaturated conditions. The results depended on the water saturation and could be divided into two regions at the critical water saturation, that is, the saturation at which the gas phase began to be immobile. To determine the hydrodynamic dispersion coefficients, the experimental responses were compared with the numerical results of a one-dimensional advection-dispersion equation. These results demonstrated that the hydrodynamic dispersion coefficients increased with a decrease in water saturation. [1973, 1974]

Cement is an essential materials to construct the subsurface radioactive waste disposal system. However, cementitious materials alter the groundwater pH to highly alkaline condition about 13. To comprehend the effect of such a hyperalkaline condition on the repository surroundings, this study focused on the dissolution rates of amorphous silica at [NaOH]=l0-1 mol·dm-3 . The used samples were three kinds of pure commercial silica and a natural silica scale which was obtained from inside wall of the hot-water pipe of a geothermal power plant. The observed dissolution rates were interpreted with using the model, which assumed that the particle sizes decrease with the progress of dissolution. Moreover, due to the particle size distribution anticipated in the natural silica scale, this analysis assumed it contained particles with various initial diameters. In the results, (1) all pure silica samples and at least 60 wt% of the silica scale showed good agreement of the activation energy of the dissolution in the range of 77 through 88 kJ-mol-1 in the highly alkaline solution, (2) these rate constants were of the order of 10-s_ 10-7 mol·m-2 -s-1 at around 310 K and were definitely larger than those already reported for quartz, (3) the specific surface area based on BET method was revealed to be an important factor to give the main difference in the dissolution rates between the synthetic silica and the natural silica.