ABSTRACT
The effective and efficient removal of radioactive Cs from contaminated soil is highly urgent for the nuclear post-accident remediation. In present study, we achieved rapid Cs desorption from both a typical micaceous clay (i.e., vermiculitized biotite, VB) and actually contaminated soil by high-speed ion exchange through temperature-controlled continuous leaching with Mg-solutions in a column reactor. Cs-sorbed VB was firstly employed as a soil surrogate to explore the macro-Cs desorption process and micro-mechanism in detail. Results showed that VB sandwiched the adsorbed Cs to its interlayers within collapsed structure (10.7 Å) and prevent Cs release even by abundant extraction with H2O at 250 °C or Mg2+ at 25 °C. However, Mg2+-extracted Cs desorption boosted significantly with elevating temperatures and 100 % of sorbed-Cs was removed from Cs-VB leached above 150 °C. Further structural and composition analysis of the leached specimen ensured that solvated Mg2+ preferentially entered into Cs+-collapsed interlayers at 150 °C than K+-interlayers above 200 °C, leading to prior complete Cs removal over K from VB at lower temperatures. By contrast, the Cs-contaminated soil reduced by â¼39 % but â¼82 % of its initial radioactivity after equally leaching with same volumes of Mg2+-solution at 150 and 200 °C, respectively. These temperature-controlled Cs desorption validated that radioactive Cs in actual soil indeed be tightly trapped by micaceous clays nearly in the Cs-K co-collapsed interlayers, to which its extraction by other cations can conditionally occur above enough high leaching temperatures. These superior features would inspire new insights for the design of novel practical technologies for treatment and decontamination of the nuclear post-accident soils.
ABSTRACT
We have studied the mixing scheme of an aqueous solution of ionic liquid tetrabutylphosphonium trifluoroacetate, [P4,4,4,4]CF3COO, in the water-rich region. The mixture shows phase separation with a lower critical solution temperature. To learn how the solute [P4,4,4,4]CF3COO species interact with each other in the dilute region, the third derivative quantities of Gibbs energy in terms of enthalpy, H, and volume, V, are evaluated. In the present study using up to the third derivative quantities, we conclude that [P4,4,4,4]CF3COO turns out to be an extremely strong hydrophobe. This finding may hint that the present IL is not dissociated in this water-rich region, despite the large dielectric permittivity of solvent water and as such it works as an extremely strong hydrophobe. An earlier 1-propanol (1P) probing study showed that [P4,4,4,4]+ is a significant amphiphile with a strong hydrophobicity and an equally strong hydrophilicity, and CF3COO- is a modest amphiphile. However, the 1-propanol (1P) probing methodology effectively uses the fourth derivative of G, and is capable of providing deeper information on the effect of the test solute on H2O. To reconcile the present conclusion with the earlier observations described above, we propose to conduct the 1P-probing of the ionic liquid salt, [P4,4,4,4]CF3COO.
ABSTRACT
Aqueous solutions of tetrabutylphosphonium trifluoroacetate, [P4444]CF3COO, exhibit a liquid-liquid phase transition with a lower critical solution temperature. Herein, we characterized the constituent ions, [P4444](+) and CF3COO(-), in terms of their effects on the molecular organization of H2O on the basis of 1-propanol probing methodology devised by Koga et al. The resulting characterization of the hydrophobicity/hydrophilicity is displayed on a two-dimensional map together with previous results, for a total of four cations and nine anions of typical ionic liquid (IL) constituents. The results indicate that [P4444](+) is the most significant amphiphile with strong hydrophobic and equally strong hydrophilic contributions among the group of constituent cations of ILs studied so far. The hydration number for [P4444](+) was evaluated to be nH = 72, which is three times larger than that of a typical imidazolium-based cation, [C4mim](+). Self-aggregation of [P4444](+) was found to occur in an aqueous solution of [P4444]CF3COO above 0.0080 mole fraction of the IL.
ABSTRACT
The length of hospital stay and effectiveness of medical treatment are analyzed using data of patients hospitalized due to hip fractures of four hospitals in Japan. The influence of the Revision of the Medical Service Fee Schedule in April, 2002, is evaluated, and factors which may have affected the length of stay and effectiveness of treatment (walking ability upon departure from the hospital) are also analyzed by a newly developed simultaneous equation model.
