Kenso Fujiwara

Analysis of Adsorption Behavior of Cations onto Quartz Surface by Electrical Double-layer Model

In a study of the adsorption behavior of cations onto quartz, the distribution coefficient of a variety of cations was determined using the batch method, and using the titration method, the surface charge densities of quartz in a number of electrolyte solutions. The two values thus determined were analyzed applying the electrical double-layer model, from which optimum parameter values were derived for double-layer electrostatics and intrinsic adsorption equilibrium constants. Based on these parameter values, the mechanism of cation adsorption is discussed: A key factor governing this mechanism proved to be the hydration behavior of cations. Consideration of the Coulomb interaction between the adsorbate ions and adsorbent surface led to the finding of a simple rule governing in common the adsorption equilibrium constants of different metal ions.

Determination of uranium(IV) hydrolysis constants and solubility product of UO2.xH2O

Summary The hydrolysis constants of tetravalent uranium were determined by a solvent extraction method using thenoyltrifluoroacetone(TTA) and 233U. The distribution ratio of U(IV) was measured as a function of the pHc value in the aqueous phase at I=0.1, 0.5 and 1.0, and was analyzed to obtain the hydrolysis constants (βm) of U(OH)m(4-m)+ at the standard state (I=0). By taking the specific ion interaction theory (SIT) for ionic strength corrections, the hydrolysis constants at I=0 were determined to be β1°=13.71±0.31, β2°=26.12±0.21 and β3°=36.85±0.36, together with the ion interaction coefficients of UOH3+, U(OH)22+ and U(OH)3+. The solubility product (Ksp) for the reaction of UO2·xH2O=U4++4OH- + (x-2)H2O was also calculated to be log Ksp° =-53.93±0.20 by considering the hydrolysis constants.

Raman spectroscopic determination of formation constant of uranyl hydrolysis species (UO2)2(OH)22

Abstract Raman spectra of uranyl species in 10 −2 M uranium(VI) perchlorate solutions were measured in pH range 2.88–3.46. The bands of ν 1 symmetrical stretching vibration were observed at 872 and 853 cm −1 which were attributed to UO 2 2+ and (UO 2 ) 2 (OH) 2 2+ , respectively. Under the coexistence of (UO 2 ) 2 (OH) 2 2+ , concentration of UO 2 2+ was accurately determined using the Raman intensity. The formation constant of (UO 2 ) 2 (OH) 2 2+ was estimated, and this constant was discussed with the values determined by other methods. The validity of this method was discussed in conjunction with the covalent-bond character of UO.

Measurement of Thermal Neutron Capture Cross Section and Resonance Integral of the 237Np(n, γ)238Np Reaction

The thermal neutron capture cross section (σ0) and the resonance integral (I 0)of 237Np have been measured by an activation method to supply basic data for the study of transmutation of nuclear waste. The neutron irradiation of 237Np samples have been done at the Research Reactor Institute, Kyoto University (KUR). Samples of 237Np were irradiated between two Cd sheets or without a Cd sheet. Since 237Np has a strong resonance at the energy of 0.49 eV, the Cd cutoff energy was adjusted at 0.358 eV (thickness of the Cd sheets: 0.125 mm). A high purity Ge detector was employed for activity measurement. The reaction rate to produce 238Np from 237Np was analyzed by the Westcotts convention. Results obtained were 141.7±5.4 barns for σ0 and 862±51 barns for I 0 above 0.358 eV of 273Np. By setting the Cd cut-off energy at 0.358 eV considering the resonance at 0.49 eV, a smaller value of σ0 was obtained in this work than the values reported by the previous authors.

Solubility product of plutonium hydrous oxide and its ionic strength dependence

Summary The solubility of PuO2·xH2O was measured at 25°C in a NaClO4 solution containing Na2S2O4 as a reductant. The experiment was carried out by an oversaturation method at I = 1.0 and by an undersaturation method at I = 0.5, 1.0 and 2.0. The concentration of Pu3+ was measured by α-spectrometry and UV/Visible spectrophotometry, and the equilibrium constant of the reaction, PuO2·xH2O + e− = Pu3+ + 4 OH− + (x–2) H2O, was obtained. From the obtained results, the solubility product (Ksp) of PuO2·x H2O, for PuO2·x H2O = Pu4+ + 4 OH− + (x − 2) H2O at I = 0.5, 1.0 and 2.0 was determined. By using the specific interaction theory (SIT), the solubility product of PuO2·x H2O at the standard state (I = 0) was determined to be log K°sp = −57.97 ± 0.24, and the ion interaction coefficient ε(Pu4+, ClO4-) was also evaluated to be 0.99 ± 0.20.

Solubility of uranium(IV) hydrous oxide in high pH solution under reducing condition

Summary The solubility of uranium(IV) hydrous oxide was measured at 25 °C in NaClO4 solution containing Na2S2O4 as a reducing agent in the pH range from 12 to 14. The experiment was carried out from oversaturation at I = 0.5, 1.0 and 2.0 mol/dm3 (M). The solubility data were analyzed to obtain the hydrolysis constants (βm) of U(OH)m(4-m). By taking the specific ion interaction theory (SIT) for ionic strength corrections and by using the solubility product log Ksp° = −53.93 ± 0.20, the hydrolysis constants at I = 0, log β5°<48.10 and log β6° = 48.95 ± 1.01, were determined together with the ion interaction coefficients of U(OH)5− and U(OH)62−.

Solubility product of hexavalent uranium hydrous oxide

The solubility of U(VI) hydrous oxide was measured in the hydrogen ion concentration (pHc) range from 4 to 6 at 25±1°C in a NaClO4 solution. The experiment was carried out by oversaturation method at ionic strength I=0.1, 0.5 and 1.0 and by undersaturation method at I=1.0. The solid phase was found to be composed of a mixture of UO3.2H2O and UO2 (OH)2 by XRD. The concentration of U(VI) was measured by inductively coupled plasma mass spectrometry (ICP-MS), and was analyzed to obtain the solubility products (Ksp ), by taking into account the participation of the U(VI) hydrolysis species such as (UO2)2 (OH)2 2+ By using the literature values of the hydrolysis species and by using the specific interaction theory (SIT), the log Ksp ° value at the standard state (I=0) was determined to be log Ksp °=—22.46±0.10. Possible differences in the log Ksp° values due to different solid phases were recognized.

Solubility product of Pu(VI) hydrous oxide

Abstract The solubility of Pu(VI) hydrous oxide was measured in the pHc range from 4 to 5.5 at 25±1°C in a NaClO4 solution containing O3 gas. The experiment was carried out by oversaturation and undersaturation methods at ionic strength I=0.1, 0.5 and 1.0. The concentration of Pu(VI) was measured by α-spectrometry and UV/visible spectrophotometry, and the equilibrium constant of the reaction, PuO2(OH)2=PuO22+ + 2 OH-, was obtained. From the obtained results, the solubility products (Ksp) of Pu hydrous oxide at I=0.1, 0.5 and 1.0 were determined. The experimental values were extrapolated to the standard state (I=0) by using the specific interaction theory (SIT), and the solubility product of Pu hydrous oxide was determined to be log Ksp°=-22.88±0.39. The ion interaction coefficient (PuO22+, ClO4-) was also evaluated to be 0.30±0.09.

Hydrolysis constants of tetravalent neptunium by using solvent extraction method

Abstract The hydrolysis constants of tetravalent neptunium (Np(IV)) were determined by solvent extraction method using thenoyltrifluoroacetone(TTA). In order to avoid colloid formation, a stock solution of carrier-free 239Np(V) was from 243Am milked. The valence of Np in the solution was then reduced to Np(IV) by using zinc amalgam. The hydrolysis constants (βm) of the reactions, Np4++mOH−=Np(OH)m(4−m)+ was evaluated by using distribution ratios at ionic strengths (I)=0.1, 0.5 and 1.0. All experiments were performed in oxygen- free 0.5% H2−N2 atmosphere (below 1.0 ppm of O2) in a glovebox at room temperature (23±2 °C) to avoid oxidation of Np(IV). The βm values were extrapolated to the standard state (I=0) by using the specific ion interaction theory (SIT), and the formation constants at I=0 were determined to be logβ1°=13.91±0.23, logβ2°=27.13±0.15, logβ3°=37.70±0.30 and logβ4°=46.16±0.30. The ion interaction coefficients were also evaluated to be ε(NpOH3+, ClO4−)=0.49±0.15, ε(Np(OH)22+, ClO4−)=0.35±0.11, and ε(Np(OH)3+, ClO4−)=0.29±0.15.

Systematics of Complexation Constants of Actinide Ions with Inorganic Ligands

Systematic trends of complexation constants of actinide ions with inorganic ligands such as carbonate and fluoride were analyzed by using an improved hard sphere model. The effective charges of actinide ions were introduced into the model by considering possible contributions of non-electrostatic interactions of actinide ions in addition to those of ordinary electrostatic ones. The systematic trends of complexation constants were well fitted by the present model, and the effective charges and radii of the ligands were obtained together with those of actinide ions.