Takaumi Kimura

Luminescence study on hydration states of lanthanide(III)–polyaminopolycarboxylate complexes in aqueous solution

Abstract The hydration states of lanthanide (Ln)(III) complexes (Ln=Sm, Eu, Tb and Dy) with a series of polyaminopolycarboxylate ligands were evaluated in detail on the basis of the linear correlation between the luminescence decay constants k obs and the inner-sphere hydration number N H 2 O in D 2 O–H 2 O solutions. The k obs of Ln(III) complexes in D 2 O showed that these ligands were not effective in causing non-radiative de-excitation of the excited states for these ions. The N H 2 O of Sm(III) in a certain polyaminopolycarboxylate complex was apparently larger than those of Eu(III), Tb(III) and Dy(III) in the complexes. These results suggest that the empirical formulae proposed in this study are valid for the calibration of k obs vs. N H 2 O and that the total coordination number, i.e. the sum of the number of ligand donor groups and the N H 2 O of Sm(III) is possibly unity larger than those of Eu(III), Tb(III) and Dy(III) in the complexes.

An Additional Insight into the Correlation between the Distribution Ratios and the Aqueous Acidity of the TODGA System

Abstract Extraction of Eu(III) and Am(III) from HNO3 into the organic solvents using N,N,N′,N′‐tetraoctyl‐diglycolamide (TODGA) was investigated in order to study the detailed extraction reaction. The chemical species: 1:2 for metal:TODGA complex is present in polar diluents. On the other hand, the metal complexes need three or more TODGA molecules to remain stable in non‐polar diluents. The HNO3 concentration dependence on the distribution ratio suggests that HNO3 participates in the metal extraction. Infrared spectra indicate that the carbonyl oxygen coordinates with Eu(III), and luminescence lifetimes suggest that there are no water molecules in the inner coordination sphere of the extracted Eu‐complex.

Extraction and separation of Am(III) and Sr(II) by N, N, N', N'-tetraoctyl-3-oxapentanediamide (TODGA)

Summary By using an extractant, N,N,N´,N´-tetraoctyl-3-oxapentanediamide (TODGA), extraction and separation of Sr(II) from Am(III) were investigated for the partitioning of high level liquid waste (HLLW). Both metal ions, accompanied with the counter anion, NO3-, and HNO3 without dissociation, were extracted by TODGA. We used two distinct methods for the separation of Am(III) and Sr(II). A mixture of TODGA and monoamide reduced the distribution ratio D of Sr(II) compared to that without monoamide, whereas D(Am) was still high value under the identical condition. After extraction of Am(III) by TODGA and monoamide, Sr(II) remaining in HLLW can be extracted by using enough concentration of TODGA at the next step. In the other method, Sr(II) was coextracted with Am(III) by TODGA. It was observed that D(Sr) decreased with an increase of HNO3 from 3 M to 6 M HNO3 at the same TODGA concentration, while D(Am) increased until 6 M HNO3. By using 6 M HNO3, Am(III) and Sr(II) were separated after coextraction.

Luminescence study on the inner-sphere hydration number of lanthanide(III) ions in concentrated aqueous salt solutions in fluid and frozen states

Luminescence lifetimes of lanthanide[Ln](III) ions [Ln=Sm, Eu, Tb and Dy] in concentrated aqueous solutions at room and at liquid nitrogen temperatures were measured by means of time-resolved laser-induced luminescence spectroscopy. The inner-sphere hydration number NH2O of Ln(III) was estimated on the basis of the correlation between the NH2O and the lifetime obtained in D2O–H2O solutions at each temperature. In fluid states of sodium chloride, nitrate and perchlorate solutions at room temperature, the NH2O of the Ln(III) ions indicate that nitrate ion forms inner-sphere complex with these ions, whereas chloride and perchlorate ions do not, and that the concentrated perchlorate ion would perturb the hydration structure of Ln(III). In frozen states of the solutions at liquid nitrogen temperature, the formation of the inner-sphere chloro and nitrate complexes of Ln(III) is suggested in chloride and nitrate solutions, respectively, but not in perchlorate solution.

Direct observation of Cm(III)-fulvate species on fulvic acid-montmorillonite hybrid by laser-induced fluorescence spectroscopy

Particulate matter plays an important role in the removal of metal ions from water in natural aquifers. Some of the most important of these materials consist of associations of inorganic particles (clay minerals, oxides) with humic substances, associations that can form readily in such an environment due to the strong affinity between inorganic particles and humic substances. These associations are referred to in this paper as organic-inorganic hybrids. However, it is not clear whether the sorbed species of metal ions in such organic-inorganic hybrids are organic or inorganic species because of the complexity of such hybrids and the lack of appropriate methods for characterizing the trace metal ions incorporated in them. In this study, laser-induced fluorescence spectroscopy (LIF) was used successfully to characterize the Cm(III) species on an FA(fulvic acid)-montmorillonite hybrid, an example of such organic-inorganic hybrids. The LIF clearly showed that Cm(III) can be sorbed as Cm(III)-fulvate complex in the FA-montmorillonite hybrid. These results were consistent with those of experiments of solid-water partitioning of Cm(III) (or Eu(III) used as an analogue) and speciation calculations based on the stability constants of Cm(III)-fulvate complexes determined in this study. The results of LIF and the partitioning experiments showed that the solid-water distribution of humic substances governed that of Cm(III) under our experimental conditions. The Cm(III) preference for forming Cm(III)-fulvate complexes was also evident under a condition that would be found in a natural aquifer with a fairly low concentration of organic matter in freshwater (dissolved organic carbon: 2 mg/dm3), as determined by our speciation calculations. These findings on the importance of humic substances in the migration of Cm(III) indicate that the clarification of the environmental behavior of humic substances is necessary to understand fully the behavior of Cm(III), or actinide(III) and lanthanide(III) ions, in natural aquifers.

Luminescence study on solvation of americium(III), curium(III) and several lanthanide(III) ions in nonaqueous and binary mixed solvents

The luminescence lifetimes of An(III) and Ln(III) ions [An=Am and Cm; Ln=Nd, Sm, Eu, Tb and Dy] were measured in dimethyl sulfoxide(DMSO), N,N-dimethylformamide(DMF), methanol(MeOH), water and their perdeuterated solvents. Nonradiative decay rates of the ions were in the order of H2O > MeOH > DMF > DMSO, indicating that O-H vibration is more effective quencher than C-H, C=O, and S=O vibrations in the solvent molecules. Maximal lifetime ratios τD/τH were observed for Eu(III) in H2O, for Sm(III) in MeOH and DMF, and for Sm(III) and Dy(III) in DMSO. The solvent composition in the first coordination sphere of Cm(III) and Ln(III) in binary mixed solvents was also studied by measuring the luminescence lifetime. Cm(III) and Ln(III) were preferentially solvated by DMSO in DMSO-H2O, by DMF in DMF-H2O, and by H2O in MeOH-H2O over the whole range of the solvent composition. The order of the preferential solvation, i.e., DMSO > DMF > H2O > MeOH, correlates with the relative basicity of these solvents. The Gibbs free energy of transfer of ions from water to nonaqueous solvents was further estimated from the degree of the preferential solvation.

Luminescence study on determination of the hydration number of Sm(III) and Dy(III)

Abstract A luminescence study of Ln(III) ion has revealed a linear correlation between the decay constant kobs (the reciprocal of the excited-state lifetime) and the number of water molecules nH2O in the first coordination sphere of complexes. From measurements of kobs of Ln(III) in D2OH2O solutions and of Ln(BrO3)3 · 9H2O, the nH2O of Sm(III) and Dy(III) in H2O were calculated to be 9.0 ± 0.5 and 8.4 ± 0.4 respectively. Using Ln(III) complexes of polyaminopolycarboxylate ligands, empirical formulae for the calibration of kobs (ms−1) vs. nH2O were proposed as nH2O = 0.026kobs − 1.6 for Sm(III) and nH2O = 0.024kobs − 1.3 for Dy(III).

Luminescence study on determination of the inner-sphere hydration number of Am(III) and Nd(III)

Abstract A correlation between the luminescence decay constant k obs (the reciprocal of the excited state lifetime) and the inner-sphere hydration number N H 2 O of Am(III) and Nd(III) in aqueous solution was investigated to establish a method for determining the N H 2 O from measurements of the luminescence lifetime. The calibration relations were proposed on the basis of the linear correlation of the k obs vs. volume percentage of H 2 O in D 2 O–H 2 O solutions and the N H 2 O in H 2 O, i.e. nine for Am(III) and Nd(III). The k obs of Am(III) and Nd(III) complexed with a series of polyaminopolycarboxylate ligands in H 2 O and D 2 O were measured to validate the calibration relations, and the N H 2 O and coordination numbers of these ions in the complexes were evaluated and compared with the other luminescent ions systematically.

Extraction Behavior of Metal Ions by TODGA, DOODA, MIDOA, and NTAamide Extractants from HNO3 to n-Dodecane

Four novel diamide and triamide extractants developed in our group, TODGA, DOODA, MIDOA, and NTAamide, were examined to see the extractability trends of up to 74 metal ions from nitric acid into n-dodecane. TODGA and DOODA have one or two etheric and two amidic oxygen donor atoms, and MIDOA and NTAamide have a nitrogen donor atom centered in the backbones and two or three diamidic O atoms. The former two extractants are expected to have high extractability for metal ions classified as hard acids and the latter ones have higher extractability for soft acids. TODGA and DOODA have high distribution ratios, D, for metal ions in the 2A-4A groups. On the other hand, MIDOA and NTAamide have high D values for group 5A-7A and 8 metal ions, which follows HSAB theory. The positive relation between the slope values of the extractant dependence and the extraction constant, α, is found, which suggests that a high order of successive formation of metal complexes with extractants gives high extractability.

Aqueous Solutions of Uranium(VI) as Studied by Time-Resolved Emission Spectroscopy: A Round-Robin Test

Results of an inter-laboratory round-robin study of the application of time-resolved emission spectroscopy (TRES) to the speciation of uranium(VI) in aqueous media are presented. The round-robin study involved 13 independent laboratories, using various instrumentation and data analysis methods. Samples were prepared based on appropriate speciation diagrams and, in general, were found to be chemically stable for at least six months. Four different types of aqueous uranyl solutions were studied: (1) acidic medium where UO22+aq is the single emitting species, (2) uranyl in the presence of fluoride ions, (3) uranyl in the presence of sulfate ions, and (4) uranyl in aqueous solutions at different pH, promoting the formation of hydrolyzed species. Results between the laboratories are compared in terms of the number of decay components, luminescence lifetimes, and spectral band positions. The successes and limitations of TRES in uranyl analysis and speciation in aqueous solutions are discussed.