Toshihide Asakura

Preparation of Novel Silica-Based Nitrogen Donor Extraction Resins and Their Adsorption Performance for Trivalent Americium and Lanthanides

In this work, we have synthesized several 2,6-bis(5,6-dialkyl-1,2,4-triazine-3-yl)pyridine (R-BTP) ligands with different alkyl groups (C=1∼3) and prepared the novel silica-based extraction resins by impregnating the ligands into the SiO 2 -P support. Furthermore, the adsorption performance of Am(III) and Ln(III) from nitrate acidic solution onto these novel silica-based nitrogen donor extraction resins was investigated experimentally.

The Adsorption Properties and Kinetics of Uranium(VI) with a Novel Fibrous and Polymeric Adsorbent Containing Amidoxime Chelating Functional Group from Seawater

The adsorption properties of U(VI) with a new type of fibrous and polymeric adsorbent containing amidoxime chelating functional group (FPAO) from seawater was studied by the method of the static state adsorption at 25 °C. The optimum conditions of the adsorption were determined by investigating the influence of the concentrations of FPAO, U(VI), feed acidity, temperature, and the shape and size of FPAO on the adsorption equilibrium. The maximum adsorption capacity of U(VI) in theory was deduced to be 384.6 mg/g dry FPAO by Langmuir isothermic adsorption equation. Freundlich isothermic adsorption equation, expressed as Q=4.116[U(VI)]0.4293, shows that this process can taken place easily because the adsorption factor 1/n equals to 0.4293, which is in the region of 0.1–0.5. Meanwhile, the adsorption kinetics of U(VI) with FPAO was also studied. The rate equation of the adsorption reaction was determined as −d[U(VI)]/dt=k[U(V)]FPAO]1.70/[H+] and the rate constant of the adsorption reaction k was calculated to be 0.5912 min−1 for pH 6.0 and ionic strength 0.1 mol/l. The activation energy of the adsorption reaction was calculated to be 28.54 kJ/mol. On the basis of the kinetics results, the adsorption mechanism of FPAO on U(VI) was discussed. The diffusion of uranium ion in internal of the adsorbent was thought to be the rate-controlling step.

Dynamic-state Adsorption and Elution Behaviour of Uranium(VI) Ions from Seawater by a Fibrous and Porous Adsorbent Containing Amidoxime Chelating Functional Groups

To develop an advanced recovery process of uranium from seawater using a macroporous fibrous polymeric material containing amidoxime chelating functional groups (FPAO), the static- and dynamic-state adsorption behaviours of U(VI) ions onto a new type of FPAO were investigated at pH 6.0. It was found that the flow rate and the column specification had a distinct influence on the adsorption of U(VI) ions onto FPAO. When the flow rate was varied from 0.95 ml/min to 3.75 ml/min, the amount of U(VI) ions adsorbed decreased from 379.3 mg/g to 340.6 mg/g while the corresponding equilibrium time diminished from 41.2 h to 10 h. When two types of column of different diameter (Φ) and height (h) were employed, viz. Φ 9.4 mm × h 525 mm and Φ 15.5 mm × h 290 mm, the amounts of U(VI) ions adsorbed and the corresponding equilibrium times were 340.6 mg/g and 10 h and 325.9 mg/g and 13.6 h, respectively, at a constant flow rate of 3.70 ml/min. The use of hydrochloric acid as an eluant for U(VI) ions was also examined by varying its concentration, elution flow rate and the column dimensions. Hydrochloric acid eluted U(VI) ions effectively from the loaded FPAO when employed in the concentration range 0.5–1.0 M. The percentage recovery of U(VI) ions calculated under all elution conditions was greater than 99%.

Preparation of Novel Silica-Based R-BTP Extraction-Resins and Their Application to Trivalent Actinides and Lanthanides Separation

To separate long-lived minor actinides and specific fission products such as Zr and Mo from nitrate acidic high-level liquid waste, we have been studying an advanced partitioning process by extraction chromatography using a minimal organic solvent and compact equipment. In this work, we have synthesized several new type of nitrogen donor ligands, 2,6-bis-(5,6-dialkyl-1,2,4 -triazine-3-yl)-pyridine with different alkyl groups and prepared the novel silica-based extraction-resins by impregnating these ligands into the SiO2-P support with a diameter of 50 μm. The adsorption performance of 243Am(III) and typical fission product Ln(III) from nitrate solution on these extraction-resins was investigated. It was found that the adsorption behavior depends strongly on the alkyl group in R-BTP. «Bu-BTP/SiO2-P and wHex-BTP/SiO2-P showed significantly higher adsorbability and selectivity for Am(lH) over Ln(m). The separation factor is about 104 for Am/Ce and near 102 for Am/Eu-Gd, respectively. It is expected that Am(III) can be effectively separated from Ln(HT) by extraction chromatography using these novel R-BTP/SiO2-P extraction-resins.

Electrochemical and spectroelectrochemical behaviour of Np(VI) ions in nitric acid solutions

Summary Electrochemical and spectroelectrochemical has been used to investigate the behaviour of neptunium (VI) in 1 ∼ 8 M HNO3 solutions. The electrochemical reactions of Np(VI) ions were found to occur quasi-reversibly. The formal redox potentials (E°) for Np(VI)/Np(V) couples were determined to be +0.906, +0.908, +0.909, +0.902, +0.896, +0.895, +0.888, and +0.884 V (vs . Ag/AgCl) for Np(VI) ions in 1, 2, 3, 4, 5, 6, 7, 8 M HNO3 solutions, respectively. The reduction processes of Np(VI) ions were followed spectroelectrochemically by using an optical transparent thin layer electrode cell. It was found that the absorption spectra measured at the applied potentials from +1.10 to +0.60 V versus Ag/AgCl reference electrode redox couple for Np(VI) in HNO3 solution have clear isosbestic points. These results indicate that the only reduction product of Np(VI) is Np(V), which is of considerable stability in HNO3 solutions.

Electrochemical redox reactions of uranium(VI) complexes with multidentate ligands in dimethyl sulfoxide

Abstract Electrochemical reactions of UO2(β-diketonato)2-dmso, UO2(trop)2dmso, UO2(sap)(dmso)2, and UO2(salen)dmso (dmso = dimethyl sulfoxide, β-diketonate = benzoylacetonate (ba), benzoyltrifluoroacetonate (btfa), and thenoyltrifluoroacetonate (ttfa), trop = tropolonate, sap = 2-salicylidenaminophenolate, and salen = N , N´-disalicylidenethylenediaminate) complexes in dmso solutions containing tetrabutylammonium perchlorate as a supporting electrolyte have been studied with cyclic voltammetry. These uranyl(VI) complexes were found to be reduced quasi -reversibly to U(V) species. The formal redox potentials (E°, vs . ferrocen/ferrocenium) for U(VI)/U(V) couples were determined to be -1.416 V for UO2(ba)2dmso, -1.073 V for UO2(btfa)2dmso, -1.082 V for UO2(ttfa)2dmso, -1.379 V for UO2(trop)2dmso, -1.500 V for UO2(sap)(dmso)2, and -1.602 V for UO2(salen)dmso. Furthermore, the resulting U(V) complexes, [UO2(btfa)2dmso]-, [UO2(ttfa)2dmso]-, and [UO2(salen)dmso]-, were found to be able to exist stably in dmso solutions.

Solvent Extraction Behavior of Minor Nuclides in Nuclear Fuel Reprocessing Process

The solvent extraction behavior of minor nuclides such as neptunium and technetium in a current PUREX process and an advanced PUREX process (PARC process) were studied by chemical flow sheet experiments using spent nuclear fuels. The uranium, plutonium, neptunium and technetium fractions distributed in the products and raffinates of the PARC process showed that n-butyraldehyde was an effective reductant of neptunium(VI) in the presence of uranium(VI) and plutonium(IV). It was also found that scrubbing with high acid concentration was effective for technetium separation.

THE SEPARATION OF NEPTUNIUM AND TECHNETIUM IN AN ADVANCED PUREX PROCESS

ABSTRACT An advanced PUREX process has been developed which can reduce TRU waste volume and the environmental hazard risk due to long-lived nuclides. The separation of neptunium and technetium from plutonium and uranium solutions has been studied before the U/ Pu partitioning step in the PUREX process. The effectiveness of normal-butyraldehyde as a reductant of Np( VI) to Np( V) and of high acid scrubbing of technetium was shown in a basic study and a chemical flowsheet study.

Reduction kinetics of Np(VI) by n-butyraldehyde in tributyl phosphate diluted with n-dodecane

Summary The reduction kinetics of Np(VI) by n-butyraldehyde in 30% TBP solution diluted with n-dodecane were analyzed by spectrophotometry. Based on the results of both n-butyraldehyde and nitric acid concentration dependences on the Np(VI) reduction reaction, the rate equation was obtained as –d[Np(VI)]/dt=k[n-C3H7CHO]0.8[HNO3]–2.0[Np(VI)]t where k=(1.0±0.2)× 10–3 M1.2 min–1 at 294±1 K. The activation energy of the reaction was 76±5 kJ/mol.

Study on Reduction of Neptunium and Uranium In Nitric Acid Solution Using Flow Type Electrolytic Cell, as a Basic Technique for Advanced Reprocessing Process

The reduction of neptunium and uranium was studied using a flow type electrolytic cell containing a carbon-fiber column electrode. Np (VI) (10-3 mol.l1) in 3 mol.l-1 HNO3 solution was quantitatively reduced into Np (V) at the potential of 0.3 V vs. Ag/AgCl using the cell. Reduction of U (VI) (0.1 mol.l-1) into U (IV) with co-existing Np and Tc at –0.3 V vs. Ag/AgCl in 6 mol.l-1 HNO3 solution was also demonstrated.