Yoshihiro Kitatsuji

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.

Extraction Behavior of Actinides and Metal Ions by the Promising Extractant, N,N,N′,N′-Tetraoctyl-3,6-dioxaoctanediamide (DOODA)

Abstract The extraction of actinides, fission products, some non-nuclear elements, and nitric acid by N,N,N′,N′-tetraoctyl-3,6-dioxaoctanediamide (DOODA-C8) in dodecane was extensively studied. Also studied was the extraction of HNO3 and Nd(III) by the tetradodecyl analog of DOODA-C8 in dodecane. Both extractants contain two ether oxygen atoms in the backbone chain carrying the two amide groups and can thus act as tetradentate ligands. The extractability of actinides decreases in the order Pu(IV) > U(VI), Am(III) > Np(V) in the extraction from nitric acid and Pu(IV) > Am(III) >> U(VI) in the extraction from perchloric acid. Ions of di-, tri-, tetra-, hexa-, and heptavalent metals strongly differ in the extractability by DOODA-C8 but, except for lanthanides(III), there is no visible correlation of their distribution ratios with ionic radii. Due to the efficient extraction of actinides, weak extraction of fission products, and sufficient extraction capacity, DOODA-C8 is a promising extractant for the recovery of minor actinides from high-level radioactive wastes.

Novel Extractant, NTAamide, and its Combination with TEDGA for Mutual Separation of Am/Cm/Ln

A novel extractant, N,N,N′,N′,N′′,N′′-hexaalkyl-nitrilotriacetamide (NTAamide), was developed for the extraction and separation of actinides (An) and lanthanide (Ln). NTAamide has a nitrogen atom in the center of a backbone and is bonded to three acetamide groups; the nitrogen and three amide oxygen atoms can work as the donor atoms. NTAamide extracted Am and Cm with a low distribution ratio of Ln in diluted HNO3, and the separation factor (SF) for An/Ln was equal to or higher than 23.6 using 0.5 M NTAamaide/n-dodecane and 0.2 M HNO3. The addition of N,N,N′,N′-tetraethyldiglycolamide as a masking agent to the NTAamide extraction system was effective for separating Am from Cm; the maximum SF was 6.5, one of the highest SF values obtained using the HNO3 and n-dodecane system.

Development of an electrochemistry apparatus for the heaviest elements

Summary We developed a new apparatus for the study of electrochemical properties of the heaviest elements. The apparatus is based on a flow electrolytic cell combined with column chromatography. Glassy-carbon fibers modified with Nafion perfluorinated cation-exchange resin are used as a working electrode as well as a cation-exchanger. The elution behavior of 139Ce with the number of 1010 atoms in 0.1 M ammonium α-hydroxyisobutyric acid solution from the column electrode was investigated at the applied potentials of 0.2–1.0 V versus the Ag/AgCl reference electrode in 1.0 M LiCl. It was found that 139Ce3+ is successfully oxidized to 139Ce4+ even with tracer concentration at around the redox potential determined by cyclic voltammetry for the macro amounts of Ce with 1017 atoms (10−3 M). The present oxidation reaction and separation of Ce4+ was accomplished within a few minutes.

Oxidation of Element 102, Nobelium, with Flow Electrolytic Column Chromatography on an Atom-at-a-Time Scale

We report here on the successful oxidation of element 102, nobelium (No), on an atom-at-a-time scale in 0.1 M alpha-hydroxyisobutyric acid (alpha-HIB) solution using a newly developed technique, flow electrolytic column chromatography. It is found that the most stable ion, No(2+), is oxidized to No(3+) within 3 min and that the oxidized No complex with alpha-HIB holds the trivalent state in the column above an applied potential of 1.0 V.

Development of a new extractant and a new extraction process for minor actinide separation

Many kinds of new extractants have been studied for the separation of minor actinides, Am and Cm in particular, from high-level liquid waste (HLLW) which is generated from spent fuel reprocessing for the recovery of U and Pu. The authors have developed a new type of extractant for the extraction of Am and Cm, N,N,N,N-tetraoctyldiglycolamide (TODGA) which is one of the diamides and shows the tridentate feature. To apply such a new extractant to the separation process for Am and Cm from HLLW, many criteria should be investigated and satisfied; e.g., high separation factor between An(III) and fission products, chemical and radiolytic stability, high extraction capacity, fast kinetics, compatibility with hydrocarbon diluents, controllability for the behaviour of U, Pu and Np which exist as residue of the former step, and so on. TODGA is fully soluble in n-dodecane, but has a relatively low extraction capacity. Therefore, TODGA was modified and a new DGA extractant, N,N,N,N-tetradodecyldiglycolamide, was developed, which can extract Ln with one-third of the extractant concentration. Since both TODGA and TDdDGA extract Zr and Pd, effective masking agents for them were examined and selected. To extract Np quantitatively, the method to reduce Np(V) to Np(IV) was studied. With those achievements, a counter-current extraction test with 0.1M TDdDGA in n-dodecane and simulated solution of HLLW was carried out using a small-scale mixer-settler. As results of the counter-current extraction test, very clear phase separation was observed without any crud formation during the operation and quantitative recovery of Nd which is a substitute for Am was obtained.

Development of a new continuous dissolution apparatus with a hydrophobic membrane for superheavy element chemistry

A new technique for continuous dissolution of nuclear reaction products transported by a gas-jet system was developed for superheavy element (SHE) chemistry. In this technique, a hydrophobic membrane is utilized to separate an aqueous phase from the gas phase. With this technique, the dissolution efficiencies of short-lived radionuclides of 91m,93mMo and 176W were measured. Yields of more than 80xa0% were observed for short-lived radionuclides at aqueous-phase flow rates of 0.1–0.4xa0mL/s. The gas flow-rate had no influence on the dissolution efficiency within the studied flow range of 1.0–2.0 L/min. These results show that this technique is applicable for on-line chemical studies of SHEs in the liquid phase.

Measurement of the Md3+/Md2+ Reduction Potential Studied with Flow Electrolytic Chromatography

The reduction behavior of mendelevium (Md) was studied using a flow electrolytic chromatography apparatus. By application of the appropriate potentials on the chromatography column, the more stable Md(3+) is reduced to Md(2+). The reduction potential of the Md(3+) + e(-) → Md(2+) couple was determined to be -0.16 ± 0.05 V versus a normal hydrogen electrode.

Chemical studies of Mo and W in preparation of a seaborgium (Sg) reduction experiment using MDG, FEC, and SISAK

The extraction and reduction behavior of Mo and W, lighter homologs of Sg, was studied in continuous on-line experiments at the JAEA tandem accelerator to develop a new chemistry assembly consisting of a membrane degasser (MDG), a flow electrolytic column (FEC), and the continuous liquid–liquid extraction apparatus (SISAK). Extraction yields of Mo and W from 0.1xa0M HCl/0.9xa0M LiCl into 4-isopropyltropolone (hinokitiol, HT) in toluene were investigated. In the reduction experiment, Mo(VI) was successfully reduced to a lower oxidation state while W(VI) showed no reduction under the given conditions.

Raman spectroscopic study on NpO 2 + –Ca 2+ interaction in highly concentrated calcium chloride

Coordination circumstance of neptunyl ion in concentrated CaCl2 solutions was analyzed by Raman spectrometry. Besides the symmetric stretch (ν1) mode of NpO2+ and NpO22+, the asymmetric stretch (ν3) mode of NpO2+ was found. The Raman intensity of the ν3 mode increased with the concentration of CaCl2 in the system. This would be attributable to the cation–cation interaction between Np(V) and Ca(II).