Hajimu Yamana

Electrochemical investigation of uranium β-diketonates for all-uranium redox flow battery

Abstract The redox flow battery using uranium as the negative and the positive active materials in polar aprotic solvents was proposed. In order to establish the guiding principle for the uranium compounds as the active materials, the investigation of uranium β-diketonate complexes was conducted on (i) the solubility of active materials, (ii) the electrode reaction of U(VI) and U(IV) β-diketonate complexes and (iii) the estimation of the open circuit voltage of the battery. The solubilities of higher than 0.8 mol dm −3 of U(VI) complexes and higher than 0.4 mol dm −3 of a U(IV) complex were obtained in the solvents. The electrode reactions of U(pta) 4 , UO 2 (dpm) 2 , UO 2 (fod) 2 and UO 2 (pta) 2 were first studied and the redox potentials of uranium β-diketonates were thermodynamically discussed. The open circuit voltage is estimated more than 1 V by using Hacac or Hdpm. The larger open circuit voltage is expected when a ligand with the larger basicity is used.

Analysis of cesium isotope compositions in environmental samples by thermal ionization mass spectrometry – 1. A preliminary study for source analysis of radioactive contamination in Fukushima prefecture

Cesium was recovered from plant samples obtained from Fukushima prefecture. The isotopic ratios of 134Cs/137Cs and 135Cs/137Cs were analyzed by thermal ionization mass spectrometry with a single filament method using a TaO activator. Samples containing 5 Bq of 137Cs were analyzed with typical analytical errors of approximately 0.5% for 134Cs/137Cs and approximately 0.1% for 135Cs/137Cs. Measurements of both ratios showed profiles that were characteristic of the measurements of among other environmental samples reported in the literature. The results showed the isotopic ratios of 134Cs/137Cs and 135Cs/137Cs were applicable for the source analysis of radioactive Cs in Fukushima prefecture.

Redox Equilibrium of U4+/U3+ in Molten NaCL-2CsCL by UV-Vis Spectrophotometry and Cyclic Voltammetry

In order to investigate the redox equilibrium of uranium ions in molten NaCL-2CsCL, UV-Vis absorption spectrophotometry measurements were performed for U4+ and U3+ in molten NaCL-2CsCL at 923 K under simultaneous electrolytic control of their ratio. Prominent absorption bands at 480 and 570 nm were assigned to U3+, and their molar absorptivities were determined to be 1,260±42 and 963±32 mol−1.l.cm−1 respectively. From the dependence of the rest potential of the melt on the spectrophotometrically determined ratio of [U4+]/[U3+], the standard redox potential of the couple U4+/U3+ at 923K was determined to be −1.481±0.004 V vs. Cl2/Cl−. Cyclic voltammetry measurements were carried out for the couple U4+/U3+, and the results agreed well with this standard redox potential value. By the results of cyclic voltammetry, a temperature dependence of the standard redox potential was found to be −2.094+6.639×10−4 T (T=823-923 K).

An application of actinide elements for a redox flow battery

The electrochemical properties of U, Np, Pu and Am were discussed from the viewpoint of cell active materials. From the thermodynamic properties and the kinetics of electrode reactions, it is found that neptunium in the aqueous system can be utilized as an active material of the redox flow battery for the electric power storage. A new neptunium redox battery is proposed in the present article: the galvanic cell is expressed by The neptunium battery is expected to have more excellent charge and discharge performance than the current vanadium battery, whereas the thermodynamic one of the former is comparable to the latter. For the development of a uranium redox flow battery, the application of the redox reactions in the non-aqueous solvents is essential.

Study on Redox Equilibrium of UO2 2+/U2 + in Molten NaCl-2CsCl by UV-Vis Spectrophotometry

In order to enhance the understanding of the redox equilibriums of uranyl ions in molten NaCl-2CsCl eutectic salt UV-Vis absorption spectrophotometry measurements were performed for UO2 2+ in molten NaCl-2CsCl at 923 K under simultaneous electrolytic control of their ratio. A prominent absorption band at 395 nm was assigned to UO2 +, and its molar absorptivity was determined to be 832±27 mol-1·l·cm-1. From the dependence of the rest potential of the melt on the spectrophotometrically determined ratio of [UO2 2+]/[UO2 +], the standard redox potential of the couple UO2 2+/UO2 + was determined to be −0.903±0.007 V vs. Cl2/Cl—.

Electronic absorption spectra of lanthanides in a molten chloride. I. Molar absorptivity measurement of neodymium(III) in molten eutectic mixture of LiCl-KCl

Abstract In order to enhance the basic understanding of the chemical constitution of lanthanides and actinides in molten salts, a new apparatus for high-temperature absorption spectrometry was developed. For the first experiment, by changing the concentration of NdCl3, the electronic absorption spectra of Nd(III) in LiCl–KCl eutectic at 873 K were measured in the wavelength region of 290∼890 nm. The molar absorptivities of detectable transitions were precisely determined.

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.

Extraction of molybdenum from nitric acid by octyl(phenyl)-N,N-diisobutylcarbamoylmethyl-phosphine oxide

The extraction behavior of molybdenum(VI) under the conditions of transuranium extraction (TRUEX) process was studied by using octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide. The extraction behavior of molybdenum(VI) under the condition of PUREX process was also investigated for comparison. The extraction of molybdenum with the copresence of uranium(VI), dysprosium(III), and the effect of oxalic acid were examined. Under the PUREX conditions, molybdenum was less extractable, while under the TRUEX process conditions, a higher distribution ratio of molybdenum was observed. Under the TRUEX conditions, the addition of oxalic acid was effective in depressing molybdenum extraction. It was concluded that, at the concentration of nitric acid around 1 mol dm−3 or higher, Mo(VI) is extracted predominantly as cationic species, while at lower concentration of nitric acid, the coextraction of anionic molybdenum as a mixed complex with other metal, that is, UO2 2+, occurs.

Effect of nitric acid distribution on extraction behavior of trivalent F-elements in a TRUEX system

Abstract The extraction characteristics of nitric acid with a typical TRUEX (transuranic elements extraction) solvent, the mixture of octyl(phenyl)‐N,N‐ diisobutylcarbamoylmethylphosphine oxide and tri‐n‐butyl phosphate dissolved in n‐dodecane, were studied. From the extraction results of lanthanum, the concentration of CMPO, which was not bound to metal ions or nitric acid, were estimated. The estimated concentration was appropriate in comparison with the extraction results of nitric acid. The applicability of the determined effective CMPO concentration to the formulation of the distribution equilibrium of other f‐elements was confirmed.

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.