Yasutoshi Ban

Extraction of Am(III) at the Interface of Organic-Aqueous Two-Layer Flow in a Microchannel

Extraction of Am(III) was performed at the interface of organic-aqueous two-layer flow in a micro-channel having an asymmetric cross section. A solution of 3 mol/dm3 nitric acid containing 243Am(III) and octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphineoxide diluted with n-dodecane were introduced into the microchannel as the aqueous phase and organic phase, respectively. The two phases formed a stable two-layer flow with an interface parallel to the sidewall of the microchannel, and they were separated from each other at the divergence point of the microchannel. The extraction reaction of Am(III) proceeded at the interface of the two phases, and reached the equilibrium state while the two phases passed through the microchannel.

Selective Extraction of U(VI) by Counter-Current Liquid-Liquid Extraction with N,N-di(2-Ethylhexyl)-2,2-Dimethylpropanamide

Abstract A continuous counter-current extraction experiment for the selective extraction of U(VI) using N,N-di(2-ethylhexyl)-2,2-dimethylpropanamide (DEHDMPA) as an extractant was carried out with mixer-settler type extractors consisting of a U extraction step, a scrub step, and a U back-extraction step. DEHDMPA selectively extracted U(VI) over Pu(IV), and the decontamination factor against Pu(IV) in the U fraction was 990. Fractional distributions of U(VI) in the U fraction and Pu(IV) in the raffinate were 94.5% and 99.9%, respectively. Numerical simulation for calculating U(VI) and Pu(IV) concentrations in each stage of the mixer-settlers was performed. The calculated values agreed with experimentally- measured U(VI) and Pu(IV) concentrations in the U extraction step, and also agreed with the experimentally-measured U(VI) concentrations in the scrub step.

Distribution of U(VI) and Pu(IV) by N,N-di(2-ethylhexyl)Butanamide in Continuous Counter-Current Extraction with Mixer-Settler Extractor

The extraction properties of 1.5 mol/dm3 (M) N,N-di(2-ethylhexyl)butanamide (DEHBA) with n-dodecane toward U(VI) and Pu(IV) were studied using a single stage batch method with different concentrations of nitric acid (0.1 – 4.9 M), U(VI) (38 μM – 0.38 M), and Pu(IV) (3.9 μM – 0.29 mM). The distribution ratios toward U(VI), D U, and Pu(IV), D Pu, were expressed by the following equations: and . These equations, and , respectively, indicate concentrations of nitrate ion and free DEHBA which can make complexes with U(VI) or Pu(IV). A continuous counter-current experiment with 1.5 M DEHBA as an extractant was performed using mixer-settler type extractors consisting of 5 steps: U-Pu extraction, scrub, U recovery, Pu back-extraction, and U back-extraction. The feed solution employed for the continuous counter-current experiment was 3 M nitric acid containing U(VI), Pu(IV), and simulated fission products. The ratios of U(VI) and Pu(IV) extracted by 1.5 M DEHBA in the U-Pu extraction step were more than 99.9%. The extracted Pu(IV) was scrubbed from the organic phase using 0.67 M nitric acid, and more than 97% of Pu(IV) in the feed was recovered in the Pu fraction. The present results indicated that DEHBA works as an extractant for mutual separation of U(VI) and Pu(IV) by adjusting the nitric acid concentration without using Pu(IV) reductants.

Application of N,N-di(2-ethylhexyl)butanamide for mutual separation of U(VI) and Pu(IV) by continuous counter-current extraction with mixer-settler extractors

Continuous counter-current extraction using N,N-di(2-ethylhexyl)butanamide (DEHBA) as an extractant was performed with mixer-settler type extractors consisting of U–Pu extraction, scrub, U recovery, Pu back-extraction, and U back-extraction steps. The feed solution used in the continuous counter-current extraction was 3 mol/dm3 (M) nitric acid containing U, Pu, and simulated fission products of Sr, Ba, Zr, Mo, Ru, Rh, Pd, and Nd. More than 99.9% of U and Pu in the feed was extracted by 1.9 M DEHBA at the U–Pu extraction step with negligible extraction of Sr, Ba, Mo, Ru, Rh, and Nd. The extracted Pu was back-extracted via contact with 0.3 M nitric acid in the Pu back-extraction step, and the ratio of Pu distributed to the Pu fraction stream was ∼ 82%. It was confirmed that 1.9 M DEHBA effectively recovered U in the U recovery step, and the ratio of U in the Pu fraction stream was less than 1%. The extracted U was back-extracted in the U back-extraction step, and more than 98% of U was recovered in the U fraction stream.

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.

Uranium and Plutonium Extraction from Nitric Acid by N,N-Di(2-Ethylhexyl)-2,2-Dimethylpropanamide (DEHDMPA) and N,N-Di(2-Ethylhexyl)Butanamide (DEHBA) using Mixer-Settler Extractors

Extraction properties of N,N-di(2-ethylhexyl)-2,2-dimethylpropanamide (DEHDMPA) for nitric acid, U(VI), and Pu(IV) were studied by a batch method using various nitric acid concentrations. The distribution ratio equations for nitric acid, U(VI), and Pu(IV) were derived. A continuous counter-current experiment was performed using mixer-settler extractors to determine the performance of a process that uses two types of monoamides, DEHDMPA and N,N-di(2-ethylhexyl)butanamide (DEHBA), as extractants. This process consisted of two cycles: one dedicated to extraction of U(VI) by DEHDMPA, and the other dedicated to the co-extraction of U(VI) and Pu(IV) by DEHBA. The feed solution used for the continuous counter-current experiment was 4 mol/dm3 nitric acid containing U(VI), Pu(IV), and simulated fission products. DEHDMPA exclusively extracted U(VI) from the feed at the 1st cycle, and the ratio of U recovered in the U fraction stream was 99.93%. The residual U and almost all Pu were extracted by DEHBA in the 2nd cycle, and the recovery of Pu in the U-Pu fraction stream was 99.94%. Concentration profiles of U and Pu in mixer-settlers were calculated using a simulation code, which confirmed that the calculation was effective for estimating the U concentration in the U fraction stream, and the U and Pu concentrations in the U-Pu fraction stream.

Recovery of U and Pu from Nitric Acid using N,N-di(2-ethylhexyl)butanamide (DEHBA) in Mixer-Settler Extractors

The recovery of U and Pu from nitric acid using N,N-di(2-ethylhexyl)butanamide (DEHBA) in mixer-settler extractors was calculated by a simulation code, and a continuous counter-current experiment using mixer-settler extractors was performed. The flow rate, stage number, and nitric acid concentration were chosen as the parameters for the calculation, and the simulation code provided appropriate experimental conditions for separating U from Pu. The continuous counter-current experiment was carried out with three mixer-settler extractors consisted of the following 5 steps: U–Pu extraction (6 stages), Scrub (10 stages), U recovery (6 stages), Pu back-extraction (10 stages), and U back-extraction (16 stages). The results of the continuous counter-current experiment showed that the percentages of U and Pu extracted using 1.5 mol/dm3 (M) DEHBA from 4 M nitric acid were > 99.9% and 97.84%, respectively. Extracted Pu was back-extracted to the aqueous phase via contact with 0.15 M nitric acid, while most of the U content remained in the organic phase. Uranium in the organic phase was then back-extracted via contact with 0.01 M nitric acid, and the percent of U in the U fraction stream was 96.06%. The percentages of U and Pu in the Pu fraction stream were 3.94 % and 97.48%, respectively.

Distribution Behavior of Neptunium by Extraction with N,N-dialkylamides (DEHDMPA and DEHBA) in Mixer-Settler Extractors

ABSTRACT The extraction properties of N,N-di(2-ethylhexyl)-2,2-dimethylpropanamide (DEHDMPA) and N,N-di(2-ethylhexyl)butanamide (DEHBA) for Np(V) and Np(VI) were studied by a batch method using various nitrate ion concentrations. The distribution ratios of Np(VI) obtained with DEHDMPA and DEHBA exceeded unity when the nitrate ion concentration was > 3 mol/dm3, while DEHDMPA and DEHBA barely extracted Np(V). A continuous counter-current experiment using mixer-settler extractors was performed to evaluate the behavior of Np in a process comprising two cycles using DEHDMPA and DEHBA as extractants. The feed was nitric acid containing U, Pu, Np, and several fission products. The results indicated that part of Np(V) changed its valence state to Np(IV) or Np(VI) after the 1st experimental cycle. The recoveries of Np in the streams of U fraction and U-Pu fraction were 63.7% and 29.1%, respectively.

Evaluation of two-phase separation in N,N-di(2-ethylhexyl)butanamide-nitric acid systems using turbidity measurements

ABSTRACT Quantitative evaluation of the two-phase separation between N,N-di(2-ethylhexyl)butanamide (DEHBA) and tri-n-butyl phosphate (TBP) diluted with n-dodecane and uranyl nitrate solution in nitric acid medium was achieved using turbidity measurements. The turbidities of DEHBA were relatively high, particularly at high DEHBA concentrations, while that of TBP rapidly decreased irrespective of nitric acid concentration. A high concentration of DEHBA, nitric acid, and uranium increased the turbidities in the organic phase, which could be ascribed to the increase in viscosity. Distribution ratios of uranium were also measured, and it was indicated that turbidity did not have a critical effect on the distribution ratio when the turbidity was below a certain value.

Spectroscopic study of Np(V) oxidation to Np(VI) in 3 mol/dm3 nitric acid at elevated temperatures

Abstract Optical absorption spectra of Np in 3 mol/dm3 nitric acid at elevated temperatures were measured using an optical glass cell with a water jacket having a light path of 1 cm. Molar extinction coefficients of Np(VI), εT M–1 cm–1, were obtained at various temperatures (297, 313, 334, 352, and 372 K). The values of εT were found to decrease with increasing temperature and could be described by the equation εT =− 0.14T + 85.5, where T is the temperature. Oxidation of Np(V) to Np(VI) in 3 M nitric acid at elevated temperatures (336, 342, 354, and 362 K) was observed using the optical glass cell. Oxidation of Np(V) was promoted by increasing the temperature and proceeded as a pseudo-first order reaction with respect to Np(V) concentration. The rate equation in the temperature range of 336–362 K was obtained as follows: − d[Np(V)]t/dt = 2.2 × 107 exp [− 65 × 103/(RT)][Np(V)]t, where R, T, and [Np(V)]t indicate the gas constant, temperature, and Np(V) concentration at time t, respectively.