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論文

Thorium oxide dissolution in HNO$$_{3}$$-HF mixture; Kinetics and mechanism

Simonnet, M.; Barr$'e$, N.*; Drot, R.*; Le Naour, C.*; Sladkov, V.*; Delpech, S.*

Radiochimica Acta, 107(4), p.289 - 297, 2019/04

 パーセンタイル:100(Chemistry, Inorganic & Nuclear)

This paper is an attempt to find out thorium oxide dissolution mechanism in HNO$$_{3}$$-HF mixture. In a previous paper, several parameters effects on thorium oxide dissolution have been described, with specific focus on hydrofluoric acid effect, which can lead to an increase of the dissolution rate if present in small amount, but precipitates as ThF$$_{4}$$ at higher content. Based on this previous study, experimental data were fitted using several dissolution models in order to find out the best one. Finally, a revisited model based on literature and considering the ThF$$_{4}$$ formation was proposed. It describes the main steps of dissolution and is able to fit the experimental data for a wide range of solution compositions. This point is crucial since it allows considering an extrapolation of the established model to not-yet-studied conditions.

論文

Cesium liquid-liquid extraction by calix-crown ethers; Solvent effect

Simonnet, M.; 宮崎 有史; 鈴木 伸一; 矢板 毅

Progress in Nuclear Science and Technology (Internet), 5, p.66 - 69, 2018/11

$$^{137}$$Cs is a dangerous fission product because of its half-life of 30 years and its high production yield. After several years, it becomes one of the main heat generator in nuclear waste; it would thus be beneficial to remove it before deep repository storage. Cesium also shows high mobility in the environment, thus being one of the most dangerous material released in accidental situation. Because the chemistry of cesium is close to these of sodium and potassium, found in great amount in water, cesium recovery requires very high separation factor towards these elements. Calix-crown-ether compounds show high extraction of Cs, and Na separation factor up to million (up to ten thousands for K), depending on experimental conditions and extractant structure. This study attempts to qualitatively and, when possible, quantitatively describe these dependencies. Focus has been made on HNO$$_{3}$$ concentration (0.01M to 6M), solvent nature, and extractant structure, based on the already well-documented di-octyloxy-calix[4]mono-crown-6.

口頭

Cesium extraction by calix-mono-crown-ethers; Extractant and solvent effects

Simonnet, M.; 宮崎 有史; 鈴木 伸一; 矢板 毅

no journal, , 

Study of cesium separation from acidic and alkaline waste has been conducted since the 90's. Calix[4]-crown-6-ethers can selectively extract cesium with higher distribution ratios than crown-ethers or dicarbollides. Several authors focused on dioctyloxycalix[4]crown-6 (DOC[4]C6), also tested on real waste in dodecane/TBP mixture. 99.9% of cesium was extracted but TBP, mandatory to solvate the calix-crown in dodecane, lowered the selectivity. The distribution ratio DCs remained also rather low. This study focuses on extractant and solvent effects. Because DOC[4]C6 showed good results and is well-documented, extractants were synthesized by modifying its structure: change of the alkoxy chain length led to didodecyloxycalix[4]crown-6 (DDC[4]C6) and diethylhexyloxycalix[4]crown-6 (DEHC[4]C6); change on the crown-ether led to dioctyloxycalix[4]benzo-crown-6 (DOC[4]BC6) and dioctyloxycalix[4]di-benzo-crown-6 (DOC[4]DBC6). Studies on DOC[4]BC6 and DOC[4]DBC6 can be found in literature. Based on literature study, pure solvents: n-octanol (n=1,2,3), methylcyclohexanone (MCHK), 2-nonanone; and mixtures of 1-octanol + 10% modifiers (nitrophenyloctylether (NPOE), TBP) have been tested.

口頭

Cesium separation from aqueous streams by calix-monocrown-arene

Simonnet, M.; 宮崎 有史*; 鈴木 伸一; 小林 徹; 土井 玲祐; 塩飽 秀啓; 矢板 毅

no journal, , 

$$^{137}$$Cs is one of the highest heat generators in nuclear waste. Removing it prior to deep geological disposal can thus help reducing the necessary volumes and costs of the final repository. This isotope is also one of the main contaminants that was released during the Fukushima Nuclear Power Plant accident. Liquid-liquid extraction can be a suitable method for decontamination. In this study, seven different extractants from the calix-mono-crown-arene family have been compared as respect to distribution ratio, separation factors and closer atoms distances to cesium. Distribution ratios also strongly depend on diluent nature. EXAFS study was thus conducted on two extractants in chloroform and 2-nonanone to investigate whether diluent nature can impact the cesium-ligand complex itself. Spectra showed that whilst no difference was observed on the first coordination shell, diluent nature impacted the second shell. However, oxygen positions remained similar in both diluents, leading to a probable change in benzene pi-electron interaction with cesium.

口頭

Extraction of cesium by calix-crown-ether

Simonnet, M.; 宮崎 有史*; 鈴木 伸一; 小林 徹; 矢板 毅

no journal, , 

Results on cesium extraction by calixarene crown-ether in several diluents are presented. An extraction mechanism was proposed, which correctly fits the different datasets. Found empirical equilibrium constants were correlated with diluent parameters for a better comparison. Afterwards, chloroform and 2-nonanone were compared on the obtained distribution ratios, separation factors and atomic scale differences. EXAFS studies proved that the modification of diluent yields a change in the local cesium environment.

口頭

1,10-phenanthroline carboxamide ligands for lanthanide separation; Diluent effect

Simonnet, M.; 小林 徹; 鈴木 伸一; 矢板 毅

no journal, , 

Efficient separation of rare-earth elements has recently been under a renewed interest. One of the most common elemental separation method is liquid-liquid extraction, for which the state of the art is wide due to the similarities with the studies on actinides separation from lanthanides. Therefore, many different extractants can be found in literature, among which 1,10-phenanthroline-based ligands have shown a strong ability for the extraction of trivalent elements. In this study, we focused on 1,10-phenanthroline carboxamide compounds, because they can selectively extract one lanthanide from the series, with the nature of this lanthanide dependent on the extractant structure. Some compounds were tested in different media, and it was found that the nature of the diluent and the composition of the aqueous feed also yield to a maximum shift among the lanthanide series. This study thus aims at emphasizing diluent effect on lanthanide extraction by 1,10-phenanthroline carboxamide ligands.

口頭

Cesium extraction by calixarenes crown-ether; Diluent effect

Simonnet, M.; 宮崎 有史*; 鈴木 伸一; 矢板 毅

no journal, , 

$$^{137}$$Cs is a troublesome fission product for both nuclear waste reprocessing and the cleaning of contaminated areas (Fukushima). Because Cs belongs to the alkali elements, it is hard to separate from Na and K, whose natural abundances are high. Calixarenes crown-ether were found to be efficient alkali extractants, with the alkali selectivity determined by the number of ether functions. It was found that ligands with 6 ether functions are optimum for cesium whilst 4 is optimum for Na, yielding great Na separation factors. However, the resulting high oxygen contents yields a low solubility in aliphatic diluents. Different diluents were thus used in literature, such as alcohols, ketones, chloroform, nitrophenylalkylether or dodecane with a modifier. Whilst the distribution ratios greatly varied along with the diluent, few studies focused on understanding this phenomenon. The aim of the present work is thus to study the diluent effect at both macroscopic (distribution ratio and separation factor comparison) and microscopic (EXAFS analysis) scales. For the latter study, two diluents, chloroform and 2-nonanone, were chosen. Their properties (density, viscosity, dielectric constant, water solubility) are all different, except from the calixarene crown-ether solubility which is high in both cases. Additional interactions between the diluent and the counterion were also investigated. The study focuses on acidic aqueous solutions only.

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