Precipitation of Thorium or Uranium(VI) Complex Ion with Cobalt(III) or Chromium(III) Complex Cation, (II)

The precipitations of thorium and uranium(VI) sulfito complex ions with hexammine cobalt(III) chloride as the precipitant have been studied.

The orange-colored uranium(VI) precipitate obtained is [Co(NH₃)₆]₄[UO₂(SO₃)₃]₃22H₂O, which is in the form of square bipyramid, about 4 μm across in a cubic symmetry of the diamond type with a=10.40Å It decomposes to an oxide mixture of Co₃O₄ and U₃O₈ above 850°C in the air through a sulfate mixture of CoSo₄ and UO₂SO₄.

Composition of the thorium precipitate varies with the precipitation conditions. Therefore, it is considered that the thorium precipitate contains thorium hydroxide and basic thorium sulfite.     

Precipitation of Thorium or Uranium(VI) Complex Ion with Cobalt(III) or Chromium(III) Complex Cation, (III)

Chloride ion (foreign ion) effect on the precipitation of thorium or uranium (VI) sulfato, carbonato and oxalato complex ions has been studied. The results are in correlation with the chemical species present in the solution.

The precipitation of highly-charged complex ions is affected by chloride ion and the precipitation yield decreases with chloride salt concentration. The precipitation of sulfato complex ion shows only slight dependency on the chloride salt concentration because of the absence of highly-charged sulfato complex ion under the experimental conditions.     

A Nuclear Magnetic Resonance Study on Ligand Exchange Reactions in La(III), Nd(III), and U(VI) Nitrato Complexes with n-Octyl(pheny1)-N,N-Diisobutylcarbamoylmethylphosphine Oxide in Non-aqueous Solvents

The exchange reactions of n-octyl(pheny1)-N, N-diisobutylcarbamoylmethylphosphine oxide (CMPO) in La(III), Nd(III), and U(VI) nitrate complexes with CMPO (La(III)-, Nd(III)-, and U(VI)-CMPO complexes) have been studied in CD₃COCD₃ by means of ³¹P NMR method. The number of CMPO coordinated to the first coordination sphere of La(III) ion was directly determined to be 3 by the area integrations of ³¹P NMR signals of free and coordinated CMPO molecules. The same coordination number of 3 was also obtained for the U(VI)-CMPO complex. The coordination number was not determined for the Nd(III)-CMPO complex, because of its paramagnetic behavior. The exchange rate constants of CMPO in La(III)- and U(VI)- CMPO complexes were obtained by the two-site exchange model. Paramagnetic line broadening was observed in the Nd(III)-CMPO complex and the rate constant for the exchange of CMPO was determined by the line-broadening method. The exchange rates of CMPO in La(III)- and Nd(III)-CMPO complexes depend on the free CMPO concentration ([CMPO]), while that in U(VI)-CMPO complex is independent of [CMPO]. The dissociative (D) and dissociative interchange (I_d ) mechanisms were proposed for the exchange reactions in the La(III)- and Nd(III)-CMPO complexes, and dissociative (D) or I_d mechanism was proposed for the U(VI)-CMPO complex. The dissociative rate constants (s^?1) at 25°C and activation parameters ΔH^# (kJ·mol^?1) and ΔS^# (J·K^?1·mol^?1) are 4.76x10³, 28.7±0.1, ?78.4±0.2 for La(III)-CMPO complex, 4.72x10³, 42.6±0.4, ?31.7±1.3 for Nd(III)-CMPO complex, and 3.20x10³, 46.9±0.6, ?20.5±2.2 for U(VI)-CMPO complex, respectively.     

Structural and Electrochemical Studies on Uranium(VI) Nitrato Complex with n-Octyl(phenyl)-N,N-Diisobutylcarbamoylmethylphosphine Oxide in Non-aqueous Solvents

The structure of uranyl nitrato complex with CMPO [n-Octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide] in solid state and in non-aqueous solvents without containing free CR/IPO has been studied by using IR spectrophotometer, ¹³C- and ³¹P-NMR. The carbonyl(vcO) and phosphoryl(vpO) stretching bands of coordinated CMPO were observed at lower wavenumber than the corresponding bands of free CMPO in both the states. The ¹³C and ³¹P peaks assigned to the carbonyl carbon and phosphoryl phosphine of coordinated CMPO was detected in the lower field than that of free CMPO. From these results, it was concluded that the uranyl nitrato complex with CMPO in both the states has the structure with two nitrate and one CMPO coordinated as bidentate in the equatorial plane of uranyl ion, i.e., UO₂(NO₃)₂·CMPO. Furthermore, the electrochemical studies of UO₂(NO₃)₂·CMPO complex in CH₃CN have been carried out using cyclic and normal pulse voltammetric methods. It was found that the UO₂(NO₃)₂·CMPO complex is reduced to U(V) complex at around ?1.22V vs. Fc/Fc⁺ (ferrocene/ferrocenium) and that the resulting reductant is oxidized to U(VI) at around +0.04V vs. Fc/Fc⁺.     

Extraction of uranium(VI) with N-octanoylpyrrolidine in sulfonated kerosene

1 INTRODUCTIONaide extractants have resistance to hydrolysis, Tadiolysis and their degradationproducts do not interfere severely in the separation process. They can buxn completely,without any solid waste. Furthermore, they extract actAndes from nitric acid mediaeffectively. Therefore, abide extractants have been proposed as an alternative to TBPfor the reprocessing of nuclear m.l.[l] However, when the acidity or concentration ofurhaum is high, the system presents third phase easily. In…     

Influence of solvents on extraction of U（VI） by N,N‘—didecanoylpiperazine

Extraction behavior of N,N‘-didecanoylpiperazine(DDPEZ)for U(VI) in a series of solvents from aqueous nitric acid media was investigated for the first time.The dependence of distribution ratios on the concentration of aqueous nitric acid,extractant and temperature has been discussed.The increasing sequence of extractive ability of DDPEZ is given:chloroform,carbon tetrachloride,dimethylbenzene,toluene,benzene.     

A Study on Hydraulic Properties of Compacted Fe(III)-montmorillonite

Hydraulic conductivities were determined for compacted Fe(III)-montmorillonite sample. The Fe(III)-montmorillonite sample used in this study, which was prepared by the ion-exchange treatment of Namontmorillonite in FeCl₃ solution, contains less than 20% of Na⁺ ions as exchangeable cations and negligibly small amounts of iron precipitates. The measured hydraulic conductivities of compacted Fe(III)-montmorillonite were determined to be the order of 10^?9, 10^?11, and 10^?13 ms^?1 at dry densities of 0.80, 1.01, and 1.20 Mgm^?3, respectively. These values were found to be kept constant during the experimental period, suggesting no significant change in the physicochemical properties of Fe(III)-montmorillonite during the experiment. When compared with Na-montmorillonite, remarkably high values of hydraulic conductivities were found for Fe(III)-montmorillonite at the dry densities of 0.8 and 1.0Mgm^?3. On the other hand, almost the same value of hydraulic conductivity was obtained at the dry density around 1.2Mgm^?3. This different effect of exchangeable cations on the hydraulic conductivity of montmorillonite could be attributed to the different sizes of macropores in compacted montmorillonite and/or the different thicknesses of electrical double layers formed over montmorillonite sheets.     

Low-Temperature Partitioning of Plutonium with High U(VI)-Loading for Fuel Reprocessing

Measurement of the distribution ratios of Pu(IV), U(VI) and HNO₃ at low temperatures and its treatment with DIST code revealed that a high U (VI)-loading of 30% TBP in n-dodecane splits Pu(IV) down to the aqueous phase more strongly than do at 25°C. Based on these findings, flowsheet conditions to separate Pu(IV) from U(VI) were investigated with EXTRA.M code including the distribution equations obtained above. And tentative flowsheets for non-reductive Pu-splitting process at a temperature of 5°C were proposed for fuel reprocessing mainly based on the effects of U (VI)-loading in the solvent and temperature on distribution ratios of Pu(IV) and U(VI). Distribution ratios of the fission products, Zr, Nb, Ru and Ce were also measured to assess their decontamination from U or Pu products in the above process. Finally behavior of Np, in the proposed partitioning process was discussed by analysis with EXTRA. M code and a redox reaction model.     

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.     

Radiation Damage of Organic Extractant in Partitioning of High-Level Liquid Waste, (I)

Di(2-ethylhexyl)phosphoric acid (DEHPA), which is a useful extractant for the treatment of high-level liquid waste, was exposed to ⁶⁰Co γ-rays and the radiolysis products and their yields were determined.

The major radiolytic decomposition process of DEHPA was found to be a stepwise splitting of two alkyl groups resulting in MEHPA and H₃PO₄. 1-Methyl-1-ethylpentyl radical, C₄H₉-C(CH₃)-C₂H₅, was found to form with a large G value in the γ-irradiated DEHPA. Reactions involving 1-methyl-1-ethylpentyl radical were also discussed.