Uranium (IV)-(VI) Electron Exchange Reactions in Anion Exchange Resin,Tri-n-Octyl Amine and Tri-Butyl Phosphate

A study has been made of the U(IV)-U(VI) electron exchange reactions taking place between natural U(IV) and depleted U(VI) in anion exchange resin, as well as in TnOA/benzene and TBP/benzene systems.

The exchange rate in the anion exchange resin was smaller than the corresponding rates in 8–10 M HCl, which might be explained by considering that the diffusion of the exchangeable species is much slower in the anion exchange resin than in 8–10 M HCl.

The exchange rates in TnOA/benzene and in TBP/benzene were accelerated by decreasing the concentration of TnOA or TBP in benzene. The reason may be that TnOA and TBP, including the exchangeable species, is more easily diffused in dilute than in concentrated solution.

Based on activation energy values, the mechanism of exchange in the anion exchange resin was estimated to be similar to that in 8–10 M HCl solution, and the corresponding mechanism for TBP/benzene similar to that for the cation exchange resin. In the case of TnOA/benzene, the exchange process was presumed to resemble that of the anion exchange resin, judging from the similarity of ionic species extracted thereinto.     

Effect of Metallic Impurities on Oxidation Reaction of Ion Exchange Resin, (II)

The catalytic effect of six metallic impurities on the oxidation reaction of cation exchange resin was investigated. The impurities, which were originally adsorbed onto the resin by an ion exchange method, combined with S present in the functional sulfonic acid group during heat-treatment in a nitrogen atmosphere to give the metal sulfides. The sulfides were subsequently oxidized to metal oxides.

In the case of Pd²⁺, Cu²⁺, Fe²⁺ and Fe³⁺ impurities, their sulfides were easily converted into oxides, which catalyzed the resin oxidation. Their catalytic activities depended on the heat of formation of the catalyst oxides ΔH‘₀; the lower was ΔH’₀, the more active the catalyst was. However, Co²⁺ and Ni²⁺ impurities had relatively low catalytic activities. This was because Co and Ni sulfides slowly changed into oxides, and the main chemical compositions of the impurities were not oxides but sulfides, which had no catalytic effect on the resin oxidation.     

HBMPPT-DOSO-甲苯体系对铀(Ⅵ)的萃取及铀(Ⅵ)、钍(Ⅳ)之间的分离

以个苯甲酰基－２,４二氢－５－甲基－２－苯基－３Ｈ－吡唑硫酮－３（ＨＢＭＰＰＴ）为萃取剂、二正辛基亚砜（ＤＯＳＯ）为协萃剂,研究其在硝酸介质中对铀（Ⅵ）的萃取行为,以及萃取剂浓度、酸度等各种因素对萃取分配比的影响,以确定两种萃取剂的协同萃取及分离效果。结果表明,ＨＢＭＰＰＴ和ＤＯＳＯ有较好的协同萃取效果,一定条件下,铀（Ⅵ）、钍（Ⅳ）的分离系数可达５２３。     

Extraction of U（VI） and Th（IV） with a novel extractant N,N‘—tetrahexylmalonamide （THMA） in toluene

The dependence of THMA extraction behaviour for U(VI) and Th(IV) on nitric acid concentration,THMA concentratioin and molecular structure of extracted complex has been studied.For nitric acid solutions of 3.0 mol/L a coordinative mechanism may possibly dominate in the extraction of metal catioins,The complex composition of UO2(NO3)2(THMA)2,Th(NO3)4(THMA)2 and Th(NO3)4(THMA03 are proved.     

Sorption and Colloidal Behavior of Np(IV) in a Bentonite-Carbonate Solution System

Abstract

Sorption of Np(IV) on bentonite in the presence of carbonate was studied by a batch method. The sorption was considered mainly due to Np(OH)₂(CO₃)₂ ^2- and Np(OH)₄(CO₃)₂ ^4- The distribution coefficient (K_d of Np(OH)₂(CO₃)₂ ^2- and Np(OH)₄ (CO₃)₂ ^4- was determined to be 10^4.01±0.24 ml/g and 10^3.93±0.37 ml/g respectively. The increasing K_d at high pH was attributed to the sorption of NpO₂(OH)_-2 with the K_d of 10^5.82±0.39 ml/g

The formation of colloidal species was observed under a reducing condition. By assuming Np(OH)₄ as the colloidal species, the formation constant was evaluated to be β_c≤10^53.85 Under an oxidizing condition, the formation of the colloidal species was less observed possibly due to the transformation of Np(OH)₄ to NpO₂OH.     

纳米零价铁去除溶液中U(Ⅵ)的研究

采用KBH4还原Fe3+制备纳米级零价铁,去除溶液中以铀酰离子形式(UO22+)存在的六价铀[U(Ⅵ)],考察纳米零价铁(NZVI)投加量、溶液pH值、U(Ⅵ)初始质量浓度以及时间等因素对铀去除效果的影响。实验结果表明:NZVI对U(Ⅵ)有很好的去除效果,当溶液pH=5.5、投加量为1.0 g/L、U(Ⅵ)初始质量浓度为45 mg/L、吸附时间为2.5 h时,对U(Ⅵ)的去除率为98.98%,吸附量为27.22 mg.g-1。     

Synergistic extraction of U（VI） and Th（IV） from nitric acid media with HBMPPT and TBP in toluene

The sysnergistic extraction of U(VI)and Th(IV) from nitric acid solution by HBMPPT(4-benzoyl-2,4-dihydro-5-methyl-2-phenyl-3H-pyrazol-3-thione) and TBP( tributylphosphate)in toluene was studied.The extraction ability of HBMPPT for U(VI) and Th(IV) was not so high.but when a little TBP was added in,the ability to extract U(VI) and Th(IV) was improved.The extracted complexes may be presented as UO2NO3.BMPPT.TBP and UO2(BMPPT)2.TBP for U(VI).and Th(NO3)3.BMPPT.TBP and Th(NO3)2(BMPPT)2.TBP for Th(IV),respectively,in the synergistic extraction system.The synergistic effect of HBMPPT and TBP makes the separation cofeeicient of U(VI)/Th (IV) or U(VI)/Eu(Ⅲ) reach a high value.     

Solidification of Spent Ion Exchange Resin Using New Cementitious Material, (II)

When using cement solidification for spent ion exchange resin, resin content in the waste form is typically controlled below 20vol%. This is because the waste forms crack and deteriorate in water at higher resin contents. The deterioration mechanism and its preventive measures were investigated in this study.

Swelling pressure of the resin was experimentally measured for various waste forms. The resin in the waste form tended to swell under a water immersion condition and tensile stress was exerted on the cement matrix. The stress value changed in the region of 1.5~5.5 MP a depending on such factors as resin content and its type. The waste form was deteriorated in water when the tensile stress was higher than the tensile strength of the cement. These results suggested that the deterioration could be prevented by increasing the tensile strength of cement. A fiber reinforced cement was developed for which tensile strength was almost doubled (~7MP a) by adding 10 wt% steel fiber to the cement. This prevented deterioration and allowed the resin content to be increased from 20 to 42 Vol%     

Precipitation ability to U(IV) and stability of 1,3-dimethyl-2-imidazolidone for selective precipitation of U(VI) in nitric acid media

As a part of the investigation of precipitants with selectivity to U(VI) in nitric acid media, a preliminary study on the precipitation ability of 1,3-dimethyl-2-imidazolidone (DMI) to U(IV), a simulant of Pu(IV), was performed. DMI is a ring compound like N-n-butyl-2-pyrrolidone (NBP) which is one of the pyrrolidone derivatives (NRPs) and a promising precipitant for U(VI). While DMI is known to precipitate U(VI) from 3 mol dm⁻³ (=M) HNO₃, no precipitate was observed in the solution containing 0.15 M U(IV) and 3 M HNO₃ by adding DMI at the ratio of [DMI]/[U(IV)] = 5. This indicates that the selectivity of DMI to U(VI) than U(IV) is much higher compared with that of NBP.On the other hand, the stability of DMI under γ-ray irradiation and heating in HNO₃ solutions (≤4 M) was also examined to evaluate the applicability of DMI to the practical process, because gradual acid hydrolysis of DMI is inevitable due to the nature of the chemical structure. As a result, it was found that the stability is strongly affected by the concentration of HNO₃. Namely, very few DMI in 2 M HNO₃ underwent the ring-opening by the irradiation up to 220 kGy and heating at 50 °C up to 5 h, respectively, indicating that these treated samples may still hold the precipitation ability to U(VI). On the contrary, the cleavage of the ring of DMI in 4 M HNO₃ was found to proceed easily. From the above results, it was concluded that DMI may be a candidate as a selective precipitant for U(VI) in HNO₃ solutions up to ca. 2 M.     

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.     

水-氢同位素汽-气并流催化交换反应动力学研究

在憎水催化剂的作用下,于固定反应床中研究了水-氢同位素汽-气并流催化交换反应的宏观动力学,讨论了该反应的速率方程和反应级数,比较了反应温度和所研制的3种憎水催化剂对反应速率常数的影响关系.研究结果表明,在本工作所拟订的实验条件下,该反应具有一级反应的动力学特征;温度对反应速率常数的影响服从阿仑尼乌斯公式,温度越高,反应的速率常数越大;Pt-SDB类催化剂的活化能小于Pt-C-PTFE类催化剂.     

Interaction between uranium and humic acid （Ⅰ）： Adsorption behaviors of U（Ⅵ） in soil humic acids

The adsorption behaviors of uranium on three soil humic acids (HAs), which were extracted from soils of different depths at the same site, were investigated under various experimental conditions. The adsorption results showed that U(Ⅵ) in solutions can be adsorbed by the three soil HAs, with the order of FHA (HA from 5 m depth of soil) >SHA (HA from the surface) >THA (HA from 10 m depth of soil) for adsorption efficiency in each desirable condition, and the adsorption reached equilibrium in about 240 min. Although the maximum adsorption efficiency was achieved at a suitable uranium concentration (10 mg·L-1 U(Ⅵ) for SHA and THA, 20 mg·L-1 U(Ⅵ) for FHA), the adsorption could be described with Langmiur isotherm or Freundlich isotherm equation. The L/S (liquid/solid, mL/g) ratio and pH were important factors influencing the adsorption in our adsorption system besides uranium concentration. The adsorption efficiency decreased with the increase of the L/S ratio and pH at the pH range of 2.0-3.0 for SHA and THA or 2.5-6.0 for FHA. However, no significant difference in adsorption of U(Ⅵ) was observed at the experimental temperature. All the results implied that humic substances have different characteristics in samples even collected at the same site.     

Kinetics and Equilibrium of Reaction between Octakis (dimethyl sulfoxide) uranium(IV) and Nitrite Ion in Dimethyl Sulfoxide

The kinetics and equilibrium of the reaction between octakis (dimethyl sulfoxide) uranium (IV), U(dmso)₈ ⁴⁺, and nitrite ion N0₂ ^? were studied in dmso solutions by using stopped-flow, diode-array and UV-visible spectrophotometers. Three different reactions were observed under the condition of an excess NaNO₂, and U(IV) was finally oxidized to U(VI) by N0₂ ^?. The first reaction is the formation of 1: 2 adduct complex [U (dmso₈)(NO₂)₂ ²⁺), the rate of which was so fast that the rate constant k_l obs was not determined accurately even by the stopped-flow method. If the concentration of N0₂ ^? was as low as that of U(IV), 1:1 adduct complex was formed. However, 1:1 complex was inert for further redox process, i.e. U(IV) was not oxidized by N0₂ ^? under this condition. The second reaction represents the substitution of coordinated dmso with N0₂ ^? forming mixed ligand complex [U(dmso) _8-x(N0₂ ^?)_x+2(^{2-x +}) The rate constant k ₂0bs for the second reaction was measured by the conventional method using a diode-array spectrophotometer and k ₂0bs increased linearly with the concentration of free N0₂ ^?. The third reaction coincides with the intra-molecular oxygen transfer from coordinated N0₂ ^? to U(IV) and this process is accompanied by the oxidation of U(IV) to U(VI). The oxygen transfer mechanism was confirmed by ¹⁷O labeled experiments using ¹⁷O-NMR. It was found from acid dependence experiments that only nitrite ion oxidized U(IV) and that nitrous acid was inert as an oxidant for U(IV).     

偶氮溴膦-mN的合成及其与铀显色反应的研究

本文主要介绍偶氮溴膦-mN(BPA-mN)的合成方法及其与铀(Ⅵ)的显色反应条件和性能。显色剂的合成采用由间硝基苯胺制得重氮盐,再与中间体偶联的工艺路线。经实验得出本试剂在强酸性介质中与铀(Ⅵ)生成稳定的兰紫色络合物,最大吸收峰在684nm处,在25ml中含铀量在0—45μg,符合比耳定律,其摩尔吸光系数ε_(684)=8.4×10~4,加入非离子型表面活性剂后,测铀灵敏度有明显提高,摩尔吸光系数提高到ε_(684)=1.0×10~5。Fe~(3+)、Al~(3+)、Ca~(2+)对显色反应干扰大,但加入掩蔽剂对Al~(3+)、Ca~(2+)有一定的掩蔽作用。本方法具有灵敏度高、选择性好、络合物稳定等特点。本试剂能作为铀(Ⅵ)分光光度法的新试剂。     

Absorption Spectrum of Pu(VI) in Alkaline Potassium Periodate Solution

We have proposed a novel isotope selective RIMS concept, which can avoid Doppler broadening in solid sample direct measurement using LA-RIMS. We have succeeded in experimentally demonstrating the principle of our RIMS concept. Through the simulation in which the resonant ionization efficiency and the ion trajectory were calculated, we verified the advantages of the use of an electrostatic lens, such as improved sensitivity and system miniaturization. We confirmed that the selectivity of 4.5 × 10¹⁰ was achievable by adopting a triple excitation scheme and that the multistep ionization scheme was also usable in our method. We concluded that the new isotope selective LA-RIMS had adequate performance as a simple and high sensitivity analysis method for solid samples.     

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.     

Photochemical Reaction of Bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato) (tetrahydrofuran)dioxouranium(VI) in Supercritical Carbon Dioxide

The emission lifetime of bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato)(teterahydrofuran)dioxouranium(VI) complex, UO₂(hfac)₂thf, has been measured in sub and supercritical carbon dioxide (sc-CO₂) under the conditions of 10 to 60 MPa and 293.2 to 340.2 K. It was found that the decay rate constants of excited UO₂(hfac)₂thf species (*UO₂(hfac)₂thf) decrease with increasing the pressure of sc-CO₂. The rate constants for quenching reactions of *UO₂(hfac)₂thf with alkenes in sc-CO₂ were determined as 4.32×10⁹(for cyclohexene), 3.04×10⁹(for cycloheptene), 2.13×10⁹(for 1-octene), and 3.801×10⁸mol^-1·dms^-1·s^-(for 1-hexene). The activation volumes for the quenching reactions of *UO₂(hfac)₂thf with cyclohexene, cycloheptene, 1-octene, and 1-hexene at 308.2 K were determined to be 16.7, 28.7, 16.7, and 24.7cm³.mol^-1, respectively.