镅在榆次地下水中的溶解度分析

利用自行开发的化学形态分析软件CHEMSPEC计算了镅在榆次地下水中的溶解度,同时研究了pH值、地下水成分、温度等因素对镅在榆次地下水中溶解度的影响.结果表明,pH值、总碳酸根离子浓度和温度对溶解度有显著影响;而硫酸根离子浓度、氯离子浓度对溶解度的影响可以忽略.计算表明,镅在榆次地下水中的溶解度在1.4×10-10-6.3×10-3mol·L-1之间.在25℃,pH=6.0时,总碳酸根离子浓度为1×10-5mol·L-1时,镅的溶解度最大,该值可用于镅在榆次浅层含水层中的扩散和迁移行为的偏保守预测.     

Hexamolybdoaluminates and Hexamolybdochromates of Some Trivalent Lanthanides and Americium

The reactions of some rare-earth elements (La, Ce, Sm, Lu, Gd) and Am(III) with heteropolymolybdate anions are studied. The complexation rate constants of Am(III) in a solution with Al(OH)₆Mo₆O₁₈ ^3- and Cr(OH)₆MoO₁₈ ^3- ₆ (₁ = 18 ± 6 and 25 ± 5, respectively) are determined by spectral methods. The Ln[Al(OH)₆Mo₆O₁₈] · nH₂O, Eu[Cr(OH)₆Mo₆O₁₈] · nH₂O, and Am[Al(OH)₆Mo₆O₁₈] · nH₂O isostructural compounds are synthesized. The crystal structure of the Sm[Al(OH)₆Mo₆O₁₈] · 11H₂O complex was determined by the X-ray diffraction analysis. The results of spectroscopic and thermogravimetric studies of the obtained compounds are presented.     

逆流色谱分离镅(Ⅲ)和铕(Ⅲ)的研究

选择0.1 mol/L NaC lO4为流动相,以二氯苯基二硫代膦酸的二甲苯溶液为固定相,研究了萃取剂浓度、流动相pH及流动相流率对逆流色谱(CCC)分离Am3 和Eu3 效果的影响。结果表明,在实验条件下,两者的分离系数随着固定相中的萃取剂浓度增加、流动相的pH升高而增大;降低流动相流率后可明显改善分离效果。通过改变分离条件,Am3 和Eu3 可基本上实现相互分离,两者间的分离系数和分离效率分别达到2.87和0.74。     

Modelling of Americium Stripping in the EXAm Process

The EXAm process aims at recovering americium alone contained in the PUREX raffinate. The americium stripping model has been revised to take into account a change of stripping aqueous phase and up-to-date experimental results conducted within DRCP to improve knowledge about complexes.This work represents a first approximation at modelling americium stripping. The modelling work has led to synthesize the knowledge on chemical phenomenology and adopt assumptions that best reflect experimental results. The modelling has been implemented in PAREX code in order to simulate this step to prepare and understand tests to be carried out in mixer settlers.     

Implementation of Americium Separation from a PUREX Raffinate

Recovering of minor actinides from spent nuclear fuel is investigated for heterogeneous recycling in Generation-IV reactors. After plutonium, americium is the main contributor to residual heat of long term radioactive waste which determines waste density within geological repository. Selective americium separation (EXAm process) by liquid-liquid extraction from a PUREX raffinate was studied. Two experiments were performed in ATALANTE facilities. The first test, on surrogate solution, validated the americium extraction performance. The second trial was carried out in the high-level shielded process line from a genuine PUREX raffinate. Tools used to manage the process are introduced to show performance process achievement.     

Modeling and Simulation of Extraction Flowsheet for FBR Fuel Reprocessing

The present work describes the mathematical basis of a computer code for the analysis of PUREX flowsheet. The model equations have been developed on the basis of the idealized model for mixer settlers. The distribution coefficients relations for U(VI), U(IV), Pu(IV), Pu(III), Ru & Zr and the redox reactions rates of the species involved in U/Pu partitioning are incorporated. The validity of the model equations is tested by carrying out experiments in an ejector mixer-settler with simulated solutions. The stage-wise experimental concentration profiles compare well with the theoretical predictions. An optimum flowsheet for FBR fuels reprocessing has been proposed.     

Americium and samarium determination in aqueous solutions after separation by cation-exchange

The concentration of trivalent americium and samarium in aqueous samples has been determined by means of alpha-radiometry and UV–Vis photometry, respectively, after chemical separation and pre-concentration of the elements by cation-exchange using Chelex-100 resin. Method calibration was performed using americium (²⁴¹Am) and samarium standard solutions and resulted in a high chemical recovery for cation-exchange. Regarding, the effect of physicochemical parameters (e.g. pH, salinity, competitive cations and colloidal species) on the separation recovery of the trivalent elements from aqueous solutions by cation-exchange has also been investigated. The investigation was performed to evaluate the applicability of cation-exchange as separation and pre-concentration method prior to the quantitative analysis of trivalent f-elements in water samples, and has shown that the method could be successfully applied to waters with relatively low dissolved solid content.     

Highly Luminescent and Stable Hydroxypyridinonate Complexes: A Step Towards New Curium Decontamination Strategies

The photophysical properties, solution thermodynamics, and in vivo complex stabilities of Cm^III complexes formed with multidentate hydroxypyridinonate ligands, 3,4,3‐LI(1,2‐HOPO) and 5‐LIO(Me‐3,2‐HOPO), are reported. Both chelators were investigated for their ability to act as antenna chromophores for Cm^III, leading to highly sensitized luminescence emission of the metal upon complexation, with long lifetimes (383 and 196 μs for 3,4,3‐LI(1,2‐HOPO) and 5‐LIO(Me‐3,2‐HOPO), respectively) and remarkable quantum yields (45 % and 16 %, respectively) in aqueous solution. The bright emission peaks were used to probe the electronic structure of the 5f complexes and gain insight into ligand field effects; they were also exploited to determine the high (and proton‐independent) stabilities of the corresponding Cm^III complexes (log β₁₁₀=21.8(4) for 3,4,3‐LI(1,2‐HOPO) and log β₁₂₀=24.5(5) for 5‐LIO(Me‐3,2‐HOPO)). The in vivo complex stability for both ligands was assessed by using ²⁴⁸Cm as a tracer in a rodent model, which provided a direct comparison with the in vitro thermodynamic results and demonstrated the great potential of 3,4,3‐LI(1,2‐HOPO) as a therapeutic Cm^III decontamination agent.     

核燃料循环中镅的氧化分离研究进展

镅离子在溶液中主要以三价形式(Am(III))存在,因其离子半径与三价镧系离子Ln(III)接近,化学特性相似,使得Am(III)与Ln(III)的有效分离被认为是核燃料循环领域最具挑战性的课题之一。利用镅的多价态特性,采用不同氧化方法可将Am(III)氧化成高价态的AmO₂⁺和AmO₂²⁺形式,再通过溶剂萃取、沉淀等方法进行分离,是实现Am与Ln分离的一种新思路。本文综述了不同氧化方法对水溶液环境中Am(III)的氧化分离研究进展,描述了相关机理,指出了不同氧化方法的优劣并展望了未来发展趋势,以期为发展新型镧系与锕系元素分离技术提供参考。     

Separation of Americium by Liquid-Liquid Extraction Using Diglycolamides Water-Soluble Complexing Agents

Recycling americium (Am) alone from spent nuclear fuels is an important option studied for the future nuclear cycle (Generation IV systems) since Am belongs to the main contributors of the long-term radiotoxicity and heat power of final waste. Since 2008, a liquid-liquid extraction process called EXAm has been developed by the CEA to allow the recovery of Am alone from a PUREX raffinate (a dissolution solution already cleared from U, Np and Pu). A mixture of DMDOHEMA (N,N’-dimethyl-N,N’-dioctyl-2-(2-(hexyloxy)ethyl)-malonamide) and HDEHP (di-2-ethylhexylphosphoric acid) in TPH is used as the solvent and the Am/Cm selectivity is improved using TEDGA (N,N,N’,N’-tetraethyldiglycolamide) as a selective complexing agent to maintain Cm and heavier lanthanides in the acidic aqueous phase (5 M HNO₃). Americium is then stripped selectively from light lanthanides at low acidity (pH=3) with a polyaminocarboxylic acid. The feasibility of sole Am recovery was already demonstrated during hot tests in ATALANTE facility and the EXAm process was adapted to a concentrated raffinate to optimize the process compactness. The speciation of TEDGA complexes formed in the aqueous phase with Am, Cm and lanthanides was studied to better understand and model the behavior of TEDGA in the process. Some Ln-TEDGA species are extracted into the organic phase and this specific chemistry might play a role in the Am/Cm selectivity improvement. Hence the hydrophilicity-lipophilicity balance of the complexing agent is an important parameter. In this comprehensive study, new analogues of TEDGA were synthesized and tested in the EXAm process conditions to understand the relationship between their structure and selectivity. New derivatives of TEDGA with different N-alkyl chain lengths and ramifications were synthesized. The impact of lipophilicity on ligand partitioning and Am/Cm selectivity was investigated.     

Americium and plutonium separation by extraction chromatography for determination by accelerator mass spectrometry

A simple method was developed to separate Pu and Am using single column extraction chromatography employing N,N,N′,N′-tetra-n-octyldiglycolamide (DGA) resin. Isotope dilution measurements of Am and Pu were performed using accelerator mass spectrometry (AMS) and alpha spectrometry. For maximum adsorption Pu was stabilized in the tetra valent oxidation state in 8 M HNO₃ with 0.05 M NaNO₂ before loading the sample onto the resin. Am(III) was adsorbed also onto the resin from concentrated HNO₃, and desorbed with 0.1 M HCl while keeping the Pu adsorbed. The on-column reduction of Pu(IV) to Pu(III) with 0.02 M TiCl₃ facilitated the complete desorption of Pu. Interferences (e.g. Ca²⁺, Fe³⁺) were washed off from the resin bed with excess HNO₃. Using NdF_3, micro-precipitates of the separated isotopes were prepared for analysis by both AMS and alpha spectrometry. The recovery was 97.7 ± 5.3% and 95.5 ± 4.6% for ²⁴¹Am and ²⁴²Pu respectively in reagents without a matrix. The recoveries of the same isotopes were 99.1 ± 6.0 and 96.8 ± 5.3% respectively in garden soil. The robustness of the method was validated using certified reference materials (IAEA 384 and IAEA 385). The measurements agree with the certified values over a range of about 1–100 Bq kg⁻¹. The single column separation of Pu and Am saves reagents, separation time, and cost.     

Americium(III) coordination chemistry: An unexplored diversity of structure and bonding

The comparison of the physicochemical behavior of the actinides with that of the lanthanides can be justified by the analogy of their electronic structure, as each of the series is made up of elements corresponding to the filling of a given (n)f atomic shell. However relatively few points of comparison are available, given the lack of available structure for trans-plutonium(III) elements and the additional difficulty of stabilizing coordination complexes of uranium(III) to plutonium(III). This contribution is a focal point of trans-plutonium(III) chemistry and, more specifically, of some americium compounds that have been recently synthesized, all related with hard acid oxygen donor ligands that may be involved in the reprocessing chain of nuclear fuel. After a brief review of the solid hydrates and aquo species for the lanthanide and actinide families, we discuss two types of ligands that have in common three carboxylic goups, namely the aminotriacetic acid and the citric acid anions. The additional roles of the nitrogen atom for the first one and of the hydroxy function for the second one are discussed. Accordingly, five new complexes with either americium or lanthanides elements are described: [Co(NH₃)₆][M(NTA)₂(H₂O)]·8H₂O with M = Nd, Yb and Am, and [Co(NH₃)₆]₂K[M₃(Cit)₄(H₂O)₃]·18H₂O with Nd and Am cations. In all cases the americium complexes are isostructural with their lanthanide equivalents.     

The EURO-GANEX Process: Current Status of Flowsheet Development and Process Safety Studies

A new hydrometallurgical grouped actinide extraction process has been developed to separate the transuranic actinide ions from dissolved spent fuel solution (after an initial uranium extraction cycle). This “EURO-GANEX” process is aimed towards the homogeneous recycling of plutonium and minor actinides in a future closed fuel cycle. The separation process is based on the co-extraction of actinides and lanthanides from aqueous nitric acid into an organic phase followed by selective co-stripping of actinides. A suitable organic phase has been formulated and distribution ratios determined for lanthanides, actinides and some problematic fission products under extraction and stripping conditions. The process flowsheet has been proven on surrogate feed solutions as well as with spent fast reactor fuel; excellent recoveries of the actinides and good decontamination factors from the lanthanides and other fission products were obtained. A variation on the EURO-GANEX flowsheet (the “TRU-SANEX” process) has now been designed to produce separate Pu+Np and Am+Cm products for heterogeneous recycling. Progress on underpinning process chemistry and safety studies as well as flowsheet tests are summarized.     

Separation of Americium from Europium Using Liquid Membrane Impregnated with Organodithiophosphinic Acid

The selective transport of Am across a supported liquid membrane (SLM) has been investigated by using bis (2,4,4-trimethylpentyl)dithiophosphinic acid (Cyanex 301) as a mobile carrier. This extractant containing soft donor atoms exhibits strong affinity for actinoids, giving a large separation factor between trivalent Am and Eu. Separation of Am from Eu was achieved by an SLM containing highly purified Cyanex 301. Americium was preferentially transported across the SLM and concentrated in the product solution, while most of Eu remained in the feed solution.     

The Study of Americium, Yttrium and Lead Complexation by Humic Acids of Different Origin

Complexation equilibrium of metals by three humic acids of different origin with ultrafiltration method was investigated at pH 4 a 5 and ionic strength I = 0.1M NaClO₄. Commercial (Aldrich) and two original humic acids (peat and soil, obtained by six step isolation process from the material from Trnava county, close to the NPP Jaslovské Bohunice) were used in this study. For the evaluation of the results, the model of metal ion charge neutralization upon humic acid functional group proposed by the Kim and Czerwinski was used. Complexation constants were calculated using the terms of this model (operational concentration, loading capacity). The values of log = 5.39±0.16 for yttrium, 6.15±0.16 for americium and 5.20±0.08 for lead were found. Correlation of free metal concentration and ratio of molar fraction of complexing functional groups confirms the validity of charge neutralisation model for metal and polyelectrolyte complexation study.     

Physicochemical Speciation of Americium in Soils from Rocky Flats, Colorado, USA

The objective of the research was to characterize the ²⁴¹Am distribution in six operationally defined chemical and mineralogical phases of soil samples taken from the Rocky Flats Environmental Technology Site (RFETS). Soil samples were subjected to selective sequential fractionation procedures to determine ²⁴¹Am association with the soluble, exchangeable, carbonate, organic, sesquioxide and silicate fractions. The highest percentage of ²⁴¹Am was found to be associated with the sesquioxide (hydrous oxide) fraction (39–47%), with lesser amounts in the soluble (14–17%), exchangeable (4–9%), carbonates (4–17%), organic (3–13%), and silicate (10–21%) soil fractions. Differences between americium and plutonium association with various soil fractions were observed.     

New Wide Rim Phosphomethylated Calix[4]arenes in Extraction of Americium and Europium

A new series of the cone-shaped tetraalkoxycalix[4]arenes substituted at the wide rim with four phosphomethyl groups have been synthesized by the Arbuzov, Michaelis–Becker and Aterthon–Todd reactions of the chloromethyl or phenylhydrophosphinylmethylcalix[4]arenes. Their binding properties towards Eu³⁺ and Am³⁺ cations were investigated by the liquid–liquid extraction method. Due to the ‘calixarene effect’ the tetraphosphorylated calixarenes are more effective extractants for the metal cations than their acyclic analogs or some industrial extractants such as trialkylphosphinoxides, carbamoylphosphinoxide, bis-2-diethylhexyl phosphoric acid.