Solvent Extraction of Am(III), Cm(III), and Ln(III) Ions from Simulated Highly Active Raffinate Solutions by TODGA Diluted in Aliquat-336 Nitrate Ionic Liquid
Péter ZsabkaK. Van HeckeL. AdriaensenAndreas WildenGiuseppe ModoloMarc VerwerftKoen BinnemansThomas Cardinaels
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Abstract:
The extraction behavior of americium(III), curium(III) (minor actinides, MA), fission products (lanthanides (Ln(III)), Mo, Ru, Pd, and Rh), and corrosion products (Zr and Fe) was studied in batch solvent extraction experiments using the room-temperature ionic liquid (IL) Aliquat-336 nitrate ([A336][NO3]) and a solvent composed of 0.05 M TODGA in [A336][NO3]. From acidic, dilute Ln(III) feed solutions, [A336][NO3] extracts nitric acid (D ≈ 0.5) and partially An(III) as well as Ln(III) (DAm = 0.02–0.1, DEu, and DCm = 0.01–0.04). The influence of the acid concentrations and kinetics on extraction and back-extraction of Ln(III) and An(III) by 0.05 M TODGA in [A336][NO3] was investigated using radiotracer-spiked dilute Ln(III) feed solutions. With the solvent composed of 0.05 M TODGA in [A336][NO3], DAn and DLn increase as a function of aqueous feed acidity. In the case of a spiked, simulated highly active raffinate (HAR) feed solution, [A336][NO3] extracts La(III) (DLa = 1.36), Ru (DRu = 1.64), and Pd (DPd = 38), while the distribution ratios of other Ln(III) and An(III) were lower than unity. The solvent composed of 0.05 M TODGA in [A336][NO3] co-extracted from HAR Zr(IV) (DZr> 300), Pd (DPd = 206), and Ln(III) (DLn> 1, except for Nd(III)), but An(III) were retained in the aqueous phase. The interference caused by the co-extraction of several fission (Zr, Pd, Ru, and Mo) and corrosion (Zr) products, which are present in the HAR at relatively high concentrations, was suppressed using masking agents (oxalic acid and trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid, CDTA). In the case of the actual HAR solution, the kinetics were found to be faster compared with the extraction from dilute Ln(III) feed solutions, possibly due to the different aqueous speciation of the Ln(III) and An(III).Keywords:
Aliquat 336
Raffinate
Nitric acid
Curium
Aqueous two-phase system
Liquid–liquid extraction
AbstractDue to the similar chemical properties between the neighboring trivalent actinide elements americium and curium, their extraction behavior is often perceived as indistinguishable. In this work, the characterization of seven extraction chromatography resins (TEVA, TRU, DGA(N), Actinide, Ln, Ln2, and Ln3) for these trivalent actinides from acidic matrices (HNO3, HCl, and HBr) has provided some evidence to the contrary. In most cases, Am(III) and Cm(III) exhibit identical extraction properties. However, separation is possible with TRU and DGA(N) resins as demonstrated in this study. The extraction shows a strong dependency on the specific anion in solution that follows the order NO3−>Br−>Cl−.Keywords: extraction chromatographyamericiumcuriumcharacterizationseparation
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The feasibility of separating americium from curium and the lanthanides was studied in batch solvent extraction experiments using an organic solvent composed of 0.01 mol L−1 2,9-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-1,10-phenanthroline (CyMe4BTPhen) in the ionic liquid Aliquat-336 nitrate [A336][NO3] from feed solutions containing N,N,N',N'-tetraethyl diglycolamide (TEDGA), stable lanthanide ions and tracers of 241Am, 244Cm, and 152Eu. The combined use of a lipophilic and a hydrophilic ligand with opposite selectivity for Am(III) vs. Cm(III) and Ln(III) allowed the separation of Am(III) from Cm(III) and Ln(III) from moderate acidic feed solutions (1 mol L−1 HNO3, SFAm/Cm = 3.1–3.9, SFAm/La > 75, SFAm/Eu ≥ 3000).
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I Historical Aspects and General Papers.- The 40th Anniversary of the Discovery of Americium and Curium.- Reminiscences of an Instrumentalist.- Americium, Its Early History and Gram-Scale Separation.- 20 Years of Americium and Curium Research at the European Institute for Transuranium Elements.- Frontiers of Chemistry for Americium and Curium.- II Solution Chemistry and Analytical Procedures.- Studies of Americium and Curium Solution Chemistry in the USSR.- Coulometric Determination of Americium and Curium for the Preparation of Reference Solutions.- A Study on the Stability of Americium(V) and Americium(VI) in Nitrate Media.- Radiopolarographic Study of Americium and Curium.- Americium Titration Methods.- III Electronic Structure and Thermodynamics.- Electronic Structure of Neutral and Singly Ionized Curium.- Shifted Homologous Relationships Between the Transplutonium and Early Rare-Earth Metals.- Thermodynamic Systematics of Oxides of Americium, Curium, and Neighboring Elements.- Preparation and Properties of Some New Curium Compounds.- The Electronic and Magnetic Properties of Am and Cm.- Delocalisation of 5f Electrons in Americium Metal Under Pressure: Recent Results and Comparison with Other Actinides.- Preparation, Characterization and Solubility Product Constant of AmOHCO3.- IV Nuclear Studies, Environmental Studies, Separations, and Other Technological Aspects.- Heavy Ion Reactions on Curium Targets.- Synthesis of Transuranium Nuclides from Interaction of 16O with 238U.- A Study of the Production of Transuranium Elements and Its Application to the Solution Chemistry in Tohoku University.- Geochemical Studies on Americium and Plutonium in Soil.- Production and Recovery of Americium-241.- Production of Americium Isotopes in France.- Americium Metal Preparation on the Multigram Scale.
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system containing “0”, enabling to accomplish a trivalent An/Ln separation at 1.0 M HNO3, the extraction of neptunium was drastically diminished, relative to “1”. The partitioning behavior of curium was also negatively impacted, introducing an effective opportunity for americium/curium separation. Radiometric and spectrophotometric studies demonstrate that the complete actinide recovery using the solvent based upon “0” and TOPO is not feasible. Additionally, the importance of radiolytic degradation processes is discussed through the comparisons of extraction properties of liquid-liquid systems based on both soft donor reagents.
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The liquid–liquid extraction process called EXAm was developed by the CEA to allow the recovery of Americium alone from a PUREX raffinate. Americium is extracted from a highly acidic feed solution (HNO3 4–6 M) by a mixture of two extractants: DMDOHEMA and HDEHP. The Am/Cm selectivity is improved using a specific diglycolamide (TEDGA) as a selective aqueous complexing agent which retains preferentially Cm and heavier lanthanides in the aqueous phase. In this study, the impact of the lipophilicity and steric hindrance of several diglycolamides on the Am/Cm selectivity was investigated in order to understand the enhancement brought by TEDGA. For this purpose, liquid–liquid extraction and partitioning experiments were performed under various conditions.
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Raffinate
PUREX
Liquid–liquid extraction
Aqueous two-phase system
Transuranium element
Lipophilicity
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A simple separation of americium from curium would support closure of the nuclear fuel cycle, assist in nuclear forensic analysis, and allow for more accurate measurement of neutron capture properties of (241)Am. Methods for the separation of americium from curium are however complicated and time-consuming due to the similar chemical properties of these elements. In this work a novel method for the separation of americium from curium in nitric acid media was developed using sodium bismuthate to perform both the oxidation and separation. Sodium bismuthate is shown to be a promising material for performing a simple and rapid separation. Curium is more strongly retained than americium on the undissolved sodium bismuthate at nitric acid concentrations below 1.0 M. A separation factor of ∼90 was obtained in 0.1 M nitric acid. This separation factor is achieved within the first minute of contact and is maintained for at least 2 h of contact. Separations using sodium bismuthate were performed using solid-liquid extraction as well as column chromatography.
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Neutron Activation Analysis
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Recycling americium from spent fuels is an important consideration for the future nuclear fuel cycle, as americium is the main contributor to the long-term radiotoxicity and heat power of the final waste, after separation of uranium and plutonium using the PUREX process. The separation of americium alone from a PUREX raffinate can be achieved by co-extracting lanthanide (Ln(III)) and actinide (An(III)) cations into an organic phase containing the diglycolamide extractant TODGA, and then stripping Am(III) with selectivity towards Cm(III) and lanthanides. The water soluble ligand H4TPAEN was tested to selectively strip Am from a loaded organic phase. Based on experimental data obtained by Jülich, NNL and CEA laboratories since 2013, a phenomenological model has been developed to simulate the behavior of americium, curium and lanthanides during their extraction by TODGA and their complexation by H4TPAEN (complex stoichiometry, extraction and complexation constants, kinetics). The model was gradually implemented in the PAREX code and helped to narrow down the best operating conditions. Thus, the following modifications of initial operating conditions were proposed: An increase in the concentration of TPAEN as much as the solubility limit allows. An improvement of the lanthanide scrubbing from the americium flow by adding nitrates to the aqueous phase. A qualification of the model was begun by comparing on the one hand constants determined with the model to those measured experimentally, and on the other hand, simulation results and experimental data on new independent batch experiments. A first sensitivity analysis identified which parameter has the most dominant effect on the process. A flowsheet was proposed for a spiked test in centrifugal contactors performed with a simulated PUREX raffinate with trace amounts of Am and Cm. If the feasibility of the process is confirmed, the results of this test will be used to consolidate the model and to design a flowsheet for a test on a genuine PUREX raffinate. This work is the result of collaborations in the framework of the SACSESS European Project.
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PUREX
Raffinate
Stripping (fiber)
Aqueous two-phase system
Transuranium element
Neptunium
Third phase
Data scrubbing
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