Extraction Of Actinides Research Articles

Effect of branching in the alkyl chain of diglycolamide on the sequestration of tetravalent actinides: solvent extraction and theoretical studies.

DGA (diglycolamide) ligands show a different extraction behavior of trivalent metal ions by changing the branching alkyl chain length as well as the branching at the methylene position. There are no studies of these factors on the extraction efficiency of these DGA derivatives for the extraction of tetravalent actinides. We have evaluated four different DGA derivatives for the extraction of Np, Pu, and Th from molecular diluents. The n-butyl derivative shows enhanced extraction efficiency and branching gives rise to a reduction in the extraction efficiency of tetravalent ions. The distribution ratios are higher in pure octanol than in a mixture of 30% octanol and 70% n-dodecane. This behavior is in marked difference to that of the extraction of trivalent ions where the addition of an alcohol generally decreases the distribution ratio of trivalent ions due to the ligand-modifier intercation, poor aggregation or micelle formation tendency of DGAs in polar solvents. This suggests that micelle-mediated extraction may not be the dominating factor for the extraction of tetravalent metal ions. Slope analysis suggests the involvement of only two DGA molecules in the extracted species suggesting no/poor possibility of micelle formation in the present system. The higher extraction in pure octanol may be due to a better solubility of the extracted complexes in this polar medium compared to the mixture of octanol and n-dodecane. The water and acid uptake, the back extraction, and the radiation stability of the solvent systems were also investigated. DFT studies were performed to get a better insight into the extraction and complexation of the different DGA solvent systems.

Understanding the effect of alkyl chain on extraction of Np4+ and Pu4+ with hexaalkyl nitrilotriacetamides into an ionic liquid vis-à-vis a molecular solvent

Extraction of actinides using exotic ligands in room temperature ionic liquids is one of the most preferred areas of research these days. Though the amides are well studied for the extraction of actinides from nitric acid feeds, multiple amides (such as tripodal amides) are of recent origin, and reports on solvent extraction with these ligands in room temperature ionic liquids are very rare. In this work, the extraction of Np4+ and Pu4+ was studied with a series of N,N,N′,N′,N″,N″-hexaalkyl nitrilotriacetamides (NTAamides) in an ionic liquid with an objective to understand the effect of the alkyl chains length on their extraction ability. Bumim⋅Tf2N was chosen as ionic liquid due to its favourable viscosity for distribution studies. The extraction of tetravalent actinides Np4+ and Pu4+ increased linearly with increasing the alkyl chain of the NTAamides from n-butyl via n-hexyl to n-octyl. The extraction pattern was surprisingly opposite to the most observed extraction patterns in an ionic liquid, where the extraction generally decreases sharply upon increasing the feed acidity. The extracted species were ascertained as M(NO3)5⋅L (LH), where M = Np4+ or Pu4+, for each ligand. Consequent to the formation of an entirely divergent extracted complex, the extraction pattern is completely different than that expected in an ionic liquid.

Extraction of Actinides and Lanthanides from Nitric Acid Solutions with Mixtures of 1,5-N,N'-Bis[(Diphenylphosphoryl)Acetyl(Hexyl)Amino]pentane and New Asymmetrical Phosphonium- and Imidazolium-Based Ionic Liquid

Extraction of Actinides and Lanthanides from Nitric Acid Solutions with Mixtures of 1,5-N,N'-Bis[(Diphenylphosphoryl)Acetyl(Hexyl)Amino]pentane and New Asymmetrical Phosphonium- and Imidazolium-Based Ionic Liquid

Burnup and neutronic parameter analysis of GAMA molten salt reactor (GAMA-MSR)

The GAMA molten salt reactor (GAMA-MSR) is a small modular MSR design developed by the Nuclear Reactor Research Team of the Department of Nuclear Engineering and Engineering Physics, Universitas Gadjah Mada. In the GAMA-MSR design, the reactor core is placed above the primary heat exchanger. The primary heat exchanger is partially filled with fuel in normal operation, allowing room to be filled with the fuel drained from the reactor. Thus, in addition to control rods, the design of GAMA-MSR provides unique reactivity control through the balance of fuel salt fuel from the reactor core to the primary heat exchanger vice versa by adjusting fuel pump capacity. This design allows to shutdown the reactor by switching off the fuel pump. The reactor is initially fueled with 7LiF-ThF4-UF4 with 75: 20.1: 4.9 mol composition. The uranium has 19.75 % U-235 mol fraction. The reactor criticality and nuclide composition in the reactor fuel are calculated using OpenMC code during the reactor operation lifetime, with periodic adjustments to the fuel composition to simulate the effects of the fissile and fertile additions to the fuel and the extraction of actinides and fission products from the fuel. The calculated reactor thermal power is 60 MWth in this paper. The reactor is operated until it achieves a burnup value of 34,000 MWd/tHM. At this burnup value, the U-235 inventory is consumed and the amount is reduced from 794 kg to 250 kg. The U-233, Pu-239 and Pu-241 are produced with the amount are 246 kg, 24 kg and 8 kg respectively at the end of reactor operation. The effects of temperature, fuel density change, and fission product neutron poisons are also calculated. The average temperature reactivity coefficient value is approximately -4.4395×10-5Δk/k per °C. The effect of thermal expansion has been included in the calculation of this temperature reactivity coefficient value. The average value of the void reactivity coefficient is +1.2606×10-3Δk/k per % of void fraction for the void fraction value range up to 50 %. However, molten salt fuel suffers only small changes in density during operation. The negative value of the temperature reactivity coefficient will be dominant; thus, the GAMA-MSR becomes inherently safe. The GAMA-MSR is designed for a 30-year operation time. The effect of the fission product to the reactor reactivity is -1.4597×10-2Δk/k. Full draining of the fuel to primary heat exchanger brings the reactor to shutdown condition with the reactivity of −0.20525. Results showed that this reactor has an inherently safe characteristic and has an effective shutdown system, especially due to the fuel draining system.

Physicochemical properties of extraction solvents for the advanced recycling of spent nuclear fuel

A comprehensive understanding of solvent physicochemical properties is essential to developing advanced solvent extraction processes, such as Advanced PUREX (Plutonium Uranium Reduction Extraction) and GANEX (Group Actinide Extraction), that can safely and efficiently recycle spent nuclear fuel. The densities, viscosities and surface tensions of binary mixtures of tributyl phosphate (TBP) (0.92–3.66 M) in n-dodecane and N,N-di (2-ethyl hexyl)isobutyramide (DEHiBA) (0.69–2.78 M) in n-dodecane were measured at atmospheric pressure from 278.15 to 333.15 K. Through these measurements, empirical expressions to predict the density and viscosity at any molar composition of these solvents within the studied temperature range were constructed and shown to be in good correlation with all experimental data across the studied variables. The relationship between temperature and viscosity of pure TBP and DEHiBA can be described by the Arrhenius equation for viscosity in the temperature range studied. Surface tension measurements (air-liquid interface) were obtained for varying extractant concentrations between 278.15 and 333.15 K, which showed that DEHiBA acts as a surfactant when mixed with n-dodecane whilst TBP exhibits a higher surface tension than n-dodecane.

Theoretical Study of Am(III) and Eu(III) Separation by a Bipyridyl Phosphate Ligand.

Actinide An(III) and lanthanide Ln(III) are known to exhibit similar chemical properties; thus, it is difficult to distinguish them in the separation of highly radioactive waste liquids. One potential method to efficiently separate actinides and lanthanides involves the design and development of phosphorus-oxygen-bonded ligands with solvent extraction separation. Here, a bipyridine phosphate ligand with two isopropyl and phosphate groups is introduced to selectively extract actinides. The electronic structure, bonding properties, thermodynamic behavior, and quantum theory of atoms in molecules (QTAIM) of Am(III) and Eu(III) complexes with the bipyridine phosphate ligands were analyzed by using density functional theory (DFT) calculations. The analysis demonstrates that the Am-N bond exhibits stronger covalent characteristics than the Eu-N bond, indicating that the bipyridine phosphate ligand had better selectivity for Am(III) than for Eu(III) in terms of binding affinity. The thermodynamic analysis established the complex [ML(NO3)2(H2O)2]+ as the most stable species during the complexation process. The results indicate great potential for utilizing the bipyridine phosphate ligand for the effective separation of An(III)/Ln(III) in spent fuel reprocessing experiments.

Complexation and extraction of trivalent actinides over lanthanides using highly soluble phenanthroline diamide ligands with different side chains

Although phenanthroline diamide ligands have been widely reported, their limited solubility in organic solvents and poor performance in the separation of trivalent actinides (An(III)) and lanthanides (Ln(III)) at high acidity are still clear demerits. In this study, we designed and synthesized three highly soluble phenanthroline diamide ligands with different side chains. By introducing alkyl chains and ester groups, the ligands solubility in 3-nitrotrifluorotoluene is increased to over 600 mmol/L, significantly higher than the previous reported phenanthroline diamide ligands. Based on anomalous aryl strengthening, benzene ring was incorporated to enhance ligand selectivity toward Am(III). Extraction experiments demonstrated favorable selectivity of all the three ligands towards Am(III). The optimal separation factor (SFAm/Eu) reaches 53 at 4 mol/L HNO3, representing one of the most effective separation of An(III) over Ln(III) under high acidity. Slope analysis, single crystal structure analysis, as well as titration of ultraviolet visible spectroscopy, mass spectrometry, and nuclear magnetic resonanc confirmed the formation of 1:1 and 1:2 complex species between the metal ions and the ligands depending on the molar ratio of metal ions in the reaction mixture. The findings of this study offer valuable insights for developing phenanthroline diamide ligands for An(III)/Ln(III) separation.

Elucidation of the extraction of trivalent actinides using the DOHyA-HDEHP system: an experimental and theoretical approach.

A combined solvent system composed of an acidic and a neutral extractant is demonstrated as an effective system for the mutual separation of lanthanides and actinides from nitric acid solutions. The geometry and stability of various possible complexes formed under extraction and stripping conditions in a combined solvent system composed of N,N-dioctyl hydroxyacetamide (DOHyA) and bis(2-ethylhexyl)phosphoric acid (HDEHP) in the n-dodecane medium were studied both experimentally and theoretically. Experimental observations of the distribution ratios of Am(III) and Eu(III) in the combined solvent system revealed synergistic extraction of trivalent metal ions at all nitric acid concentrations. Density functional theory (DFT) calculations were employed to understand the geometric and electronic properties of the ligands and their corresponding complexes with Am(III) and Eu(III). The calculated results indicate that the feasibility and behaviour of complex formation in the combined solvent system using different methods are based on the energetic aspects of the formation reactions. The study also reveals the participation of the neutral and acid extractants in the combined solvent system facilitating the separation of Eu(III) and Am(III) from high-level liquid waste.

Theoretical investigation on the ligands constructed from phenanthroline and five-membered N-heterocyclic rings for bonding and separation properties of Am(III) and Eu(III).

The ligands, derived from the combination of phenanthroline and various five-membered N-heterocyclic rings, were subject to a comprehensive investigation for their potential in the extraction and separation of actinides and lanthanides. This study employed DFT methods to thoroughly explore the properties of both phenanthroline (Ph) and the diverse five-membered N-heterocyclic rings (R1-R8). Additionally, tridentate ligands RlPh (l = 1-8) and tetradentate ligands RlPhRr (l, r = 1-8) were analyzed in detail, encompassing their electrostatic potential (ESP), protonation energy, coordination bonding with the metals Am(III) and Eu(III), and the thermodynamics of extraction separation for Am(III) and Eu(III). The findings highlight that the electrostatic potential (ESP) and binding capabilities of the five-membered N-heterocyclic ring units serve as effective predictors for the properties of intricate tridentate and tetradentate ligands, as well as their coordination bonding affinity with metals. The ligands' binding energy is closely associated with their ESP, and notably, the binding energy of tridentate and tetradentate ligands correlates well with the binding energies of their constituent structural units. The computational results reveal that the R2 unit, along with its corresponding tridentate ligand R2Ph and tetradentate ligands R2PhRr, exhibits the highest ESP, superior binding energies, and the strongest coordination bonding affinity with the metals. The theoretical calculations further identify several promising extractants for the effective separation of Am(III) and Eu(III). The tridentate ligands R1Ph, R7Ph, and R4Ph, and the tetradentate ligands R4PhR4, R6PhR6, R2PhR2, R1PhR5 and R3PhR6 were identified as having excellent separation performance for Am(III) and Eu(III). This study would provide insights for the design of extractants for the separation of Am(III) and Eu(III) by use of five-membered N-heterocyclic rings as structural units.

Progress in phenanthroline-derived extractants for trivalent actinides and lanthanides separation: where to next?

Spent nuclear fuel (SNF) released from reactors possesses significant radioactivity, heat release properties, and high-value radioactive nuclides. Therefore, using chemical methods for reprocessing can enhance economic efficiency and reduce the potential environmental risks of nuclear energy. Due to the presence of relatively diffuse f-electrons, the chemical properties of trivalent lanthanides (Ln(III)) and actinides (An(III)) in SNF solutions are quite similar. Separation methods have several limitations, including poor separation efficiency and the need for multiple stripping agents. The use of novel multi-dental phenanthroline-derived extractants with nitrogen donor atoms to effectively separate An(III) over Ln(III) has been widely accepted. This review first introduces the development history of phenanthroline-derived extractants for extraction and complexation with An(III) over Ln(III). Then, based on structural differences, these extractants are classified into four categories: nitrogen-coordinated, N,O-hybrid coordinated, highly preorganized structure, and unsymmetric structure. Each category's design principles, extraction, and separation performance as well as their advantages and disadvantages are discussed. Finally, we have summarized and compared the unique characteristics of the existing extractants and provided an outlook. This work may offer a reliable reference for the precise identification and selective separation between An(III) and Ln(III), and point the way for future development and exploration.

A hydrolytically stable complexant for minor An separation from Ln in process relevant diluents.

The evaluation of bis-1,2,4-triazine complexants containing eight-carbon, alkoxy-functionalized phenyl substituents at the 3,3'-positions for selective minor actinide extraction in simulated high level waste is reported. The complexant retained chemoselective extraction efficiency of actinides over lanthanides while breaking through the nonpolar diluent solubility and hydrolytic stability barriers that limit many BTP complexants. Thus, we report a BTP complexant that is readily soluble in both kerosene and isooctanol without forming precipitates, emulsions, or third phase after contact with nitric acid and extracts 241Am3+ from 154Eu3+. Separations and spectroscopic data are reported herein.

Radiolytic degradation of selective actinide extractants from the bis-1,2,4-triazine family in cyclohexanone solutions.

Early stages of radiolysis of solutions with 2,6-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzo-[1,2,4]triazin-3-yl)pyridine (CyMe4-BTP) and 6,6'-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzo-[1,2,4-]triazin-3-yl)-[2,2']bipyridine (CyMe4-BTBP) ligands in cyclohexanone, proposed as a solvent for selective actinide extraction, were studied by means of the pulse radiolysis technique with spectrophotometric detection. Transient UV-vis spectra of excited triplet states of ligands, formed by energy transfer from cyclohexanone excited triplet states to ligands, were recorded for the first time. The influence of typical extraction conditions (the presence of diluted acid and O2 from air) on the mechanisms of reactions in the system studied was assessed. It was shown that an addition of benzophenone in high concentrations to the system together with its continuous saturation by O2 could partially protect ligands from radiation damage, caused by the high-energy radiation emitted by the spent nuclear fuel.

Theoretical design of polyazole based ligands for the separation of Am(III)/Eu(III)

The extraction of radioactive minor actinides (An(III)) from lanthanides (Ln(III)) is an extremely important step in nuclear waste reprocessing. Designing ligands with high-performance actinide-selectivity remains an essential task. Recent works have reported that some polyazole based ligands exhibit good An(III)/Ln(III) separation performance. Herein, we first evaluated the effects of different polyazole side chains on the Am(III)/Eu(III) selectivity by exploring three pyridine-derived polyazole ligands L1, L2 and L3 with 1,2,4-triazole, 1,2,3-triazole, and pyrazole side chains, respectively, using scalar relativistic theoretical methods. The coordination structures, bonding properties and thermodynamic behaviors of AmL(NO3)3 and EuL(NO3)3 complexes were investigated, which clarifies that the side chains do affect the electronic structure of ligand and its selectivity for Am(III)/Eu(III) ions. Moreover, L1 with 1,2,4-triazole side chains exhibited the highest selectivity for Am(III) over Eu(III) while the lowest complexation ability for metal ions among the three pyridine-derived polyazole ligands. Subsequently, we designed a new ligand L4 containing 1,2,4-triazole side chains and a preorganized phenanthroline backbone. Theoretically, such a new ligand was verified to show stronger complexation ability and higher selectivity for Am(III)/Eu(III) ions than L1. This work clarifies the complexation nature of polyazole based ligands with Am(III)/Eu(III) ions and provides design strategies for highly efficient polyazole based ligands for An(III)/Ln(III) separation.

Generalized Pitzer-Debye-Hückel (PDH) Framework for the Deep Eutectic Solvent Assisted Extraction of Europium (III), Americium (III), and Uranium (VI)

ABSTRACT This study focuses on modeling of deep eutectic solvents (DESs) assisted liquid-liquid-extraction of Am(III), U(VI), Eu(III). In the present work, DESs are having tri – n octyl phosphine oxide (TOPO) and choline chloride acetate as hydrogen bond acceptor and malonic acid, oxalic acid and glycolic acid as hydrogen bond donor. The UNIQUAC-extended-PDH* model is used in the extraction formulation incorporating weak long-range interactions and short-range interactions. Metaheuristic algorithm, such as genetic algorithm, is employed for the determination of thermodynamically consistent binary interaction parameters using a pool of 40 tielines across six systems. The estimation of efficiency evaluation and extraction quantification contributes to a deeper understanding of the behavior of deep eutectic solvents in the extraction of lanthanides and actinides.

Extraction of actinides and lanthanides from nitric acid solutions with phosphorylated pyrazines

The extraction of U(VI), Th(IV), Am(III), and lanthanides(III) from nitric acid solutions with solutions of phosphorylated pyrazines in organic solvents has been studied. The stoichiometry of the extracted complexes was determined, and the in uence of the structure of the extractant and the concentration of HNO3 in the aqueous phase on the e ciency of the extraction of metal ions into the organic phase was considered. It has been established thatm among the studied compounds, bis(diphenylphosphine)quinoxaline dioxide has the highest extraction ability with respect to actinides and lanthanides in nitric acid media.

Extraction of actinides and lanthanides from nitric acid solutions with diphosphine dioxides in the presence of an ionic liquid

The e ect of 1-butyl-3-methylimidazolium bis[(tri uoromethyl)sulfonyl]imide ionic liquid on the extraction of lanthanides(III), U(VI), and Th(IV) from nitric acid solutions with 1,2-bis(diphenylphosphinyl)ethane I and 1,2-bis(diphenylphosphinyl)benzene II has been studied. The stoichiometry of the extractable complexes was determined. A solution of dioxide II in dichloroethane extracts metal ions much more e ciently than a solution of dioxide I. It has been established that, in the presence of an ionic liquid in the organic phase, the e ciency of extraction of metal ions from nitric acid solutions with solutions of dioxide I increases signi cantly, while that of dioxide II decreases. As a result, in the presence of an ionic liquid in the organic phase, dioxide II is signi cantly inferior to dioxide I in terms of the e ciency of extraction of Ln(III), U(VI), and Th(IV) from nitric acid solutions, which is associated with a much higher ability of dioxide II to extract HTf2N.

Theoretical investigation on the N, O-hybrid donor ligands formed by pyridine rings and ester groups for extraction separation of actinides (III)

The reprocessing of spent nuclear fuel (SNF) is crucial for sustainable nuclear energy development. Efficient extraction and separation of actinides from SNF have garnered significant attention in nuclear research. Mixed extractants, such as Et-Tol-DAPhen, which combine soft and hard donors, exhibit selectivity in extracting transuranium elements. In this study, we investigated three N, O-hybrid donor ligands: L1 (dimethyl pyridine-2,6-dicarboxylate), L2 (dimethyl 1,10-phenanthroline −2,9-dicarboxylate), and L3 (dimethyl [2,2′,6′,2″-terpyridine] −6,6″-dicarboxylate). We systematically compared their bonding ability and separation efficiency with Np(III), Pu(III), Am(III) and Cm(III) using the DFT method. Molecular orbital and electrostatic potential analyses revealed that L2 exhibited strong coordination ability than L1 and L3. Bonding analysis indicated decreased covalency of metal–ligand bonds from Np to Cm, attributed to diminishing involvement of 5f orbitals. Thermodynamic analysis demonstrated that these ligands exhibited good extraction effects and successfully separated Cm from Am and Pu. These findings provide valuable guidance for developing efficient extractants.

Extraction of Actinides and Lanthanides from Nitric Acid Solutions with Phosphorylated Pyrazines

Extraction of Actinides and Lanthanides from Nitric Acid Solutions with Phosphorylated Pyrazines

Effect of Bridging Group Nature on the Extraction Ability of Diphenylphosphorylketones toward Actinides and Lanthanides

Effect of structure of phosphorylketones containing flexible alkyl and conformationally rigid fragments in the linker on extraction ability toward actinides and lanthanides has been studied. It has been shown that the introduction of conformationally rigid cycloalkanediyl and alkenediyl fragments in the bridge between P=O and C=O groups in the structure of molecule decreases efficiency of extractants for both actinides and lanthanides. At the same time, the introduction of flexible alkyl groups in linker structure increases complexing and extraction ability. This dependence has been explained theoretically by modeling complexation (DFT, PBE, cc-pVDZ), monodentate coordination was observed for all studied phosphorylalkanones

A Hydrophobic Deep Eutectic Solvent for Nuclear Fuel Cycle: Extraction of Actinides and Dissolution of Uranium Oxide

AbstractHydrophobic Deep Eutectic Solvents (DESs) have been attracting attention for metal ion extraction in solvent extraction process due to their favorable properties. A Trioctyl phosphine oxide (TOPO) and Thenoyl trifluoroacetone (HTTA) based hydrophobic DES was synthesized and characterized by FTIR and NMR spectroscopy. Actinide ions ( UO22+, Pu4+ and Am3+) and Eu3+ ion extraction was carried out using the DES which shows that it extracts these metal ions from aqueous nitric acid medium depending upon the molarity of nitric acid. At higher molarity of nitric acid (>5 M) the extraction becomes insignificant only for trivalent metal ions and open up the possibility to selectively strip trivalent metal ions from tetravalent and hexavalent ions. This DES was also used for dissolution of uranium oxide (UO3). The dissolution kinetics was studied and it was shown that oxide was dissolved within an hour at 80 °C. The maximum solubility of UO3 in DES was measured and found to be 130±5 mg/mL which is one of the highest reported solubility of UO3 in ILs and DES. The species of uranium which is formed in situ in DES was ascertained to be UO2(TTA)2.TOPO after dissolution of UO3 as supported by FTIR and NMR (1H and 31P) investigations.