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The first pre-edge feature with an intensity of 0.16 in the S K-edge X-ray absorption spectra of UO2(S2PR 2) (R = Ph and o-CF3C6H4) is entirely attributed to the transitions from S 1s orbitals to the unoccupied molecular orbitals due to the mixing between U 5f and S 3p orbitals., The dithiophosphinic acids (HS2PR 2) have been used for the selective separation of trivalent actinides (AnIII) from lanthanides (LnIII) over the past decades. The substituents on the di­thio­phosphinic acids dramatically impact the separation performance, but the mechanism is still open for debate. In this work, two di­thio­phosphinic acids with significantly different AnIII/LnIII separation performance, i.e. di­phenyl di­thio­phosphinic acid (HS2PPh2) and bis­(ortho-trifluoro­methyl­phenyl) di­thio­phosphinic acid [HS2P(o-CF3C6H4)2], are employed to understand the substituent effect on the bonding covalency between the S2PR 2 − anions (R = Ph and o-CF3C6H4) and the uranyl ion by sulfur K-edge X-ray absorption spectroscopy (XAS) in combination with density functional theory calculations. The two UO2(S2PR 2)(EtOH) complexes display similar XAS spectra, in which the first pre-edge feature with an intensity of 0.16 is entirely attributed to the transitions from S 1s orbitals to the unoccupied molecular orbitals due to the mixing between U 5f and S 3p orbitals. The Mulliken population analysis indicates that the amount of S 3p character in these orbitals is essentially identical for the UO2(S2PPh2)2(EtOH) and UO2[S2P(o-CF3C6H4)2]2(EtOH) complexes, which is lower than that in the U 6d-based orbitals. The essentially identical covalency in U—S bonds for the two UO2(S2PR 2)2(EtOH) complexes are contradictory to the significantly different AnIII/LnIII separation performance of the two di­thio­phosphinic acids, thus the covalency seems to be unable to account for substituent effects in the AnIII/LnIII separation by the di­thio­phosphinic acids. The results in this work provide valuable insight into the understanding of the mechanism in the AnIII/LnIII separation by the di­thio­phosphinic acids.

5f covalency in [U(C7H7)2]− was probed with carbon K-edge X-ray absorption spectroscopy (XAS) and electronic structure theory. The results are compared with earlier studies which show that the extent of δ-orbital mixing in [U(C7H7)2]1− is larger than reported previously for U(C8H8)2.

Separation studies during the past decades have demonstrated that ligands with “soft” donor atoms (e.g., N and S, relative to O) show greater affinity to An(III) over Ln(III) in solvent extraction....

Comparatively revealing the complexation behavior of trivalent actinides and lanthanides with functional ligands in aqueous solution is of great importance to enrich our knowledge on the fundamental coordination chemistry of trivalent f-block elements and to control the fate of minor actinides in nuclear fuel cycles. In this work, the complexation of Am(III) and Nd(III), representatives for trivalent actinides and lanthanides, respectively, with a N,O-hybrid ligand 6-(dimethylcarbamoyl)picolinic acid (DMAPA, denoted as HL) was investigated by absorption spectroscopy, calorimetry, X-ray crystallography, and density functional theory (DFT) calculations. Successive formation of 1:1, 1:2, and 1:3 (metal/ligand) complexes of Am(III) and Nd(III) with DMAPA was identified, and the corresponding thermodynamic parameters were determined. The binding strength of Am(III) with DMAPA is slightly stronger than that of Nd(III), and the complexation of Nd(III) with DMAPA is mainly entropy-driven. The crystal structure of the 1:2 Nd(III)/DMAPA complex and the DFT calculation shed additional light on the coordination and structural characteristics of the complexes. In contrast to the Nd-N bond in the Nd(III)/DMAPA complex, the Am-N bond in the Am(III)/DMAPA complex exhibits more covalency, which contributes to the slightly stronger complexation of Am(III) with DMAPA.

Monodentate organophosphorus ligands have been used for the extraction of the uranyl ion (UO22+) for over half a century and have exhibited exceptional extractability and selectivity toward the uranyl ion due to the presence of the phosphoryl group (O═P). Tributyl phosphate (TBP) is the extractant of the world-renowned PUREX process, which selectively recovers uranium from spent nuclear fuel. Trialkyl phosphine oxide (TRPO) shows extractability toward the uranyl ion that far exceeds that for other metal ions, and it has been used in the TRPO process. To date, however, the mechanism of the high affinity of the phosphoryl group for UO22+ remains elusive. We herein investigate the bonding covalency in a series of complexes of UO22+ with TRPO by oxygen K-edge X-ray absorption spectroscopy (XAS) in combination with density functional theory (DFT) calculations. Four TRPO ligands with different R substituents are examined in this work, for which both the ligands and their uranyl complexes are crystallized and investigated. The study of the electronic structure of the TRPO ligands reveals that the two TRPO molecules, irrespective of their substituents, can engage in σ- and π-type interactions with U 5f and 6d orbitals in the UO2Cl2(TRPO)2 complexes. Although both the axial (Oyl) and equatorial (Oeq) oxygen atoms in the UO2Cl2(TRPO)2 complexes contribute to the X-ray absorption, the first pre-edge feature in the O K-edge XAS with a small intensity is exclusively contributed by Oeq and is assigned to the transition from Oeq 1s orbitals to the unoccupied molecular orbitals of 1b1u + 1b2u + 1b3u symmetries resulting from the σ- and π-type mixing between U 5f and Oeq 2p orbitals. The small intensity in the experimental spectra is consistent with the small amount of Oeq 2p character in these orbitals for the four UO2Cl2(TRPO)2 complexes as obtained by Mulliken population analysis. The DFT calculations demonstrate that the U 6d orbitals are also involved in the U-TRPO bonding interactions in the UO2Cl2(TRPO)2 complexes. The covalent bonding interactions between TRPO and UO22+, especially the contributions from U 5f orbitals, while appearing to be small, are sufficiently responsible for the exceptional extractability and selectivity of monodentate organophosphorus ligands for the uranyl ion. Our results provide valuable insight into the fundamental actinide chemistry and are expected to directly guide actinide separation schemes needed for the development of advanced nuclear fuel cycle technologies.

5f covalency in [U(C

Bis[o-(trifluoromethyl)phenyl]dithiophosphinate is a sulfur-donating ligand capable of providing the largest reported trivalent lanthanide (Ln3+)–actinide (An3+) group separation factors. Literatur...

Comparative extraction of Am3+ over Eu3+ from nitric acid media by three dithiophosphinic acids (L) bearing different substituent aryl groups was studied. Within the experimental pH range, the distribution ratio of Am3+ and Eu3+ increases with the increase of pH due to deprotonation of the acidic extractant. Both the extraction and separation ability toward Am3+/Eu3+ by these extractants were affected drastically by the substituent aryl groups. The bis-phenyl substituted extractant shows almost no ability to extract and separate Am3+ from Eu3+, while bis(ortho-trifluoromethylphenyl) dithiophosphinic acid has the optimum extraction and separation capabilities. To help reveal the complexation and extraction behavior, the structure and bonding characters of neutral ML3 (M = Am or Eu) complexes as well as the biphasic extraction reaction were studied by density functional theory (DFT). The conduct-like screening model implicit solvation model was used to simulate the extraction reaction in the aqueous-toluene biphasic system. The calculated sequence of the Gibbs free energy difference of extraction (ΔΔG ext Am/Eu ) is consistent with the experimental results.

The complexation of two representative trivalent lanthanides, Nd(III) and Eu(III), with three monodentate organophosphorus ligands, tributyl phosphate (TBP), dibutyl butyl phosphonates (DBBP) and tributylphosphine oxide (TBPO) in the ionic liquid (IL) C4mimNTf2 was investigated by absorption spectroscopy, luminescence spectroscopy, and microcalorimetry. The Nd(III) complexes formed in the IL were successfully identified and their corresponding thermodynamic parameters were determined. As the alkoxyl group is gradually replaced by an alkyl group from TBP to TBPO, the stability of the Nd(III) complexes increases significantly. Moreover, the nature of the complexes was further elucidated on the basis of thermodynamic analysis as well as luminescence characterization. The overall endothermic feature of the complexation process indicates that Nd(III) and the ligands form inner-sphere coordination complexes in the ionic liquid, which is further supported by luminescence studies with Eu(III) as the surrogate. Upon introduction of organophosphorus ligands, the symmetry of Eu(III) complexes becomes lower and water molecules in the primary coordination sphere of Eu(III) were gradually replaced by the organophosphorus ligands. The results from this work provide valuable thermodynamic and structural insights into the coordination chemistry of lanthanides in ionic liquids.

The selective separation of trivalent americium from lanthanides in a nitric acid medium by a tetradentate ligand, N,N′-diethyl-N,N′-ditolyl-2,9-diamide-1,10-phenanthroline (Et-Tol-DAPhen), in an i...

Fluorescent polydopamine nanoparticles (FPD) are a kind of promising fluorescent nanoparticles for biosensing and imaging, while the rapid and controllable synthesis of FPD is still challenging. In this paper, we developed a microplasma electrochemistry strategy to regulate the oxidative polymerization process of dopamine, resulting in a controlled formation of FPD. Treating the dopamine solution with microplasma anode could not only generate oxidative species to trigger the nucleation of polydopamine nanoparticles at the plasma-liquid interface, but also provide an acidic environment to inhibit their further growing up during the diffusion process. Thus, uniform FPD with a diameter of 3.1 nm could be prepared within minutes. And, continuous generation of FPD could be achieved without the formation of aggregates when prolonging the reaction time. The obtained FPD had abundant functional groups on the surfaces, showing tunable fluorescent emission properties. These luminescent nanoparticles were demonstrated for highly selective detection of uranium with a detection limit of 2.1 mg/L. The novel microplasma electrochemistry strategy established in this work provided better opportunity for controllable synthesis of FPD, as well as other luminescent nanoparticles, and broadened their application in chemical sensing area.

Bis(2-propyloxy)calix[4]arene-crown-6 ( L1 ) is a ligand with high affinity in the extraction of Cs(I). In this work, acrylamido and propionamido groups are decorated at the opposite site of 2-propyloxy on the phenyl ring of L1 , giving rise to the derivatives L2 and L3 , respectively. Complexation of all the three ligands with Cs(I) is characterized by NMR, spectrophotometric titration, crystal structure and DFT calculation. Both the NMR and spectrophotometric analysis suggest more significant variation of electron density on the phenyl rings in L2 and L3 than that in L1 in complexation with Cs(I). The stability constants (log β ) of the complexes are calculated to be 6.0 ± 0.1, 6.2 ± 0.1 and 6.3 ± 0.1 for Cs- L1 , Cs- L2 and Cs- L3 , respectively, by fitting of the absorption spectra. As reflected by the crystal structures and DFT calculations, the complexed cesium cation interacts with the crown ether moiety, the two rotated phenyl rings and the acrylamido/propionamido groups in L2 / L3 , which can be regarded as an intramolecular triple cooperative effect. Extraction of Cs(I) from aqueous solution is performed, and the distribution ratio is in line with the findings in stability constant and interaction energy. This work contributes to further improvement of the extraction of cesium cation by 1,3-alternate calix[4]arene-crown-6.

The extraction of lanthanide series by Cyanex301, i.e., bis(2,4,4-trimethylpentyl)dithiophosphinic acid (HC301), has been modeled by density functional theory calculation, taking into account the formation of both inner- and outer-sphere complexes. The inner-sphere complex Ln(C301)3 and the outer-sphere complex Ln(H2O)9(C301)3 are optimized, followed by the analysis of interaction energy, bond length, Laplacian bond orders, and Mulliken populations. The covalency degree increases in Ln–S and Ln–O bonds in the inner- and outer-sphere complexes, respectively, as the lanthanide series is traversed. Mulliken population analysis indicates the important role of the 5d-orbital participation in bonding in the formation of inner- and outer-sphere complexes. Two thermodynamic cycles regarding the formation of inner- and outer-sphere complexes are established to calculate the extraction Gibbs free energies (ΔGextr), and relaxed potential energy surface scan is utilized to model the kinetic complexation of C301 anion with hydrated metal ions. Light lanthanides can form both inner- and outer-sphere complexes, whereas heavy lanthanides only form outer-sphere complexes in biphasic extraction. After adopting the data of forming inner-sphere complex for light Ln(III) and that of forming outer-sphere complexes for heavy Ln(III), the trend of the calculated −ΔGextr agrees very well with that of the experimental distribution ratios on crossing the Ln(III) series. Results from this work help to theoretically understand the extraction behavior of Cyanex301 with respect to different Ln(III).

The complexation of U(VI) with diphenyldithiophosphinic acid (denoted as HL) in acetonitrile was studied by UV–Vis, FT-IR, crystallography and DFT calculations. UV–Vis absorption spectrophotometry implies that three successive complexes, UO2L+, UO2L2, UO2L3−, form in the solution. Significant ligand to metal charge transfer occurs from soft atom S to U(VI) in all the three complexes. A crystal of UO2L2 complex was successfully synthesized from the solution. In the crystal both the two ligands coordinate to U(VI) in bidentate form. DFT calculations confirm the formation of UO2L3− complex and help illustrate the structures of all the U(VI) species in the solution.

Fundamental coordination chemistry of metal ions in ionic liquids (ILs) is of great importance to extend the application of ILs in the area of metal separation. In this work, the solvation of representative trivalent lanthanides (Nd, Eu and La) and their complexation with a functional ligand, octylphenyl-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO, denoted as L), in the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (C4mimNTf2) have been probed by spectroscopic, calorimetric and theoretical techniques. Absorption spectrophotometric titrations suggest that four successive Nd/CMPO complexes, NdLj3+ (j = 1–4), form both in “dry” (water content

The hydraulic characteristics of the 30% TRPO (trialkylphosphine oxide)/kerosene―1.0 M HNO3 and 0.025 M iPr-C [4]C-6 (25,27-bis(isopropoxy) calix [4]-26,28-crown-6)/n-octanol―1.3 M HNO3 systems were systematically investigated in a φ20 ACE (annular centrifugal extractor) to find the cause of the hydraulic performance problem of the CECE (calixcrown ether extraction) process operated in ACEs. The results show that the operating and structure parameters have different influences on the F (A/O) (phase ratio (A/O)) and V (liquid hold-up volume). Moreover, the Vr (V of the rotor) of the 30%TRPO/kerosene―HNO3 and iPr-C [4]C-6/n-octanol―HNO3 systems are almost same, while the Vm (V of the mixing zone) and Vt (total V of the ACE) for the former are slightly higher than those for the latter under the same experimental conditions. Meanwhile, both the Fm (A/O) (F (A/O) of the mixing zone) and Fs(A/O) (F (A/O) of the separating zone) for the 30%TRPO/kerosene―HNO3 system are also higher than those for the iPr-C [4]C-6/n-octanol―HNO3 system under the same experimental conditions. Moreover, the Fs(A/O) of the iPr-C [4]C-6/n-octanol―HNO3 system is less than 1.5 under most of the present experimental conditions, which shows organic phase entrainment may easily occur in the outlet aqueous phase. This may be the cause of the hydraulic performance problem of the CECE process operated in ACEs.

Bis(trifluoromethylsulfonyl)imide (NTf 2 − ) and hexafluorophosphate (PF 6 − ) are the most frequently used anions for hydrophobic ionic liquids (ILs) which have been considered as promising solvents in the extraction of cesium ions. The interactions of NTf 2 − and PF 6 − with Cs + were explored in this work. The results of DFT calculation indicated that both Cs + and Cs(18C6) + prefer to interact with two NTf 2 − or PF 6 − anions in gas phase, where 18C6 is 18-crown-6. The complex of Cs(NTf 2 ) 2 − was observed in electrospray ionization mass spectrometry (ESI-MS), and the complexes of [Cs(18C6)NTf 2 ] 2 and [Cs(18C6)PF 6 ] 2 were crystallized in which Cs(18C6) + interacted with two anions. The interactions of NTf 2 − with cesium resulted in a synergistic effect between dicyclohexano-18-crown-6 (DCH18C6) and NTf 2 − in the extraction of Cs + using n -octanol as diluent. However, DFT calculation revealed that the complex Cs(DCH18C6) + interacted with one NTf 2 − anion was more thermodynamically stable than that with two anions in organic phase, different from that in gas phase.

In the extraction of U(VI) by tri-n-butyl phosphate (TBP) in bis(trifluoromethylsulfonyl)imides (NTf2−) based ionic liquids (ILs), an unexpected high distribution ratio was observed when P6,4,4,4NTf2 was used as the solvent, where P6,4,4,4+ is hexyltributylphosphonium. Further research showed that P6,4,4,4NTf2 was able to extract U(VI) in the absence of extractants, and the extraction ability of P6,4,4,4NTf2 was attributed to the combination of the outer-sphere interaction between NTf2− and U(VI) and the intramolecular interaction between NTf2− and P6,4,4,4+. The outer-sphere interaction of NTf2− with U(VI) was theoretically explored by DFT calculation. Walden plot were employed to discover the intramolecular interaction in ILs, among which P6,4,4,4NTf2 showed a much stronger intramolecular interaction than other NTf2− based ILs. Stripping of U(VI) from P6,4,4,4NTf2 was also investigated by use of supercritical carbon dioxide (Sc-CO2). This work shed a light on the role of intramolecular interactions in ILs in the extraction of metal ions.

The extraction of Am3+ and Eu3+ by octyl(phenyl)-N,N-diisobutyl carbamoylmethylphosphine oxide (CMPO) in eight imidazolium-based ionic liquids and in n-dodecane was studied and compared. Slope analysis indicates that the ligand/metal ratio in the extracted complexes in ionic liquids is much larger than that in n-dodecane. Nitric acid has different impacts on the extraction, depending greatly on the nature of the ionic liquids. A mixed-extraction mechanism, namely cation exchange plus the formation of neutral complexes (solvation), was proposed for the extraction in the ionic liquid systems. In addition, temperature was found to have a remarkable influence on the extraction. Highly exothermic enthalpy changes were obtained for the extraction in ionic liquid systems. This work provides further insight into the particular role played by the unique properties of ionic liquids in the extraction of metal ions from nitric acid media.

Denitration of simulated high level liquid waste (HLLW) by formic acid was performed for the connection of Plutonium Uranium Recovery by EXtraction (PUREX) process with trialkyl phosphine oxide (TRPO) process. The concentration of acid, anions and metal ions in solution were monitored under different mole ratios of formic acid to nitric acid and denitration time. Precipitates formed were characterized by Scanning electron microscope, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy and X-ray absorption near edge structure. This work presents a promising strategy for the connection of PUREX process with TRPO process and also provides some new information on the precipitation behavior in denitration of HLLW.

Developing facile and robust technologies for effective enrichment of uranium from seawater is of great significance for resource sustainability and environmental safety. By exploiting mussel-inspired polydopamine (PDA) chemistry, diverse types of PDA-functionalized sorbents including magnetic nanoparticle (MNP), ordered mesoporous carbon (OMC), and glass fiber carpet (GFC) were synthesized. The PDA functional layers with abundant catechol and amine/imine groups provided an excellent platform for binding to uranium. Due to the distinctive structure of PDA, the sorbents exhibited multistage kinetics which was simultaneously controlled by chemisorption and intralayer diffusion. Applying the diverse PDA-modified sorbents for enrichment of low concentration (parts per billion) uranium in laboratory-prepared solutions and unpurified seawater was fully evaluated under different scenarios: that is, by batch adsorption for MNP and OMC and by selective filtration for GFC. Moreover, high-resolution X-ray photoelectron spectroscopic and extended X-ray absorption fine structure studies were performed for probing the underlying coordination mechanism between PDA and U(VI). The catechol hydroxyls of PDA were identified as the main bidentate ligands to coordinate U(VI) at the equatorial plane. This study assessed the potential of versatile PDA chemistry for development of efficient uranium sorbents and provided new insights into the interaction mechanism between PDA and uranium.

The removal and separation of uranium from aqueous solutions are quite important for resource reclamation and environmental protection. Being one of the most effective techniques for metal separation, adsorption of uranium by a variety of adsorbent materials has been a subject of study with high interest in recent years. However, current methods for monitoring the adsorption process require complicated procedures and tedious measurements, which hinders the development of processes for efficient separation of uranium. In this work, we prepared a type of luminescent mesoporous silica-carbon dots composite material that has high efficiency for the adsorption of uranium and allows simultaneous in situ monitoring of the adsorption process. Carbon dots (CDs) were prepared in situ and introduced onto amino-functionalized ordered mesoporous silica (SBA-NH2) by a facile microplasma-assisted method. The prepared CDs/SBA-NH2 nanocomposites preserved the high specific surface area of the mesoporous silica, as well as...

Complexation of trivalent lanthanides with a sulfur-bearing ligand, bis(2,4,4-trimethylpentyl) dithiophosphinate, was studied in ethanol under identical conditions by optical spectroscopy, microcalorimetry, luminescence lifetime measurement, and extended X-ray absorption fine structure (EXAFS). Three successive complexes, LnL2+, LnL2+, and LnL3, where Ln and L denote the trivalent lanthanide and the dithiophosphinate ligand, respectively, formed in the solution. In contrast to the general findings that heavier lanthanides form stronger complexes due to the lanthanide contraction effect, the complexation strength between Ln(III) and dithiophosphinate first increases from La(III) to Nd(III) and then decreases gradually toward heavier Ln(III) across the lanthanide series. This trend agrees well with the results of solvent extraction using the same ligand as an extractant. The complexation is driven by highly positive entropies and opposed by endothermic enthalpies. The enthalpies of complexation become less ...

Bis[

Recently, phenanthroline-based ligands have received increasing attention due to their excellent separation capabilities for trivalent actinides over lanthanide. In this work, we designed a soft-hard donor combined tetradentate phenanthroline-based extractant, tetraethyl (1,10-phenanthrolin-2,9-diyl)phosphonate (C2-POPhen), for the selective separation of trivalent Am(III) over Ln(III) from HNO3 media. The solvent extraction and complexation behaviors of Am(III) and Ln(III) by C2-POPhen were investigated both experimentally and theoretically. C2-POPhen could selectively extract Am(III) over Eu(III) with an extremely fast extraction kinetics. NMR titration studies suggest that only 1:1 complexes of Ln(III) with C2-POPhen formed in CH3OH in the presence of a significant amount of nitrate, while both 1:1 and 2:1 complexes species could form between C2-POPhen and Ln(III) perchlorate in CH3OH without nitrate ions. The stability constants for the complexation of Am(III) and Ln(III) with C2-POPhen in CH3OH were determined by spectrophotometric titrations and the Am(III) complexes are approximately 1 order of magnitude stronger than those of Ln(III), which is consistent with the extraction results. Theoretical calculations indicate that the Am-N bonds in Am/C2-POPhen complexes possess more covalent characters than the Eu-N bonds in Eu/C2-POPhen complexes, shedding light on the underlying chemical force responsible for the Am/Eu selectivity by C2-POPhen. This work represents the first report utilizing phenanthroline-based phosphonate ligands for selective separation of actinides from highly acidic solutions.

Correction for ‘Enhanced 5f-δ bonding in [U(C7H7)2]−: C K-edge XAS, magnetism, and ab initio calculations’ by Yusen Qiao et al., Chem. Commun., 2021, 57, 9562–9565, DOI: 10.1039/D1CC03414F.

The reversed micelles formed in solvent extraction of thorium(IV) by bis(2-ethylhexyl) phosphoric acid (HDEHP) in n-heptane were studied. IR spectra, dynamic/static light scattering and zero shear viscosity measurements indicated that thorium complexes formed rodlike reversed micelles, and both the size of aggregates and the viscosity of the organic phase increased with the increasing loadage of thorium(IV). The entanglement of reversed micelles resulted in their transformation to wormlike reversed micelles, inducing the very high viscosity of the organic phase. The structural composition of thorium complexes was proposed to be Th(DEHP)3(NO3) according to the results of log -log plot and job method analysis. Furthermore, molecular modeling was employed to clarify the structures of reversed micelles as well as the state of water inside. It was found that the complexes linked together via hydrogen bonding and van der Waals forces and that the existence of NO3 – and H2O improved the stability of reversed micelles.

The complexation of hexavalent plutonyl Pu(VI) with N,N,N′,N′-tetramethyl-3-oxa-glutar-amide (TMOGA) and its carboxylate analogs, N,N-dimethyl-3-oxa-glutaramic acid (DMOGA) and oxydiacetic acid (ODA), has been studied in 1.0 M NaClO4 by absorption spectrophotometry and density functional theory (DFT). Both 1 : 1 and 1 : 2 complexes of Pu(VI) with TMOGA, DMOGA and ODA have been identified and their stability constants were obtained and compared with those of hexavalent U(VI) and pentavalent Np(V). The resultant stability constants indicate that the ability of the three ligands to complex with Pu(VI) decreases in the order of ODA > DMOGA > TMOGA. While for one given ligand, the stability constants of both the 1 : 1 and 1 : 2 complexes decrease generally in the order U(VI) > Pu(VI) > Np(V). The trends of the complexation strength have been elucidated by the calculated Mulliken atomic charges of the central metal cations. Furthermore, the coordination modes of the Pu(VI) complexes with TMOGA, DMOGA and ODA have been illustrated by analyses of the optical features of the complexes as well as by DFT calculations. The results demonstrate that the 1 : 2 Pu(VI)/TMOGA complex is centrosymmetric, while the 1 : 2 complexes of Pu(VI) with DMOGA and ODA are non-centrosymmetric. Moreover, different coordination modes have been observed in actinyl complexes with the same ligand, suggesting the structurally similar actinyl ions (U(VI), Pu(VI) and Np(V)) could exhibit quite different coordination behavior due to the variation of cation size and electronic structure.

A TRPO (tri-alkyl phosphine oxide) process with 30% TRPO–kerosene as extractant for the removal of actinides from high level liquid waste (HLLW) has been developed in China. It is important to decrease the extraction of Fe to prevent third phase formation in the TRPO process. In this paper, the separation of Nd 3+ and Fe 3+ with 30% TRPO–kerosene from nitric acid solution by non-equilibrium solvent extraction using a 20-mm-diam. annular centrifugal contactor (ACC) was investigated. The extraction stage efficiency ( E A ) of Nd 3+ was more than 95%, much higher than that of Fe 3+ . The E A of Nd 3+ and Fe 3+ varied with the changes of the total flow rate, the flow ratio (aqueous phase/organic phase, A/O), the rotor speed, the width of the annular gap, and the height of the clearance, but the effects of these parameters on the E A of Nd 3+ is different from that of Fe 3+ . These results show that non-equilibrium solvent extraction using ACCs can be used for the separation of Nd 3+ and Fe 3+ with 30% TRPO–kerosene from nitric acid solution. Accordingly, non-equilibrium solvent extraction using ACCs can also be used for the separation of trivalent actinides and Fe 3+ with 30% TRPO–kerosene, based on the fact that the extraction behavior of trivalent actinides is similar to that of Nd 3+ with 30% TRPO–kerosene from nitric acid solution, and thus avoiding third phase formation in the TRPO process.

The complexation of U(VI) with octylphenyl-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO, denoted as L) in ionic liquid (IL) C4mimNTf2 was investigated by UV–vis absorption spectrophotometry and isothermal titration calorimetry. Spectro-photometric titration suggests that three successive complexes, UO2Lj2+ (j = 1–3), formed both in “dry” (water content < 250 ppm) and “wet” (water content ≈ 12 500 ppm) ionic liquid. However, the thermodynamic parameters are distinctly different in the two ILs. In dry IL, the complexation strength between CMPO and U(VI) is much stronger, with stability constants of the respective complexes more than 1 order of magnitude higher than that in wet IL. Energetically, the complexation of U(VI) with CMPO in dry IL is mainly driven by negative enthalpies. In contrast, the complexation in wet IL is overwhelmingly driven by highly positive entropies as a result of the release of a large amount of water molecules from the solvation sphere of U(VI). Moreover, comparisons between ...

The formation of water-in-oil (W/O) microemulsions during the extraction of the series of trivalent lanthanides Ln(III) by bis(2,4,4-trimethylpentyl)dithiophosphinic acid (HC301, also known as purified Cyanex 301) was studied. The phenomena in the formation of W/O microemulsions were similar in the extraction of all Ln(III) by HC301 at a high neutralization degree (50%), according to the measurement of the distribution ratios of Ln(III) and the concentrations of Na+ and NO3- in the organic phase, IR spectroscopy, and dynamic light scattering (DLS). W/O microemulsions also formed at a low neutralization degree (15%) for the extraction of heavy Ln(III). The coordination environment of the representative heavy lanthanide Ho(III) in the extracted complexes was monitored by absorption spectroscopy and extended X-ray absorption fine structure (EXAFS). Unlike the light lanthanide, Nd(III) and Ho(III) in the organic phase did not directly coordinate with the HC301 anions regardless of whether W/O microemulsions formed, which further demonstrated the different extraction behavior of HC301 toward the light lanthanides and the heavy lanthanides.

A calixcrown extraction process using bis(2-propyloxy)calix[4]-crown-6 (iPr-C[4]C-6) as extractant and n-octanol as diluent for the separation of cesium from Chinese High Level Liquid Waste (HLLW) has been developed at INET. Chinese HLLW is acidic defense waste with high salt content, which is now stored in underground stainless steel tanks. The intention is to use a process to extract cesium from HLLW conducted on multistage 20-mm-diameter annular centrifugal contactors (ACCs), so it is necessary to study the hydraulic and mass-transfer performance of a 20-mm-diameter ACC for the extraction system. In this work, the effects of the parameters such as the rotor speed, the diameter of heavy weir, and the acid concentration on the hydraulic performance were investigated. An operational envelope of the 20-mm-diameter ACC for the n-octanol/aqueous solution system was identified. The mass-transfer efficiency of the single stage 20-mm-diameter ACC for the extraction and stripping of cesium with iPr-C[4]C-6 in n-...

The extraction of U(VI) from nitrate solution was investigated using a polyazamacrocycle-type C8-cyclen ligand as extractant. The effect of aqueous phase acidity, temperature, ligand concentration, nitrate concentration and irradiation dose on the distribution ratio of U(VI) was studied. The extraction of U(VI) was significantly affected by pH due to the protonation of C8-cyclen and the hydrolysis of U(VI). Uranyl nitrate was extracted via neutral complex reaction mechanism, forming a 1:1 complex with C8-cyclen. The extraction is an exothermic reaction with entropy reduction. U(VI) could be easily stripped from the loaded organic phase by sodium carbonate solution. C8-cyclen showed good stability toward γ-irradiation. No obvious decomposition was observed under the dose of 104 Gy. A small amount of C8-cyclen decomposed at the dose of 105 Gy and the distribution ratio of U(VI) increased to some extent.

The interactions between hydrophobic anions of ionic liquids (ILs) and Triton X-114 (TX-114) micelles were studied in this work. The 1-alkyl-3-methylimidazolium based ILs with the anions bromide (Br−), tetrafluoroborate (BF4−), hexafluorophosphate (PF6−) and bis(trifluoromethylsulfonyl)imide (NTf2−) were selected to study their effects on physicochemical properties of the TX-114 micellar solution. Both the hydrophilic ILs with long alkyl (e.g., C12mimBr) and hydrophobic ILs (e.g., C4mimNTf2) significantly influenced the aggregate size and increased the absolute value of zeta potential as well as the cloud point. However, C4mimNTf2 changed the critical micellar concentration (CMC) and the aggregation number much less whereas made the micellization enthalpy decrease more obviously than C12mimBr did. It was suggested that the hydrophobic IL anions (PF6−, NTf2−) are located at the head group area of TX-114 micelles and interact with the ethylene oxide groups of TX-114 molecules. This work gives a further understanding of the interactions between IL cation/anion and micelles.

The cloud point extraction (CPE) of uranyl ions by different kinds of extractants in Triton X-114 (TX-114) micellar solution was investigated upon the addition of ionic liquids (ILs) with various anions, i.e., bromide (Br(-)), tetrafluoroborate (BF4(-)), hexafluorophosphate (PF6(-)) and bis[(trifluoromethyl)sulfonyl]imide (NTf2(-)). A significant increase of the extraction efficiency was found on the addition of NTf2(-) based ILs when using neutral extractant tri-octylphosphine oxide (TOPO), and the extraction efficiency kept high at both nearly neutral and high acidity. However, the CPE with acidic extractants, e.g., bis(2-ethylhexyl) phosphoric acid (HDEHP) and 8-hydroxyquinoline (8-HQ) which are only effective at nearly neutral condition, was not improved by ILs. The results of zeta potential and (19)F NMR measurements indicated that the anion NTf2(-) penetrated into the TX-114 micelles and was enriched in the surfactant-rich phase during the CPE process. Meanwhile, NTf2(-) may act as a counterion in the CPE of UO2(2+) by TOPO. Furthermore, the addition of IL increased the separation factor of UO2(2+) and La(3+), which implied that in the micelle TOPO, NTf2(-) and NO3(-) established a soft template for UO2(2+). Therefore, the combination of CPE and IL provided a supramolecular recognition to concentrate UO2(2+) efficiently and selectively.

The extraction of Th(IV) from aqueous phase into the ionic liquids (ILs) 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imides (C n mimNTf 2 , n = 2, 4, 6, 8) by the β -diketone extractant 2-thenoyltrifluoroacetone (HTTA), and the stripping of Th(IV) from the IL phase using supercritical carbon dioxide (sc-CO 2 ) were studied. Th(IV) was extracted efficiently by HTTA-C n mimNTf 2 systems. A neutral complex extraction mechanism was proposed via log–log plot analysis method and ion chromatograph (IC) method. The formed neutral complex partitioning in all four IL systems was Th(TTA) 4 , and the structure was further confirmed by Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS). Supercritical CO 2 with ethanol showed good stripping of Th(IV) from the IL phase. The pressure and temperature of CO 2 , the volume and polarity of modifiers, and the dynamic extraction time influencing on the stripping efficiency were examined.

The cation exchange mechanism was further investigated during the extraction of Sr2+ and Cs+ using the extractant dicyclohexano-18-crown-6 (DCH18C6) in an ionic liquid (IL) 1-ethyl-3-methyimidazolium bis[(trifluoromethyl)sulfonyl]imide (C2mimNTf2). The concentrations of both the cation C2mim+ and the anion NTf2 − in aqueous phase were detected. The concentration of NTf2 − in the aqueous phase decreased as Sr2+ or Cs+ exchanged into the IL phase. Addition of C2mim+ or NTf2 − as well as the variation of the solubility of C2mimNTf2 influenced the extraction efficiency of Sr2+ or Cs+.

A precipitate was found at the interface between the aqueous phase and the ionic liquid (IL) phase during the separation of UO22+/Eu3+ using irradiated IL 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imides (C(4)mimNTf(2)), and was analyzed by SEM, EDS, XPS and PXRD. The anions F- and SO42- were identified as the radiolytic products of C(4)mimNTf(2). The radiation effect on the extraction of UO22+ from aqueous solution by tri-n-butyl phosphate (TBP) in C(4)mimNTf(2) was studied. For the presence of F- and SO42-, the utilization of irradiated C(4)mimNTf(2) as diluent reduced the extraction efficiency of UO22+. The EXAFS measurement showed that the degradation of C(4)mimNTf(2) insignificantly influenced the coordination environment of UO22+ in the IL phase. Furthermore, it was suggested that the complex of uranyl ion with four TBP molecules is predominant during the extraction of UO22+ by TBP in C(4)mimNTf(2) from aqueous solution in the absence of nitric acid. This work gives a further assessment for the application of ILs in the processing of spent nuclear fuel. (C) 2012 Elsevier Ltd. All rights reserved.

The development of economical and green technologies for the effective recovery of palladium has attracted worldwide attention in recent years. Magnetic separation involving the use of functional magnetic nanoparticles (MNPs) with superparamagnetic characteristics holds great promise in this respect. This study presents a novel class of core-shell structured superparamagnetic microspheres decorated with polyazamacrocyclic receptors, which show a highly-selective binding to Pd(ii) in HNO3 media. The superparamagnetic microspheres possess a high saturation magnetization (53.8 emu g(-1)) and high adsorption capacity (qmax≈ 105.3 μmol g(-1)), affording efficient enrichment and fast separation (within 13 seconds) of palladium under an applied magnetic field. Adsorptive behavior was fully investigated combined with the corresponding theoretical analysis by using kinetic equations and Langmuir/Freundlich isotherm models. Moreover, the coordination mechanism of the polyazamacrocyclic receptors to Pd(ii) was carefully examined based on high resolution X-ray photoelectron spectroscopy (XPS) and FT-IR spectrophotometry. A suggested mechanism involving the synergistic effect of the cyclic amines and carboxyl arms of the polyazamacrocyclic receptors was proposed to describe the coordination manner, while explaining the selectivity to Pd(ii) in HNO3 solutions. From a practical perspective, the Pd(ii)-enriched microspheres could be readily regenerated for cycle use. We conclude that this kind of polyazamacrocyclic receptor decorated superparamagnetic microsphere is of potential use for the effective recovery of Pd(ii) as well as other precious metals.

A complex of Cs + with the calixcrown bis(2-propyloxy)calix[4]crown-6 (BPC6) and bis[(trifluoromethyl)sulfonyl]imide (NTf 2 − ), an anion of ionic liquid (IL), was crystallized in the interface region between n -octanol and water. The compound was characterized by single crystal X-ray diffraction, ESI-MS, FT-IR, TGA and PXRD. Cs + is coordinated with BPC6 by both the six oxygen atoms of the crown and the cation–π interactions, and with the anion NTf 2 − via one oxygen atom of the sulfonyl group. This single crystal explains the good extraction ability of BPC6 to Cs + and reflects a coordinating interaction of NTf 2 − with the deficient complex [Cs·BPC6] + during the extraction with an IL as diluent.