Time-resolved Laser Fluorescence Spectroscopy Research Articles

Natural and synthetic plagioclases: Surface charge characterization and sorption of trivalent lanthanides (Eu) and actinides (Am, Cm)

The environmental fate of radiotoxic actinides may be controlled by their interactions with feldspars. Here, the sorption of trivalent minor actinides (Am, Cm) and their rare earth analog Eu onto synthetic pure Ca-feldspar (anorthite) and natural plagioclases of different Ca contents is investigated, covering ranges of [M3+] (52 nM–10 μM), solid-liquid ratios (1–3 g/L), pH (3–9), and ionic strengths (0.01–0.1 M NaCl) under both ambient and CO2-free conditions. As a first step to understand the uptake behavior of the heavy metals, the hitherto unknown surface charge and (de-)protonation reaction of Ca-feldspars is characterized. The zeta potential shows an unusual increase and charge reversal between pH 4 and 7 , which becomes more pronounced with increasing amounts of Ca in the crystal lattice and is likely connected to adsorption and/or surface precipitation of dissolved Al3+. Streaming potential measurements yield (de)protonation constants for anorthite surface sites of log K- = −6.94 ± 0.38 and log K+ = +6.84 ± 0.38. Batch sorption data shows strong immobilization of M3+ by plagioclases at mildly acidic and basic pH. Time-resolved laser fluorescence spectroscopy using Cm indicates the formation of an inner-sphere complex and its two hydrolyzed forms. The complex reactivity of dissolved Al3+ at the plagioclase-water interface severely complicated the development of a surface complexation model, emphasizing the need for additional research in this area. Our study highlights the importance of molecular-level studies to understand surface reactions and uncover unknown processes, which may have significant impact on the transport of (radiotoxic) contaminants in the geosphere.

U(VI) sorption on illite in the presence of carbonate studied by cryogenic time-resolved laser fluorescence spectroscopy and parallel factor analysis

Identification of sorption species of uranium (U) on clay minerals by spectroscopic techniques would consolidate the reliability of predicted sorption models. However, it is still challenging, especially, under complex environmental conditions, where the surface loading is low, and quenching elements for spectroscopic analyses hamper the application. In light of this, the sorption of U(VI) on illite at different pH and dissolved inorganic carbon (DIC) levels was investigated by using batch experiments, surface complexation modeling, and cryogenic time-resolved laser fluorescence spectroscopy (cryo-TRLFS) combined with parallel factor analysis (PARAFAC). The inhibiting effect of DIC on U(VI) sorption was revealed by the macroscopic batch experimental results. However, there was still sorption of U(VI) on illite even at a high DIC (19 mM), validating certain retention capacities of illitic clay minerals for U(VI) even from pore waters with high DIC. An updated 2-site protolysis non-electrostatic surface complexation and cation exchange model considering the formation of two uranyl-carbonate sorption complexes was able to reproduce the experimental results well. Based on the PARAFAC analysis on the cryo-TRLFS spectra, there was clear correspondence in the variation trend of the derived components with the sorption species from the modeling results, validating the formation of ternary uranyl-carbonate sorption species. The results imply that ternary uranyl-carbonate sorption species need particular consideration in the modeling of U(VI) sorption on clay minerals at high DIC levels. Identifying the sorption species adds more credibility to the predictive sorption model, which provides more confidence in the safety assessment of deep geological disposal. In addition, these results help better understand the fate of uranium during transport in geological disposal-related environments.

Spectroscopic characterization of europium binding to a calmodulin-EF4 hand peptide-polymer conjugate.

The emergence of biological ligand as an alternative to chemical ligands enables a sustainable lanthanide extraction route. In this study, a peptide originating from the loop of domain 4 calmodulin (EF4) was synthesized and the interaction with europium ions was monitored using time resolved laser fluorescence spectroscopy (TRLFS). Despite being retracted from its full protein structure, the twelve amino acids of calmodulin-EF4 showed binding to europium. Europium-peptide complex formation was evident by an increase in decay time from 110 to 187 μs. The spectra of europium bound to peptide can be easily distinguished from the free europium ion as the 5D0 → 7F2 peak intensifies. When europium bound to the peptide-polymer conjugate, the decay time was further increased to 259 μs. This suggests that lanthanide binding can be enhanced by immobilizing the short peptide into a polymer matrix. The europium-peptide/conjugate bond was reversible, triggered by pH, promoting peptide reusability. Due to the fact that the study was conducted exclusively in water, it suggests minimal use of chemicals is possible while maintaining peptide affinity. This makes the calmodulin-EF4 peptide an ideal candidate as biological ligand. This study lays the groundwork for developing a peptide-based filter material for lanthanide separation.

Thermodynamics of the Eu(III)-Mg-SO4-H2O and Eu(III)-Na-SO4-H2O systems. Part II: spectroscopy experiments, complexation and Pitzer/SIT models.

A time-resolved laser fluorescence spectroscopy (TRLFS) study was carried out to investigate the Eu(III)-SO4 complexation at room temperature over a wide range of Na2SO4 concentrations (0-2 mol kg-1). Spectroscopic observations confirm the step-wise formation of the aqueous complexes Eu(SO4)+, Eu(SO4)2- and Eu(SO4)33- over the investigated Na2SO4 concentrations. Combining TRLFS data obtained in this study and solubility data reported in Part I of this work for the Eu2(SO4)3-Na2SO4-H2O and Eu2(SO4)3-MgSO4-H2O systems, thermodynamic and activity models were derived based on the SIT and Pitzer formalisms. A combination of the geochemical calculation codes PhreeqC (SIT), PhreeSCALE (Pitzer) and the parameter estimation code PEST was used to determine the solubility products of Eu2(SO4)3·8H2O(cr) and Na2Eu2(SO4)4·2H2O(cr), stability constants of the Eu(III)-SO4 complexes (β0i), and the specific binary and ternary interaction parameters (εij, β(0)ij, β(1)ij, Cϕij, θik, Ψijk) for both activity models. The thermodynamic constants determined in this work are discussed with reference to values available in the literature.

Uranium(VI) Sorption onto Hardened Cement Paste under High Saline and Alkaline Conditions

Evaluation of the mobility behaviour of radionuclides under highly saline and alkaline conditions is a major concern for the performance assessment of radioactive waste disposal. The aim of this study was to determine the effect of up to 2.8 mol/kgsolution content of NaNO3, on the solubility and the retention of U(VI) at 22 °C onto a hardened cement paste (HCP) prepared from ordinary Portland cement (CEM I). To avoid the interference of the high salt concentration and ionic strength, and because of the expected low solubility of uranium under such alkaline conditions, time-resolved laser fluorescence spectroscopy (TRLFS) was selected to accurately measure U(VI) concentration in solution using the standard addition method in 85% H3PO4. This allows both limiting the dilution and matrix effects and determining the resulting [U(VI)] in solution with acceptable precision for the distribution factor (Rd) in both sorption and desorption experiments. The operational solubility limit measured at high ionic strength lowered by a factor of three compared to the reference cementitious condition, and its Rd values decreased by a factor ca. four. The sorption of U(VI) appears to be reversible under these conditions.

Thermodynamic Study of Am(III)-Isosaccharinate Complexation at Various Temperatures Implicating a Stepwise Reduction in Binding Denticity.

Isosaccharinic acid, a major final product of cellulose degradation under highly alkaline cement porewater conditions, is known to increase the mobility of actinides via strong complex formation. In this study, the formation of Am(III) complexes with α-d-isosaccharinate (ISA) was studied in terms of thermodynamics and coordination structures by combining spectrophotometry, time-resolved laser fluorescence spectroscopy (TRLFS), and density functional theory (DFT) calculations. The formation constants of the Am(III)-ISA complexes were determined by absorption spectroscopy at temperatures in the range of 15-70 °C. The measured reaction enthalpy and entropy changes indicate that the formation of a 1:1 Am(III)-ISA complex is driven by an increase in entropy. By contrast, the 1:2 complex formation is exothermic with a much less increase in entropy. DFT calculations predict that C2- and C4-hydroxyl groups, along with the carboxyl group, participate in the tridentate chelate binding of the primary ISA. The thermodynamic, TRLFS, and DFT results collectively suggest the tridentate binding of the primary ISA to Am(III) via a carboxylate and C2- and C4-hydroxyl groups in the protonated state and reduced dentate binding of the secondary ISA, such as bidentate binding, forming a four-membered ring structure via the carboxylate group.

Insights into the Complexation Mechanism of a Promising Lipophilic PyTri Ligand for Actinide Partitioning from Spent Nuclear Fuel.

The challenging issue of spent nuclear fuel (SNF) management is being tackled by developing advanced technologies that point to reduce environmental footprint, long-term radiotoxicity, volumes and residual heat of the final waste, and to increase the proliferation resistance. The advanced recycling strategy provides several promising processes for a safer reprocessing of SNF. Advanced hydrometallurgical processes can extract minor actinides directly from Plutonium and Uranium Reduction Extraction raffinate by using selective hydrophilic and lipophilic ligands. This research is focused on a recently developed N-heterocyclic selective lipophilic ligand for actinides separation to be exploited in advanced Selective ActiNide EXtraction (SANEX)-like processes: 2,6-bis(1-(2-ethylhexyl)-1H-1,2,3-triazol-4-yl)pyridine (PyTri-Ethyl-Hexyl-PTEH). The formation and stability of metal-ligand complexes have been investigated by different techniques. Preliminary studies carried out by electrospray ionization mass spectrometry (ESI-MS) analysis enabled to qualitatively explore the PTEH complexes with La(III) and Eu(III) ions as representatives of lanthanides. Time-resolved laser fluorescence spectroscopy (TRLFS) experiments have been carried out to determine the ligand stability constants with Cm(III) and Eu(III) and to better investigate the ligand complexes involved in the extraction process. The contribution of a 1:3 M/L complex, barely identified by ESI-MS analyses, was confirmed as the dominant species by TRLFS experiments. To shed light on ligand selectivity toward actinides over lanthanides, NMR investigations have been performed on PTEH complexes with Lu(III) and Am(III) ions, thereby showing significant differences in chemical shifts of the coordinating nitrogen atoms providing proof of a different bond nature between actinides and lanthanides. These scientific achievements encourage consideration of this PyTri ligand for a potential large-scale implementation.

Complexation and Extraction Studies of Trivalent Actinides and Lanthanides with Water-Soluble and CHON-Compatible Ligands for the Selective Extraction of Americium.

Novel hydrophilic ligands to selectively separate Am(III) are synthesized: 3,3'-([2,2'-bipyridine]-6,6'-diylbis(1H-1,2,3-triazole-4,1-diyl))bis(propan-1-ol) (PrOH-BPTD) and 3,3'-([2,2'-bipyridine]-6,6'-diylbis(1H-1,2,3-triazole-4,1-diyl))bis(ethan-1-ol) (EtOH-BPTD). The complexation of An(III) and Ln(III) with PrOH- and EtOH-BPTD is studied by time-resolved laser fluorescence spectroscopy. [ML2]3+ is found for both Cm(III) and Eu(III), while [ML]3+ is only formed with Cm(III). Stability constants show a preferential coordination of Cm(III) over Eu(III) with PrOH-BPTD being the stronger ligand. The distribution of Am(III), Cm(III), and Ln(III) between an organic phase containing the extracting agent N,N,N',N'-tetra-n-octyl-3-oxapentanediamide (TODGA) and aqueous phases containing PrOH-BPTD is studied as a function of time and temperature as well as the TODGA, BPTD, and HNO3 concentrations. A system composed of 0.2 mol/L TODGA and 0.04 mol/L PrOH-BPTD in 0.33-0.39 mol/L HNO3 allows for selective Am(III) back-extraction into the aqueous phase while keeping Cm(III) and Ln(III) in the organic phase, marking PrOH-BPTD as an excellent complexant for an optimized AmSel process (Am(III) selective extraction).

Humic fractions from Amazon soils: Lifetime study and humification process by fluorescence spectroscopy

The Amazon Forest is an important and primordial ecosystem, as it controls the dynamics of soil organic matter (SOM) and is considered one of the crucial carbon reservoirs in the world. Based on that, this study evaluated the molecular properties of humic (HA) and fulvic (FA) acid from Amazon soil, with and without Cu(II) ions, by Time-Resolved Laser Fluorescence Spectroscopy (TRLFS) and Fluorescence Spectroscopy (FS). Fluorescence excitation-emission matrix (EEM) was obtained by FS, and EEM spectra were treated by canonical polyadic/parallel factor analysis (EEM-CP/PARAFAC). The results showed that the humification index (A465nm) determined by FS is directly dependent on fluorophores’ CII/CI ratio in these soils with depth (r = 0.89), especially for HA samples in deep horizons, which demonstrated that the CII consists more complex and humified structure of the SOM. The lifetime decay showed the presence of static quenching in the humic fractions. From the lifetime data provided by TRLFS and the different correlations with carbon content and A465nm, it can be suggested that the fluorescence suppression modifies the molecular properties of the humic fractions with the addition of Cu(II) ions, such as altering the mobility and availability of the metal in the complexation reactions in these Amazonian Spodosols, mainly for the fulvic fraction.

Combining batch experiments and spectroscopy for realistic surface complexation modelling of the sorption of americium, curium, and europium onto muscovite

For a safe enclosure of contaminants, for instance in deep geological repositories of radioactive waste, any processes retarding metal migration are of paramount importance. This study focusses on the sorption of trivalent actinides (Am, Cm) and lanthanides (Eu) to the surface of muscovite, a mica and main component of most crystalline rocks (granites, granodiorites). Batch sorption experiments quantified the retention regarding parameters like pH (varied between 3 and 9), metal concentration (from 0.5 µM Cm to 10 µM Eu), or solid-to-liquid ratio (0.13 and 5.25 g·L−1). In addition, time-resolved laser fluorescence spectroscopy (TRLFS) using the actinide Cm(III) identified two distinct inner-sphere surface species. Combining both approaches allowed the development of a robust surface complexation model and the determination of stability constants of the spectroscopically identified species of (S-OH)2M3+ (logKo −8.89), (S-O)2M+ (logKo −4.11), and (S-O)2MOH (logKo −10.6), with all values extrapolated to infinite dilution. The inclusion of these stability constants into thermodynamic databases will improve the prognostic accuracy of lanthanide and actinide transport through groundwater channels in soils and crystalline rock systems.

Spectroscopic investigation of the different complexation and extraction properties of diastereomeric diglycolamide ligands

Abstract (2R,2′S)-2,2′-oxybis-(N,N-didecylpropanamide) (cis-mTDDGA) and (2R,2′R)-2,2′-oxybis-(N,N-didecylpropanamide) (trans-mTDDGA) were studied using time-resolved laser fluorescence spectroscopy (TRLFS), vibronic side-band spectroscopy (VSBS) and density functional theory calculations (DFT) to find reasons for their different extraction properties. Stability constants of the respective Cm(III) and Eu(III) complexes show cis-mTDDGA to be the superior ligand which is in agreement with results from extraction experiments. cis-mTDDGA extracts Cm(III) and Eu(III) as 1:3 complexes. In case of trans-mTDDGA, 1:2 complexes of the form [M(trans-mTDDGA)2(η1-NO3)(H2O)2]2+ (M = Cm, Eu) are extracted additionally to the 1:3 complexes. VSBS and DFT confirm the presence of inner-sphere nitrate in the 1:2 complex.

Structural characterisation of hydrolysed Cm(III)-EDTA solution species under alkaline conditions: a TRLFS, vibronic side-band and quantum chemical study

We present a combined theoretical and experimental study of the Cm(III)-EDTA system in alkaline aqueous solutions. Time-resolved laser-fluorescence spectroscopy and vibronic side-band spectroscopy measurements are performed with , and . The evaluation of the TRLFS spectra and corresponding fluorescence lifetimes hints towards the predominance of Cm(EDTA) at pH = 7, with the subsequent formation of the hydrolysis species Cm(OH)(EDTA) with increasing pH. This speciation scheme is further supported by the excellent agreement obtained between experimental and calculated vibronic side bands. The relative stabilities of the complexes Cm(OH)(EDTA) with n = 0−2 and p = 1−2 are discussed on the basis of the equilibrium constants calculated from quantum chemical calculations.

Structural and spectroscopic studies of spontaneously formed crystalline Eu(iii)-aliphatic dicarboxylates at room temperature.

Complexation of actinides and lanthanides with carboxylic organic ligands is a critical issue affecting radionuclide migration from deep geological disposal systems of spent nuclear fuel. A series of Eu(iii)–aliphatic dicarboxylate compounds, as chemical analogs of radioactive Am(iii) species, Eu2(Ox)3(H2O)6, Eu2(Mal)3(H2O)6, and Eu2(Suc)3(H2O)2, were synthesized and characterized using X-ray crystallography and time-resolved laser fluorescence spectroscopy to examine the ligand-dependent binding modes and the corresponding changes in spectroscopic properties. Powder X-ray crystallography results confirmed that all of the compounds presented a crystalline polymer structure with a trigonal prism square-face tricapped polyhedron geometry centered on Eu(iii) in a nine-coordinate environment involving nine oxygen atoms. This study captures the transition of the coordination modes of aliphatic dicarboxylate ligands from side-on to end-on binding as the carbon chain length increases. This transition is illustrated in malonate bindings involving a combination of side-on and end-on modes. Strongly enhanced luminescence, especially for the hypersensitive peak, indicates a low site symmetry in the formation of solid compounds. The number of remaining bound water molecules was estimated from the resultant increased luminescence lifetimes, which were in good agreement with crystal structures. The excitation–emission matrix spectra of these crystalline polymers suggest that Ox ligands promote the sensitized luminescence of Eu(iii), especially in the UV region. In the case of Mal and Suc ligands, charge transfer occurs in the opposite direction from Eu(iii) to the ligands under UV excitation, resulting in weaker luminescence.

Uranium (VI) sorption on illite under varying carbonate concentrations: Batch experiments, modeling, and cryogenic time-resolved laser fluorescence spectroscopy study

Dissolved inorganic carbon (DIC) present in groundwaters can affect both the aqueous and surface species of hexavalent uranium (U(VI)) owing to its strong complexation ability with U(VI). However, the effect of DIC on U(VI) sorption on illite, which is a critical component of argillaceous rocks, is still unclear. In this study, we investigated the sorption of U(VI) on conditioned illite du Puy with varying DIC concentrations (up to 250 mM DIC) as a function of pH through batch sorption experiments, surface complexation modeling, and cryogenic time-resolved laser fluorescence spectroscopy (TRLFS). The distribution coefficients of U(VI) decreased with an increase in the DIC concentration. At relatively high DIC concentrations with respect to experimentally investigated range (≥100 mM DIC), no U(VI) sorption was observed. The U(VI) sorption on illite was modeled using the two-site protolysis non-electrostatic surface complexation and cation exchange model. Two ternary surface complexation reactions with carbonate were needed to depict the experimental sorption data in addition to binary and ternary hydroxo surface complexation reactions used to describe the U(VI) sorption to illite without carbonate. Cryogenic TRLFS data revealed that U(VI) did sorb to illite at high DIC concentrations (up to 10 mM DIC). The spectra were unchanged with varying DIC concentrations (2.0, 5.0, and 10 mM DIC) at pH ∼8.5, indicating that the surface speciation of U(VI) remained the same. The decay curves were biexponential, which further indicates that at least two surface species were responsible for the sorption. These results could improve the performance assessment of a deep geological disposal system in a sedimentary host rock.

Complexation of Cm(III) with blood serum proteins: recombinant human serum albumin (rHSA)

Abstract The complexation of Cm(III) with the recombinant human serum albumin (rHSA) (characterized by single deletion of residue Asp-1), is studied in dependence of pH and rHSA concentration using time-resolved laser fluorescence spectroscopy (TRLFS). A Cm(III) rHSA species is formed between pH 6.4 and 10.0 with the conditional stability constant being logK = 6.47 at pH = 7.4. Competition titration experiments with Cu(II) and Zn(II) confirm complexation at the N-terminal binding site (NTS) of rHSA and exclude the involvement of the Multi-Metal Binding Site (MBS). Comparison with a previous study on Cm(III) interaction with native albumin, HSA, points out, that residue Asp-1 is involved in Cm(III) binding to HSA but is not crucial for Cm(III) complexation at the NTS. The results are of major importance for a better understanding of fundamental actinide-protein interaction mechanisms which are highly required for the identification and characterization of relevant distribution pathways of incorporated radionuclides.

The use of Raman and TRLF spectroscopy for differentiating early stage alteration products of spent nuclear fuel

Non-invasive techniques capable of distinguishing the alteration products of spent nuclear fuel during prolonged storage would be of great benefit when assessing the potential mobility of uranium from the fuel matrix. Two potential alteration products, becquerelite (Ca(UO2)6O4(OH)6·8(H2O)) and vandendriesscheite (Pb1.5(UO2)10O6(OH)11·11(H2O)), were characterised by multiple laser-wavelength Raman and time-resolved laser fluorescence spectroscopy (TRLFS). Chemical composition was confirmed by scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray diffraction. Well-defined Raman features were obtained, particularly with a 785 nm laser, allowing subtle differences between the two minerals to be observed. Differences were also found in the Raman spectra using lasers at 457, 532 and 633 nm, with the degree of luminescence depending on the metal cation present. Chemical quenching of luminescence in Raman data correlated with luminescence excitation and emission spectra results. Five and seven luminescence emission peaks were resolved for becquerelite and vandendriesscheite, respectively. The first reported luminescence excitation spectra were collected for each mineral but not all of the spectral ranges could be resolved into individual peaks. A luminescence decay lifetime of 5.5 ± 0.9 μs was obtained for vandendriesscheite. This study demonstrates that Raman spectroscopy and TRLFS are potentially valuable techniques for characterising uranyl oxy-hydroxides and could be used in conjunction with other methods, such as laser induced breakdown spectroscopy (LIBS), as part of a remote analysis package in nuclear waste management.

Excitation and Emission Properties of Adsorbed U(VI) on Amorphous Silica Surface

In the geochemical field, the chemical speciation of hexavalent uranium (U(VI)) has been widely investigated by performing measurements to determine its luminescence properties, namely the excitation, emission, and lifetime. Of these properties, the excitation has been relatively overlooked in most time-resolved laser fluorescence spectroscopy (TRLFS) studies. In this study, TRLFS and continuous-wave excitation–emission matrix spectroscopy are adopted to characterize the excitation properties of U(VI) surface species that interact with amorphous silica. The luminescence spectra of U(VI) measured from a silica suspension and silica sediment showed very similar spectral shapes with similar lifetime values. In contrast, the excitation spectra of U(VI) measured from these samples were significantly different. The results show that distinctive excitation maxima appeared at approximately 220 and 280 nm for the silica suspension and silica sediment, respectively.

Complexation of Nd(III)/Cm(III) with gluconate in alkaline NaCl and CaCl2 solutions: Solubility, TRLFS and DFT studies

The effect of gluconate on the solubility and aqueous speciation of An(III) and Ln(III) was studied using a combination of Nd(III) solubility experiments, Cm(III) time-resolved laser fluorescence spectroscopy (TRLFS) and density functional theory (DFT) calculations.Solubility experiments were performed under an Ar-atmosphere using a well-defined Nd(OH)3(s) solid phase equilibrated in NaCl (0.1–5.0 M) and CaCl2 (0.1–3.5 M) solutions with 9 ≤ pHc ≤ 13 and 10−6 M ≤ [GLU]tot ≤ 10−2 M. The solubility of Nd(OH)3(s) remains mostly unaffected in NaCl solutions with [GLU]tot = 10−3 M, whereas a clear increase in solubility is observed in dilute CaCl2 solutions with the same [GLU]tot and pHc ≥ 11. In concentrated CaCl2 solutions, gluconate does not affect the solubility of Nd(III) due to the competition with Ca–GLU complexes.Cm(III) TRLFS spectra collected in NaCl solutions with pHc ≈ 12 confirm the formation of weak Cm(III)–GLU complexes. The very strong red shift observed in dilute CaCl2 solutions in connection with high fluorescence intensities supports the formation of ternary Ca–Cm(III)–GLU complexes. The speciation of Cm(III) in 3.5 M CaCl2 solutions is mostly dominated by the complex Ca3[Cm(OH)6]3+, although the formation of ternary Ca–Cm(III)–GLU species is hinted at high gluconate concentrations. DFT calculations provide additional support to the formation of stable ternary Ca–Nd(III)–GLU aqueous complexes.This work provides key information to understand the chemical speciation and relevant equilibrium processes of An(III) and Ln(III) in the presence of gluconate under conditions relevant for nuclear waste disposal.

Characterisation of meta-autunite: Towards identifying potential alteration products of spent nuclear fuel

Laser-based spectroscopic techniques offer potential for characterising the alteration products of spent nuclear fuel in settings where the use of more traditional analytical methods is impracticable. Among these alteration products, uranyl phosphate phases have long attracted interest owing to their potential to form passivating surfaces on primary uranium phases inhibiting further uranium dissolution. Two strontium-rich meta-autunite ((Ca,Sr)(UO2)2(PO4)2·2–8(H2O)) samples from the Mount Spokane uranium deposit, Washington, USA were characterised by multiple laser wavelength Raman and time-resolved laser fluorescence spectroscopy. Well-defined Raman features were obtained, particularly at a laser wavelength of 785 nm, but partially hydrated meta-autunite phases could not be differentiated by Raman alone. However, subtle differences in three key modes were observed between meta-autunite and published data for fully hydrated autunite specimens enabling these minerals to be distinguished. Seven luminescence emission and several excitation features were resolved for the two samples, with the latter being the first reported excitation data for meta-autunite. The luminescence decay lifetime was found to be significantly longer than previously reported and sensitive to the meta-autunite dehydration phase.

Electrochemical and Spectroscopic Study of EuIII and EuII Coordination in the 1-Ethyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide Ionic Liquid.

Separation processes based on room temperature ionic liquids (RTIL) and electrochemical refining are promising strategies for the recovery of lanthanides from primary ores and electronic waste. However, they require the speciation of dissolved elements to be known with accuracy. In the present study, Eu coordination and EuIII /EuII electrochemical behavior as a function of water content in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIm][NTf2 ]) was investigated using UV-visible spectrophotometry, time-resolved laser fluorescence spectroscopy, electrochemistry, and X-ray absorption spectroscopy. In situ measurements were performed in spectroelectrochemical cells. Under anhydrous conditions, EuIII and EuII were complexed by NTf2 , forming Eu-O and Eu-(N,O) bonds with the anion sulfoxide function and N atoms, respectively. This complexation resulted in a greater stability of EuII , and in quasi-reversible oxidation-reduction with an E0 ' potential of 0.18 V versus the ferrocenium/ferrocene (Fc+ /Fc) couple. Upon increasing water content, progressive incorporation of water in the EuIII coordination sphere occurred. This led to reversible oxidation-reduction reactions, but also to a decrease in stability of the +II oxidation state (E0 '=-0.45 V vs. Fc+ /Fc in RTIL containing 1300 mm water).