Time-resolved laser-induced fluorescence spectroscopy and chemometrics for fast identification of U(VI)-bearing minerals in a mining context.

We evaluated the potential of time-resolved laser-induced fluorescence spectroscopy (TRLFS) combined with chemometric methods for fast identification of U(VI)-bearing minerals in a mining context. We analyzed a sample set which was representative of several environmental conditions. The set consisted of 80 uranium-bearing samples related to mining operations, including natural minerals, minerals with uranium sorbed on the surface, and synthetic phases prepared and characterized specifically for this study. The TRLF spectra were processed using the Ward algorithm and the K-nearest neighbors (KNN) method to reveal similarities between samples and to rapidly identify the uranium-bearing phase and the associated mineralogical family. The predictive models were validated on an independent dataset, and then applied to test samples mostly taken from U mill tailings. Identification results were found to be in accordance with the available characterization data from X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDX). This work shows that TRLFS can be an effective decision-making tool for environmental investigations or geological prospection, considering the large diversity of uranium-bearing mineral phases and their low concentration in environmental samples.

Influence of the First Coordination of Uranyl on Its Luminescence Properties: A Study of Uranyl Binitrate with N,N-Dialkyl Amide DEHiBA and Water.

Uranyl binitrate complexes have a particular interest in the nuclear industry, especially in the reprocessing of spent nuclear fuel. The modified PUREX extraction process is designed to extract U(VI) in the form of UO2(NO3)2(L)2 as has been confirmed by extended X-ray absorption fine structure (EXAFS), X-ray diffraction (XRD), and time-resolved laser-induced fluorescence spectroscopy (TRLFS) measurements. In this study, the L ligands are two molecules of N,N-di-(ethyl-2-hexyl)isobutyramide (DEHiBA) monoamide used to bind uranyl in its first coordination sphere. DEHiBA ligands can coordinate uranyl in either trans- or cis-position with respect to the nitrate ligands, and these two conformers may coexist in solution. To use luminescence spectroscopy as a speciation technique, it is important to determine whether or not these conformers can be discriminated by their spectroscopic properties. To answer this question, the spectra of trans- and cis-UO2(NO3)2(DEiBA)2 conformers were modeled with ab initio methods and compared to the experimental time-resolved luminescence spectra on UO2(NO3)2(DEHiBA)2 systems. Moreover, the hydrated uranyl binitrate UO2(NO3)2(H2O)2 complexes in the same trans and cis configurations were modeled to quantify the impact of organic DEHiBA on the luminescence properties.

Spectroluminescence measurements of the stability constants of CanUO2(CO3)3(4-2n)- complexes in NaClO4 medium and the investigation of interaction effects.

The stability constants of ternary calcium uranyl tricarbonate complexes, CaUO2(CO3)32- and Ca2UO2(CO3)3(aq), were determined in NaClO4 medium at various ionic strengths using time-resolved laser-induced luminescence spectroscopy (TRLS) - also known as time-resolved laser-induced fluorescence spectroscopy (TRLFS). As in a previous study, the potential precipitation of schoepite (UO3·2H2O) and calcite (CaCO3) was avoided via titration of the triscarbonatouranyl complex with Ca2+ at varying pH values. The Ringböm coefficients relative to UO2(CO3)34- were individually evaluated under test sample conditions. Steadily enhanced luminescence intensity and increased decay-times were representative of complexation processes. The stoichiometry of calcium was quantified by slope analysis, and its measured intensity was corrected by using the corresponding Ringböm coefficient. The conditional formation constants, i.e. log10 Kn.1.3, were then assessed after rounding off the slope values to their nearest integers. Cumulative formation constants at infinite dilution log10 ß°n.1.3, and specific ion interaction parameters ε were determined based on the experimental origin and slope values, respectively, over the range of 0.1-2.46 mol kgw-1 NaClO4 using the specific ion interaction theory (SIT) approach. The cumulative stability constants are log10 ß°(CaUO2(CO3)32-) = 27.26 ± 0.04 and log10 ß°(Ca2UO2(CO3)3(aq)) = 30.53 ± 0.06. The specific ion interaction coefficients are estimated to be ε(CaUO2(CO3)32-,Na+) = (0.02 ± 0.04) kgw mol-1 and ε(Ca2UO2(CO3)3(aq),NaClO4) = (0.18 ± 0.07) kgw mol-1. These latter values are different from the ones that were previously obtained in NaCl, and underlying causes are discussed from different aspects. This work provides valuable information to address the interaction effects between Ca-UO2-CO3 species and 1 : 1 type electrolytes. It is suggested that the affinity of the cation in a background electrolyte with CanUO2(CO3)3(4-2n)- (n = {1;2}) has to be taken into consideration at high ionic strengths, especially for globally non-charged species.

Influence of Alkaline Earth Metal Ions on Structures and Luminescent Properties of NamMnUO2(CO3)3(4-m-2n)- (M = Mg, Ca; m, n = 0-2): Time-Resolved Fluorescence Spectroscopy and Ab Initio Studies.

The luminescence spectra of triscarbonatouranyl complexes were determined by experimental and theoretical methods. Time-resolved laser-induced fluorescence spectroscopy was used to monitor spectra of uranyl and bicarbonate solutions at 0.1 mol kgw-1 ionic strength and pH ca. 8. The concentrations of Mg2+ and Ca2+ in the samples were chosen in order to vary the proportions of the alkaline earth ternary uranyl complexes MgUO2(CO3)32-, CaUO2(CO3)32-, and Ca2UO2(CO3)3. The luminescence spectrum of each complex was determined by decomposition in order to compare it with the simulated spectra of model structures NamMnUO2(CO3)3(4-m-2n)- (M = Mg, Ca; m, n = 0-2) obtained by quantum chemical methods. The density functional theory (DFT) and time-dependent (TD)-DFT methods were used with the PBE0 functional to optimize the structures in the ground and excited states, respectively, including relativistic effects at the spin-free level, and water solvent effects using a continuum polarizable conductor model. The changes in the structural parameters were quantified with respect to the nature and the amount of alkaline earth counterions to explain the luminescence spectra behavior. The first low-lying excited state was successfully computed, together with the vibrational harmonic frequencies. The DFT calculations confirmed that uranyl luminescence originates from electronic transitions from one of the four nonbonding 5f orbitals of uranium to an orbital that has a uranyl-σ (5f, 6d) character mixed with the 2p atomic orbitals of the carbonate oxygens. Additional single-point calculations using the more accurate TD-DFT/CAM-B3LYP allow one to determine the position of the luminescence "hot band" for each structure in the range 467-476 nm and compared fairly well with experimental reports at around 465 nm. The complete luminescence spectra were built from theoretical results with the corresponding assignment of the electronic transitions and vibronic modes involved, mainly the U-Oax stretching mode. The resulting calculated spectra showed a very good agreement with experimental band positions and band spacing attributed to MgUO2(CO3)32-, CaUO2(CO3)32-, and Ca2UO2(CO3)3. The evolution of luminescence intensities with the number of alkaline earth metal ions in the structure was also correctly reproduced.

Investigation of the Luminescence of [UO2X4]2- (X = Cl, Br) Complexes in the Organic Phase Using Time-Resolved Laser-Induced Fluorescence Spectroscopy and Quantum Chemical Simulations.

The luminescence properties of the [UO2Cl4]2- complex in an organic phase, especially the influence of large organic countercations, have been studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS) and ab initio modeling. The experimental spectrum was assigned by vibronic Franck-Condon calculations on quantum chemical methods on the basis of a combination of relativistic density functional approaches. The shape of the luminescence spectrum of the uranyl tetrachloride complex is determined by symmetrical vibrations and geometrical change upon emission. The possible change in the luminescence properties depending on the first and second uranyl coordination spheres was predicted theoretically for the [UO2Br4]2- and [R4N]2[UO2Cl4] ([R4N] = [Bu4N], [A336]) systems. The computations reveal that, for U(VI), the second coordination sphere has little influence on the spectrum shape, making speciation of uranyl complexes with identical first-coordination-sphere ligands tedious to discriminate. The computed structural changes agreed well with experimental trends; theoretical spectra and peak attributions are in good accordance with TRLFS and magnetic circular dichroism (MCD) data, respectively.

Uranium removal from mining water using Cu substituted hydroxyapatite.

In this study, synthetic copper substituted hydroxyapatite (Cu-Hap), CuxCa10-x(PO4)6(OH)2 were prepared by co-precipitation method and were used as reactive materials in batch experiments to immobilize uranyl. The limit of incorporation of Cu into a single-phased Cu-Hap reached xCu ≤1.59. The synthetic Cu-Hap samples obtained with various Cu contents were contacted with synthetic uranyl doped solutions and with real mining waters showing various pH and chemical compositions. A fast and strong decrease of the uranium concentration was observed, followed by the establishment of an equilibrium after 1-4 days of contact with the solutions. Examination of the solid phase after uranium uptake was performed using a combination of techniques. Depending on the composition of the solution and the copper content of the Cu-Hap, various mechanisms of uranium removal were observed. Based on the experimental results and geochemical simulations, it appeared that the main interest for using Cu-Hap is to enlarge the domain of water compositions for which the precipitation of meta-torbernite, (H3O)0.4Cu0.8(UO2)2(PO4)2·7.6 H2O is the predominant mechanism associated to the uranium removal, especially for pH > 6.7 where carbonate uranium species are predominant.

Selective solid phase extraction of lanthanides from tap and river waters with ion imprinted polymers.

For the first time, an ion imprinted polymer (IIP) able to selectively extract simultaneously all the lanthanide ions was successfully synthesized in acetonitrile using Nd3+ as a template ion, methacrylic acid as a complexing monomer, and ethylene glycol dimethacrylate as a cross-linker. A non-imprinted polymer (NIP) was synthesized under the same conditions as those of the IIP, but in the absence of the template ion. After the removal of the template ions, grounding and sieving, the IIP particles were packed in solid phase extraction (SPE) cartridges. The selectivity of the IIP was evaluated by comparing its behavior with the one of the NIP. Each SPE step (percolation, washing, and elution) was optimized in order to find the best compromise between the selectivity and the extraction recoveries. Using the optimized SPE conditions, the extraction recoveries of eight lanthanide ions representative of the lanthanide family were higher than 77% with an average value of 83% with the IIP, whereas, in the case of the NIP, they ranged between 14 and 36% and they were below 3% for the interfering ions from alkali, transition, and post-transition metal families with the IIP. A first evaluation of the reproducibility of the SPE profiles was carried out by performing statistical tests on the data obtained with several cartridges filled with particles obtained from two different IIP and NIP syntheses. Promising results were obtained. The specific capacity, i. e. the adsorption capacity of Nd3+ ions by the specific cavities of the imprinted polymer, was about 9 mg of Nd3+ per gram of IIP (60 µmol g-1), which is more than enough for the extraction of the lanthanide ions at trace levels. The breakthrough volume was about 1 mL per mg of IIP, leading to an enrichment factor of 15, which allows not only to selectively extract the lanthanides but also to concentrate them. Finally, the imprinted polymer was successfully used to selectively extract lanthanides from tap and river waters spiked at 1 µg L-1.

Potential of ion imprinted polymers synthesized by trapping approach for selective solid phase extraction of lanthanides.

Ion imprinted polymers (IIPs) specific to lanthanides were synthesized using neodymium ions (Nd3+) as template ions. Nd3+ ions form binary complex ions with 5,7-dichloroquinoline-8-ol (DCQ) or vinylpyridine (VP), or ternary complex ions with both DCQ and VP in 2-methoxyethanol, before copolymerization in the presence of styrene and divinylbenzene as monomer and cross-linker, respectively. DCQ was expected to be trapped in the synthesized polymers pores. The template ion removal was then optimized. For the first time, the DCQ leakage was determined by HPLC-UV during the template removal and the sedimentation steps before solid-phase extraction (SPE) packing. It was observed that the trapped DCQ was unfortunately lost in significant amounts, up to 51%, and that this amount varied from one synthesis to another. The grinded and sieved polymers were next packed in SPE cartridges. The study of the SPE profiles obtained with the IIPs synthesized either with the binary or the ternary complex confirmed the prominent role of DCQ on the selectivity of an IIP by comparison with a non-imprinted polymer (NIP), i.e. a polymer synthesized under the same conditions as those of the IIP but without template ions. The influence of the porogenic solvent on the selectivity was also investigated by replacing 2-methoxyethanol by acetonitrile or dimethylsulfoxyde (DMSO). The polymers synthesized in DMSO led to the most repeatable results when elution solutions with a gradual decrease in pH were percolated through the cartridge. This is why DMSO was used to optimize the SPE protocol in order to maximize the difference of extraction yield between the IIP and the NIP, i.e. promoting a selective retention on the IIP. A value of about 30% was obtained for La3+, Ce3+, Nd3+, and Sm3+. Nevertheless, with the optimized SPE protocol, IIPs from different syntheses did not have the same SPE behavior, which may result from different random leakages of DCQ. This demonstrates for the first time the main limitation of the IIPs synthesized in bulk with the trapping approach for their use in SPE.

Characterization of Actinides Complexed to Nuclear Fuel Constituents Using ESI-MS.

Electrospray ionization-mass spectrometry (ESI-MS) was tested for its use in monitoring spent nuclear fuel (SNF) constituents including U, Pu, dibutyl phosphate (DBP), and tributyl phosphate (TBP). Both positive and negative ion modes were used to evaluate the speciation of U and Pu with TBP and DBP. Furthermore, apparent stability constants were determined for U complexed to TBP and DBP. In positive ion mode, TBP produced a strong signal with and without complexation to U or Pu, but, in negative ion mode, no TBP, U-TBP, or Pu-TBP complexes were observed. Apparent stability constants were determined for [UO2(NO3)2(TBP)2], [UO2(NO3)2(H2O)(TBP)2], and [UO2(NO3)2(TBP)3]. In contrast DBP, U-DBP, and Pu-DBP complexes were observed in both positive and negative ion modes. Apparent stability constants were determined for the species [UO2(DBP)], [UO2(DBP)3], and [UO2(DBP)4]. Analyzing mixtures of U or Pu with TBP and DBP yielded the formation of ternary complexes whose stoichiometry was directly related to the ratio of TBP to DBP. The ESI-MS protocols used in this study will further demonstrate the utility of ESI-MS and its applicability to process control monitoring in SNF reprocessing facilities.

Introduction of organic/hydro-organic matrices in inductively coupled plasma optical emission spectrometry and mass spectrometry: a tutorial review. Part I. Theoretical considerations.

Due to their outstanding analytical performances, inductively coupled plasma optical emission spectrometry (ICP-OES) and mass spectrometry (ICP-MS) are widely used for multi-elemental measurements and also for isotopic characterization in the case of ICP-MS. While most studies are carried out in aqueous matrices, applications involving organic/hydro-organic matrices become increasingly widespread. This kind of matrices is introduced in ICP based instruments when classical "matrix removal" approaches such as acid digestion or extraction procedures cannot be implemented. Due to the physico-chemical properties of organic/hydro-organic matrices and their associated effects on instrumentation and analytical performances, their introduction into ICP sources is particularly challenging and has become a full topic. In this framework, numerous theoretical and phenomenological studies of these effects have been performed in the past, mainly by ICP-OES, while recent literature is more focused on applications and associated instrumental developments. This tutorial review, divided in two parts, explores the rich literature related to the introduction of organic/hydro-organic matrices in ICP-OES and ICP-MS. The present Part I, provides theoretical considerations in connection with the physico-chemical properties of organic/hydro-organic matrices, in order to better understand the induced phenomena. This focal point is divided in four chapters highlighting: (i) the impact of organic/hydro-organic matrices from aerosol generation to atomization/excitation/ionization processes; (ii) the production of carbon molecular constituents and their spatial distribution in the plasma with respect to analytes repartition; (iii) the subsequent modifications of plasma fundamental properties; and (iv) the resulting spectroscopic and non spectroscopic interferences. This first part of this tutorial review is addressed either to beginners or to more experienced scientists who are interested in the analysis of organic/hydro-organic matrices by ICP sources and would like to consider the theoretical background of effects induced by such matrices. The second part of this tutorial review will be dedicated to more practical consideration on instrumentation, such as adapted introductions devices, as well as instrumental and operating parameters optimization. The analytical strategies for elemental quantification in such matrices will also be addressed.

Introduction of organic/hydro-organic matrices in inductively coupled plasma optical emission spectrometry and mass spectrometry: a tutorial review. Part II. Practical considerations.

Inductively coupled plasma optical emission spectrometry (ICP-OES) and mass spectrometry (ICP-MS) are increasingly used to carry out analyses in organic/hydro-organic matrices. The introduction of such matrices into ICP sources is particularly challenging and can be the cause of numerous drawbacks. This tutorial review, divided in two parts, explores the rich literature related to the introduction of organic/hydro-organic matrices in ICP sources. Part I provided theoretical considerations associated with the physico-chemical properties of such matrices, in an attempt to understand the induced phenomena. Part II of this tutorial review is dedicated to more practical considerations on instrumentation, instrumental and operating parameters, as well as analytical strategies for elemental quantification in such matrices. Two important issues are addressed in this part: the first concerns the instrumentation and optimization of instrumental and operating parameters, pointing out (i) the description, benefits and drawbacks of different kinds of nebulization and desolvation devices and the impact of more specific instrumental parameters such as the injector characteristics and the material used for the cone; and, (ii) the optimization of operating parameters, for both ICP-OES and ICP-MS. Even if it is at the margin of this tutorial review, Electrothermal Vaporization and Laser Ablation will also be shortly described. The second issue is devoted to the analytical strategies for elemental quantification in such matrices, with particular insight into the isotope dilution technique, particularly used in speciation analysis by ICP-coupled separation techniques.

Use of combined microscopic and spectroscopic techniques to reveal interactions between uranium and Microbacterium sp. A9, a strain isolated from the Chernobyl exclusion zone.

Although uranium (U) is naturally found in the environment, soil remediation programs will become increasingly important in light of certain human activities. This work aimed to identify U(VI) detoxification mechanisms employed by a bacteria strain isolated from a Chernobyl soil sample, and to distinguish its active from passive mechanisms of interaction. The ability of the Microbacterium sp. A9 strain to remove U(VI) from aqueous solutions at 4 °C and 25 °C was evaluated, as well as its survival capacity upon U(VI) exposure. The subcellular localisation of U was determined by TEM/EDX microscopy, while functional groups involved in the interaction with U were further evaluated by FTIR; finally, the speciation of U was analysed by TRLFS. We have revealed, for the first time, an active mechanism promoting metal efflux from the cells, during the early steps following U(VI) exposure at 25 °C. The Microbacterium sp. A9 strain also stores U intracellularly, as needle-like structures that have been identified as an autunite group mineral. Taken together, our results demonstrate that this strain exhibits a high U(VI) tolerance based on multiple detoxification mechanisms. These findings support the potential role of the genus Microbacterium in the remediation of aqueous environments contaminated with U(VI) under aerobic conditions.

Hydration properties of lanthanoid(III) carbonate complexes in liquid water determined by polarizable molecular dynamics simulations.

In this work we have studied the structure and dynamics of complexes formed by three and four carbonates and a central lanthanoid(III) ion in liquid water by means of polarizable molecular dynamics simulations. With this aim we have developed a force field employing an extrapolation procedure that was previously developed for lanthanoid(III) aqua ions and then we have validated it against DFT-based data. In this way we were able to shed light on properties of the whole series, finding some similarities and differences across the series, and to help in interpreting experiments on those systems. We found that the bi-dentate tri-carbonate complexes are the most stable for all the atoms, but a variation of the number of water molecules in the first ion shell, and the associated exchange dynamics, is observed from lighter to heavier elements. On the other hand, for four-carbonate systems only one water molecule is observed in the first shell, with 10-20% probability, for La(III) and Ce(III), while for the rest of the series it seems impossible for a water molecule to enter the first ion shell in the presence of such an excess of carbonate ligands. Finally, the good performance of our extrapolation procedure, based on ionic radii, makes us confident in extending such approaches to study the structure and dynamics of other systems in solution containing Ln(III) and An(III) ions. This parametrization method results particularly useful since it does not need expensive quantum chemistry calculations for all the atoms in the series.

Formation of MSeO(4)(aq) complexes (M(2+) = Mg(2+), Co(2+), Ni(2+), Cu(2+), Cd(2+)) studied as a function of temperature by affinity capillary electrophoresis.

Complexation of divalent cations (Mg(2+), Co(2+), Ni(2+), Cu(2+), Cd(2+)) by selenate ligand was studied by ACE (UV indirect detection) in 0.1 mol/L NaNO(3) ionic strength solutions at various temperatures (15, 25, 35, 45 and 55°C). For each solution, a unique peak was observed as a result of a fast equilibrium between the free ion and the complex (labile systems). The migration time corresponding to this peak changed as a function of the solution composition, namely the free and complexed metal concentrations, according to the complexation reactions. The results confirmed the formation of a unique 1:1 complex for each cation. The thermodynamic parameters were fitted to the experimental data at 0.1 mol/L ionic strength: (25°C) = -(6.5 ± 0.3), -(7.5 ± 0.3), -(7.7 ± 0.3), -(7.7 ± 0.3), and -(8.1 ± 0.3) kJ/mol and = 2.5 ± 0.2, 4.7 ± 0.4, 4.5 ± 0.6, 8.4 ± 1.1, and 7.2 ± 0.6 kJ/mol for M(2+) = Mg(2+), Co(2+), Ni(2+), Cu(2+), and Cd(2+), respectively. Complexes with alkaline earth and transition metal cations could be distinguished by their relative stabilities. The effect of the ionic medium was treated using the specific ion interaction theory and the thermodynamic parameters at infinite dilution were compared to previously published data on metal-selenate, metal-sulfate, and metal-chromate complexes.

New insights into formation of trivalent actinides complexes with DTPA.

Complexation of trivalent actinides with DTPA (diethylenetriamine pentaacetic acid) was studied as a function of pcH and temperature in (Na,H)Cl medium of 0.1 M ionic strength. Formation constants of both complexes AnHDTPA(-) and AnDTPA(2-) (where An stands for Am, Cm, and Cf) were determined by TRLFS, CE-ICP-MS, spectrophotometry, and solvent extraction. The values of formation constants obtained from the different techniques are coherent and consistent with reinterpreted literature data, showing a higher stability of Cf complexes than Am and Cm complexes. The effect of temperature indicates that formation constants of protonated and nonprotonated complexes are exothermic with a high positive entropic contribution. DFT calculations were also performed on the An/DTPA system. Geometry optimizations were conducted on AnDTPA(2-) and AnHDTPA(-) considering all possible protonation sites. For both complexes, one and two water molecules in the first coordination sphere of curium were also considered. DFT calculations indicate that the lowest energy structures correspond to protonation on oxygen that is not involved in An-DTPA bonds and that the structures with two water molecules are not stable.

Formation of CaSO4(aq) and CaSeO4(aq) studied as a function of ionic strength and temperature by CE.

Ca(2+) complexation by both sulfate and selenate ligands was studied by CE. The species were observed to give a unique retention peak as a result of a fast equilibrium between the free ions and the complexes. The change in the corresponding retention time was interpreted with respect to the equilibrium constant of the complexation reaction. The results confirmed the formation of CaSO(4)(aq) and CaSeO(4)(aq) under our experimental conditions. The formation data were derived from the series of measurements carried out at about 15, 25, 35, 45 and 55 degrees C in 0.1 mol/L NaNO(3) ionic strength solutions, and in 0.5 and 1.0 mol/L NaNO(3) ionic strength solutions at 25 degrees C. Using a constant enthalpy of reaction enabled to fit all the experimental data in a 0.1 mol/L medium, leading to the thermodynamic parameters: Delta(r)G(0.1M)(25 degrees C)=-(7.59+/-0.23) kJ/mol, Delta(r)H(0.1 M)=5.57+/-0.80 kJ/mol, and Delta(r)S(0.1 M)(25 degrees C)=44.0+/-3.0 J mol(-1) K(-1) for CaSO(4)(aq) and Delta(r)G(0.1 M)(25 degrees C)=-(6.66+/-0.23) kJ/mol, Delta(r)H(0.1 M)=6.45+/-0.73 kJ/mol, and Delta(r)S(0.1 M)(25 degrees C)=44.0+/-3.0 J mol(-1) K(-1) for CaSeO(4)(aq). Both formation reactions were found to be endothermic and entropy driven. CaSO(4)(aq) appears to be more stable than CaSeO(4)(aq) by 0.93 kJ/mol under these experimental conditions, which correlates with the difference of acidity of the anions as expected for interactions between hard acids and hard bases according to the hard and soft acids and bases theory. The effect of the ionic medium on the formation constants was successfully treated using the Specific ion Interaction Theory, leading to significantly different binary coefficients epsilon(NA+,SO(2-)(4)) = -(0.15 +/- 0.06) mol/kg-1 and epsilon(NA+,SO(2-)(4)) = -(0.26 +/- 0.10) mol/kg-1.

Uranium speciation in drinking water from drilled wells in southern Finland and its potential links to health effects.

Exceptionally high concentrations of natural uranium have been found in drinking water originating from drilled wells in Southern Finland. However, no clear clinical symptoms have been observed among the exposed population. Hence a question arose as to whether uranium speciation could be one reason for the lack of significant adverse health effects. Uranium species were determined using time-resolved laser-induced fluorescence spectroscopy. We performed multi-element chemical analyses in these water samples, and predictive calculations were carried out using up-to-date thermodynamic data. The results indicated good agreement between measurements and modeling. The low toxicity of Finnish bedrockwater may be due to the predominance of two calcium-dependent species, Ca2UO2(CO3)3(aq) and CaUO2(CO3)3(2-), whose nontoxicity for cells has been described previously. This interdisciplinary study describes chemical speciation of drinking water with elevated uranium concentrations and the potential consequence on health. From these results, it appears that modeling could be used for a better understanding of uranium toxicity of drinking water in the event of contamination.

Trace metal speciation by capillary electrophoresis hyphenated to inductively coupled plasma mass spectrometry: sulfate and chloride complexes of Np(V) and Pu(V).

In the framework of nuclear waste disposal, it is very important to well understand the behavior of actinides in the presence of the common environmental inorganic ligands such as sulfate and chloride. In this work, the AnO2SO4(-) and AnO2Cl 1-1 complexes have been evidenced by capillary electrophoresis-inductively coupled plasma mass spectrometry (CE-ICPMS) in perchlorate/chloride and in perchlorate/sulfate media for An = Np and Pu. Their binding constants have been measured: log beta(PuO2SO4(-))(0) = 1.30 +/- 0.11, log beta(PuO2Cl)(1 M NaCl) = -(0.40 +/- 0.07), log beta(NpO2SO4(-))(0) = 1.34 +/- 0.12, and log beta(NpO2Cl)(1 M NaCl) = -(0.40 +/- 0.07). These results are consistent with published values for Np(V). They confirm the expected analogy between Np(V) and Pu(V) for the weak bonding with chloride ligand, log10 beta(PuO2Cl) approximately = log10 beta(NpO2Cl), attributed to mainly electrostatic interactions. Conversely, a slight shift is observed for the bonding with sulfate ligand, log10 beta(NpO2SO4(-)) > log10 beta(PuO2SO4(-)), indicating that some covalency might stabilize the sulfate complexes.

Evidence of different stoichiometries for the limiting carbonate complexes across the lanthanide(III) series: a capillary electrophoresis-mass spectrometry study.

The electrophoretic mobilities (mu ep,Ln) of twelve lanthanides (not Ce, Pr and Yb) were measured by CE-ICP-MS in 0.15 and 0.5 mol L(-1) Alk2 CO3 aqueous solutions for Alk+ = Li+, Na+, K+ and Cs+. In 0.5 mol L(-1) solutions, two different mu ep,Ln values were found for the light (La to Nd) and the heavy (Dy to Tm) lanthanides, which suggests two different stoichiometries for the carbonate limiting complexes. These results are consistent with a solubility study that attests the Ln(CO3)3(3-) and Ln(CO3)4(5-) stoichiometries for the heavy (small) and the light (big) lanthanides, respectively. The Alk+ counterions influence the mu ep,Ln Alk2 CO3 values, but not the overall shape of the mu ep,Ln Alk2 CO3 plots as a function of the lanthanide atomic numbers: the counterions do not modify the stoichiometries of the inner sphere complexes. The influence of the Alk+ counterions decreases in the Li+ > Na+ >> K+ > Cs+ series. The K3,Ln stepwise formation constants of the Ln(CO3)3(3-) complexes slightly increase with the atomic numbers of the lanthanides while K4,Ln, the stepwise formation constants of Ln(CO3)4(5-) complexes, slightly decrease from La to Tb, and is no longer measurable for heavier lanthanides.

Stoichiometries and thermodynamic stabilities for aqueous sulfate complexes of U(VI).

The formation constants of UO2SO4 (aq), UO2(SO4)2(2-), and UO2(SO4)3(4-) were measured in aqueous solutions from 10 to 75 degrees C by time-resolved laser-induced fluorescence spectroscopy (TRLFS). A constant enthalpy of reaction approach was satisfactorily used to fit the thermodynamic parameters of stepwise complex formation reactions in a 0.1 M Na(+) ionic medium: log 10 K 1(25 degrees C) = 2.45 +/- 0.05, Delta r H1 = 29.1 +/- 4.0 kJ x mol(-1), log10 K2(25 degrees C) = 1.03 +/- 0.04, and Delta r H2 = 16.6 +/- 4.5 kJ x mol(-1). While the enthalpy of the UO2(SO4)2(2-) formation reaction is in good agreement with calorimetric data, that for UO2SO4 (aq) is higher than other values by a few kilojoules per mole. Incomplete knowledge of the speciation may have led to an underestimation of Delta r H1 in previous calorimetric studies. In fact, one of the published calorimetric determinations of Delta r H1 is here supported by the TRLFS results only when reinterpreted with a more correct equilibrium constant value, which shifts the fitted Delta r H1 value up by 9 kJ x mol(-1). UO2(SO 4) 3 (4-) was evidenced in a 3 M Na (+) ionic medium: log10 K3(25 degrees C) = 0.76 +/- 0.20 and Delta r H3 = 11 +/- 8 kJ x mol(-1) were obtained. The fluorescence features of the sulfate complexes were observed to depend on the ionic conditions. Changes in the coordination mode (mono- and bidentate) of the sulfate ligands may explain these observations, in line with recent structural data.