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Nuclear power will continue to provide energy for the foreseeable future, but it can pose significant challenges in terms of the disposal of waste and potential release of untreated radioactive substances. Iodine is a volatile product from uranium fission and is particularly problematic due to its solubility. Different isotopes of iodine present different issues for people and the environment. 129 I has an extremely long half-life of 1.57 × 10 7 years and poses a long-term environmental risk due to bioaccumulation. In contrast, 131 I has a shorter half-life of 8.02 days and poses a significant risk to human health. There is, therefore, an urgent need to develop secure, efficient and economic stores to capture and sequester ionic and neutral iodine residues. Metal-organic framework (MOF) materials are a new generation of solid sorbents that have wide potential applicability for gas adsorption and substrate binding, and recently there is emerging research on their use for the selective adsorptive removal of iodine. Herein, we review the state-of-the-art performance of MOFs for iodine adsorption and their host-guest chemistry. Various aspects are discussed, including establishing structure-property relationships between the functionality of the MOF host and iodine binding. The techniques and methodologies used for the characterisation of iodine adsorption and of iodine-loaded MOFs are also discussed together with strategies for designing new MOFs that show improved performance for iodine adsorption.

Transformation products of two-line ferrihydrite associated with Lu(III) were studied after 12 years of aging using aberration-corrected high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), high-efficiency energy-dispersive X-ray spectroscopy (EDXS), and density functional theory (DFT). The transformation products consisted of hematite nanoparticles with overgrown goethite needles. High-efficiency STEM-EDXS revealed that Lu is only associated with goethite needles, and atomic-resolution HAADF-STEM reveals structural incorporation of Lu within goethite, partially replacing structural Fe sites. This finding corroborates those recently obtained by AsFlFFF and EXAFS spectroscopy on the same sample (Finck et al. 2018). DFT calculations indicate that Lu incorporation within goethite or hematite are almost equally likely, suggesting that experimental parameters such as temperature and reaction time which affect reaction kinetics, play important roles in determining the Lu uptake. It seems likely that these results may be transferable to predict the behavior of chemically homologous trivalent actinides.

Trace elements analysis is a fundamental challenge in environmental sciences. Scientists measure trace elements in environmental media in order to assess the quality and safety of ecosystems and to quantify the burden of anthropogenic pollution. Among the available analytical techniques, X-ray based methods are particularly powerful, as they can quantify trace elements in situ . Chemical extraction is not required, as is the case for many other analytical techniques. In the last few years, the potential for X-ray techniques to be applied in the environmental sciences has dramatically increased due to developments in laboratory instruments and synchrotron radiation facilities with improved sensitivity and spatial resolution. In this report, we summarize the principles of the X-ray based analytical techniques most frequently employed to study trace elements in environmental samples. We report on the most recent developments in laboratory and synchrotron techniques, as well as advances in instrumentation, with a special attention on X-ray sources, detectors, and optics. Lastly, we inform readers on recent applications of X-ray based analysis to different environmental matrices, such as soil, sediments, waters, wastes, living organisms, geological samples, and atmospheric particulate, and we report examples of sample preparation.

Coherent diffraction imaging (CDI) or lensless X-ray microscopy has become of great interest for high spatial resolution imaging of, e.g., nanostructures and biological specimens. There is no optics required in between an object and a detector, because the object can be fully recovered from its far-field diffraction pattern with an iterative phase retrieval algorithm. Hence, in principle, a sub-wavelength spatial resolution could be achieved in a high-numerical aperture configuration. With the advances of ultrafast laser technology, high photon flux tabletop Extreme Ultraviolet (EUV) sources based on the high-order harmonic generation (HHG) have become available to small-scale laboratories. In this study, we report on a newly established high photon flux and highly monochromatic 30 nm HHG beamline. Furthermore, we applied ptychography, a scanning CDI version, to probe a nearly periodic nanopattern with the tabletop EUV source. A wide-field view of about 15 × 15 μm was probed with a 2.5 μm-diameter illumination beam at 30 nm. From a set of hundreds of far-field diffraction patterns recorded for different adjacent positions of the object, both the object and the illumination beams were successfully reconstructed with the extended ptychographical iterative engine. By investigating the phase retrieval transfer function, a diffraction-limited resolution of reconstruction of about 32 nm is obtained.

We report the unambiguous detection of phenyl groups covalently attached to functionalised graphene using non-linear spectroscopy. Sum-frequency generation was employed to probe graphene on a gold surface after chemical functionalisation using a benzene diazonium salt. We observe a distinct resonance at 3064 cm-1 which can clearly be assigned to an aromatic C-H stretch by comparison with a self-assembled monolayer on a gold substrate formed from benzenethiol. Not only does sum-frequency generation spectroscopy allow one to characterise functionalised graphene with higher sensitivity and much better specificity than many other spectroscopic techniques, but it also opens up the possibility to assess the coverage of graphene with functional groups, and to determine their orientation relative to the graphene surface.

During nuclear waste disposal process, radioactive iodine as a fission product can be released. The widespread implementation of sustainable nuclear energy thus requires the development of efficient iodine stores that have simultaneously high capacity, stability and more importantly, storage density (and hence minimized system volume). Here, we report high I 2 adsorption in a series of robust porous metal-organic materials, MFM-300(M) (M = Al, Sc, Fe, In). MFM-300(Sc) exhibits fully reversible I 2 uptake of 1.54 g g -1 , and its structure remains completely unperturbed upon inclusion/removal of I 2 . Direct observation and quantification of the adsorption, binding domains and dynamics of guest I 2 molecules within these hosts have been achieved using XPS, TGA-MS, high resolution synchrotron X-ray diffraction, pair distribution function analysis, Raman, terahertz and neutron spectroscopy, coupled with density functional theory modeling. These complementary techniques reveal a comprehensive understanding of the host-I 2 and I 2 -I 2 binding interactions at a molecular level. The initial binding site of I 2 in MFM-300(Sc), I 2 I , is located near the bridging hydroxyl group of the [ScO 4 (OH) 2 ] moiety [I 2 I ···H-O = 2.263(9) Å] with an occupancy of 0.268. I 2 II is located interstitially between two phenyl rings of neighboring ligand molecules [I 2 II ···phenyl ring = 3.378(9) and 4.228(5) Å]. I 2 II is 4.565(2) Å from the hydroxyl group with an occupancy of 0.208. Significantly, at high I 2 loading an unprecedented self-aggregation of I 2 molecules into triple-helical chains within the confined nanovoids has been observed at crystallographic resolution, leading to a highly efficient packing of I 2 molecules with an exceptional I 2 storage density of 3.08 g cm -3 in MFM-300(Sc).

Structural information of nanostructures plays a key role in synthesis of novel nano-sized materials for promising applications such as high-performance nanoelectronics and nanophotonics. In this study, we apply for the first time the state-of-the-art coherent diffractive imaging method to characterize the structure of graphite nanoparticles. A sample with nanographites on a Si 3 N 4 support was exposed to 30 nm radiation from a tabletop laser-driven high-order harmonic generation extreme ultraviolet (EUV) source. From the measured far-field diffraction pattern, we were able to reconstruct the distribution of the graphite nanoparticles with a spatial resolution of ∼330 nm using the standard iterative phase retrieval algorithms. A closer look at the reconstructed images reveals possible absorption effects of graphite nanoparticles. This experiment demonstrates the first step towards wide-field and high-resolution imaging of nuclear materials using the newly established lab-scale EUV source. Having such a source opens the door to performing investigations of nuclear graphite and other radioactive material in the lab, thus avoiding the need to transport samples to external facilities.

CAT-ACT-the hard X-ray beamline for CATalysis and ACTinide/radionuclide research at the KIT synchrotron radiation facility ANKA-is dedicated to X-ray spectroscopy, including "flux hungry" photon-in/photon-out and correlative techniques and combines state-of-the-art optics with a unique infrastructure for radionuclide and catalysis research. Measurements can be performed at photon energies varying between 3.4 keV and 55 keV, thus encompassing the actinide M- and L-edge or potassium K-edge up to the K-edges of the lanthanide series such as cerium. Well-established X-ray absorption fine structure spectroscopy in transmission and fluorescence detection modes is available in combination with high energy-resolution X-ray emission spectroscopy or X-ray diffraction techniques. The modular beamline design with two alternately operated in-line experimental stations enables sufficient flexibility to adapt sample environments and detection systems to many scientific challenges. The ACT experimental station focuses on various aspects of nuclear waste disposal within the mission of the Helmholtz association to contribute to the solution of one of the greatest scientific and social challenges of our time-the safe disposal of heat producing, highly radioactive waste forms from nuclear energy production. It augments present capabilities at the INE-Beamline by increasing the flux and extending the energy range into the hard X-ray regime. The CAT experimental station focuses on catalytic materials, e.g., for energy-related and exhaust gas catalysis. Characterization of catalytically active materials under realistic reaction conditions and the development of in situ and operando cells for sample environments close to industrial reactors are essential aspects at CAT.

One of the long standing debates in actinide chemistry is the level of localization and participation of the actinide 5f valence orbitals in covalent bonds across the actinide series. Here we illuminate the role of the 5f valence orbitals of uranium, neptunium and plutonium in chemical bonding using advanced spectroscopies: actinide M 4,5 HR-XANES and 3d4f RIXS. Results reveal that the 5f orbitals are active in the chemical bonding for uranium and neptunium, shown by significant variations in the level of their localization evidenced in the spectra. In contrast, the 5f orbitals of plutonium appear localized and surprisingly insensitive to different bonding environments. We envisage that this report of using relative energy differences between the 5fδ/φ and 5fπ*/5fσ* orbitals as a qualitative measure of overlap-driven actinyl bond covalency will spark activity, and extend to numerous applications of RIXS and HR-XANES to gain new insights into the electronic structures of the actinide elements.

The first hydrophilic, 1,10-phenanthroline derived ligands consisting of only C, H, O and N atoms for the selective extraction of Am(iii) from spent nuclear fuel are reported herein. One of these 2,9-bis-triazolyl-1,10-phenanthroline (BTrzPhen) ligands combined with a non-selective extracting agent, was found to exhibit process-suitable selectivity for Am(iii) over Eu(iii) and Cm(iii), providing a clear step forward.

More than a century after its discovery the structure of the Pa(4+) ion in acidic aqueous solution has been investigated for the first time experimentally and by quantum chemistry. The combined results of EXAFS data and quantum chemically optimized structures suggest that the Pa(4+) aqua ion has an average of nine water molecules in its first hydration sphere at a mean Pa-O distance of 2.43 Å. The data available for the early tetravalent actinide (An) elements from Th(4+) to Bk(4+) show that the An-O bonds have a pronounced electrostatic character, with bond distances following the same monotonic decreasing trend as the An(4+) ionic radii, with a decrease of the hydration number from nine to eight for the heaviest ions Cm(4+) and Bk(4+). Being the first open-shell tetravalent actinide, Pa(4+) features a coordination chemistry very similar to its successors. The electronic configuration of all open-shell systems corresponds to occupation of the valence 5f orbitals, without contribution from the 6d orbitals. Our results thus demonstrate that Pa(iv) resembles its early actinide neighbors.

Arsenic (As) co-precipitation is one of the major processes controlling As solubility in soils and waters. When As is co-precipitated with Al and Mg, the possible formation of layered double hydroxides (LDHs) and other nanocomposites can stabilize As in their structures thus making this toxic element less available. We investigated the nature and reactivity of Mg-Al-arsenate [As(V)] co-precipitated LDHs formed in solution affected by As concentration, pH, and aging. At the beginning of the co-precipitation process, poorly crystalline LDH and non-crystalline Al(Mg)-oxides form. Prolonged aging of the samples promotes crystallization of LDHs, evidenced by an increase in As K XANES intensities and XRD peak intensities. During aging Al- and/or Mg-oxides are likely transformed by dissolution/re-precipitation processes into more crystalline but still defective LDHs. Surface area, chemical composition, reactivity of the precipitates, and anion exchange properties of As(V) in the co-precipitates are influenced by pH, aging, and As concentration. This study demonstrates that (i) As(V) retards or inhibits the formation and transformation of LDHs and (ii) more As(V) is removed from solution if co-precipitated with Mg and Al than by sorption onto well crystallized LDHs., (Copyright © 2015 Elsevier B.V. All rights reserved.)

A new, regioselective synthesis of V-shaped 2,9-bis(6-(4-halophenyl)-1,2,4-triazin-3-yl)-1,10-phenanthrolines (4XPhBTPhen) ligands was developed, creating access to a simple and reliable synthesis of precursors for future supramolecular actinide complexing systems. Described is a reactant-directed regioselective synthetic method, which was found to be high yielding and reliable and yields exclusively 6,6'-phenyl BTPhen derivatives (including 4-chloro and 4-bromo) in five simple steps. Molecular and crystal structures of PhBTP and PhBTPhen products are fully determined and both were found to be in space group C2/c. Additionally, molecular and crystal structures of Z and E isomers of 2-hydrazono-2-phenylacetaldehyde oxime, a reagent in the synthetic route, reveal existence of strong intramolecular N-H···O hydrogen bonding in the Z isomer explaining its lower solubility in water.

After internal contamination, uranium rapidly distributes in the body; up to 20 % of the initial dose is retained in the skeleton, where it remains for years. Several studies suggest that uranium has a deleterious effect on the bone cell system, but little is known regarding the mechanisms leading to accumulation of uranium in bone tissue. We have performed synchrotron radiation-based micro-X-ray fluorescence (SR μ-XRF) studies to assess the initial distribution of uranium within cortical and trabecular bones in contaminated rats' femurs at the micrometer scale. This sensitive technique with high spatial resolution is the only method available that can be successfully applied, given the small amount of uranium in bone tissue. Uranium was found preferentially located in calcifying zones in exposed rats and rapidly accumulates in the endosteal and periosteal area of femoral metaphyses, in calcifying cartilage and in recently formed bone tissue along trabecular bone. Furthermore, specific localized areas with high accumulation of uranium were observed in regions identified as micro-vessels and on bone trabeculae. These observations are of high importance in the study of the accumulation of uranium in bone tissue, as the generally proposed passive chemical sorption on the surface of the inorganic part (apatite) of bone tissue cannot account for these results. Our study opens original perspectives in the field of exogenous metal bio-mineralization.

Synchrotron-based techniques are increasingly used to characterize radioactive materials and elucidate determinant processes relevant to the nuclear fuel cycle. Many recent advances are driven by the need to characterize such materials with high resolution, for example spatial resolution for studies of localized components of heterogeneous systems and energy resolution for characterising the 5f-element oxidation state. Examples of synchrotron-based investigations into f-element chemistry are presented, which illustrate utilizing such high resolution, while pointing out various aspects of synchrotron R&D related to the nuclear fuel cycle. Specifically an example related to separation chemistry performance, an example elucidating immobilisation processes in bedrock, and high energy X-ray emission spectral fingerprint for hexavalent uranium are summarised. Synchrotron-based tools are providing insight into f-element chemistry and geochemistry and are providing data for benchmarking theoretical calculations; the future looks bright.

Dicesium uranyl tetrachloride (Cs2UO2Cl4) has been a model compound for experimental and theoretical studies of electronic structure of U(VI) in the form of UO2(2+) (uranyl ion) for decades. We have obtained angle-resolved electronic structure information for oriented Cs2UO2Cl4 crystal, specifically relative energies of 5f and 6d valence orbitals probed with extraordinary energy resolution by polarization dependent high energy resolution X-ray absorption near edge structure (PD-HR-XANES) and compare these with predictions from quantum chemical Amsterdam density functional theory (ADF) and ab initio real space multiple-scattering Green's function based FEFF codes. The obtained results have fundamental value but also demonstrate an experimental approach, which offers great potential to benchmark and drive improvement in theoretical calculations of electronic structures of actinide elements.

The coordination structure in the solid state and solution complexation behavior of 6-(tetrazol-5-yl)-2,2'-bipyridine (HN4bipy) with samarium(III) was investigated as a model system for actinide(III)/lanthanide(III) separations. Two different solid 1:2 complexes, [Sm(N4bipy)2(OH)(H2O)2] (1) and [Sm(N4bipy)2(HCOO)(H2O)2] (2), were obtained from the reaction of samarium(III) nitrate with HN4bipy in isopropyl alcohol, resuspension in N,N-dimethylformamide (DMF), and slow crystallization. The formate anion coordinated to samarium in 2 is formed by decomposition of DMF to formic acid and dimethylamine. Time-resolved laser fluorescence spectroscopy (TRLFS) studies were performed with curium(III) and europium(III) by using HN4bipy as the ligand. Curium(III) is observed to form 1:2 and 1:3 complexes with increasing HN4bipy concentration; for europium(III), formation of 1:1 and 1:3 complexes is observed. Although the solid-state samarium complexes were confirmed as 1:2 species the 1:2 europium(III) solution complex in ethanol was not identified with TRLFS. The determined conditional stability constant for the 1:3 fully coordinated curium(III) complex species is more than 2 orders of magnitude higher than that for europium(III) (log β3[Cm(N4bipy)3] = 13.8 and log β3[Eu(N4bipy)3] = 11.1). The presence of added 2-bromodecanoic acid as a lipophilic anion source reduces the stability constant for formation of the 1:2 and 1:3 curium(III) complexes, but no ternary complexes were observed. The stability constants for the 1:3 metal ion-N4bipy complexes equate to a theoretical separation factor, SF(Cm(III)/Eu(III)) ≈ 500. However, the low solubility of the HN4bipy ligand in nonpolar solvents typically used in actinide-lanthanide liquid-liquid extractions prevents its use as a partitioning extractant until a more lipophilic HN4bipy-type ligand is developed.

Calcite-water interface reactions are of major importance in various environmental settings as well as in industrial applications. Here we present resonant interface diffraction results on the calcite(104)-aqueous solution interface, measured in solutions containing either 10 mmol L(-1) RbCl or 0.5 mmol L(-1) Se(VI). Results indicate that Rb(+) ions enter the surface adsorbed water layers and adsorb at the calcite(104)-water interface in an inner-sphere fashion. A detailed analysis based on specular and off-specular resonant interface diffraction data reveals three distinct Rb(+) adsorption species: one 1.2 Å above the surface, the second associated with surface adsorbed water molecules 3.2 Å above the surface, and the third adsorbed in an outer-sphere fashion 5.6 Å above the surface. A peak in resonant amplitude between L = 1.5 and L = 3.0 is interpreted as signal from a layered electrolyte structure. The presence of a layered electrolyte structure seems to be confirmed by data measured in the presence of Se(VI).

The molecular origin of the selectivity of N-donor ligands, such as alkylated bis-triazinyl pyridines (BTPs), for actinide complexation in the presence of lanthanides is still largely unclear. NMR investigations of an Am(nPrBTP)3(3+) complex with a (15)N labelled ligand showed that it exhibits large differences in (15)N chemical shift for coordinating N-atoms in comparison to both lanthanide(III) complexes and the free ligand. The temperature dependence of NMR chemical shifts observed for this complex indicates a weak paramagnetism. This fact and the observed large chemical shift for bound nitrogen atoms allow us to conclude that metal-ligand bonding in the reported Am(III) N-donor complex has a larger share of covalence than in lanthanide complexes. This may account for the observed selectivity.

Ionic radii of actinide(III) cations (from U(III) to Cf(III)) in aqueous solution have been derived for the first time starting from accurate experimental determination of the ion-water distances obtained by combining extended X-ray absorption fine structure (EXAFS) results and molecular dynamics (MD) structural data. A strong analogy has been found between the lanthanide and actinide series concerning hydration properties. The existence of a contraction of the An-O distance along the series has been highlighted, while no decrease of the hydration number is evident up to Cf(III).

We present an X-ray absorption near-edge structure (XANES) study of a series of uranium coordination complexes that possess nearly identical first coordination spheres and geometries in a range of oxidation states from U(III) to U(VI). These compounds were obtained through the activation of small molecules, such as ketones, azides, and carbon dioxide, and upon oxidation of a high-valent U(V)≡O to [U(VI)≡O](+). Most of the compounds have been reported previously. All of them are fully characterized and their oxidation states have been confirmed by various spectroscopic methods (SQUID, (1)H NMR, and UV/vis/near-IR). Each uranium complex consists of a triazacyclononane anchor bearing three aryloxide side arms with bulky tert-butyl (t-Bu) or adamantyl (Ad) ortho substituents. All complexes have approximate C(3) symmetry and possess an axial cavity that is either empty (U(III)) or occupied by a seventh ligand, namely, terminal oxygen (U(V) and U(VI)) or an oxygen-containing ligand (U(IV)). The only exception is [(((t-Bu)ArO)(3)tacnU(VI)(O)][SbF(6)], which is the rare case of a complex that shows a strong inverse trans influence. The determined correlation between the uranium oxidation state and the U L(III)-edge XANES absorption in this series includes a single terminal oxo ligand bonded uranium(V,VI), for which data are essentially nonexistent. The correct assignment of the uranium valence in a U(IV)-L(•-) compound (L(•-) = ketyl radical) is shown to be only possible by a comparison to structurally similar compounds.

The N-donor complexing ligand 2,6-bis(5-(2,2-dimethylpropyl)-1H-pyrazol-3-yl)pyridine (C5-BPP) was synthesized and screened as an extracting agent selective for trivalent actinide cations over lanthanides. C5-BPP extracts Am(III) from up to 1 mol/L HNO(3) with a separation factor over Eu(III) of approximately 100. Due to its good performance as an extracting agent, the complexation of trivalent actinides and lanthanides with C5-BPP was studied. The solid-state compounds [Ln(C5-BPP)(NO(3))(3)(DMF)] (Ln = Sm(III), Eu(III)) were synthesized, fully characterized, and compared to the solution structure of the Am(III) 1:1 complex [Am(C5-BPP)(NO(3))(3)]. The high stability constant of log β(3) = 14.8 ± 0.4 determined for the Cm(III) 1:3 complex is in line with C5-BPP's high distribution ratios for Am(III) observed in extraction experiments.

Since its inauguration in 2005, the INE-Beamline for actinide research at the synchrotron source ANKA (KIT North Campus) provides dedicated instrumentation for x-ray spectroscopic characterization of actinide samples and other radioactive materials. R&D work at the beamline focuses on various aspects of nuclear waste disposal within INE's mission to provide the scientific basis for assessing long-term safety of a final nuclear waste repository. The INE-Beamline is accessible for the actinide and radiochemistry community through the ANKA proposal system and the European Union Integrated Infrastructure Initiative ACTINET-I3. Experiments with activities up to 1 × 10(+6) times the European exemption limit are feasible within a safe but flexible containment concept. Measurements with monochromatic radiation are performed at photon energies varying between ~2.1 keV (P K-edge) and ~25 keV (Pd K-edge), including the lanthanide L-edges and the actinide M- and L3-edges up to Cf. The close proximity of the INE-Beamline to INE controlled area labs offers infrastructure unique in Europe for the spectroscopic and microscopic characterization of actinide samples. The modular beamline design enables sufficient flexibility to adapt sample environments and detection systems to many scientific questions. The well-established bulk techniques x-ray absorption fine structure (XAFS) spectroscopy in transmission and fluorescence mode have been augmented by advanced methods using a microfocused beam, including (confocal) XAFS/x-ray fluorescence detection and a combination of (micro-)XAFS and (micro-)x-ray diffraction. Additional instrumentation for high energy-resolution x-ray emission spectroscopy has been successfully developed and tested., (© 2012 American Institute of Physics)

The zetapotential of calcite in contact with aqueous solutions of varying composition is determined for pre-equilibrated suspensions by means of electrophoretic measurements and for non-equilibrium solutions by means of streaming potential measurements. Carbonate and calcium are identified as charge determining ions. Studies of the equilibrium solutions show a shift of isoelectric point with changing CO(2) partial pressure. Changes in pH have only a weak effect in non-equilibrium solutions. The surface structure of (104)-faces of single crystal calcite in contact to solutions corresponding to those of the zetapotential investigations is determined from surface diffraction measurements. The results reveal no direct indication of calcium or carbonate inner-sphere surface species. The surface ions are found to relax only slightly from their bulk positions; the most significant relaxation is a ∼4° tilt of the surface carbonate ions towards the surface. Two ordered layers of water molecules are identified, the first at 2.35±0.05Å above surface calcium ions and the second layer at 3.24±0.06Å above the surface associated with surface carbonate ions. A Basic-Stern surface complexation model is developed to model observed zetapotentials, while only considering outer-sphere complexes of ions other than protons and hydroxide. The Basic-Stern SCM successfully reproduces the zetapotential data and gives reasonable values for the inner Helmholtz capacitance, which are in line with the Stern layer thickness estimated from surface diffraction results., (Copyright © 2010 Elsevier Inc. All rights reserved.)

Microbial processes can affect the environmental behavior of redox sensitive radionuclides, and understanding these reactions is essential for the safe management of radioactive wastes. Neptunium, an alpha-emitting transuranic element, is of particular importance because of its long half-life, high radiotoxicity, and relatively high solubility as Np(V)O(2)(+) under oxic conditions. Here, we describe experiments to explore the biogeochemistry of Np where Np(V) was added to oxic sediment microcosms with indigenous microorganisms and anaerobically incubated. Enhanced Np removal to sediments occurred during microbially mediated metal reduction, and X-ray absorption spectroscopy showed this was due to reduction to poorly soluble Np(IV) on solids. In subsequent reoxidation experiments, sediment-associated Np(IV) was somewhat resistant to oxidative remobilization. These results demonstrate the influence of microbial processes on Np solubility and highlight the critical importance of radionuclide biogeochemistry in nuclear legacy management.

With the aim of better understanding the selectivity of the established system 2,6-ditriazinylpyridine (BTP) for actinide(III)/lanthanide(III) separations, a related model system was synthesized and studied. The N donor complexing ligand 6-(3,5-dimethyl-1H-pyrazol-1-yl)-2,2'-bipyridine (dmpbipy) was synthesized having a fused N heterocycle ring structure modified from the BTP partitioning ligand, and its extraction performance and selectivity for trivalent actinide cations over lanthanides was evaluated. X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS), and time-resolved laser fluorescence spectroscopy (TRLFS) results show that 1:1 complexes are formed, unlike the 1:3 complex for BTP systems. The equilibrium constant for curium complex formation with dmpbipy was determined to be log K = 2.80, similar to that for nitrate. The Gibbs free energy, ΔG(20 °C), of 1:1 Cm-dmpbipy formation in n-octan-1-ol was measured to be -15.5 kJ/mol. The dmpbipy ligand in 1-octanol does not extract Am(III) Eu(III) from HNO(3) but was found to extract Am(III) with limited selectivity over Eu(III) (SF(Am(III)/Eu(III)) ≈ 8) dissolved in 2-bromohexanoic acid and kerosene at pH > 2.4.

In the present study, the sorption of europium and lutetium onto titanium dioxide from aqueous solutions is presented, as a function of pH, ionic strength and concentration. An acid base model for the titanium dioxide surface was determined from potentiometric titrations and zeta-potential measurements. The common intersection point of potentiometric titrations coincided with the isoelectric point from electrokinetic experiments, resulting in a pristine point of zero charge of about 6.1. The experimental data were in agreement with previously published results and a previously published MUSIC-type model was used as the basis to model the acid-base behavior. Comparison of europium and lutetium showed no difference in the adsorption behavior. Furthermore, no difference was observed both in uptake and spectroscopic studies whether carbonate was absent or present. The absence of a noticeable effect of the ionic strength on the adsorption behavior was indicative of strong binding. EXAFS revealed rough conservation of the coordination with 9-8 water and surface hydroxyl groups upon sorption. EXAFS results suggested the existence of different metal-oxygen distances, more varied than that observed for the respective aquo complex and thus indicative for inner-sphere surface complexation. A clear differentiation of surface complexation denticity was not possible based on spectroscopic data. A multisite surface complexation model approach was applied by assuming monodentate and multidentate binding to describe the trivalent metal uptake data. It is conceivable that mono- and multidentate species contribute to lanthanide sorption to titanium dioxide. In other words a distribution of states occurs in cation surface complexation reactions., (Copyright 2010 Elsevier Inc. All rights reserved.)

Direct mercury (Hg) speciation was assessed for soil samples with a Hg concentration ranging from 7 up to 240 mg kg(-1). Hg chemical forms were identified and quantified by sequential extractions and bulk- and micro-analytical techniques exploiting synchrotron generated X-rays. In particular, microspectroscopic techniques such as mu-XRF, mu-XRD and mu-XANES were necessary to solve bulk Hg speciation, in both soil fractions <2 mm and <2 microm. The main Hg-species found in the soil samples were metacinnabar (beta-HgS), cinnabar (alpha-HgS), corderoite (Hg(3)S(2)Cl(2)), and an amorphous phase containing Hg bound to chlorine and sulfur. The amount of metacinnabar and amorphous phases increased in the fraction <2 microm. No interaction among Hg-species and soil components was observed. All the observed Hg-species originated from the slow weathering of an inert Hg-containing waste material (K106, U.S. EPA) dumped in the area several years ago, which is changing into a relatively more dangerous source of pollution., (Copyright 2010 Elsevier Ltd. All rights reserved.)

Spectroscopic, solvent extraction methods and computational chemistry are applied for the characterization of redox sensitive trivalent plutonium complexed with the N-donor extracting agent alkylated 2,6-ditriazinylpyridines (n-C3H7-BTP) in organic solution. The redox stabilization and speciation of Pu(III) is discussed. Extraction of Pu(III) with n-C3H7-BTP is compared to that for redox stable Am(III). The speciation of Pu(III) with n-C3H7-BTP in organic solution is studied by UV-Vis/NIR and XAFS spectroscopy. Only the 1:3 complex, [Pu(n-C3H7-BTP)3](3+) is observed to form, which is confirmed by EXAFS and solvent extraction. The [Pu(n-C3H7-BTP)3](3+) complex is compared to the isostructural U(III), Am(III), and Cm(III) complexes studied earlier.

Humic acids (HA) have a high binding capacity towards traces of toxic metal cations, thus affecting their transport in aquatic systems. Eu(III)-HA aggregates are studied by synchrotron-based scanning transmission X-ray microscopy (STXM) at the carbon K-edge and laser scanning luminescence microscopy (LSLM) at the (5)D(0) --> (7)F(1,2) fluorescence emission lines. Both methods provide the necessary spatial resolution in the sub-micrometre range to resolve characteristic aggregate morphologies: optically dense zones embedded in a matrix of less dense material in STXM images correspond to areas with increased Eu(III) luminescence yield in the LSLM micrographs. In the C 1s-NEXAFS of metal-loaded polyacrylic acid (PAA), used as a HA model compound, a distinct complexation effect is identified. This effect is similar to trends observed in the dense fraction of HA/metal cation aggregates. The strongest complexation effect is observed for the Zr(IV)-HA/PAA system. This effect is confirmed by quantum chemical calculations performed at the ab initio level for model complexes with different metal centres and complex geometries. Without the high spatial resolution of STXM and LSLM and without the combination of molecular modelling with experimental results, the different zones indicating a ;pseudo'-phase separation into strong complexing domains and weaker complexing domains of HA would never have been identified. This type of strategy can be used to study metal interaction with other organic material.

Coprecipitation experiments of Np(V) and U(VI) with calcite were performed in mixed-flow reactors under steady state conditions at room temperature for up to 400 h at precipitation rates of 1.0 x 10(-8) to 6.8 x 10(-8) mol/(m2 s). The saturation index with respect to calcite varied between 0.04 and 0.95. Initial Np(V) or U(VI) concentrations were 1 micromol/L, 0.01 mol/L NaCl was used as background electrolyte, and pH ranged from 7.8 to 12.8. Partition coefficients for Np(V) were in the range of 0.5-10.3, compared to 0.02 for U(VI). Np L(III) and U L(III) EXAFS were used to characterize the local structural environment of the incorporated actinides. In the case of U(VI), the structural environment is not unambiguously characterized. Our data suggest that Np(V) ions occupy calcium lattice sites. The two axial oxygen atoms of the linear neptunyl moiety substitute two calcite carbonate groups in the first coordination sphere. Thus, four carbonate groups coordinate the neptunyl-ion in a monodentate fashion with four equatorial oxygen atoms (Oeq) at 2.4 A and associated carbon atoms (C) at 3.2 A. The interatomic distances indicate slight structural relaxation of the carbonate groups from their ideal sites. A similar structural model has been reported for U(VI) incorporated into natural calcite.

A hitherto unknown type of aqueous complex, ternary Ca-MIV-OH complexes (M = Zr and Th), causes unexpectedly high solubilities of zirconium(IV) and thorium(IV) hydrous oxides in alkaline CaCl2 solutions (pHc = 10-12, [CaCl2] > 0.05 mol.L(-1), and pHc = 11-12, [CaCl2] > 0.5 mol.L(-1), respectively). The dominant aqueous species are identified as Ca3[Zr(OH)6]4+ and Ca4[Th(OH)8]4+ and characterized by extended X-ray absorption fine structure (EXAFS) spectroscopy. The number of OH- ligands in the first coordination sphere detected by EXAFS, NO = 6 (6.6 +/- 1.2) for Zr and NO = 8 (8.6 +/- 1.2) for Th, are consistent with the observed slopes of 2 and 4 in the solubility curves log [M]tot vs pHc. The presence of polynuclear hydrolysis species and the formation of chloride complexes can be excluded. EXAFS spectra clearly show a second coordination shell of calcium ions. The [Zr(OH)6]2- and [Th(OH)8]4- complexes with an unusually large number of OH- ligands are stabilized by the formation of associates or ion pairs with Ca2+ ions. The number of neighboring Ca2+ ions around the [Zr(OH)6]2- and [Th(OH)8]4- units is determined to be NCa = 3 (2.7 +/- 0.6) at a distance of RZr-Ca = 3.38 +/- 0.02 A and NCa = 4 (3.8 +/- 0.5) at a distance of RTh-Ca = 3.98 +/- 0.02 A. The Ca3[Zr(OH)6]4+ and Ca4[Th(OH)8]4+ complexes have first (M-O) and second (M-Ca) coordination spheres with the Ca2+ ions bound to coordination polyhedra edges.

Micro-focused synchrotron radiation techniques to investigate actinide elements in geological samples are becoming an increasingly used tool in nuclear waste disposal research. In this article, results using mu-focus techniques are presented from a bore core section of a U-rich tertiary sediment collected from Ruprechtov, Czech Republic, a natural analog to nuclear waste repository scenarios in deep geological formations. Different methods are applied to obtain various, complementary information. Elemental and element chemical state distributions are obtained from micro-XRF measurements, oxidation states of As determined from micro-XANES, and the crystalline structure of selected regions are studied by means of micro-XRD. We find that preparation of the thin section created an As oxidation state artifact; it apparently changed the As valence in some regions of the sample. Results support our previously proposed hypothesis of the mechanism for U-enrichment in the sediment. AsFeS coating on framboid Fe nodules in the sediment reduced mobile groundwater-dissolved U(VI) to less-soluble U(IV), thereby immobilizing the uranium in the sediment.

Combining spectroscopic techniques (TRES and EXAFS) and molecular dynamics simulations, we have investigated the state of trivalent europium dissolved in room-temperature ionic liquids (RTILs), as a function of the RTIL anion and in the presence of added chloride anions. The studied RTILs are based on the 1-butyl-3-methyl-imidazolium (Bumim+) cation and differ by their anionic counterparts: BF4-, PF6-, Tf- (triflate, CF3SO3-), and Tf2N- [(CF3SO2)2N-]. The results show the strong influence of the RTIL nature on the first solvation shell of europium and on its complexation with chloride. Depending on the RTIL, europium(III), which was introduced in solution as a triflate salt, is found to be solvated either by RTIL anions only or as neutral undissociated EuTf3 moieties completed by solvent anions. Kinetic effects, related to the viscosity of the RTIL and the nature of the europium salt, also markedly influence the coordination of added Cl- or F- anions to the metal.

The complexation of Cm(III) and Eu(III) with 2,6-di(5,6-dipropyl-1,2,4-triazin-3-yl)pyridine (n-C3H7-BTP) in nonaqueous organic solution is studied with extended X-ray absorption spectroscopy. Bond lengths are the same in both complexes. Quantum-chemical calculations performed at different levels support this finding. On the other hand, the Cm.(n-C3H7-BTP)3 complex is formed at much lower ligand-to-metal concentration ratio than the Eu.(n-C3H7-BTP)3 complex, as shown by time-resolved laser-induced fluorescence spectroscopy. This is in good agreement with n-C3H7-BTP's high selectivity for trivalent actinides over lanthanides in liquid-liquid extraction.

The solubility of Zr(OH)4(am)--in other words hydrated Zr(IV) oxyhydroxide--is determined by means of coulometric titration (CT), and colloids are detected by laser-induced breakdown when the solubility limit is exceeded. Our results at pH 3-8 demonstrate that the solubility of Zr(OH)4(am) is several orders of magnitude higher than reported classical solubility data for acidic solutions, determined from undersaturation with a less soluble microcrystalline Zr(IV) oxide precipitate. Analysis of extended X-ray absorption fine structure (EXAFS) data shows that the microcrystalline colloids in a 0.1 mol l(-1) Zr aqueous solution at pH 0.2 contain tetrameric units, similar to those present in the structure of ZrOCl2.8H2O. Characterization of the CT solutions by means of EXAFS shows that oligomeric species form as the solubility limit is approached. The current lack of data on equilibrium constants for polynuclear hydroxide complexes prohibits the use of a realistic speciation model to describe the solubility of pH-dependent Zr(OH)4(am). However, the solubility curve is obtained using the mononuclear hydrolysis constants estimated in the present paper, along with the solubility constant (log K'sp=-49.9+/-0.5 in 0.5 mol l(-1) NaCl; log K degrees(sp)=-53.1+/-0.5 at I=0).

The complexes of trivalent actinide curium (Cm(III)) with di(chlorophenyl)dithiophosphinic acid ((ClPh)2PSSH) and three different neutral complexing agents as synergists in tert-butylbenzene are studied by EXAFS and time-resolved laser fluorescence spectroscopy (TRLFS). The results are compared with those from the corresponding europium (Eu(III)) complexes. The aim of these investigations is to understand the chemical interactions responsible for the high selectivity of the synergistic systems of (ClPh)2PSSH and neutral complexing agents tri-n-octylphosphine oxide, tributylphosphate and tris(2-ethylhexyl)phosphate for trivalent actinide cations in liquid-liquid extraction. In our structural chemistry study, we find that the inner coordination sphere of extracted Cm(III) and Eu(III) complexes are different. In all complexes the (ClPh)2PSSH is bound to the metal cation in a bidentate fashion and the oxygen donor of the neutral complexing agent used as synergist is directly coordinated to the metal cation. Comparison of the Cm(III) and Eu(III) complexes shows that Cm(III) preferentially binds to the sulfur of (ClPh)2PSSH, whereas Eu(III) is preferentially bound to oxygen. A good selectivity in liquid-liquid extraction is correlated with a high ratio of the sulfur coordination number to oxygen coordination number. This leads to the conclusion that the observed differences in the coordination structure between Cm(III) and Eu(III) complexes play an important role in the selectivity of these extraction systems.

Investigations by micrometer-scale X-ray fluorescence and X-ray absorption fine structure (micro-XRF and micro-XAFS) recorded in a confocal geometry on a bore core section of a uranium-rich tertiary sediment are performed in order to assess mechanisms leading to immobilization of the uranium during diagenesis. Results show uranium to be present as a tetravalent phosphate and that U(IV) is associated with As(V). Arsenic present is either As(V) or As(O); we found no evidence for As(III). The As(O) is observed to be intimately associated with the surface of Fe(II) nodules and likely arsenopyrite. A hypothesis for the mechanism of uranium immobilization is proposed, where arsenopyrite acted as reductant of groundwater-dissolved U(VI), leading to precipitation of less soluble U(IV) and thereby forming As(V).

X-ray absorption near edge structure (XANES) spectroscopy for in situ metal valence determination has become a powerful analytical tool in heterogeneous systems. This is in part because it is applicable without prior separation procedures. For some systems, however, determining the oxidation state from XANES spectra is not straightforward and caution must be used. We show that the analysis of L3,2 edge EXAFS (extended X-ray absorption fine structure) spectra is better suited to distinguish between Np(IV) and Np(V) than from their XANES spectra. Whereas evidence for the oxidation of Np(IV) in solution samples from their Np L3 XANES is unclear, their EXAFS data unequivocally reveals Np(V) formation in the solutions.

Pu(IV) oxyhydroxide colloid growth is investigated with XAFS and LIBD. From combined results a model of colloid formation is proposed, which leads to a face-centered cubic Pu sublattice having cation defects, as observed with EXAFS, and a linear dependency of log [Pu(IV)] on -log [H+] with slope -2, in accord with LIBD. The solubility for Pu(IV) measured with LIBD is close to the lower limit of the solubility curve from previously reported data., (Copyright 2004 American Chemical Society)

The time dependent changes of Lu speciation (used as Am(III) homologue), initially sorbed onto 2-line ferrihydrite at pH 5.9, during tempering (70 degrees C) to stable crystalline transformation products, goethite and hematite, is studied. Microscopies (AFM, SEM), XRD and FTIR spectroscopy confirm transformation to both goethite and hematite, with a predominance of hematite. XRD investigation of another transformation series at pH 8.0 (75 degrees C, [Lu(III)initial] 7 times higher) shows that the cell volume of hematite increases, suggesting the incorporation of Lu in the crystal structure. Extended X-ray absorption fine structure (EXAFS) (pH 5.9 series, 70 degrees C) reveals a shortening of the Lu-O bond distance and an increase in asymmetry of the first shell with increasing tempering time in the intermediate temper time samples. The intensity of the second peak in the Fourier transform (FT) of the EXAFS increases and splits into two components. The EXAFS data of the end product can be modeled well using a hematite-like cluster, with an isotropic expansion of distances to account for incorporation of Lu into the hematite structure. These results demonstrate that the Lu is incorporated in the crystal lattice of the transformation product, as opposed to being occluded or remaining a sorbed species on the surface.

X-ray absorption fine structure (XAFS) spectroscopy at the Th L3 edge is applied for the characterization of crystalline, anhydrous ThO(2)(cr), microcrystalline ThO(2).xH(2)O(s), amorphous ThO(n)(OH)(4-2n).xH(2)O(am), aqueous Th(IV) solutions, and colloidal suspensions up to p(c)H 3.7. The microcrystalline, possibly hydrated thorium dioxide, is formed at p(c)H 1.5-2.5 by precipitation from suspensions of 16-23 nm thorium dioxide colloids. The solubility data determined for this solid is several orders of magnitude lower than the values for amorphous Th(IV) hydroxide or hydrous oxide. The EXAFS spectrum of the isolated microcrystalline particles shows that their structure is different from that of anhydrous crystalline ThO(2)(cr) and amorphous ThO(n)(OH)(4-2n).xH(2)O(am) precipitated at higher pH and dried at room temperature. The solubility measured for the amorphous Th(IV) precipitate is comparable to that previously reported for a solid prepared in a similar manner. In other solubility studies with amorphous Th(IV) hydroxide or hydrous oxide, considerably higher thorium concentrations are measured at p(c)H 3.5-5. The aqueous speciation is made by EXAFS for solutions prepared by careful coulometric titration under comparable conditions (p(c)H and thorium concentration). The spectra of these solutions demonstrate the presence of a large amount of Th(IV) polynuclear species or colloids of small size, having a highly asymmetric Th-O coordination. The EXAFS spectrum of these colloids is similar to that of the amorphous solid.

Soft X-ray spectromicroscopy investigations of the interaction of aquatic humic acid (HA) and montmorillonite colloids have been performed in situ at the NSLS X1-A STXM endstation. Images have been recorded of montmorillonite particles, HA aggregates, and mixed suspensions of both montmorillonite + HA and montmorillonite + carboxyl polystyrene microspheres, as reference organic colloids. Special emphasis has been placed on the sample preparation technique in order to keep the colloid particles hydrated during all measurements. C 1s near edge absorption fine structure extracted from STXM image stacks reveals electronic transitions corresponding to functional -COOH and -C(6)H(5) groups present in HA and polystyrene. XANES peak intensities reflect the relative amounts of these two carbon functional groups in the organic particles. For example, the greater amount of carboxyl groups in HA compared to the latex reference particles affects a larger 1s-->pi* transition intensity. A specific form of montmorillonite-HA particle agglomeration at near-neutral pH has been observed. Under these conditions, we found no separate clustering of HA. Instead, STXM images show the HA to coat the clay mineral surface, leading to nearly a fractal manner of aggregation. Copyright 2000 Academic Press.

The structures of aqueous M(4+)(aq) and MF(3+)(aq), where M is uranium(IV) or thorium(IV), have been determined by L(III) edge EXAFS using data from solutions of 1.5 M HClO(4) in which the M(IV) concentrations ranged from 0.03 to 0.3 M. A least-squares refinement of the data for the aqua ions indicated 10.8 +/- 0.5 water molecules in the first hydration sphere of both ions and M-O bond distances for U(IV) and Th(IV) of 2.42 +/- 0.01 and 2.45 +/- 0.01 Å, respectively. By considering both previous structure information and the EXAFS data, we selected N = 10 +/- 1 as the most likely coordination number of both M(IV) aqua ions. EXAFS measurements from acidic aqueous uranium(IV) and thorium(IV) solutions containing fluoride show that large changes in the first coordination sphere occur. The experimental data indicates an asymmetrical distribution of the distances, probably as a result of differing M-F and M-O bond lengths. These can be described by a model that contains two different bond distances, one M-F distance at 2.10 Å and one M-O distance at 2.45 Å for U(IV); for Th(IV), the corresponding distances are 2.14 and 2.48 Å. The total coordination number in this model is unchanged from the aqua ions, i.e., 10 +/- 1.