Structural Studies and Thermal Analysis in the Cs2MoO4-PbMoO4 System with Elucidation of ß-Cs2Pb(MoO4)2.

The quaternary compound Cs2Pb(MoO4)2 was synthesized and its structure was characterized using X-ray and neutron diffraction from 298 to 773 K, while thermal expansion was studied from 298 to 723 K. The crystal structure of the high-temperature phase ß-Cs2Pb(MoO4)2 was elucidated, and it was found to crystallize in the space group R3̅m (No. 166), i.e., with a palmierite structure. In addition, the oxidation state of Mo in the low-temperature phase α-Cs2Pb(MoO4)2 was studied using X-ray absorption near-edge structure spectroscopy. Phase diagram equilibrium measurements in the Cs2MoO4-PbMoO4 system were performed, revisiting a previously reported phase diagram. The equilibrium phase diagram proposed here includes a different composition of the intermediate compound in this system. The obtained data can serve as relevant information for thermodynamic modeling in view of the safety assessment of next-generation lead-cooled fast reactors.

Implementation of cryogenic tender X-ray HR-XANES spectroscopy at the ACT station of the CAT-ACT beamline at the KIT Light Source.

The ACT experimental station of the CAT-ACT wiggler beamline at the Karlsruhe Institute of Technology (KIT) Light Source is dedicated to the investigation of radionuclide materials with radioactivities up to 1000000 times the exemption limit by various speciation techniques applying monochromatic X-rays. In this article, the latest technological developments at the ACT station that enable high-resolution X-ray absorption near-edge structure (HR-XANES) spectroscopy for low radionuclide loading samples are highlighted - encompassing the investigation of actinide elements down to 1 p.p.m. concentration - combined with a cryogenic sample environment reducing beam-induced sample alterations. One important part of this development is a versatile gas tight plexiglass encasement ensuring that all beam paths in the five-analyzer-crystal Johann-type X-ray emission spectrometer run within He atmosphere. The setup enables the easy exchange between different experiments (conventional X-ray absorption fine structure, HR-XANES, high-energy or wide-angle X-ray scattering, tender to hard X-ray spectroscopy) and opens up the possibility for the investigation of environmental samples, such as specimens containing transuranium elements from contaminated land sites or samples from sorption and diffusion experiments to mimic the far field of a breached nuclear waste repository.

Ammonium Pertechnetate in Mixtures of Trifluoromethanesulfonic Acid and Trifluoromethanesulfonic Anhydride.

Ammonium pertechnetate reacts in mixtures of trifluoromethanesulfonic anhydride and trifluoromethanesulfonic acid under final formation of ammonium pentakis(trifluoromethanesulfonato)oxidotechnetate(V), (NH4 )2 [TcO(OTf)5 ]. The reaction proceeds only at exact concentrations and under the exclusion of air and moisture via pertechnetyl trifluoromethanesulfonate, [TcO3 (OTf)], and intermediate TcVI species. 99 Tc nuclear magnetic resonance (NMR) has been used to study the TcVII compound and electron paramagnetic resonance (EPR), 99 Tc NMR and X-ray absorption near-edge structure (XANES) experiments indicate the presence of the reduced technetium species. In moist air, (NH4 )2 [TcO(OTf)5 ] slowly hydrolyses under formation of the tetrameric oxidotechnetate(V) (NH4 )4 [{TcO(TcO4 )4 }4 ] ⋅10 H2 O. Single-crystal X-ray crystallography was used to determine the solid-state structures. Additionally, UV/Vis absorption and IR spectra as well as quantum chemical calculations confirm the identity of the species.

Two-dimensional Wide-Angle X-ray Scattering on a Cm-doped borosilicate glass in a beryllium container.

The two-dimensional wide-angle X-ray diffraction technique was applied to a Cm-doped borosilicate glass in a beryllium container. The experiment involved a high-energy X-ray beam and an image plate. It is shown that it is possible to extract the structure factor of the radioactive glass successfully from diffraction patterns and compare it with that of the pristine one. Striking differences appear under the first diffraction peak, revealing new sub-structures for the radioactive glass. It is suggested that they could be related to structural changes in the medium-range order, in particular the size distribution of rings or chains under the influence of mixed interactions between the glass network, α-particles and recoil nuclei.

Relativistic Multiconfigurational Ab Initio Calculation of Uranyl 3d4f Resonant Inelastic X-ray Scattering.

We applied relativistic multiconfigurational all-electron ab initio calculations including the spin-orbit interaction to calculate the 3d4f resonant inelastic X-ray scattering (RIXS) map (3d3/2 → 5f5/2 U M4 absorption edge and 4f5/2 → 3d3/2 U Mß emission) of uranyl (UO22+). The calculated data are in excellent agreement with experimental results and allow a detailed understanding of the observed features and an unambiguous assignment of all involved intermediate and final states. The energies corresponding to the maxima of the resonant emission and the non-resonant (normal) emission were determined with high accuracy, and the corresponding X-ray absorption near edge structure spectra extracted at these two positions were simulated and agree well with the measured data. With the high quality of our theoretical data, we show that the cause of the splitting of the three main peaks in emission is due to the fine structure splitting of the 4f orbitals induced through the trans di-oxo bonds in uranyl and that we are able to obtain direct information about the energy differences between the 5f and 4f orbitals: Δ5f δ/ϕ - 4f δ/ϕ, Δ5f π* - 4f π, and Δ5f σ* - 4f σ from the 3d4f RIXS map. RIXS maps contain a wealth of information, and ab initio calculations facilitate an understanding of their complex structure in a clear and transparent way. With these calculations, we show that the multiconfigurational protocol, which is nowadays applied as a standard tool to study the X-ray spectra of transition metal complexes, can be extended to the calculation of RIXS maps of systems containing actinides.

A Combined Study of Tc Redox Speciation in Complex Aqueous Systems: Wet-Chemistry, Tc K-/L3-Edge X-ray Absorption Fine Structure, and Ab Initio Calculations.

The combination of wet-chemistry experiments (measurements of pH, Eh, and [Tc]) and advanced spectroscopic techniques (K- and L3-edge X-ray absorption fine structure spectroscopy) confirms the formation of a very stable Tc(V)-gluconate complex under anoxic conditions. In the presence of gluconate and an excess of Sn(II) (at pe + pH ≈ 2), technetium forms a very stable Tc(IV)-gluconate complex significantly enhancing the solubility defined by TcO2(s) in hyperalkaline gluconate-free systems. A new setup for "tender" X-ray spectroscopy (spectral range, ∼2-5 keV) in transmission or total fluorescence yield detection mode based on a He flow cell has been developed at the INE Beamline for radionuclide science (KIT light source). This setup allows handling of radioactive specimens with total activities up to one million times the exemption limit. For the first time, Tc L3-edge measurements (∼2.677 keV) of Tc species in liquid (aqueous) media are reported, clearly outperforming conventional K-edge spectroscopy as a tool to differentiate Tc oxidation states and coordination environments. The coupling of L3-edge X-ray absorption near-edge spectroscopy measurements and relativistic multireference ab initio methods opens new perspectives in the definition of chemical and thermodynamic models for systems of relevance in the context of nuclear waste disposal, environmental, and pharmaceutical applications.

Complexation of Np(V) with the Dicarboxylates, Malonate, and Succinate: Complex Stoichiometry, Thermodynamic Data, and Structural Information.

The complexation of Np(V) with malonate and succinate is studied by different spectroscopic techniques, namely, attenuated total reflection Fourier transform infrared (ATR FT-IR) and extended X-ray absorption fine-structure (EXAFS) spectroscopy, as well as by quantum chemistry to determine the speciation, thermodynamic data, and structural information of the formed complexes. For complex stoichiometries and the thermodynamic functions (log ßn°(Θ), ΔrHn°, ΔrSn°), near infrared absorption spectroscopy (vis/NIR) is applied. The complexation reactions are investigated as a function of the total concentration of malonate ([Mal2-]total) and succinate ([Succ2-]total), ionic strength [Im = 0.5-4.0 mol kg-1 Na+(Cl-/ClO4-)], and temperature (Θ = 20-85 °C). Besides the solvated NpO2+ ion, the formation of two Np(V) species with the stoichiometry NpO2(L)n1-2n (n = 1, 2, L = Mal2-, Succ2-) is observed. With increasing temperature, the molar fractions of both complex species increase and the temperature-dependent conditional stability constants log ßn'(Θ) at given ionic strengths are determined by the law of mass action. The log ßn'(Θ) are extrapolated to IUPAC reference-state conditions (Im = 0) according to the specific ion interaction theory (SIT), revealing thermodynamic log ßn°(Θ) values. For all formed complexes, [NpO2(Mal)-: log ß1°(25 °C) = 3.36 ± 0.11, NpO2(Mal)23-: log ß2°(25 °C) = 3.95 ± 0.19, NpO2(Succ)-: log ß1°(25 °C) = 2.05 ± 0.45, NpO2(Succ)23-: log ß2°(25 °C) = 0.75 ± 1.22], an increase of the stability constants with increasing temperature was observed. This confirmed an endothermic complexation reaction. The temperature dependence of the log ßn°(T) values is described by the integrated Van't Hoff equation, and the standard reaction enthalpies and entropies for the complexation reactions are determined. Furthermore, the sum of the specific binary ion-ion interaction coefficients Δεn°(Θ) for the complexation reactions are obtained as a function of the t from the respective SIT modeling as a function of the temperature. In addition to the thermodynamic data, the structures of the complexes and the coordination modes of malonate and succinate are investigated using EXAFS spectroscopy, ATR-FT-IR spectroscopy, and quantum chemical calculations. The results show that in the case of malonate, six-membered chelate complexes are formed, whereas for succinate, seven-membered rings form. The latter ones are energetically unfavorable due to the limited space in the equatorial plane of the Np(V) ion (as NpO2+ cation).

Fe(II) Induced Reduction of Incorporated U(VI) to U(V) in Goethite.

Over 60 years of nuclear activities have resulted in a global legacy of radioactive wastes, with uranium considered a key radionuclide in both disposal and contaminated land scenarios. With the understanding that U has been incorporated into a range of iron (oxyhydr)oxides, these minerals may be considered a secondary barrier to the migration of radionuclides in the environment. However, the long-term stability of U-incorporated iron (oxyhydr)oxides is largely unknown, with the end-fate of incorporated species potentially impacted by biogeochemical processes. In particular, studies show that significant electron transfer may occur between stable iron (oxyhydr)oxides such as goethite and adsorbed Fe(II). These interactions can also induce varying degrees of iron (oxyhydr)oxide recrystallization (<4% to >90%). Here, the fate of U(VI)-incorporated goethite during exposure to Fe(II) was investigated using geochemical analysis and X-ray absorption spectroscopy (XAS). Analysis of XAS spectra revealed that incorporated U(VI) was reduced to U(V) as the reaction with Fe(II) progressed, with minimal recrystallization (approximately 2%) of the goethite phase. These results therefore indicate that U may remain incorporated within goethite as U(V) even under iron-reducing conditions. This develops the concept of iron (oxyhydr)oxides acting as a secondary barrier to radionuclide migration in the environment.

Thermodynamics and Structure of Neptunium(V) Complexes with Formate. Spectroscopic and Theoretical Study.

The temperature and ionic strength dependences of the complex formation of NpO2+ with formate in aqueous solution are studied by absorption spectroscopy (Im = 0.5-4.0 mol kg-1, T = 20-85 °C, [Form-]total = 0-0.65 mol kg-1), extended X-ray absorption fine structure spectroscopy (EXAFS) and quantum chemical methods. The complex stoichiometry and the thermodynamic functions of the complexation reactions are determined by peak deconvolution of the absorption spectra and slope analyses. Besides the solvated NpO2+ ion, two NpO2+ formate species (NpO2(Form)n1-n; n = 1, 2) are identified. Application of the law of mass action yields the temperature dependent conditional stability constants log ß'n(T) at a given ionic strength. These data are extrapolated to IUPAC reference state conditions (Im = 0) using the specific ion interaction theory (SIT). The results show, that log ß01(20 °C) = 0.67 ± 0.04 decreases by approximately 0.1 logarithmic units with increasing temperature, log ß02(20 °C) = 0.11 ± 0.11 increases by about 0.2 logarithmic units. The temperature dependence of the log ß0n(T) values is modeled with the integrated Van't Hoff equation yielding the standard reaction enthalpy ΔrH0 and entropy ΔrS0 of the complexation reactions. The results show that the formation of NpO2(Form) is exothermic (ΔrH01 = -2.8 ± 0.9 kJ mol-1) whereas the formation of NpO2(Form)2- is endothermic (ΔrH02 = 6.7 ± 4.1 kJ mol-1). Furthermore, the binary ion-ion interaction coefficients εT(i,k) of the formed complexes are determined in NaClO4 and NaCl media as a function of the temperature. The coordination mode of formate toward the metal ion is investigated by EXAFS spectroscopy and quantum chemical calculations. A coordination of the ligand via only one O atom of formate to the metal ion is identified.

Competitive Reaction of Neptunium(V) and Uranium(VI) in Potassium-Sodium Carbonate-Rich Aqueous Media: Speciation Study with a Focus on High-Resolution X-ray Spectroscopy.

Neptunium(V) and uranium(VI) are precipitated from an aqueous potassium-sodium-containing carbonate-rich solution, and the solid phases are investigated. U/Np M4,5-edge high-energy resolution X-ray absorption near edge structure (HR-XANES) spectroscopy and Np 3d4f resonant inelastic X-ray scattering (3d4f RIXS) are applied in combination with thermodynamic calculations, U/Np L3-edge XANES, and extended X-ray absorption fine structure (EXAFS) studies to analyze the local atomic coordination and oxidation states of uranium and neptunium. The XANES/HR-XANES analyses are supported by ab initio quantum-chemical computations with the finite difference method near-edge structure code (FDMNES). The solid precipitates are also investigated with powder X-ray diffraction, scanning electron microscopy-energy dispersive X-ray spectroscopy, and Raman spectroscopy. The results strongly suggest that K[NpVO2CO3](cr), K3[NpVO2(CO3)2](cr), and K3Na[UVIO2(CO3)3](cr) are the predominant neptunium and uranium solid phases formed. Despite the 100 times lower initial neptunium(V) concentration at pH 10.5 and oxic conditions, neptunium(V)-rich phases predominately precipitate. The prevailing formation of neptunium(V) over uranium(VI) solids demonstrates the high structural stability of neptunium(V) carbonates containing potassium. It is illustrated that the Np M5-edge HR-XANES spectra are sensitive to changes of the Np-O axial bond length for neptunyl(V/VI).

In situ high-temperature EXAFS measurements on radioactive and air-sensitive molten salt materials.

The development at the Delft University of Technology (TU Delft, The Netherlands) of an experimental set-up dedicated to high-temperature in situ EXAFS measurements of radioactive, air-sensitive and corrosive fluoride salts is reported. A detailed description of the sample containment cell, of the furnace design, and of the measurement geometry allowing simultaneous transmission and fluorescence measurements is given herein. The performance of the equipment is tested with the room-temperature measurement of thorium tetrafluoride, and the Th-F and Th-Th bond distances obtained by fitting of the EXAFS data are compared with the ones extracted from a refinement of neutron diffraction data collected at the PEARL beamline at TU Delft. The adequacy of the sample confinement is checked with a mapping of the thorium concentration profile of molten salt material. Finally, a few selected salt mixtures (LiF:ThF4) = (0.9:0.1), (0.75:0.25), (0.5:0.5) and (NaF:ThF4) = (0.67:0.33), (0.5:0.5) are measured in the molten state. Qualitative trends along the series are discussed, and the experimental data for the (LiF:ThF4) = (0.5:0.5) composition are compared with the EXAFS spectrum generated from molecular dynamics simulations.

Unprecedented Inversion of Selectivity and Extraordinary Difference in the Complexation of Trivalent f†Elements by Diastereomers of a Methylated Diglycolamide.

When considering f elements, solvent extraction is primarily used for the removal of lanthanides from ore and their recycling, as well as for the separation of actinides from used nuclear fuel. Understanding the complexation mechanism of metal ions with organic extractants, particularly the influence of their molecular structure on complex formation is of fundamental importance. Herein, we report an extraordinary (up to two orders of magnitude) change in the extraction efficiency of f elements with two diastereomers of dimethyl tetraoctyl diglycolamide (Me2 -TODGA), which only differ in the orientation of a single methyl group. Solvent extraction techniques, extended X-ray absorption fine structure (EXAFS) measurements, and density functional theory (DFT) based ab initio calculations were used to understand their complex structures and to explain their complexation mechanism. We show that the huge differences observed in extraction selectivity results from a small change in the complexation of nitrate counter-ions caused by the different orientation of one methyl group in the backbone of the extractant. The obtained results give a significant new insight into metal-ligand complexation mechanisms, which will promote the development of more efficient separation techniques.

Pu Coexists in Three Oxidation States in a Borosilicate Glass: Implications for Pu Solubility.

Pu(III), Pu(IV), and a higher oxidation state of Pu, likely Pu(VI), are for the first time characterized simultaneously present in a borosilicate glass using Pu M5 edge high energy resolution X-ray absorption near edge structure (HR-XANES) technique. We illustrate that the method can be very efficiently used to determine Pu oxidation states, which control the solubility limit of Pu in a glass matrix. HR-XANES results show that the addition of excess Si3N4 is not sufficient for complete reduction of Pu to Pu(III), which has a relatively high solubility limit (9-22 wt % Pu) due to its network-modifying behavior in glasses. We provide evidence that the initially added Pu(VI) might be partly preserved during vitrification at 1200/1400 °C in Ar atmosphere. Pu(VI) could be very advantageous for vitrification of Pu-rich wastes, since it might reach solubility limits of 40 wt % comparable to U(VI).

Uranium Redox Transformations after U(VI) Coprecipitation with Magnetite Nanoparticles.

Uranium redox states and speciation in magnetite nanoparticles coprecipitated with U(VI) for uranium loadings varying from 1000 to 10 000 ppm are investigated by X-ray absorption spectroscopy (XAS). It is demonstrated that the U M4 high energy resolution X-ray absorption near edge structure (HR-XANES) method is capable to clearly characterize U(IV), U(V), and U(VI) existing simultaneously in the same sample. The contributions of the three different uranium redox states are quantified with the iterative transformation factor analysis (ITFA) method. U L3 XAS and transmission electron microscopy (TEM) reveal that initially sorbed U(VI) species recrystallize to nonstoichiometric UO2+x nanoparticles within 147 days when stored under anoxic conditions. These U(IV) species oxidize again when exposed to air. U M4 HR-XANES data demonstrate strong contribution of U(V) at day 10 and that U(V) remains stable over 142 days under ambient conditions as shown for magnetite nanoparticles containing 1000 ppm U. U L3 XAS indicates that this U(V) species is protected from oxidation likely incorporated into octahedral magnetite sites. XAS results are supported by density functional theory (DFT) calculations. Further characterization of the samples include powder X-ray diffraction (pXRD), scanning electron microscopy (SEM) and Fe 2p X-ray photoelectron spectroscopy (XPS).

Monolithic integration of a silicon nanowire field-effect transistors array on a complementary metal-oxide semiconductor chip for biochemical sensor applications.

We present a monolithic complementary metal-oxide semiconductor (CMOS)-based sensor system comprising an array of silicon nanowire field-effect transistors (FETs) and the signal-conditioning circuitry on the same chip. The silicon nanowires were fabricated by chemical vapor deposition methods and then transferred to the CMOS chip, where Ti/Pd/Ti contacts had been patterned via e-beam lithography. The on-chip circuitry measures the current flowing through each nanowire FET upon applying a constant source-drain voltage. The analog signal is digitized on chip and then transmitted to a receiving unit. The system has been successfully fabricated and tested by acquiring I-V curves of the bare nanowire-based FETs. Furthermore, the sensing capabilities of the complete system have been demonstrated by recording current changes upon nanowire exposure to solutions of different pHs, as well as by detecting different concentrations of Troponin T biomarkers (cTnT) through antibody-functionalized nanowire FETs.

Combined time-resolved laser fluorescence spectroscopy and extended X-ray absorption fine structure spectroscopy study on the complexation of trivalent actinides with chloride at T = 25-200 °C.

The complexation of trivalent actinides (An(III)) with chloride is studied in the temperature range from 25 to 200 °C by spectroscopic methods. Time-resolved laser fluorescence spectroscopy (TRLFS) is applied to determine the thermodynamic data of Cm(III)-Cl(-) complexes, while extended X-ray absorption fine structure spectroscopy (EXAFS) is used to determine the structural data of the respective Am(III) complexes. The experiments are performed in a custom-built high-temperature cell which is modified for the respective spectroscopic technique. The TRLFS results show that at 25 °C the speciation is dominated mainly by the Cm(3+) aquo ion. Only a minor fraction of the CmCl(2+) complex is present in solution. As the temperature increases, the fraction of this species decreases further. Simultaneously, the fraction of the CmCl2(+) complex increases strongly with the temperature. Also, the CmCl3 complex is formed to a minor extent at T > 160 °C. The conditional stability constant log ß'2 is determined as a function of the temperature and extrapolated to zero ionic strength with the specific ion interaction theory approach. The log ß°2(T) values increase by more than 3 orders of magnitude in the studied temperature range. The temperature dependency of log ß°2 is fitted by the extended van't Hoff equation to determine ΔrH°m, ΔrS°m, and ΔrC°p,m. The EXAFS results support these findings. The results confirm the absence of americium(III) chloride complexes at T = 25 and 90 °C ([Am(III)] = 10(-3) m, [Cl(-)] = 3.0 m), and the spectra are described by 9-10 oxygen atoms at a distance of 2.44-2.48 Å. At T = 200 °C two chloride ligands are present in the inner coordination sphere of Am(III) at a distance of 2.78 Å.

Arsenic-rich acid mine water with extreme arsenic concentration: mineralogy, geochemistry, microbiology, and environmental implications.

Extremely arsenic-rich acid mine waters have developed by weathering of native arsenic in a sulfide-poor environment on the 10th level of the Svornost mine in Jáchymov (Czech Republic). Arsenic rapidly oxidizes to arsenolite (As2O3), and there are droplets of liquid on the arsenolite crust with high As concentration (80,000-130,000 mg·L(-1)), pH close to 0, and density of 1.65 g·cm(-1). According to the X-ray absorption spectroscopy on the frozen droplets, most of the arsenic is As(III) and iron is fully oxidized to Fe(III). The EXAFS spectra on the As K edge can be interpreted in terms of arsenic polymerization in the aqueous solution. The secondary mineral that precipitates in the droplets is kaatialaite [Fe(3+)(H2AsO4)3·5H2O]. Other unusual minerals associated with the arsenic lens are behounekite [U(4+)(SO4)2·4H2O], stepite [U(4+)(AsO3OH)2·4H2O], vysokýite [U(4+)[AsO2(OH)2]4·4H2O], and an unnamed phase (H3O)(+)2(UO2)2(AsO4)2·nH2O. The extremely low cell densities and low microbial biomass have led to insufficient amounts of DNA for downstream polymerase chain reaction amplification and clone library construction. We were able to isolate microorganisms on oligotrophic media with pH ∼ 1.5 supplemented with up to 30 mM As(III). These microorganisms were adapted to highly oligotrophic conditions which disabled long-term culturing under laboratory conditions. The extreme conditions make this environment unfavorable for intensive microbial colonization, but our first results show that certain microorganisms can adapt even to these harsh conditions.

Combined X-ray absorption and SEM-EDX spectroscopic analysis for the speciation of thorium in soil.

Mobility and bioavailability of radionuclides in the environment strongly depend on their aqueous speciation, adsorption behavior and the solubility of relevant solid phases. In the present context, we focus on naturally occurring Th-232 at a location in central Sri Lanka presenting high background radiation levels. Four different soil samples were characterized using X-ray Absorption Spectroscopy (XAS) at the Th L3-edge (16.3 keV), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) spectroscopy. X-ray Absorption Near Edge Structure (XANES) spectra are applied as a fingerprint indication for Th existing in different chemical environments. Linear combination fitting (LCF) of the Extended X-ray Absorption Fine Structure (EXAFS) data involving reference Th-monazite (phosphate) and thorianite (oxide) compounds suggested that Th is mostly present as Th-phosphate (76 ± 2%) and Th-oxide (24 ± 2%), even though minor amounts of thorite (silicate) were also detected by SEM-EDX. Further studies on selected individual particles using micro-focus X-ray Fluorescence (µ-XRF) and micro-X-ray Absorption Spectroscopy (µ-XAS) along with SEM-EDX elemental mapping provided information about the nature of Th-bearing mineral particles regarding mixed phases. This is the first study providing quantitative and XAS based speciation information on Th-mineral phases in soil samples from Sri Lanka.

2,6-Bis(5-(2,2-dimethylpropyl)-1H-pyrazol-3-yl)pyridine as a ligand for efficient actinide(III)/lanthanide(III) separation.

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 ß(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.

Uranium speciation control by uranyl sulfate and phosphate in tailings subject to a Sahelian climate, Cominak, Niger.

Long-term uranium mobility in tailings is an environmental management issue. The present study focuses on two U-enriched layers, surficial and buried 14.5 m, of the tailings pile of Cominak, Niger. The acidic and oxidizing conditions of the tailings pile combined with evapotranspiration cycles related to the Sahelian climate control U speciation. Uraninite, brannerite, and moluranite as well as uranophane are relict U phases. EXAFS spectroscopy, HR-XRD, and SEM/WDS highlight the major role of uranyl sulfate groups in uranium speciation. Uranyl phosphate neoformation in the buried layer (paleolayer) acts as an efficient trap for uranium.