Immobilization of Chromium by Iron Oxides in Nickel-Cobalt Laterite Mine Tailings.

Mine tailings generated from hydrometallurgical processing of nickel-cobalt laterite deposits contain high levels of chromium (Cr), with the hexavalent species being a toxic pollutant and carcinogen. However, the partitioning, speciation, and local bonding environment of Cr in the mine tailings remain largely unknown, hindering our ability to predict its toxicity and long-term behavior. Coupling detailed mineralogical, spectroscopic, and geochemical characterization with sequential extraction of tailings from active and rehabilitated dams, we show that Cr is present in its least toxic form, Cr(III), and largely immobilized by recalcitrant minerals.

Influence of Sintering Conditions on the Structure and Redox Speciation of Homogeneous (U,Ce)O Ceramics: A Synchrotron Study.

Although uranium-cerium dioxides are frequently used as a surrogate material for (U,Pu)O nuclear fuels, there is currently no reliable data regarding the oxygen stoichiometry and redox speciation of the cations in such samples. In order to fill this gap, this manuscript details a synchrotron study of highly homogeneous (U,Ce)O sintered samples prepared by a wet-chemistry route. HERFD-XANES spectroscopy led to determining accurately the O/M ratios (with M = U + Ce).

Presence of uranium(V) during uranium(VI) reduction by Desulfosporosinus hippei DSM 8344.

Microbial U(VI) reduction influences uranium mobility in contaminated subsurface environments and can affect the disposal of high-level radioactive waste by transforming the water-soluble U(VI) to less mobile U(IV). The reduction of U(VI) by the sulfate-reducing bacterium Desulfosporosinus hippei DSM 8344, a close phylogenetic relative to naturally occurring microorganism present in clay rock and bentonite, was investigated. D.

Selenium Nanowire Formation by Reacting Selenate with Magnetite.

The mobility of Se, a fission product of U and long-lived radioisotope, is an important parameter in the safety assessment of radioactive nuclear waste disposal systems. Nonradioactive selenium is also an important contaminant of drainage waters from black shale mountains and coal mines. Highly mobile and soluble in its high oxidation states, selenate (Se()O) and selenite (Se()O) oxyanions can interact with magnetite, a mineral present in anoxic natural environments and in steel corrosion products, thereby being reduced and consequently immobilized by forming low-solubility solids.

Pb(OH) cluster formation and anomalous thermal behaviour in STI framework-type zeolites.

For the first time, the structural investigation of a Pb-exchanged zeolite (Pb(OH)AlSiO ∙38HO) with STI framework type, revealed a highly unusual and intriguing sudden volume increase under continuous heating. Understanding the fundamental mechanisms leading to such an unusual behaviour is essential for technological applications and interpretation of chemical bonding in zeolites. The dehydration was tracked in situ from 25 to 450 °C by single crystal X-ray diffraction, infrared and X-ray absorption spectroscopy.

Quality versus emergency: How good were ventilation fittings produced by additive manufacturing to address shortages during the COVID19 pandemic?

Objective: The coronavirus disease pandemic (COVID-19) increased the risk of shortage in intensive care devices, including fittings with intentional leaks. 3D-printing has been used worldwide to produce missing devices. Here we provide key elements towards better quality control of 3D-printed ventilation fittings in a context of sanitary crisis.

Oxidation of Micro- and Nanograined UO Pellets by In Situ Synchrotron X-ray Diffraction.

When in contact with oxidizing media, UO pellets used as nuclear fuel may transform into UO, UO, and UO. The latter starts forming by stress-induced phase transformation only upon cracking of the pristine UO and is associated with a 36% volumetric expansion with respect to the initial UO. This may pose a safety issue for spent nuclear fuel (SNF) management as it could imply a confinement failure and hence dispersion of radionuclides within the environment.

A spectroscopic hike in the U-O phase diagram.

The U-O phase diagram is of paramount interest for nuclear-related applications and has therefore been extensively studied. Experimental data have been gathered to feed the thermodynamic calculations and achieve an optimization of the U-O system modelling. Although considered as well established, a critical assessment of this large body of experimental data is necessary, especially in light of the recent development of new techniques applicable to actinide materials.

Charge Distribution in UCeO Nanoparticles.

In view of safe management of the nuclear wastes, a sound knowledge of the atomic-scale properties of UMO nanoparticles is essential. In particular, their cation valences and oxygen stoichiometries are of great interest as these properties drive their diffusion and migration behaviors into the environment. Here, we present an in-depth study of UCeO, over the full compositional domain, by combining X-ray diffraction and high-energy resolution fluorescence detection X-ray absorption near-edge structure.

ROBL-II at ESRF: a synchrotron toolbox for actinide research.

ROBL-II provides four different experimental stations to investigate actinide and other alpha- and beta-emitting radionuclides at the new EBS storage ring of ESRF within an energy range of 3 to 35 keV. The XAFS station consists of a highly automatized, high sample throughput installation in a glovebox, to measure EXAFS and conventional XANES of samples routinely at temperatures down to 10 K, and with a detection limit in the sub-p.p.

Size Dependence of Lattice Parameter and Electronic Structure in CeO Nanoparticles.

Intrinsic properties of a compound (e.g., electronic structure, crystallographic structure, optical and magnetic properties) define notably its chemical and physical behavior.

Assisted reproduction mediated resurrection of a feline model for Chediak-Higashi syndrome caused by a large duplication in LYST.

Chediak-Higashi Syndrome (CHS) is a well-characterized, autosomal recessively inherited lysosomal disease caused by mutations in lysosomal trafficking regulator (LYST). The feline model for CHS was originally maintained for ~20 years. However, the colonies were disbanded and the CHS cat model was lost to the research community before the causative mutation was identified.

Probing the local structure of nanoscale actinide oxides: a comparison between PuO and ThO nanoparticles rules out PuO hypothesis.

Actinide research at the nanoscale is gaining fundamental interest due to environmental and industrial issues. The knowledge of the local structure and speciation of actinide nanoparticles, which possibly exhibit specific physico-chemical properties in comparison to bulk materials, would help in a better and reliable description of their behaviour and reactivity. Herein, the synthesis and relevant characterization of PuO and ThO nanoparticles displayed as dispersed colloids, nanopowders, or nanostructured oxide powders allow to establish a clear relationship between the size of the nanocrystals constituting these oxides and their corresponding An(iv) local structure investigated by EXAFS spectroscopy.

Deciphering the Crystal Structure of a Scarce 1D Polymeric Thorium Peroxo Sulfate.

The preparation and structural characterization of an original Th peroxo sulfate dihydrate, crystallizing at room temperature in the form of stable 1D polymeric microfibres is described. A combination of laboratory and synchrotron techniques allowed solution of the structure of the Th(O )(SO )(H O) compound, which crystallizes in a new structure type in the space group Pna2 of the orthorhombic crystal system. Particularly, the peroxide ligand coordinates to the Th cations in an unusual μ -η :η :η bridging mode, forming an infinite 1D chain decorated with sulfato ligands exhibiting simultaneously monodentate and bidentate coordination modes.

The GALAXIES inelastic hard X-ray scattering end-station at Synchrotron SOLEIL.

GALAXIES is an in-vacuum undulator hard X-ray micro-focused beamline dedicated to the study of the electronic structure of materials with high energy resolution using both photoelectron spectroscopy and inelastic X-ray scattering and under both non-resonant (NR-IXS) and resonant (RIXS) conditions. Due to the penetrating power of hard X-rays and the `photon-in/photon-out' technique, the sample environment is not a limitation. Materials under extreme conditions, for example in diamond anvil cells or catalysis chambers, thus constitute a major research direction.

Peculiar Thermal Behavior of UO Local Stucture.

Most materials expand with temperature because of the anharmonicity of lattice vibration, and only a few shrink with increasing temperature. UO, whose thermal properties are of significant importance for the safe use of nuclear energy, was considered for a long time to belong to the first group. This view was challenged by recent in situ synchrotron X-ray diffraction measurements, showing an unusual thermal decrease of the U-O distances.

Optimization of Uranium-Doped Americium Oxide Synthesis for Space Application.

Americium 241 is a potential alternative to plutonium 238 as an energy source for missions into deep space or to the dark side of planetary bodies. In order to use the Am isotope for radioisotope thermoelectric generator or radioisotope heating unit (RHU) production, americium materials need to be developed. This study focuses on the stabilization of a cubic americium oxide phase using uranium as the dopant.

Aliovalent Cation Substitution in UO: Electronic and Local Structures of ULaO Solid Solutions.

For nuclear fuel related applications, the oxygen stoichiometry of mixed oxides UMO is an essential property as it affects fuel properties and may endanger the safe operation of nuclear reactors. A careful review of the open literature indicates that this parameter is difficult to assess properly and that the nature of the defects, i.e.

On the Role of the Electrical Field in Spark Plasma Sintering of UO.

The electric field has a large effect on the stoichiometry and grain growth of UO during Spark Plasma Sintering. UO is gradually reduced to UO as a function of sintering temperature and time. A gradient in the oxidation state within the pellets is observed in intermediate conditions.

Retinal axon guidance at the midline: Chiasmatic misrouting and consequences.

The visual representation of the outside world relies on the appropriate connectivity between the eyes and the brain. Retinal ganglion cells are the sole neurons that send an axon from the retina to the brain, and thus the guidance decisions of retinal axons en route to their targets in the brain shape the neural circuitry that forms the basis of vision. Here, we focus on the choice made by retinal axons to cross or avoid the midline at the optic chiasm.

Characteristics of chemical bonding of pentavalent uranium in La-doped UO.

The effect of La doping on the electronic structure of U in UO was studied using an advanced technique, namely, X-ray absorption spectroscopy (XAS) in the high-energy-resolution fluorescence-detection (HERFD) mode, at the U 3d (M) edge. Thanks to a significant reduction of the core-hole lifetime broadening and distinct chemical shifts of the HERFD-XAS lines, the U(v) formation as a result of La doping was identified. The isolated contribution of U(v) in the M HERFD-XAS spectrum reveals the so-called charge-transfer satellites due to the U 5f-O 2p hybridization.

Further insights into the chemistry of the Bi-U-O system.

Cubic fluorite-type phases have been reported in the U(IV)O2-Bi2O3 system for the entire compositional range, but an unusual non-linear variation of the lattice parameter with uranium substitution has been observed. In the current extensive investigation of the uranium(iv) oxide-bismuth(iii) oxide system, this behaviour of the lattice parameter evolution with composition has been confirmed and its origin identified. Even under inert atmosphere at 800 °C, U(IV) oxidises to U(V)/U(VI) as a function of the substitution degree.

Structural Properties and Charge Distribution of the Sodium Uranium, Neptunium, and Plutonium Ternary Oxides: A Combined X-ray Diffraction and XANES Study.

The charge distributions in α-Na2UO4, Na3NpO4, α-Na2NpO4, Na4NpO5, Na5NpO6, Na2PuO3, Na4PuO5, and Na5PuO6 are investigated in this work using X-ray absorption near-edge structure (XANES) spectroscopy at the U-L3, Np-L3, and Pu-L3 edges. In addition, a Rietveld refinement of monoclinic Na2PuO3, in space group C2/c, is reported for the first time, and the existence of the isostructural Na2NpO3 phase is revealed. In contrast to measurements in solution, the number of published XANES data for neptunium and plutonium solid phases with a valence state higher than IV is very limited.