Crystal Structure and Stability in Aqueous Solutions of Na[NpO(OH)]·0.5HO and Na[NpO(OH)].

The ternary neptunium(V) (Np(V)) hydroxides Na[NpO(OH)]·0.5HO and Na[NpO(OH)] were synthesized in aqueous NaOH solutions at = 80 °C, and their crystal structures were determined to be monoclinic, 2, = 2, = 5.9859(2), = 10.

Pu(iii) and Cm(iii) in the presence of EDTA: aqueous speciation, redox behavior, and the impact of Ca(ii).

The impact of calcium on the solubility, redox behavior, and speciation of the An(iii)-EDTA (An = Pu or Cm) system under reducing, anoxic conditions was investigated through batch solubility experiments, X-ray absorption spectroscopy (XAS), density functional theory (DFT), and time-resolved laser fluorescence spectroscopy (TRLFS). Batch solubility experiments were conducted from undersaturation using Pu(OH)(am) as the solid phase in contact with 0.1 M NaCl-NaOH-HCl-EDTA-CaCl solutions at [EDTA] = 1 mM, pH = 7.

Paving the way for examination of coupled redox/solid-liquid interface reactions: 1 ppm Np adsorbed on clay studied by Np M-edge HR-XANES spectroscopy.

The recently emerged actinide (An) M-edge high-energy resolution X-ray absorption near-edge structure (HR-XANES) technique has proven to be very powerful for oxidation state studies of actinides. In this work, for the first time, Np M-edge HR-XANES was applied to study Np sorption on illite. By improving the experimental conditions, notably by operation of the spectrometer under He atmosphere, it was possible to measure Np M-edge HR-XANES spectra of a sample with ≈ 1 μg Np/g illite (1 ppm).

Impact of Ca(II) on the aqueous speciation, redox behavior, and environmental mobility of Pu(IV) in the presence of EDTA.

The impact of calcium on the solubility and redox behavior of the Pu(IV)-EDTA system was investigated using a combination of undersaturation solubility studies and advanced spectroscopic techniques. Batch solubility experiments were conducted in 0.1 M NaCl-NaOH-HCl-EDTA-CaCl solutions at constant [EDTA] = 1∙10 M, 1 ≤ pH ≤ 11, and 1∙10 M ≤ [CaCl] ≤ 2∙10 M.

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 M-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 L-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).

Exploring the electronic structure and speciation of aqueous and colloidal Pu with high energy resolution XANES and computations.

Pu L3 HR-XANES and FEFF9 computations provide evidence for band-like 6d states in colloidal Pu contrasting to narrow 6d states in molecular Pu(iv). Pu L3 HR-XANES is valuable for bond length estimation in plutonyl, whereas Pu M5 HR-XANES is an advanced tool for analysing Pu redox states and 5f unoccupied density of states.

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 M 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 SiN 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.

Oxidation state and local structure of plutonium reacted with magnetite, mackinawite, and chukanovite.

Due to their redox reactivity, surface sorption characteristics, and ubiquity as corrosion products or as minerals in natural sediments, iron(II)-bearing minerals control to a large extent the environmental fate of actinides. Pu-L(III)-edge XANES and EXAFS spectra were used to investigate reaction products of aqueous (242)Pu(III) and (242)Pu(V) reacted with magnetite, mackinawite, and chukanovite under anoxic conditions. As Pu concentrations in the liquid phase were rapidly below detection limit, oxidation state and local structure of Pu were determined for Pu associated with the solid mineral phase.