30 Search Results

A microextraction liquid sampling system coupled to a quadrupole inductively coupled plasma-mass spectrometer (ICP-MS) was utilized to spatially discern uranium particles, isotopically, on a cellulose-based swipe material (i.e., J-type swipe). These types of swipes are often used by the International Atomic Energy Agency (IAEA) as part of their environmental sampling program. Here, a grid was created such that extraction locations covered the center circle (n = 34 without overlapping). Uranium (U) particulates (<20 μm) of varying U isotopic abundance and chemical form (i.e., uranyl fluoride and uranyl nitrate hexahydrate) were mechanically placed on the swipes in random locations and detectedmore » via the microextraction-ICP-MS methodology. Heat maps were subsequently generated to show the placement of the particulate with their respective intensity and isotopic determination. This detection of the uranium particulates, via isotopic determination, agreed with reference values for these materials. Additionally, depleted (²³⁵U/²³⁸U = 0.002) uranium particulates were placed directly within a clay matrix, on the swipe surface, and subjected to analysis by microextraction-ICP-MS. The mapping of the swipe demonstrated, for the first time, the employment of the microextraction-ICP-MS method for extracting sample from a complex matrix, and correctly identifying the uranium isotopic composition. This example ultimately demonstrates the utility of the methodology for detecting particles of interest in complex matrices.« less

Uranyl sulfates are important constituents of uranium ores and represent a significant fraction of U(VI) minerals discovered in recent years owing to their propensity to form in mine tailings and legacy sites related to uranium exploration. Recently, we surveyed all published Raman spectra for uranium minerals and found significantly less easily accessible data available for uranyl sulfates relative to other groups of uranium minerals (Spano et al. 2023). In that work, we described average spectra for groups of uranyl minerals to understand common vibrational spectroscopic features attributable to similarities in oxyanion chemistry among U(VI) minerals, but only data for threemore » uranyl sulfate minerals were included in the study. The present work reports on Raman spectra collected for 18 additional uranyl sulfate minerals. In conclusion, to better understand underlying structural and chemical features that give rise to spectroscopic observables, we relate differences in structural topology, charge-balancing cations, and locality of origin to features observed in the Raman spectra of selected natural uranyl sulfates.« less

Voloxidation is a potential alternative reprocessing scheme for spent nuclear fuel that uses gas–solid reactions to minimize aqueous wastes and to separate volatile fission products from the desired actinide phase. The process uses NO₂(g) as an oxidant for uranium dioxide (UO₂) fuel, ideally producing soluble uranium powders which can then be processed for full recycle. To continue development of the process flowsheet for voloxidation, ongoing examination of the process chemistry and associated process materials is required: discrepancies in the proposed chemical reactions that occur when spent nuclear fuel is exposed to NO₂(g) atmospheres must be addressed. The objective of thismore » work is to analyze the intermediate solid phases produced during voloxidation to support verification of the proposed NO₂(g) voloxidation reaction mechanisms. This objective was achieved through using (1) powder X-ray diffraction and Raman spectroscopy to identify bulk uranium phases and (2) scanning electron microscopy to describe the morphology and microstructure of the powders at each reaction stage. The initial oxidation of UO₂ under NO₂(g) reactions produced ε-UO₃. Further exposure to NO₂(g) did not nitrate the solid to produce uranyl nitrate, as reported in some literature. However, after the powder was hydrated with steam and then further exposed to NO₂(g), some traces of uranyl nitrate hexahydrate were found. The results of this study suggest that surface hydration of powders plays a vital role in uranyl nitrate formation under voloxidation conditions and raises questions about the kinetics of the oxide-to-nitrate voloxidation conversion process. Future chemical and engineering design decisions for the voloxidation process may benefit from an improved understanding of these chemical mechanisms.« less

To develop strategies for incorporating transition metal taggants (Fe, Cr, and Ni) into oxide fuels and to understand how these taggant candidates persist through early fuel cycle processes, synthetic procedures are modified from established production routes to yield intentionally tagged early fuel cycle intermediates including uranyl nitrate hexahydrate (UNH, UO₂(NO₃)₂·6H₂O), uranyl peroxide tetrahydrate (studtite, UO₂O₂·4H₂O), and uranyl peroxide dihydrate (metastudtite, UO₂O₂·2H₂O). First, Fe, Cr, and Ni nitrate solutions are introduced to an aqueous solution of UNH followed by precipitation to produce tagged UNH. Then, studtite is precipitated from UNH followed by dehydration to metastudtite. Structural influences of taggant incorporation withinmore » all synthesized phases are investigated using powder X-ray diffraction (PXRD) and Raman spectroscopy to provide insight into crystallographic modifications resulting from the addition of tags to these early fuel cycle materials and elucidate the chemical form of taggants introduced at these stages. The possibility of segregation of taggant species into discrete phases within U matrices was examined using scanning electron microscopy with energy dispersive X-ray spectroscopy. Taggant concentrations in solid-phase materials were determined using inductively coupled plasma-optical emission spectroscopy. Observations from Raman spectroscopy and PXRD indicate that introducing transition metal tags during uranyl nitrate precipitation results in potential impurity phase segregation in UNH, but transition metal incorporation is suggested by results for tagged uranyl peroxide materials. Further, results from this study will inform strategies for optimizing taggant incorporation in UO₂.« less

The work presented herein employs two laser-based analytical techniques (laser-induced breakdown spectroscopy (LIBS) and laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS)) to spatially determine the elemental and isotopic composition of uranium bearing minerals. Uniquely, this work leverages the high-speed applicability of LIBS to “screen” the sample(s) for their elemental constituents. After determining the location of the uranium inclusions (via LIBS), high-resolution LA-ICP-MS was employed to further characterize the inclusions. The high-resolution (sub-µm) capabilities of LA-ICP-MS were able to extract important information from the uranium minerals including discerning its chemical form (e.g., finchite from carnotite, Sr- and K-bearingmore » uranyl vanadates, respectively) as well as their ²³⁵U/²³⁸U isotopic composition. This approach, LIBS followed by LA-ICP-MS, significantly reduces the analysis time (~95 %) in comparison to employing a LA-ICP-MS only approach. Furthermore, this work presented a novel approach to analyzing inclusions via a particle/inclusion analysis tool which is commercially available within the iolite 4 software. This tool allowed for a more accurate characterization of the isotopic distribution of the inclusions, as well as allowing for rapid sizing of the inclusions. Finally, this analytical approach could readily be applied to other sample types in which the target species (e.g., µm-sized inclusions) are embedded in complex matrices (e.g., cm-sized samples).« less

Finchite (IMA2017-052), Sr(UO₂)₂(V₂O₈)·5H₂O, is the first uranium mineral known to contain essential Sr. The new mineral occurs as yellow-green blades up to ~10 µm in length in surface outcrops of the calcrete-type uranium deposit at Sulfur Springs Draw, Martin County, Texas, U.S.A. Crystals of finchite were subsequently discovered underground in the Pandora mine, La Sal, San Juan County, Utah, U.S.A., as diamond-shaped golden-yellow crystals reaching up to 1 mm. In this work, the crystal structure of finchite from both localities was determined using single-crystal X-ray diffraction and is orthorhombic, Pcan, with a = 10.363(6) Å, b = 8.498(5) Å, cmore » = 16.250(9) Å, V = 1431.0(13) ų, Z = 4 (R₁ = 0.0555) from Sulfur Springs Draw; and a = 10.3898(16), b = 8.5326(14), c = 16.3765(3) Å, V = 1451.8(4) ų, Z = 4 (R₁ = 0.0600) from the Pandora mine. Electron-probe microanalysis provided the empirical formula (Sr_0.88K_0.17Ca_0.10Mg_0.07Al_0.03Fe_0.02)_Σ1.20(UO₂)₂(V_2.08O₈)·5H₂O for crystals from Sulfur Springs Draw, and (Sr_0.50Ca_0.28Ba_0.22K_0.05)_Σ0.94(U_0.99O₂)₂(V_2.01O₈)·5H₂O for crystals from the Pandora mine, based on 17 O atoms per formula unit. The structure of finchite contains uranyl vanadate sheets based upon the francevillite topology. Finchite is a possible immobilization species for both uranium and the dangerous radionuclide ⁹⁰Sr because of the relative insolubility of uranyl vanadate minerals in water.« less

Uranium trioxide displays a complex chemical phase space, with at least six structurally distinct polymorphs accessible via different synthetic routes. Remarkably, despite its technological importance, full structural and electronic characterization of these polymorphs remains an open area of study. δ-UO₃ in particular has attracted significant theoretical attention due to its high point group and space group symmetries, having U (VI) in octahedral coordination with polyhedra interconnected through corner-sharing to build a 3-D cubic lattice with space group symmetry Pm-3m and Z = 1. Critical experimental information, such as its optical vibrational spectra, are not known. Here, we study the Ramanmore » and infrared (IR) spectra of δ-UO₃ together with the support of density functional theory (DFT) calculations for spectral interpretation. A symmetry analysis of the DFT-predicted phonon eigenmodes indicates that δ-UO₃ should have two IR active modes and no Raman active modes. Experimental results, however, indicate significant Raman scattering from δ-UO₃. We therefore propose four potential explanations for this apparent contradiction: a possible tetragonal distortion to the cubic cell, the existence of a surface impurity layer, vacancy scattering, and structural activation of Raman signal. We use powder X-ray diffraction and confocal Raman spectroscopy with depth profiling to investigate these possibilities and suggest future experiments to explore this phenomenon in more detail. Understanding the lattice dynamics of δ-UO₃ is important for identification of technogenic U phases via Raman and infrared spectroscopy and our results indicate that the simple understanding of δ-UO₃ as a high-symmetry cubic structure should be reconsidered.« less

Over 3000 mercury (Hg)-contaminated sites worldwide contain liquid metallic Hg [Hg(0)₁] representing a continuous source of elemental Hg(0) in the environment through volatilization and solubilization in water. Currently, there are few effective treatment technologies available to remove or sequester Hg(0)₁ in situ. We investigated sonochemical treatments coupled with complexing agents, polysulfide and sulfide, in oxidizing Hg(0)₁ and stabilizing Hg in water, soil and quartz sand. Results indicate that sonication is highly effective in breaking up and oxidizing liquid Hg(0)₁ beads via acoustic cavitation, particularly in the presence of polysulfide. Without complexing agents, sonication caused only minor oxidation of Hg(0)₁ butmore » increased headspace gaseous Hg(0)_g and dissolved Hg(0)_aq in water. However, the presence of polysulfide essentially stopped Hg(0) volatilization and solubilization. As a charged polymer, polysulfide was more effective than sulfide in oxidizing Hg(0)₁ and subsequently stabilizing the precipitated metacinnabar (β-HgS) nanocrystals. Sonochemical treatments with sulfide yielded incomplete oxidation of Hg(0)₁, likely resulting from the formation of HgS coatings on the dispersed µm-size Hg(0)₁ bead surfaces. Sonication with polysulfide also resulted in rapid oxidation of Hg(0)₁ and precipitation of HgS in quartz sand and in the Hg(0)₁-contaminated soil. This research indicates that sonochemical treatment with polysulfide could be an effective means in rapidly converting Hg(0)₁ to insoluble HgS precipitates in water and sediments, thereby preventing its further emission and release to the environment. We suggest that future studies are performed to confirm its technical feasibility and treatment efficacy for remediation applications.« less

Here, an automated microextraction method coupled to an inductively coupled plasma – mass spectrometer (ICP-MS) was developed for the direct analysis of solid uranium particulates on the surface of cotton swipes. The microextraction probe extracts particulates from the sample surface, in a flowing solvent, and directs the removed analyte to an ICP-MS for isotopic determination. The automated system utilizes a mechanical XY stage that is software controlled with the capability of saving and returning to specific locations and a camera focused to the swipe surface for optimal viewing of the extracted locations (i.e., material present). Here, particulates (n = 135)more » were extracted and measured by ICP-MS, including 35 depleted uranyl nitrate hexahydrate (UN) (used for mass bias corrections), 50 uranyl fluoride (UO₂F₂), and 50 uranyl acetate (UAc) particulates. Blank extractions were performed on the cotton swipes between triplicate sample analyses. Between each swipe extraction, the probe was sent between two wells containing 10% and 5% HNO₃ to clean the probe head and to eliminate any analyte carryover between particulates. The measured ²³⁵U/²³⁸U and ²³⁴U/²³⁸U isotope ratios for the UO₂F₂ particulates were 0.00725(8) and 0.000054(4), a percent relative difference (% RD) of –0.041% and –1.7% from the reference isotope ratios determined in-lab through multi-collector ICP-MS analysis of dissolved aliquots of the U material. The UAc samples had a measured ²³⁵U/²³⁸U isotope ratio of 0.00206(7), a –0.96% relative difference from the reference value of 0.00208(1). The ²³⁴U/²³⁸U and ²³⁶U/²³⁸U isotope ratios were 0.000008(1) and 0.000031(4), –5.1% RD and –4.3% RD, respectively. The automated sample stage enabled seamless and rapid particle analysis, leading to a significant increase in throughput versus what was previously possible. Additionally, the saved location capability reduced user sampling error as sampling locations were easily stored and recalled. Analysis of U particles on the swipe surface – including blanks, mass bias, and triplicate extractions – was completed in less than an hour without any sample preparation necessary.« less

Smart Spectral Matching (SSM) catalogs spectroscopic data and, within the platform, investigates subtle attributes of spectral signatures from Raman and infrared spectroscopic data and enables statistical identification of connections between underlying structural units and spectroscopic information, particularly in fuel cycle materials that are amorphous or a mixture of several phases. Catalogs spectroscopic data, provides UIs for machine learning training either via JupyterHub for notebooks or domain scientist-specific views, machine learning and catalog REST API Python client libraries, and ability to identify features in files uploaded using pre-trained machine learning models. This is a "service-based" architecture with multiple applications represented bymore » each repository in the group https://github.com/smart-spectral-matching« less