Uranium Incorporation Research Articles

Infrared spectral library of tooth enamel from African ungulates for accurate electron spin resonance dating

Electron spin resonance coupled with uranium-series dating (ESR/U-series) of carbonate hydroxyapatite in tooth enamel is the main technique used to obtain age determinations from Pleistocene fossils beyond the range of radiocarbon dating. This chronological information allows to better understand diachronic change in the palaeontological record, especially with regard to the evolution of the genus Homo. Given the relative paucity of human teeth at palaeontological and archaeological localities, ESR/U-series is widely applied to the teeth of ungulate species. However, the accuracy of ESR/U-series ages is greatly affected by the incorporation of uranium in the enamel during burial in sediments. It has been shown that uranium content is positively correlated with an increased degree of atomic order in carbonate hydroxyapatite crystals, the latter determined using infrared spectroscopy. Here we present a reference infrared spectral library of tooth enamel from African ungulates, based on the grinding curve method, which serves as baseline to track the diagenetic history of carbonate hydroxyapatite in different species and thus select the best-preserved specimens for dating.

Insight into the influence mechanism of chloride ions towards in-situ electric-induced uranium incorporation into magnetite

The application of electrochemical methods for incorporating uranium into the magnetite lattice has demonstrated efficacy and durability in remediating radioactive contamination. However, the impact of different ions, particularly electrolyte ions, on this process remains unclear. Herein, we successfully achieved simultaneous magnetite crystallization and uranium incorporation within an electrochemical system using an iron anode. Chloride ions have been identified as having a pivotal role in the generation of ferrous ions via pitting corrosion, thereby establishing an advantageous reducing environment that promotes the transformation of γ-FeOOH to magnetite. Unlike the surface adsorption process of γ-FeOOH, magnetite predominantly eradicates uranium through an incorporation mechanism. Consequently, the existence of chloride ions markedly boosts the effectiveness of uranium elimination and the stability of the resultant substance. Specifically, under conditions of a pH of 5 and a chloride ions concentration of 18 mM, uranium removal reaches nearly 100%. Additionally, findings from uranium leaching experiments indicate that γ-FeOOH removed 25.4% stable, 63.57% metastable, and 11.03% unstable uranium, while magnetite removed 60.35% stable, 24.81% metastable, and 14.84% unstable uranium. This research offers insight into the potential role of electrolyte ions in facilitating in-situ electric-induced uranium incorporation.

First-Principles Investigation of the Effects of UF4 and ThF4 Fuels on the Structural, Dynamic, and Thermodynamic Properties of LiF-NaF.

An in-depth understanding and characterization of molten salt properties are necessary for the optimized design, efficient operation, and safety assurance of molten salt reactors (MSRs). Investigating molten salt properties in experimental settings can be challenging and time-consuming due to the high temperatures of interest, the salt's corrosiveness, purity and composition control, and health and safety concerns. Therefore, it is beneficial to perform computational screening to assist in the ultimate experimental measurements. Herein, we used first-principles molecular dynamics simulations to calculate several thermophysical, structural, and dynamic properties of eutectic LiF-NaF with fuel additives UF4 and ThF4. We found that with the incorporation of uranium or thorium, a prepeak appears in the structure factor, indicative of a medium-range structural ordering. Furthermore, we explore the mechanism through which these structural changes enhance shear stress correlations, thereby increasing the salt's viscosity. This work highlights the importance of studying the atomic-scale structure of molten salts and how the addition of fuel elements can substantially affect it.

Chemical durability and corrosion-induced microstructure evolution of compositionally complex titanate pyrochlore waste forms with uranium incorporation

Chemical durability of compositionally-complex rare-earth titanate pyrochlore solid solutions with or without uranium incorporation was investigated by semi-dynamic leaching testing. A Ti-enriched amorphous passivation film formed on the surface due to the surface alteration-reorganization mechanism with preferential release of the weakly oxygen-bonded rare earth elements. Elemental release was found to be strongly correlated with chemical disorder, with a negligible correlation with entropy. The release rate of the uranium gradually decreased with increasing numbers of components, implying a possibility of designing and optimizing waste form performance with enhanced chemical durability by controlling composition complexity and chemical disorder for effective nuclear waste management.

Enhanced mechanism of calcium towards uranium incorporation and stability in magnetite during electromineralization

Doping uranium into a room-temperature stable Fe3O4 lattice structure effectively reduces its migration. However, the synergistic or competitive effects of coexisting ions in an aqueous solution directly affect the uranium mineralization efficiency and the structural stability of uranium-bearing Fe3O4. The effects of calcium, carbonate, and phosphate on uranium electromineralization were investigated via batch experiments and theoretical calculations. Calcium incorporated into the Fe3O4 lattice increased the level and stability of doped uranium in Fe3O4. Uranium and calcium occupied the octahedral and tetrahedral sites of Fe3O4, respectively; the formation energy was only −10.23 eV due to strong hybridization effects between Fe1s, U4f, O2p, and Ca3d orbitals. Compared to the uranium-doped Fe3O4, uranium leaching ratios decreased by 19.2 % and 48.9 % under strongly acidic and alkaline conditions after 120 days. However, high concentrations of phosphate inhibited Fe3O4 crystallization. These results should provide new avenues for the development of multi-metal co-doping technologies and mineralization optimization to treat uranium-containing complex wastewater.

Evidence for in-situ electric-induced uranium incorporation into magnetite crystal in acidic wastewater

Incorporating uranium (U) from wastewater into a magnetite crystal to limit its mobility has been proposed as long-term remediation for radioactive contamination. Unfortunately, this process is accompanied by reduction or surface adsorption, thereby significantly reducing the incorporation capacity and resulting in a high probability of U release. Inducing U growth into the crystal during magnetite crystallization yields U-doped magnetite (UDM), which is an effective solution. Herein, magnetite crystallization and U incorporation were simultaneously performed by precisely controlling the sacrificial Fe-anode during the electrochemical reaction. The pathway underlying U entry into magnetite crystal, local coordination environment of U in the crystal, and release properties of U from UDM were investigated. U(VI) enters magnetite crystal through the substitution of Fe atoms in the octahedral sites, resulting in a partial reduction to U(IV) by Fe(II) in the crystal. Co-existing U(IV) and U(VI) states in the crystal significantly increased the incorporation capacity. U was present in the three following forms: surface adsorption (5%), conditionally stable incorporation (20 – 30%), and stabilized incorporation (> 65%). Within 400 days, 10.21% and 4.23% of total U were released at pH = 9.0 and pH = 5.6, respectively. The results provide new insights into reducing the risk of long-term migration contamination in wastewater by regulating U incorporation into the magnetite crystals.

Evidence for In-Situ Electric-Induced Uranium Incorporation to Magnetite Crystal in Acidic Wastewater

Evidence for In-Situ Electric-Induced Uranium Incorporation to Magnetite Crystal in Acidic Wastewater

Synthesis and thermodynamics of uranium-incorporated α-Fe2O3 nanoparticles

• Uranium-incorporated hematite is thermodynamically metastable. • Increasing uranium incorporation within hematite increases its formation enthalpy. • Hydrothermal treatment can increase uranium concentrations in hematite. • U-Fe 2 O 3 coordination in radioactive waste environments may be process-dependent. Hematite nanoparticles were synthesized with U(VI) in circumneutral water through a coprecipitation and hydrothermal treatment process. XRD, TEM, and EXAFS analyses reveal that uranium may aggregate along grain boundaries and occupy Fe sites within hematite. The described synthesis method produces crystalline, single-phase iron oxide nanoparticles absent of surface-bound uranyl complexes. EXAFS data were comparable to spectra from existing studies whose syntheses were more representative of naturally occurring, extended aging processes. This work provides and validates an accelerated method of synthesizing uranium-immobilized iron oxide nanoparticles for further mechanistic studies. High temperature oxide melt solution calorimetry measurements were performed to calculate the thermodynamic stability of uranium-incorporated iron oxide nanoparticles. Increasing uranium content within hematite resulted in more positive formation enthalpies. Standard formation enthalpies of U x Fe 2–2x O 3 were as high as 76.88 ± 2.83 kJ/mol relative to their binary oxides, or -764.04 ± 3.74 kJ/mol relative to their constituent elements, at x = 0.037. Data on the thermodynamic stability of uranium retention pathways may assist in predicting waste uranyl remobilization, as well as in developing more effective methods to retain uranium captured from aqueous environments.

Uranium incorporation in fluorite and exploration of U–Pb dating

Abstract. The age of ore deposits constitutes a decisive element in understanding their formation. Deciphering their precise chronology may be a challenge in the absence of mineral phases that can be dated by conventional geochronometers. Fluorite is very common either as the major or accessory mineral in a wide variety of ores and may provide information regarding the origin and timing of mineralizing fluid flows. In this contribution, we explore U–Pb dating on fluorite crystals from the world-class carbonate strata-bound fluorite ore of Pierre-Perthuis in Burgundy (Morvan massif, France). The uranium distribution within fluorite is mapped using induced fission-track and synchrotron radiation X-ray fluorescence nano-imaging, showing that higher U content is measured in an overgrowth of fluorite (Flog) as a discrete band. Preservation of a micrometer-thick zonation in U, associated with other substituted elements such as Sr, Y, Fe and Zr, implies that neither solid-state diffusion nor dissolution–recrystallization occurred. These U-bearing external fluorite overgrowths contain solid inclusions of about 30 µm globular pyrite crystals with a mean δ34S of −23.6 ± 0.4 ‰V-CDT. We propose that the U incorporation in the fluorite lattice results from the development of a redox front during bacterial sulfate reduction. Flog generation sampled and analyzed by laser ablation–inductively coupled plasma mass spectrometry (LA-ICP-MS) on four different crystals provides identical U–Pb ages within the limits of analytical uncertainty. Considered altogether, these four crystals yield an age estimate of 40.0 ± 1.7 Ma, not corrected for matrix-related elemental fractionation. Our results show that fluorite LA-ICP-MS U–Pb geochronology has potential for dating distinct crystal growth stages, although further research should be conducted to evaluate its accuracy.

Uranium Distribution and Incorporation Mechanism in Deep-Sea Corals: Implications for Seawater [CO32–] Proxies

A conservative element in seawater, uranium is readily incorporated into the aragonitic skeletons of scleractinian corals, making them an important paleoclimate archive that can be absolutely dated with U-Th techniques. In addition, uranium concentrations (U/Ca ratios) in corals have been suggested to be influenced by the temperature and/or carbonate ion concentration of the ambient seawater based on empirical calibrations. Microsampling techniques have revealed strong heterogeneities in U/Ca within individual specimens in both surface and deep-sea corals, suggesting a biological control on the U incorporation into the skeletons. Here we further explore the mechanism of uranium incorporation in coral skeletons with the deep-sea species Desmophyllum dianthus, an ideal test organism for the biomineralization processes due to its relatively constant growth environment. We find a negative correlation between bulk coral U/Ca and temperature as well as ambient pH and [CO32–] that is consistent with previous studies. By sampling the growth bands of individual corals, we also find a twofold change in U/Ca within individual corals that is strongly correlated with the δ18O, δ13C, and other Me/Ca ratios of the bands. A similar correlation between U/Ca and stable isotopes as well as other Me/Ca ratios are observed in bulk deep-sea coral samples. With a numerical coral calcification model, we interpret the U/Ca-stable isotope correlation as a result of changes in uranium speciation in response to internal pH elevations in the extracellular calcifying fluid (ECF) of the corals, and suggest that the Ca2UO2(CO3)3(aq) complex, the dominant U species in seawater, may be the major species incorporated into the coral skeleton. Therefore, the correlation between U/Ca and ambient [CO32–] is likely a result of the response of the biomineralization process, especially the magnitude of internal pH elevation, to the growth environment of the corals. Our data suggest overall lower alkalinity pump rates in corals from low saturation seawater compared to those from high saturation seawater, and possible increases in Ca2+ supply from active pumping relative to seawater transport in response to the environmental stress of low saturation.

Multicomponent pyrochlore solid solutions with uranium incorporation – A new perspective of materials design for nuclear applications

Multicomponent pyrochlore solid solutions with and without uranium incorporation were fabricated and their thermal-mechanical properties were characterized. Multicomponent pyrochlore solid solutions without uranium exhibit comparable thermal conductivity and higher mechanical strength compared to baseline single component rare-earth titanate pyrochlore (A2Ti2O7). Uranium incorporation reduces hardness as compared with single component compositions. High entropy pyrochlore with uranium displays the highest thermal conductivity within multicomponent pyrochlore solid solutions with significantly better mechanical properties than UO2. The measured thermal conductivity correlates well with A-site cation mixing entropy and a modified size disorder parameter, and thus the size disorder and mixing entropy could be good indicators for predicting thermal conductivity of multicomponent pyrochlore solid solutions. This work opens up the possibility of designing multicomponent oxide solid solutions by controlling their chemical disorder/mixing entropy to achieve acceptable thermal-mechanical properties, desired radiation and corrosion performance for potential nuclear waste form and inert matrix fuel applications.

Uranyl binding mechanism in microcrystalline silicas: A potential missing link for uranium mineralization by direct uranyl co-precipitation and environmental implications

Genetic models for the formation of uranium deposits almost invariably invoke the reduction of U(VI) to U(IV) as the deposition mechanism. However, the questions of when and how this reduction occurred are often not clear in most uranium deposits. For example, mineralization in the giant Olympic Dam Cu-U-Au-Ag deposit (Australia) occurs mainly in hematite-rich breccias of the oxidizing hematite-quartz-barite assemblage. Similarly, unconformity-related uranium deposits in the Athabasca Basin (Canada) are accompanied by extensive and intensive hematite- and quartz-rich alteration halos, pointing to a possible linkage between uranium mineralization and silicification. However, this linkage is not understood due to the lack of knowledge about the speciation and mechanism of uranium incorporation in microcrystalline and macrocrystalline silicas. In this contribution, microcrystalline silicas (agate and opal-CT) containing 27–137 ppm U have been investigated by microbeam synchrotron X-ray fluorescence mapping, microbeam synchrotron X-ray diffraction analysis, synchrotron X-ray absorption spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and electron paramagnetic resonance spectroscopy. These data unravel the binding mechanism of uranyl silicate complexes in microcrystalline silicas and suggest a new mechanism of uranium deposition involving uranyl co-precipitation without the putative reduction process, providing a potential missing link between uranium mineralization and silicification for the formation of uranium deposits. In addition, new data on the uptake and long-term retention of elevated uranyl contents in microcrystalline silicas extend previous findings from their amorphous counterparts on these materials as an effective sink for uranium attenuation to higher temperatures, important to the storage and disposal of heat-generating nuclear waste in deep geological repositories.

Cellular reactions of the mucous membrane of the intestinal system after uranium incorporation

A pilot study, which was performed on white laboratory male rats and included a morphological study of the mucous membrane of the jejunum and colon, revealed the long-term effect of a single oral exposure to an aqueous solution of depleted uranium oxides; this supported dynamic changes in the studied criteria determining metabolic, regenerative, and local regulatory processes in one, three and six months. A lymphoid component appeared to be the criterion of high radio sensitivity and a marker of nonspecific protection indicating deterioration of homeostasis. In the time dynamics of long-term periods, a change in all the parameters was detected when using immunohistochemical, histochemical, and specific methods at the level of the epithelium lining the relief formations of the mucous membranes of the intestinal system organs. The oxidative stress resulting in three months after exposure to depleted uranium, which was evidenced by a significant decrease in the content of anti-apoptotic Bcl-2 protein in the epithelial cells of the jejunely mucosa. Signs of its delayed effect after six months in the colon induced the pronounced nature of the reactions of stromal cell components that determined patterns of protective mechanisms of the intestinal-associated immune system with a greater expressiveness in the jejunum. The factual material cited in the work suggests the existence of a homeostatic immune response in the mucous membrane of the small and large intestines that controls cell proliferation, as a special form of immune surveillance of the state of cytodifferentiation.

Does trace element composition of bivalve shells record utra-high frequency environmental variations?

Saint-Pierre and Miquelon (SPM) is a small archipelago where instrumental measures based on water column velocity and temperature profiles compiled comprehensive evidence for strong near-diurnal (25.8h) current and bottom temperature oscillations (up to 11.5 °C) which is possibly the largest ever observed — at any frequency — on a stratified mid-latitude continental shelf. The main objective of our study was to identify if Placopecten magellanicus can record on its shell these high frequency environmental variations. To this end, we have tried to identify proxies for water temperature and food availability through development of a new ultra-high resolution LA-ICPMS analyses method capable of resolving shell surface elemental composition with a 10 μm resolution. This method was applied on two shell fragments, both representing the third year of growth and 2015 annual growth period, respectively coming from two environmentally contrasted sites, more (30 m depth) or less (10 m depth) affected by high frequency thermal oscillations. Our results strongly suggest a relationship between phytoplankton biomass and barium incorporation into P. magellanicus shells at both sites. Even if P. magellanicus might present a physiological control of magnesium incorporation, the shape of the two Mg/Ca profiles seems to illustrate that temperature also exerts a control on magnesium incorporation in P. magellanicus shells from SPM. While U/Ca and Mg/Ca profiles show a strong positive correlation for 30 m site shell, suggesting that uranium incorporation in P. magellanicus shell is at least partially temperature dependent. The absence of such correlation for 10 m site shell suggests differences in uranium environmental availability or in P. magellanicus biomineralization between these two sites. The resolution of this new analytical method raises questions about such data interpretation related to P. magellanicus growth dynamics and physiology or individual scale based environmental measurements.

Radionuclide incorporation in negative thermal expansion [formula omitted]-Zr(WO4)2: A density functional theory study

The incorporation of uranium, plutonium and technetium in the negative thermal expansion (NTE) α-Zr(WO4)2 has been investigated within the framework of density functional theory (DFT). It is found that the vacancy formation energies of the charged vacancies are overall larger than that of its counterpart neutral Frenkel defects and Schottky defects. DFT calculations suggest that U and Pu substitutions for the Zr site are preferred in α-Zr(WO4)2. In case of Tc substitution, both Tc(IV) for the Zr site and Tc(VII) for the W site are considered under oxygen-poor and oxygen-rich conditions, while Tc(VII) substitution can be improved significantly by including Y2O3 (charge compensation).

Can mineral growth by oriented attachment lead to incorporation of uranium(vi) into the structure of goethite?

Atomic and bulk scale measurements demonstrate that goethite grown by oriented aggregation does not readily incorporate U(vi) into structural sites.

Interaction of Uranium(VI) with α-Amylase and Its Implication for Enzyme Activity.

Because of its chemo- and radiotoxicity, the incorporation of uranium into human body via ingestion potentially poses a serious health risk. When ingested, the gastrointestinal fluids are the primary media to interact with uranium, eventually influencing and even determining its biochemical behavior in the gastrointestinal tract and thereafter. The chemical interactions between uranium and the components of gastrointestinal fluids are, however, poorly understood to date. In this study, the complexation of uranium(VI) (as the uranyl ion, UO22+) with the protein α-amylase, one of the major enzymes in saliva and pancreatic juices, was investigated over a wide range of pH or uranium/α-amylase concentrations covering physiological conditions. Macroscopic sorption experiments suggested a strong and fast complexation of UO22+ to α-amylase between pH 5 and 7. Potentiometric titration was employed to determine the complex stability constants for the relevant UO22+ α-amylase complexes, which is crucial for reliable thermochemical modeling to assess the potential health risk of uranium. Extended X-ray absorption fine structure (EXAFS) spectroscopy revealed that α-amylase is interacting with UO22+ primarily via its carboxylate groups presumably from the aspartic acid and glutamic acid side chains. The effect of UO22+ on the enzyme activity was also investigated to understand the potential implication of uranium for the in vivo functions of the digestive fluids, indicating that the presence of uranium inhibits the enzyme activity. This inhibitory effect can be, however, suppressed by an excess of calcium.

XANES and EXAFS investigation of uranium incorporation on nZVI in the presence of phosphate

Effect of phosphate on the reduction of U(VI) on nZVI was determined by batch, XPS, XANES and EXAFS techniques. The batch experiments showed that nZVI was quite effective for the removal of uranium under the anaerobic conditions, whereas the addition of phosphate enhanced uranium removal over wide pH range. At low pH, the reduction of U(VI) to U(IV) significantly decreased with increasing phosphate concentration by XPS and XANES analysis. According to EXAFS analysis, the occurrence of UU shell at 10 mg/L phosphate and pH 4.0 was similar to that of U(IV)O2(s), whereas the UP and UFe shells were observed at 50 mg/L phosphate, revealing that reductive co-precipitate (U(IV)O2(s)) and precipitation of uranyl-phosphate were observed at low and high phosphate, respectively. The findings are crucial for the prediction of the effect of phosphate on the speciation and binding of uranium by nZVI at low pH, which is significant in controlling the mobility of U(VI) in contaminated environments.

Concentration of uranium in groundwater and its correlation with the gamma activity of primordial radionuclides in the bedrock samples: A study from northeastern part of Bengaluru city, India

The present investigation aims to study the incorporation of uranium from the bedrock to groundwater through leaching. In view of this, rock powder samples were collected in the form of slurry from the bedrock of freshly drilled borewells of the study area. The rock powder and the supernatant were separated. The gamma activity concentrations of primordial radionuclides-238U (226Ra), 232Th, and 40K in the rock powder samples were measured using HP-Ge gamma-ray spectrometer. The supernatant was analyzed for the concentration of Unatusing laser-induced fluorimeter. A strong positive correlation was observed between the concentration of uranium in the rock powder and the corresponding concentration in the water samples indicating the possible leaching of uranium from the bedrock to groundwater under favorable conditions.

Uranium(V) Incorporation Mechanisms and Stability in Fe(II)/Fe(III) (oxyhydr)Oxides

Understanding interactions between radionuclides and mineral phases underpins site environmental cleanup and waste management in the nuclear industry. The transport and fate of radionuclides in many subsurface environments are controlled by adsorption, redox, and mineral incorporation processes. Interactions of iron (oxyhydr)oxides with uranium have been extensively studied because of the abundance of uranium as an environmental contaminant and the ubiquity of iron (oxyhydr)oxides in engineered and natural environments. Despite this, detailed mechanistic information regarding the incorporation of uranium into Fe(II)-bearing magnetite and green rust is sparse. Here, we present a co-precipitation study in which U(VI) was reacted with environmentally relevant iron(II/III) (oxyhydr)oxide mineral phases. On the basis of diffraction, microscopic, dissolution, and spectroscopic evidence, we show the reduction of U(VI) to U(V) and stabilization of the U(V) by incorporation within the near surface and bulk of the ...