Uranium Research Articles

Radiological Hazard Assessment of High-Level Natural Radionuclides in Surface Sediments Along Red River, Vietnam.

The Red River is one of the largest rivers that plays an important role in the economic development of North Vietnam. There are many radionuclides bearing rare earth, uranium ore mines, mining industrial zones and magma intrusive formations along this river. The contamination and accumulation of radionuclides could exist at high concentration in surface sediments of this river. Thus, the present investigation aims to study the activity concentrations of 226Ra, 232Th (228Ra), 40K, and 137Cs in Red River surface sediments. Thirty sediment samples were collected, and their activity concentration was calculated using high-purity germanium gamma-ray detector. The observed results ranged from 51.0 ± 2.1 to 73.6 ± 3.7 for 226Ra, 71.4 ± 3.6 to 103 ± 5.2 for 232Th, 507 ± 24.0 to 846 ± 42.3 for 40K, and ND (not detected) to 1.33 ± 0.06Bq/kg for 137Cs, respectively. In general, the natural radionuclides concentration of 226Ra, 232Th (228Ra), and 40K is higher than the average world average values. This indicated that the natural radionuclides could contribute from similar and principal sources surrounding the upstream of Lao Cai where distributed uranium ore mines, radionuclide bearing rare earth mines, mining industrial zones and intrusive formations. Regarding the radiological hazard assessment, results of the indices computed such as absorbed gamma dose rate (D), the excess lifetime cancer risk (ELCR), and the annual effective dose equivalent (AEDE) were nearly two times higher than world average values.

An artificial neural network potential for uranium metal at low pressures

Based on machine learning, the high-dimensional fitting of potential energy surfaces under the framework of first principles provides density-functional accuracy of atomic interaction potential for high-precision and large-scale simulation of alloy materials. In this paper, we obtained the high-dimensional neural network (NN) potential function of uranium metal by training a large amount of first-principles calculated data. The lattice constants of uranium metal with different crystal structures, the elastic constants, and the anisotropy of lattice expansion of alpha-uranium obtained based on this potential function are highly consistent with first-principles calculation or experimental data. In addition, the calculated formation energy of vacancies in alpha- and beta-uranium also matches the first-principles calculation. The calculated site of the most stable self-interstitial and its formation energy is in good agreement with the findings from density functional theory (DFT) calculations. These results show that our potential function can be used for further large-scale molecular dynamics simulation studies of uranium metal at low pressures, and provides the basis for further construction of potential model suitable for a wide range of pressures.

Chlorination of Pu and U Metal Using GaCl3.

The oxidative chlorination of the plutonium metal was achieved through a reaction with gallium(III) chloride (GaCl3). In DME (DME = 1,2-dimethoxyethane) as the solvent, substoichiometric (2.8 equiv) amounts of GaCl3 were added, which consumed roughly 60% of the plutonium metal over the course of 10 days. The salt species [PuCl2(dme)3][GaCl4] was isolated as pale-purple crystals, and both solid-state and solution UV-vis-NIR spectroscopies were consistent with the formation of a trivalent plutonium complex. The analogous reaction was performed with uranium metal, generating a dicationic trivalent uranium complex crystallized as the [UCl(dme)3][GaCl4]2 salt. The extraction of [UCl(dme)3][GaCl4]2 in DME at 70 °C followed by crystallization produced [{U(dme)3}2(μ-Cl3)][GaCl4]3, a product arising from the loss of GaCl3. This method of halogenation worked on a small scale for plutonium and uranium, providing a route to cationic Pu3+ and dicationic U3+ complexes using GaCl3 in DME.

Amplified Single-Atom U-O Interfacial Effect Originated from U 5f-O 2p Hybridization over UOx/GO for Enhanced Nitrogen Reduction Reaction.

Uranium-based catalysts have been regarded as promising candidates for N2 fixation owing to the low-valent uranium metal active sites possessing the ability to enhance the electron back-donating to the π* antibonding orbitals of N2 for N≡N dissociation. Herein, we report a directional half-wave rectified alternating current electrochemical method to confine oxygen-rich uranium precursors over ultrathin 2D GO nanosheets. The as-prepared uranium catalysts exhibit a considerable Faradaic efficiency of 12.7% for NH3 and the NH3 yield rate of 18.7 μg h-1 mg-1 for N2 electroreduction. Operando XAS and isotope-labeling FTIR further unravel the preferred nitrogen adsorption reaction intermediate N-(2Oax-1 U-4Oeq) and confirm the key *N2Hy intermediate species derived from the fed N2 gas. Theoretical simulations demonstrate that the U-O atomic interface originated from U 5f-O 2p orbital hybridization can accumulate partial charge from GO, which can facilitate the N≡N dissociation and lower the thermodynamic energy barrier of the first hydrogenation step.

Uranium Retention in Silica-Rich Natural Glasses: Nuclear Waste Disposal Aspect

Uranium-containing glass samples with an age of 140–145 million years were collected within the volcanic rocks of the largest volcanic-related uranium ore deposit in the world. Main features of their composition are high concentrations of silica and uranium, the largest for the rocks of this type. In contrast to this, the ages of fresh (unaltered) low-silica natural glasses of a basic composition (basalts) usually do not exceed a few million years. The volcanic low-silica glass is unstable at longer times and in older ancient rocks is transformed into a crystalline mass. The geochemistry of uranium including the behavior in solids and solutions is similar to that of long-lived transuranic actinides such as radioactive Np and Pu from high-level radioactive waste. This allows uranium to be used as a simulant of these long-lived hazardous radionuclides both at the synthesis and for the study of various nuclear wasteforms: glasses, glass crystalline materials and crystalline ceramics. The data obtained on long-term behavior of natural glasses are of importance for prognosis and validation of stability of nuclear wasteforms disposed of in geological disposal facilities (GDF).

The Department of Veterans' Affairs Depleted Uranium Cohort in the Time of COVID-19: Translating a Traditional Surveillance Protocol to a Telehealth Platform.

In 2021, 37 members of a cohort of depleted uranium-exposed Gulf War I veterans were evaluated using a protocol tailored to accommodate COVID-19 safety practices on a telehealth platform. Individual elements of the legacy protocol were reviewed for urgency and feasibility of inclusion in a modified, telehealth platform. The redesigned protocol included a participant readiness for telehealth assessment, nurse and physician telehealth visits, collection of usual health questionnaires, and urine collections for exposure monitoring for uranium and other fragment-related metal measures. Despite some limitations in scope, the telehealth platform permitted a visual "visit" with surveillance participants who expressed a high comfort level with the format. The telehealth platform has apparent utility for occupational surveillance and should be explored as a standard approach for surveillance outside of public health emergencies.

Nonaqueous Electrochemistry of Uranium Complexes: A Guide to Structure-Reactivity Tuning.

Uranium complexes can be stabilized in a wide range of oxidation states, ranging from UII to UVI and a very recent example of a UI complex. This review provides a comprehensive summary of electrochemistry data reported on uranium complexes in nonaqueous electrolyte, to serve as a clear point of reference for newly synthesized compounds, and to evaluate how different ligand environments influence experimentally observed electrochemical redox potentials. Data for over 200 uranium compounds are reported, together with a detailed discussion of trends observed across larger series of complexes in response to ligand field variations. In analogy to the traditional Lever parameter, we utilized the data to derive a new uranium-specific set of ligand field parameters UEL(L) that more accurately represent metal-ligand bonding situations than previously existing transition metal derived parameters. Exemplarily, we demonstrate UEL(L) parameters to be useful for the prediction of structure-reactivity correlations in order to activate specific substrate targets.

To the question of application of new physical and chemical geotechnologies in the development of uranium ore deposits

Background. Underground uranium leaching is a promising geotechnological process due to its potential to provide for a radical increase in the technical and economic efficiency, as well as environmental safety, of uranium deposit development. In this article, we discuss the main results in this direction obtained by specialists of the Russian State University for Geological Prospecting.Aim. To study the processes of uranium leaching by activated solutions, which undergo electrophotochemical treatment prior to contacting with the ore.Materials and methods. Activation preparation of leaching solutions enables the synthesis of active hydrated forms of oxygen and hydrogen with collectivized protons and hydroxyl ions clustered by water molecules. Following the stage of pre-oxidation with an active carbonate solution, a model downhole leaching with chloride-hypochlorite, soda, and sulfuric acid solutions was carried out. Testing percolation leaching of uranium from the ores of the Uchkuduk and Sugraly deposits by activated solutions was conducted at laboratory installations designed by the the Russian State University for Geological Prospecting jointly with the Institute of Mining of Far-East Branch of the Russian Academy of Sciences and Zabaikalsky State University. As a result, the potential of a significant increase in uranium extraction was noted.Results. When leaching with sodium carbonate and ammonium carbonate solutions, the uranium extraction from ore samples from the Sugraly deposit comprised 52% and 59%, respectively. At the same time, the use of an activated solution of sodium percarbonate, which combines the functions of an oxidizing agent and a complexing agent, resulted in an 87–88% uranium extraction into productive solutions during 21 days without preliminary pre-oxidation.Conclusion. The results obtained confirm the prospects of using mine (block) and downhole uranium leaching with activated solutions.

ELECTROREFINING OF URANIUM ALLOYS CONTAINING PALLADIUM AND NEODYMIUM IN 3LiCl–2KCl–UCl<sub>3</sub> MELTS

The technology of pyrochemical processing of mixed nitride uranium-plutonium spent fuel, realizable at the experimental and demonstration energy complex of the site of the Siberian Chemical Plant, includes several operations with the ultimate goal of isolating the target fission products. It’s planned to use the electrofining of the products of the previous stage, metallized spent nuclear fuel, аs the penultimate stage of processing. It’s necessary to determine the processes and technological modes of electrolytic refining of alloys modeling the product of this stage of the processing module to implement electrolytic refining. This paper presents the results of electrofining of model alloys (simulating the raw materials of the stage of electrofining processing) on an enlarged laboratory electrolyzer. The initial parameters of uranium refining processes in melts based on 3LiCl–2KCl–UCl3 were determined earlier. The basic parameters of refining were the use of electrolyte 3LiCl–2KCl–UCl3 (10.1 wt % UCl3) and conducting experiments at 550°C. Uranium alloys containing palladium and neodymium were prepared by direct fusion of uranium metal, PdAP-1 grade palladium metal powders and neodymium metal (99.99%) in a medium of high-purity argon (99.998%). The data obtained showed that at a temperature of 550°C, cathode precipitates are typical dendritic forms of alpha-uranium in rhombic syngony with a tendency to needle formation with an increase in cathode current density. An increase in the company time and cathode current density leads to a decrease in the current output due to short-circuiting of the electrodes with cathode sediment needles or metal shedding from the cathode. The modes of the cathode process have been experimentally refined as a result of electrofining. When electrofining alloys U–Pd(1.59 wt %), U–Pd(1.62 wt %), U–Pd(1.54 wt %), U–Pd(1.58 wt %)–Nd(5.64 wt %), U–Pd(1.84 wt %)–Nd(6.49 wt %), U–Pd(1.79 wt %)–Nd(6.54 wt %), uranium cathode precipitates were obtained, which were subjected to chemical analysis, which showed the high purity of the resulting metallic uranium, as well as the absence of metallic palladium and molybdenum in it. The palladium purification coefficient exceeds 5000, the neodymium purification coefficient exceeds 1000, which meets the requirements for purification from fission products at this stage of pyrochemical processing of spent fuel. Palladium accumulates in anode slime, while the bulk of neodymium passes into the molten electrolyte.

Synthesis and physical properties of uranium thin-film hydrides UH2 and UH3

Formation of thin uranium hydrides films, UH2 and UH3, synthesized by direct current reactive sputtering of a uranium metal in an Ar-H2 atmosphere, was explored using variable deposition conditions. Obtained U-H films were studied by a variety of methods, both in situ (photoelectron spectroscopy) and ex situ (x-ray diffraction, transmission electron microscopy, electrical resistivity, and magnetometry). Preparation of thin films allowed us to stabilize the non-existent in bulk UH2 phase as well as the transient α-UH3 (as a residual phase in UH2) and the common stable β-UH3 phase. All types of hydrides are ferromagnetic, the Curie temperatures of UH2 and UH3 (both α and β) are approx. 120 and 170 K, respectively. Ferromagnetism in the thin films is robust and does not depend on structure details while electrical resistivity data reflect disorder in both types of hydrides.

Results from a controlled depleted uranium metal casting experiment designed to investigate nuclear Forensic Radiochronometry Signatures

Results from a controlled depleted uranium metal casting experiment designed to investigate nuclear Forensic Radiochronometry Signatures

Reactive transport model of uranium by CO2 + O2 in situ leaching

Uranium is an important strategic resource, and its safe and efficient development and utilization are of great significance to ensuring a nation's energy supply and strategic security. Sandstone-type uranium ore is commonly mined by CO2 + O2 in situ leaching, for which understanding the coupling mechanism between the hydrodynamic and chemical fields is key to predicting uranium leaching. This study focused on a coal-uranium ore deposit in China. A convection and dispersion model of the solute transport by in situ leaching was constructed in COMSOL, and a thermodynamic model of CO2 + O2 in situ leaching in sandstone-type uranium ore was constructed in PHREEQC. The two models were coupled to simulate the reactive transport and dynamic leaching processes of uranium by CO2 + O2 in situ leaching. A sensitivity analysis was performed to quantitatively analyze the effects of different model parameters on the uranium leaching efficiency and uranium contamination remediation. The results showed that the coupled model could simulate and predict the reaction and transport of uranium. The sensitivity analysis indicated that the production rate and the injected CO2 and O2 concentrations are the key parameters that control the uranium leaching efficiency, followed by the formation permeability and injection rate. The uranium leaching efficiency does not increase monotonically with the formation permeability and production rate. The results also indicated that natural dilution is insufficient for remediating uranium-contaminated groundwater, but the remediation efficiency can be improved by increasing solution extraction. The results of this study can be used to develop guidelines for the safe and efficient development and utilization of uranium ore while protecting the ecological environment.

The role of uranyl complex decomposition and redox conditions in the precipitation of hydrothermal uranium deposits: Insights from chlorite mineralogy and geochemistry in the Shazhou uranium deposit, Xiangshan, SE China

Uranium precipitation involves the decomposition of uranyl complexes and the reduction of hexavalent uranium, which can occur sequentially or simultaneously within one redox reaction. The redox condition of hydrothermal fluid plays a vital role in controlling the migration and precipitation of uranium in hydrothermal uranium deposits. However, little attention has been paid to the role of uranyl complex decomposition in uranium precipitation. In this study, chlorite mineralogy and geochemistry were examined to clarify the process of uranium precipitation in the Shazhou deposit, Xiangshan uranium orefield, Southeast China. Based on comprehensive petrographic and mineral chemistry studies of chlorites obtained from altered granite porphyries and uranium ores, five types of chlorites were identified: (1) chlorite present in the form of pseudomorphous biotite, which was produced by the hydrothermal alteration of biotite in rocks that underwent hematitization and chloritization (Chl-I); (2) chlorite filling the cleavage cracks in biotite in rocks that underwent hematitization and chloritization (Chl-II); (3) chlorite occurring in pyrite veins (Chl-III); (4) chlorite intergrown with pitchblende in ore veins (Chl-IV); and (5) chlorite occurring in calcite veins (Chl-V). Chlorite geothermometry revealed that the formation temperatures of the five types of chlorites ranged from 219 °C to 254 °C. Mineral chemistry analyses revealed that the five types of chlorites formed in a reductive fluid environment, where the oxygen fugacity at different stages is similar, with log fO2 values ranging from −41.6 to −39.1. Uranium precipitation started only in stage Chl-IV. The examination of the mineral assemblage revealed that the ore-forming fluid was rich in F−, HPO32−, and CO32−. Comprehensive investigation of chemistry and physicochemical conditions of the ore-forming fluid revealed that oxidized uranium (UO22+) could be complexed with HPO42− and F−, and uranyl phosphate and the uranyl fluoride complexes were the main uranium species when uranium precipitation and the decomposition occurred at stage Chl-IV. However, the assessment of oxygen fugacity of the solution equilibria between the UO2(s) and the uranyl phosphate and uranyl fluoride complexes revealed that the reducibility of the fluid favoring the reduction of uranyl ions (UO22+) to U4+ was insufficient to reduce the uranyl phosphate and uranyl fluoride complexes. This indicates that the breakup of uranyl phosphate and the uranyl fluoride complexes to release uranyl ions should occur first at stage Chl-IV, reducing uranyl ions to U4+, and leading to uranium precipitation. Hence, the decomposition of uranyl complexes played an important role in uranium precipitation. With the increase in pH, uranyl phosphate and the uranyl fluoride complexes gradually decomposed and became reducible. Moreover, the decrease in ligand concentration was conducive to the decomposition of uranyl phosphate and the uranyl fluoride complexes. During the formation of the Shazhou deposit, the fluid boiling process induced the loss of volatiles, such as CO2, CH4, HF, and H2S, leading to an increase in pH and decrease in HPO42−, F−, and CO32− concentrations in the fluid. These factors also led to the decomposition of uranyl fluoride and the uranyl phosphate complexes and the precipitation of fluorapatite and calcite. Uranium was then reduced by the action of Fe2+ and S− (pyrite) from a hexavalent to a tetravalent, and finally, uranium was precipitated to form uranium ores.

Evolution, Magmatic Source and Metallogenesis of A-Type Granites in the Fanchang Volcanic Basin, Middle and Lower Yangtze Metallogenic Belt: A Review

The Fanchang volcanic basin (FVB) is located in the Middle and Lower Yangtze Metallogenic Belt (MLYMB) between the ore districts of Ningwu and Tongling. The existing ore deposits in the FVB are relatively small in scale and related to late Mesozoic A-type granites. In this paper, the crystallization age, major and trace element composition, and Sr-Nd and Hf isotope compositions of the A-type granites are summarized from the literature; in addition, the magnetite composition, H and O isotopes of fluid inclusions, and sulfur isotope composition of metal sulfides in some typical ore deposits in the FVB are also summarized to give insights into the petrogenesis and mineralization of the A-type granites intruding into the FVB. The results show that: (1) Orthopyroxene, plagioclase, K-feldspar, and biotite are the main fractionating minerals controlling the evolution of the magmas of A-type granites in the FVB and other areas in the MLYMB. (2) The whole-rock Sr-Nd and zircon Hf isotopic characteristics show that the source of A-type granite magma is complex and includes the enriched mantle, lower crust, and upper crust, probably with stronger participation of Archaean–Paleoproterozoic crustal materials in the FVB granites than in other regions of the MLYMB. (3) The ores in the FVB are dominated by skarn and hydrothermal deposits. H and O isotopes of fluid inclusions indicate that ore-forming fluids have been derived from mixtures of magmatic hydrothermal fluid, meteoric waters, and deep brine related to gypsum layers. S isotopes of metal sulfides indicate that the sulfur may be a mixture of magmatically derived sulfur and sulfur originating from the Triassic gypsum-bearing layers. The deposit and ore characteristics of the main deposits in the FVB are also illustrated, and the evaluation of metal resources indicates that the skarn and hydrothermal iron–zinc ores in the FVB also have potential as sources of Cd, Ga, and Se. In addition, in terms of the oxygen fugacity, rock type, and geochemical characteristics of magmatic rocks, the metallogenic characteristics and potential of the A-type granites in the FVB are evaluated. It is considered that in addition to the dominant constituents of iron and zinc and the minor constituents listed above, the FVB could have the potential for providing copper, gold, molybdenum, uranium, and other metals as well.

Effect of mono- vs. bi-functionality of aminophosphonate derivatives on the enhancement of U(VI) sorption: physicochemical properties and sorption performance

Aminophosphonates are excellent complexing agents for numerous metal ions (including uranyl). Based on this property, two sorbents have been synthesized using simple one-pot reaction: thiocarbazide (amine source), p-phthaldehyde (di-aldehyde), and trimethylphosphite (phosphorous precursor) are mixed with different molar ratios to produce bis- (2:1:2) and mono (1:1:1) α-aminophosphonate-based derivatives (B-AmPh and M-AmPh, respectively). Materials are characterized using XRD, BET, SEM, titration, elemental, FTIR, and XPS analyses to evaluate the effect of substitution rate on the physicochemical properties. FTIR and XPS are also used for elucidating binding mechanisms. Sorption properties of the materials have been tested for U(VI): the pH effect is completed by investigating uptake kinetics and sorption isotherms. At pH 4.5 (and T: 55 °C), sorption capacity increases from 0.89 to 1.22 mmol/g with the increase in the substitution degree (M-AmPh < B-AmPh). This increase is not correlated to the fraction of grafted reactive groups, meaning that steric hindrance probably contributes to limiting the accessibility and availability of aminophosphonate moieties. Pseudo-second order and Crank equation preferentially fit kinetic profiles. Langmuir equation successfully describes sorption isotherms. Sorption process is systematically endothermic and spontaneous: enthalpy and entropy changes decrease with the substitution rate. Uranium successfully desorbed using HCl (0.2 M); allows six cycles of re-use with limited loss in sorption/desorption efficiencies. The sorbents were used for U(VI) recovery from acidic leachate of uranium ore. This test shows remarkable affinity and selectivity of B-AmPh for uranium; however, after elution and precipitation the U concentrate contains about 10 % of impurities.

Efficacious selective separation of U(VI) over Mo(VI) using novel 2,9-diamide-1,10-phenanthroline ligands: Liquid-liquid extraction and coordination chemistry

Uranium and molybdenum are important strategic elements. The production of 99Mo and the hydrometallurgical process of uranium ore face difficult problems of separation of uranium and molybdenum. In this study, the four phenanthroline diamide ligands were synthesized, and extraction and stripping experiments were performed under different conditions to evaluate the potential application of these ligands for separation of U(VI) over Mo(VI). With the growth of alkyl chain, the solubility of ligands could be greatly improved, and the separation effect of U(VI) over Mo(VI) gradually increased. The SFU/Mo were around 10,000 at 4 mol/L HNO3. Three stripping agents were tested with the stripping efficiency of Na2CO3 (5%) > H2O > HNO3 (0.01 mol/L). The stripping percentages of the three stripping agents were all close to unity, indicating that the ligands had the potential to be recycled. The chemical stoichiometry of U(VI) complexes with ligands was evaluated as 1:1 using electrospray ionization mass spectrometry, ultraviolet visible spectroscopy and single-crystal X-ray diffraction. The consistency between theoretical calculation and experimental results further explains the coordination mechanism.

Optimization of Ball Mill Grinding of a Limestone-Type Brecciated Uranium Ore

Optimization of Ball Mill Grinding of a Limestone-Type Brecciated Uranium Ore

Prospects for the natural uranium world market

Various scenarios for development of the world uranium industry are considered, and an assumption is made of a high probability of the rapid growth scenario, according to the IAEA, which assumes an annual growth rate of the total nuclear power plants (NPPs) capacity of 2-2.5%. Based on this forecast, an assessment is made of capabilities of the uranium world mineral base to meet the NPPs needs in the nuclear fuel. It is demonstrated that only the restoration of production at temporary closed down mining enterprises, the growth of output at existing mines, and using secondary sources of uranium guarantee a sufficient amount of the raw materials to meet the demand for uranium in the next decade. Moreover, the shortage of raw materials for nuclear fuel in the near future may again be replaced by its excess. However, by the end of the current or early next decade, due to the depletion of the resource base of some operating mines, including Four Mile and Cigar Lake in Canada, the capacities of mining enterprises will be insufficient to meet the fuel needs of NPPs. A shortage of uranium may appear again, that will grow rapidly in the future. This will mean a new round of growth in prices for natural uranium, which, in turn, will stimulate an increase in uranium production throughout the world and will expand the prospects for the implementation of projects for the development of new uranium deposits in Russia, primarily Argunskoe and Zherlovoe in the Streltsovskoe uranium ore region

Existent forms and ecological risk assessment of uranium and heavy metals in soil at a uranium mining area in northern Guangdong, China

Existent forms and ecological risk assessment of uranium and heavy metals in soil at a uranium mining area in northern Guangdong, China

Determination of rare earth elements in uranium ores by ICP-MS after total dissolution with NH4F and matrix separation with TRU resin

Determination of rare earth elements in uranium ores by ICP-MS after total dissolution with NH4F and matrix separation with TRU resin