State Of Uranium Research Articles

Study on uranium leaching from uranium purification residue with ammonium hydrogen fluoride

Residues generated from the uranium purification process, characterized by a high uranium content, pose a significant challenge for recovery through leaching and present a considerable environmental threat. After using XRD and SEM-mapping characterization analysis combined with the BCR continuous graded extraction test to analyze the content of different states of uranium, it was found that the main reason why the uranium in the residue was difficult to leach because it was encapsulated by SiO2 crystals. Using NH4HF2 as a leaching agent, a leaching study of uranium in the residue was carried out, and the results showed that the H+ and F− produced by NH4HF2could react with SiO2, destroying the crystal lattice of SiO2 and causing the encapsulated uranium to come into contact with the leaching agent, facilitating the leaching of uranium in the residue. The optimum conditions for uranium leaching were 10% mass fraction of NH4HF2, a liquid-solid ratio of 30:1, a reaction temperature of 30 °C and a reaction time of 120 min, and the leaching efficiency of uranium from the residue was as high as 98.95%. The leaching kinetics of uranium by NH4HF2 were consistent with the mixed controlled model in the shrinking core models, indicating that the surface chemical reaction and mass diffusion dominated both uranium leaching processes. This may provide a viable method for resource recovery and the treatment of uranium purification residues.

Investigating the electronic states of UTe2 using X-ray spectroscopy

The recent discovery of superconductivity in paramagnetic UTe2 turns spotlight on a serious candidate for spin-triplet state. To draw a complete picture of the superconducting state in UTe2 precise knowledge of the electronic properties of the 5 f states of Uranium is missing. We report on x-ray absorption and magnetic circular dichroism experiments performed at the U M4,5 edges at 2.7 K. At ambient pressure the 5 f electron count is found to be in-between 2.6 and 2.8. Partial delocalization of the 5 f electrons is further confirmed by the reduced value of the U orbital to spin magnetic moment ratio. The 5 f count is reduced by as large as 7 percent at the transition to a magnetically ordered state at Pc ≈ 1.5 GPa. At pressures above 4 GPa, the 5 f count increases back towards U3+ in the tetragonal phase. The observed “valence instabilities” and their interplay with magnetism seem to be important ingredients to understand the electronic structure in UTe2 in different phases.

Forms of Uranium Presence in Soil on the Territory of the Sublimate Shop at AEKhK AO

Integrated study of the physicochemical state of uranium in radioactively contaminated soils of the sublimate shop of Angara electrolysis chemical combine AO (SS AEKhK AO). According to the X-ray absorption spectroscopy, the predominant form of uranium is (UVIO2)2+ in all the soil samples studied. The scanning electron microscopy combined with X-ray fluorescence microanalysis was used to characterize the composition and morphology of uranium-containing particles with sizes of fractions to several tens of micrometers everywhere occurring in the soils. It was shown that the predominant fractions of accessible uranium in the soils are the “carbonate” fraction (40–60%) and that associated with Fe/Mn oxides. A considerable part of uranium is bound to clayey minerals. Data on the forms of uranium were used to develop a technology for purification of the radioactively contaminated soil by the method of hydroseparation with reagent processing of the isolated target fraction.

Electronic and Magnetic Structures, Magnetic Hyperfine Fields and Electric Field Gradients in UX3 (X = In, Tl, Pb) Intermetallic Compounds

Cubic uranium compounds such as UX3 (X is a non-transition element of groups IIIA or IVA) exhibit highly diverse magnetic properties, including Pauli paramagnetism, spin fluctuation and anti-ferromagnetism. In the present paper, we explore the structural, electronic and magnetic properties as well as the hyperfine fields (HFFs) and electric field gradients (EFGs) with quadrupole coupling constant of UX3 (X = In, Tl, Pb) compounds using local density approximation, Perdew–Burke–Ernzerhof parametrization of generalized gradient approximation (PBE-GGA) including the Hubbard U parameter (GGA + U), a revised version of PBE-GGA that improves equilibrium properties of densely packed solids and their surfaces (PBEsol-GGA), and a hybrid functional (HF-PBEsol). The spin orbit-coupling calculations have been added to investigate the relativistic effect of electrons in these materials. The comparison between the experimental parameters and our calculated structural parameters we confirm the consistency and effectiveness of our theoretical tools. The computed magnetic moments show that magnetic moment increases from indium to lead in the UX3 family, and all these compounds are antiferromagnetic in nature. The EFGs and HFFs, as well as the quadrupole coupling constant of UX3 (X = In, Tl, Pb), are discussed in detail. These properties primarily originate from f and p states of uranium and post-transition sites.

Physicochemical transformations in multicomponent melts containing uranium, zirconium, and iron oxides and calcium silicates and aluminates

The properties and crystallization nature of melts of the U4+–U6+–Zr4+–Fe2+–Fe3+–Ca2+–Si4+–Al3+–O2– system were studied. It was found that the main factors changing the physicochemical characteristics of the melt are the concentration and valence state of uranium and the concentrations of iron oxide and silicon oxide. The results obtained in the analysis of the physicochemical properties of the multicomponent melt can be used in nuclear power engineering to preclude disintegration of a WWER type nuclear reactor in the course of a hypothetical severe reactor accident.

Structure and hydrolytic durability of a glass containing waste from spent tributyl phosphate reprocessing

The structure of the glass obtained by incorporation of the residue from reprocessing of the spent extractant, tributyl phosphate, into sodium aluminophosphate glass and the structural state of uranium in this glass were studied by vibration (IR, Raman) and X-ray absorption (XAFS) spectroscopy. An IR and Raman spectroscopic study shows that the structural network of the glasses is formed by ortho- and pyrophosphate groups linked by tetrahedral AlO4 units. As follows from the XAFS data, uranium is present in the glass in the form of uranyl ions and of separate UO2+x particles. The glass has high hydrolytic durability: The uranium leach rate determined in accordance with GOST (State Standard) R 52 126–2003 is of the order of 10–8 g cm–2 day–1.

Estimation of the oxidation state of uranium in microparticles by using scanning electron microscope in the backscattered electrons mode

This paper considers the results of applying of scanning electron microscopes in the backscattered electron mode for the specifying of the contents of multielemental samples and minerals, which are presented in publications. This approach is used for estimation of oxidation state of uranium in microparticles. The possibility of this goal achieving is demonstrated on the example of the analysis of the UO2 and U3O8 microparticles and the samples of In, Sn, Pt and Pb.

Studies on Some Dioxouranium(VI) Complexes with Dithiocarbamate Ligands

A number of dioxouranium(VI) complexes of some monobasic biden- tate dithiocarbamate(dtc) ligands have been synthesized. Monobasic bidentate dithiocarbamate ligands were prepared by the reaction of 1:1 molar ratio of ethylenediamine, N,N-dimethylethylenediamine, N,N-diethylethylenediamine, 1,3-propanediamine, N,N-dibutyl-tri-methylenediamine, 1,6-hexanediamine with carbondisulphide. Physico-chemical analytical, e.g. elemental analysis, IR Spectral data suggest the formation of (UO 2 L 2 ) type complexes. The molar conductance values obtained for a number of complexes indicate the non-elec- trolytic nature of the complexes. The magnetic and electronic spectral studies of the prepared complexes indicate the presence of the 5f 0 6d 0 7s 0 electronic configuration characteristic of the 6+ oxidation state of uranium.

ChemInform Abstract: New Reactivity of the Uranyl(VI) Ion

AbstractReview: 117 refs.

Imaging the Formation of High-Energy Dispersion Anomalies in the ActinideUCoGa5

We use angle-resolved photoemission spectroscopy (ARPES) to image the emergence of substaintial dispersion anomalies in the electronic renormalization of the actinide compound UCoGa$_5$ which was presumed to belong to a conventional Fermi liquid family. Kinks or abrupt breaks in the slope of the quasiparticle dispersion are detected both at low ($\sim$130 meV) and high ($\sim$1 eV) binding energies below the Fermi energy, ruling out any significant contribution of phonons. We perform numerical calculations to demonstrate that the anomalies are adequately described by coupling between itinerant fermions and spin fluctuations arising from the particle-hole continuum of the spin-orbit split $5f$ states of uranium. These anomalies are resemble the `waterfall' phenomenon of the high-temperature copper-oxide superconductors, suggesting that spin fluctuations are a generic route toward multiform electronic phases in correlated materials as different as high-temperature superconductors and actinides.

Radiogenic uranium in paragenetic mineral associations

Isotope composition of U in minerals of two mineral associations based on aeschynite and pyrochlore was studied. Although the ratio of U isotopes in the mineral associations as a whole is equilibrium (or close to equilibrium), the distribution of the radiogenic 234U isotope between separate parts of these associations is essentially nonuniform. Two models of the disturbance of the radioactive equilibrium are discussed: dependence of the 234U/238U ratio on the U concentration in the mineral (Adloff-Roessler model) and transfer of 234Th recoil atoms from one phase to another (Sheng-Kuroda model). It is impossible within the framework of any of the models to consistently account for the observed distribution of the radiogenic U between different mineral phases. For the quasi-closed mineral system based on aeschynite, a model of the redistribution of the radiogenic U under the action of natural solutions mainly within the mineral association is suggested; for the open system involving pyrochlore, the effects of natural leaching are explained taking into account the valence and chemical state of uranium in the minerals.

ChemInform Abstract: “Programme of Natural Analogues Studies” and Identification of the Chemical State of Uranium in Natural Substances

ChemInform Abstract: “Programme of Natural Analogues Studies” and Identification of the Chemical State of Uranium in Natural Substances

The state of natural radionuclides of uranium, radium, and thorium in soils

A review of publications is presented on the state of uranium, radium, and thorium in soils. It is shown that the properties of radionuclides in soils provide the diversity of the forms and mechanisms of their fixation in the soil exchange complex. Organic substances and clay minerals are the most important sorbents of uranium, radium, and thorium. According to the available data, the processes of ion exchange, complexing, hydrolysis, and reduction-oxidation are responsible for the uranium and thorium fixation in soils. For radium, the ion exchange and coprecipitation with its chemical macro analogs and iron hydroxides are considered to be the most important. The initial chemical form of the elements and the presence of macrocomponents affect the sorption behavior of radionuclides from technogenic sources. It is emphasized that the current methods of investigation do not allow assessing in full measure the transformation of the forms and the mechanisms of uranium, radium, and thorium fixation in soils. The causes are presented that make the interpretation of the results obtained difficult.

Association of Actinides with Microorganisms and Clay: Implications for Radionuclide Migration from Waste-Repository Sites

We conducted a series of basic studies on the microbial accumulation of actinides to elucidate their migration behavior around backfill materials used in the geological disposal of radioactive wastes. We explored the interactions of U(VI) and Pu(VI) with Bacillus subtilis, kaolinite clay, and within a mixture of the two, directly analyzing their association with the bacterium in the mixture by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The accumulation of U by the mixture rose as the numbers of B. subtilis cells increased. Treating the kaolinite with potassium acetate (CH 3 COOK) removed approximately 80% of the associated uranium while only 65% was removed in the presence of B. subtilis. TEM-EDS analysis confirmed that most of the U taken from solution was associated with B. subtilis. XANES analyses revealed that the oxidation state of uranium associated with B. subtilis, kaolinite, and with the mixture containing both was U(VI). The amount of Pu sorbed by B. subtilis increased with time, but did not reach equilibrium in 48 h; in kaolinite alone, equilibrium was attained within 8 h. After 48 h, the oxidation state of Pu in the solutions exposed to B. subtilis and to the mixture had changed to Pu(V), whereas the oxidation state of the Pu associated with both was Pu(IV). In contrast, there was no change in the oxidation state of Pu in the solution nor on kaolinite after exposure to Pu(VI). SEM-EDS analysis indicated that most of the Pu in the mixture was associated with the bacteria. These results suggest that U(VI) and Pu(VI) preferentially are sorbed to bacterial cells in the presence of kaolinite clay, and that the mechanism of accumulation of U and Pu differs. U(VI) is sorbed directly to the bacterial cells, whereas Pu(VI) first is reduced to Pu(V) and then to Pu(IV), and the latter is associated with the cells. These results have important implications on the migrations of radionuclides around the repository sites of geological disposal. Microbial cells compete with clay colloids for radionuclides accumulation, and because of their higher affinity and larger size, the microbes accumulate radionuclides and migrate much slower than do the clay colloids. Additionally, biofilm coatings formed on the fractured rock surfaces also accumulate radionuclides, thereby retarding radionuclide migration.

Investigations on the solubility of corrosion products on depleted uranium projectiles by simulated body fluids and the consequences on dose assessment

Ingestion and inhalation of corrosion products covering weathered penetrators made of depleted uranium (DU) represent potential radiological exposure pathways. In order to study the bioavailability of these corrosion products, their solubility was determined using simulated gastric and pulmonary juices. About 75 and 36% of the uranium in the corrosion products were found to be soluble in simulated gastric and pulmonary juices, respectively. The effective dose coefficient for adults after ingestion was calculated to be 0.61 muSv mg(-1) DU. This compares to an effective dose coefficient for an adult of 0.71 muSv mg(-1) for DU materials given by the World Health Organization (WHO). The effective dose coefficient for inhalation was calculated to be 3.7 x 10(-6 )Sv Bq(-1) for workers and 5.3 x 10(-6 )Sv Bq(-1) for members of the public, respectively, which is between those of particles of Types M and S as defined by the International Commission on Radiological Protection (ICRP). The speciation of the corrosion products was investigated by time-of-flight secondary ion mass spectrometry (TOF-SIMS). The mean oxidation state of uranium was found to be 4.6, which suggests that the uranium in the corrosion products consists of a mixture of U(IV) and U(VI) species.

EXTECH IV: Geology and Uranium EXploration TECHnology of the Proterozoic Athabasca Basin, Saskatchewan and Alberta.: C. W. JEFFERSON and G. DELANEY, Editors. Geological Survey of Canada Bulletin 588, Saskatchewan Geological Society Special Publication 18, and Mineral Deposits Division of the Geological Association of Canada Special Publication 4. 645 Pp. 2007. Report and CD-ROM. ISBN 978-0-660-19492-9. Price Can$70 in Canada; Can$91

The Mineral Deposits Division of the Geological Association of Canada, the Geological Survey of Canada, the Saskatchewan Geological Society, and, in particular, the editors of this volume (Jefferson and Delaney) are to be congratulated on their efforts and timing to bring together the research results of EXTECH IV at a time of dramatic resurgence in global uranium exploration. So often the final published results of interagency multidisciplinary projects of this magnitude languish for years after termination of their funding and in the end the outcomes are typically dispersed as graduate theses archived in universities and as individual papers submitted across a variety of geoscience journals. To have brought together the results of this four-year-long interagency, multidisciplinary study so quickly and thoroughly after the termination of the EXTECH IV funding is a significant accomplishment by the sponsoring agencies and the editors. To set the stage for the importance of this volume, a little background on the state of uranium within the geologic community probably is required. Since the early 1980s, uranium exploration has been in the doldrums, with the spot price for uranium dropping below US$9 per lb by the mid-1990s and exploration expenditures nearly dropping off the radar screen in terms of overall global exploration. It is only in the last few years that uranium prices have seen dramatic increases exceeding US$130 per lb by mid-2007. Prior to this recent surge in the price of uranium, it is not surprising that the wider geologic community and academia had largely neglected research on uranium deposits and their environs during the past 25 years. Nevertheless, a few research centers, funded through collaborations with the rather small fraternity of uranium explorers, kept the flame of research going during this period. These results have been typically held as proprietary by the companies or dispersed …

Computational Investigation of the Formation of Hyperstoichiometric Uranium Dioxide (UO2+x)

AbstractThe stability of spent nuclear fuel as a waste form largely depends upon the oxidation behavior of uranium dioxide (UO2) under repository conditions. Because U6+ phases are more soluble than U4+ phases, and changes in oxidation state can lead to volume changes which increase the susceptibility of spent fuel to corrosion, understanding the mechanisms behind the formation of more highly oxidized UO2 phases is important. While a variety of diffraction and spectroscopic studies have been used to investigate the oxidation behavior of UO2 to U4O9, questions still remain as to the effect of interstitial oxygen on the oxidation state of uranium in hyperstoichiometric UO2. In this study, computational techniques were used to investigate questions such as: Is the formation of U5+ or U6+ more energetically favorable upon the oxidation of UO2A density functional theory (DFT) approach was used to investigate energetically favorable locations of interstitial oxygen atoms and to determine their effect on the charge distribution of uranium in U4O9, specifically. A single unit cell of U4O9 is used as a starting model, and the optimized geometry and charge distribution is tested by using starting models with different U charge assignments. Results from our calculations suggest that the formation of one U5+ per addition of interstitial oxygen at a perpendicular bisector site is favorable. Deflection of two lattice oxygen atoms along the body diagonal of the cubic sites is also observed upon the addition of one interstitial oxygen atom. Structural and bond length data are compared with experimental data whenever possible.

Electronic properties of UNi2Si2 intermetallic compound

The uranium ternary compound UNi2Si2 was studied using the magneto-optical Kerr effect, optical reflectivity at near normal incidence, and spectroscopic ellipsometry. The compound UNi2Si2 exhibited metallic behavior, however, with only small contribution of free carriers to the optical conductivity. The strong interband transitions originating from the f states to higher empty d states of uranium were observed to extend to low photon energies.

Electronic structure, magnetic, and transport studies of single-crystallineUCoGa5

The magnetic susceptibility, electrical resistivity in zero and in magnetic fields up to $8\phantom{\rule{0.3em}{0ex}}\mathrm{T}$, thermopower and thermal conductivity measurements in a wide temperature range have been performed on ${\mathrm{UCoGa}}_{5}$ single crystals. On the basis of the susceptibility maximum at $650\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and the phonon part of the thermal conductivity, a mixed-valence state of uranium in this compound has been postulated. On the other hand, a normal positive behavior of magnetoresistivity rules out the possibility of spin fluctuation as a mechanism driving the susceptibility through the maximum. In turn, the thermopower results may support both kinds of many-body behaviors. The electronic structure has also been studied by combining x-ray photoemission spectroscopy results with those obtained in the band structure calculations. In the latter the tight-binding linear muffin-tin orbital method in the atomic sphere approximation has been applied. A very good agreement between the experimental and calculated data has been achieved. A complex satellite structure of the core level spectra supports an idea of the presence of the valence instability in this compound. This idea is also concluded from the comparison of obtained experimental data with some similar rare earth and uranium ternary compounds.

Resonant Inelastic Soft X-ray Scattering Studies of U(VI) Reduction on Iron Surfaces

ABSTRACTWe report on the spectroscopic analysis of several samples relevant to the processes governing the behavior of oxidized uranium species in groundwater solutions under anoxic conditions. Both Fe samples with different times of exposure to the U(IV) solution and Fe metal-solution inetrfaces in the liquid cell ex-situ and in-situ, respectively. Resonant inelastic soft x-ray scattering is shown to be sensitive to the chemical state of uranium. The measurements were performed at a number of energies of the primary photon beam across the U 5d absorption edge. The results unambiguously indicate the reduction of U(VI) to U(IV) on the Fe surface.