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A tetravalent uranium compound with a radical azobenzene ligand, namely, [{(SiMe2NPh)3-tacn}UIV(η2-N2Ph2.)] ( 2), was obtained by one-electron reduction of azobenzene by the trivalent uranium compound [UIII{(SiMe2NPh)3-tacn}] ( 1). Compound 2 was characterized by single-crystal X-ray diffraction and 1H NMR, IR, and UV/Vis/NIR spectroscopy. The magnetic properties of 2 and precursor 1 were studied by static magnetization and ac susceptibility measurements, which for the former revealed single-molecule magnet behaviour for the first time in a mononuclear UIV compound, whereas trivalent uranium compound 1 does not exhibit slow relaxation of the magnetization at low temperatures. A first approximation to the magnetic behaviour of these compounds was attempted by combining an effective electrostatic model with a phenomenological approach using the full single-ion Hamiltonian. [ABSTRACT FROM AUTHOR]

The ex-situ qualitative study of the kinetic formation of the poly-oxo cluster U38, has been investigated after the solvothermal reaction. The resulting products have been characterized by means of powder XRD and scanning electron microscopy (SEM) for the solid phase and UV/Vis, X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), and NMR spectroscopies for the supernatant liquid phase. The analysis of the different synthesis batches, stopped at different reaction times, revealed the formation of spherical crystallites of UO2 from t=3 h, after the formation of unknown solid phases at an early stage. The crystallization of U38 occurred from t=4 h at the expense of UO2, and is completed after t=8 h. Starting from pure uranium(IV) species in solution ( t=0-1 h), oxidation reactions are observed with a UIV/UVI ratio of 70:30 for t=1-3 h. Then, the ratio is inversed with a UIV/UVI ratio of 25/75, when the precipitation of UO2 occurs. Thorough SEM observations of the U38 crystallites showed that the UO2 aggregates are embedded within. This may indicate that UO2 acts as reservoir of uranium(IV), for the formation of U38, stabilized by benzoate and THF ligands. During the early stages of the U38 crystallization, a transient crystallized phase appeared at t=4 h. Its crystal structure revealed a new dodecanuclear moiety (U12), based on the inner hexanuclear core of {U6O8} type, decorated by three additional pairs of dinuclear U2 units. The U12 motif is stabilized by benzoate, oxalates, and glycolate ligands. [ABSTRACT FROM AUTHOR]

The ex-situ qualitative study of the kinetic formation of the poly-oxo cluster U38, has been investigated after the solvothermal reaction. The resulting products have been characterized by means of powder XRD and scanning electron microscopy (SEM) for the solid phase and UV/Vis, X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), and NMR spectroscopies for the supernatant liquid phase. The analysis of the different synthesis batches, stopped at different reaction times, revealed the formation of spherical crystallites of UO2 from t=3 h, after the formation of unknown solid phases at an early stage. The crystallization of U38 occurred from t=4 h at the expense of UO2, and is completed after t=8 h. Starting from pure uranium(IV) species in solution ( t=0-1 h), oxidation reactions are observed with a UIV/UVI ratio of 70:30 for t=1-3 h. Then, the ratio is inversed with a UIV/UVI ratio of 25/75, when the precipitation of UO2 occurs. Thorough SEM observations of the U38 crystallites showed that the UO2 aggregates are embedded within. This may indicate that UO2 acts as reservoir of uranium(IV), for the formation of U38, stabilized by benzoate and THF ligands. During the early stages of the U38 crystallization, a transient crystallized phase appeared at t=4 h. Its crystal structure revealed a new dodecanuclear moiety (U12), based on the inner hexanuclear core of {U6O8} type, decorated by three additional pairs of dinuclear U2 units. The U12 motif is stabilized by benzoate, oxalates, and glycolate ligands. [ABSTRACT FROM AUTHOR]

Here we present a nuclear forensic study of uranium from German nuclear projects which used different geometries of metallic uranium fuel.,, Through measurement of the 230Th/234U ratio, we could determine that the material had been produced in the period from 1940 to 1943. To determine the geographical origin of the uranium, the rare-earth-element content and the 87Sr/86Sr ratio were measured. The results provide evidence that the uranium was mined in the Czech Republic. Trace amounts of 236U and 239Pu were detected at the level of their natural abundance, which indicates that the uranium fuel was not exposed to any major neutron fluence. [ABSTRACT FROM AUTHOR]

Strontium borophosphate (SrBPO 5 ) with and without uranium doped samples were synthesized through solid state reaction route in air atmosphere at different annealing temperatures. The dopant ion concentration was varied between 1 and 8 mol%. X-ray diffraction studies confirmed the formation of single phase compound in all the samples without any impurity phase up to 8 mol% of the dopant ion. The overall morphology and particle size was confirmed by scanning electron microscopic studies which suggested the presence of uneven, agglomerated particles with less than 1 µm individual size. It was observed that upon annealing at higher temperatures, the particles get agglomerated more and more with smooth boundaries. Photoluminescence (PL) studies confirmed stabilization of uranium as uranyl ion ( UO 2 2 + ) in the system. Based on the PL emission data concentration quenching was observed beyond 7 mol% of the dopant ion concentration. The critical distance ( L c ) was estimated to be 3 Å suggesting Dexter type of energy transfer mechanism responsible for the quenching. The life time decay studies indicated the presence of two different types of environment around Uranyl ion. On annealing at temperatures beyond 900 °C the PL emission and decay time reduced drastically. It was concluded that on annealing at temperatures beyond 900 °C, defect centres get agglomerated around the metal ion providing non radiative pathways for the energy to get dissipated thereby reducing the PL emission and decay time. Color coordinates were evaluated for the 7 mol% uranium doped sample annealed at 900 °C. The values suggested that the system can be used as a potential green emitting phosphor material. [ABSTRACT FROM AUTHOR]

The results regarding uranium (U) and rhenium (Re) sorption from solutions containing both metals by AN-21 weakly basic anion exchange resin are presented in this article. The effects of the salt forms (sulphate, chloride, nitrate, hydroxide), the nature of the sulphate, nitrate, and chloride compounds (acids, sodium and zinc salts), and the carbonates at concentrations of 1 to 1000 mol/m3were studied under static conditions. It was determined that rhenium from different solutions is well-sorbed by the salt forms and poorly sorbed by the hydrate forms. The nitrate and chloride compounds reduce rhenium sorption when their concentration is increased in contrast to the behaviour exhibited by the sulphate compounds. Uranium is well-sorbed by sulphate form of weakly basic anion exchange resin but only from sulphate solutions and dilute carbonate solutions. The different sorption characteristics of the metals were explained by considering their ionic states in the solutions. [ABSTRACT FROM AUTHOR]

We report the synthesis and structural determination of three uranium(IV) complexes bearing two, four, and six salicylaldiminate ligands. Reaction of UI4(1,4-dioxane)2with two, four, and six equivalents of K[OC6H4C(H)=N(2,6-iPr2C6H3)],1, yielded [(2,6-iPr2C6H3)N=C(H)C6H4O-κ2(O,N)]2UI2(NCCH3),2, [(2,6-iPr2C6H3)N=C(H)C6H4O-κ1(O)]2[(2,6-iPr2C6H3)N=C(H)C6H4O-κ2(O,N)]2U(THF),3, and {[2,6-iPr2C6H3)N=C(H)C6H4O-κ1(O)]6U}2−,4. While2shows normalκ2-coordination through both oxygen and nitrogen donors,3has two salicylaldiminate ligands bound only through oxygen and4has all six ligands bound only through oxygen. This is an exceedingly rare example of a chelating ligand not completing its chelation in f-element chemistry. In addition,4is the first report of a homoleptic octahedral actinide complex with a Schiff base ligand. [ABSTRACT FROM AUTHOR]

UNiZn is the first Zn containing U TX ternary with the ZrNiAl structure type. Zn is smaller than other p -metals (Al, Ga, Sn, In) forming this type of structure. This compound can be seen as analogous to UNiAl and UNiGa, but the small X ligand leads to a non-magnetic ground state with moderately enhanced Sommerfeld coefficient γ = 100 mJ/mol K 2 . H absorption leads to analogous effects (amount of hydrogen absorbed, crystal structure changed) as in UNiAlH 2.3 , in which the ordering temperature increases. UNiZnH 2.3 exhibits antiferromagnetic order below the Néel temperature T N = 55 K. [ABSTRACT FROM AUTHOR]

The extraction of uranium from seawater and the safe treatment of wastewater containing uranium (VI) were important to ensure the sustainable development of nuclear-related energy sources. Two-dimensional silica nanomaterials have been extensively investigated in the field of uranium adsorption due to their high adsorption capacity, short equilibration times, and easily modified surface groups. However, the two-dimensional mesoporous silica nanomaterial preparation has become a challenge due to the lack of natural sheet templating agents. The reason will hinder the development of silica nanomaterials for uranium extraction. Here, the specific surface area silica nanomeshes (HSMSMs) uranium adsorbent was prepared by a high shear method to induce nanobubble formation. HSMSMs showed a high uranium adsorption capacity of 822 mg -U /g -abs in seawater with the uranium adsorption concentration was 50 mg/L, which was approximately 2 times higher than the conventional mesoporous silica nanomaterials. Compared to HSMSMs, the amidoxime-modified high specific surface area silica nanomesh (HSMSMs-AO) demonstrated good selectivity for U(VI), and the uranium ions uptake was 877 mg -U /g -abs in 50 mg/L uranium-spiked simulated seawater. Due to HSMSMs-AO's stable chemical properties and high mechanical strength, HSMSMs-AO also displayed long service life. Benefiting from the simple preparation method and high adsorption capacity of HSMSMs, HSMSMs could be a promising candidate for large-scale extraction of uranium from seawater. [Display omitted] • The high specific surface area mesoporous SiO 2 nano-meshes (HSMSMs) were facilely prepared via high shear mixer. • The high surface area and abundant accessible sites of HSMSM/HSMSM-AO benefited for U adsorption. • HSMSM-AO exhibits very high uranium extraction capability and selectivity. • Green and economy HSMSMs are promising in industrial uranium extraction. [ABSTRACT FROM AUTHOR]

[Display omitted] • The HWB-AO adsorbent was a porous, processable and non-biologically toxic monolith. • The HWB-AO exhibited high selectivity and long service life. • The adsorption capacity for uranium was 256.4 mg g−1 at pH = 6. Uranium is not only toxic and radioactive, even more an important resource to ensure the nuclear energy development. This work reported an amidoxime-based hyper-crosslinked polymeric resin adsorbent (HWB-AO) to extract uranium from ocean. The monolithic matrix was prepared by suspension polymerization using styrene (St) and divinylbenzene (DVB), followed by post-polymerization modification to graft diaminomaleonitrile (DAMN) and conduct amidoximation to introduce amidoxime groups (AO) in its interior and surface. AO can enhance the affinity to uranium and hydrophilicity to accelerate the uranium adsorption. The monolithic structure overcome the problem that powder adsorbent is easy to drain in real seawater, so the monolithic is easier to apply. The batch adsorption experiments results showed that HWB-AO has an magnificent uranium removal rate (85%) and the maximum adsorption capacity (q e,max) is 256.4 mg g−1. In addition, HWB-AO still maintains a giant adsorption efficiency after eight times adsorption–desorption cycles and is environmentally friendly. Concurrently, HWB-AO exhibits excellent selectivity and removal rate (greater than88%) in modified seawater. Therefore, HWB-AO is considered as a potential adsorbent to perform uranium extraction from natural seawater. [ABSTRACT FROM AUTHOR]

• Air oxidation of chemically inert IMCs (intermetallic compounds) of uranium and noble metals UM 3 (M = Ru, Rh, Pd) - potential components of nitride SNF (spent nuclear fuel), has been studied. • Upon IMC oxidation uranium converts to U 3 O 8 , noble metals to PdO, RuO 2 and Rh 2 UO 6 , respectively. • Complete oxidation of IMCs occurs in the temperature range 800–1200 °C, its mechanism is determined by the properties of the noble metal in the alloy composition. • It is advisable to reprocess investigated IMCs as part of SNF using volume oxidation (voloxidation) at temperatures above 1200 °C. Mixed uranium and plutonium nitride (U,Pu)N is a promising candidate fuel for fast reactors. Fission of U and Pu during reactor operation is accompanied by the formation of chemically inert compounds of uranium and noble metals - intermetallides (IMCs) with the general formula UM 3 (M = Ru, Rh, Pd). One of possible steps in reprocessing of spent nitride nuclear fuel is voloxidation - oxidation in an oxygen-containing environment aimed at removal of gaseous components of SNF. In contrast to well-studied oxidation of uranium nitride in air at high temperatures, the oxidation of intermetallic compounds of uranium and noble metals has not been studied in sufficient detail. In the present work, it is shown that UM 3 (M = Ru, Rh, Pd) IMCs are completely oxidized in the temperature range 800–1200 °C. UPd 3 and URu 3 oxidation leads to the formation of U 3 O 8 , PdO and RuO 2. Upon oxidation of URh 3 , the formation of an intermediate phase Rh 2 UO 6 is observed; upon further heating, it decomposes into U 3 O 8 and metallic Rh. It is shown that peculiarities of oxidation of the studied IMCs are determined by reactivities of relevant noble metals with respect to oxygen. This study demonstrates that voloxidation of IMCs from nitride SNF should be performed at temperatures above 1200 °C. [ABSTRACT FROM AUTHOR]

The present work examines the effect of surface geometry on the reaction between hydrogen gas and uranium metal, forming uranium hydride (UH 3 ), a pyrophoric compound of significance to the civil nuclear industry. Hydride formation was initiated on uranium samples that had been patterned with a focused ion beam instrument to form surface arrays of triangular prisms and pillars with differing apex angles. Post reaction analysis indicated preferential hydride formation at the apex of these features. Additionally, once hydride formation had commenced the observed growth rate on the prisms appeared to accelerate in comparison to the rate exhibited on the surrounding surface. [ABSTRACT FROM AUTHOR]

UV–VIS spectra of uranium ions provided information not only on the electronic state of U(III)–Cl and U(IV)–Cl species, but also on the metal–ligand bonding properties. The 5f – 6d transition lines in the electronic absorption spectra of U(III) and U(IV) provided key information on the covalent bonding properties of U(III)–Cl and U(IV)–Cl complexes. The position and intensities of 5f – 6d and 5f – f5 transitions varied depending on the oxidation state and bonding properties. The 5f – 6d transitions of U(III) ion occur at a lower energy of as low as the 400–600 nm range with decreased intensity. However, U(IV) ions occur at the much higher ~ 250 nm range. The 5f – 6d / 5f – 5f intensity ratio indicated the degree of covalency. The U(III)–Cl species exhibited stronger covalent bonding than the U(IV)–Cl. This means that U(III)–Cl bonding is stronger than U(IV)–Cl species. Compared with uranium ions, Eu(II) ion showed no measurable covalent bonding under the same conditions, which means that Eu(II)–Cl bonding is predominantly ionic in nature. The bond strength (covalency) was evaluated in the order of U(III)–Cl > U(IV)–Cl ≫ Eu(II)–Cl. The reduction rate of U(IV) is ~ 4 times faster than that of the oxidation of U(III), indicating that U(III)–Cl is more stable than U(IV)–Cl species. The UV–VIS spectral analysis method may also be effective in investigating the bonding properties of neptunium and plutonium ions with chloride ligands in molten salt media. [ABSTRACT FROM AUTHOR]

800 L washing-electrokinetic soil separation equipment was manufactured to decontaminate uranium contaminated soils from Korean nuclear facilities. For the removal of uranium at more than 95% from radioactive soil through soil washing-electrokinetic technology, several decontamination experiments were carried out. For a reduction of the generation of large quantities of metal oxides in a cathode, a pH controller is used to control the pH of the electrolyte solution between 0.5 and 1.0 for the formation of UO 2+ . More than 60% metal oxides were removed through pre-washing, an electrolyte solution was circulated by a pump, and a metal oxide separator filtered the metal oxide particles. 60–65% of the uranium was removed from the soil by soil washing as a part of the pre-treatment. When the initial 238 U concentration of the soil was 22.2 Bq/g, the required electrokinetic separation time for the removal of below the clearance 238 U concentration of 0.4 Bq/g was 35 days, and the generated electrolyte solution rate was 1.4 ml/g. When the initial concentration of 238 U in the soil was higher, a longer decontamination time was needed, but the removal rate of 238 U from the soil was higher. [ABSTRACT FROM AUTHOR]

The effect of concentration of U(VI), hydrazine, nitric acid and the amount of catalyst, and the thermodynamics and kinetics of the reaction in preparing U(IV) by catalyzing and reducing U(VI) are studied in catalytic reduction of U(VI) with hydrazine as reductant and Pt as catalyst. The comparison of calculated theoretical reaction heat value and practical value is also given. The result shows that with the increase of density of U(VI) and hydrazine, increase of amount of catalyst and decrease of nitric acid, reaction rate slows down. The reaction kinetic rate equation is as follow: − d C(UO22+)/d t = kC1.11(UO22+) C1.42(N2H5+) C−0.72(H+), and the reaction rate constant is 1.3 · 10 -3 (mol/L) -0.81/min when rS/L is 0.008 kg/L at 50 ℃. The theoretical reaction equation of unit volume is as follows: Q = aΔf Hm,1 Θ + Δf Hm,2 Θ[ C(N2H4) − C(UO22+) a/2 − β]/3. The comparison shows the coincidence in 1 h of theoretical value and practical value. [ABSTRACT FROM AUTHOR]

One of the main problems faced at the Allouga uranium project during the recovery of uranium was the presence of high chloride content in the uranium mineralization that ranged between 6 and 8%. It was necessary to remove the chloride by washing the uranium-bearing material several times with freshwater. This procedure used a large amount of water and the washed pregnant solution contained higher than 12 g/l of chloride and 10 mg/l of U(VI). The obtained solution had to be kept in vats and tanks which presented environmental problems due to the inability of quaternary amine resins such as D263B (Chinese resin which is considered to be the most suitable tool for uranium recovery) to extract the solution containing high chloride. Synthetic acrylamidoxime and hydrazinyl amine resins were used on polyethylene non-woven fibers, followed by Fourier transform infrared spectroscopy, SEM, and elemental analysis. The synthetic resins have a chelating site for theand exhibited a very high capacity for metal sorption. It seems that this synthetic resin has 1,000 times higher rate of adsorption than D263B. This was due to its high affinity for U(VI) and low affinity for chloride. [ABSTRACT FROM AUTHOR]

The gas phase reaction of U atom with water molecule was investigated by means of the density functional theory calculations. Taking different possible spin states into account, a close description of the reaction mechanisms is presented. The nature of the chemical bonding evolution was investigated using diverse topological analyses including electron localization function and atoms in molecules. [ABSTRACT FROM AUTHOR]

The mesoporous silica SBA-15 with short channels was prepared and added into the solution of polyvinyl chloride (PVC) to form the SBA-15-PVC membrane via the phase-inversion process. Under the optimized preparation conditions with 5 (wt%) of SBA-15 and 10 (wt%) of PVC, the adsorption capacity of uranium(VI) can reach 2,519.8 mg/m at pH 6. Nine repeated adsorption-desorption cycles were carried out, and the adsorption capacity is almost kept the same in the last eight cycles. Therefore, SBA-15-PVC membrane could be as a promising adsorbent for uranium(VI) from aqueous solutions with large adsorption capacity and reusability. [ABSTRACT FROM AUTHOR]

The use of a polymeric sorbent material embedded with oleic acid coated magnetic particles as selective sorbents for the removal of U(VI) ions from industrial waste effluents was studied. In the presence of other competing ions [Th(IV) and Ni(II)], U(VI) was preferentially adsorbed. Inclusion of nano-magnetic particles in the polymer matrix aided the separation of the sorbents from aqueous solutions by application of external magnetic field. High recoveries indicated that the sorbent is suitable for application in contaminated water. [ABSTRACT FROM AUTHOR]

A measurement technique enabling the determination of low uranium concentration utilizing system used for time resolved laser induced fluorescence spectroscopy (TRLFS), based on a commercially available kinetic phosphorescence analysis method has been developed. The effect of the matrix, complexing agent, and the level of acidification on the fluorescence spectra and integral intensity was studied. The method is highly influenced by the sample matrix; particularly if different starting uranium salts are in the calibration solutions and in the samples. In the initial study of these effects, TRLFS measurements have been used in order to clarify this behavior. [ABSTRACT FROM AUTHOR]

For the determination of uranium in contaminated sea sand samples by alpha-spectroscopy, we have investigated the applicability of different pre-analytical procedures. The direct electrodeposition after acidic dissolution of uranium from sea sand particles can be successfully applied only to relatively pure silica sands. Analysis of uranium in sand samples containing increased amounts of limestone and iron minerals requires the additional liquid-liquid extraction step to separate uranium from iron and calcium. The overall efficiency of the proposed method is above 70 % and the detection limit of alpha-spectroscopy is 70 Bq kg. [ABSTRACT FROM AUTHOR]

Distribution of rare earth elements (REEs), thorium and uranium in 54 marine sediments collected from five selected areas along the Gulf of Thailand is discussed in this paper. These areas have been selected as potential sites to set up thermal and nuclear power plants. Concentration of elements was determined using inductively coupled plasma mass spectrometry (ICP-MS). Absolute concentrations of REEs, Th and U show a sample-to-sample variation and may be due to different geological characteristic of area as well as grain size effect. Total REE concentrations (not including Y) range between 9.4 and 206 μg/g. The chondrite-normalized REE patterns of all samples are similar to Post-Archean Australian Shale (PAAS) and average Upper Continental Crust, with LREEs' enrichment relative to HREEs (La/Yb = 6.5-29), fairly flat HREEs' patterns (Gd/Yb = 1.0-3.8) and ubiquitous negative Eu anomaly (Eu/Eu* = 0.3-0.7). Th concentrations (0.9-28 μg/g) are relatively higher than those of uranium (0.4-4.0 μg/g). Th/U ratios (1.5-9.9) are higher than the average upper crust. These results are consistent with terrigenous sediments that formed from the weathering and erosion of felsic rocks. [ABSTRACT FROM AUTHOR]

The interaction between the Pseudomonas fluorescens biofilm and U(VI) were studied using extended X-ray absorption fine structure spectroscopy (EXAFS), and time-resolved laser fluorescence spectroscopy (TRLFS). In EXAFS studies, the formation of a stable uranyl phosphate mineral, similar to autunite (Ca[UO][PO]•2-6HO) or meta-autunite (Ca[UO][PO]•10-12HO) was observed. This is the first time such a biomineralization process has been observed in P. fluorescens. Biomineralization occurs due to phosphate release from the cellular polyphosphate, likely as a cell's response to the added uranium. It differs significantly from the biosorption process occurring in the planktonic cells of the same strain. TRLFS studies of the uranium-contaminated nutrient medium identified aqueous CaUO(CO) and UO(CO) species, which in contrast to the biomineralization in the P. fluorescens biofilm, may contribute to the transport and migration of U(VI). The obtained results reveal that biofilms of P. fluorescens may play an important role in predicting the transport behavior of uranium in the environment. They will also contribute to the improvement of remediation methods in uranium-contaminated sites. [ABSTRACT FROM AUTHOR]

The hydrothermally altered vein type uranium mineralization has been reported at different places along the South Purulia Shear Zone (SPSZ) towards 50 km north of the Singhbhum Shear Zone. An integrated close grid gravitymagnetic study over nearly one km area between Kutni and Dandudih villages within this shear zone has been performed to delineate the detail structural features, depth continuation, and associated uranium mineralization zones. The observed Bouguer and calculated residual gravity anomaly map depicts an ESE-WNW (on the east) to E-W (on west) trending low gravity zone on the extreme northern side of the area. The total field magnetic anomaly map also depicts the presence of high anomaly patches which is in accordance with the field observation of the exposed iron oxides (e.g. magnetite and goethite) over the same part of the study area. The 2D inverse modeling across the northern low residual gravity anomaly zones reveals steeply dipping low density structures with dip due north, south or vertical at places. The NS widths of these zones vary from 50-300 m with maximum probable depth extent of ~220 m. Previous researcher has also reported high radioactivity over the exposed quartz-magnetite-apatite bands on the northern part of the area. This band is exactly coinciding with the presently identified low gravity and high magnetic anomaly zones. These anomaly zones on the northern part of the study area are concluded to be hydrothermally altered uranium mineralization target zones. Thus, the results of this study will provide important guiding parameters for the future exploration programme over this region. [ABSTRACT FROM AUTHOR]

The extraction of uranium and iron (III) from mixed sulfate/chloride media with Cyanex 272 was studied, and a mechanism proposed involving cation exchange of UO 2 2 + and Fe(OH) 2 + . Cyanex 272 exhibited good selectivity for uranium over iron (III), with β U/Fe = 129 at pH 1. An antagonistic effect was observed with the addition of Alamine 336 to Cyanex 272, causing a decrease in the extraction of iron (III). In contrast, synergism was observed for the extraction of uranium with the Cyanex 272/Alamine 336 combination. Based on the results obtained, a new chloride tolerant process for uranium recovery from acidic sulfate liquors is proposed, based on Cyanex 272 alone. McCabe–Thiele analysis of the uranium extraction isotherm for 0.1 M Cyanex 272 showed 99% uranium extraction with 3 equilibrium stages, from a sulfate feed liquor containing 1 g/L U, 2 g/L Fe(III), and 20 g/L Cl at pH 1.75. High uranium loadings were achieved (9 g/L U), with 0.2 g/L Fe co-extracted. Sulfuric acid stripping with 4 M H 2 SO 4 was effective, with the McCabe–Thiele diagram indicating that a 5 stage strip circuit would produce a loaded strip containing approximately 45 g/L U. [ABSTRACT FROM AUTHOR]

Uranium occurs naturally in soil and rocks, and therefore where it is present in water-soluble form it also occurs naturally in groundwater as well as in drinking water obtained from groundwater. Animal studies suggest that the toxicity of uranium is mainly due to its damage to kidney tubular cells following exposure to soluble uranium compounds. The assessments of the absorption of uranium via the gastrointestinal tract vary, and this has consequences for regulation, in particular the derivation of e.g. drinking water limit values. Absorption rates vary according to the nature and solubility of the compound in which uranium is presented to the test animals and depending on the animal species used in the test. No differences for sex have been observed for absorption in either animals or humans. However, human biomonitoring data do show that boys excrete significantly more uranium than girls. In animal studies neonates took up more uranium than adults or older children. Nutritional status, and in particular the iron content of the diet, have a marked influence on absorption, and higher uranium levels in food intake also appear to increase the absorption rate. If the pointers to an absorption mechanism competing with iron are correct, these mechanisms could also explain the relatively high concentration and chemical toxicity of uranium in the kidneys. It is here (and in the duodenum) that divalent metal transporter 1 (DMT1), which is primarily responsible for the passage of iron (or uranium?) through the cell membranes, is most strongly expressed. [ABSTRACT FROM AUTHOR]

Counter-current solvent extraction runs have been carried out to develop a suitable flow sheet for fast reactor fuel reprocessing with 1.1M Tri-iso-amyl Phosphate (TiAP)/Heavy Normal Paraffin (HNP) as the solvent by using an ejector mixer-settler facility. A spent solvent of 1.1M TiAP/HNP used for earlier runs has been employed in the present study after the regeneration. Separation of U(VI) and Pu(IV) from Am(III) and lanthanides such as La(III), Pr(III), Nd(III), Sm(III), and Eu(III) as fission product representatives with the above solvent has been investigated with an optimized flow sheet. Stage profile data generated for the extraction and strip runs for the above separation have been reported. Overall and stage-wise mass balance data for the above runs are also discussed. [ABSTRACT FROM PUBLISHER]

A series of phosphonate-based uranyl-organic hybrids has been assembled based on the reaction of uranyl cations with 2,5-dihydroxy-1,4-benzenediphosphonic acid in the presence of a variety of alkali metal and organoammonium cations: K[(UO2)2F2{H0.5O3PC6H2(OH)2PO3H0.5}](H2O)2 ( 1), Cs[(UO2)2{H0.75O3PC6H2(OH)2PO3H0.75}](H2O)4 ·2H2O ( 2), [(CH3)4N]2[UO2{HO3PC6H2(OH)2PO3H}2] ( 3), [(CH3CH2)4N][UO2F{HO3PC6H2(OH)2PO3H}] ( 4), and [(CH3CH2)2N(CH3)2][UO2F{HO3PC6H2(OH)2PO3H}] ( 5). In compounds 1, 4, and 5, chains of UO5F2 pentagonal bipyramids are linked by the hydroxyphosphonate moiety into three-dimensional frameworks, and compound 4 is isostructural with 5. However, the structures of 2 and 3 are composed of monomeric UO7 pentagonal bipyramids assembled to form layered structural units. Additional steric influences from the -OH groups appended on the diphosphonate species play a vital role in directing the structure topologies. [ABSTRACT FROM AUTHOR]

Common duckweed ( Lemna minor L.) is ideally suited to test the impact of metals on freshwater vascular plants. Literature on cadmium (Cd) and uranium (U) oxidative responses in L. minor are sparse or, for U, non-existent. It was hypothesised that both metals impose concentration-dependent oxidative stress and growth retardation on L. minor. Using a standardised 7-day growth inhibition test, the adverse impact of these metals on L. minor growth was confirmed, with EC50 values for Cd and U of 24.1 ± 2.8 and 29.5 ± 1.9 μ m, respectively, and EC10 values of 1.5 ± 0.2 and 6.5 ± 0.9 μ m, respectively. The metal-induced oxidative stress response was compared through assessing the activity of different antioxidative enzymes [catalase, glutathione reductase, superoxide dismutase ( SOD), ascorbate peroxidase ( APOD), guaiacol peroxidase ( GPOD) and syringaldizyne peroxidase ( SPOD)]. Significant changes in almost all antioxidative enzymes indicated their importance in counteracting the U- and Cd-imposed oxidative burden. However, some striking differences were also observed. For activity of APODs and SODs, a biphasic but opposite response at low Cd compared to U concentrations was found. In addition, Cd (0.5-20 μ m) strongly enhanced plant GPOD activity, whereas U inhibited it. Finally, in contrast to Cd, U up to 10 μ m increased the level of chlorophyll a and b and carotenoids. In conclusion, although U and Cd induce similar growth arrest in L. minor, the U-induced oxidative stress responses, studied here for the first time, differ greatly from those of Cd. [ABSTRACT FROM AUTHOR]

Colorless crystals of ThSiO 4 (huttonite) ( 1 ) and (Ca 0.5 Na 0.5 ) 2 NaThSi 8 O 20 ( 2 ) have been synthesized by the solid-state reactions of ThO 2 , CaSiO 3 , and Na 2 WO 4 at 1073 K. Green crystals of (Ca 0.5 Na 0.5 ) 2 NaUSi 8 O 20 ( 3 ) have been synthesized by the solid-state reactions of UO 2 , CaSiO 3 , and Na 2 WO 4 at 1003 K. All three compounds have been characterized by single-crystal X-ray diffraction. Compound 1 adopts a monazite-type three-dimensional condensed structure, which is built from edge- and corner-shared ThO 9 polyhedra and SiO 4 tetrahedra. Compounds 2 and 3 are isostructural and they crystallize in a steacyite-type structure. The structure consists of discrete pseudocubic [Si 8 O 20 ] 8− polyanions, which are connected by An 4+ cations into a three-dimensional framework. Each An atom coordinates to eight monodentate [Si 8 O 20 ] 8− moieties in a square antiprismatic geometry. Na + and Ca 2+ ions reside in the void within the framework. Raman spectra of 1 , 2 , and 3 were collected on single crystal samples. 1 displays more complex vibrational bands than thorite. Raman spectra of 2 and 3 are analogous with most of vibrational bands located at almost the same regions. [ABSTRACT FROM AUTHOR]

This paper studied the recovery of uranium (VI) from 5.3 M phosphoric acid by bis(1,3-dibutoxypropan-2-yl) phosphoric acid (BiDiBOPP)/di- n -hexyl octyl metoxy phosphine oxide (di-n-HMOPO) and 5 analogs of BiDiBOPP mixed with tri- n -octylphosphine oxide (TOPO) diluted in Isane IP 185. First, this paper shows that the experimental and calculated distribution coefficients of uranium (VI) as a function of the concentration of BiDiBOPP and di- n -HMOPO match by using a thermodynamic model previously developed and validated on the bis(2-ethylhexyl) phosphoric acid (D2EHPA)-TOPO system. In this model the formation of complexes between the cationic extractant (HL) and the solvatant extractant (S) such as (HL) 2 , (HL) 2 S, (HL) 2 S 2 and (HL) 5 S and the recovery of uranium (VI) as UO 2 (HL) 2 L 2 S, UO 2 L 2 S and UO 2 (HL) 2 L 2 were taken into account where L refers to the deprotonated form of the cationic extractant HL. Secondly, the investigation of the extraction of uranium (VI) by the BiDiBOPP analogs mixed with TOPO in Isane IP 185 showed that the presence of oxygen atoms in the two aliphatic chains of BiDiBOPP and the increase of the hydrophobicity of these chains influence strongly the extraction properties. [ABSTRACT FROM AUTHOR]

Recovery of uranium from phosphoric acid on a commercial scale was first attempted in 1952 in the United States; at a plant operated by the Blockson Chemical Co. in Joilet, Ill, and used a chemical precipitation technique to recover the uranium as uranous phosphate. This plant was followed by two others, both in the United States. These plants started operating in 1955 and 1957, and both used octy-pyro-phsophoric acid as a solvent. While it was inexpensive, it had a short life and had to be replaced daily. All three uranium recovery plants were operated for several years until the price of uranium fell. With the large increase in the cost of energy in the mid-1970s, the price of uranium also rose. In the United States, where the indigenous phosphate rock contains relatively high uranium concentrations, the proposition of recovering it from phosphoric acid again became attractive; as a result 8 plants were built. (6 in Florida and 2 in Louisiana) Subsequently, plants were also built in Canada, Spain, Belgium, Israel, Iraq, Iran, and Taiwan. Again the price of uranium fell and most of the plants shut down quickly as they could not operate at a profit. However, at least 4 plants had long term contracts with United States utilities and were able to operate quite profitably for 10-15 years. During these years they were able to improve the process economics and efficiency. Operating costs of these plants were in the $11-13/pound range. Even though there may not have been any operating plants after 1997, research on the recovery of uranium from phosphoric acid did not stop. If any new plants are to be built, most likely they will be based on solvent extraction as this is the most proven and still the most economic process. [ABSTRACT FROM AUTHOR]

Mixed-metal uranium compounds are very attractive candidates in the design of single-molecule magnets (SMMs), but only one 3d-5f hetero-polymetallic SMM containing a uranium center is known. Herein, we report two trimeric heterodimetallic 3d-5f complexes self-assembled by cation-cation interactions between a uranyl(V) complex and a TPA-capped MII complex (M=Mn (1), Cd (2); TPA= tris(2-pyridylmethyl)amine). The metal centers were strategically chosen to promote the formation of discrete molecules rather than extended chains. Compound 1, which contains an almost linear {Mn-O=U=O-Mn} core, exhibits SMM behavior with a relaxation barrier of 81±0.5 K-the highest reported for a mono-uranium system-arising from intramolecular Mn-U exchange interactions combined with the high Ising anisotropy of the uranyl(V) moiety. Compound 1 also exhibits an open magnetic hysteresis loop at temperatures less than 3 K, with a significant coercive field of 1.9 T at 1.8 K. [ABSTRACT FROM AUTHOR]

One hundred and twenty one samples from every major plutonic body (mainly granitic) of Greece have been analyzed by γ-ray spectrometry to determine the specific activities of 238 U, 232 Th and 40 K (Bq/kg). The range of the activity concentrations of these radionuclides was 2.3–266.4, 1.8–375.5 and 55.0–1632.0 Bq/kg and their average values were 79.2, 85.3 and 881.4 Bq/kg respectively. Any possible connection between the specific activities of 238 U, 232 Th and 40 K and some characteristics of the studied samples (age, rock-type, colour, grain-size, occurrence and chemical composition) is investigated. Samples of particular colour, rock-type, occurrence and chemical composition have been identified for their distinctive levels of natural radioactivity, while age and grain-size do not affect the concentrations of 238 U, 232 Th and 40 K. The range of the Th/U ratio was 0.7–12.69. This great variation in the Th/U ratios, especially when it is found among the samples of the same pluton, is also discussed and explained by alteration and tectonic–metamorphic processes. [ABSTRACT FROM AUTHOR]

The effect of Paecilomyces catenlannulatus ( P. catenlannulatus ) on removal of U(VI) onto illite as a function of contact time, pH, ionic strength, and solution concentration was conducted by batch techniques. The adsorption kinetics indicated that the removal of U(VI) on illite and illite coated P. catenlannulatus can be fitted by pseudo-second order kinetic model very well. The removal of U(VI) on illite and illite coated P. catenlannulatus increased with increasing pH from 1.0 to 7.0, whereas the decrease of U(VI) adsorption on illite and illite coated P. catenlannulatus was observed at pH > 7.5. The adsorption behavior of U(VI) on illite and illite coated P. catenlannulatus can be simulated by the double diffuse model under various pH conditions. The ionic strength-dependent experiments showed that the removal of U(VI) on illite was outer-sphere surface complexation, whereas the inner-sphere surface complexation predominated the U(VI) adsorption onto illite coated P. catenlannulatus at pH 5.0–7.0. The maximum adsorption capacity of U(VI) on illite and illite coated P. catenlannulatus calculated from Langmuir model at pH 5.0 and T = 298 K was 46.729 and 54.347 mg/g, respectively, revealing enhanced adsorption of U(VI) on illite coated P. catenlannulatus . This paper highlights the effect of microorganism on the removal of radionuclides from aqueous solutions in environmental pollution management. [ABSTRACT FROM AUTHOR]

This work presents the electrochemical study of lanthanum and uranium compounds in fused 3LiCl-2KCl eutectic vs . Cl − /Cl 2 reference electrode in the temperature range 723–823 K on liquid gallium-indium eutectic alloy. Thermodynamics and the activity coefficients of lanthanum and uranium were studied. The separation factor of uranium from lanthanum on gallium-indium eutectic alloy was determined. [ABSTRACT FROM AUTHOR]

Direct isotope ratio analysis of solid uranium particulates on cotton swipes was achieved using a solution-based microextraction technique, coupled to a quadrupole inductively coupled plasma - mass spectrometer (ICP-MS). This microextraction-ICP-MS methodology provides rapid isotopic analysis which could be applicable to nuclear safeguards measurements. Particulates of uranyl nitrate hexahydrate (UO 2 (NO 3) 2 ·6H 2 O) and uranyl fluoride (UO 2 F 2) ranging from 6 μm to 40 μm in length were transferred to cotton swipes with a particle manipulator. The microextraction probe then delivers a 5% nitric acid (HNO 3) solvent onto the swipe surface to extract the uranium species. The extracted sample is then delivered to the ICP-MS for isotopic determination. The majority of uranium signal (∼99% and ∼94% for UO 2 (NO 3) 2 ·6H 2 O and UO 2 F 2 , respectively) was detected in the first 15 s extraction, while subsequent extractions on the same location had low or no U signal, suggesting near complete removal of the solid uranium compounds from the swipe surface. Ten samples (for each of the uranium compounds), were analyzed for their isotopic composition. For UO 2 (NO 3) 2 ·6H 2 O, the determined isotope ratios resulted in a % relative difference (% RD) from the referenced isotope ratios of 0.97, 1.0, and 7.3% for 234U/238U, 235U/238U, and 236U/238U, respectively. The % RD of the UO 2 F 2 isotope ratios were 1.9 and 0.60% for 234U/238U and 235U/238U, respectively. The preliminary limits of detection were determined to be 0.002, 0.4, and 60 pg for 234U, 235U and 238U, respectively This work demonstrates that microextraction ICP-MS is a rapid and sensitive method that could directly determine uranium isotope ratios of UO 2 (NO 3) 2 ·6H 2 O and UO 2 F 2 particulates on cotton swipes. [Display omitted] • Novel method for direct sampling of particulates on cotton swipe by microextraction-ICP-MS. • Femtogram detection limits achieved for minor uranium isotopes. • Determination of uranyl nitrate and uranyl fluoride particulates on swipes. [ABSTRACT FROM AUTHOR]

Benzil was hypercrosslinked to produce a novel hypercrosslinked porous organic polymer skeleton (HCP-CO) with an ultrahigh Brunauer-Emmett-Teller (BET) surface area of 605.4 m2·g−1. The skeleton was grafted with diaminomaleonitrile (DAMN) via a simple Schiff base reaction, and then reacted with hydroxylamine hydrochloride (NH 2 OH·HCl) to produce an amidoxime-modified hypercrosslinked benzil polymer (HCP-AO) possessing many amidoxime groups. The chelation of the amidoxime group and uranium (VI) and porous structure provided HCP-AO with excellent adsorption performance. The maximum adsorption capacity for the uranium of HCP-AO can reach 370.9 mg·g−1 at pH = 6. Moreover, the adsorption process agreed well with the Langmuir and pseudo-second-order models, thus indicating it was monolayer chemical adsorption. HCP-AO demonstrated excellent selectivity and recyclability; furthermore, the removal rate for uranium still remained at 66.35% in the coexistence of metal ions in simulated seawater. Furthermore, after five adsorption–desorption cycles, the adsorption capacity of HCP-AO slightly reduced. To summarize, we synthesized an efficient adsorbent that possesses high adsorption capacity, selectivity, and recyclability; it has good potential for uranium extraction from water. [Display omitted] • A novel amidoxime-modified hypercrosslinked polymer HCP-AO are prepared for uranium adsorption. • HCP-AO shows good uranium adsorption capacity of 370.9 mg/g. • Excellent uranium adsorption selectivity in simulated seawater. [ABSTRACT FROM AUTHOR]

Fundamental observations of particle size distributions are needed to develop models that predict the fate and transport of radioactive materials in the atmosphere following a nuclear incident. The extent of material transport is influenced by the time scales of particle formation processes (e.g., condensation, coagulation). In this study, we investigated the influence of cooling time scales on size distributions of uranium, aluminum, and iron oxide particles that are synthesized separately under identical run conditions inside the controlled environment of an argon plasma flow reactor. Two distinct temperature distributions are imposed along the flow reactor by varying the argon flow rate downstream of the plasma torch. The vaporized reactants of uranium, aluminum, and iron are cooled from about 5000 K to 1000 K before they are collected on silicon wafers for ex situ scanning electron microscope analysis. The microscope images show that the sizes of the largest aluminum and iron oxide particles heavily depend on the cooling time scales, whereas significant size variation with cooling rate is not observed for uranium oxide particles. In addition, the size distribution of aluminum oxide particles exhibits the broadest range among all three metal oxides studied. We performed simulations of particle size distributions using a kinetic model that couples gas phase oxidation chemistry with particle formation processes, including nucleation, condensation, and coagulation. The model results demonstrate the strong sensitivity of particle size distribution to different cooling histories (i.e., temperature vs residence time) along the flow reactor. The kinetic model also helps identify directions for future research to improve the predictions. • The kinetic model results demonstrate the strong sensitivity of particle size distribution to different cooling histories. • The largest sizes of aluminum and iron oxide nanoparticles decrease by increasing the rate of temperature drop. • Aluminum oxide nanoparticles exhibit the broadest size range among all three metal oxides studied [ABSTRACT FROM AUTHOR]