Separation of thorium from uranium ore

Thorium-230 has many research applications, but there is not a commercial source of this isotope. However, since ²³⁰Th is part of the ²³⁸U decay chain, it can be separated from naturally occurring uranium. In this work, a novel procedure was developed to separate thorium from uranium ore, consisting of leaching, liquid–liquid extraction, precipitations and ion exchange chromatography. The final product was 91.32?±?0.77 mg of thorium with a purity of 99.5?±?1.2 wt%. Of that, 7.65?±?0.10 mg was ²³⁰Th and the remainder ²³²Th. The total yield of ²³⁰Th was 71.1?±?5.4%. Ways to improve the yield by further processing the back-extraction solution are suggested.

     

Measurement of the 238U(n,γ)239U reaction cross sections in the energy range of 2.0–5.0 MeV by using a neutron activation technique

The neutron capture cross-sections of ²³⁸U at the neutron energies of 4.38?±?0.05 MeV, 3.02?±?0.49 MeV and 2.04?±?0.26 MeV have been measured using the activation method and off-line gamma-ray spectrometric technique. The effects of neutron flux fluctuation, multiple scattering, flux self-shielding and gamma-ray self-absorption were corrected. The excitation function of the ²³⁸U(n,γ)²³⁹U reaction was also calculated using the TALYS-1.9 code. The experimental results were compared with the evaluated data, the theoretical data and the previous experimental data.

     

Heterometallic Fe2II–UV and Ni2II–UV Exchange‐Coupled Single‐Molecule Magnets: Effect of the 3 d Ion on the Magnetic Properties

Uranium‐based compounds have been put forward as ideal candidates for the design of single‐molecule magnets (SMMs) with improved properties, but to date, only two examples of exchange‐coupled 3d–5f SMM containing uranium have been reported and both are based on the Mn^II ion. Here we have synthesized the first examples of exchange‐coupled uranium SMMs based on Fe^II and Ni^II. The SMM behavior of these complexes containing a quasi linear {M?O?U?O?M} core arises from intramolecular Fe?U and Ni?U exchange interactions combined with the high Ising anisotropy of the uranyl(V) moiety. The measured values of the relaxation barrier (53.9±0.9 K in the UFe₂ complex and of 27.4±0.5 K in the UNi₂ complex) show clearly the dependency on the spin value of the transition metal, providing important new information for the future design of improved uranium‐based SMMs.     

New methodology for uranium analysis in swipe samples for nuclear safeguards purposes

Environmental swipe sampling for safeguards purpose has been used by International Atomic Energy Agency since 1997, being a powerful tool to detect undeclared materials and activities. This work describes a new methodology for swipe samples analysis based on ultrasound-assisted acid leaching and compares it with traditional total digestion bulk analysis. The proposed method requires few preparation steps, decreasing the risk of contamination, reduced amounts of reagents and a good option to extract uranium from swipe sample. In a real case study, the swipe samples were collected in a conversion plant at IPEN/CNEN, Brazil. The measurements were carried out by ICP-MS and the results showed relative error lower than 0.96 % for uranium isotopic ratios for the certified reference material (NBS U200). The uncertainties were estimated by following the ISO GUM, with a confidence level of 95 %. The uncertainties percentage for n(²³⁵U)/n(²³⁸U) ratio of the samples ranged from 2.5 to 4.3 %. The values of uranium isotopic ratio obtained for each method demonstrate the viability of using the methodology proposed in this work.     

Highly efficient sorption of U(VI) from aqueous solution using amino/amine-functionalized magnetic mesoporous silica nanospheres

The amino/amine-functionalized magnetic mesoporous silica nanospheres (MSN-DETA) exhibited relatively high sorption capacity (q_m?=?153.68 mg/g) as well as excellent selectivity for U(VI). The U4f_7/2 X-ray photoelectron spectrometry revealed two binding energies at 380.8?±?0.3 eV (with the proportion of 75.2%) and 382.3?±?0.3 eV, which indicated the inner-surface complexation mechanism. The sorption isotherms fitted well with the Langmuir model, whereas the sorption kinetics could be fitted by pseudo-second-order model. The U(VI)-loaded MSN-DETA could be efficiently regenerated by acidified EDTA (0.4 M). These findings indicated that MSN-DETA could be used as a potential material for the efficient sorption/separation of U(VI) from wastewater.

     

Mathematical modeling of solvent extraction of uranium from sulphate media employing 2-ethylhexyl phosphonic acid-mono-2-ethylhexyl ester (PC88A) and its mixture with trioctylphosphine oxide (TOPO) as extractants

The extraction of U(VI) from sulphate medium with 2-ethylhexyl phosphonic acid-mono-2-ethylhexyl ester (PC88A, H₂A₂ in dimeric form) in n-dodecane has been investigated under varying concentrations of sulphuric acid and uranium. Slope analysis of uranium (VI) distribution data as a function of PC88A concentration suggests the formation of monomeric species, viz. UO₂(HA₂)₂. This observation was further supported by the mathematical expression obtained during non-linear least square regression analysis of U(VI) distribution data correlating the percentage extraction (%E) and the acidity (H _i). A mathematical model correlating the experimental distribution ratio values of U(VI) (D _U) with initial acidity (H _i) and initial uranium concentrations (C _i) was developed: D_\textU = 12.98( ±0.90)/{ C_\texti ^{- 0.75( ±0.05)} ×[ H_\texti ]² } D_{\text{U}} = 12.98( \pm 0.90)/\left\{ {C_{\text{i}}^{ - 0.75( \pm 0.05)} \times \left[ {H_{\text{i}} } \right]^{2} } \right\} . This expression can be used to predict the concentration of uranium in organic as well as in aqueous phase at any C _i and H _i. The extraction data were used to calculate the conditional extraction constant (K _ex) values at different acidities (2–7 M H⁺), uranium (0.02–0.1 M) and PC88A (0.2–0.6 M) concentrations. These studies were also extended for the extraction of U(VI) using synergistic mixtures of PC88A and TOPO from sulphate medium.     

Analyses of radionuclides in the Oued Awlitis 001 and Galb Inal lunar meteorites by HPGe gamma-ray spectrometry

Highly sensitive nondestructive HPGe gamma-ray spectrometry was used for the analysis of the cosmogenic (²⁶Al) and primordial (⁴⁰K, ²³⁸U, and ²³²Th) radionuclides in the Oued Awlitis 001 and Galb Inal lunar meteorites. The measured ²⁶Al activities were very different (84.0?±?4.8 dpm/kg vs. 8.4?±?1.2 dpm/kg, respectively), mainly because of different cosmic-ray exposure ages of the investigated meteorites. The pre-atmospheric radii were 5?±?1 cm and 11?±?2 cm, respectively, which would result in total pre-atmospheric masses in the range of 0.7–2.5 kg and 7–23 kg, respectively.

     

Electrochemical behavior of uranium(III) in NaCl–KCl molten salt

The electro-redox behavior of uranium(III) on Mo electrode in NaCl–KCl molten salt in the temperature range 973–1073 K has been investigated using cyclic voltammetry electrochemical method and so on, such research will help to understand uranium behavior in pyro-reprocessing. The results showed that UCl₃ could be reduced into uranium metal in a quasi-reversible one-step process exchanging three electrons. The diffusion coefficients of U(III) ions were determined and the activation energy for diffusion was found to be 55.794 kJ mol⁻¹. The apparent standard potentials of U(III)/U(0) at several temperatures were calculated. The thermodynamic properties of UCl₃ have also been investigated.

     

Isotopic concentration of uranium from alpha spectrum of electrodeposited source on 4H-SiC detector at 500 °C

4H-SiC alpha detectors were fabricated with a 21-μm thick depletion depth and were packaged into a stainless-steel casing with a mineral insulation cable and a standard BNC connector. The packaged detectors had a resolution of 0.624% FWHM at 5.486 MeV prior to salt immersion. The detectors were then immersed in a LiCl–KCl–UCl₃ molten salt at 500 °C, from which a thin layer of depleted uranium was electrodeposited onto the detectors. Alpha particle emission spectra were collected from the electrodeposited source. The energy resolution of the surviving detector was 2.29% FWHM at 4.198 MeV and was sufficient to separate the ²³⁴U from ²³⁸U alpha emissions (577 keV difference). The ²³⁴U/²³⁸U activity ratio and the isotopic concentrations of ²³⁴U and ²³⁸U were determined and are representative of the uranium source used in the electrodeposition.

     

A variable temperature 1H NMR and DFT study of procyanidin B2 conformational interchange

Two procyanidin B2 conformers were identified in a relative abundance ratio of approximately 3:1 at 298 K by ¹H NMR experiments in acetonitrile. The conformational interchange reactions between these two conformers are 1st order in both reactions, with ?G^? for forward and reverse of 57.12?±?5.62 and 54.56?±?5.48 kJ mol^?1, respectively. The experimentally obtained standard thermodynamic energies for this reaction are ΔH⁰_rxn (3.67?±?0.22 kJ mol^?1), ΔS⁰_rxn (4.05?±?1.57 kJ mol^?1 K^?1), and ΔH⁰_rxn (2.96?±?0.33 kJ.mol^?1). Conformational search results at the DFT (PBE, PBE-D2, and B3LYP with 6-311++g**) level of theory yielded four novel conformations, named fully compact (FC), partially compact (PC), partially extended (PE), and fully extended (FE). Although the FC conformer is electronically the most stable of the four as a result of extensive intramolecular non-covalent interactions, the PC and FE conformers are thermodynamically favored in a 5:1 ratio (B3LYP), with the FC and PE conformers present in negligible amounts at equilibrium. The DFT computed standard reaction energies using the B3LYP functional for the PC_major to FE_minor conformational interchange reaction compare exceptionally well with experimental data at 298 K: ?G⁰_rxn (3.86 kJ mol^?1), ΔH⁰_rxn (5.34 kJ mol^?1), and ?S⁰_rxn (4.97 kJ mol^?1 K^?1). It was found that inclusion of solvation energies is crucial to obtain accurate thermodynamic energies. The secondary equilibria found in chromatographic separations are predicted to be highly dependent on solvent polarity and temperature. Similar conformational diversity and hierarchies should exist for all non-rigid procyanidin oligomers and the unique chromatographic behavior of these compounds may be a result of conformational interchange.

     

Biological Applications of Synthesized ZnO Nanoparticles Using Pleurotus djamor Against Mosquito Larvicidal,Histopathology, Antibacterial,Antioxidant and Anticancer Effect

The present study pertained to biosynthesis, characterization and biomedical application (larvicidal, histopathology, antibacterial, antioxidant and anticancer activity) of Zinc oxide nanoparticles (ZnONPs) from Pleurotus djamor. The synthesized NPs were characterized using spectral and microscopic analyses and further confirmed by UV–Visible spectrophotometer with apeak of 350 nm. The ZnONPs showed strong antioxidant property (DPPH, H₂O₂ and ABTS⁺ radical assay) and expressed good larval toxicity against Ae. aegypti and Cx. quinquefasciatus (IVth instar larvae) with the least LC₅₀ and LC₉₀ values (10.1, 25.6 and 14.4, 31.7 mg/l) after 24 h treatment, respectively. We noticed the morphological changes (damaged anal papillae area and the cuticle layers) in the treated larvae. For the antibacterial assay, the highest growth inhibition zone was recorded in C. diphteriae (28.6?±?0.3 mm), followed by P. fluorescens (27?±?0.5 mm) and S. aureus (26.6?±?1.5 mm). The in vitro cytotoxicity assay depicted a significant level of cytotoxic effects (LC₅₀ values 42.26 μg/ml) of ZnONPs against the A549 lung cancer cells, even at low dose. The overall findings of the study suggest that P. djamor had the ability for the biosynthesis of ZnONPs and could act as an alternative biomedical agent for future therapeutic applications in medical avenues.

     

Uranium age-dating using in-situ isotope ratios by thermal ionization mass spectrometry for nuclear forensics

The model dates of two enriched uranium materials were determined using a new method for nuclear forensics investigation. In this method, without spike addition, the ²³⁰Th/²³⁴U ratio was calculated from the measured ratios of ²³⁰Th/²³⁴Th and ²³⁴U/²³⁸U and from calculated ²³⁴Th/²³⁸U ratio in secular equilibrium. The model date obtained for the low-enriched uranium material was in agreement with the known production date. For the highly enriched uranium material, a more recent model date than the known production date was obtained. The ²³⁴U interference on ²³⁴Th counting in thermal ionization mass spectrometer measurement was suspected as a potential cause.

     

Determination of uranium and thorium isotopes in soil samples by coprecipitation

Summary The paper presents a procedure to prepare soil samples for U and Th isotope measurement by alpha-spectrometry after coprecipitation with LaF₃. In this procedure the reduction of U(VI) to U(IV) was performed by Zn metal in 4M HCl solution. The recoveries of chemical separation equal to e_U-chemistry = 78±4% for uranium and e_Th-chemistry = 82±4% for thorium. Canberra alpha-spectrometer was used with PIPS detectors of A-1200-37-AM Model of 1200 mm² active area. The counting efficiency of the measuring system equals to e_counting = 18% and the total efficiencies were e_U = e_counting ^.e_U-chemistry = 14.0±0.7% for uranium and e_Th = e_counting ^.e_Th-chemistry = 14.7±0.7% for thorium. The recoveries of chemical separation were rather high (about 80%), that leads to the use of a small weight of soil sample (about 0.5 g). The efficiencies were also stable, that allows analyzing the soil sample without using radiotracers. They are advantages of the sample preparation procedure of this work.     

Determination of naturally occurring uranium concentrations in seawater,sediment, and marine organisms in Japanese estuarine areas

For safety assessments of geological repositories of nuclear waste, understanding of uranium (U) fate in estuarine areas is important because U chemical behavior in the areas is expected to be complex. Environmental transfer parameters such as sediment–water distribution coefficients (K _d) and concentration ratios (CRs) for marine organisms are useful in mathematical models for the assessment. However, due to its low concentration in estuarine water, K _d and CF data for U are scarce. Thus we studied a rapid method for separation and concentration of U from estuarine water samples using NOBIAS-CHELATE PA1 resin columns followed by inductively coupled plasma mass spectrometry (ICP-MS) for U measurement. Chemical recovery was about 100% at pH of 5.7 ± 0.1 from the water samples and alkali and alkaline earth metals were removed. The method was used to measure U concentrations in estuarine water samples collected at eight Japanese estuarine areas; they ranged from 0.1 to 3.8 μg L⁻¹. We also measured U concentrations in sediment and marine organism samples by ICP-MS after acid digestion. Using these values, we observed K _d (range: 39–284 L kg⁻¹) and CRs (0.86–52 L kg⁻¹ for macroalgae, 0.087–15 L kg⁻¹ for crustaceans, and 0.52–93 L kg⁻¹ for molluscs).     

Alpha spectroscopic analysis of actinides (Th,U and Pu) after separation from aqueous solutions by cation-exchange and liquid extraction

The radioactivity concentration of ²³⁶Pu, ²³²U and ²²⁸Th in aqueous samples has been determined by means of alpha spectroscopy after chemical separation and pre-concentration of the radionuclides by cation exchange and liquid–liquid extraction using the Chelex-100 resin and 30% TBP/dodecan, respectively. Method calibration using a ²³⁶Pu standard solution containing the daughter radionuclides results in a detector efficiency of 18% and in a chemical recovery for cation-exchange which is (30 ± 7)%, (90 ± 5)% and (20 ± 5)% for plutonium, uranium and thorium, respectively. The chemical recovery for liquid–liquid extraction is found to be (60 ± 7)%, (50 ± 5)% and (70 ± 5)%, for plutonium, uranium and thorium, respectively. The differences in the efficiencies can be ascribed to the oxidation states, the different actinides present in solution. Taking into account that the electrodeposition of the radionuclides under study is quantitative, the total method efficiency is calculated to be (18 ± 15)%, (46 ± 7)% and (15 ± 5)%, for plutonium, uranium and thorium, respectively, at the mBq concentration range. The detection limit of the alpha spectrometric system has been found to be 0.2 mBq/L, suggesting that the method could be successfully applied for the radiometric analysis of the studied radionuclides and particularly uranium in aqueous samples.     

Direct determination of uranium in sintered deeply depleted uranium oxide pellets by wavelength dispersive X-ray fluorescence spectrometry

This paper presents studies on direct non-destructive determination of uranium in sintered deeply depleted (DD) uranium oxide (UO₂) pellets by wavelength dispersive X-ray fluorescence (WDXRF) spectrometry. A special collet was designed and fabricated for holding the sintered DDUO₂ pellets for direct analysis, thus avoiding the sample preparation steps. The samples were analyzed using a calibration plot obtained from WDXRF spectra of matrix matched calibration standards. The WDXRF determined uranium values were found to be in very close agreement with titrimetric values and has reproducibility better than 0.05% (RSD, 1 s, n = 10) for the sintered DDUO₂ pellets having U: 86.81–88.04 wt%.

     

Complexation of aqueous uranium(IV) with phosphate investigated using time-resolved laser-induced fluorescence spectroscopy

Heavy metals like the actinides possess a high risk potential to the environment not only because of their radiotoxicity but also due to their chemical toxicology. Uranium as one of the major actinide elements has to be considered in particular. Under reducing conditions, tetravalent uranium occurs primarily in the environment. To date, a lack of appropriate analytical techniques that featured sufficient sensitivity made it difficult to study the aqueous phosphate chemistry of uranium(IV) as such complexes show only low solubility. A novel time-resolved laser fluorescence spectroscopy system was set up recently and optimized to do research on uranium(IV). By application of this laser system we could successfully study uranium(IV) phosphate in concentration ranges where no precipitation or formation of colloids occurred. At pH = 1.0, U⁴⁺ and one uranium(IV) phosphate complex existed in parallel in aqueous solution. The complex could be identified as [U(H₂PO₄)]³⁺. Determination of its corresponding complex formation constant via two different evaluation methods resulted in the finding of (1) logb₁₂₁ ^° = 2 6. 3 7 ±0. 7 6 \log \beta_{121}^{ \circ } = 2 6. 3 7 \pm 0. 7 6 and (2) logb₁₂₁ ^° = 2 6. 4 3 ±0. 2 3 \log \beta_{121}^{ \circ } = 2 6. 4 3 \pm 0. 2 3 . Both values prove that [U(H₂PO₄)]³⁺ is a very stable complex in solution under experimental conditions. As they are in very good agreement with each other, the total complex formation constant was determined by means of the weighted average out of (1) and (2). It was calculated to be logb₁₂₁ ^° = 2 6. 4 2 ±0. 2 2 \log \beta_{121}^{ \circ } = 2 6. 4 2 \pm 0. 2 2 .     

Assessment of natural radioactivity in silt samples from Moticher lake near Kakrapar Atomic Power Station,India

The naturally occurring radioisotopes such as ²³⁸U, ²³²Th and ⁴⁰K in the silt samples collected from Moticher lake, Gujarat were evaluated. The activity of ²³⁸U, ²³²Th and ⁴⁰K was found to be 4.4-9.7 Bq kg⁻¹ with a mean 6.4 ± 1.3 Bq kg⁻¹, 10.5–21.2 Bq kg⁻¹ with a mean 15.6 ± 2.5 Bq kg⁻¹ and 102–231 Bq kg⁻¹ with a mean 160 ± 40 Bq kg⁻¹, respectively. The depth profile study could not reveal any significant vertical correlation on radioactivity levels of ²³⁸U, ²³²Th and ⁴⁰K. Radium equivalent activity (Ra_eq), external hazard index (H _ex) and internal hazard index (H _int) were calculated by using the activity of ²³⁸U or ²²⁶Ra, ²³²Th and ⁴⁰K in silt samples. Annual Effective Dose Equivalent (AEDE) level in Moticher silt was found to be 24.8 ± 5.0 μSv year⁻¹, which is much lower than the worldwide average value. The relative contribution to dose due to ²³⁸U and ²³²Th series were found to be 14% and 53%, followed by the contribution of 33% due to ⁴⁰K.     

Validation of a Monte Carlo HPGe detector model against irradiated foil gamma-ray spectroscopy measurements

In order to separate and pre-concentrate uranium from aqueous phase, a novel silica-based adsorbent was prepared by impregnating nalidixic acid (HNA) into a macroreticular silica/polymer composite support (SiO₂-P) with a mean diameter of 60 μm. Adsorption behavior of uranium from aqueous solution onto the adsorbent was studied. Experimental results indicated that HNA/SiO₂-P showed strong adsorption for uranium in a wide range of pH from 3.5 to 10.0, and the maximum adsorption capacity was 35.4 mg g⁻¹. In addition, HNA/SiO₂-P exhibited good selectivity for U(VI) and showed weak or bare adsorption affinity to foreign ions. Kinetic and isotherm of uranium adsorption were in accordance with the pseudo-second-order kinetic model and Langmuir isotherm adsorption model, respectively. Moreover, U(VI) sorption was found to be an endothermic reaction and spontaneous under experimental state. The synthesized adsorbent showed an admirable stability at lower pH values in aqueous solution.

     

Interaction of the divalent lead cation with cyclosporin A: an experimental and theoretical study

On the basis of extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Pb²⁺(aq) + 1·Sr²⁺(nb) ? 1·Pb²⁺(nb) + Sr²⁺(aq) occurring in the two-phase water–nitrobenzene system (1 = cyclosporin A; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K _ex (Pb²⁺, 1·Sr²⁺) = 0.1 ± 0.1. Further, the stability constant of the 1·Pb²⁺ complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log β _nb (1·Pb²⁺) = 9.2 ± 0.2. Finally, applying quantum chemical DFT calculations, the most probable structure of the proven 1·Pb²⁺ cationic complex species was derived. In the resulting complex, the “central” cation Pb²⁺ is bound by four bonding interactions to the corresponding four oxygen atoms of the parent cyclosporin A ligand. The interaction energy, E(int), of the considered 1·Pb²⁺ complex was found to be ?1016.3 kJ/mol, confirming also the formation of this complex.