Removal of uranium (VI) from nuclear effluents onto aluminophosphate and silicoaluminophosphate molecular sieves

Aluminophosphate and silicoaluminophosphate molecular sieves with both five (AFI) and eleven (AEL) type structures are synthesized by hydrothermal crystallization at 473 K, using tripropylamine and dipropylamine as a structure-directing template. The as-prepared AFI and AEL sieves are characterized and then assessed as sorbents for uranium (VI) from radioactive effluents. The sorption process is used to reduce the volumes of effluents and convert them into a stable solid waste. The batch experimental studies are carried out to evaluate the AEL and AFI structure effect on the removal of uranium. The AlPO₄-5, SAPO-5, AlPO₄-11 and SAPO-11 are applied to radioactive effluents with different activities obtained from Nuclear Research Center of Draria, Algeria. Important decontamination factor values are obtained for AFI sorbents. Thermodynamic parameters, namely, the enthalpy (ΔH), entropy (ΔS) and free energy (ΔG) for each sorption process are calculated. The collected results indicated that sorbents are effective materials for the removal of uranium (VI) ions, the sorbent with AFI structure being a highly effective material for the removal of uranium (VI) ions from nuclear effluents.     

UV–vis absorption spectroscopic study for on-line monitoring of uranium concentration in LiCl–KCl eutectic salt

UV–vis absorption spectroscopy of uranium in LiCl–KCl eutectic salt at 773 K was studied for the on-site use in pyrochemical process. Uranium(III) chloride was electrochemically prepared from uranium metal in LiCl–KCl eutectic salt at 773 K by using chronopotentiometry. Three absorption peak positions were selected and calibrated for the quantitative analysis of uranium in the molten salt medium. The molar absorptivity and minimum detectable concentration for the selected wavelength were obtained with a confidence level of 99%.     

Lab on valve-multisyringe flow injection system (LOV-MSFIA) for fully automated uranium determination in environmental samples

The hyphenation of lab-on-valve (LOV) and multisyringe flow analysis (MSFIA), coupled to a long path length liquid waveguide capillary cell (LWCC), allows the spectrophotometric determination of uranium in different types of environmental sample matrices, without any manual pre-treatment, and achieving high selectivity and sensitivity levels. On-line separation and preconcentration of uranium is carried out by means of UTEVA resin. The potential of the LOV-MSFIA makes possible the fully automation of the system by the in-line regeneration of the column. After elution, uranium(VI) is spectrophotometrically detected after reaction with arsenazo-III. The determination of levels of uranium present in environmental samples is required in order to establish an environmental control. Thus, we propose a rapid, cheap and fully automated method to determine uranium(VI) in environmental samples. The limit of detection reached is 1.9 ηg of uranium and depending on the preconcentrated volume; it results in ppt levels (10.3 ηg L⁻¹). Different water sample matrices (seawater, well water, freshwater, tap water and mineral water) and a phosphogypsum sample (with natural uranium content) were satisfactorily analyzed.     

Theoretical study of adsorption of water vapor on surface of metallic uranium

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Fission-track dating of Macusanite glasses with plateau and size correction methods

Two Macusanite pebbles (MB1 and MB2) were dated with the fission-track method. Six irradiations were carried out in different nuclear reactors: Pavia (Italy), IPEN-CNEN (Brazil) and IPEN-Lima (Peru). Measurements of the thorium and uranium induced-fission per target nucleus using natural thorium thin films and natural U-doped glasses calibrated against natural uranium thin films, together with a λ_F of 8.46×10⁻¹⁷ a⁻¹ were used to determine the ages. The apparent ages were corrected using the plateau and size correction methods. Track measurements were performed by different analysts, using different counting criteria. In addition, tracks were measured on samples which had been submitted to thermal treatment as well as on samples which had not been heated. Thermal treatments were carried out to erase the fossil tracks before neutron irradiation. No significant differences have been found in individual results, using the two Macusanite pebbles and the different nuclear reactors, age correction techniques, analysts, track-counting criteria, and thermal treatments before neutron irradiation. The great majority of the results (14/17) is compatible with the Ar–Ar ages of 5.12±0.11 and 5.10±0.11 Ma, Macusanite MB1 and MB2, respectively. However, the fission-track ages are systematically less (8%) than the Ar–Ar ages of the two Macusanite samples studied.     

RECOVERY OF URANIURN FROM CARBONATE SOLUTIONS USING STRONGLY BASIC ANION EXCHANGER 3. THE MECHANISMS OF RECOVERY PROCESSES

INTRODUCTIONForthebinaryionexchangereactionmovingboundarymodelwasreported:(a)undertheassumptionofconstantvolumeofresinbeadsduringionexchange['--21,(b)withchangingsphericalvolumeofion...h..g...[3).Thismodelimpliesthreetypesofrate--determiningsteps:liquid--filmdiffusion,diffusionthroughtheso--calledinertlayerofthesorbent,andchemicalreactiontakingplaceattheboundaryoftheunreactednucleus.SongYlnjie.t.[4]carefullyrededucedsolutionscorrespondingtoabovethreetypesofrate-determiningsteps,andtheexpr…     

TOPO－TBP萃淋树脂在盐酸、硝酸溶液中萃取铀、钍平衡常数的测定

本文测定了在盐酸、硝酸溶液中，ＴＯＰＯ－ＴＢＰ萃淋树脂萃取铀、钍的平衡常数，结果表明，在相同酸性溶液中，ＴＯＰＯ－ＴＢＰ萃淋树脂萃取铀、钍平衡常数与液－液体系基本一致。     

Simultaneous solvent extraction and high-performance liquid chromatographic determination of uranium, iron, nickel and copper in mineral ore samples and phosphate rock residues using N,N′-ethylenebis(salicylaldimine) as complexing reagent

The reagent N,N-ethylenebis(salicylaldimine) (H₂SA₂en) has been examined for precolumn derivatization, followed by solvent extraction in chloroform and HPLC determination of uranium, iron, nickel and copper on a Hypersil ODS 3 μm column. Complexes were eluted isocratically using a ternary mixture of methanol-acetonitrile-water and UV detection was at 260 nm. The detection limit was 12 ng/injection for each of the elements. The method has been applied for the determination of metals in mineral ore samples and phosphate rock residues. The results obtained are compared using atomic absorption.     

Magnetic brillouin zone effect on the resistivity of semimetallic-like fermi surface in USb

To probe the effect of the protein environment on the retinal chromophore of rhodopsin, we performed molecular dynamics simulations using combined quantum mechanics/molecular mechanics (QM/MM). The starting geometry of the protein is based on the 2.6Å X-ray structure of bovine rhodopsin of Okada et al. [T. Okada, et al. Proc. Natl. Acad. Sci. USA 99 5982 (2002)]. The wild-type chromophore of rhodopsin according to our calculations shows a highly twisted conformation around the central region, from C10 to C13, due to non-bonded interaction with the protein pocket. The absolute sense of twist of the C11–C12 and C12–C13 bonds is negative (?19 ± 9°) and positive (170 ± 8°), respectively. The 13-demethyl retinal chromophore, in which the methyl group at the C13 position is removed, is less distorted in this region. The C11–C12 bond is less twisted (?15 ± 10°) and the C12–C13 bond is planar (179 ± 9°) . The flattened geometry of this artificial chromophore is supported by spectroscopic evidence.     

The dynamics of hydrogen adsorption on polycrystalline uranium

The dynamics of dissociative hydrogen adsorption on clean polycrystalline uranium has been studied using temperature programmed desorption and supersonic molecular beams. The initial sticking probability was measured as a function of incident kinetic energy between 3 and 255 meV. Two adsorption channels were observed; a non-activated direct channel was shown to be active over the entire energy range studied and a low energy indirect channel that was characterised by a decrease in sticking probability with increasing beam energy, and an insensitivity to both surface temperature and a range of hydrogen coverages. Together these results suggest the existence of an unaccommodated molecular precursor that has sufficient lifetime and mobility to locate favourable sites and dissociatively adsorb.