scispace - formally typeset
Search or ask a question

Showing papers on "Uranyl published in 1997"


Journal ArticleDOI
TL;DR: In this article, the crystal chemistry of the various oxidation states of actinide elements of environmental concern was examined to identify possible incorporation mechanisms, and the incorporation of An 3+ into the sheets of the structures of ct-uranophane and boltwoodite, as well as interlayer sites of various uranyl phases, may occur.

215 citations


Journal ArticleDOI
19 Mar 1997-Langmuir
TL;DR: In this paper, the role of various physical and physicochemical parameters related to chitosan was investigated and it was shown that the crystallinity, the particle dimensions, and the swelling in water are connected together and govern the kinetic laws of metal diffusion and sorption.
Abstract: This work corresponds to the first part of our studies on the interactions between chitosan particles dispersed in water and uranyl ions. The measurements were obtained by ICP, and we considered the role of various physical and physicochemical parameters related to chitosan. We showed that the crystallinity, the particle dimensions, and the swelling in water of chitosan are parameters which are connected together and govern the kinetic laws of metal diffusion and sorption. The molecular mobility of the polymer chains is then the essential parameter.

125 citations


Journal ArticleDOI
TL;DR: Pseudomonas aeruginosa CSU, a nongenetically engineered bacterial strain previously shown to bind dissolved hexavalent uranium, shows promise as the basis of an immobilized‐cell process for removal of dissolved uranium from contaminated wastewaters.
Abstract: Pseudomonas aeruginosa CSU, a nongenetically engineered bacterial strain previously shown to bind dissolved hexavalent uranium (as UO22+ and/or its cationic hydroxy complexes), shows promise as the basis of an immobilized-cell process for removal of dissolved uranium from contaminated wastewaters. A number of polymeric materials, including calcium alginate, polyacrylamide, polysulfone, and polyurethane, were evaluated as possible immobilization matrices for lyophilized biomass of P. aeruginosa CSU. Polyurethane-based materials such as hydrogel were identified as superior candidates for biomass immobilization. A novel polyurethane gel-bead fabrication technique was developed and successfully demonstrated at pilot-plant scale for producing mass quantities of spherical, uniform-size beads. The immobilized bacterial biomass was evaluated via the measurement of sorption isotherms and dynamics within a batch, stirred-tank reactor; and loading and elution behavior within a continuous, upflow, packed-bed columnar reactor. Sorption equilibrium and dynamics in a batch stirred tank were modeled with a pore-diffusion mass transfer model, by which a pore-diffusion coefficient was determined to be approximately 2.0 × 10−6 cm2/s for uranyl ion transport through the polyurethane gel matrix. The biosorbent beads were regenerable with dilute (0.01–0.1 M) sodium carbonate solutions. Preliminary column breakthrough-elution studies indicated that P. aeruginosa CSU biomass immobilized within polyurethane gel beads was effective for removal of uranium from low-concentration, acidic wastewaters.

119 citations


Journal ArticleDOI
TL;DR: Considering low toxicity, effectiveness, and reasonable cost, the structurally simple linear tetradentate ligands based on the 5-LI backbone (diaminopentane) offer the most promising approach to a clinically acceptable therapeutic agent for U(VI.
Abstract: Soluble uranyl ion [UO2(2+), U(VI)] is a kidney poison. Uranyl ion accumulates in bone, and the high specific activity uranium isotopes induce bone cancer. Although sought since the 1940's, no multidentate ligand was identified, until now, that efficiently and stably binds U(VI) at physiological pH, promotes its excretion, and reduces deposits in kidneys and bone. Ten multidentate ligands patterned after natural siderophores and composed of sulfocatechol [CAM(S)], carboxy-catechol [CAM(C)], or hydroxypyridinone [Me-3,2-HOPO] metal-binding units have been tested for in vivo chelation of U(VI). Ligands were injected intraperitoneally (i.p.) into mice 3 min after intravenous (i.v.) injection of 233U or (232+235)U as UO2Cl2 [ligand-to-metal molar ratio 75 to 92]. Regardless of backbone structure, denticity, or binding unit, all 10 ligands significantly reduced kidney U(VI) compared with controls or with mice given CaNa3-DTPA, and four CAM(S) or CAM(C) ligands also significantly reduced skeleton U(VI). Several ligands removed U(VI) from kidneys, when injected at 1 or 24 h. Injected at molar ratios > or = 300, 5-LIO(Me-3,2-HOPO) and TREN-(Me-3,2-HOPO) reduced kidney U(VI) to about 10% of control. Given orally to fasted mice at molar ratios > or = 300, those ligands significantly reduced kidney U(VI). In mice injected i.v. with 0.42 micromol kg(-1) of 235U and given 100 micromol kg(-1) of one of those Me-3,2-HOPO ligands i.p. daily for 10 d starting at 1 h after the U(VI)) loss of kidney U(VI) was greatly accelerated, and the kidneys of treated mice showed no microscopic evidence of renal injury. Crystals of uranyl chelates with linear tetradentate ligands containing bidentate Me-3,2-HOPO groups demonstrate a 1:1 structure. Considering low toxicity, effectiveness, and reasonable cost, the structurally simple linear tetradentate ligands based on the 5-LI backbone (diaminopentane) offer the most promising approach to a clinically acceptable therapeutic agent for U(VI). Work is in progress to identify the most suitable CAM or HOPO binding unit(s).

88 citations


Journal ArticleDOI
TL;DR: Ianthinite as discussed by the authors is the only known uranyl oxide hydrate mineral that contains U 4+, and it has been proposed that ianthinite may be an important Pu 4+ -bearing phase during the oxidative dissolution of spent nuclear fuel.

85 citations


Journal ArticleDOI
TL;DR: In this article, a linear-chain β-uranyl phenylphosphonate (β-UPP) was synthesized using a single-crystal method and it was shown that the coordination of the uranium atoms is pentagonal bipyramidal, and the metal-to-phosphoneate ratio is 1:2.
Abstract: Single crystals of a recently prepared, at room temperature non-luminescent, linear-chain α-uranyl phenylphosphonate (α-UPP), [UO2(HO3PC6H5)2(H2O)]2·8H2O, transform at room temperature and moderate humidity into a new strongly luminescent linear-chain β-uranyl phenylphosphonate (β-UPP), UO2(HO3PC6H5)2(H2O)·2H2O. Both compounds have also been synthesized separately and characterized by single-crystal methods. The α-phase crystallizes in the triclinic space group P1, with a = 11.724(4) A, b = 16.676 A, c = 11.375 A, α = 101.61(5)°, β = 106.76(3)°, γ = 102.57(4)°, and Z = 2, whereas the β-phase crystallizes in the monoclinic space group P21/c with a = 7.766(2) A, b = 11.255(2) A, c = 20.959(4) A, β = 100.38(3)°, and Z = 4. In both compounds, the coordination of the uranium atoms is pentagonal bipyramidal, and the metal-to-phosphonate ratio is 1:2. The most obvious difference between the two linear-chain compounds is the manner in which their phenyl rings are arranged. When viewed along the appropriate axes,...

80 citations



Journal ArticleDOI
TL;DR: It is suggested that the architecture of the bacterial cell surface provides a means of access of uranyl ion to the inner and outer membranes and enzymically liberated phosphate in a way that minimizes fouling in whole cells.
Abstract: A heavy-metal-accumulating Citrobacter sp. has been used for the treatment of metal-laden industrial wastes. Metal uptake is mediated via a cell-bound phosphatase that liberates inorganic phosphate which precipitates with heavy metals as cell-bound metal phosphate. A phosphatase-efficient mutant accumulated little UO(2)2+, while a phosphatase-overproducing mutant accumulated correspondingly more metal, with a uranium loading equivalent to the bacterial dry weight achieved after 6 h exposure of resting cells to uranyl ion in the presence of phosphatase substrate (glycerol 2-phosphate). The phosphatase, visualized by immunogold labelling in the parent and overproducing strains, but not seen in the deficient mutant, was held within the periplasmic space with, in some cells, a higher concentration at the polar regions. Enzyme was also associated with the outer membrane and found extracellularly. Accumulated uranyl phosphate was visible as cell-surface- and polar-localized deposits, identified by energy-dispersive X-ray analysis (EDAX), proton-induced X-ray emission analysis (PIXE) and X-ray diffraction analysis (XRD) as polycrystalline HUO2PO4.4H2O. Nucleation sites for initiation of biocrystallization were identified at the cytoplasmic and outer membranes, prompting consideration of an in vitro biocatalytic system for metal waste remediation. Phosphatidylcholine-based liposomes with entrapped phosphatase released phosphate comparably to whole cells, as shown by 31P NMR spectroscopy in the presence of 'NMR-silent' 112Cd2+. Application of liposome-immobilized enzyme to the decontamination of uranyl solutions was, however, limited by rapid fouling of the biocatalyst by deposited uranyl phosphate. It is suggested that the architecture of the bacterial cell surface provides a means of access of uranyl ion to the inner and outer membranes and enzymically liberated phosphate in a way that minimizes fouling in whole cells.

78 citations


Journal ArticleDOI
TL;DR: In this article, an alteration phase that formed during the corrosion of commercial oxide spent nuclear fuel has been characterized with analytical transmission electron microscopy (AEM), and the phase is a CsBa uranyl molybdate oxide hydrate that has an orthorhombic structure related to the alkaline earth uranyl oxide hydrates of the protasite-group minerals.

71 citations


Journal ArticleDOI
TL;DR: The decrease of metal uptake with an increase of DA and the lack of influence of ionic strength, confirm the results obtained with pH and allow us to suppose the formation of a complex with chitosan amino groups rather than interactions of an electrostatic nature.

62 citations


Journal ArticleDOI
TL;DR: In this article, the properties of sol−gel glasses templated with uranyl ions have been investigated and the enhanced capacity and selectivity are tentatively attributed to the change of the binding constant and the modification of the microporous structure of the sol-gel glasses induced by the imprinting technique.
Abstract: The properties of sol−gel glasses templated with uranyl ions have been investigated. Techniques have been developed to remove the template uranyl ions from silica matrixes to create uranyl-imprinted sol−gel silica glasses. A significant increase in affinity and selectivity of the imprinted sol−gel sorbents over control blanks has been observed while the surface areas of both remain equal. The enhanced capacity and selectivity are tentatively attributed to the change of the binding constant and the modification of the microporous structure of the sol−gel glasses induced by the imprinting technique.

Journal ArticleDOI
TL;DR: In this paper, X-ray absorption spectroscopy (XAS) is used to determine the uranium speciation in exchanged and surface modified clays, and the implications of the uranyl reduction to environmental remediation are discussed.
Abstract: X-ray absorption spectroscopy (XAS) is used to determine the uranium speciation in exchanged and surface-modified clays. XAS data from uranyl-loaded bentonite clays are compared with those obtained after the particle surfaces have been coated with alkylsilanes. These silane films, which render the surface of the clay hydrophobic, are added in order to minimize the ability of extemal water to exchange with the water in the clay interlayer, thereby decreasing the release rate of the exchanged-uranium species. Mild hydrothermal conditions are used in an effort to mimic potential geologic conditions. The uranyl monomer species remain unchanged in most samples, except for those samples that were both coated with an alkylsilane and hydrothermally treated. When the clay is coated with an organic film, hydrothermal treatment results in the aggregation of a U(IV) species. This uranyl reduction, which occurs only in the presence of both the clay and the organic coating, is compared to similar Fe and Cu reductions that occur when exchanged clays are used as catalysts for organic reactions. The implications of the uranyl reduction to environmental remediation are discussed.

Journal ArticleDOI
TL;DR: In this paper, the interatomic uranium-oxygen distances of reaction products at the mineral surface were determined using extended X-ray absorption fine structure (EXAFS) spectroscopy.

Journal ArticleDOI
TL;DR: The structure of vandendriesscheite has been solved by direct methods and refined by full-matrix least squares techniques to an agreement factor (R) of 12.1% and a goodness-of-fit (S) of 1.28 using 4918 unique observed reflections (ZFoz $ 4sF) collected with MoKa X-radiation and a CCD (chargecoupled device) detector as mentioned in this paper.
Abstract: The structure of vandendriesscheite, Z 5 8, Pb1.57[(UO2)10O6(OH)11](H2O)11, orthorhombic, a 5 14.1165(6), b 5 41.378(2), c 5 14.5347(6) A ˚, V 5 8490 A ˚ 3 , space group Pbca, has been solved by direct methods and refined by full-matrix least-squares techniques to an agreement factor (R) of 12.1% and a goodness-of-fit (S) of 1.28 using 4918 unique observed reflections ( zFoz $ 4sF) collected with MoKa X-radiation and a CCD (chargecoupled device) detector. The structure contains ten unique U 61 positions, each of which is part of a nearly linear (UO2) 21 uranyl ion that is further coordinated by five equatorial (O 22 ,OH 2 ) anions to form pentagonal bipyramidal polyhedra. There are two unique Pb positions; one is fully occupied, but site-scattering refinement gives an occupancy factor of 0.573(8) for the other. The Pb positions are coordinated by O atoms of the uranyl ions and by H2O groups. There are 11 unique H2O groups; five are bonded to Pb and the other six are held in the structure by hydrogen bonds only. The U polyhedra link by the sharing of equatorial edges to form sheets parallel to (001). The sheet of U polyhedra is not known from another structure and is the most complex yet observed in a uranyl oxide hydrate. The sheets are structurally intermediate to those in schoepite and becquerelite and are linked by bonds to the interlayer Pb cations and the H2O groups. The extensive network of hydrogen bonds that link adjacent sheets is derived on the basis of crystal-chemical constraints. The high mobility of U 61

Journal ArticleDOI
TL;DR: In this paper, it was shown that neptunium can become incorporated into the uranyl secondary phase, dehydrated schoepite (UO{sub 3 lg_bullet}0.8H{sub 2}O).
Abstract: Uranyl oxide hydrate phases are known to form during contact of oxide spent nuclear fuel with water under oxidizing conditions; however, less is known about the fate of fission and neutron capture products during this alteration. We describe, the first time, evidence that neptunium can become incorporated into the uranyl secondary phase, dehydrated schoepite (UO{sub 3}{lg_bullet}0.8H{sub 2}O). Based on the long-term durability of natural schoepite, the retention of neptunium in this alteration phase may be significant during spent fuel corrosion in an unsaturated geologic repository.

Journal ArticleDOI
Abstract: A new polymeric adsorbent bearing both hydrophilic groups providing swelling in water and amidoxime groups for chelating with uranyl ions (UO22+), has been developed and its adsorptive ability for recovering uranium from aqueous media has been investigated. The polymers obtained by irradiating the solution of polyethylene glycol (PEG) in acrylonitrile (AN) are defined as interpenetrating polymer networks (IPNs) and the adsorbent has been obtained by applying the amidoximation reaction to the IPNs with a conversion ratio of ∼ 60%. Kinetics of the conversion reaction of the cyano (CN) group to the amidoxime (HONCNH2) group has been studied by reacting with hydroxylamine (NH2OH) solution at a molar ratio of NH2OH/CN = 1.25 in aqueous media at three different temperatures, 30, 40, and 50°C, for 3–4 days. The degree of amidoximation ratio was determined by UO22+ ion adsorption and FTIR spectrometry and the UO22+ ion adsorption values were found by both UV and gamma spectrometry and also by gravimetry. It was found that the polymeric adsorbent has a very high adsorption ability for uranium and quite a good stability in aqueous media. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2475–2480, 1997

Journal ArticleDOI
TL;DR: The optimum pH for uranium uptake was between 50.8501_20 M NaCl enhanced uranyl, while Cu2+, Ni2+, Zn2+, Cd2+ and Mn2+ competed slightly with uranyl as mentioned in this paper.
Abstract: Accumulation of UO 2 2 + by Scenedesmus obliquus 34 was rapid and energy-independent and the biosorption of UO 2 2 + could be described by the Freundlich adsorption isotherm below the maximum adsorption capacity (75 mg g-1 dry wt) The optimum pH for uranium uptake was between 50_8501_20 M NaCl enhanced uranyl, while Cu2+, Ni2+, Zn2+, Cd2+ and Mn2+ competed slightly with uranyl Pretreatment had an unexpected effect on biosorption After being killed by 01 M HCl, S Obliquus 34 showed 45% of the uptake capacity of the control in which fresh cells were suspended directly in uranyl solution, while the pretreatment of cells by 01 M NaOH, 20 M NaCl, ethanol or heating decreased uptake slightly Fresh S obliquus 34 at 12_24 mg dry wt mL-1 was able to decrease U from 50 to 005 mg L-1 after 4_6 equilibrium stages with batch adsorption Deposited U could be desorbed by pH 40 buffer It is suggested that U was captured by effective groups or by capillary action in the cell wall in the form of [UO2OH]+

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the effect of phosphoric acid, CYANEX-921 and HDEHP concentrations, as well as temperature on the extraction of uranyl ions.
Abstract: The extraction of uranyl ions from different phosphoric acid media by CYANEX-921 (a commercial trioctyl phosphine oxide) mixed with di-2-ethylhexyl phosphoric acid diluted with odourless kerosene has been investigated. The effect of phosphoric acid, CYANEX-921 and HDEHP concentrations, as well as temperature on the extraction were studied. The extraction rate for UO22+ transfer from 5 M phosphoric acid to the organic phase containing a CYANEX-921–HDEHP mixture in a single drop column without external force was also studied. The mass transfer of uranium in the organic extractant single drop was investigated in terms of drop size, uranium concentration as well as other parameters. The extraction rate was found to be mainly dependent on uranium, HDEHP and phosphoric acid concentrations, and found to be mainly controlled by diffusion in the single drop. Further, it was found that CYANEX-921 can substitute TOPO to synergise the extraction of UO22+ by HDEHP. © 1997 SCI.

Journal ArticleDOI
01 Feb 1997-Talanta
TL;DR: This paper deals with the development and standardization of procedures for the determination of uranium on a routine basis in various process streams of a uranium extraction plant, covering a wide range of concentrations from 350 g 1 (-1) down to 5 mg 1(-1) using only a spectrophotometric technique.

Journal ArticleDOI
TL;DR: In this paper, the photo-oxidation of 2,6-dimethylphenol and o -, m - and p -phenylphenols by uranyl ion was investigated in aqueous solution.
Abstract: The photo-oxidation of 2,6-dimethylphenol and o -, m - and p -phenylphenols by uranyl ion was investigated in aqueous solution. Steady state and dynamic luminescence quenching studies at pH 0.8 show the rapid dynamic deactivation of excited uranyl ions by the phenols. At the natural pH of uranyl salt solutions (pH 2.3), differences are observed between the steady state and dynamic quenching behaviour, and it is suggested that these differences are due to uranyl hydrolysis. Flash photolysis studies with uranyl ion in the presence of 2,6-dimethylphenol and m - and p -phenylphenols show that the initial photoreaction leads to phenoxyl radical formation. The photolysis products were identified by high performance liquid chromatography (HPLC) and UV absorption spectroscopy. With 2,6-dimethylphenol in aerated solution, both quinone and dimer formation are observed. Kinetic studies show that these processes occur concurrently. In contrast, photolysis of degassed solutions leads to dimer formation only. The quantum yields for these processes are reported. The photo-oxidation of aerated solutions of o -phenylphenol in the presence of uranyl ions leads to the production of two dimers and the quinone, whereas with degassed solutions only the dimers are observed. The photo-oxidation of these substrates by uranyl ion is contrasted with the behaviour of [Co(NH 3 ) 5 N 3 ] 2+ as photooxidant of the same substrates. With m -phenylphenol, quinone and dimers are observed in aerated solution, whereas only the dimer is observed in deoxygenated solution. With p -phenylphenol, only dimer formation is observed. Possible mechanistic origins of the differences in the selectivity of oxidation by the different metal complexes are discussed.

Journal ArticleDOI
TL;DR: In this paper, a relation between symmetric V1 and asymmetric v3 O-U-O frequencies independent on the masses of oxygen (Mo) and uranium (Mu) atoms was proposed.
Abstract: New series of uranyl complexes derived from 7-formyl-8-hydroxy quinoline with hydrazine hydrate (HL1), methyl hydrazine (HL2), 1,2-diaminoethane (HL3), 1,2-diaminobenzene (HL4) and 2-aminopyridine (HL5) have been prepared and characterized by elemental analyses, (1H NMR and 13C NMR, electronic and vibrational spectra) and different physical techniques. The magnetic and spectral data suggest a distorted octahedral structure for all complexes. The labile EtOH molecule in compounds (5), (7) and (9) is equatorially bonded to the uranium ion and its hydrogen is bonded to the axial oxygen of the uranyl moiety. The ligands contain intramolecular hydrogen bonds. The FU-O(mydn/Ao) and the bond length RU-O(Ao) of the bond were calculated from the IR data. In the present work it has been proposed a novel relationship between symmetric “V1” and asymmetric “v3” O-U-O frequencies independent on the masses of oxygen (Mo) and uranium (Mu) atoms.

Journal ArticleDOI
TL;DR: In this paper, an analysis and ab initio calculation of the EXAFS and XANES spectra corresponding to the model compound UO2(NO3)2(TIBP)2] (with TIBP = tri-iso-butylphosphate) for which the crystal structure is known.

Journal ArticleDOI
B. Teiten1, A. Burneau1
TL;DR: In this paper, a quantitative study of the SER spectra as a function of total uranyl concentrations in the colloid, ranging between 5 ×10-9 and 1×10-5M, shows that half of the sorption sites are occupied by uranyl for a total uranium concentration of about 10-7M; from this value, a 100fold concentration increase induces only a twofold enhancement of the uranyl band at 840 cm-1, although no appreciable change of the colloidal appears.
Abstract: An aqueous silver colloid activated at 514 nm with 10-3MN-(2-mercaptopropionyl)glycine (MPG) involves surface-active sites for the complexation of uranyl ions and displays the νs UO22+ SER spectrum at 840 cm-1, allowing uranyl detection at concentrations as low as 5×10-9M. This level of detection competes successfully with spectrophotometric and fluorimetric determination. A quantitative study of the SER spectra as a function of total uranyl concentrations in the colloid, ranging between 5×10-9 and 1×10-5M, shows that half of the sorption sites are occupied by uranyl for a total uranyl concentration of about 10-7M; from this value, a 100-fold concentration increase induces only a twofold enhancement of the uranyl band at 840 cm-1, although no appreciable change of the colloid appears. As a result of an analysis of the uranyl complexation either in solution or simultaneously with several sorbed MPG molecules, the surface site concentration for uranyl sorption in the colloid used is estimated to be close to 10-8M. This value corresponds to about one complexation site per primary particle of silver, perhaps at contacts between aggregated particles. At such sites, MPG molecules bonded to the metal surfaces through S—Ag bonds still involve amide and carboxylate groups free to coordinate an uranyl ion. The mean enhancement of the Raman cross-section of uranyl at the surface complexation sites reaches 3×105 with respect to uranyl nitrate aqueous solution. © John Wiley & Sons, Ltd.

Journal ArticleDOI
TL;DR: In this article, the biexponential decay of aqueous uranyl was investigated through pH, lifetime and steady state absorption and emission spectral studies, and the luminescence above 5 × 10 −4 M could be attributed to the hydrated monomer (UO 2 2 2+ ) aq and the dimer (uO 2 ) 2 (OH) 2 2 + formed by the hydrolysis of uranyl giving lifetimes of 1.37 ± 0.04 and 8.71 ± 0.60 μ s respectively with K eq = (2

Journal ArticleDOI
TL;DR: In this article, the use of capillary electrophoresis (CE) and time-resolved laser-induced fluorescence (TRLIF) is used to characterize the different complexes of uranium.
Abstract: The study of the chemical behavior of uranium in biological medium is still of great interest. By the use of capillary electrophoresis (CE) and time-resolved laser-induced fluorescence (TRLIF), it is possible to characterize the different complexes of uranium. Hence, CE, using the isoelectric focusing mode (CIEF), allows for the separation of the different complexes as a function of their isoelectric points (pI) and TRLIF as a speciation method leads to the identification at very low level of different uranyl complexes by temporal resolution and spectral deconvolution. Results obtained on various inorganic chemical systems (phosphate, bicarbonate) together with biological systems (citrate, transferrin) will be presented and discussed. The complexation between uranium and human transferrin has been pointed out through CIEF.

Journal ArticleDOI
TL;DR: In this paper, a ternary alkali-metal carbonate melt (Li-Na-K)2CO3 containing added chlorides or sulfates has been studied in the range 723-1023 K and a variety of uranium(VI) species was obtained.
Abstract: The oxidation of uranium dioxide to uranates in the ternary alkali-metal carbonate melt (Li–Na–K)2CO3 containing added chlorides or sulfates has been studied in the range 723–1023 K and a variety of uranium(VI) species was obtained. Increased oxygen solubility in fused carbonates was achieved by adding alkali-metal chloride or sulfate. The yield of uranates in chloride-containing melts decreased with increasing radius of the alkali-metal chloride cation, Li Na > K > Cs. When UO2 was oxidised in alkali chloride containing carbonate melts no intermediate uranium chloride complexes were observed. The temperature required for complete oxidation of UO2 can be lowered by 100–150 K by the addition of alkali-metal chlorides to carbonate melts. The addition of chloride and aluminium ions to form AlCl4− effected UO2 oxidation by a different mechanism, through intermediate formation of uranyl complexes, but the yield of uranates was not significantly altered. Attempts at oxidation by direct addition of potassium superoxide at 723 K were inefficient owing to thermal instability of the reagent, but UO2 oxidation was enhanced, by more than 10%, by superoxide formed insitu by the reaction of peroxide and nitrate, compared with oxidation by peroxide or nitrate individually. Optimum conditions for complete oxidation at 723 K required a peroxide:nitrate mole ratio of ca. 3. The major reaction pathway in melts containing nitrate and peroxide, at various concentrations of these reactants, was determined. At a mole ratio of oxidiser to UO2 of 0.3, the percentage of UO2 oxidised and the yield of uranates, increased in the order Na2O2 ≈ KO2 < KNO2 < KNO3 < KNO3 + Na2O2. Evidence has been obtained for a new sodium uranate, Na2O(UO3−y)x (1 < x <2 ; y < 0.02).

Journal ArticleDOI
01 Jan 1997
TL;DR: The synthesis and crystal structure of the inclusion complex between uranyl and p-tert-butylcalix[5]arene were reported in this article, where the UO2 was shown to have a conventional R value of 0043 for 4155 reflections.
Abstract: The synthesis and crystal structure of the inclusion complex between uranyl and p-tert-butylcalix[5]arene are reported [UO2 (p-tert-butylcalix[5]arene-4H]2- ·\({\text{2HNE}}_{{\text{t}}_{\text{3}} }^{\text{ + }} \) &·2MeOH(1) crystallizes in the monoclinic space group C2/c, a = 3006(2), b = 1820(3), c = 3135(2) A, β = 12851(6)°, V = 13423(40) A3, Z = 8 Refinement led to a final conventional R value of 0043 for 4155 reflections The uranyl ion is bonded, in its equatorial plane, to the five oxygen atoms of the calixarene, four of which are deprotonated A protonated triethylamine molecule is located inside the calixarene cavity and hydrogen bonded to a uranyl oxygen atom, and another one outside and hydrogen bonded to a calixarene oxygen atom The calixarene conformation is the usual cone one

Journal ArticleDOI
TL;DR: In this article, the uranyl polychalcogenide compounds Cs 4 (UO 2 )(S 2 ) 3 and Na 4(S2 ) 3 ·Na 2 S 3 were synthesized in molten polysulfide salts in the temperature range of 350-400°C and were characterized with single crystal X-ray crystallography.

Journal ArticleDOI
TL;DR: In this article, the effect of pH and anions on the complexation of uranyl with arsenazo III was investigated using spectrophotometric techniques together with computer simulations, and it was found that the 1 ǫ: 1 arsenazoIII-uranyl complex has four protonation states which respectively dominate at pH 2.2, 5.0, 7.8 and > 10.0.

Journal ArticleDOI
TL;DR: In this article, the longest luminescence lifetime, 0.269±0.006 ms, was observed from uranyl in 1 M HF+1 M HClO4 at 296 K and decreased with increasing temperature.