Complex formation of peroxouranyl (and uranyl) with polyaminocarboxylate ligands

Complexation of the uranyl ion (UO₂²⁺) and of the peroxouranyl species (UO₄) by some polyaminocarboxylate ligands has been investigated in solution (3M NaClO₄) at 25°C. The logarithms of the cumulative formation constants of the UO₂²⁺ chelates formed are: UO₂edta^2? (15.65), UO₂Hedta^? (18.59), (UO₂)₂edta (20.24); UO₂edda (16.02); UO₂Hnta (12.19); UO₂ida (9.63), UO₂H₂(ida)₂ (23.80). The equilibrium UO₂²⁺ + H₂O₂ ? UO₄ + 2H⁺ has a stability log K = ?3.99. The peroxocomplexes formed are UO₄Hedda^? (14.81, expressed from UO₂²⁺ and H₂O₂) and UO₄Hnta^2? (8.50). Solution structures of the chelates are proposed.     

Ein neues Oxouranat(VI): K2Li4[UO6]. Mit einer Bemerkung über Rb2Li4[UO6] und Cs2Li4UO6

A New Oxouranate(VI): K₂Li₄[UO₆]. With a Remark about Rb₂Li₄[UO₆] and Cs₂Li₄[UO₆] For the first time K₂Li₄UO₆ has been prepared by an exchange reaction of α-Li₆UO₆ with K₂O [K:U = 2.0:1, sealed au-tube; 750°C; 30 d single crystals; 680°C, 10 d powder]. The irregular shaped single crystals, which are of yellow color and sensitive to moisture crystallize in P3 m1 (Z = 1) with a = 619.27(5), c = 533.76(6) pm. The structure determination (PW 1100, AgKα R = 4.80%, R_w = 4.81% for 220 unique reflexions) reveals a new type of structure. The characteristic elements are the isolated group [UO₆] and the C.N. = 12 for K⁺. While Li(1) has a nearly regular square of 4 O^2? as coordination polyhedron, Li(2) is octahedrally surrounded. The Madelung Part of Lattice Energy (MAPLE) is calculated and discussed. In addition to K₂Li₄[UO₆] the new oxides Rb₂Li₄[UO₆] and Cs₂Li₄[UO₆] are prepared as pale yellow powders which are little sensitive to moisture (both: au-tube, 680°C, 10 d). According to powder datas both compounds are isotypic with K₂Li₄[UO₆] [Rb₂Li₄[UO₆]: a = 622.91(5), c = 535.93(6) pm; Cs₂Li₄[UO₆]: a = 626.70(6), c = 539.92(6) pm].     

Syntheses and structures of three disulfoxide uranyl complexes

Three disulfoxide uranyl complexes [UO₂(DBSOB)(NO₃)₂] _n (1), [UO₂(DBM)₂]₂(DBSOB) (2), and [UO₂(PMBP)₂]₂(DBSOB) (3) (DBSOB = 1,4-di(butylsulfinyl)butane, HDBM = dibenzoylmethane, HPMBP = 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone) were synthesized and characterized. The [UO₂(NO₃)₂] groups are connected by bridging disulfoxide ligands DBSOB to form a 1-D zigzag chain in 1. Two [UO₂(DBM)₂] or [UO₂(PMBP)₂] groups are connected by a bridging DBSOB to form the dimeric structures of 2 or 3, respectively. Complexes 1, 2, and 3 are the first structurally characterized disulfoxide–actinide compounds. Thermal stabilities of 1, 2, and 3 were investigated.     

Polarography of Uranium Chelate with 2,3-Cresotic Acid

The polarography of uranyl ion in 2,3-cresotic acid solution has been studied at 25°C under varying conditions of ligand concentration and pH. The ligands species were proved to be a 2,3-cresotate anion. The half-wave potential vs. pH value interpreted on the basis of pK value for the acid ionization, and resulted in agreement with the deduction. The mole ratio of metal to ligand was found to be 1:1 and 1:2 by conductometric titration. At pH < pK₁, the complex species of UO₂(H₂A)²⁺ and UO₂(HA)⁺ was identified. At pK₁ < pH < pK₂, the co-existence of UO₂(HA)⁺, UO₂(OH)(HA)₂^? and UO₂(A)₂^2– was confirmed. At pH > pK₂, the complex species of UO₂(OH) (A)₂^3– was formed.     

Modulation of the unpaired spin localization in Pentavalent Uranyl Complexes

The electronic structure of various complexes of pentavalent uranyl species, namely UO₂⁺, is described, using DFT methods, with the aim of understanding how the structure of the ligands may influence the localisation of the unpaired 5f electron of uranium (V) and, finally, the stability of such complexes towards oxidation. Six complexes have been inspected: [UO₂py₅]⁺ (1), [(UO₂py₅)KI₂] (2), [UO₂(salan-^tBu₂)(py)K] (3), [UO₂(salophen-^tBu₂)(thf)K] (4), [UO₂(salen-^tBu₂)(py)K] (5), [and UO₂-cyclo[6]pyrrole]^1? (6), chosen to explore various ligands. In the five first complexes, the UO₂⁺ species is well identified with the unpaired electron localized on the 5f uranium orbital. Additionally, for the salan, salen and salophen ligands, some covalent interactions have been observed, resulting from the presence of both donor and acceptor binding sites. In contrast, the last complex is best described by a UO₂²⁺ uranyl (VI) coordinated by the anionic radical cyclopyrrole, the highly delocalized π orbitals set stabilizing the radical behaviour of this ligand.     

Study of solvent extraction of <Superscript>114m</Superscript>In(III) using quinaldic acid into isoamyl alcohol

A complementary study of hydroxyl radical formation in the depleted uranium (DU)-hydrogen peroxide (H₂O₂) system and the effect of biosubstances on the system were examined using the spin-trapping method. Hydroxyl radical was formed in the uranyl ion (UO₂ ²⁺), 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), and hydrogen peroxide (H₂O₂) mixture solution. The pseudo first order rate constants of DMPO-OH formation were estimated to be 0.033 s⁻¹ for UO₂ ²⁺-H₂O₂-DMPO solution and 0.153 s⁻¹ for UO₂₊-H₂O₂-DMPO solution. The obtained results indicated that the hydroxyl radical formation in the UO₂ ²⁺-H₂O₂ solution could be described as a stepwise reaction process including the reduction of UO₂ ²⁺ to UO₂ ²⁺ by H₂O₂ and the Fenton-type reaction of UO₂ ⁺ with H₂O₂. Biosubstances, such as proteins, amino acids and saccharides, decreased the DMPO-OH formation, which was caused by the direct hydroxyl radical scavenging and the suppression of hydroxyl radical formation by coupling with uranyl ion.     

The potential/pO2− diagrams of uranium and the feasibility of a pyrochemical head-end treatment of nuclear fuels in molten chlorides

In this paper, the values of the solubility products of UO₂ and MgUO₄ in the (K–Na–Mg 1/2)Cl eutectic and the solubility products of UO₂ and (K,Na)UO₃ in the (K–Na)Cl eutectic are reported. The complete potential/pO^2– diagram of uranium is set up in these liquid melts and a method of separation UO₂/PuO₂ is discussed in the molten chlorides media.     

Vibrational spectroscopic studies of uranyl complexes in aqueous and non-aqueous solutions

Vibrational spectra have been obtained for aqueous solution of uranyl-perchlorates, -fluorides, -chlorides, -acetates and -sulphates over a range of solution composition with added anions. We have prepared [Buⁿ₄N][UO₂Cl₄], [Me₄N][UO₂Cl₄], [Prⁿ₄N][[UO₂(NO₃)₃], [Buⁿ₄N][UO₂(NO₃)₃], with the expectation that the large cation would give a better approximation to vibrational frequencies of the free anion and would allow measurements in non-coordinating solvents. As the perchlorate is not coordinated to [UO₂]²⁺ in aqueous solution the expected structure is a solvated cation [UO₂(OH₂)₅]²⁺ with characteristic infrared 962.5, 253 and 160 cm⁻¹ and Raman 874 and 198 cm⁻¹ bands. The formation of weak, solvated [UO₂X]⁺ complexes (X=F, Cl) has been established with frequencies at 908, 827, 254, 380 cm⁻¹ and 956, 871, 254 and 222 cm⁻¹ for [UO₂F]⁺ and [UO₂Cl]⁺, respectively. Bidentate NO₃ coordination has been established for solid and dissolved (in CH₂Cl₂) [R₄N][UO₂(NO₃)₃] (R=Prⁿ, Buⁿ). Aqueous solutions of UO₂(NO₃)₂ and Cs[UO₂(NO₃)₃] show no clear evidence that bidentate or monodentate nitrate is present. Both unidentate and bidentate linkage of acetate-uranyl were established for acetate complexes in aqueous solutions. For the uranyl sulphate system, monodentate sulphate coordination is the major mode at low SO₄:U ratios, and even at a ratio of 3:1 there is very little free sulphate.     

A new series of pillared uranyl-vanadates based on uranophane-type sheets in the uranium-vanadium-linear alkyl diamine systems

A new family of three-dimensional (3D) uranyl vanadates (C₃N₂H₁₂){[(UO₂)(H₂O)][(UO₂)(VO₄)]₄}·1H₂O (C3UV), (C₄N₂H₁₄){[(UO₂)(H₂O)][(UO₂)(VO₄)]₄}·2H₂O (C4UV), (C₅N₂H₁₆) {[(UO₂)(H₂O)][(UO₂)(VO₄)]₄} (C5UV), (C₆N₂H₂₀) {[(UO₂)(H₂O)][(UO₂)(VO₄)]₄} (C6UV) and (C₇N₂H₂₂) {[(UO₂)(H₂O)][(UO₂)(VO₄)]₄} (C7UV) was prepared from mild-hydrothermal reactions using 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane and 1,7-diaminoheptane as structure directing agents. The five compounds are orthorhombic, space group Cmc2₁, with a≈15.6, b≈14.1, c≈13.6 Å. The structures were solved using single-crystal X-ray diffraction data. The compounds contain the same three-dimensional inorganic framework built from uranyl-vanadate layers of uranophane-type anion topology pillared by [UO₆(H₂O)] pentagonal bipyramids. The doubly protonated diamines reside in the cavities created by the inorganic framework and are linked to the inorganic framework through hydrogen bonds involving one nitrogen atom. The structure is compared with that of uranyl-phosphates and uranyl-arsenates containing alkaline metals. The use of alkaline metals for the synthesis of uranyl-vanadates leads to carnotite-type compounds.     

Uranium(VI) sequestration by polyacrylic and fulvic acids in aqueous solution

Stability data on the formation of dioxouranium(VI) species with polyacrylic (PAA) and fulvic acids (FA) are reported with the aim to define quantitatively the sequestering capacity of these high molecular weight synthetic and naturally occurring ligands toward uranium(VI), in aqueous solution. Investigations were carried out at t = 25 °C in NaCl medium at different ionic strengths and in absence of supporting electrolyte for uranyl–fulvate ( \textUO₂²⁺ {{\text{UO}}_{2}}^{2+} –FA) and uranyl–polyacrylate ( \textUO ₂ ²⁺ {{\text{UO}}_{ 2}}^{ 2+ } –PAA, PAA MW 2 kDa) systems, respectively. The experimental data are consistent with the following speciation models for the two systems investigated: (i) UO₂(FA₁), UO₂(FA₁)(FA₂), UO₂(FA₁)(FA₂)(H) for \textUO ₂ ²⁺ {{\text{UO}}_{ 2}}^{ 2+ } –fulvate (where FA₁ and FA₂ represent the carboxylic and phenolic fractions, respectively, both present in the structure of FA), and (ii) UO₂(PAA), UO₂(PAA)(OH), (UO₂)₂(PAA)(OH)₂ for \textUO ₂ ²⁺ {{\text{UO}}_{ 2}}^{ 2+ } –polyacrylate. By using the stability data obtained for all the complex species formed, the uranium(VI) sequestration by PAA and FA was expressed by the pL₅₀ parameter [i.e. the −log(total ligand concentration) necessary to bind 50% of uranyl ion] at different pH values. A comparison between pL₅₀ values of FA and PAA and some low molecular weight carboxylic ligands toward uranyl ion is also given.     

Reactions of tetrachlorodioxouranate(VI) ion with neutral and protic ligands

Summary The reactions of [bipyH₂][UO₂Cl₄]·3H₂O (bipyH₂=diprotonated 2,2-bipyridyl) with a series of neutral and protic oxygen donor ligands have been investigated. N,N-dimethyl formamide (DMF), N,N-dimethyl acetamide (DMA) and dimethyl sulphoxide (DMSO) gave compounds of the type [bipyH₂][UO₂Cl₄(L)₂] (L=DMF or DMA) and [bipyH₂][UO₂Cl₄(DMSO)_n] (DMSO)_3-n (n=1 or 2), while [bipyH₂][UO₂Cl₄-(3PNO)(DMSO)_n](DMSO)_2-n (n=1 or 2) and [bipyH][UO₂Cl₃(4PNO)(DMSO)] were obtained with 3-picoline N-oxide (3PNO) and 4-picoline N-oxide (4PNO) respectively from DMSO medium. With excess 2-picoline N-oxide (2PNO) the compound [bipyH][UO₂Cl₃(2PNO)](DMSO) was obtained. Reaction with acetyl acetone (AcAcH) and 8-hydroxy quinoline (QH) in 1:1 mole ratio in DMSO gave compounds of the type [bipyH₂][UO₂Cl₃(L)(DMSO)] (L=AcAc or Q). The compounds have been investigated by i.r. spectra, powder x-ray diffraction and molar conductivity measurements.     

Dissolution of uranium oxides under alkaline oxidizing conditions

Bench scale experiments were conducted to determine the dissolution characteristics of UO₂, U₃O₈, and UO₃ in aqueous peroxide-containing carbonate solutions. The experimental parameters investigated included carbonate countercation (NH₄ ⁺, Na⁺, K⁺, and Rb⁺) and H₂O₂ concentration. The carbonate countercation had a dramatic influence on the dissolution behavior of UO₂ in 1 M carbonate solutions containing 0.1 M H₂O₂, with the most rapid dissolution occurring in (NH₄)₂CO₃ solution. The initial dissolution rate (y) of UO₂ in 1 M (NH₄)₂CO₃ increased linearly with peroxide concentration (x) ranging from 0.05 to 2 M according to: y = 2.41x + 1.14. The trend in initial dissolution rates for the three U oxides under study was UO₃ ≫ U₃O₈ > UO₂.     

Framework Polymorphism and Modular Crystal Structures of Uranyl Vanadates of Divalent Cations: Synthesis and Characterization of M(UO2)(V2O7) (M = Ca,Sr) and Sr3(UO2)(V2O7)2

Uranyl vanadate compounds with divalent cations, M(UO₂)(V₂O₇) (M = Ca, Sr) and Sr₃(UO₂)(V₂O₇)₂, were synthesized by flux crystal growth, and their crystal structures were solved using single‐crystal X‐ray diffraction data. Ca(UO₂)V₂O₇ and Sr(UO₂)V₂O₇ were synthesized from reactants with molar ratios M:U:V of 1:1:2 and identical heating conditions, and increasing the M:U:V ratio to 3:1:4 resulted in Sr₃(UO₂)(V₂O₇)₂. Crystallographic data for M(UO₂)V₂O₇ compounds are: a = 7.1774(18) Å, b = 6.7753(17) Å, c = 8.308(2) Å; V = 404.01(18) ų; space group Pmn2₁, Z = 2 for Ca; a = 13.4816(11) Å, b = 7.3218(6) Å, c = 8.4886(7) Å; V = 837.91(12) ų; space group Pnma, Z = 4 for Sr. Compound Sr₃(UO₂)(V₂O₇)₂ has a = 6.891(3) Å, b = 7.171(3) Å, c = 14.696(6) Å, α = 85.201(4)?, β = 78.003(4)?, γ = 89.188(4)?; V = 707.9(5) ų; space group P1 , Z = 2. The framework structure of Sr(UO₂)(V₂O₇) is related to that of Pb(UO₂)(V₂O₇) reported previously, while that of Ca(UO₂)(V₂O₇) has a different topology. The topological polymorphism of the [(UO₂)(V₂O₇)]‐type framework may be due to the differing ionic radii of the guest M²⁺ cations. Compound Sr₃(UO₂)(V₂O₇)₂ has a modular structure based on two different types of electroneutral layers: [Sr(UO₂)(V₂O₇)] and [Sr₂(V₂O₇)]. Structural complexities were calculated, and Raman spectra were collected and their peaks were assigned.     

Effect of cobalt-60 gamma radiation on the determination of uranium(IV) in phosphoric acid solutions of uranium(iv) oxide

The effect of ⁶⁰Co γ-radiation on aerated and deaerated phosphoric acid solutions of uranium(IV) oxide (UO₂) was studied as a function of temperature, concentration of UO₂, and radiation dose rate. The effect was measured in terms of the radiolytic yield of uranium(VI),Gu_VI. For solutions of high initial UO₂ concentration, Gu(VI) is largest for the aerated solutions at 25°; it is lowest for the deaerated solutions at 140°. The Gu(VI) is lower for the solution of low initial UO₂ concentration than for any of the solutions of high initial UO₂ concentration. At the high starting UO₂ concentration, the initial Gu(VI) values are always higher than the succeeding values; this effect is attributed to the depletion of oxygen originally present in the solution. Gamma radiation causes an error in the determination of the stoichiometry of UO₂; the error is a function of the radiation dose. This error can be minimized by excluding oxygen from solutions of UO₂ and by keeping the initial UO₂ concentration as low as possible.     

Synthesis of a new ionic imprinted polymer for the extraction of uranium from seawater

The ionic imprinted polymer (IIP) of uranyl ion (UO₂ ²⁺) as the template was synthesized by the formation of binary complexes of UO₂ ²⁺ with 2,4-dioxopentan-3-yl methacrylate as functional monomer followed by thermal copolymerization with ethylene glycol dimethacrylate as cross-linking monomer in the presence of 2,2′-azobisisobutyronitrile as initiator and 1,4-dioxane as porogenic solvent. 50 mmol L^?1 HCl solution was used to leach out UO₂ ²⁺ ions from the IIP. Similarly, the control polymer was prepared under identical experimental conditions without using UO₂ ²⁺ ions. The above synthesized polymers were characterized by infra-red spectroscopy, thermo-gravimetric analysis and Barrett–Emmett–Teller surface area measurement. The maximum adsorption capacities of IIP and CP in (NH₄)₄[UO₂(CO₃)₃] solution were 15.3 and 11.2 mg U g^?1, respectively. The kinetics of adsorption followed a pseudo-second-order rate equation. The prepared IIP was successfully used to extract uranium from real seawater sample.     

ADSORPTION OF UO2 2+ BY POLYETHYLENE HOLLOW FIBER MEMBRANE WITH AMIDOXIME GROUP

The polyethylene (PE) membrane was prepared by the radiation-induced grafting of acrylonitrile (AN) onto PE hollow fiber and by the subsequent amidoximation of cyano groups in poly-AN graft chains. The adsorption characteristics of the chelating hollow fiber membrane was examined as the solution of UO₂ ²⁺ permeated across the chelating hollow fiber membrane. The inner and outer diameter increased with an increasing grafting yield, whereas, the pure water flux and pore diameter decreased with an increasing grafting yield. The adsorption of UO₂ ²⁺ by the chelating hollow fiber membranes increased with an increasing amidoxime group. The adsorbed amount of UO₂ ²⁺ in the uranyl acetate solution was higher than that in the uranyl nitrate solution. The adsorbed amount of UO₂ ²⁺ is higher than that of Cu²⁺ when the solution of UO₂ ²⁺ and Cu²⁺ permeated across the chelating membrane, respectively. The adsorption characteristics of UO₂ ²⁺ by the amidoxime group-chelating fiber membrane in the presence of Na¹⁺ and Ca²⁺ showed a high selectivity for UO₂ ²⁺ even though there was a high concen-tration of Na¹⁺ and Ca²⁺ in the inlet solution.     

Dioxouranium Complexes with Acetylpyridine Benzoylhydrazones and Related Ligands

Acetylpyridine benzoylhydrazone and related ligands react with common dioxouranium(VI) compounds such as uranyl nitrate or [NBu₄]₂[UO₂Cl₄] to form air‐stable complexes. Reactions with 2, 6‐diacetylpyridinebis(benzoylhydrazone) (H₂L^1a) or 2, 6‐diacetylpyridinebis(salicylhydrazone) (H₂L^1b) give yellow products of the composition [UO₂(L¹)]. The neutral compounds contain doubly deprotonated ligands and possess a distorted pentagonal‐bipyramidal structure. The hydroxo groups of the salicylhydrazonato ligand do not contribute to the complexation of the metal. The equatorial coordination spheres of the complexes can be extended by the addition of a monodentate ligand such as pyridine or DMSO. The uranium atoms in the resulting deep‐red complexes have hexagonal‐bipyramidal coordination environments with the oxo ligands in axial positions. The sterical strains inside the hexagonal plane can be reduced when two tridentate benzoylhydrazonato ligands are used instead of the pentadentate 2, 6‐diacetylpyridine derivatives. Acetylpyridine benzoylhydrazone (HL²) and bis(2‐pyridyl)ketone benzoylhydrazone (HL³) deprotonate and form neutral, red [UO₂(L)₂] complexes. The equatorial coordination spheres of these complexes are puckered hexagons. X‐ray diffraction studies on [UO₂(L^1a)(pyridine)], [UO₂(L^1b)(DMSO)], [UO₂(L²)₂] and [UO₂(L³)₂] show relatively short U—O bonds to the benzoylic oxygen atoms between 2.328(6) and 2.389(8) Å. This suggests a preference of these donor sites of the ligands over their imino and amine functionalities (U—N bond lengths: 2.588(7)—2.701(6) Å ).     

3D Uranyl Organic Frameworks Supported by Rigid Octadentate Carboxylate Ligand: Synthesis,Structure Diversity,and Luminescence Properties

Seven three dimensional (3D) uranyl organic frameworks (UOFs), formulated as [NH₄][(UO₂)₃(HTTDS)(H₂O)] ( 1 ), [(UO₂)₄(HTTDS)₂](HIM)₆ ( 2 , IM=imidazole), [(UO₂)₄(TTDS)(H₂O)₂(Phen)₂] ( 3 , Phen=1,10-phenanthroline), [Zn(H₂O)₄]_0.5[(UO₂)₃(HTTDS)(H₂O)₄] ( 4 ), and {(UO₂)₂[Zn(H₂O)₃]₂(TTDS)} ( 5 ), {Zn(UO₂)₂(H₂O)(Dib)_0.5(HDib)(HTTDS)} ( 6 , Dib=1,4-di(1H-imidazol-1-yl)benzene) and [Na]{(UO₂)₄[Cu₃(u₃-OH)(H₂O)₇](TTDS)₂} ( 7 ) have been hydrothermally prepared using a rigid octadentate carboxylate ligand, tetrakis(3,5-dicarboxyphenyl)silicon(H₈TTDS). These UOFs have different 3D self-assembled structures as a function of co-ligands, structure-directing agents and transition metals. The structure of 1 has an infinite ribbon formed by the UO₇ pentagonal bipyramid bridged by carboxylate groups. With further introduction of auxiliary N-donor ligands, different structure of 2 and 3 are formed, in 2 the imidazole serves as space filler, while in 3 the Phen are bound to [UO₂]²⁺ units as co-ligands. The second metal centers were introduced in the syntheses of 4–7 , and in all cases, they are part of the final structures, either as a counterion ( 4 ) or as a component of framework ( 5 − 7 ). Interesting, in 7 , a rare polyoxometalate [Cu₃(μ₃-OH)O₇(O₂CR)₄] cluster was found in the structure. It acts as an inorganic building unit together with the dimer [(UO₂)₂(O₂CR)₄] unit. Those uranyl carboxylates were sufficiently determined by single crystal X-ray diffraction, and their topological structures and luminescence properties were analyzed in detail.     

Synthesis,X-ray crystallography,spectroscopy, electrochemistry,thermal and kinetic study of uranyl Schiff base complexes

Uranyl(VI) complexes [UO₂(L)(solvent)], where L denotes an asymmetric N₂O₂ Schiff base (salpyr, 3-MeOsalpyr, 4-MeOsalpyr, 5-MeOsalpyr, 5-Clsalpyr or 5-Brsalpyr; salpyr is N,N′-bis(salicyliden)-2,3-diaminopyridine), were synthesized and characterized in solution (UV–vis, ¹H NMR, cyclic voltammetry) and in the solid-state (X-ray crystallography, IR, TGA, C H N.). X-ray crystallography of UO₂(3-MeOsalpyr) revealed coordination of the uranyl by the tetradentate Schiff base and one disordered solvent, resulting in seven-coordinate uranium. Another disordered solvent was not coordinated. Cyclic voltammetry of [U^VIO₂(L)(solvent)] in acetonitrile was used to investigate the effect of the substituents of the Schiff base ligands on oxidation and reduction potential. The quasi-reversible redox reaction without any successive reactions was accelerated by groups with lesser electron withdrawing. We also investigated the kinetics and mechanism of the exchange reaction of the coordinated solvent with tributylphosphine using spectrophotometric method. The second-order rate constants at four temperatures and activation parameters showed an associative mechanism for all corresponding complexes with the following trend: UO₂(5-Clsalpyr)?>?UO₂(5-Brsalpyr)?>?UO₂(3-MeOsalpyr)?>?UO₂(4-MeOsalpyr)?>?UO₂(salpyr)?>?UO₂(5-MeOsalpyr). It was concluded that the steric and electronic properties of the complexes were important for the reaction rate.     

Preparation of uranium oxide powder for nuclear fuel pellet fabrication with uranium peroxide recovered from uranium oxide scraps by using a carbonate–hydrogen peroxide solution

This work studied a way to reclaim uranium from contaminated UO₂ oxide scraps as a sinterable UO₂ powder for UO₂ fuel pellet fabrication, which included a dissolution of the uranium oxide scraps in a carbonate solution with hydrogen peroxide and a UO₄ precipitation step. Dissolution characteristics of reduced and oxidized uranium oxides were evaluated in a carbonate solution with hydrogen peroxide, and the UO₄ precipitation were confirmed by acidification of uranyl peroxo–carbonate complex solution. An agglomerated UO₄ powder obtained by the dissolution and precipitation of uranium in the carbonate solution could not be pulverized into fine UO₂ powder by the OREOX process, because of submicron-sized individual UO₄ particles forming the agglomerated UO₄ precipitate. The UO₂ powder prepared from the UO₄ precipitate could meet the UO₂ powder specifications for UO₂ fuel pellet fabrication by a series of steps such as dehydration of UO₄ precipitate, reduction, and milling. The sinterability of the reclaimed UO₂ powder for fuel pellet fabrication was improved by adding virgin UO₂ powder in the reclaimed UO₂ powder. A process to reclaim the contaminated uranium scraps as UO₂ fuel powder using a carbonate solution was finally suggested.