Solution Of UO2 Research Articles

Use of Layered Double Oxides and Hydroxides of Mg and Al for Removing Dyes from Aqueous Solutions Containing 137Cs, 90Sr, 90Y, and U(VI)

The possibility of removing dyes from aqueous solutions containing 137Cs, 90Sr, 90Y, and U(VI) using layered double oxides (LDOs) and hydroxides (LDHs) of Mg and Al was examined. The use of LDO-Mg-Al allows rapid and efficient pretreatment of radioactive solutions containing Cs and Sr radionuclides to remove dyes for the subsequent recovery of Cs and Sr with other selective sorbents. The use of LDO-Mg-Al, LDH-Mg-Al-OH, and LDH-Mg-Al-CD (CD is β-cyclodextrin) allows simultaneous removal from aqueous solutions of UO2(NO3)2 (initial concentration 90%).

Modeling of systems with aqueous solutions of UO 2 2+ salts. Asymmetric model of excess thermodynamic functions, based on virial expansion of the Gibbs free energy of the solution, VD-AS

An asymmetric model of virial expansion of the Gibbs free energy of solution, VD-AS, was suggested. Partial and molar thermodynamic functions of UO2(ClO4)2–H2O, UO2Cl2–H2O, and UO2(NO3)2–H2O binary solutions at 25°C were calculated using this model. The calculations show that the solutions are characterized by different, sometimes extremely large, deviations from ideality. The suggested model is considerably more accurate and stable than the most widely used Pitzer’s model of electrolyte solutions.

ChemInform Abstract: Mild Hydrothermal Crystal Growth of New Uranium(IV) Fluorides, Na3.13Mg1.43U6F30 and Na2.50Mn1.75U6F30: Structures, Optical and Magnetic Properties.

AbstractSingle crystals of the title compounds are hydrothermally synthesized from solutions of UO2(OAc)2, NaF, HF, and MgCl2 or MnCl2 (autoclave, 200 °C, 1 d, ≈100% yield).

Isolation of Uranyl Dicyanamide Complexes from N-Donor Ionic Liquids.

An ionic liquid (IL) approach for soft-donor f-element chemistry has been demonstrated by the isolation of several new uranyl dicyanamide complexes through reactions of UO2(NO3)2·6H2O with dicyanamide ([N(CN)2](-))-containing ILs. The [N(CN)2](-) ions are able to rapidly substitute uranium's O-donor ligands, as evidenced by single-crystal X-ray diffraction studies on two anhydrous adducts of UO2(NO3)2 with [N(CN)2](-) ILs as well as by IR and NMR spectroscopic studies on solutions of UO2(NO3)2 in these ILs. By contrast, the slow reaction of UO2(OAc)2·2H2O with a nitrile-functionalized imidazolium dicyanamide IL in solvent and the reaction of UO2(NO3)2·6H2O with NaN(CN)2 at elevated temperature resulted in irreversible hydrolysis. The reaction of UO2SO4 with [N(CN)2](-) ions in an acidified aqueous solution resulted in the crystallization of a [UO2](2+) complex with biuret, a N(CN)2](-) hydrolysis product. [N(CN)2](-) ions in the form of ILs react rapidly with [UO2](2+) at room temperature, allowing ligand substitution with [N(CN)2](-) to out-compete the slower hydrolysis reaction, enabling the isolation of uranyl dicyanamide complexes and challenging assumptions regarding the affinity of uranium for O-donors.

Selective Facilitated Transport of Uranium(VI) Across a Bulk Liquid Membrane Containing Benzoyltrifluoroacetone as Extractant-Carrier

A study has been made on carrier-mediated transport of uranium(VI) using a bulk liquid membrane prepared by dissolving benzoyltrifluoroacetone (HBTA) in carbon tetrachloride. The source phase comprised of a solution of UO2 2+ or its binary mixture with other cations such as Th4+, Hf4+, Zr4+, Fe3+, La3+, Cu2+, Co2+, Mn2+, Ni2+, and Zn2+ in aqueous solutions of pH 6.0, while 0.1 M hydrochloric acid was serving as a stripping agent in the receiving compartment. The interference from Th4+ and a few other cations could be eliminated by using trans-1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (DCTA) as a proper masking agent in the feed solution. Various factors influencing the transport process have been studied and an uphill transport (>99%) of uranium(VI) from the source phase could be accomplished under optimum conditions.

Chiral open-framework uranyl molybdates. 1. Topological diversity: synthesis and crystal structure of [(C 2H 5) 2NH 2] 2[(UO 2) 4(MoO 4) 5(H 2O)](H 2O)

Crystals of a new framework uranyl molybdate, [(C 2H 5) 2NH 2] 2[(UO 2) 4(MoO 4) 5(H 2O)](H 2O), were synthesized from a solution of UO 2(CH 3COO) 2 · 2H 2O, MoO 3, diethylamine and HCl in H 2O at 220 °C. The structure was studied at −127 °C. The compound is hexagonal, space group P6 522, a = 11.3612(13), c = 52.698(8) Å, V = 5890.7(13) Å 3, Z = 3. The structure has been refined to R 1 = 0.050 ( wR 2 = 0.100; S = 0.985) on the basis of 3103 unique observed reflections. The structure consists of a three-dimensional framework of composition [(UO 2) 4(MoO 4) 5(H 2O)] 2− that consists of UO 7 pentagonal bipyramids that share equatorial corners with MoO 4 tetrahedra. The framework contains a three-dimensional system of channels. The first system of channels is parallel to [0 0 1] and has the dimensions 7.0 × 7.0 Å, which result in a crystallographic free diameter (effective pore width) of 4.3 × 4.3 Å (based on an oxygen radius of 1.35 Å). Other channels run parallel to [1 0 0], [1 1 0] and [0 1 0] and have dimensions 5.2 × 7.1 Å (giving an effective pore width of 2.5 × 4.4 Å). One symmetrically unique [(C 2H 5) 2NH 2] + cation and H 2O molecule reside in the framework cavities. The channels parallel to [0 0 1] are chiral and are centered about a 6 5 screw axis. The uranyl framework with U:Mo = 4:5 in the structure of [(C 2H 5) 2NH 2] 2[(UO 2) 4(MoO 4) 5(H 2O)](H 2O) represents the third known type of chiral uranyl molybdate framework. Its relationships to the frameworks with U:Mo = 5:7 and 6:7 can be understood in terms of fundamental chains that have related but yet different topological structure.

Polyoxometal cations within polyoxometalate anions. Seven-coordinate uranium and zirconium heteroatom groups in [(UO2)12(μ3-O)4(μ2-H2O)12(P2W15O56)4]32− and [Zr4(μ3-O)2(μ2-OH)2(H2O)4 (P2W16O59)2]14−

Two new composite polyoxotungstate anions with unprecedented structural features, [(UO2)12(μ3-O)4(μ2-H2O)12(P2W15O56)4]32− (1) and [Zr4(μ3-O)2(μ2-OH)2(H2O)4 (P2W16O59)2]14− (2) contain polyoxo-uranium and -zirconium clusters as bridging units. The anions are synthesized by reaction of Na12[P2W15O56] with solutions of UO2(NO3)2 and ZrCl4. The structure of 1 in the sodium salt contains four [P2W15O56]12− anions assembled into an overall tetrahedral cluster by means of trigonal bridging groups formed by three equatorial-edge-shared UO7 pentagonal bipyramids. The structure of anion 2 consists of a centrosymmetric assembly of two [P2W16O59]12− anions linked by a {Zr4O2(OH)2(H2O)4}10+ cluster. Both complexes in solution yield the expected two-line 31P-NMR spectra with chemical shifts of −2.95, −13.58 and −6.45, −13.69 ppm, respectively.

Formation of Excited Uranyl in Oxidation of U(IV) with Oxygen in HClO4 Aqueous Solutions: I. Effect of pH on Kinetic and Chemiluminescence Parameters of the Reaction

Chemiluminescence accompanying U(IV) oxidation with atmospheric oxygen in 0.1-0.0004 M HClO4 was studied. It was found that the electronically excited uranyl ion, (UO2 2 +)*, is the luminescence emitter. The maximum on the kinetic curve is due to accumulation in the solution of UO2 + and H2O2, which are intermediates of U(IV) oxidation. The kinetic scheme of U4 + reaction with O2 suggests that uranyl excitation proceeds in the elementary stage of electron transfer from UO2 + to the oxidant, which is OH radical. With increasing pH from 1 to 3.4, the rate constant of the chemiluminescent stage (k) of the reaction increases almost 50 times and the luminescence efficiency (ηcl), 3 times. The effect of pH on the oxidation rate is due to the high reactivity of U4 + hydrolysis products UOH3+ and U(OH)22+ with respect to O2. The rate constant k of the reaction between U4+ and O2 and the chemiluminescence efficiency are the least among the other U(IV) chemiluminescence reactions: at 298 K and 0.1 M HClO4, k (l mol- 1 s-1) is equal to 3, 36, 40, and 108 and ηc l, to 7.4 × 10- 8, 8.1 × 10- 5, 1.6 × 10- 6, and 3 × 10- 7 for O2, XeO3, H2O2, and HSO5 - as oxidants, respec- tively. The activation energy of the chemiluminescent stage of U(IV) oxidation with oxygen in 0.001 M HClO4 E a is 90.5 kJ mol-1 within the 285-310 K range.

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.

Electrochemistry of uranium in sodium chloroaluminate melts

The electrochemical behaviour of uranium has been studied in basic, NaCl-saturated NaAlCl4 melts at 175°C. Solutions of UO3 exhibit two oxidation/reduction waves (cyclic voltammetry). The first wave corresponds to the U(VI)/U(IV) redox couple and is irreversible (slow electron transfer). The second wave corresponds to the deposition and stripping of an insoluble U(III) compound (U(IV)/U(III)). Solutions of UO2 or UCl4 and U(IV) solutions prepared by exhaustive electrolysis of UO3 behave identically. The cyclic voltammograms of U(IV) solutions are the same as those of UO3, but they show additional anodic peaks. Analysis of the peak currents (cyclic voltammetry), the limiting currents (pulse polarography) and the non-linear log i-t curves (anodic controlled potential coulometry) leads to the conclusion that uranium (IV) in the basic chloroaluminate melt exists as two different species in slow equilibrium with one another, of which only one species can be oxidized to U(VI). E.m.f. measurements of U(VI)-U(IV) mixtures indicate that the electron transfer process involves the formation of an intermediate U(V) species in a disproportionation equilibrium.

Preparation and application of237U for the study of heterogeneous isotope exchange on an ion exchanger

The possibility of preparation of237U by the238U(γ, n)237U reaction, realized by irradiation of UO3 on the microtron, has been verified. The relation between yields for (γ, n) and (γ, f) reaction was determined. The activated uranium was separated from fission products by extraction into diethyl ether.237U was used for the study of the kinetics of heterogeneous isotope exchange in the system aqueous solution of UO2(NO3)2 — ion exchanger Wofatit CA-20 in UO22+ form. The experimental results were evaluated by a model based on particle diffusion with simultaneous isotope exchange between two uranium forms in the ion exchanger.

The system U-UO 3: Phase diagram and oxygen potential

The U-UO 2 and UO 2-UO 3 phase diagrams were calculated using the Hoch-Arpshofen model: ΔG ex mix/R = n(z − z n)Ω . The U-UO 2 system is treated as a mixture of U and UO 2. In solid UO 2−x, U follows Henry's law, UO 2 Raoult's law (very narrow homogeneity range). In the liquid U-UO 2, n = 5 and Ω = 390 K in the above formula, z being the mole fraction of U. The UO 2-UO 3 system is treated as a solution of UO 2 and UO 3. In the UO 2+ x region, from the measured oxygen pressures, the values n = 3 and Ω = − 959 K were found, with z being the mole fraction of UO 2. The same parameters are used for the liquid. The Schottky-Wagner disorder model is used to describe UO 2± x close to the stoichiometric composition. The oxygen pressure for stoichiometric UO 2 is then calculated as T In P O 2 = − 110.75+ 21.72 T for the solid, T In P O 2 = −98.823 + 16.88 T for the liquid, P O 2 expressed in MPa, T in kK.

Synthesis and structural assessment of ammonium and caesium difluorodioxoperoxouranates(VI), A2[UO2(O2)F2](A = NH4or Cs), and alkali-metal difluorodioxoperoxouranate(VI) monohydrates, A2[UO2(O2)F2]·H2O (A = K or Rb)

The product obtained by treating an aqueous solution of UO2(NO3)2·6H2O with NH4OH or KOH reacts with AF (A = NH4, Rb, or Cs) or KF, 30% H2O2, and a very small amount of 40% HF, in the mol ratio UO2(NO3)2·6H2O:AF:H2O2 of 1:4:110.8, at pH 6.5–7 to afford ammonium and caesium difluorodioxoperoxouranates(VI), A2[UO2(O2) F2](A = NH4 or Cs), and potassium and rubidium difluorodioxoperoxouranate(VI) monohydrates, A2[UO2(O2)F2]·H2O (A = K or Rb). The i.r. spectra suggest that the peroxo-ligand is bonded to the UO22+ centre in a triangular bidentate (C2v,) manner.

Preparation of HUO2PO4·4H2O single crystals from gel

Abstract Single crystals of HUO2PO4·4H2O were grown by diffusing a solution of UO2(NO3)2·6H2O into a sodium metasilicate gel set with phosphoric acid. The crystals grew with a tetragonal morphology and had maximum dimensions of 2.0 mm × 2.0 mm × 0.4 mm.

The critical concentration for magnetic order in solid solutions of UO2with Th02and Zr02

Changes in Neel temperature and the changes in the localized magnetic moment on the uranium ion in solid solutions of UO2 with ZrO2 and ThO2 have been measured by neutron diffraction methods. The localized magnetic moment per uranium atom falls immediately UO2 is diluted and vanishes well before the expected critical concentration for the breakdown of long-range order. These observations are shown to be consistent with spin-lattice interaction effects.

Precipitation and hydrolysis of uranium(VI) in aqueous solutions—VII: Boundary conditions for precipitation from solutions of UO 2(NO 3) 2KOHK, Ba, La and Eu nitrate

The hydrolytic precipitation of uranium(VI) has been studied over a large concentration range of uranyl nitrate solutions. It was shown that the presence of a neutral electrolyte (potassium, barium, lanthanum or europium nitrate) controls the character of uranium(VI) precipitation boundary, which is caused by the specific coagulation and constitution effect of interaction of the above mentioned counter ions with negatively charged metastable colloid particles. The experimentally obtained slope of precipitation line: pH-log UO 2(NO 3) 2 was used to predict the average composition of hydrolytic species in equilibrium with the first solid phase formed in the system. This was correlated with possible reaction mechanism of precipitate formation. The quantitative analysis have shown that the composition of first precipitation product, which is formed at the precipitation boundary in a large concentration range of uranium(VI), corresponds to potassium and barium heptauranate, respectively.

Enthalpy of formation of uranium tetrachloride

The enthalpy of formation of uranium tetrachloride, UCl 4 (s), has been determined from measurements of the enthalpies of solution of uranium metal and of UCl 4 (s) in 4 M and 6 M HCl containing added Na 2 SiF 6 and combined with the enthalpy of formation of aqueous HCl of corresponding concentration. The necessity of making the measurements in the absence of dissolved oxygen is emphasized. The weighted mean of the two sets of measurements gives Δ H ° f (UCl 4 ,s,298 K) = −(243.4 ± 0.7) kcal mol −1 . This result was compared with that obtained by a series of measurements including the enthalpies of solution of UO 2 (s) and UCl 4 (s) in sulfuric acid solutions. (The details of the reaction scheme are given in the text.) These latter measurements lead to a value for the enthalpy of formation of UCl 4 (s) of −(244.0 ± 1.0) kcal mol −1 . The weighted average of the two determinations gives Δ H ° f (UCl 4 ,s,298 K) = −(243.6 ± 0.6) kcal mol −1 .

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 (UO 2) was studied as a function of temperature, concentration of UO 2, and radiation dose rate. The effect was measured in terms of the radiolytic yield of uranium(VI),Gu VI. For solutions of high initial UO 2 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 UO 2 concentration than for any of the solutions of high initial UO 2 concentration. At the high starting UO 2 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 UO 2; the error is a function of the radiation dose. This error can be minimized by excluding oxygen from solutions of UO 2 and by keeping the initial UO 2 concentration as low as possible.

Critical parameters of aqueous solutions of UO2(NO3)2 salt

Experimental results on a determination of the criticai parameters of aqueous solutions of UO2(NO3)2 salt are reported.