Reaction of ozone with Np(IV) and Pu(IV) oxalates in water

The reaction of the ozone–oxygen mixture with aqueous suspensions of Np(IV) and Pu(IV) oxalates was studied. Both metal cations and oxalate anions are oxidized in the process. The final products are Np(VI) and Pu(VI) hydroxides. The composition of Np(VI) hydroxide was confirmed by X-ray diffraction analysis. Oxidation of Np(IV) oxalate with oxygen leads to the accumulation of Np(V) oxalate and oxalic acid in the solution. At incomplete oxidation of Np(IV) oxalate with ozone in water, Np(V) is also accumulated. Heating considerably accelerates the ozonation. The possible reaction mechanism is briefly discussed. The Np(V) and Np(VI) ions participate in the catalytic cycle of the decomposition of oxalate ions with ozone.     

Reaction of ozone with Np(V) and Np(IV) in carbonate solutions

A spectrophotometric study showed that ozone in concentrated carbonate solutions forms complexes with CO ₃ ^2? ions, which inhibits the ozone decomposition. Free ozone oxidizes Np(V) at high rate. The bound ozone reacts with Np(V) at moderate rate. Np(IV) reacts with O₃ slowly, with Np(VI) formed in NaHCO₃ solution and only Np(V) formed in Na₂CO₃ solution.     

Oxidation of Am(III) to Am(IV) with ozone in solutions of heteropolyanions

Oxidation of Am(III) in the presence of K₁₀P2W₁₇O₆₁ and K₈SiW₁₁O₃₉ (L) at 20dGC was studied by spectrophotometry. Am(III) is oxidized with ozone to Am(IV) only in the pH range 3.5–1.0. In the case of formation of a complex with Am: L = 1: 1, the reaction is approximately first-order with respect to the metal, and its rate decreases with a decrease in pH from 3.5 to 1.0. Am(IV) in solution in the presence of ozone is slowly reduced with products of water α-ray radiolysis, predominantly with ?₂?₂. The rate constant of the reaction of Am(IV) with ?₂?₂ was estimated.     

Reaction of Np(V) with U(IV) in solutions with pH > 2

Oxidation of U(IV) with Np(V) in bicarbonate-carbonic acid solutions and the nature and reactivity of actinide(IV) compounds formed in these media were studied spectrophotometrically.     

Reaction of [60]Fullerene with Terbium(IV) Fluoride

Abstract

A reaction between [60]fullerene and terbium(IV) fluoride is shown to be a new example of the thermally induced disruption of the fullerene skeleton. “Hyperfluorination” occurs at the elevated temperature (350° C) thereby producing species C₆₀ Fx (x > 60). The fluorination products were characterized by mass spectrometry and IR spectroscopy methods.     

Reduction of Pu(IV) and Np(VI) with hydroxylamine in solutions of low acidity with high uranium content

Decomposition of hydroxylamine in HNO₃ solutions containing 350 to 920 g l^?1 U(VI) was studied. In the absence of fission and corrosion products (Zr, Pd, Tc, Mo, Fe, etc.), hydroxylamine is stable for no less than 6 h at [HNO₃] < 1 M and 60°C. In the presence of these products, the stability of hydroxylamine appreciably decreases. The reduction of Pu(IV) and Np(VI) with hydroxylamine in aqueous 0.33 and 0.5 M HNO₃ solutions containing 850 g l^?1 U(VI) and fission and corrosion products at 60°C was studied. Np(VI) is rapidly reduced to Np(V), after which Np(V) is partially reduced to Np(IV). The rate of the latter reaction in such solutions is considerably higher than the rate of the Np(V) reduction with hydroxylamine in HNO₃ solutions without U(VI). At [HNO₃] = 0.33 M, the use of hydroxylamine results in the conversion of Pu to Pu(III) and of Np to a Np(IV,V) mixture, whereas at [HNO₃] = 0.5 M the final products are Pu(IV) and Np(V).     

Reaction of water with alkaline-earth stabilized bismuth(III) oxide

The reaction of water with various compositions of calcium, strontium and barium-stabilized bismuth sesquioxide has been examined. X-ray diffraction, TGA, DTA and optical studies were used. The reaction of water with these oxides occurs at room temperature and forms a new, low-temperature, single-phase material. The speed of the reaction is particle-size dependent. The water-containing phase can be decomposed back to the rhombohedral-stabilized structure at temperatures between 400 and 700°C. It appears that the reaction is an intercalation-type process with pronounced exfoliation.     

Reaction of Np(IV) with Orthosilicic Acid,Si(OH)4, in Acid Solutions

Reaction of Np(IV) with Si(OH)₄ within the range of pH 0-2.2 was studied spectrophotometrically. Under these conditions, a complex NpOSi(OH)₃ ^{3 +} is formed. This composition was derived from the dependences of the complex concentration on [H⁺] and [Si(OH)₄]. From the experimental electronic absorption spectra, the spectrum of NpOSi(OH)₃ ^{3 +} was reconstructed. In this spectrum, the narrow band of the aqua ion at 723.2 nm shifts to 729.2 nm and becomes weaker by approximately half. The equilibrium constant K ₁ of the complex formation reaction and the stability constant of the complex ₁ at the ionic strengths I = 0.1 and 1.0 were determined: logK ₁ = 0.71±0.05 and 0.41±0.02, ₁ = 10.52±0.05 and 10.22±0.02, respectively. The Np(IV) speciation in the acid solution in the presence of Si(OH)₄ was calculated.     

Reaction of metallic uranium with NO2 in TBP

Low-temperature nonaqueous nitration of metallic uranium in the system TBP tetrachloroethylene-NO₂ is studied. Dissolution of U in a dipolar aprotic solvent (TBP, DMF, acetonitrile, nitromethane, DMSO, diethylformamide) proceeds with the formation of U(VI) compounds. The activation energy of the process is estimated at 48.2 kJ mol^?1, and the partial order of the reaction with respect to NO₂ is 1. The effects of the TBP concentration and water addition on the nitration are examined. In the system TBP-tetrachloroethylene, the nitration rate is maximal at a water content of 1.0–2.0 vol %.     

A small-angle X-ray scattering study of aqueous solutions of uranium(IV) complexes with lacunar heteropolytungstates

The behavior of aqueous and acid solutions of U(IV) complexes with lacunar heteropolyanions was studied by small-angle X-ray scattering. The polytungstate forms in solutions and in crystals are generally similar. The polyanionic complexes in solutions can exhibit ordering with a period of approximately 5.6–7.8 nm. Such species are probably precursors of the crystalline form.     

Oxidation of uranium(IV) with oxygen in NaHCO<Subscript>3</Subscript> solution

The kinetics of U(IV) oxidation with atmospheric oxygen in NaHCO₃ solutions was studied by spectrophotometry. In 1 M NaHCO₃ at [U(IV)]₀ = 20 mM, an induction period is observed, which virtually disappears with decreasing [U(IV)]₀ to 1.0 mM. The induction period is caused by the fact that initially U(IV) exists in a weakly active polymeric form. Addition of U(VI) to the initial solution accelerates the oxidation. In a 1 M NaHCO₃ solution containing 0.1–1.0 mM U(IV), the U(IV) loss follows the first-order rate law with respect to U(IV) and O₂. The pseudo-first-order rate constants, bimolecular rate constants, and activation energy of the U(IV) oxidation were calculated. In dilute NaHCO₃ solutions (0.5–0.01 M), the hydrolysis and polymerization of U(IV) become more pronounced. The autocatalysis mechanism presumably involves formation of a complex [U(IV) · U(VI)] with which O₂ reacts faster than with U(IV). Oxidation of U(IV) occurs by the two-electron charge-transfer mechanism.     

Coprecipitation of neptunium(IV) and plutonium(IV) with hydrolyzed iron(III) in carbonate solutions

In regeneration of Np(IV)-and Pu(IV)-containing recycled solvent by treatment with aqueous sodium carbonate contaminated with iron, some portion of Np(IV) and Pu(IV) coprecipitates with hydrolyzed iron. The degree of coprecipitation of Np and Pu depends on both the iron and sodium carbonate concentrations. The presence of n-dibutyl hydrogen phosphate in the recycled solvent before its regeneration does not noticeably affect the coprecipitation of Np and Pu. The possible mechanisms of coprecipitation of actinides with hydrolyzed iron in carbonate solutions are discussed.     

Use of o-phenylene dioxydiacetic acid impregnated in Amberlite XAD resin for separation and preconcentration of uranium(VI) and thorium(IV)

The impregnation of o-phenylene dioxydiacetic acid (OPDA) into a polymeric matrix, Amberlite XAD-2000, is reported and was characterized by infrared spectroscopy. The amount of attached OPDA to the polymer resin was found to be 1.77mmolg(-1) resin. The resin was used for the sorption of U(VI) and Th(IV) from aqueous solution. This sorbent was capable of preconcentrating U(VI) and Th(IV) from weakly acidic or neutral solution. The retained metals were eluted sequentially using 0.25molL(-1) HCl for U(VI) and 1molL(-1) HCl for Th(IV) and determined spectrophotometrically using arsenazo-(III). The capacity of the resin for U(VI) and Th(IV) was found to be 0.121 and 0.113mmolg(-1), respectively. The impregnated resin exhibits a high chemical stability, reusability and fast equilibration. The method was used for the determination of U(VI) and Th(IV) in synthetic samples and rock samples.     

Nanoscale etching and flattening of metals with ozone water

Etchants used for metal etching are generally harmful to the environment. We propose an environmentally friendly method that uses ozone water to etch metals. We measured the dependencies of ozone water etching on the temperature and ozone concentration for several metals and evaluated the surface roughness of the etched surfaces. The etching rate was proportional to the dissolved ozone concentration, and the temperature and the surfaces were smoothed by etching.     

High-temperature interaction of uranium and zirconium with water vapor

We analyze physicochemical processes of interaction between uranium, zirconium, and its alloy (with 1% Nb) with water vapor at temperatures up to 1500°K and study mechanisms and kinetics of these processes. It is shown that, up to 700°K, the kinetics of the process of oxidation of uranium is described by a linear function of time; at temperatures higher than 900°K, this dependence becomes parabolic. Our interpretation of the mechanism of the process of oxidation of uranium takes into account the influence of structural defects and electrochemical properties of uranium oxides formed in the course of this process. The process of oxidation of zirconium and its alloy with 1% Nb by water vapor obeys a cubic law in the temperature range 900–1200°K and a parabolic law in the range 1300–1500°K. The comparative analysis demonstrates that the hydrogen release rate in the process of uranium oxidation is about twice as high as in the process of vapor-zirconium reaction.Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 31, No. 3, pp. 36–43, May–June 1995.     

Mechanism of Np(VI) oxidation with ozone in alkaline solutions

Bubbling of an ozone-oxygen mixture containing 0.1?C0.5 vol % O₃ at a rate of 15?C20 l h^?1 through 13 ml of a 2 × 10^?5?1 × 10^?4 M solution of Np(VI) in 0.1 and 1 M LiOH leads to the formation of Np(VII). The initial rate increases approximately in proportion to [Np(VI)] and [O ₃ ^gas ]^0.5. Up to 80% of Np(VI) is oxidized at maximum. At the O₃ concentration in the gas phase increased to 1?C4 vol %, Np(VI) is oxidized completely. Under the same conditions, Np(VI) in a concentration of (1?C5) × 10^?3 M is oxidized to almost 100%. Analysis of published data and additional experiments on the reaction of O₃ with Np(VI) ions in LiOH solutions allow a conclusion that the ozonation involves the reactions O₃ + OH^? = HO ₂ ^? + O₂, O₃ + HO ₂ ^? + OH^? = O ₃ ^? + O ₂ ^? + H₂O, and O₃ + O ₂ ^? = O ₃ ^? + O₂, followed by O ₃ ^? + NpO₂(OH) ₄ ^2? = O₂ + NpO₄(OH) ₂ ^3? + H₂O. In addition, HO ₂ ^? reduces Np(VII) and Np(VI) and reacts with O ₃ ^? . Certain contribution is made by the reaction Np(VI) + O₃ = Np(VII) + O ₃ ^? . The dependence of the Np(VII) accumulation rate on [O ₃ ^gas ]^0.5 was interpreted in terms of the concept of a heterogeneous-catalytic process.     

Oxidation of Ce(III) with ozone in concentrated hydrochloric acid

Oxidation of Ce(III) with ozone in concentrated hydrochloric acid was studied. Ozonation of hydrochloric acid solutions containing CeCl₃ and CsCl results in precipitation of crystalline Cs₂CeCl₆. The precipitate is not formed when chlorine-saturated hydrochloric acid solutions containing CeCl₃ and CsCl are stored in the dark. Exposure of such solution to the radiation of a mercury lamp for several minutes results in precipitation of Cs₂CeCl₆. The mechanism of the ozonation of HCl_conc containing CeCl₃ is discussed with consideration of radiation-chemical data.