Formation of Peroxidic Precipitate in the Radiolysis of Uranyl Nitrate Ketone Solutions

Teplý, J.; Štulík, Václav

doi:10.1038/200671a0

Cited by 2 publications

(5 citation statements)

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“…Finally, reaction (7) may have taken place when the natural U peroxides have formed in solutions containing very high oxidant concentrations. However, it is not known which concentrations of H 2 O 2 are necessary in laboratory experiments to induce reaction (7).…”

Section: Discussionmentioning

confidence: 99%

“…As a strong oxidant, this substance oxidizes most redox-sensitive metallic elements in solution to higher oxidation states, and, finally, can form precipitates with metal ions by addition compound formation. This was observed in the case of uranium where uranium peroxide (having the semi-structural formula UO 2 -O 2 ) was formed when H 2 O 2 was radiolytically produced in a solution containing uranyl ions [7]. It was found that radiolytically produced H 2 O 2 can lead to the precipitation of uranium peroxide (meta-studttite) on UO 2 surfaces [8].…”

Section: Introductionmentioning

confidence: 92%

“…If available H 2 O 2 is decomposed in the bulk solution before a contact with the solid UO 2 surface, the overall Eh value of the solution is raised and the precipitation of U(VI) is favoured but (since peroxide units are lacking) normal U(VI) oxyhydroxides will be formed. In laboratory tests, U peroxide was found as a solid product when H 2 O 2 was formed in U containing solutions due to water radiolysis [7,8]. It is not sure which natural conditions prevailed during the formation of natural uranium peroxides.…”

Section: Uranium Peroxide Versus Schoepitementioning

confidence: 99%

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Contrary effects of the water radiolysis product H₂O₂upon th dissolution of nuclear fuel in natural ground water and deionized water

Amme¹

2002

Radiochimica Acta

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Radiolysis of water is a phenomenon which alters the prevailing conditions in the nearfield of a final geological repository for high-level nuclear waste (HLW), because the nominally anoxic conditions in the repository may change due to the production of oxidants close to the solidliquid interface of the fuel, caused by the alpha radiolysis of water.The influence of water chemistry and oxidant concentration in the liquid phase was tested by experiments which simulate chemical radiolysis effects. Leaching experiments with solutions of de-ionized water (DI) and natural groundwater (GW) containing the water radiolysis product H 2 O 2 in various concentrations were performed contacting pellets of depleted UO 2 as a solid phase. After the experiment, U concentration was measured and the solid surfaces was examined with scanning electron microscopy and electron-dispersive X-ray analysis (SEM-EDX). Uranium concentrations showed an unexpected behaviour; at low H 2 O 2 concentrations in solution, U concentrations were highest. U concentrations in the groundwater leachates were always lower than in pure water. The SEM-EDX examination showed the presence of different alteration phases on the sample. The sample surfaces treated in pure water showed optically a yellow discolouration and were covered with a thick layer of oxidation products. In the case of the treatment in groundwater, the samples remained black, and no dense layer was formed. Instead, crystals of octahedral shape were found on the surface, while the matrix grain structure remained intact. All alteration phases were found to contain only U (and possibly O, H, and C also). A reaction mechanism is proposed for the oxidation reactions taking place under the various conditions. Comparisons with natural analogues and previous work are made, and geochemical solubility limits of possible newly formed substances are examined. The results suggest that different polymorphs of uranium(IV) oxyhydroxides (para-, meta-schoepite, hemihydrate) and of uranium(VI) peroxide (Studtite, meta-studtite) have formed, and that in the case of the samples treated with groundwater, a scavenging mechanism, possibly controlled by an ion present in groundwater, leads to the deactivation of H 2 O 2 in the solution.*

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 92%

Section: Uranium Peroxide Versus Schoepitementioning

confidence: 99%

See 1 more Smart Citation

Contrary effects of the water radiolysis product H₂O₂upon th dissolution of nuclear fuel in natural ground water and deionized water

Amme¹

2002

Radiochimica Acta

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“…It is expected that OH • , either formed primarily by water radiolysis or by Fenton reactions with Fe(II), will have an influence on the rate of the UO 2 dissolution during the reaction of U(IV) with H 2 O 2 . At higher peroxide concentra tions, the precipitation of uranium peroxide ( , ) is expected to compete with Fenton reactions: Uranium peroxide formed by this reaction was measured to have solubilities in the order of 10 -7 mol/L at pH 3.1−3.7 and [H 2 O 2 ] = 10 -3 M ().…”

Section: Introductionmentioning

confidence: 99%

“…It is expected that OH influence on the rate of the UO2 dissolution during the reaction of U(IV) with H2O2. At higher peroxide concentrations, the precipitation of uranium peroxide (10,34) is expected to compete with Fenton reactions:…”

Section: Introductionmentioning

confidence: 99%

Effects of Fe(II) and Hydrogen Peroxide Interaction upon Dissolving UO₂under Geologic Repository Conditions

Amme

Bors

Michel

et al. 2004

Environ. Sci. Technol.

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Iron redox cycling is supposed to be one of the major mechanisms that control the geochemical boundary conditions in the near field of a geologic repository for UO2 spent nuclear fuel. This work investigates the impact of reactions between hydrogen peroxide (H2O2) and iron (Fe2+/Fe3+) on UO2 dissolution. The reaction partners were contacted with UO2 in oxygen-free batch reactor tests. The interaction in absence of UO2 gives a stoichiometric redox reaction of Fe2+ and H2O2 when the reactants are present in equal concentration. Predomination of H202 results in its delayed catalytic decomposition. With UO2 present, its dissolution is controlled by either a slow mechanism (as typical for anoxic environments) or uranium peroxide precipitation, depending strongly on the reactant ratio. Uranium peroxide (UO4 x nH2O, m-studtite), detected on UO2 surfaces after exposure to H2O2, was not found on the surfaces exposed to solutions with stoichometric Fe(II)/ H2O2 ratios. This suggests that H2O2 was deactivated in redox reactions before a formation of UO4 took place. ESR measurements employing the spin trapping technique revealed only the DMPO-OH adduct within the first minutes after the reaction start (high initial concentrations of the OH radical); however, in the case of Fe(II) and H2O2 reacting at 10(-4) mol/L with UO2, dissolved oxygen and Fe2+ concentrations indicate the participation of further Fe intermediates and, therefore, Fenton redox activities.

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Formation of Peroxidic Precipitate in the Radiolysis of Uranyl Nitrate Ketone Solutions

Cited by 2 publications

References 1 publication

Contrary effects of the water radiolysis product H₂O₂upon th dissolution of nuclear fuel in natural ground water and deionized water

Contrary effects of the water radiolysis product H₂O₂upon th dissolution of nuclear fuel in natural ground water and deionized water

Effects of Fe(II) and Hydrogen Peroxide Interaction upon Dissolving UO₂under Geologic Repository Conditions

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Formation of Peroxidic Precipitate in the Radiolysis of Uranyl Nitrate Ketone Solutions

Cited by 2 publications

References 1 publication

Contrary effects of the water radiolysis product H2O2upon th dissolution of nuclear fuel in natural ground water and deionized water

Contrary effects of the water radiolysis product H2O2upon th dissolution of nuclear fuel in natural ground water and deionized water

Effects of Fe(II) and Hydrogen Peroxide Interaction upon Dissolving UO2under Geologic Repository Conditions

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Contrary effects of the water radiolysis product H₂O₂upon th dissolution of nuclear fuel in natural ground water and deionized water

Contrary effects of the water radiolysis product H₂O₂upon th dissolution of nuclear fuel in natural ground water and deionized water

Effects of Fe(II) and Hydrogen Peroxide Interaction upon Dissolving UO₂under Geologic Repository Conditions