Stoichiometry of uranyl hydrolysis reaction in acidic aqueous solutions from the evidence of oxygen exchange kinetics

Mashirov, L.G.; Mikhalev, V. A.; Suglobov, D.N.

doi:10.1016/j.crci.2004.06.005

Cited by 11 publications

(22 citation statements)

References 15 publications

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“…Uranium in aqueous solution exists as the uranyl ion, UO 2 2+ , which is known under acidic conditions to exhibit very slow oxygen isotope exchange with water. 14,15,42 Mashirov et al (2004) noted that at acid concentrations greater than 0.2 M, the exchange between water and uranyl oxygen isotopes was negligible and at 0.1 M, found the equilibration times for this exchange to be on the order of hundreds to thousands of hours. 15 The average pH of dissolved uranyl nitrate solutions prior to precipitation used in this study was 1.0, corresponding to a H + concentration of 0.1 M. Given the bulk δ 18 O values found for each UO 4 replicate (Table 1) and the water δ 18 O value (−15.5‰), the process in this case likely reflects incomplete oxygen isotope exchange with the uranyl oxygens while in solution.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…Uranium in aqueous solution exists as the uranyl ion, UO 2 2+ , which is known under acidic conditions to exhibit very slow oxygen isotope exchange with water. ,, Mashirov et al. (2004) noted that at acid concentrations greater than 0.2 M, the exchange between water and uranyl oxygen isotopes was negligible and at 0.1 M, found the equilibration times for this exchange to be on the order of hundreds to thousands of hours .…”

Section: Resultsmentioning

confidence: 99%

“…At the beginning of the fuel processing cycle, purification of uranium usually requires leaching, or dissolution, into an aqueous phase . Once dissolved, oxygen can exchange between a uranyl molecule (UO 2 2+ ) and water, although the kinetics of this exchange can be slow, with equilibration times on the order of thousands of hours. , The dissolution of uranium ores also requires the use of reagents which may include sulfuric acid, sodium chlorate, bicarbonate, and hydrogen peroxide . The additional oxygen introduced by these reagents can change the overall oxygen isotopic composition of the solution and consequently the composition of oxygen associated with each uranyl ion.…”

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confidence: 99%

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Fractionation of Oxygen Isotopes in Uranium Oxides during Peroxide Precipitation and Dry Air Calcination

Klosterman

Oerter

Chakraborty

et al. 2021

ACS Earth Space Chem.

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The interaction between uranium and oxygen-containing substrates is nearly ubiquitous within the nuclear fuel cycle. Given the well-known and predictable oxygen stable isotope compositions of atmospheric oxygen and meteoric waters around the world, the use of these isotopes as a potential geolocation or processing signature of uranium compounds has been of interest within the nuclear safeguards community. This study focuses on measuring the oxygen-stable isotope composition of synthetically produced uranium oxides to determine the mechanism and extent of fractionation during materials processing relevant to the nuclear fuel cycle. Metastudtite [UO2O2(H2O)2] samples were first produced using water and hydrogen peroxide of a known oxygen isotope composition. This starting material was calcined in dry air at temperatures ranging from 300 °C to 1000 °C for 20 h producing oxides ranging in composition from UO3 +x (0 ≤ x ≤ 0.5) to U3O8. In addition, calcinations between 500 and 800 °C were performed at different time intervals to evaluate the rate of isotopic equilibration. The δ18O values of water bound to metastudtite were measured by thermogravimetric analysis coupled to isotope ratio infrared spectroscopy (TGA–IRIS). A redesigned fluorination manifold was constructed at the University of Utah and was used to extract the bulk oxygen from precipitated and calcined products using bromine pentafluoride (BrF5). Mineralization water on metastudtite (measured by TGA–IRIS) was closely associated with the aqueous environment of precipitation with a fractionation of +3.5 ± 0.6‰. In contrast, bulk oxygen from metastudtite (measured by fluorination and gas chromatography combined with isotope ratio mass spectrometry) was found to have an inconsistent fractionation with precipitation water. Samples calcined in dry air exhibited a wide range of oxygen isotope compositions which increased from δ18O = +1.4 ± 0.9‰ at 300 °C to +17.3 ± 0.9‰ at 1000 °C. This variation in δ18O values was a result of oxygen exchange with atmospheric O2 and was found to be rapid at calcination temperatures greater than 600°Cwith equilibration occurring in less than 2 h. These results provide insights into the incorporation and exchange of oxygen isotopes during precipitation and calcination processes comparable to those employed within the nuclear fuel cycle and establish a foundation for future investigations to build upon.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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confidence: 99%

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Fractionation of Oxygen Isotopes in Uranium Oxides during Peroxide Precipitation and Dry Air Calcination

Klosterman

Oerter

Chakraborty

et al. 2021

ACS Earth Space Chem.

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“…However, the increased fraction of the (3,4) species at this rather low pH and low concentration, compared to previous studies, might originate from a similar but less pronounced continuous hydrolysis effect. For high uranium concentrations a continuous hydrolysis was postulated before by Mashirov et al, [35] leading to the formation of (3,4) complexes. Nevertheless the other suggested complexes [35] supporting the hypothesis, like (2, 3) species, were not detected within our studies.…”

Section: Discussionmentioning

confidence: 88%

“…For high uranium concentrations a continuous hydrolysis was postulated before by Mashirov et al, [35] leading to the formation of (3,4) complexes. Nevertheless the other suggested complexes [35] supporting the hypothesis, like (2, 3) species, were not detected within our studies.…”

Section: Discussionmentioning

confidence: 88%

On the polymerization of hexavalent uranium. An electrospray mass spectrometry study

Steppert

Walther

Fuss

et al. 2012

Rapid Comm Mass Spectrometry

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Polymerization in hexavalent uranium solutions was measured by electrospray ionization time-of-flight mass spectrometry in three different acidic media at pH values from 3 to 5.3 in order to detect all hydrolysis species present in solution. The aqueous solutions were directly measured without further dilution in organic solvents. At high uranyl concentrations ([U(VI)] = 10(- 3) M) artifacts were observed due to the presence of more than one solution species per formed microdroplet. Those artifacts were composed of ions and neutral species being present in the same droplet. However, by analyzing the detected species carefully, the origin of the artifacts could be traced back to the physically meaningful species. Still, only general trends of the hydrolysis behavior can be deduced from the measurements at [U(VI)] = 1 ⋅ 10(- 3) M. The solutions at [U(VI)] = 5 ⋅ 10(- 5) M did not show any comparable artifact formation. The detected species distributions resemble the expected trends calculated from the equilibrium constants published in the Nuclear Energy Agency Thermodynamic Database (NEA-TDB). The neutral (UO(2))(CO(3))(0) species present in solution causes, if located in the same microdroplet as a charged species, the apparent formation of dimeric and trimeric ternary hydroxo carbonate complexes at pH 5.3. As the uncharged species is not repelled from the ionic species, it might remain in the same droplet during the droplet fission process. By dividing those detected species into the uncharged (UO(2))(CO(3))(0) and a second ionic species, the relative abundances of the solution species can be corrected, leading to a good agreement with the predictions of the published equilibrium constants. In addition to the well-known trimer, we report the direct mass spectrometric detection of the dimeric (UO(2))(2)(OH)(2)(2+) species.

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Dioxouranium(VI) Hydrolysis at 75 and 100 °C in 3.6 mol⋅kg−1 LiClO4 Aqueous Medium

et al. 2008

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Stoichiometry of uranyl hydrolysis reaction in acidic aqueous solutions from the evidence of oxygen exchange kinetics

Cited by 11 publications

References 15 publications

Fractionation of Oxygen Isotopes in Uranium Oxides during Peroxide Precipitation and Dry Air Calcination

Fractionation of Oxygen Isotopes in Uranium Oxides during Peroxide Precipitation and Dry Air Calcination

On the polymerization of hexavalent uranium. An electrospray mass spectrometry study

Dioxouranium(VI) Hydrolysis at 75 and 100 °C in 3.6 mol⋅kg−1 LiClO4 Aqueous Medium

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