Kinetics of oxidation and dissolution of uranium dioxide in aqueous acid solutions

Gaulard-Balandret, Coralie; Larabi-Gruet, Nathalie; Miserque, F.; Radwan, J.; Ferry, Cécile; Chaussé, A.

doi:10.1016/j.electacta.2012.04.022

Cited by 5 publications

(4 citation statements)

References 21 publications

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“…Consequently, the most likely reaction pathway was the oxidation of tetravalent uranium to hexavalent uranium because of the leaching [63]. Some studies indicated that the oxidation of UO2 possibly proceeded through two successive electrochemical reactions, coupled with a U 5+ intermediate at the UO2 surface noticeable between the U 4+ and U 6+ oxidation states [64,65], but it was not detected in this study. In addition, the binding energy of the uranium oxide tended to rise due to the increase in the oxygen coefficient (ko).…”

Section: Acid Leaching Accessibility Of Uraninitementioning

confidence: 54%

Geochemistry and Acid Hydrometallurgy Accessibility of Uraninite from Mianhuakeng Granite-Hosted Uranium Deposit, South China

Wang

Sun

et al. 2020

Minerals

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Systematic study of the surface chemical properties of uranium minerals is necessary to improve the uranium ore extracting process. The presented work aims to argue geochemistry and acid hydrometallurgy accessibility of uraninite from the Mianhuakeng (MHK) granite-hosted uranium deposit, South China, which provides insight on this ore extracting domain. Mineralogy, geochemical composition, U–Th–Pb chemical age, and uranium deportment of the uraninite were systematically analyzed by using scanning electron microscope with energy dispersion spectrum (SEM-EDS), an electron probe microanalyzer (EPMA), and x-ray photoelectron spectroscopy (XPS). The results showed that uraninite was intergrowth with coffinite, probably due to uraninite being partly metasomatized into coffinite along the fissures. The major element content of uraninite such as for UO2, SiO2, and CaO were 79.46 ± 2.03 wt%, 6.19 ± 1.36 wt%, and 5.09 ± 0.80 wt%, respectively. Single-point U–Th–Pb chemical ages for uraninite grains were calculated with the EPMA data, and the results showed ages ranging from a few million to dozens of million years, indicating Pb loss after uraninite formed. Uranium deportment in uraninite generally existed in the forms of UO2, U3O8, and UO3, and mostly showed high valence states suggested by XPS. Uranium on the surface of the uraninite grain was partially oxidized by sulfuric acid leaching, which led to tetravalent uranium converting to hexavalent uranium, suggesting uraninite in the MHK uranium deposit is accessible to be leached by sulfuric acid.

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Section: Acid Leaching Accessibility Of Uraninitementioning

confidence: 54%

Geochemistry and Acid Hydrometallurgy Accessibility of Uraninite from Mianhuakeng Granite-Hosted Uranium Deposit, South China

Wang

Sun

et al. 2020

Minerals

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“…1 a). These contributions were attributed to U 4+ , U 5+ and U 6+ oxidation states with U-4f 7/2 peak binding energies of 379.7 ± 0.3 eV; 380.8 ± 0.3 eV and 382.3 ± 0.3 eV, respectively 14 , 30 . The presence of shake-up satellite peaks at 6.8 eV and 8.1 eV from the main U-4f 7/2 peaks showed that uranium oxidation states were mainly U 4+ and U 5+ .…”

Section: Resultsmentioning

confidence: 99%

Coffinite formation from UO2+x

Szenknect

Alby

García

et al. 2020

Sci Rep

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Most of the highly radioactive spent nuclear fuel (SNF) around the world is destined for final disposal in deep-mined geological repositories. At the end of the fuel's useful life in a reactor, about 96% of the SNF is still UO 2. Thus, the behaviour of UO 2 in SNF must be understood and evaluated under the weathering conditions of geologic disposal, which extend to periods of hundreds of thousands of years. There is ample evidence from nature that many uranium deposits have experienced conditions for which the formation of coffinite, USiO 4 , has been favoured over uraninite, UO 2+x , during subsequent alteration events. Thus, coffinite is an important alteration product of the UO 2 in SNF. Here, we present the first evidence of the formation of coffinite on the surface of UO 2 at the time scale of laboratory experiments in a solution saturated with respect to amorphous silica at pH = 9, room temperature and under anoxic conditions. Uraninite, UO 2+x is the most common U 4+ mineral in nature followed by coffinite, USiO 4 , which is found as a primary phase or an alteration product in many uranium deposits. Coffinite, tetragonal, is isostructural with zircon (ZrSiO 4) and thorite (ThSiO 4); however, coffinite can contain some water either as H 2 O or OH groups 1. Altered uraninite and coffinite have been documented from Oklo, Gabon 2-5 , deposits in the Athabasca Basin 4,6,7 and Elliot Lake, Canada 8. Other examples include Jachymov, Czech Republic 9 or La Crouzille district, France 10. For many years, coffinite had gone unrecognized in most uranium deposits, particularly uranium roll-front deposits, as a distinct phase because of its fine grain size and intimate association with uraninite 5,6,11,12. The alteration of uraninite to coffinite is a key event for UO 2 in nature and UO 2 in spent fuel in a geologic repository. Coffinite, being a U 4+-silicate, is associated with reducing environments, with sulphides and organic matter 1 , where it likely precipitated from neutral to weakly alkaline fluids. Coffinite formation in sedimentary uranium deposits is associated with relatively low temperatures, 80-130 °C. A detailed investigation of meteoric roll-front deposits in the Athabasca basin, suggest an estimated temperature of coffinite precipitation in the uranium front of no greater than 50 °C 13. Even though laboratory experiments report coffinite formation at 150-250 °C 14,15 , it appears that these elevated temperatures are not required to form coffinite in nature. Although coffinite is abundant in uranium ore deposits, its synthesis has been a major challenge since its initial description as a mineral in 1955 16. A number of investigators have sought to obtain pure synthetic coffinite, but only a few have succeeded 14,15,17-21. Synthetic coffinite was always obtained under hydrothermal conditions. Systematically, the samples obtained were a mixture of phases, mainly composed of fine grains of USiO 4 , nanoparticles of UO 2 and amorphous SiO 2. All of these attempts to synthesize coffinite indicate that there i...

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“…Acidic media prevents formation of precipitates during oxidation, removing passivation concerns for pure UO 2 (Gaulard-Balandret et al, 2012). The threshold for the onset of anodic dissolution (640 mV vs. SHE) was shown not to change significantly between 20°C and 60°C.…”

Section: Effect Of E Hmentioning

confidence: 93%