Kinetics of corrosion and dissolution of uranium dioxide as a function of pH

Abstract

A continuous flow-through reactor with a thin layer of solid particles (size ranging from 100 to 300 m) was used to obtain a deeper knowledge on the mechanism of dissolution of UO 2 under oxidizing conditions. Using this methodology the dissolution rate of uranium dioxide was determined at three different oxygen partial pressures (5, 21, and 100% in nitrogen) and as a function of pH (between 3 and 12) in a noncomplexing medium.From the results of these experiments the following rate equation was derived:In addition, XPS characterizations were performed to determine the U(IV)/U(VI) ratio on the solid surface at different experimental times and conditions. These results showed that at acidic conditions (pH below 6.7) the final solid surface presents a stoichiometry close to UO 2 , while at alkaline conditions the final solid surface average composition is close to UO 2.25 . This information was integrated with the results of the leaching experiments to present a model for the mechanism of dissolution of uranium dioxide under the experimental conditions.

Comparative dissolution kinetics of biogenic and chemogenic uraninite under oxidizing conditions in the presence of carbonate

“…Gimenez et al (2005) concluded in their study that the non-stoichiometry was not due to deposition of a secondary solid phase. Torrero et al (1997) determined an average solid surface stoichiometry of UO 2.25 at pH 8.2 as opposed to UO 2.0 at pH 5 and explained this difference by a diminishing rate of proton-promoted dissolution with increasing pH, enabling the incorporation of O 2À species into the UO 2 lattice. Thus, in the absence of more soluble aqueous U-carbonate species at neutral and alkaline conditions, the oxidative dissolution of UO 2+x will be controlled by the detachment of U(VI) and U(V) from the UO 2+x surface.…”

Influence of β radiation on UO2dissolution at different pH values

“…4), the composition of the surface of the solid is near UO 2.3 , determined from the deconvolution of the U 4 f(7/2) peak [18]. This composition was also found in UO 2 dissoBrought to you by | New York University Bobst Library Technical Services Authenticated Download Date | 5/29/15 2:40 PM lution experiments in the presence of oxidants at alkaline pH [19,20] and corresponds to the maximum degree of oxidation observed in electrochemical experiments [21].…”

“…At acidic pH the U(VI) formed would dissolve rapidly, while at more alkaline pH, the U(VI) would remain on the surface, as has been also observed for UO 2 oxidation/dissolution by other oxidants [20]. The formation of oxidizing species in solution resulting from β irradiation was studied with the MAK-SIMA code [22] by using the radiolytical model developed by Quiñones et al [5] and the effective G values from Kelm et al [23] that are given in Table 2.…”

Kinetic reactive transport modelling of column tests for uranium In Situ Recovery (ISR) mining

“…Uraninite dissolution kinetics was taken from Torrero et al (1997): This law established for a synthetic uraninite and for a pH in the range of 3 to 6.7, could not model the batch tests in a satisfactory way. Even by applying a very high reactive surface area (900 m²/g) and imposing an oxygen fugacity at equilibrium with the atmosphere (0.2) for the duration of the simulation, it was not possible to simulate enough U dissolution to fit the experiments.…”