Oxidative dissolution mechanism of both undoped and GdO-doped UO(s) at alkaline to hyperalkaline pH.

Dalton Trans

Department of Chemical Engineering, EEBE and Barcelona Research Center in Multiscale Science and Engineering, Universitat Politècnica de Catalunya (UPC), 08019 Barcelona, Spain.

Published: July 2023

The dissolution rates of unirradiated UO and unirradiated UO doped with GdO were determined as a function of pH using flow-through experiments in the presence of O(g) and bicarbonate. The dissolution rate of non-doped UO was very low under hyperalkaline conditions (pH 12-13) whereas it increased drastically as the pH decreased to 9. The dissolution of non-doped UO in the pH range of 9-13 was consistent with the oxidative dissolution mechanism already described for UO dissolution in the presence of bicarbonate and oxygen. XPS analysis performed on the solid after dissolution experiments at pH 10 and 13 supported the bicarbonate effect to complex UO and accelerate dissolution. Moreover, UO doped with GdO (5 wt% and 10 wt%) showed dissolution rates as low as non-doped UO under hyperalkaline conditions, which were maintained throughout the pH range studied (9-13). No substantial differences in the dissolution rates between these two doping levels were found. XPS analysis evidenced a similar surface composition both at pH 10 and 13, with U(V) being the dominant oxidation state. The low dissolution rates were assumed to be a consequence of the gadolinium capacity to retard the oxidation of U(V) to U(VI). The slight increase in dissolution rates observed in the hyperalkaline region was attributed to a shift in the oxidative dissolution mechanism, in which the presence of OH promotes the formation of soluble uranyl hydroxo complexes.

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http://dx.doi.org/10.1039/d3dt01268aDOI Listing

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