The kinetics of dissolution of UO 2 under reducing conditions and the influence of an oxidized surface layer (UO 2+x ): Application of a continuous flow-through reactor

Details The kinetics of dissolution of UO 2 under reducing conditions and the influence of an oxidized surface layer (UO 2+x ): Application of a continuous flow-through reactor The kinetics of dissolution of UO 2 under reducing conditions and the influence of an oxidized surface layer (UO 2+x ): Application of a continuous flow-through reactor

Mar 1991

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991gecoa..55..647b&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 55, Issue 3, pp.647-658

Computer Science

8

Scientific paper

We have studied the kinetics of dissolution of uranium dioxide, UO 2 (s), under strongly reducing conditions (H 2 (g)/Pd). We have investigated the dependence of the rate of dissolution as a function of critical geochemical parameters: pH, pCO 2 , and carbonate concentration. By using a stirred batch reactor, the kinetics of dissolution of an UO 2+x surface layer and the subsequent precipitation of UO 2 have also been studied. Although the initial UO 2 is pretreated before starting the experiments, it seems to be very difficult to avoid the formation of the oxidized surface layer. For this reason we have developed a thin layer continuous flow-through reactor in order to study the kinetics of dissolution of pure UO 2 (s). The dependence of the rate of dissolution of these solids on the proton concentration of the solution may be expressed according to the following equations: r diss ( UO 2 )(mol sec -1 m -2 ) = 1.4(±0.3) × 10 -8 [ H + ] 0.53 ± 0.08 (3 pH 7) r diss ( UO 2 )(mol sec -1 m -2 ) = 1.9(±0.8) × 10 -12 (7 pH 11) r diss ( UO 2+ x )(mol sec -1 m -2 ) = 1.1(±0.3) × 10 -12 [ H + ] -0.30 ± 0.02 (3 pH 9) mechanism of dissolution of these solids is surface controlled. rate of dissolution of UO 2 in acidic solutions may be described in terms of an integer dependence on the activity of the protonated surface complexes: r diss ( UO 2 )(mol sec -1 m -2 ) = 1.11 × 10 13 {> UOH 2 + } + (2 pH 6)

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