Abstract
The dissolution of UO 2 in a continuously stirred tank reactor (CSTR) in the presence of Ca 2+ and Zn 2+ was investigated under experimental conditions relevant to contaminated groundwater systems. Complementary experiments were performed to investigate the effect of adsorption and precipitation reactions on UO 2 dissolution. The experiments were performed under anoxic and oxic conditions. Zn 2+ had a much greater inhibitory effect on UO 2 dissolution than did Ca 2+. This inhibition was most substantial under oxic conditions, where the experimental rate of UO 2 dissolution was 7 times lower in the presence of Ca 2+ and 1450 times lower in the presence of Zn 2+ than in water free of divalent cations. EXAFS and solution chemistry analyses of UO 2 solids recovered from a Ca experiment suggest that a Ca-U(VI) phase precipitated. The Zn carbonate hydrozincite [Zn 5(CO 3) 2(OH) 6] or a structurally similar phase precipitated on the UO 2 solids recovered from experiments performed in the presence of Zn. These precipitated Ca and Zn phases can coat the UO 2 surface, inhibiting the oxidative dissolution of UO 2. Interactions with divalent groundwater cations have implications for the longevity of UO 2 and the mobilization of U(VI) from these solids in remediated subsurface environments, waste disposal sites, and natural uranium ores.
| Original language | English |
|---|---|
| Pages (from-to) | 2731-2737 |
| Number of pages | 7 |
| Journal | Environmental Science and Technology |
| Volume | 46 |
| Issue number | 5 |
| DOIs | |
| State | Published - Mar 6 2012 |