Department of Energy, Environmental, and Chemical Engineering, One Brookings Drive, Washington University, St Louis, Missouri 63130, United States.
Environ Sci Technol. 2012 Mar 6;46(5):2731-7. doi: 10.1021/es203751t. Epub 2012 Feb 17.
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.
在与受污染地下水系统相关的实验条件下，研究了连续搅拌槽式反应器 (CSTR) 中存在 Ca(2+) 和 Zn(2+) 时 UO(2) 的溶解情况。进行了补充实验以研究吸附和沉淀反应对 UO(2)溶解的影响。实验在缺氧和有氧条件下进行。Zn(2+) 对 UO(2)溶解的抑制作用比 Ca(2+) 大得多。在有氧条件下，这种抑制作用最为显著，在有氧条件下，Ca(2+) 存在时 UO(2)的溶解速率比水中无二价阳离子时低 7 倍，Zn(2+) 存在时低 1450 倍。从 Ca 实验中回收的 UO(2)固体的 EXAFS 和溶液化学分析表明，形成了 Ca-U(VI)相。在存在 Zn 的实验中从 UO(2)固体上回收的 Zn 碳酸盐氢氧化物 [Zn(5)(CO(3))(2)(OH)(6)] 或结构相似的相沉淀。这些沉淀的 Ca 和 Zn 相可以覆盖 UO(2)表面，抑制 UO(2 的氧化溶解。与二价地下水中阳离子的相互作用对 UO(2)的寿命以及修复地下环境、废物处置场和天然铀矿石中这些固体中 U(VI)的迁移性具有重要意义。
