Beijing National Laboratory for Molecular Sciences, Fundamental Science Laboratory on Radiochemistry & Radiation Chemistry, College of Chemistry and Molecular Engineering, Peking University , Beijing, 100871, China.
Environ Sci Technol. 2014 Sep 16;48(18):10716-24. doi: 10.1021/es502181x. Epub 2014 Sep 2.
Reductive precipitation is an effective method of attenuating the mobility of uranium (U) in subsurface environments. The reduction of U(VI) by synthetic and naturally occurring pyrite was investigated at pH 3.0-9.5. In contrast to thermodynamic calculations that were used to predict UO2(s) precipitation, a mixed U(IV) and U(VI) product (e.g., U3O8/U4O9/U3O7) was only observed at pH 6.21-8.63 and 4.52-4.83 for synthetic and natural pyrite, respectively. Under acidic conditions, the reduction of UO2(2+) by surface-associated Fe(2+) may not be favored because the mineral surface is nearly neutral or not negative enough. At high pH, the sorption of negatively charged U(VI) species is not favored on the negatively charged mineral surface. Thus, the redox reaction is not favored. Trace elements generally contained within the natural pyrite structure can affect the reactivity of pyrite and lead to a different result between the natural and synthetic pyrite. Because UO2(s) is extremely redox-sensitive toward U(VI), the observed UO2+x(s) phase reduction product indicates a surface reaction that is largely controlled by reaction kinetics and pyrite surface chemistry. These factors may explain why most laboratory experiments have observed incomplete U(VI) reduction on Fe(II)-bearing minerals.
还原沉淀是降低地下环境中铀（U）迁移性的有效方法。在 pH 值为 3.0-9.5 条件下，研究了合成和天然黄铁矿对 U(VI)的还原作用。与用于预测 UO2(s)沉淀的热力学计算相反，仅在 pH 值为 6.21-8.63 和 4.52-4.83 时，观察到合成和天然黄铁矿分别生成 U(IV)和 U(VI)的混合产物（例如 U3O8/U4O9/U3O7）。在酸性条件下，UO2(2+) 被表面结合的 Fe(2+)还原可能不受青睐，因为矿物表面几乎呈中性或不够负电性。在高 pH 值下，带负电荷的 U(VI)物种在带负电荷的矿物表面上的吸附不受青睐。因此，氧化还原反应不受青睐。天然黄铁矿结构中通常包含的微量元素可以影响黄铁矿的反应性，并导致天然和合成黄铁矿之间产生不同的结果。由于 UO2(s)对 U(VI)非常敏感，因此观察到的 UO2+x(s)相还原产物表明这是一个主要受反应动力学和黄铁矿表面化学控制的表面反应。这些因素可能解释了为什么大多数实验室实验都观察到在含铁(II)的矿物上 U(VI)还原不完全。
