Stewart Brandy D, Nico Peter S, Fendorf Scott
Environmental Earth System Science, Stanford University, Stanford, California 94305, USA.
Environ Sci Technol. 2009 Jul 1;43(13):4922-7. doi: 10.1021/es803317w.
Reaction pathways resulting in uranium-bearing solids that are stable (i.e., having limited solubility) under aerobic and anaerobic conditions will limit dissolved concentrations and migration of this toxin. Here, we examine the sorption mechanism and propensity for release of uranium reacted with Fe (hydr)oxides under cyclic oxidizing and reducing conditions. Upon reaction of ferrihydrite with Fe(II) under conditions where aqueous Ca-UO2-CO3 species predominate (3 mM Ca and 3.8 mM total CO3), dissolved uranium concentrations decrease from 0.16 mM to below detection limit (BDL) after 5-15 d, depending on the Fe(II) concentration. In systems undergoing 3 successive redox cycles (14 d of reduction, followed by 5 d of oxidation) and a pulsed decrease to 0.15 mM total CO3, dissolved uranium concentrations varied depending on the Fe(II) concentration during the initial and subsequent reduction phases. U concentrations resulting during the oxic "rebound" varied inversely with the Fe(II) concentration during the reduction cycle. Uranium removed from solution remains in the oxidized form and is found adsorbed onto and incorporated into the structure of newly formed goethite and magnetite. Our results reveal that the fate of uranium is dependent on anaerobic/ aerobic conditions, aqueous uranium speciation, and the fate of iron.
在有氧和无氧条件下，能生成稳定（即溶解度有限）含铀固体的反应路径将限制这种毒素的溶解浓度和迁移。在此，我们研究了在循环氧化和还原条件下，铀与铁（氢）氧化物反应的吸附机制及释放倾向。在水相Ca-UO₂-CO₃物种占主导（3 mM钙和3.8 mM总碳酸根）的条件下，当水铁矿与Fe(II)反应时，根据Fe(II)浓度的不同，溶解态铀浓度在5 - 15天后从0.16 mM降至检测限以下（BDL）。在经历3个连续氧化还原循环（14天还原，随后5天氧化）且总碳酸根脉冲式降至0.15 mM的体系中，溶解态铀浓度在初始和后续还原阶段随Fe(II)浓度而变化。在有氧“反弹”过程中产生的铀浓度与还原循环期间的Fe(II)浓度呈反比。从溶液中去除的铀保持氧化态，被发现吸附并结合到新形成的针铁矿和磁铁矿结构中。我们的结果表明，铀的归宿取决于厌氧/好氧条件、水相铀的形态以及铁的归宿。
