Uranium redox transition pathways in acetate-amended sediments
Uranium redox transition pathways in acetate-amended sediments
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DOI：
10.1073/pnas.1219198110
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发表时间：
2013-03-19
影响因子：
11.1
通讯作者：
Bernier-Latmani, Rizlan
中科院分区：
文献类型：
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作者：
Bargar, John R.;Williams, Kenneth H.;Bernier-Latmani, Rizlan
低温沉积物中铀的氧化还原转变[从U(VI)到U(IV)]控制着环境中铀的流动性和矿体中铀的积累，并帮助我们了解地球的地球化学历史。这些转变的分子尺度机制路径决定了 U(IV) 产物的形成，从而影响沉积物中的铀同位素分馏、再氧化和传输。提高我们对这些路径的理解的研究有可能大大促进对许多地球科学学科的过程的理解。由于直接观察地下分子尺度过程的困难以及地下系统的组成/物理复杂性，有关野外沉积物中铀氧化还原转变的详细机制信息基本上不存在。在这里，我们介绍了硫酸盐还原条件下含水层沉积物中发生的铀氧化还原转变的原位研究结果。基于分子尺度光谱、孔隙尺度地球化学和宏观水相证据，我们提出了一种生物-非生物转变途径，其中生物质托管的马基纳维特（FeS）作为电子源将U（VI）还原为U（IV），随后与生物质反应产生单体U（IV）物种。还存在类似纳米级铀矿的物质，这意味着至少有两个氧化还原转变途径的运行。低温沉积物中多种途径的存在将明显对比的先前观察结果统一起来，有助于解释不同生物地球化学条件下铀的持续减少。这些发现对我们了解铀生物修复、矿石形成和全球地球化学过程具有直接影响。
Redox transitions of uranium [from U(VI) to U(IV)] in low-temperature sediments govern the mobility of uranium in the environment and the accumulation of uranium in ore bodies, and inform our understanding of Earth's geochemical history. The molecular-scale mechanistic pathways of these transitions determine the U(IV) products formed, thus influencing uranium isotope fractionation, reoxidation, and transport in sediments. Studies that improve our understanding of these pathways have the potential to substantially advance process understanding across a number of earth sciences disciplines. Detailed mechanistic information regarding uranium redox transitions in field sediments is largely nonexistent, owing to the difficulty of directly observing molecular-scale processes in the subsurface and the compositional/physical complexity of subsurface systems. Here, we present results from an in situ study of uranium redox transitions occurring in aquifer sediments under sulfate-reducing conditions. Based on molecular-scale spectroscopic, pore-scale geochemical, and macroscale aqueous evidence, we propose a biotic-abiotic transition pathway in which biomass-hosted mackinawite (FeS) is an electron source to reduce U(VI) to U(IV), which subsequently reacts with biomass to produce monomeric U(IV) species. A species resembling nanoscale uraninite is also present, implying the operation of at least two redox transition pathways. The presence of multiple pathways in low-temperature sediments unifies apparently contrasting prior observations and helps to explain sustained uranium reduction under disparate biogeochemical conditions. These findings have direct implications for our understanding of uranium bioremediation, ore formation, and global geochemical processes.