Redox Transformation of Arsenic by Fe(II)-Activated Goethite (α-FeOOH)
Redox Transformation of Arsenic by Fe(II)-Activated Goethite (α-FeOOH)
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DOI：
10.1021/es901274s
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发表时间：
2010-01-01
影响因子：
11.4
通讯作者：
Kappler, Andreas
中科院分区：
文献类型：
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作者：
Amstaetter, Katja;Borch, Thomas;Kappler, Andreas
类金属砷 (As) 的氧化还原态和形态决定了其环境归趋和毒性。因此，了解影响砷氧化还原态的生物地球化学过程对于理解和预测其环境行为是必要的。在这里，我们使用湿化学和同步加速器 X 射线吸收 (XANES) 分析，通过用 Fe(II) 修正的 pH 中性针铁矿 [α-(FeOOH)-O-III] 矿物悬浮液来量化砷氧化还原变化。针铁矿本身不会氧化 As(III)，并且与热力学预测相反，Fe(II)-针铁矿体系不会还原 As(V)。然而，我们观察到 Fe(II)-针铁矿体系中 As(III) 快速氧化为 As(V)。穆斯堡尔光谱表明，添加 Fe-57(II) 加上迄今为止尚未识别的附加 Fe(II) 相后，初步形成了 Fe-57-针铁矿。 Mossbauer、EXAFS、SEM、XRD 或 HR-TEM 无法检测到其他 Fe(III) 相。这表明，在添加 Fe(II) 并将电子转移到块状针铁矿中时，但在新形成的 Fe(III) 结晶为针铁矿之前，反应性 Fe(III) 物质形成为中间 Fe(III) 相。总之，这项研究表明，当 Fe(III) 羟基氧化物和 Fe(II) 同时存在时，正如在铁还原微生物栖息的环境中常见的那样，可能会发生 As(III) 氧化。这可能解释了地下水含水层减少时 As(V) 的存在。
The redox state and speciation of the metalloid arsenic (As) determine its environmental fate and toxicity. Knowledge about biogeochemical processes influencing arsenic redox state is therefore necessary to understand and predict its environmental behavior. Here we quantified arsenic redox changes by pH-neutral goethite [alpha-(FeOOH)-O-III] mineral suspensions amended with Fe(II) using wet-chemical and synchrotron X-ray absorption (XANES) analysis. Goethite itself did not oxidize As(III) and, in contrast to thermodynamic predictions, Fe(II)-goethite systems did not reduce As(V). However, we observed rapid oxidation of As(III) to As(V) in Fe(II)-goethite systems. Mossbauer spectroscopy showed initial formation of Fe-57-goethite after Fe-57(II) addition plus a so far unidentified additional Fe(II) phase. No other Fe(III) phase could be detected by Mossbauer, EXAFS, SEM, XRD, or HR-TEM. This suggests that reactive Fe(III) species form as an intermediate Fe(III) phase upon Fe(II) addition and electron transfer into bulk goethite but before crystallization of the newly formed Fe(III) as goethite. In summary this study indicates that in the simultaneous presence of Fe(III) oxyhydroxides and Fe(II), as commonly observed in environments inhabited by iron-reducing microorganisms, As(III) oxidation can occur. This potentially explains the presence of As(V) in reduced groundwater aquifers.