Thermodynamic constraints on the oxidation of biogenic UO2 by Fe(III) (hydr) oxides
Thermodynamic constraints on the oxidation of biogenic UO2 by Fe(III) (hydr) oxides
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DOI：
10.1021/es052305p
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发表时间：
2006-06-01
影响因子：
11.4
通讯作者：
Fendorf, Scott
中科院分区：
文献类型：
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作者：
Ginder-Vogel, Matthew;Criddle, Craig S.;Fendorf, Scott
铀在环境中的流动性部分受其氧化态的控制，在氧化态下，它以U（VI）或U（IV）的形式存在。在有氧环境中，铀通常以六价形式存在，溶解度很高，很容易与碳酸盐和钙形成络合物。在厌氧条件下，常见的金属呼吸细菌可以减少可溶性U（VI）的物种微溶UO 2（晶质铀矿），这些细菌的刺激，事实上，正在探索作为一种原位铀修复技术。然而，土壤和沉积物中生物沉淀的晶质铀矿的稳定性还没有得到很好的表征。在这里，我们表明，晶质铀矿氧化Fe（III）（氢）氧化物是在有限的地球化学条件下的结晶有利。我们的分析表明，针铁矿和赤铁矿有一个有限的能力氧化二氧化铀（生物），而水铁矿可以导致二氧化铀（生物）氧化。水铁矿对二氧化铀（生物）氧化的程度随碳酸氢盐和钙浓度的增加而增加，但随Fe（II）（（aq））和U（VI）（aq））浓度的升高而降低。因此，我们的研究结果表明，由Fe（III）（氢）氧化物的UO 2（生物）的氧化可能会在温和的还原条件下，当水铁矿存在。
Uranium mobility in the environment is partially controlled by its oxidation state, where it exists as either U(VI) or U(IV). In aerobic environments, uranium is generally found in the hexavalent form, is quite soluble, and readily forms complexes with carbonate and calcium. Under anaerobic conditions, common metal respiring bacteria can reduce soluble U(VI) species to sparingly soluble UO2 (uraninite); stimulation of these bacteria, in fact, is being explored as an in situ uranium remediation technique. However, the stability of biologically precipitated uraninite within soils and sediments is not well characterized. Here we demonstrate that uraninite oxidation by Fe(III) (hydr)oxides is thermodynamically favorable under limited geochemical conditions. Our analysis reveals that goethite and hematite have a limited capacity to oxidize UO2(biogenic) while ferrihydrite can lead to UO2(biogenic) oxidation. The extent of UO2(biogenic) oxidation by ferrihydrite increases with increasing bicarbonate and calcium concentration, but decreases with elevated Fe(II)((aq)) and U(VI)((aq)) concentrations. Thus, our results demonstrate that the oxidation of UO2(biogenic) by Fe(III) (hydr) oxides may transpire under mildly reducing conditions when ferrihydrite is present.