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Interactions of ferrous iron with clay mineral surfaces during sorption and subsequent oxidation.
Environmental Science: Processes & Impacts ( IF 5.5 ) Pub Date : 2020-05-06 , DOI: 10.1039/d0em00063a
Natacha Van Groeningen 1 , Laurel K ThomasArrigo 1 , James M Byrne 2 , Andreas Kappler 2 , Iso Christl 1 , Ruben Kretzschmar 1
Affiliation  

In submerged soils and sediments, clay minerals are often exposed to anoxic waters containing ferrous iron (Fe2+). Here, we investigated the sorption of Fe2+ onto a synthetic montmorillonite (Syn-1) low in structural Fe (<0.05 mmol Fe per kg) under anoxic conditions and the effects of subsequent oxidation. Samples were prepared at two Fe-loadings (0.05 and 0.5 mol Fe added per kg clay) and equilibrated for 1 and 30 days under anoxic conditions (O2 < 0.1 ppm), followed by exposure to ambient air. Iron solid-phase speciation and mineral identity was analysed by 57Fe Mössbauer spectroscopy and synchrotron X-ray absorption spectroscopy (XAS). Mössbauer analyses showed that Fe(II) was partially oxidized (14–100% of total added Fe2+) upon sorption to Syn-1 under anoxic conditions. XAS results revealed that the added Fe2+ mainly formed precipitates (layered Fe minerals, Fe(III)-bearing clay minerals, ferrihydrite, and lepidocrocite) in different quantities depending on the Fe-loading. Exposing the suspensions to ambient air resulted in rapid and complete oxidation of sorbed Fe(II) and the formation of Fe(III)-phases (Fe(III)-bearing clay minerals, ferrihydrite, and lepidocrocite), demonstrating that the clay minerals were unable to protect ferrous Fe from oxidation, even when equilibrated 30 days under anoxic conditions prior to oxidation. Our findings clarify the role of clay minerals in the formation and stability of Fe-bearing solid phases during redox cycles in periodically anoxic environments.

中文翻译:

在吸附和随后的氧化过程中,亚铁与粘土矿物表面的相互作用。

在淹没的土壤和沉积物中,粘土矿物经常暴露于含亚铁(Fe 2+)的缺氧水中。在这里,我们研究了在缺氧条件下Fe 2+在结构Fe(<0.05 mmol Fe / kg)低的合成蒙脱石(Syn-1)上的吸附以及后续氧化的影响。样品以两种铁负载量(每千克粘土中添加0.05和0.5摩尔铁)制备,并在缺氧条件下(O 2 <0.1 ppm)平衡1天和30天,然后暴露于环境空气中。铁的固相形态和矿物特性通过57 FeMössbauer光谱和同步加速器X射线吸收光谱(XAS)进行分析。Mössbauer分析表明,Fe(II)在缺氧条件下吸附到Syn-1时被部分氧化(占总Fe 2+的14-100%)。XAS结果表明,根据Fe的负载量,添加的Fe 2+主要形成不同数量的析出物(层状Fe矿物,Fe(III)粘土矿物,水铁矿和锂铁云母)。将悬浮液暴露于环境空气中会导致吸附的Fe(II)快速而完全氧化,并形成Fe(III)相(Fe(III)的粘土矿物,三水铁矿和锂蒙脱石),表明即使在氧化前在缺氧条件下平衡了30天,该粘土矿物也无法保护铁亚铁免于氧化。我们的发现阐明了粘土矿物质在周期性缺氧环境中氧化还原循环中含铁固相的形成和稳定性中的作用。
更新日期:2020-06-24
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