Atom Exchange between Aqueous Fe(II) and Goethite: An Fe Isotope Tracer Study
Atom Exchange between Aqueous Fe(II) and Goethite: An Fe Isotope Tracer Study
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DOI：
10.1021/es802402m
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发表时间：
2009-02-15
影响因子：
11.4
通讯作者：
Scherer, Michelle M.
中科院分区：
文献类型：
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作者：
Handler, Robert M.;Beard, Brian L.;Scherer, Michelle M.
Fe（II）水溶液与Fe（III）氧化物的反应是一个复杂的过程，包括吸附、电子转移以及在某些情况下还原溶解和转化为次生矿物。为了更好地了解这些反应的动力学，我们测量了Fe（II）水溶液和针铁矿之间的Fe同位素交换的程度和速率使用Fe-57同位素示踪剂的方法。在30天的时间内，我们观察到水相和针铁矿纳米棒之间的Fe原子几乎完全交换。尽管有直接的同位素证据广泛的水和针铁矿铁之间的混合，没有观察到相变，也没有针铁矿棒的大小或形状发生明显变化。然而，高分辨率透射电子显微镜图像，似乎表明，一些重结晶的针铁矿颗粒可能已经发生。Fe（II）水溶液和针铁矿之间的近完全交换，再加上可以忽略不计的变化，在针铁矿的矿物学和形态，表明耦合生长（通过吸附和电子转移）和溶解在单独的结晶针铁矿网站的机制。我们建议，吸附和溶解的网站通过散装晶体的传导，最近证明了赤铁矿。Fe（II）水溶液和针铁矿（一种相对稳定的氧化铁）之间的广泛混合对重金属螯合和释放具有重要意义（例如，砷和铀），以及减少土壤和地下水污染物。
The reaction of aqueous Fe(II) with Fe(III) oxides is a complex process, comprising sorption, electron transfer, and in some cases, reductive dissolution and transformation to secondary minerals. To better understand the dynamics of these reactions, we measured the extent and rate of Fe isotope exchange between aqueous Fe(II) and goethite using a Fe-57 isotope tracer approach. We observed near-complete exchange of Fe atoms between the aqueous phase and goethite nanorods over a 30-day time period. Despite direct isotopic evidence for extensive mixing between the aqueous and goethite Fe, no phase transformation was observed, nor did the size or shape of the goethite rods change appreciably. High-resolution transmission electron microscopy images, however, appear to indicate that some recrystallization of the goethite particles may have occurred. Near-complete exchange of Fe between aqueous Fe(II) and goethite, coupled with negligible change in the goethite mineralogy and morphology, suggests a mechanism of coupled growth (via sorption and electron transfer) and dissolution at separate crystallographic goethite sites. We propose that sorption and dissolution sites are linked via conduction through the bulk crystal, as was recently demonstrated for hematite. Extensive mixing between aqueous Fe(II) and goethite, a relatively stable iron oxide, has significant implications for heavy metal sequestration and release (e.g., arsenic and uranium), as well as reduction of soil and groundwater contaminants.