Heterogeneous oxidation of Fe(II) on iron oxides in aqueous systems: Identification and controls of Fe(III) product formation
Heterogeneous oxidation of Fe(II) on iron oxides in aqueous systems: Identification and controls of Fe(III) product formation
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DOI：
10.1016/j.gca.2012.05.031
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发表时间：
2012-08-15
影响因子：
5
通讯作者：
Haderlein, Stefan B.
中科院分区：
文献类型：
--
作者：
Larese-Casanova, Philip;Kappler, Andreas;Haderlein, Stefan B.
水溶液Fe（II）-氧化物Fe（III）系统是通过界面Fe（II）吸附和电子转移过程的许多类氧化还原敏感化合物的反应物。由于污染物还原和铁氧化物上的Fe（II）氧化而形成的溶解性差的Fe（III）产物可能能够改性铁氧化物表面并影响污染物如卤代乙烯或硝基芳族化合物的后续还原速率。本研究的范围是确定的次生Fe（III）矿物相后，Fe（II）氧化后形成的常见的铁氧化物在非均质污染物还原直接针对次生矿物使用穆斯堡尔活性同位素。在（56）赤铁矿、（56）针铁矿、（56）磁铁矿和（56）磁赤铁矿的pH缓冲悬浮液中，使用硝基苯作为模型氧化剂氧化溶解的Fe-57（II）后，使用Fe-57-穆斯堡尔谱、μ-X射线衍射和电子显微镜进行Fe（III）矿物表征。穆斯堡尔谱证实，吸附的Fe-57（II）被氧化的母体Fe-56（III）-氧化物吸附剂和吸收的吸附剂氧化物之前，任何硝基苯还原，在文献中的几个报告一致。除了氧化物吸附剂的生长外，硝基苯对Fe（II）的吸附和氧化也会导致次生Fe（III）矿物的形成。针铁矿形成的三个赤铁矿形态（菱面体，针，和六方片晶），针铁矿的典型针状针的形状出现在微米级的六方片晶，在60度取向的（001）面的时间对齐。三个赤铁矿针铁矿形成的比例与表面位点的数量有关。仅观察到针铁矿在针铁矿吸附剂上形成。与此相反，观察到lepidocrotite形成磁铁矿和磁赤铁矿吸附剂（与均匀的Fe（II）氧化O-2）和假定的球晶形态。所有次级Fe（III）相在μ-X-射线衍射图案内被确认。在赤铁矿上，针铁矿的定向形成与纤铁矿相反，这表明赤铁矿可能具有对α-FeOOH原子排列的模板能力，而不是γ-FeOOH。所有二次铁氧化物的形成发生后，支持矿物吸附剂上的单层覆盖四至六当量的启动。总体而言，Fe（III）的产品身份形成的非均相Fe（II）氧化过程中似乎主要是由身份的基础吸附剂和部分由可用的表面位点的量。(C)2012爱思唯尔有限公司保留所有权利。
The aqueous Fe(II)-oxide Fe(III) system is a reactant for many classes of redox sensitive compounds via an interfacial Fe(II) sorption and electron transfer process. The poorly soluble Fe(III) products formed as a result of contaminant reduction and Fe(II) oxidation on iron oxides may be capable of modifying iron oxide surfaces and affecting subsequent reduction rates of contaminants such as halogenated ethenes or nitroaromatic compounds. The scope of this study was to identify the secondary Fe(III) mineral phases formed after Fe(II) oxidation on common iron oxides during heterogeneous contaminant reduction by directly targeting the secondary minerals using Mossbauer-active isotopes. Fe(III) mineral characterization was performed using Fe-57-Mossbauer spectroscopy, mu-X-ray diffraction, and electron microscopy after oxidation of dissolved Fe-57(II) using nitrobenzenes as a model oxidant in pH-buffered suspensions of (56)hematite, (56)goethite, (56)magnetite, and (56)maghemite. Mossbauer spectra confirmed sorbed Fe-57(II) becomes oxidized by the parent Fe-56(III)-oxide sorbent and assimilated as the sorbent oxide prior to any nitrobenzene reduction, consistent with several reports in the literature. In addition to oxide sorbent growth, Fe(II) sorption and oxidation by nitrobenzene result also in the formation of secondary Fe(III) minerals. Goethite formed on three hematite morphologies (rhombohedra, needles, and hexagonal platelets), and acicular needle shapes typical of goethite appeared on the micron-sized hexagonal platelets, at times aligned in 60 degrees orientations on (001) faces. The proportion of goethite formation on the three hematites was linked to number of surface sites. Only goethite was observed to form on a goethite sorbent. In contrast, lepidocrocite was observed to form on magnetite and maghemite sorbents (consistent with homogeneous Fe(II) oxidation by O-2) and assumed spherulite morphologies. All secondary Fe(III) phases were confirmed within mu-X-ray diffraction patterns. On hematite, the directed formation of goethite as opposed to lepidocrocite suggests hematite may possess a templating ability for the alpha-FeOOH atom arrangement as opposed to gamma-FeOOH. The initiation of all secondary Fe-oxide formations occurred after four to six equivalents of monolayer coverage on the supporting mineral sorbent. Overall, Fe(III) product identity formed during heterogeneous Fe(II) oxidation appears to be governed mainly by the identity of the underlying sorbent and partly by the amount of available surface sites. (C) 2012 Elsevier Ltd. All rights reserved.