还原态蒙脱石结构Fe(II)催化水铁矿转化特性及影响因素
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湖南农业大学资源环境学院

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Characteristics and influencing factors of the catalytic transformation of ferrihydrite by the structural Fe(II) in reduced montmorillonite
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College of resources and environment,Hunan Agricultural University

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    摘要:

    还原条件下土壤中Fe(II)催化水铁矿转化在调控营养元素和污染物的生物地球化学过程中具有重要作用。然而,作为土壤中Fe(II)存在的主要形态之一,蒙脱石结构中Fe(II)催化水铁矿转化的特性及其影响因素目前尚不清楚。本文以化学还原的蒙脱石为研究对象,探究了还原态蒙脱石(rSWy-2)结构中Fe(II)催化水铁矿转化的特性及其影响因素。结果表明,贫铁的蒙脱石结构中Fe(II)可催化水铁矿向纤铁矿转化,反应96 h后水铁矿转化量达到83.3%。X射线衍射(XRD)、高分辨透射(HRTEM)、球差电镜(STEM)和表面吸附态Fe(II)含量分析表明,rSWy-2结构Fe(II)催化水铁矿转化主要经历矿物间固相吸附、电子传递和水铁矿转化三个阶段。形成纤铁矿呈板状纳米片,尺寸大小为100~200 nm。溶液中Na+和Cl-离子对rSWy-2催化水铁矿转化影响较弱,而Ca2+、SO42-、有机质和As(III)均对水铁矿转化具有明显的抑制作用。

    Abstract:

    【Objective】Fe(II)-induced transformations of amorphous ferrihydrite to more crystalline iron oxide phases is a widely occurring geochemical process in soils under reduced conditions, and play an important role in regulating the biogeochemical processes of nutrient elements and pollutants. As one of the main species of Fe(II) in soils, Fe(II)-containing clay minerals are ubiquitous in soils under reduced conditions. However, the catalytic properties of structural Fe(II) in clay minerals for ferrihydrite transformation and its influencing factors are still not fully understood.【Method】In this study, the transformation of ferrihydrite induced by the structural Fe(II) in reduced montmorillonite (rSWy-2), which was produced by a chemical method, were investigated at neutral pH under anoxic conditions. Also, the influencing factors including types of cations and anions, organic matter, and As(III) on the transformation were studied. 【Result】The X-ray diffraction (XRD) and chemical extraction analyses results showed that the structural Fe(II) in rSWy-2 with low Fe content can catalyze the transformation from ferrihydrite to more crystalline lepidocrocite, and 83.3% of initial ferrihydrite converted to lepidocrocite after mixing reaction for 96 h. XRD, high-resolution transmission electron microscope (HRTEM), scanning transmission electron microscopy (STEM) and surface adsorbed Fe(II) content analyses showed that the processes of ferrihydrite transformation induced by the structural Fe(II) in rSWy-2 mainly included three stages: Firstly, positively charged ferrihydrite nanoparticles adsorption on negatively charged rSWy-2 surface through electrostatic interaction. Secondly, interfacial electron transfer from the structural Fe(II) in rSWy-2 to the adsorbed ferrihydrite and partly reducing Fe(III) to surface adsorbed Fe(II). Finally, the surface adsorbed Fe(II) catalyzed the transformation of ferrihydrite to more crystalline lepidocrocite phases. HRTEM analyses showed that the formed lepidocrocite phases presented nanoplates with a size range of 100~200 nm. XRD and chemical extraction analyses results showed that Na+ and Cl- ions in the mineral suspension had a weak effect on the catalyzed transformation from ferrihydrite to lepidocrocite phases by the structural Fe(II) in rSWy-2. In contrast, Ca2+, SO42-, organic matter, and As(III) all had obvious inhibition on the transformation due to their strong interactions with minerals. 【Conclusion】The structural Fe(II) in rSWy-2 could catalyze the transformation of ferrihydrite to lepidocrocite at neutral pH under anoxic conditions, and coexisting divalent cations and anions, As(III), and organic matter could inhibit the transformation reaction. The results provide a theoretical basis for further understanding the role of iron-bearing clay minerals in regulating abiotic transformations of iron oxides in soils under anaerobic reduction conditions.

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廖文娟,彭薇,吴聪,宁雅琪,王帅,崔浩杰†.还原态蒙脱石结构Fe(II)催化水铁矿转化特性及影响因素[J].土壤学报,,[待发表]
LIAO Wenjuan, PENG Wei, WU Chong, NING Yaqi, WANG Shuai, CUI Haojie†. Characteristics and influencing factors of the catalytic transformation of ferrihydrite by the structural Fe(II) in reduced montmorillonite[J]. Acta Pedologica Sinica,,[In Press]

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