Chromium contamination is a serious environmental issue in areas affected by leather tanning and metal plating, and green rust sulfate has been tested extensively as a potential material for in situ chemical reduction of hexavalent chromium in groundwater. Reported products and mechanisms for the reaction have varied, most likely because of green rust's layered structure, as reduction at outer and interlayer surfaces might produce different reaction products with variable stabilities. Based on studies of Cr(III) oxidation by biogenic Mn (IV) oxides, Cr mobility in oxic soils is controlled by the solubility of the Cr(III)-bearing phase. Therefore, careful engineering of green rust properties, i.e., crystal/particle size, morphology, structure, and electron availability, is essential for its optimization as a remediation reagent. In the present study, pure green rust sulfate and green rust sulfate with Al, Mg and Zn substitutions were synthesized and reacted with identical chromate (CrO42-) solutions. The reaction products were characterized by X-ray diffraction, pair distribution function analysis, X-ray absorption spectroscopy and transmission electron microscopy and treated with synthetic δ-MnO2 to assess how easily Cr(III) in the products could be oxidized. It was found that Mg substitution had the most beneficial effect on Cr lability in the product. Less than 2.5% of the Cr(III) present in the reacted Mg-GR was reoxidized by δ-MnO2 within 14 days, and the particle structure and Cr speciation observed during X-ray scattering and absorption analyses of this product suggested that Cr(VI) was reduced in its interlayer. Reduction in the interlayer lead to the linkage of newly-formed Cr(III) to hydroxyl groups in the adjacent octahedral layers, which resulted in increased structural coherency between these layers, distinctive rim domains, sequestration of Cr(III) in insoluble Fe oxide bonding environments resistant to reoxidation and partial transformation to Cr(III)-substituted feroxyhyte. Based on the results of this study of hexavalent chromium reduction by green rust sulfate and other studies, further improvements can also be made to this remediation technique by reacting chromate with a large excess of green rust sulfate, which provides excess Fe(II) that can catalyze transformation to more crystalline iron oxides, and synthesis of the reactant under alkaline conditions, which has been shown to favor chromium reduction in the interlayer of Fe(II)-bearing phyllosilicates.

中文翻译：

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金属阳离子取代对绿锈还原六价铬的影响。

在受皮革鞣制和金属电镀影响的地区，铬污染是一个严重的环境问题，并且已对绿锈硫酸盐进行了广泛的测试，以作为就地化学还原地下水中六价铬的潜在材料。报道的反应产物和反应机理各不相同，这很可能是由于生锈的分层结构所致，因为外层和中间层表面的还原可能会产生具有不同稳定性的不同反应产物。根据对生物型Mn（IV）氧化物氧化Cr（III）的研究，在含氧土壤中Cr的迁移率受含Cr（III）相的溶解度控制。因此，仔细设计绿锈特性，即晶体/颗粒大小，形态，结构和电子利用率，对于优化其作为修复剂至关重要。在本研究中，合成了纯的绿锈硫酸盐和具有Al，Mg和Zn取代的绿锈硫酸盐，并与相同的铬酸盐（CrO42-）溶液反应。通过X射线衍射，对分布函数分析，X射线吸收光谱和透射电子显微镜对反应产物进行表征，并用合成δ-MnO2处理以评估产物中的Cr（III）氧化的难易程度。发现镁替代对产品中的Cr不稳定性具有最有益的作用。反应后的Mg-GR中少于2.5％的Cr（III）在14天之内被δ-MnO2再氧化，并且在该产品的X射线散射和吸收分析中观察到的颗粒结构和Cr形态表明，Cr（III VI）的中间层减少了。中间层的减少导致新形成的Cr（III）与相邻八面体层中的羟基键合，从而导致这些层之间的结构连贯性增强，独特的边缘区域，不溶性Fe氧化物键合中的Cr（III）螯合抗再氧化和部分转化为Cr（III）取代的铁氧酸盐的环境。根据这项研究的结果，该研究通过生铁锈硫酸盐还原六价铬和其他研究结果，也可以通过使铬酸盐与大量过量的生铁锈硫酸盐反应来进一步改善该修复技术，从而提供过量的Fe（II），催化转化为更多的结晶铁氧化物，并在碱性条件下合成反应物，