Organic Matter Counteracts the Enhancement of Cr(III) Extractability during the Fe(II)-Catalyzed Ferrihydrite Transformation: A Nanoscale- and Molecular-Level Investigation,Environmental Science & Technology

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Organic Matter Counteracts the Enhancement of Cr(III) Extractability during the Fe(II)-Catalyzed Ferrihydrite Transformation: A Nanoscale- and Molecular-Level Investigation
Environmental Science & Technology ( IF 10.8 ) Pub Date : 2023-08-28 , DOI: 10.1021/acs.est.3c03848
Xing Xia _{1,

2} , Jin Liu ₃ , Lin Jin ₂ , Jian Wang ₄ , Aminu Inuwa Darma ₂ , Chao He ₂ , Mohsen Shakouri ₄ , Yongfeng Hu ₄ , Jianjun Yang ₅

Affiliation

Phase transformation of ferrihydrite to more stable Fe (oxyhydr)oxides, catalyzed by iron(II) [Fe(II)], significantly influences the mobility of heavy metals [e.g., chromium (Cr)] associated with ferrihydrite. However, the impact of organic matter (OM) on the behavior of Cr(III) in the Fe(II)-catalyzed transformation of ferrihydrite and the underlying mechanisms are unclear. Here, the Fe(II)-catalyzed transformation of the coprecipitates of Fe(III), Cr(III), or rice straw-derived OM was studied at the nanoscale and molecular levels using Fe and Cr K-edge X-ray absorption spectroscopy and spherical aberration corrected scanning transmission electron microscopy (Cs-STEM). Batch extraction results suggested that the OM counteracted the enhancement of Cr(III) extractability during the Fe(II)-catalyzed transformation. Cs-STEM and XAS analysis suggested that Cr(III) could be incorporated into the goethite formed by Fe(II)-catalyzed ferrihydrite transformation, which, however, was inhibited by the OM. Furthermore, Cs-STEM analysis also provided direct nanoscale level evidence that residual ferrihydrite could re-immobilize the released Cr(III) during the Fe(II)-catalyzed transformation process. These results highlighted that the decreased extractability of Cr(III) mainly resulted from the inhibition of OM on the Fe(II)-catalyzed transformation of ferrihydrite to secondary Fe (oxyhydr)oxides, which facilitates insightful understanding and prediction of the geochemical cycling of Cr in soils with active redox dynamics.

中文翻译：

有机物抵消 Fe(II) 催化水铁矿转化过程中 Cr(III) 萃取能力的增强：纳米级和分子级研究

在铁(II) [Fe(II)]的催化下，水铁矿向更稳定的Fe(羟基)氧化物的相变显着影响与水铁矿相关的重金属[例如铬(Cr)]的迁移率。然而，有机物 (OM) 对 Fe(II) 催化水铁矿转化中 Cr(III) 行为的影响及其潜在机制尚不清楚。在这里，使用 Fe 和 Cr K 边 X 射线吸收光谱在纳米级和分子水平上研究了 Fe(III)、Cr(III) 或稻草衍生的 OM 共沉淀物的 Fe(II) 催化转化和球差校正扫描透射电子显微镜（Cs-STEM）。批量萃取结果表明，OM 抵消了 Fe(II) 催化转化过程中 Cr(III) 萃取率的提高。Cs-STEM 和 XAS 分析表明，Cr(III) 可以并入由 Fe(II) 催化的水铁矿转化形成的针铁矿中，然而，这被 OM 抑制。此外，Cs-STEM 分析还提供了直接的纳米级证据，表明残留的水铁矿可以在 Fe(II) 催化转化过程中重新固定释放的 Cr(III)。这些结果表明，Cr(III)的萃取率下降主要是由于OM抑制了Fe(II)催化的水铁矿向次生Fe(羟基)氧化物的转化，这有助于深入了解和预测Cr的地球化学循环在具有活跃氧化还原动力学的土壤中。

更新日期：2023-08-28

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