Mechanism of mineral adsorption enhancing the reduction of hexavalent chromium by natural organic matter

IF 4.5 1区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Geochimica et Cosmochimica Acta Pub Date : 2025-03-14 DOI:10.1016/j.gca.2025.03.011

Peng Zhang , Yiran Liu , Yingxiao Tian , Chenglong Yu , Songhu Yuan

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Abstract

Natural organic matter (NOM) serves a crucial electron reservoir for the reduction of hexavalent chromium (Cr(VI)) in subsurface environments. However, the influence of mineral adsorption on Cr(VI) reduction by NOM remains poorly understood, despite the widespread interaction among NOM, mineral matrices and Cr(VI) in natural environments. In this study, aluminum oxides (Al₂O₃) and Fe oxyhydroxides (such as ferrihydrite) were chosen as representative minerals to investigate how mineral adsorption influences on the reduction of Cr(VI) by both native and reduced NOM across a pH range of 5–9. Results of this study showed that the extent of Cr(VI) reduction (10 μM) was 1.5–11.1 % in the native NOM (12 mg/L) system, while it increased to 10.6–19.4 % in the native NOM-Al₂O₃ systems and to 19.4–25.4 % in the native NOM-ferrihydrite systems. Similarly, the extent of Cr(VI) reduction was 16.7–23.1 % in the reduced NOM system, while it increased to 17.5–38.3 % in the reduced NOM-Al₂O₃ systems and to 30–54.9 % in the reduced NOM-ferrihydrite systems. This enhancement effect increased with higher amounts of Al₂O₃ and ferrihydrite but diminished as the solution pH increased from 5 to 9. The enhancement of Cr(VI) reduction by Fe oxyhydroxides at the same dosage followed by the sequence: ferrihydrite > lepidocrocite > goethite > hematite. In NOM system alone, phenolic moieties in NOM mainly contributed to Cr(VI) reduction. In NOM-Al₂O₃/Fe oxyhydroxide systems, mineral adsorption shifted the reaction site from solution phase to mineral surface, subsequently inducing oxidative polymerization of polyphenolic compounds in NOM, which generated more phenolic moieties that further facilitated the reduction of Cr(VI). Additionally, Fe oxyhydroxides served as electron shuttles, facilitating electron transfer from NOM to Cr(VI). This study highlights a previously unrecognized catalytic role of mineral adsorption in enhancing Cr(VI) reduction by NOM in subsurface environments.

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矿物吸附促进天然有机物还原六价铬的机理

天然有机物（NOM）在地下环境中为六价铬（Cr(VI)）的还原提供了一个重要的电子储集层。然而，尽管在自然环境中NOM、矿物基质和Cr（VI）之间存在广泛的相互作用，但矿物吸附对NOM还原Cr（VI）的影响仍然知之甚少。在本研究中，选择氧化铝（Al2O3）和铁氢氧化物（如铁水合铁）作为代表性矿物，研究在5-9的pH范围内，矿物吸附对天然和还原的NOM还原Cr（VI）的影响。结果表明：在天然NOM （12 mg/L）体系中，Cr（VI）的还原幅度（10 μM）为1.5 ~ 11.1%，而在天然NOM- al2o3体系中，Cr（VI）的还原幅度为10.6 ~ 19.4%，在天然NOM-铁水合体体系中，Cr（VI）的还原幅度为19.4 ~ 25.4%。同样，在还原的NOM体系中，Cr（VI）的还原程度为16.7 ~ 23.1%，而在还原的NOM- al2o3体系中，Cr（VI）的还原程度增加到17.5 ~ 38.3%，在还原的NOM-铁水合体体系中，Cr（VI）的还原程度增加到30 ~ 54.9%。随着Al2O3和铁酸盐含量的增加，这种增强效果增强，但随着溶液pH从5增加到9而减弱。相同剂量下铁氧化物对Cr（VI）还原的促进作用顺序为：水合铁>；纤铁矿比;针铁矿比;赤铁矿。仅在NOM体系中，NOM中的酚类部分对Cr（VI）的还原起主要作用。在NOM- al2o3 /Fe氢氧体系中，矿物吸附将反应位点从溶液转移到矿物表面，从而诱导了NOM中多酚类化合物的氧化聚合，产生了更多的酚类基团，进一步促进了Cr（VI）的还原。此外，铁氧氢氧化物充当电子穿梭器，促进电子从NOM转移到Cr（VI）。本研究强调了以前未被认识到的矿物吸附在地下环境中增强NOM还原Cr（VI）的催化作用。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Geochimica et Cosmochimica Acta 地学-地球化学与地球物理

CiteScore

9.60

自引率

14.00%

发文量

437

审稿时长

6 months

期刊介绍： Geochimica et Cosmochimica Acta publishes research papers in a wide range of subjects in terrestrial geochemistry, meteoritics, and planetary geochemistry. The scope of the journal includes: 1). Physical chemistry of gases, aqueous solutions, glasses, and crystalline solids 2). Igneous and metamorphic petrology 3). Chemical processes in the atmosphere, hydrosphere, biosphere, and lithosphere of the Earth 4). Organic geochemistry 5). Isotope geochemistry 6). Meteoritics and meteorite impacts 7). Lunar science; and 8). Planetary geochemistry.