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Coupling of Dissolved Organic Matter Molecular Fractionation with Iron and Sulfur Transformations during Sulfidation–Reoxidation Cycling
Journal article   Peer reviewed

Coupling of Dissolved Organic Matter Molecular Fractionation with Iron and Sulfur Transformations during Sulfidation–Reoxidation Cycling

Qian Sun, Edward D. Burton, Dunfeng Si, Tingting Fan, Hu Cheng, Zhenghong Yu, Xiaohou Shao, Peixin Cui and Yujun Wang
Environmental science & technology, Vol.57(43), pp.16327-16339
31/10/2023
DOI: https://doi.org/10.1021/acs.est.3c03613
PMID: 37859467

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19 Times Cited - Web of Science

Abstract

dissolved organic matter iron transformation sulfur transformation sulfidation reoxidation adsorption aromatic compounds molecules redox reactions
Iron (oxyhydr)oxides and organic matter (OM) are intimately associated in natural environments, and their fate might be linked to sulfur during sulfidation–reoxidation cycling. However, the coupling of DOM molecular fractionation with Fe and S transformations following a full sulfidation–reoxidation cycle remains poorly understood. Here, we reacted Fh and Fh–OM associations with S(−II) anaerobically and then exposed the sulfidic systems to air. S(−II) preferentially reacted with Fh to form inorganic S (e.g., mackinawite, S0, and S22–) over being incorporated into OM as organic S and therefore indirectly affected OM fate by altering Fe speciation. Fh sulfidation was inhibited by associated OM, and the main secondary Fe species were mackinawite, Fe(II)–OM compounds, and lepidocrocite. Concomitantly, organic molecules high in unsaturation, aromaticity, and molecular weight were detached from solid-phase Fe species due to their lower affinities for secondary Fe species than for Fh. During the reoxidation stage, the previously formed Fe(II) species were reoxidized to Fh with a stronger aggregation, which recaptured formerly released OM with higher selectivity. Additionally, •OH was generated from Fe(II) oxygenation and degraded a portion of the DOM molecules. Overall, these results have significant implications for Fe, C, and S cycling in S-rich environments characterized by oscillating redox conditions.

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