化学
铬
柠檬酸
锰
无机化学
有机酸
有机质
氧化还原
环境化学
金属
没食子酸
有机化学
抗氧化剂
作者
Fatai O. Balogun,Miranda Aiken,Alireza Namayandeh,Owen W. Duckworth,Matthew L. Polizzotto
出处
期刊:Chemosphere
[Elsevier]
日期:2023-12-01
卷期号:344: 140424-140424
标识
DOI:10.1016/j.chemosphere.2023.140424
摘要
Oxidation of chromium (Cr)-bearing minerals by manganese (Mn) oxides is viewed as the dominant mechanism controlling geogenic production of Cr(VI) and its contamination of groundwater. This process may be modulated by other chemical constituents found in the natural environment, but such confounding factors have not been quantified. Here, we evaluated the mechanism of Cr(III) oxidation by mixed-valence Mn oxide in the presence of citric and gallic acids, two natural organic matter (NOM) constituents commonly found in the soil environment. Incubation experiments showed that each organic acid enhanced solubilization of Cr(III) and Mn over controls without organic addition but increasing organic acid concentration decreased production of Cr(VI), with approximately 8.5 times less Cr(VI) produced in the citric acid than gallic acid experiments. X-ray absorption spectroscopy showed that negligible Cr(VI) was present in solid-phase reaction products, regardless of treatment. Geochemical modeling revealed that in the citric acid experiments, unprotonated Cr(III)-citrate was the dominant organo-metallic complex in solution, while (CrOH)2+ distribution positively correlated with concentrations of Cr(VI) produced. Collectively, these results illustrate how NOM can modify expected chemical pathways driving Cr cycling, and such mechanistic information should be better integrated into models predicting Cr redox dynamics and availability in the environment.
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