Persistent arsenate–iron(III) oxyhydroxide–organic matter nanoaggregates observed in coal,Environmental Science: Nano

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Persistent arsenate–iron(III) oxyhydroxide–organic matter nanoaggregates observed in coal
Environmental Science: Nano ( IF 5.8 ) Pub Date : 2021-08-13 , DOI: 10.1039/d1en00502b
Yinfeng Zhang _{1,

2} , Shehong Li ₂ , Jing Sun ₂ , Benjamin C Bostick ₃ , Yan Zheng _{4,

5}

Affiliation

Understanding how natural nanoaggregates of iron (Fe) and organic matter (OM), currently identified in organic rich soil or peat, interact with metals and metalloids is environmentally significant. Coal is also organic-rich and exemplifies anoxic sedimentary environments with Fe usually as pyrite and not oxides. Here, we analyze the local structure of Fe (6880–21 700 mg kg⁻¹) and As (45–5680 mg kg⁻¹) in representative Guizhou coal samples using X-ray absorption near-edge structure and extended X-ray absorption fine structure (XANES and EXAFS) to illustrate how Fe(III) and As(V) are preserved in coal formed from reduced, organic-rich precursors. Arsenic XANES indicates that >80% of As exists as As(V) with <14% of As associated with sulfides in 5 Guizhou coal samples, confirming published but unexplained results. An As–Fe shell at 3.25–3.29 Å in the As EXAFS suggests that this As(V) is adsorbed on Fe(III) oxyhydroxides as evidenced by Fe EXAFS in these coal samples. Significantly, lower Fe–Fe coordination numbers (CN) of 0.6–1.1 relative to those in 2-line ferrihydrite (CN = 1.6) and goethite (CN = 2.1) suggest that these Fe(III) oxyhydroxides are likely Fe–OM nanoaggregates protected by OM encapsulation and adsorption of arsenate. Such structurally stabilized composites of As(V)–Fe(III)–OM may be more widely distributed and allow oxidized As and Fe to persist in other organic-rich, reducing environments.

中文翻译：

在煤中观察到的持久性砷酸盐 - 羟基氧化铁 (III) - 有机物纳米聚集体

了解目前在富含有机物的土壤或泥炭中发现的铁 (Fe) 和有机物 (OM) 的天然纳米聚集体如何与金属和准金属相互作用具有重要的环境意义。煤也富含有机物，是缺氧沉积环境的例证，其中铁通常是黄铁矿而不是氧化物。在这里，我们使用 X 射线吸收近边结构和扩展 X 射线吸收分析了代表性贵州煤样品中 Fe (6880–21 700 mg kg ^-1 ) 和 As (45–5680 mg kg ^-1 ) 的局部结构精细结构（XANES 和 EXAFS）来说明 Fe( III ) 和 As( V ) 如何保存在由还原的富含有机物的前体形成的煤中。砷 XANES 表明 >80% 的 As 以 As( V) 在 5 个贵州煤样中与硫化物相关的砷含量 <14%，证实了已发表但未解释的结果。As EXAFS 中 3.25–3.29 Å 的 As-Fe 壳表明，这种 As( V ) 吸附在 Fe( III ) 羟基氧化物上，这些煤样品中的 Fe EXAFS 证明了这一点。值得注意的是，相对于 2 线水铁矿 (CN = 1.6) 和针铁矿 (CN = 2.1) 中的低 Fe-Fe 配位数 (CN) 为 0.6-1.1，这表明这些 Fe( III ) 羟基氧化物可能是受保护的 Fe-OM 纳米聚集体通过 OM 包封和吸附砷酸盐。这种结构稳定的 As( V )-Fe( III ) 复合材料)–OM 可能分布更广，并允许氧化的 As 和 Fe 在其他富含有机物的还原环境中持续存在。

更新日期：2021-08-31

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