煤中微尺度重金属赋存特征

煤矿开采导致的重金属环境污染是全球面临的重要生态环境难题。煤作为重金属的源，由表面性质和微观结构各异的微域构成，控制了重金属的分布、形态转化和生物有效性。但在环境意义尺度上探究微尺度重金属在非均相煤微域中的赋存形态仍有很多不明之处。因此，本文以贵州省兴仁县交乐高砷煤为研究对象，综合运用电子微探针分析仪（EPMA）、扫描电子显微镜-X射线能谱（SEM-EDS）、X射线荧光光谱（XRF）和X射线衍射（XRD）等高精度、微纳米级空间分辨率技术，阐明重金属在非均相煤微域中的浓度分布规律及形态赋存特征。结果表明：煤的矿物成分复杂，主要矿物为石英、绿泥石、高岭石、锐钛矿和黄铁矿。结合XRF的结果（Si，Al，S，Fe，K和Ti为主量元素），煤中的Si主要来源于石英和伊利石；Al和K主要赋存于伊利石；S和Fe来源于黄铁矿；Ti来源于锐钛矿。有趣的是，假设全部的Fe来源于黄铁矿，那么煤的S/Fe摩尔比为4，大于2（黄铁矿的化学计量比，FeS₂）。这表明煤中约一半的S来源于其他矿物质或有机物质。为了阐明煤中S的其他来源，通过SEM-EDS分析发现含S的有机质赋存于煤中，支持了上述XRF和XRD的分析结果。EPMA结果表明煤中的另一个关键元素As，主要赋存于黄铁矿中。

Occurrence and Speciation of Heavy Metals in Coals from a Microscale Perspective

Heavy metals pollution caused by coal mining activities is a crucial environmental issue worldwide. The behavior and bioavailability of heavy metals are susceptible to the heterogeneity and complexity of coal, together with the varied sizes of coal particles from millimeter to nanometer with different microstructures and surface properties. However, it is still unclear to explore the occurrence of microscale heavy metals in heterogeneous coal microdomains on the scale of environmental significance. Therefore, we collected coal samples at a coalfield and employed more efficient yet comprehensive monitoring (e.g., electron probe microanalyzer (EPMA), scanning electron microscope-X-ray energy dispersive spectrometer (SEM-EDS), X-ray diffraction (XRD), and X-ray fluorescence spectroscopy (XRF)) to interpret the occurrence and speciation of heavy metals in coal at a microscale. The results showed that the mineral composition of coal is complex, and the main minerals are quartz, chlorite, kaolinite, anatase and pyrite. For major elements (Si, Al, S, Fe, K, and Ti), Si in the coals was dominated by quartz and illite, Al and K by illite, S and Fe by pyrite, and Ti by anatase. It is interesting to note that S/Fe molar ratio of mine tailings was 4, which was greater than 2 (the stoichiometry of pyrite, FeS₂), assuming that the total amount of Fe was originated from pyrite. It suggests that about half of S in coal was contributed by other mineral and/or organic matter. The SEM-EDS analysis found organic matter with sulfur, that confirmed other forms of sulfur in coal. This finding supports the results of the above-mentioned XRF and XRD. The results of EPMA showed that As in coal mainly occurs in pyrite.