煤汞同位素地球化学研究进展

汞是煤中普遍存在的痕量元素,煤炭消耗总量之巨使燃煤成为全球汞污染主要来源之一。汞具有7种稳定同位素,并且兼具质量分馏和非质量分馏效应,使通过汞同位素对涉煤汞污染源和汞迁移、转化示踪成为理想途径。煤中汞同位素研究获得长足进展。第一,初步给出了世界11个产煤国煤中汞同位素δ~(202)Hg的特征值及分布范围,为示踪环境介质汞的燃煤源污染源创造了条件。第二,发现了原煤中汞存在奇数质量汞的非质量分馏效应(Δ~(199)Hg≠0),有助于配合δ~(202)Hg开展示踪研究。第三,中国不同产煤地及不同成煤期原煤中汞同位素δ~(202)Hg与Δ~(199)Hg值已被测试,为中国开展煤源汞污染示踪研究打下一定基础。进一步工作可能有待加强的4个方面:(1)全球不同地域和时代煤中汞同位素数据库的不断补充、修正和完善;(2)煤炭生产遗存物,如残留煤和煤矸石等与气-水环境相互作用中的汞同位素问题;(3)燃煤派生的且影响人类健康的环境介质如大气细颗粒物(PM_(2.5))的汞同位素问题;(4)涉及煤火汞的迁移转化是复杂的,部分汞具有二次释放特性,其中汞同位素问题仍是未知的。总之煤中汞及其关联的汞同位素研究方兴未艾。

Progresses on Mercury Isotopic Geochemistry of Coal

Mercury is one of the widespread trace elements in coal. The large amount of coal consumption makes it as a main source of global mercury pollution. Seven kinds of stable isotopes, both mass-dependent fractionation (MDF) and mass-independent fractionation (MIF), and significant variations in isotopic composition of the involved coal samples, make Hg isotope an ideal way to assess sources of Hg pollution. Mercury isotope studies of coals have made significant progress over the past twenty years, which can be summarized as follows. Firstly, δ202Hg value and its distribution of coals from 11 countries were preliminarily researched, which from the basis of identifying coal Hg pollution source. Secondly, MIF was found in coals, which was beneficial to do tracing studies with δ202Hg. Thirdly, δ 202Hg and Δ199Hg values in different areas and geologic periods were preliminary determined in our country. Further work may focus on the following areas: Mercury isotope database of coals from different areas and geologic periods in the world should be supplemented, revised and perfect. Mercury isotopes changes associated with the interactions between gas-water environment and coal mining residues such as coal gangue and residual coal should not be neglected. Mercury isotopes of coal combustion products such as atmospheric fine particulate matter (PM2.5) should be studied. Migration and transformation of the coal fire surface mercury is complex because partial mercury on the surface may become secondary mercury release. This fractionation process of mercury isotope will no doubt make it difficult to trace the pollution source with mercury isotope studies. In a word, the study of mercury and mercury isotopes of coal is burgeoning.