煤火硫的环境归趋

Coal fire is a natural phenomenon that coal seam and gangue dump undergo spontaneous combustion after long-term air exposure and eventually experience open-fire combustion or underground smoldering. After Industrial Revolution, the anthropogenic activities have greatly intensified the coal fire worldwide, and today the northern China suffers from the most severe coal fire in the world. Before, it is generally acknowledged that the sulfur and sodium sulfate condensate on the ground surface of the coal fire area were regarded as markers of coal fire. Our previous work also observed surface corrosive soil caused by sulfuric acid derived from coal fire and abnormally enriched sulfur in the coal fire smoke. Therefore, this project, based on these known traits, field evidence, and lab analysis of sulfur isotopes, aims to rationalize the transformation mechanism of the sulfur and its multiple derivatives in coal, and further disclose the underlying mechanism of the release and environmental fate of the coal fire sulfur. This project also targets the synergistic release of heavy metal with sulfur from coal fire and their environmental effect on local soil, water body and atmosphere with help of chemical analysis instruments such as ICP-MS and ion chromatography. The multivariant environmental fate study of coal fire sulfur and heavy metal release would provide theoretical and policy-making evidence for coal fire pollution control. In addition, the study of the surface condensate (sulfur and sodium sulfate) and fine particle (PM2.5) of coal fire with single particle analysis method using SEM-EDX would examine the long-range transportation and haze-inducing potentials of coal fire sulfur, which might bring new thinking to the understanding of the ambient air quality of the northern China.

煤层及矸石山长期接触空气导致自发氧化的现象及隐燃和自燃现象统称为煤火，工业革命以来全球煤火不断但当代我国北方煤火当属世界之最。古今中外煤矿人视地表凝析物硫磺和芒硝(水合硫酸钠)为地下煤火标识；前期工作新察觉，煤火衍生硫酸而出现地表腐蚀土，煤火烟霾则异常富硫。本项目将以煤火硫的这些迹象为线索，深入现场取证，系统测定硫同位素，厘清煤中硫与诸形态硫的演化模式，揭示煤火硫的排放与环境归趋机制；系统运用ICP-MS等定量分析，验证煤火存在硫协同下的重金属排放；结合离子色谱分析等，区分煤火硫及重金属污染土、水和空气的环境效应。基本目标是阐明煤火硫与重金属的多元环境归趋，为煤火污染治理提供决策依据。同期，运用扫描电镜-单颗粒分析等表征凝析物和细颗粒物(芒硝、硫磺和烟霾PM2.5)，验证部分煤火硫排放物的远距离传输本领和潜在致霾作用，为深刻认识我国北方区域背景大气质量提供新思路。

煤火即煤层和煤矸石因自发吸入含氧空气和水(H2O)而风化或氧化且引起隐燃和自燃并伴随自发升温的现象。煤层和煤矸石普遍含硫（黄铁矿(FeS2)为主），本研究揭示煤火硫排放在演化机制上迥异于主要排放SO2的煤及煤矸石的高温快速氧化如燃煤电厂等。隐燃阶段(≤120℃)黄铁矿分解为硫化铁(FeS)和单质硫(S)，硫排放形式以硫磺(S8)的为主，并伴随汞和轻烃(蜡质)排放；自燃阶段(≥120℃)残余硫化铁经多级氧化、水合形成水合硫酸(H2SO4·nH2O)，硫排放形式主要为硫酸并伴随少量二氧化硫(SO2)和多环芳烃(PAHs)排放等。. 本研究还证实了以酸形式排放的煤火硫参与了一系列相关物质的转化。首先水合硫酸会将煤及煤矸石中的氟化物(CaF2)转化为氢氟酸(HF)排放。该证据有力支持HF为燃煤地氟病传播关键媒介的学说。其次，煤火硫酸还汲取石炭-二叠世煤及煤系地层黏土岩(包括煤矸石)普遍存在的铵伊利石(NH4Al2Si3AlO10(OH)2)层间铵(NH4+)并以硫酸氢铵(NH4HSO4)形式排放，从而解释了自燃煤矸石堆场硫酸氢铵排放的现象。. 本研究发现煤火矿区、毗邻农田和下风向人居区地表土、尘伴随硫酸盐、氟、汞和PAHs含量的显著升高，pH值从8.4下降到7-6，个别场所达到4，个别点位(如CFS)甚至为1-2，说明酸污染是首要污染。研究还揭示，煤火硫污染物必然进入总悬浮物(TSP)和可吸入细颗粒物(PM2.5)。. 据此推论在煤火矿区及毗邻区存在硫酸、硫酸氢铵及氢氟酸等带来的健康风险；亦存在区域雾霾风险；还存在与地表土酸化共同作用的地表去植被化的现实。PM2.5中煤火硫污染物终将进入高层大气引起辐射抑制效应进而影响全球气候。全球煤及煤矸石普遍含硫(FeS2),因此，本项目以内蒙古乌达煤田为样本的煤火硫演化与环境归趋研究成果对于认识全球煤火环境影响议题有着广泛的推广意义。

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