煤火汞释放初探

The most severe underground coal fire (coal seam spontaneous ignition) in the world is dispersed in the vast strip area of north China ranging 4,800 km from Heilongjiang to Xinjiang, endangering over thirteen provinces. It is considered as one of the five global environmental and ecological catastrophes in 21st century, yet related environmental study is falling behind, which may be attributed to extreme harsh field condition and lack of proper measuring instrument. It is well known that burning coal releases mercury, but whether or how coal fire releases mercury still remains a mystery, for not only the complexity of the specific forms and multiple phases of coal fire, but also the dichotomy nature of its genesis-started by natural weathering and strongly influenced by anthropogenic activities. On the basis of previous repeated field pre-study investigation on coal fire zones in Inner Mongolia, Ningxia and Xinjiang, this project prompts a novel set of field measuring methods on a typical coal fire zone and initiates mercury release origin and comparison studies focusing on coal seam and coal gangue hill with manifestations of all phases of coal fire process. The aim is to preliminarily define the magnitude and severity of mercury release from a broader sense coal fire. The result will provide essential data for future calculation of global coalfire mercury emission inventory, and shed light in the potential significant environment hazard of coal-mining industry in arid and semiarid area. This project also fills the blank of related environmental study of coal fire in China.

中国北方煤火星星点点分布在自内蒙东部到新疆西部延绵4800公里的宽阔条带上，是全球煤火之最，被外国舆论指为世纪环境与生态灾难之源，却未引起我国地理科学领域足够重视。申请者与众研究生志愿者持续三年先后寻访了内蒙、宁夏和新疆的煤层自燃、矸石山自燃和露天矿自燃等形式的煤火，尝试开展了现场研究超100工作日，渐生以汞为切入点之念以致提出本项目。针对煤火自萌生到消亡经历八个阶段，将研究各阶段汞释放权重，以揭示汞释放峰值所处阶段；针对煤火发生场合和形式的多样性，将普查典型矿区究竟有多少汞释放源，以评估其相对释放强度；针对中国煤火汞排放总量目前无法计量，将尝试估算几座自燃矸石山等的汞排放总量。现场用Lumex测汞仪并辅以室内外其他仪器。结果会丰富人类对煤源汞污染的认识；会产生基础数据；会创造条件以便今后思考或研究中国北方煤火汞排放全局；很可能还会酝酿新发现。本项目实施还将促进兴起多角度研究中国北方煤火。

地球关键带中的地表层广泛分布着煤炭。煤炭开发伴生的环境遗煤海量累积，持续暴露于有氧大气，渐成煤火---自发风化、蓄热、分解、隐燃或自燃等。环境遗煤中原生或次生有毒有害物质因此不断活化和迁移并最终反作用于地球关键带，影响当代环境、生态和人类健康。本项目从汞入手揭露相关事实和解读相关机制。.环境遗煤及煤矸石---全球汞排放源: 以煤火流行半个多世纪的中国内蒙古乌达煤田为样本，根据野外实测，系统证实了地下煤层煤火普遍排放烟气（气态单质）汞，浓度总均值464ng/m3（154 -992，n=30×20）；地表煤矸石山煤火普遍强烈排放烟气汞，总均值5908 ng/m3（2513 -10930，n=46×20）。汞通量现场测量结果进一步给出，煤田全境未受煤火烟气直接影响的地表仍存在显著汞通量值，如3号区均值99ng/m2h和6号区均值177ng/m2h等。这些数据指示了乌达煤田全境（2km2）普遍存在汞向大气的持续排放。根源是煤及煤矸石普遍含汞且在风化直至自燃的煤火过程中得到活化，但目前这类排放既无法控制又难以定量计量。.煤火海绵体---极端汞污染点源与矿区局地汞污染: 煤火烟气汞主要进入大气循环，而对局地大气、土壤和植物的影响较小。然而，深入研究揭露，一旦地下煤火烟气被地表土吸附并“生长”出黏土质凸起物---煤火海绵体(CFS)，煤火汞的环境归趋则发生逆转：“滞留”于矿区局地。表现是：CFS极端富集汞，总均值13964ng/g（2653-38470ng/g，n=73）；CFS周边地表土呈劣五类汞污染（汞阈值1500ng/g）。建议将煤矿区的CFS及其周边表土纳入重金属污染控制对象。CFS极端富集汞的机制可能是：挥发性煤火烟气汞(Hg0和少量HgO)当遇到CFS吸附的烟气硫酸，则自发反应形成相对稳定且非挥发性的硫酸汞(HgSO4)。.环境遗煤及煤矸石---硫酸及氢氟酸的持续排放源: 在典型地下煤火区现场采用Piccaro G1205分子氟化氢分析仪检测烟气和监测空气，实证了煤火普遍排放分子氟化氢(HF)，典型强度可达到11165ppb。容量分析获得CFS富集硫酸，[H+]=5.60mol/L(pH值-0.75)，[SO4=]=3.17mol/L。.煤炭是地球关键带中的“软”层。煤炭回采率决定了我国环境遗煤海量，其风化直至自燃难以避免，认识其中科学奥秘，本项目研究只是开头.