煤炭地下气化是一种新的煤炭利用技术，具有安全、经济、环保等优势；然而，地下气化残渣的稳定性一直是人们关注的重点问题，也是地下气化技术应用的瓶颈问题之一。研究煤炭地下气化残渣中微量元素的化学形态对于理解残渣中微量元素的迁移和转化以及保护地下环境具有重要的意义。以乌兰察布褐煤为研究对象，制备了煤炭地下气化不同反应阶段的产物。采用逐级提取法研究了微量元素(Hg，F，Se，Zn，Pb，Ba)不同形态的分布。引入风险评价指数(Risk Assessment Code,RAC)评估了地下气化残渣中微量元素的危害级别。结果表明，Ba在热解半焦中以BaSO4的形式存在，F存在于碳酸盐矿物中。在900～1 300 ℃的气化灰渣中，大部分的Hg已经挥发到气相中，此时Hg对地下环境已无危害。Zn在900 ℃和1 000 ℃的还原灰渣中对地下环境具有高风险。Ba和Pb对地下环境的危害级别随着反应温度的升高而逐渐降低。氧化残渣(1 100～1 500 ℃)中F，Zn，Ba，Se和Pb主要是以残渣态的形式稳定存在。Zn和Se在1 100 ℃的氧化残渣中对地下环境是中等危害，随着氧化温度的升高，风险等级变为低风险。Ba和Pb在地下气化残渣中处于低风险等级。当地下反应温度达到1 200 ℃时，地下气化残渣中微量元素主要是以残渣态的形式稳定存在，其对地下环境的危害级别处于低风险范围(RAC<10%)，表明地下残渣已经达到了稳定。该研究可以为地下气化残留物的环境风险评估提供科学的指导。

Underground coal gasification (UCG) is a new coal utilization technology with safety,economy and environmental protection.However,the stability of underground coal gasification residues has always been the focus of people’s attention,and it is also one of the bottlenecks in the application of the UCG technology.It is of great significance to study the chemical speciation of trace elements (TEs) in the underground coal gasification residues to understand the release and transformation of trace elements and to protect the underground environment.In this paper,Ulanqab lignite was used as the research object,the underground coal gasification sequential transformation products were prepared,and the chemical speciation of trace elements (Hg,F,Se,Zn,Pb,Ba) in the UCG products were studied by using a chemical analysis.The risk assessment code (RAC) was introduced to assess the risk level of trace elements in UCG residues to the underground environment.The results indicate that during the UCG pyrolysis process,Ba exists in the form of BaSO4 and F exists in carbonate minerals.At 900-1 300 ℃ reduction ash,most of Hg has volatilized into the gas and it has no risk to the underground environment.Zn in 900 ℃ and 1 000 ℃ reduction ash has high risk to environment.The risk level of Ba and Pb to underground environment decreases with the increase of reaction temperature.F,Zn,Ba,Se and Pb in the oxidation residue (1 100-1 500 ℃) are mainly in the form of residue.Zn and Se are moderately harmful to the underground environment in the oxidation residue at 1 100 ℃.With the increase of oxidation temperature,the risk level becomes low.Ba and Pb are in low risk level in the residue of underground gasification.When the reaction temperature reaches 1 200 ℃,the risk level of trace elements in the UCG residues is in the low-risk range (RAC<10%),indicating that the UCG residues has reached stability.

1 实验部分

   1.1 实验煤样

   1.2 实验装置及方法

   1.3 煤炭地下气化残渣中微量元素的化学形态

   1.4 产物表征与分析

   1.5 风险评价指数

2 结果与讨论

   2.1 原煤和半焦中微量元素的质量分数

   2.2 还原灰渣中微量元素的质量分数

   2.3 氧化残渣中微量元素的质量分数

3 结论