Hu Xin, Sun Qiang, Shi Qingmin, Wang Nianqin, Geng Jishi, Xue Shengze
College of Geology and Environment, Xi'an University of Science and Technology, Xi'an, Shaanxi 710054, China.
College of Geology and Environment, Xi'an University of Science and Technology, Xi'an, Shaanxi 710054, China; Shaanxi Provincial Key Laboratory of Geological Support for Coal Green Exploitation, 710054, China; Key Laboratory of Coal Resources Exploration and Comprehensive Utilization, Ministry of Land and Resources, China.
Sci Total Environ. 2023 Dec 15;904:167228. doi: 10.1016/j.scitotenv.2023.167228. Epub 2023 Sep 19.
Coal pyrolysis is a important method for classifying and utilizing coal resources and contributes to enhanced comprehensive resource utilization. However, In high-temperature areas such as coal pyrolysis, there is an abnormal phenomenon release of radioactive gas radon, understanding the relationship between temperature and radon exhalation characteristics, as well as the underlying mechanisms, holds great importance for assessing radon pollution in mining areas. After coal undergoes pyrolysis under high temperature conditions, its material composition, pore structure, water content, and other properties have changed. The pyrolysis products in different atmosphere environments have differences, and the characteristics of radon emission are also different. To address this, the present study conducted coal pyrolysis experiments in both aerobic and anaerobic environments, using long flame coal sourced from Yulin, China. The radon release concentration of the pyrolysis products was measured. The research findings indicate that during pyrolysis at elevated temperatures, the ratio of coal mass loss is constantly increasing. High temperatures promote the development of pores and fissures, and significant changes in coal properties at temperature thresholds (300 °C and 500 °C). The specific surface area, pore volume, and fracture ratio all display substantial increases, and the amplitude of change is greater under aerobic conditions. The fractal dimension of total pores and macropores shows continuous growth, while the specific surface area, pore volume, and fracture ratio exhibit a strong negative correlation with the radon emission rate of pyrolysis products. The expansion and penetration of pores and cracks, along with the release of a substantial amount of pyrolysis gas, accelerate the transformation, migration, and exhalation of radon, resulting in a negative correlation between the heat treatment temperature and the radon release rate of pyrolysis products. Under aerobic conditions, the radon release rate of pyrolysis products decreases more significantly.
煤炭热解是煤炭资源分类与利用的重要方法，有助于提高资源综合利用水平。然而，在煤炭热解等高温区域，存在放射性气体氡异常释放的现象，了解温度与氡析出特性之间的关系及其潜在机制，对于评估矿区氡污染具有重要意义。煤炭在高温条件下热解后，其物质组成、孔隙结构、含水量等性质发生了变化。不同气氛环境下的热解产物存在差异，氡的析出特征也不同。为此，本研究采用中国榆林的长焰煤，在有氧和厌氧环境下进行了煤炭热解实验。测定了热解产物的氡释放浓度。研究结果表明，在高温热解过程中，煤的质量损失率不断增加。高温促进了孔隙和裂隙的发育，在温度阈值（300℃和500℃）时煤的性质发生了显著变化。比表面积、孔隙体积和裂隙率均大幅增加，且有氧条件下变化幅度更大。总孔隙和大孔隙的分形维数呈持续增长趋势，而比表面积、孔隙体积和裂隙率与热解产物的氡析出率呈强烈负相关。孔隙和裂隙的扩展与贯通，以及大量热解气体的释放，加速了氡的转化、迁移和析出，导致热处理温度与热解产物的氡释放率呈负相关。在有氧条件下，热解产物的氡释放率下降更为显著。
