Influence of soil cover on reducing the environmental impact of spontaneous coal combustion in coal waste gobs: A review and new experimental data

The process of spontaneous combustion of coal and coal waste gobs including emitted gases, condensation of inorganic and organic species in vents, and leachable potential are examined in this study which encompasses a literature review and new experimental data. Furthermore, the potential environmental benefits of cover soil reclamation for reduction of atmospheric and water leachable pollutant emissions are also considered. The Datong district (Shanxi province) is one of the most important coal production areas in China. The resulting large accumulations of mining waste are susceptible to spontaneous combustion. Three coal gangue dumps in the Datong region subjected to a range of reclamation conditions were investigated to assess the influence on coal fires. Coal, coal gangue, and condensates from gaseous emissions were characterized in terms of chemical composition, particle morphology, mineralogy, and leaching potential. The condensates include tar-like deposits, elemental sulfur, gypsum/anhydrite, ammonium and Hg salts, and a broad array of Al-K-Fe sulfates. The latter may give rise to strongly acidic leachates with high metal loads, which may pose a serious threat to the environment. These findings led to the development of a proposed condensation sequence model for coal gangue fires. The presence and distribution of organic compounds in the condensates deposited at vents were used as geothermometers in support of the proposed condensation model. Additionally, the present study has also explored some feasible remediation measures. It was found that covering these coal waste dumps with a layer of compacted soils appears to be an excellent cost-effective method to reduce spontaneous combustion, scavenge pollutants from gaseous emissions, and minimize risks associated with the leaching of readily soluble salts condensed on the surface. (C) 2010 Elsevier B.V. All rights reserved.