Abstract
Twenty-seven gases and sixteen rock wastes from the thermal active Rymer coal waste dump were collected. The composition and origin of gaseous, liquid, and solid pollutants emitted during the self-heating process and the development of these processes with time were established. Gases were subjected to determination of molecular and stable isotope (δ13C and δ2H) composition. Rock-Eval pyrolysis and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) were applied for evaluation of the quantity and molecular composition of pyrolysates released during the heating of rocks in temperatures from 100 to 650 °C. The main products of Py-GC-MS are released between 350 and 650 °C, namely alkanes, aromatic hydrocarbons, and aromatic alcohols. These components were also recorded in Py-GC-MS products of samples collected from the dump surface. Besides the high-molecular-weight organic compounds, in emitted gases CO2, CO, gaseous hydrocarbons, and S-compounds were recorded. The stable isotope data indicated that methane was generated mainly during the low-temperature thermogenic process, but a share of the microbial-originated gas was visible. The source of the CO2 was the oxidation of organic matter. The gaseous S-compounds were products of high-temperature decomposition of sulphides and organic S-compounds. The hydrocarbon and CO contents of the emitted gases proved to be good indicators for tracking of the self-heating processes.
Highlights
The by-product of coal mining, regardless of the method of exploitation, is coal waste, usually deposited in dumps [1,2,3,4]
Due to the fact that studied gas samples were collected in the subsurface area, where gas is the mixture of bacterial gas generated in-situ, air, and gases diffused from deeper parts of the dump, molecular indices should be regarded with caution
The complex investigation of rocks and gases collected at the Rymer coal waste dump allowed conclusions to be drawn: (i) total organic carbon (TOC) content in coal wastes is high, from 7.3 to 27.2 wt.%, whereas subsurface layers are richer than surface one
Summary
The by-product of coal mining, regardless of the method of exploitation (opencast or deep mining), is coal waste, usually deposited in dumps [1,2,3,4]. At the end of the 1980s, in 1995–1999, and in 2004 the reclaim of the dump was made This action was intended to inhibit self-heating processes by isolating combustible material from oxygen sources and cooling the fire outbreaks. The old material was separated from the air (in assumptions) with new coal wastes and inert incombustible material, mostly clays and fly ash from the power station [2]. During this process, thermal processes were intensified and pollutants were significantly emitted due to the disruption of the dump structure. Heavy hydrocarbons and organic compounds with heteroatoms may condensate in the forms of bitumen or tars [15]
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