Thermal transformation of organic matter in coal waste from Rymer Cones (Upper Silesian Coal Basin, Poland)

Abstract

Abstract Coal wastes produced at various stages of coal mining, washing and deposition on dumps are a source of many pollutants. In some cases, the dumped coal waste undergoes self-heating and self-combustion processes that reflect the properties of the organic matter present (maceral composition and rank) and the history of heating (rate, time and temperature of heating). In the examination of the coal wastes from the Rymer Cones dump, petrographic- and gas chromatography-mass spectrometry (GC-MS) techniques were used to provide different sets of complementary data. Unaltered- and variably-altered macerals (mostly vitrinite) characterise the investigated material. Vitrinite of elevated reflectance and massive coke particles indicate that the rate of heating was low and that the availability of air was very limited; heating took place under pyrolytic conditions. Irregular cracks in particles probably also resulted from slow heating. The temperature of the heating processes, dynamically changing in time and place throughout the dump, led to chemical changes in organic matter such as the formation of phenols and their derivatives, and alteration in distributions of n-alkanes, hopanes and moretanes and polycylic aromatic hydrocarbons (PAHs) occurring in pyrolysates. Some of these compounds formed as a result of the thermal destruction of liptinite and vitrinite macerals at various temperatures and migrated from within the dump. The changes that occurred within the dump are also reflected in values of geochemical parameters based on the same compounds, such as CPI, Ts/(Ts + Tm), MNR, DNR, TNR-1, TNR-2. Lighter compounds were probably released into the atmosphere and others, especially phenols that are easily soluble in water and PAHs, were most probably leached into deeper parts of the dump and even into underground waters since they are absent in some samples or significantly decreased in concentration. These processes probably still continue — it is this fact that creates a potential hazard to the environment.