The carbon stable isotope composition of PAHs released during thermal processes in self-heating coal waste Heřmanice dump, Czech Republic

Coal wastes are a by-product of coal mining. Regardless of the extraction technique (opencast or deep mining), coal wastes are disposed of in dumps. The heaps are an integral element of the industrial landscape of the Czech part of the Upper Silesian Coal Basin, where bituminous coal has been mined since the 18^th century. The Heřmanice dump is the largest, partially burning dump in the Czech part of the Upper Silesian Coal Basin. The dump was used to store waste from several mines in northern Ostrava (Ida Mine, Viktoria - Generalissimus Stalin II - Rudý Říjen – Heřmanice Mine) up to 1970. The self-heating process began in the dump's southeast in the early 1990s and has extended northward to the eastern part of the heap. Polycyclic aromatic hydrocarbons (PAHs), naturally occurring in coaly material during waste self-burning are emitted into the atmosphere with particulate matter (PM).

The concentrations and stable carbon isotope compositions of PAHs associated with PM collected on glass fibre filters using a Senya high-flow aspirator were analysed using gas chromatography coupled with tandem mass spectrometry (GC-MS/MS) and compound-specific isotope analysis (CSIA). The PM samples were collected from the same three exhalations on the dump in the winter, spring, and autumn. Following sample collection, the internal temperature of the dump was measured at a depth up to 100 cm below the surface. In dichloromethane extracts of glass fibre filters obtained by ultrasonic extraction, phenanthrene and fluorene predominate regardless of subsurface temperature or season. PAHs emissions differ depending on the stage of combustion. The highest levels of PAHs emission are related to subsurface temperatures ranging from 200 to 250 °C (the main stage of the self-heating process). At low (initial stage) and high (final stage) temperatures PAHs are released in low concentrations. However, the composition of stable carbon isotopes of phenanthrene and fluorene might be helpful to distinguish the stage of the process. Phenanthrene and fluorene related to low temperatures are isotopically heavier than those exhaled at high temperatures. As a result, CSIA might help evaluate the progress of the self-heating process at coal waste heaps.

This study was financed by the AGH University of Krakow as a part of the programme Excellence Initiative – Research University, Action 4, Grant No. 4113.