The impact of water-washing, biodegradation and self-heating processes on coal waste dumps in the Rybnik Industrial Region (Poland)

Water-washing, biodegradation and self-heating impacts on coal waste features were investigated on four sample sets: fresh coal wastes (sampled less than one week after dumping), samples from gullies in coal-waste dumps, self-heated material and Bierawka river sediment mixed with coal/coal-waste particles. Rock Eval pyrolysis, petrography and gas chromatography-mass spectrometry (GC-MS) were applied to assess degree of organic-matter alteration. It was found that water-washing and self-heating did not influence the vitrinite reflectance. Rock-Eval pyrolysis results better reflected the secondary changes in organic matter, namely, S-2-TOC and HI-T-max allowed their extent to be defined. Changes were noted in other geochemical e.g., n-alkane parameters Sigma 2/Sigma 1 increased and n-C-23/n-C-31 decreased whereas, Pr/Ph, Pr/n-C-17 and Ph/n-C-18 ratios increased slightly compared to fresh coal waste. The Hunt diagram allows discrimination between water-washed- and biodegraded samples from unaltered, fresh coal waste. Similarly, changes in distributions of phenols, alkyl aromatic hydrocarbons and polycyclic aromatic hydrocarbons (PAHs) reflect degree of water-washing. Self-heating strongly affects distributions of some biomarkers such as n-alkanes, Pr, and Ph, whereas pentacyclic triterpane distributions were generally well preserved. Phenols occur in greatest amount in self-heated wastes, probably released from heated vitrinite. Domination of 2-3 ring PAH rings indicated the bitumen precipitation zone and well-differentiated burnt-out wastes. Recent organic-matter input is seen in increased CPI (Carbon Preference Index) values. (C) 2016 Elsevier B.V. All rights reserved.