Effect of the Heat Input by Dolerite Intrusions and the Propensity for Spontaneous Combustion in the Highveld Coalfields, South Africa

Abstract

The spontaneous combustion of coal has been a major problem for the industry, human health and the environment worldwide. The chemical data of two coal samples taken from the Highveld coalfields in the Mpumalanga Province of South Africa was utilized to evaluate the effects of the heat input by the Karoo-aged dolerite intrusions on the coal and consequently, determine the propensity of the coal to spontaneously combust. The coal sampling focused on positions proximal and distal to the intrusion at 0 and 20 m, respectively. The chemical data was represented in terms of ‘area-%’ derived from the chemical compound identification peaks of the chromatographic analyses. Organic compounds detected were grouped into aromatic and aliphatic groups in order to compare their concentration within the sampled coal. The main aromatic compounds present in both coal samples but abundant in proximal coal are benzene, naphthalene, phenanthrene, biphenyl, xanthene, phenol and furan, and the main aliphatic compounds are higher alkanes (n-C10 to n-C31) and ethanol which are abundant in distal coal. Oxidation processes leading to spontaneous combustion will mostly affect the aliphatic-rich coal complexes due to their high reactivity. The aromatic compounds are more stable and have low reactivity. Thus, the propensity of spontaneous combustion increases with increasing distance from the dolerite intrusion.