Geochemical Study of Weathered Coal, a Co-Substrate for Bioremediation of South African Coal Discard Dumps

Abstract

Coal mining creates large volumes of waste in the form of discard coal that is stockpiled. In South Africa, rehabilitation of coal discard dumps remains a challenge due to reliance on topsoil for establishment of vegetation. Exploitation of fungal bio liquefaction/degradation of coal resulted in the emergence of Fungcoal as a bioprocess for the rehabilitation of coal discard dumps and opencast spoils. In this process, a suite of fungi is used to bio liquefy/degrade recalcitrant waste coal to form a soil-like material which promotes reinvigoration of the microbial component, grass growth, and re-vegetation. Here, the role of outcrop weathered coal as a mineral/carbon source to ensure biologically induced humic acid-like substance enrichment of discard and spoil to increase efficacy of fungi-plant mutualism and stimulate revegetation without the need for topsoil was investigated. Mineralogical, elemental, and pyrolysis gas chromatography-mass spectroscopic analyses show that outcrop weathered coal has decreased volatile material and increased humics, ash, and mineral bound water in comparison to bituminous coal. These changes occur coincidently with decreased C, N, and H contents, and a substantial increase in O concentration. No apparent stoichiometric relationship between sulphur and iron oxide content of weathered coal could be discerned suggesting little residual pyrite in this material and a dominance of oxy-hydroxides of Fe. Organic analysis showed weathered coal to be enriched in C-16 and C-18 fatty acids and the presence of the indicator, 17α(H),21β(H)-homohopane but not the β,β-stereoisomer, was interpreted to indicate that bacteria may only have been active prior to transformation of hard coal into weathered coal.