Greenhouse gas emissions from low-temperature oxidation and spontaneous combustion at open-cut coal mines in Australia

Abstract Spontaneous combustion and low-temperature oxidation of waste coal in open-cut coal mines represents a potentially large source of greenhouse gas emissions. In this paper, emission fluxes of CO2 and CH4 from spoil piles and waste coal dumps measured at 11 mines in the Hunter Valley and Bowen Basin in Australia are presented. The data displayed considerable scatter, which is consistent with the inhomogeneous nature of spoil pile material and permeability of surfaces. Despite the scatter, emissions were able to be classified into three broad categories according to the intensity of the spontaneous combustion present in the material. Average emissions ranged from about 12 kg CO2-e yr− 1 m− 2 to 8200 kg CO2-e yr− 1 m− 2, depending on the intensity of the spontaneous combustion. There was also, within the scatter of the data, an approximately linear trend of increasing emission flux with increasing surface temperature. A key finding of the research is that the emission rates of greenhouse gases from spoil piles where there is no spontaneous combustion, but only low-temperature oxidation of coal and coal waste, are similar to the emission rates due to biological activity from vegetated surfaces. However, further research is required to quantify the degree to which spoil piles that have no spontaneous combustion contribute to the anthropogenic atmospheric CO2 burden.