Coal from the outburst hazardous mine seams: Spectroscopic study

Abstract

Purpose is to analyze influence mechanisms of physicochemical coal properties on the degree of outburst risk as well as desorption kinetics of methane. Methods of scanning electron microscopy (SEM), electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), infrared spectroscopy (IR) and Raman scattering (RS) have been applied. The samples have been taken from Donbas coal seams varying in their ranks (i.e. carbonization degree). Findings. It has been identified that in the context of outburst hazardous zones, the ratio between integral intensity of spectral RS bands D and G, K = I(D)/I(G) shows abnormal dependence upon the nominal amount of volatile compounds connected with the impact by iron impurities. It has been defined that within the ferriferous coal samples, concentration of spins ns (i.e. the broken carbon bonds) correlates with iron content. Methane adsorption/desorption processes in the studied coal samples have been studied with the help of NMR method; in addition, they have been described using superposition of diffusion and filtration mechanisms. Originality. It has been understood that high iron content is typical for coal with a greater outburst hazardous degree. The abovementioned iron content and I(D)/I(G) and Ns correlation between the values determines the key role of iron impurities for coal metamorphism processes. For the first time, correlation between the outburst hazardous degree of coal seam and intensity of 3030 cm-1 IR band, stipulated by aromatic CH groups where hydrogen is in atomic status, has been identified. Practical implications. Predictability of outburst risk has been improved in the context of coal seam mining.