Influence of magmatic intrusions on organic nitrogen in coal: A case study from the Zhuji mine, the Huainan coalfield, China

Although the influence of magmatic intrusions on coal has been studied extensively at many locations, data on changes of organic nitrogen forms in coal in response to this kind of geological instantaneous heating is still scarce. To fill this information gap, a total of five coal samples, including four coal samples collected along a coal transect approaching a magmatic intrusion and one unaltered coal sample, were collected from the No. 3 coal seam of the Zhuji mine in the Huainan coalfield, China and were analyzed for organic nitrogen forms using X-ray photoelectron spectroscopy (XPS), together with the determination of coal quality parameters and elemental composition. Due to the effect of magmatic intrusion, ash yield and carbon content of the coals increase, whereas moisture, volatile matter, oxygen, nitrogen and total sulfur decrease. The N-5 peak is dominant in unaltered and moderately altered coals, but disappears entirely in the coals adjacent to the magmatic intrusion due to the strong thermal influence. The N-Q peak mainly represents “protonated” quaternary nitrogen in unaltered and moderately altered coals. The N-Q peak can be transformed to the N-6 peak through the deprotonation of “protonated” quaternary nitrogen resulting from the loss of oxygen groups under the thermal influence of the magmatic intrusion. Closer to the magmatic intrusion, the N-Q peak is assigned to “graphitic” quaternary nitrogen, which increases sharply and becomes the predominant form eventually. Magmatic intrusion is responsible for the conversion of less stable nitrogen forms to more stable forms in coal.