Identification of inorganic nitrogen in an Australian bituminous coal using x-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOFSIMS)

Abstract

Evidence has been found indicating that inorganic nitrogen species may also occur in middle rank coal in addition to anthracite and semi-anthracite. The sample studied in this work is a bituminous coal from the Young Wallsend seam, New South Wales, Australia. X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOFSIMS) surface studies indicate that pyrrolic and pyridinic functionalities are the dominant forms of nitrogen in both bright and dull bands of the coal. XPS spectra for the dull bands of the coal show an additional nitrogen component peak, the position of which (401.7 ± 0.5 eV, after charge correction) is consistent with reported values for ammonium species. In addition, the charging properties of this nitrogen component suggest that it is associated with clay mineral elements, such as Si, Al and K. TOFSIMS mass spectra from the dull bands of the coal include peaks corresponding to ammonium ions (NH 4 +) and ammonium-containing fragment ions (e.g. C 8H 17NH 3 +). TOFSIMS ion imaging of the coal surfaces shows a spatial association between the ammonium-containing ions and elements contained in clay species (i.e. Si, Al and K). The discovery of inorganic nitrogen matter in bituminous coal implies that NH 4-bearing illite is not necessarily a parameter uniquely related to the absolute age of coalification.