Inorganic nitrogen in Australian semi-anthracites; implications for determining organic nitrogen functionality in bituminous coals by X-ray photoelectron spectroscopy

Abstract

Inorganic nitrogen in the form of ammonium-bearing clay material has been identified in an Australian (Bowen Basin) semi-anthracite by means of chemical analysis and X-ray photoelectron spectroscopy (XPS). Such an occurrence is similar to the previously reported presence of ammonium-bearing illite in anthracite from eastern Pennsylvania, and consistent with the recently presented X-ray diffraction evidence for ammonium-bearing illite in another Bowen Basin coal of similar rank. The bulk concentration of inorganic nitrogen in the semi-anthracite was ca. 0.1% (5% of the total nitrogen), however the ammonium-bearing clay material was not uniformly distributed throughout the coal; some surfaces prepared for XPS analysis contained no ammonium nitrogen whereas other surfaces contained up to 40% of the total nitrogen in ammonium form. No evidence was obtained for inorganic nitrogen in Australian bituminous coals, including those from the Bowen Basin, nevertheless the presence of very low concentrations could not be excluded. The implications of low concentrations of ammonium nitrogen in bituminous coals for the assignment of the component near 401.5 eV observed in the N(1s) photoelectron spectra of these coals have been considered. It was concluded that any ammonium nitrogen present in bituminous coals would be expected to have a N(1s) binding energy of at least 402.0 cV, and therefore would not be the source of the component near 401.5 eV.