Sulfur and nitrogen in the high-sulfur coals of the Late Paleozoic from China

• S and N in Chinese superhigh organic sulfur (So > 8%) coals were investigated via XPS.
• Aromatic and aliphatic sulfur were closely related to the coal rank.
• Oxidized N uncommonly dominated in the coals with only bituminous rank.
• Oxidized N occurred as ammonium illite, suggesting volcanic/hydrothermal origin.
• Amine N existed in some samples, which should not appear in normal coals.

The chemical states of sulfur and nitrogen in high-sulfur coals were investigated via X-ray photoelectron spectroscopy (XPS). Twenty-five high-organic-sulfur coal samples of the Late Paleozoic from China were reported, fourteen of which were superhigh organic sulfur (SHOS) coals collected from southern China with organic sulfur contents >8% (on dry and ash-free basis). The aromatic fraction of organic sulfur increased with the increasing carbon content and was inversely proportional to aliphatic sulfur, indicating that the relative abundance of thiophenic and thiol sulfur compounds were probably related to the coal rank. The nitrogen contents of the SHOS coals from southern China were much lower than expected. In an uncommon manner, inorganic oxidized nitrogen, instead of pyrrolic and pyridinic nitrogen, was the predominant nitrogen form in the SHOS coals with only bituminous rank. Some signs pointed to ammonium illite as the probable form of inorganic nitrogen, which may provide another piece of evidence for the new viewpoint of the volcanic and/or hydrothermal origin of SHOS coals. The presence of the amine N peak in coals requires further study, which is selectively lost during thermal maturation and should not appear in normal coal.

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