AP-TPR investigation of the effect of pyrite removal on the sulfur characterization of different rank coals

The effect of pyrite removal on the determination of organic sulfur functionalities of different rank coals by atmospheric pressure-temperature-programmed reduction (AP-TPR) method was studied. The nitric acid treatment and sink–float separation were performed to reduce the content of pyritic sulfur in the samples. Microscopic examination of raw coals was performed to determine the mode of pyrite occurrence and to estimate the possibility of its removal using high-density liquids, i.e. ZnCl2 and CHBr3/CCl4 mixture. The AP-TPR investigation showed a different impact of nitric acid treatment and sink–float separation on the distribution of organic sulfur functionalities in coal. The evolution of sulfur dioxide observed by AP-TPR-mass spectrometry (MS) confirmed the formation of oxidized sulfur compounds during nitric acid treatment. Organic sulfonic groups are nearly totally decomposed to SO2 without reduction of the latter to H2S under AP-TPR conditions. Some sulfur species remained in the TPR residue which was proven by AP-TPO-MS analysis through SO2 monitoring.