Transformations of pyrite in different associations during pyrolysis of coal

The samples of pure pyrite, the mixtures of FeS2 or FeS loaded on a low-ash coal char, and an acid-washed coal with high content of pyrite were used to investigate the transformations of pyrite with different physical associations during pyrolysis. The presence of low-ash coal char, although affected the evolution of sulfur-containing gases in vapor phase, had little influence on thermal decomposition of pyrite at 450–650°C. Pyrite conversion above 920°C, especially transformation of the formed FeS into elemental iron, was facilitated primarily by the char matrix entity. During pyrolysis of coal, isolated agglomerates of single pyrite crystals were transformed into individual aggregates in the gaps of coke grains, while most of pyrite embedded in the coal particles or located at the edge of coal particles decomposed to the Fe–S phases which remain inside or closely in contact with the carbon matrix. Meanwhile low-sulfur Fe–S phases in the pyrolysis products of coal were mainly represented as FeSy (0