Modes of occurrence and thermal stability of mercury in different samples from Guandi coal preparation plant

- The Hg in samples was studied by TPD-AFS technique coupled with acid leaching.
- The Hg is enriched in gangue and slime and decreased in cleaned coal and middlings.
- The Hg has close relation with ash-forming mineral in the samples.
- The distributions of modes of occurrence of Hg in all samples are different.
- The thermal stability of HCl-soluble and pyrite-bound Hg is similar in all samples.

The raw coal, cleaned coal, middlings, gangue and slime samples were collected from Guandi coal preparation plant, China. The modes of occurrence and thermal stability of mercury in the samples were characterized by the temperature programmed decomposition-atomic fluorescence spectroscopy (TPD-AFS) technique coupled with acid leaching. The results show that the Hg contents of cleaned coal and middlings are lower than that in raw coal while the Hg content of raw coal is less than that of gangue or slime. HCl-soluble Hg, organic-bound Hg, pyrite-bound Hg and silicate-bound Hg exist in all the samples. However, the distributions of modes of occurrence of Hg in all samples are different. The contents of HCl-soluble Hg and pyrite-bound Hg are in the order of gangue > slime > raw coal > middlings > cleaned coal. The silicate-bound Hg contents are the least and in the order of middlings > gangue > slime > raw coal > cleaned coal. The organic-bound Hg proportion has significant correlation with the organic material content of the samples. For HCl-soluble Hg and pyrite-bound Hg, the thermal stability is similar in all coal samples. The thermal stability of the silicate-bound Hg is highest among all the modes of occurrence of Hg and shows a certain dependency upon mineral in samples. The organic-bound Hg is complex and its thermal stability is different with different samples.

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