Release behavior of mercury during mild pyrolysis of coals and nitric acid-treated coals

Seven powdery coals (four SS coals and three Argonne premium coals) were subjected to pyrolysis at 300 °C under a flow of nitrogen, and the release of Hg from coal was examined. The % release of Hg greatly varied from 24 to 83% depending upon the type of coals. In order to remove pyrite from coal, powdery coal was treated with 0.5 M HNO3 at 80 °C. The HNO3-treated coals were also subjected to the 300 °C-pyrolysis, and the release of Hg was evaluated. Even for coals, which gave low %Hg release when the raw coal was pyrolyzed, nearly complete release of Hg was attained when the treated coal was pyrolyzed. The release behavior of Hg was discussed on the basis of the mode of occurrence of Hg in coal.