Hg occurrence in coal and its removal before coal utilization

Mercury emission control technology in the combustion flue gas of coal-fired power plants has been under intensive development, but none has been implemented commercially because of the high cost. Treatment of coal before combustion provides an alternative option for Hg emission control. In this study, samples of one anthracite, one lignite and three bituminous coals were investigated to determine the feasibility of pre-combustion Hg emission control. Density separation, temperature-programmed pyrolysis, HNO3 extraction and sequential selective extraction (SSE) were used to determine the occurrence and speciation of mercury in the different types of coal. The results showed that the characteristic temperature range for Hg release is <150 °C for Hg0, 150-250 °C for HgCl2/organic-bound Hg, 250-400 °C for HgS/silicate-bound Hg, and 400-600 °C for pyrite-bound Hg. HNO3 extraction and sink-float were found to be effective for the removal of pyrite-bound Hg and then the coal can be pyrolysed at 400 °C to remove other forms of Hg.