Mercury species and potential leaching in sludge from coal-fired power plants

[Display omitted] •Hg species partitioning in WFGD sludge was studied by TPD and the improved BCR method.•Residual Hg was related to HgS and the content of this fraction was 2–3 %.•HgCl2, HgO and HgSO4 were assigned to the water/acid-soluble fractions.•Hg leaching increased with increasing concentration and decreasing particulate size. Wet flue gas desulfurization (WFGD) sludge, generated from the WFGD effluent treatment process, is suitable for multiple uses in various industries. However, risk assessments of its utilization are limited. Systematic study of Hg species occurrences, partitioning and risks of leaching is required, and these concerns were addressed in the present study. Hg temperature-programmed decomposition (Hg-TPD) and an improved European Community Bureau of Reference (BCR) method indicated residual Hg in WFGD sludge was related to HgS, and the content of this fraction was from 2 to 3%. HgCl2, HgO and HgSO4 were assigned to the water/acid-soluble fractions, and reducible Hg was related to Fe species in the sludge. Leachate evaluation of the WFGD sludge indicated potentially high Hg leaching risk. WFGD sludge with higher Hg concentrations and smaller particulate diameters exhibited greater leaching potential. Leaching of Hg from WFGD sludge in China into the environment was estimated at 7.46 t/yr.