Removal of Mercury from Fine Coal Based on Combined Coal Processing Approaches
2017
Liu, Cheng | Zhou, Changchun | Cong, Longfei | Zhang, Ningning | Pan, Jinhe | Tang, Mengcheng | Cao, Shanshan
Hg is one of the most harmful trace elements in coal. Removal of Hg from fine coal by combined coal processing approaches was investigated in this paper. Two flotation feed coal samples collected from Fangezhuang (FGZ) and TaiXi (TX) coal preparation plants in China were used as the research objects. FGZ coal was identified as high-sulfur coal, while TX coal was ultralow-sulfur coal. Sequential chemical extraction was used to determine the modes of occurrence of Hg in coal samples. Two combined coal processing methods, namely, the flotation–gravity separation process and the flotation–chemical leaching process, respectively, were used to obtain a reduction of the Hg content in clean coal. The results indicate that the dominant mode of occurrence of Hg in FGZ coal is the sulfide-bound form, while that in TX coal is the unleachable form. Dosages of collector and frother influence the removal of Hg in the flotation process, and the addition of calcium oxide as a depressant contributes to the Hg removal. However, simply using conventional flotation has a limitation in reducing the Hg content in clean coal. The flotation–gravity separation process has good applicability in the treatment of FGZ coal, in which Hg is mainly associated with inorganic minerals and distributed unevenly in different density fractions, and clean coal with a Hg content of 48.98 μg/kg can be produced when the gravity separation density is 1.4 kg/m³. The flotation–chemical leaching process is effective in reducing the Hg content in both FGZ coal and TX coal. Through the latter advanced coal processing approach, relative removal rates of Hg of FGZ coal and TX coal can reach up to 61 and 66%, respectively, and clean coals with a Hg content of 59.87 and 93 μg/kg, respectively, can be obtained.
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