The utilization of coal gangue in a power plant has attracted wide interest in China; however, coal gangue represents a new anthropogenic source of mercury pollution due to its high mercury content. Understanding the modes of occurrence of mercury in coal gangue is crucial for developing the mercury control technology used during coal gangue combustion. In this study, the mercury in four typical coal gangues in China was characterized by a sequential extraction procedure (SEP) coupled with a temperature-programmed decomposition (TPD) method. The method is proved to be an effective approach in studying the modes of occurrence of mercury as well as the thermal stability of coal gangues by distinguishing the characteristic release temperature during the thermal decomposition process. The iron–manganese oxide-bound Hg releases at a temperature range of 200–600 °C, while the carbonate-bound Hg releases at a temperature range of 250–300 °C. The organic-bound Hg, sulfide-bound Hg, and silicate-bound Hg release at temperature ranges of 200–400, 400–600, and above 1200 °C, respectively. Furthermore, the sulfide-bound Hg is found to be the dominant form of mercury in the four coal gangue samples.
The utilization of coal gangue in power plants has become a new anthropogenic discharge source of mercury and attracted much concern in China. It is crucial to obtain the information about the mercury release during thermal treatment of coal gangue. In this study, the mercury release behavior of two coal gangues selected from two power plants were studied under different thermal treatment conditions of heating rate, residence time, and atmosphere. The results of mercury release profile show that the specified release temperature ranges for the different modes of occurrence of Hg are scarcely affected by the heating rate of 10, 20, and 40 °C/min. A higher heating rate could promote the Hg release to some extent. The mercury release ratio gradually increases with the extension of residence time for both coal gangues. The oxidizing environment has a positive effect on mercury release < 600 °C and has a minor effect > 600 °C. Mercury in coal gangue is more volatile than coal gangue matrix and the mercury in GD coal gangue is more easily released out than that in ED coal gangue.
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