Characterization of the Modes of Occurrence of Mercury and Their Thermal Stability in Coal Gangues

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.