Removal of elementary mercury by solid sorbents at different temperatures: Variation of the desorption activation energy through thermal desorption analysis

Abstract The interaction of gaseous elemental mercury with the sorbent surface is generally related to the adsorption temperature. Our adsorption–desorption experiments at various temperatures have proved that the adsorption temperature has a direct impact on the location of the desorption peak. By studying the desorption activation energy (Ed) of Hg0 on coal-based activated carbon (AC), SiO2 powder, and montmorillonite (MMT) at different adsorption temperature ( T ads ), it was found that Ed evolved with T ads via two steps for MMT: first increasing from 70 kJ/mol to 100 kJ/mol as T ads exceeded 150 °C, and then to over 150 kJ/mol when T ads is above 300 °C. The first increase in Ed indicated the transition from physisorption to chemisorption for mercury removal, consistent with enhanced the time-averaged removal rate of mercury ( η ) with T ads (≤300 °C) over MMT. The second increase suggested possible oxidation of mercury, of which the exothermal nature explained the decreasing ƞ when Tads＞300 °C, By contrast, Ed for AC and SiO2 remained approximately constant and ƞ monotonically decayed with T ads , both suggesting physisorption for the main removal mechanism. By examining the variation of Ed and ƞ with T ads , this work demonstrated a useful approach to clarify the temperature effect on mercury adsorption mechanism on various types of solid sorbents. Such knowledge is important to optimize the operating temperature for the removal of elementary mercury.