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

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 (E-d) of Hg-0 on coal-based activated carbon (AC), SiO2 powder, and montmorillonite (MMT) at different adsorption temperature (T-ads), it was found that E-d evolved with T-ads via two steps for MMT: first increasing from 70 kJ/mol to 100 kJ/mol as T-ads exceeded 150 degrees C, and then to over 150 kJ/mol when T-ads is above 300 degrees C. The first increase in E-d indicated the transition from physisorption to chemisorption for mercury removal, consistent with enhanced the time-averaged removal rate of mercury (eta) with T-ads (<= 300 degrees C) over MMT. The second increase suggested possible oxidation of mercury, of which the exothermal nature explained the decreasing eta when T-ads>300 degrees C, By contrast, E-d for AC and SiO2 remained approximately constant and eta monotonically decayed with Tads, both suggesting physisorption for the main removal mechanism. By examining the variation of E-d and eta 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.

Automated summary

The interaction of gaseous elemental mercury with solid sorbents is influenced by the adsorption temperature, which affects the desorption peak location. Desorption activation energy (E-d) on different sorbents evolves with adsorption temperature, indicating a transition from physisorption to chemisorption for mercury removal on montmorillonite (MMT). The study provides insights into the temperature effect on mercury adsorption mechanisms on different solid sorbents, which is important for optimizing operating temperatures for elemental mercury removal.