Abstract:To inquire the impacts of acid gases (such as SO2, NO, and HCl), water vapor and mechanism on gas-phase elemental mercury removal by acid-iodine modified chitosan-bentonite adsorbents, the adsorption tests were conducted in a laboratory-scale fixed-bed reactor. The results showed that the presence of SO2 inhibited mercury capture due to the competition adsorption of SO2 and Hg0 on the active site of the adsorbent surface. An obvious promotion was observed when the concentration of NO added to 1000μg/m3and H2O was added. However, the addition of HCl had no favor to improve the efficiency of mercury removal due to higher energy barrier of the HCl and Hg0 reaction. Compared with single flue gas constituent, the long-term mercury capture efficiency was greatly enhanced because of the cooperative effects of SO2, NO, HCl and H2O. The mechanism for mercury removal by modified adsorbent was that in the acidic medium, the amine group of chitosan was protonated with a positive charge. KI reacted with H2SO4 and produced the I2. Then the produced I2 could be strongly adsorbed by protonated chitosan. Thus, Hg0 reacted with the active I2 of the adsorbent. The quantum chemical calculations indicated that chitosan exhibited strong adsorptive ability for elemental iodine under acidic conditions, and the modified adsorbents showed excellent mercury adsorption performance and its adsorption energy for Hg0 was approximately 127kJ/mol.