Role of SO3 in Elemental Mercury Removal by Magnetic Biochar

Magnetic biochar (MBC) has been proven to be an efficient sorbent for elemental mercury (Hg-0) removal from coal-fired flue gas in our previous studies. However, SO3 is an acidic component of flue gas, and its role in Hg-0 removal by MBC has not been determined. In this work, the Hg-0 removal behaviors and the mechanisms involved were investigated in the presence of SO3. The results showed that SO3 notably impeded the Hg-0 adsorption process, whereas the oxidation efficiency of Hg-0 increased as the SO3 concentration increased. The inhibitory effect of SO3 on Hg-0 adsorption was attributed to competitive adsorption between SO3 and Hg-0 as well as the formation of metal sulfates on the MBC surface. Moreover, the addition of SO3 into the atmosphere resulted in the generation of HgSO4, especially when H2O was also present. Additionally, the deposition of HgSO4 and H2SO4 further hindered the removal of Hg-0 by MBC. Nevertheless, SO3 promoted the formation of C=O groups, resulting in the higher Hg-0 oxidation efficiency observed. In addition, more mercury that was adsorbed on the MBC was transformed into HgO in the presence of SO3. This work illustrated the effect of SO3 on Hg-0 removal by MBC and explained the mechanism involved, which will help with the further development of an efficient sorbent for Hg-0 removal.