Study Of The Influence Of HCl,HBr And SO₂ On Hg⁰ Adsorption Over Iron Oxide

Coal combustion is the major source of artificial mercury emission, and many technologies have been proposed and tested to control mercury pollution in recent years. Among all the mercury reduction technologies, the post-combustion sorbent injection technologies are the most studied and considered to be promising.Fly ash is normally considered to be a potential sorbent to reduce mercury emission, it has also been proved that Fe2O3 in fly ash plays a dominating role in removing mercury. However, the reseaches about Fe2O3 are relatively deficient. Therefore, the influences of HCl, HBr as well as SO2 in the flue gas on the demercuration activity of ?-Fe2O3 sorbent were studied in this paper. Besides, relevant experiments were designed to corroborate the theoretical results derived from density functional theory(DFT) calculation. The theoretical result shows that the adsorption behaviors of HCl and HBr that performed on mercury on ?-Fe2O3(001) surface have similar functional mechanism, and both HCl and HBr produce violent chemical reactions and dissociation on the surface of iron oxide, which improves the adsorptive capacity of the adsorbent surface on Hg. The subsequent relevant experiment result shows that HCl certainly promote the adsorption of Hg0 on the surface of ?-Fe2O3. In the presence of both HCl and Hg0, mercury removal efficiency is about 50% and the pretreatment of HCl demonstrates that it can react with the surface of ?-Fe2O3 first and then promotes the adsorption of Hg0 significantly, which proves the accuracy of theoretical calculations. According to the DFT results, SO2 is inclined to produce dissociative adsorption on the surface of ?-Fe2O3(001) and then generates S active sites, which have strong adsorptive function on Hg0. Meanwhile, more O active sites generate which have weaker adsorptive function than that of S while compete with S active sites and restrain the generation of S. It turns out in relevant experiment that SO2 promotes the adsorption of Hg0 on the surface of ?-Fe2O3 and its removal efficiency is up to 40% and then declines to lower level. SO2 can also be adsorbed on the surface and possesses demercuration capacity, which shows that its promotion on Hg0 adsorption abides by Eley-Rideal mechanism.