Role of acid gases in Hg-0 removal from flue gas over a novel cobalt-containing biochar prepared from harvested cobalt-enriched phytoremediation plant

摘要

A novel biochar containing highly-dispersed cobalt oxides was prepared by one-step pyrolysis using Co-enriched Siberian Iris as the raw material, and it was used for elemental mercury removal from flue gas. The presence of NO or HCl could approximately keep Hg-0 removal efficiency over 85%, while the presence of SO2 suppressed Hg-0 removal. The role of aforementioned acid gases in Hg-0 removal over such biochar was systematically studied. The surface active oxygen species derived from the reversible conversion between Co3+ and Co2+ could activate the adsorbed NO (HCl) to produce active nitrogenous (chlorine) species, which functioned as active site for Hg-0 oxidation removal. The reaction between NO (HCl) and Hg-0 occurred mainly through the Eley-Rideal mechanism. SO2 consumed active oxygen and reacted with active Co3+ to generate Co2+ bonded with SO42-, resulting in irreversible damage on the biochar. The formation of active nitrogenous (chlorine) species as well as its reaction with Hg-0 would be hampered by the generation of sulfate. This study can give some basic insights into the application of such heavy metal enriched phytoremediation plants for elemental mercury removal from flue gas.