Oxidative absorption of elemental mercury in combustion flue gas using biochar-activated peroxydisulfate system

In the article, rice straw biochar was applied to activate peroxydisulfate to induce center dot OH and SO4 center dot to oxidize Hg-0 in flue gas. The oxidative absorption mechanism of gaseous Hg0 in this designed system was explored. The main technological variables affecting Hg0 oxidative absorption, and the yields of products and free radicals were also studied. Research indicates that Hg-0 is mainly removed by SO4 center dot oxidation and center dot OH oxidation. SO4 center dot is the first important free radical for oxidizing Hg-0, and center dot OH is the second important free radical for oxidizing Hg-0. Hg-0 is mainly oxidized to bivalent mercury (Hg2+) in spent solution by the developed absorption system. Peroxydisulfate direct oxidation and biochar catalytic oxidation are also two other Hg-0 removal paths, but they only play minor supplementary roles in the Hg-0 removal. Hg-0 removal efficiency is improved first and then decreased by increasing peroxydisulfate concentrations or rice straw biochar concentrations. Increasing reaction temperature improves the Hg-0 removal. Hg-0 removal efficiency reduces with higher pH values and Hg-0 concentrations. The maximum removal efficiency of Hg-0 is up to 96.9% based on the best tested conditions.