Recycle of waste activated coke as an efficient sorbent for Hg0 removal from coal-fired flue gas

Abstract

The desulfurized activated coke was recycled through thermal regeneration to recover Hg0 from coal-fired flue gas. And the thermal treated activated coke was also prepared for comparison. BET, acid-base titration, XPS and O2-TPD characterizations were performed to identify the structural and chemical properties. Although possessing decreased BET surface area and enlarged pore diameter after thermal treatment, AC-400 exhibited the enhanced Hg0 removal performance due to the generation of oxygen functional groups, while the treatment at 900 °C resulted in the decomposition of surface active oxygen species. Besides, not only the strengthened promotion on the formation of carbonyl and ester groups, but also the deposition of SO42− during regeneration should be responsible for the superior activity of regenerated desulfurized activated coke (RAC) for Hg0 removal. Besides, O2 addition could weaken the competition between NO/SO2 and Hg0, and facilitate the formation of Hg(NO3)2/HgSO4. In combination with Hg-TPD, the specific surface area was in closely correlation with the physisorption of Hg0 on activated coke, and the chemisorption, as the predominant mechanism, of Hg0 mainly depended on the surface active oxygen species. Moreover, when reacted at 60 °C, the Hg0 adsorption priority on RAC was as follows: ester ≥ carbonyl ≥ SO42− ≥ physisorption, and the carbonyl was the leading active sites for mercury adsorption.