Using H2S plasma to modify activated carbon for elemental mercury removal

Non-thermal plasma was applied to modify activated carbons (ACs) in the presence of H2S for improving the elemental mercury (Hg-0) removal performance. The physical and chemical properties of raw and modified ACs were characterized by scanning electron microscopy with energy disperse X-ray spectroscopy, Brunauer-Emmett-Teller and X-ray photoelectron spectroscopy. The Hg-0 removal performance of modified AC was tested by a bench-scale fixed bed. The results indicated that H2S plasma treatment enhanced S content of raw AC. Moreover, S content and Hg-0 removal efficiency of modified AC increased with the increase of H2S concentration. The reason was that higher concentration H2S resulted in more S active sites on modified AC and S active site played a significant role during the Hg-0 removal process. Besides, non-thermal plasma treatment in the presence of H2S had a weak impact on BET surface area. By further analysis, it could be inferred that the improvement of Hg-0 removal performance was ascribed to the chemisorption rather than physisorption. Combined the results of temperature programmed desorption and XPS analysis, the mechanism of Hg-0 removal was that elemental S on the surface of modified AC reacted with Hg-0 to form HgS.