Elemental mercury removal using biochar pyrolyzed from municipal solid waste

• A biochar pyrolyzed from municipal solid waste was used to remove Hg0 from the coal combustion flue gas.
• The biochar by physical and chemical activation (NH4Cl) exhibited excellent performance for Hg0 removal.
• The C–Cl group was proved to be a crucial factor in the process of mercury oxidation and capture.
• The CO group and O2 possibly accepted the electron from Hg0 during the capture process.

The paper investigated the Hg0 capture using a low-cost biochar pyrolyzed from municipal solid waste. The results indicated that C6WN5 (represents the biochar prepared by both microwave and 5 wt.% NH4Cl loading) was a cost-effective Hg0-capture sorbent when compared with other sorbents. Proximate and ultimate analyses, Brunauer–Emmett–Teller (BET) analysis, and inductively coupled plasma mass spectrometry (ICP-MS) were used to characterize the sorbents (C400 and C600), and X-ray photoelectron spectroscopy (XPS) was applied to investigating elemental states of C6WN5. The results indicated that the biochar pyrolyzed at 600 °C showed better performance for Hg0 removal than that pyrolyzed at 400 °C. Both microwave activation and NH4Cl modification enhanced the Hg0-removal capacity of the sorbents, whereas chemisorption of Hg0 was the main reaction. It was proven by XPS analysis that most of the combined Cl in the C–Cl groups on the surface of C6WN5 was converted into ionic Cl in the Hg0-adsorption process, which illustrated that the main mechanism of Hg0 removal was the oxidation of Hg0 to HgCl2 by the C–Cl groups. CO groups and possibly O2 served as electron acceptors facilitating electron transfer for Hg0 oxidation during this process.

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