Display omitted •Both physisorption and chemisorption of Hg0 occurred on the surface of M6WN5.•Chemisorption process was an absolute predominant route for Hg0 removal by M6WN5.•The effect of NO, H2O, SO2 and O2 on Hg0 removal by M6WN5 was investigated.•M6WN5 demonstrated to be a promising Hg0 sorbent in flue gas. Pyrolyzed biochars from an industrial medicinal residue waste were modified by microwave activation and NH4Cl impregnation. Mercury adsorption of different modified biochars was investigated in a quartz fixed-bed reactor. The results indicated that both physisorption and chemisorption of Hg0 occurred on the surface of M6WN5 which was modified both microwave and 5wt.% NH4Cl loading, and exothermic chemisorption process was a dominant route for Hg0 removal. Microwave activation improved pore properties and NH4Cl impregnation introduced good active sites for biochars. The presence of NO and O2 increased Hg0 adsorption whereas H2O inhibited Hg0 adsorption greatly. A converse effect of SO2 was observed on Hg0 removal, namely, low concentration of SO2 promoted Hg0 removal obviously whereas high concentration of SO2 suppressed Hg0 removal. The Hg0 removal by M6WN5 was mainly due to the reaction of the CCl with Hg0 to form HgCl2, and the active state of CCl* groups might be an intermediate group in this process. Thermodynamic analysis showed that mercury adsorption by the biochars was exothermic process and apparent adsorption energy was 43.3kJ/mol in the range of chemisorption. In spite of low specific surface area, M6WN5 proved to be a promising Hg0 sorbent in flue gas when compared with other sorbents.