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 Hg-0 occurred on the surface of M6WN5 which was modified both microwave and 5 wt.% NH4Cl loading, and exothermic chemisorption process was a dominant route for Hg-0 removal. Microwave activation improved pore properties and NH4CI impregnation introduced good active sites for biochars. The presence of NO and 02 increased Hg adsorption whereas H2PO inhibited Hg-0 adsorption greatly. A converse effect of SO2 was observed on Hg removal, namely, low concentration of SO2 promoted Hg-0 removal obviously whereas high concentration of SO2 suppressed Hg-0 removal. The Hg-0 removal by M6WN5 was mainly due to the reaction of the C-Cl with Hg to form HgCl2, and the active state of C-Cl-* 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 43.3 Isl/mol in the range of chemisorption. In spite of low specific surface area, M6WN5 proved to be a promising Hg-0 sorbent in flue gas when compared with other sorbents. (C) 2015 Published by Elsevier B.V.