Comparative study of element mercury removal by three bio-chars from various solid wastes

摘要

Three kinds of bio-chars derived from various solid wastes, such as municipal solid wastes, agricultural wastes and medicinal residues, were modified by physical and/or chemical modification. The Hg~0 adsorption capacities of the modification bio-chars in flue gas were comparatively studied. Physical modification increased the surface areas of the bio-chars, which was favorable in the physisorption of Hg°. Chemical modification resulted in the chemisorption of Hg~0. Both physisorption and chemisorptions played a role in Hg~0 capture, whereas chemisorption was more important The X-ray photoelectron spec-troscopy (XPS) analysis results suggested that chemisorption of Hg~0 was due to the C-Cl groups generating on the surfaces of bio-chars during NH_4Cl impregnation, which could transform Hg~0 into HgCl_2 or other Hg-Cl complexes. The bio-chars modified by combined physical and chemical modification all had an excellent performance for Hg~0 removal, especially for C6WN5 exhibiting higher Hg~0 adsorption than modified activated carbons or modified activated carbon fibers. It indicated that the sequence for Hg~0 removal capacity decreased as: C6WN5 (from agricultural wastes, 11,400 μg/g)＞MW6N5 (from medicinal residues, 840 μg/g) ＞ W6WN5 (from municipal solid wastes, 160 μg/g).