Efficient removal of elemental mercury by magnetic chlorinated biochars derived from co-pyrolysis of Fe(NO3)3-laden wood and polyvinyl chloride waste

Chlorinated biochars (Cl/biochars) prepared by co-pyrolysis of biomass and polyvinyl chloride (PVC) waste were demonstrated as cost-effective sorbents for elemental mercury (Hg-0) removal in our previous study. But the decrease in specific surface area of Cl/biochars caused by PVC melting inhibits the further increase of Hg-0 removal performance. Moreover, the difficulty in separating the used Cl/biochars from fly ash restricts the utilization of fly ash as a cement additive. To solve these problems, magnetic chlorinated biochars (Fe-Cl/biochars) are synthesized through one-step pyrolysis of Fe(NO3)(3)-laden wood/PVC mixtures in this study. The sample characterization showed that magnetic Fe3O4 was introduced into the Fe-Cl/biochars. Besides the magnetism, both increased specific surface area and more C=O groups were obtained under Fe catalysis. The FeCl/biochars showed far better Hg-0 removal performance compared to the Cl/biochars over a broad reaction temperature range (25-220 degrees C). O-2, HCl and NO promoted Hg-0 removal whereas SO2 had little effect on Hg-0 removal H2O slightly suppressed Hg-0 removal. Compared to the commercial activated carbon manufactured specifically for Hg-0 removal, Fe-Cl/biochars was superior in both Hg-0 adsorption capacity and adsorption rate at 140 degrees C. The mechanism of Hg-0 removal over Fe-Cl/biochars was chemisorption reaction, where Fe3O4, C-Cl and C=O provided active sites for Hg-0 removal.