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

Abstract

Chlorinated biochars (Cl/biochars) prepared by co-pyrolysis of biomass and polyvinyl chloride (PVC) waste were demonstrated as cost-effective sorbents for elemental mercury (Hg0) removal in our previous study. But the decrease in specific surface area of Cl/biochars caused by PVC melting inhibits the further increase of Hg0 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 CO groups were obtained under Fe catalysis. The Fe-Cl/biochars showed far better Hg0 removal performance compared to the Cl/biochars overa broad reaction temperature range (25–220 °C). O2, HCl and NO promoted Hg0 removal whereas SO2 had little effect on Hg0 removal H2O slightly suppressed Hg0 removal. Compared to the commercial activated carbon manufactured specifically for Hg0 removal, Fe-Cl/biochars was superior in both Hg0 adsorption capacity and adsorption rate at 140 °C. The mechanism of Hg0 removal over Fe-Cl/biochars was chemisorption reaction, where Fe3O4, CCl and CO provided active sites for Hg0 removal.