Enhanced elemental mercury removal in coal-fired flue gas by modified algal waste-derived biochar: Performance and mechanism

Abstract

A novel biochar involving pyrolysis of dewatered algal waste combined with KOH and residual FeCl3 co-activation was synthesized as an efficient sorbent specifically for Hg0 removal from coal-fired flue gas. It was found that the SBET of biochar co-activated by KOH and FeCl3 (BCFK) was 195.82 m2 g−1, much higher than that of single FeCl3 activated biochar (BCF) of 133.38 m2 g−1 and un-activated biochar (UBC) of 20.36 m2 g−1. Furthermore, BCFK exhibited higher magnetization characteristics as well as elemental Fe and Cl contents of 2.71% and 10.33%, respectively, based on the combined characterization of XPS and VSM, etc., which is a jump of about 10-fold compared to BCF. This allows BCFK to show the best Hg0 removal capability of 689.66 μg g−1 under the inlet Hg0 concentration of 100 μg m−3 and 150 °C, according to pseudo-second-order kinetic model. Further analysis by XPS and Hg-TPD (Temperature Programmed Desorption) revealed that oxidation by Cl∗ radicals and C–Cl as well as weak chemisorption contributed to the removal of Hg0. Eventually, this efficient, simply prepared, low-cost and easily separable biochar distinguished itself in comparison to other materials. This will undoubtedly promote the valorization of algae and provide a reliable alternative material for the treatment of coal-fired flue gas.