Hierarchically porous biochar synthesized with CaCO3 template for efficient Hg0 adsorption from flue gas

A hierarchical porous carbon sorbent was fabricated by pyrolysis of rice straw in the presence of nanoscale CaCO3 for effectively removal of Hg-0 from flue gas. The hierarchical structure of the sorbent was generated by CaCO3 and shaped by using staged pyrolysis temperatures. Large numbers of oxygen-containing functional groups were generated with the hierarchical pore formation. Because of their hierarchical porous structures and large numbers of ligands, the efficiency of Hg-0 removal by the hierarchical sorbent was higher than that of conventional biochar by 40% to 65% at temperature range from 80 to 180 degrees C. Mechanistic studies showed that Hg-0 was adsorbed on the surfaces of the hierarchical pores with different binding energies, and the ratio of mesopores could be a more critical factor in the Hg-0 adsorption capacity of adsorbents with hierarchical porous structures. Meanwhile, the Hg-0 removal with the hierarchical sorbent showed better resistance toward flue gas components (SO2 and H2O) than that with traditional biochar probably because of better transfer of the complex components in the sorbent. The high-performance and cost-effective carbon adsorbent described in this paper has great promise for Hg-0 removal from flue gas.