Influences of Copper(II) Chloride Impregnation on Activated Carbon for Low-Concentration Elemental Mercury Adsorption from Simulated Coal Combustion Flue Gas

In this study, the Hg^0 adsorption equilibrium and kinetics of a coconut-shell-based activated carbon impregnated with CuCl_2 were examined with respect to their resulting physical and chemical properties. Integrating the results from N_2 adsorption isotherm at 77 K, scanning electron microscopy, elemental analysis, X-ray photoelectron spectroscopy, and Hg^0 adsorption experiments under N_2 and simulated coal-combustion flue gases conditions, it was found that HCl pretreatment could enhance Hg^0 adsorption of crude activated carbon; the Hg^0 adsorption capacities of crude and HCl-pretreated activated carbon under N_2 condition were 95.8 and 225.4 μg g^(-1), respectively. Additionally, CuCl_2 impregnation further increased the adsorption capacity of crude. The Hg^0 adsorption capacity of crude activated carbon with 8% CuCl_2 impregnation was 631.1 μg g^(-1). However, the equilibrium Hg^0 adsorption capacity decreased when Cu loading exceeded 8 wt%, suggesting that adequate forms of surface Cu, O and Cl interacting with flue gas components and Hg^0, as well as the presence of pores with specific size ranges allowing rapid transport of the Hg molecules into the interior of the activated carbon and as energy sinker govern the overall chemisorption process. Pseudo-second-order kinetic model could best describe the adsorption behaviors of tested samples under both test conditions, indicating that Hg^0 adsorbed on the activated carbon surface could be explained by bimolecular reaction mechanisms.