Abstract
In this study, the Hg0 adsorption equilibrium and kinetics of a coconut-shell-based activated carbon impregnated with CuCl2 were examined with respect to their resulting physical and chemical properties. Integrating the results from N2 adsorption isotherm at 77 K, scanning electron microscopy, elemental analysis, X-ray photoelectron spectroscopy, and Hg0 adsorption experiments under N2 and simulated coal-combustion flue gases conditions, it was found that HCl pretreatment could enhance Hg0 adsorption of crude activated carbon; the Hg0 adsorption capacities of crude and HCl-pretreated activated carbon under N2 condition were 95.8 and 225.4 µg g–1, respectively. Additionally, CuCl2 impregnation further increased the adsorption capacity of crude. The Hg0 adsorption capacity of crude activated carbon with 8% CuCl2 impregnation was 631.1 µg g–1. However, the equilibrium Hg0 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 Hg0, 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 Hg0 adsorbed on the activated carbon surface could be explained by bimolecular reaction mechanisms.
Highlights
Mercury (Hg) and its compounds emitted from anthropogenic sources, e.g., coal-fired power plants, industrial boilers, waste incinerators, sinters, and cement plants, have tempted substantial attention due to their high toxicity, bioaccumulability, and global transport behaviors in atmosphere (Kumari et al, 2015; Chen et al, 2016; Marusczak et al, 2016; Wang et al, 2016)
Detailed descriptions pertaining to experimental apparatus and procedures for Hg0 adsorption tests have been described elsewhere (Hsi et al, 2011, 2012, 2013; Chiu et al, 2014; Hsi et al, 2014); we present them here again for clarity
Pronounced difference in the Smicro, SBET, and Smicro/SBET between crude CAC and HCAC samples was not observed, indicating that the surface area and pore structure of activated carbon are less affected by acid treatment, or in other words, by the introduction of additional oxygenated groups
Summary
Mercury (Hg) and its compounds emitted from anthropogenic sources, e.g., coal-fired power plants, industrial boilers, waste incinerators, sinters, and cement plants, have tempted substantial attention due to their high toxicity, bioaccumulability, and global transport behaviors in atmosphere (Kumari et al, 2015; Chen et al, 2016; Marusczak et al, 2016; Wang et al, 2016). Coal-fired power plants were reported as the largest single source in most countries in Hg emissions (Pacyna et al, 2010). Hg is present in the coal-combustion flue gases in three major forms, namely, particle-bound (Hgp), oxidized (Hg2+), and elemental (Hg0) forms (Hsi et al, 2010; Wilcox et al, 2012). Hgp and Hg2+ can be readily captured by traditional air Numerous studies pertaining to develop effective technologies on low-concentration Hg0 control have been conducted (Li et al, 2015). Especially activated carbons as adsorbents, have been shown as profitable Hg0 emission control approaches (Lin et al, 2015). The adsorptive environment, namely, flue gas condition, plays a key role influencing the Hg0 adsorption effectiveness of activated carbon.
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