Single and Dual Adsorption of Vapor-Phase Hg0 and/or HgCl2 by Innovative Composite Activated Carbons Impregnated with both S0 and Na2S

Abstract

This study investigated the single and dual adsorption of vapor-phase Hg 0 and/or HgCl 2 using an innovative composite sulfurized activated carbon prepared by combining two sulfur impregnation methods. Thermogravimetric analysis (TGA) technology was applied to determine the saturated adsorptive capacity of INTRODUTIONThe environmental issues derived from the discharge of toxic heavy metals from stationary sources have attracted much attention worldwide, especially the Hg discharge. Mercury (Hg) compounds are highly toxic pollutants, and of great concern with regard to the global environment. Human health hazards from these pollutants are associated with their persistence in the environment and their potential bioaccumulation in the food chain (Fang et al., 2010;Jen et al., 2012). If Hg is not treated properly, it would cause serious impacts on human health and living environment * Corresponding author.Tel.: 886-7-5252000 ext. 4409; Fax: 886-7-5254449 E-mail address: ycsngi@mail.nsysu.edu.tw due to its high toxicity and long life time. In comparison to other toxic heavy metals, the melting point of elemental mercury (Hg 0 ) is -39°C, and the boiling point is 357°C. It has very high saturated vapor pressure (0.246 Pa at 25°C). It can be volatilized at 150°C, and has very low water solubility (20 µg/L). These physicochemical characteristics make Hg exist in gaseous state in combustion stack gas and it cannot be caught by traditional air pollution control devices effectively. Levin et al. (2000) indicated that Hg 0 has high volatibility and low water solubility, which make its residence time in the atmosphere is approximately 1-2 years, while the residence time of HgCl 2 in the atmosphere is only several days, due to its relatively high water solubility (69 µg/L) and low saturated vapor pressure (0.13 kpa at 136°C). Comparatively, Hg 0 is capable of being transported globally, whereas Hg 2+ tends to settle down by dry and wet deposition in the region nearby its emission sources.Previous studies reported that the dominant species in

Impact of Sulfur Loading on Brominated Biomass Ash on Mercury Capture

“…To synthesize more effective sorbents, several studies on understanding the mercury removal mechanism by various AC sorbents have been performed. − These studies showed that several factors influence the adsorption of Hg 0 onto AC, including contact time, flue gas temperature and composition, unburned carbon content in the fly ash, and carbon type (which influences amount of mercury active sites) . For sulfur impregnated sorbents, previous studies indicated that mercury uptake is influenced by sulfur content − and speciation, ,− impregnation temperature, , and sorbent specific surface area − ,, and pore characteristics. ,, Most mechanistic studies showed that Hg is present on the surface of the AC in its oxidized form. − ,,, Mechanisms of mercury removal by chemically impregnated sorbents have therefore been generally proposed to include some form of oxidation of the Hg 0 , followed by binding to available surface species on the AC. − However, Huggins et al also suggested that a different Hg 0 capture mechanism could be present for each type of AC sorbent.…”

“…Many previous studies investigated the effect of sulfur addition to activated carbon on mercury capture. The main methods of sulfur addition include adsorption of H 2 S, ,− vapor impregnation by heating the carbon sorbent with elemental sulfur (S 0 ), ,,,,,− or liquid impregnation using other sulfur species with subsequent thermal treatment to remove the moisture. ,,, In addition, experiments involving the injection of sulfur chlorides (SCl 2 and S 2 Cl 2 ) and sulfur monobromide (S 2 Br 2 ) into flue gases for Hg 0 removal have also been investigated. Speciation of sulfur on S-impregnated sorbents has been found to be a key parameter for mercury removal, ,, with sulfide and elemental sulfur being effective species. , For this reason, the physical impregnation of S 0 onto the biomass ash was chosen for this study at the known maximum sulfur loading temperature of 600 °C .…”

“…1−17 These studies showed that several factors influence the adsorption of Hg 0 onto AC, including contact time, flue gas temperature and composition, 18 unburned carbon content in the fly ash, 19 and carbon type (which influences amount of mercury active sites). 19 For sulfur impregnated sorbents, previous studies indicated that mercury uptake is influenced by sulfur content 20−23 and speciation, 22,24−26 impregnation temperature, 21,22 and sorbent specific surface area [23][24][25]27,28 and pore characteristics. 20,24,25 Most mechanistic studies showed that Hg is present on the surface of the AC in its oxidized form.…”

“…The main methods of sulfur addition include adsorption of H 2 S, 20,41−45 vapor impregnation by heating the carbon sorbent with elemental sulfur (S 0 ), 21,22,27,43,44,46−51 or liquid impregnation using other sulfur species with subsequent thermal treatment to remove the moisture. 23,25,27,28 In addition, experiments involving the injection of sulfur chlorides (SCl 2 and S 2 Cl 2 ) 52 and sulfur monobromide (S 2 Br 2 ) 53 into flue gases for Hg 0 removal have also been investigated. Speciation of sulfur on Simpregnated sorbents has been found to be a key parameter for mercury removal, 26,44,46 with sulfide and elemental sulfur being effective species.…”