Enhanced mercuric chloride adsorption onto sulfur-modified activated carbons derived from waste tires

A number of activated carbons derived from waste tires were further impregnated by gaseous elemental sulfur at temperatures of 400 and 650 °C, with a carbon and sulfur mass ratio of 1:3. The capabilities of sulfur diffusing into the micropores of the activated carbons were significantly different between 400 and 650 °C, resulting in obvious dissimilarities in the sulfur content of the activated carbons. The sulfur-impregnated activated carbons were examined for the adsorptive capacity of gas-phase mercuric chloride (HgCl₂) by thermogravimetric analysis (TGA). The analytical precision of TGAwas up to 10^-6 g at the inlet HgCl₂ concentrations of 100, 300, and 500 mg/m3, for an adsorption time of 3 hr and an adsorption temperature of 150 °C, simulating the flue gas emitted from municipal solid waste (MSW) incinerators. Experimental results showed that sulfur modification can slightly reduce the specific surface area of activated carbons. High-surface-area activated carbons after sulfur modification had abundant mesopores and micropores, whereas low-surface-area activated carbons had abundant macropores and mesopores. Sulfur molecules were evenly distributed on the surface of the inner pores after sulfur modification, and the sulfur content of the activated carbons increased from 2-2.5% to 5-11%. After sulfur modification, the adsorptive capacity of HgCl₂ for high-surface-area sulfurized activated carbons reached 1.557 mg/g (22 times higher than the virgin activated carbons). The injection of activated carbons was followed by fabric filtration, which is commonly used to remove HgCl₂ from MSW incinerators. The residence time of activated carbons collected in the fabric filter is commonly about 1 hr, but the time required to achieve equilibrium is less than 10 min. Consequently, it is worthwhile to compare the adsorption rates of HgCl₂ in the time intervals of <10 and 10-60 min. Implications: Waste tires constitute potential carbonaceous materials for the production of activated carbons, which is a typical control technology for removing HgCl₂ from municipal solid waste (MSW) incinerators. The adsorption of HgCl₂ with sulfurimpregnated activated carbons has seldom been investigated in regard to the variation in HgCl₂ adsorption with a specific surface area and pore size distribution of the activated carbons during the HgCl₂ adsorption process. In this work, sulfur-impregnated activated carbons were produced from waste tires and then examined for their adsorptive capacities of HgCl₂ using thermogravimetric analysis (TGA).