| Efficient sulfur-impregnated activated carbon-based (SIAC) sorbents for elemental mercury vapors were developed and evaluated in this study. The key parameters of the impregnation protocol included impregnation temperature and initial sulfur to carbon ratio (SCR). Gas constituents and temperature were the key process parameters studied for their impact on sorbent performance.; Impregnation temperature is the major impregnation parameter that dominated the performance of SIACs. Performance deteriorated quickly as the impregnation temperature was lowered below 400°C. Higher impregnation temperatures facilitated the presence of more active short-chain S molecules, larger adsorbent surface area, greater fraction of meso-pores, and stronger sulfur-carbon bonding. SCR showed moderate impact on mercury uptake with a 50% decrease in sorbent capacity from highest SCR (4:1) to lowest SCR (1:2).; Impact of gas constituents was investigated individually. CO2 (5 and 15%) behaved as inert gas and did not change the performance of SIAC. Also, trace amount of SO2 (300 ppm) and NO (500 ppm) did not alter its performance. Thermogravimetric Analysis showed that micro-structure of SIAC was unchanged after contacting trace pollutants. Low O2 concentration (3%) did not change the performance of SIAC, while high O2 concentration (6% and 9%) increased its capacity by 16% and 30%, respectively. It is postulated that SIAC catalyzed the formation of HgO in the presence of high O2 concentrations. High moisture concentration (10%) decreased SIAC's capacity by 25% while low moisture concentration (5%) showed no impact. It was assumed that water blocked the entrances to the active sites of carbon. H2 formation and hydrogen bonding could have also retarded mercury-sulfur reaction.; SIAC's performance was negligible at 250 or 400°C due to the exothermic nature of Hg and S reaction, while its capacity at 140°C increased by 14% as smaller sorbent particle size (170 x 230) was used instead of 60 x 80. The fate of spent SIAC was assessed using a modified toxicity characteristics leaching procedure (TCLP). Mercury concentration in all leachates was below the TCLP limit (0.2 mg/L), and no mercury loss was found from SIAC. It is suggested that SIAC can be treated as non-hazardous wastes. |
