Studies on Mercury Adsorption Species and Equilibrium on Activated Carbon Surface

Mercury adsorption capability of raw activated carbon (R-AC) and NH4Br modified activated carbon (NH4Br-AC) was evaluated in a fixed-bed reactor. The effect of inlet Hg-0 concentration and flue gas components on mercury adsorption was investigated. The mercury adsorption species on the sorbent surface was analyzed by the Temperature Programmed Desorption (TPD) method. Finally, the mercury adsorption equilibrium of R-AC and NH4Br-AC was explored. Mercury adsorption results show that the mercury adsorption capability of NH4Br-AC is significantly larger than that of R-AC and increased with higher inlet Hg-0 concentration. O-2 and NO promote mercury adsorption on NH4Br-AC, but SO2 inhibits the mercury adsorption. The TPD result shows that mercury adsorption on RAC is mainly physical in nature, enhanced by chemisorption with the product of HgO. Mercury adsorption on NH4Br-AC is in the major form of chemisorption with the product of HgBr2. O-2 has little effect on the mercury adsorption mechanism. SO2 reduces the generation of HgBr2, but promotes little of HgS generation on NH4Br-AC. NO significantly improves the generation of Hg-2(NO3)(2) on NH4Br-AC. Adsorption equilibrium analysis shows that Langmuir and Temkin equations are more suitable to describe the mercury adsorption on R-AC, indicating the uniformity of the R-AC surface. Mercury adsorption on the NH4Br-AC surface can be described well by the Freundlich equation, illustrating the nonuniformity of the NH4Br-AC surface.