Removal of elemental mercury by clays impregnated with KI and KBr

• Clay impregnated with halogen (Br/I) enhanced the capacity of Hg0 removal.
• KI-clay performed better than KBr-clay in Hg0 removal under the same conditions.
• The reaction of KI and O2 to form I2 was an key step in the chemisorption of Hg0.
• O2 and SO2 showed a promotion whereas H2O showed an inhibition on Hg0 removal.

The removal of elemental mercury (Hg0) by KI and KBr modified clays (KI-clays and KBr-clays) was studied under simulated flue gas conditions. The physicochemical properties of these catalysts were investigated by a variety of characterization methods. The effects of KI and KBr loading, adsorption temperatures and the flue gas components (such as O2, SO2 and H2O (g)) on Hg0 removal efficiency were investigated. A pseudo-second-order model simulation was also introduced to reveal the mechanisms of Hg0 removal. The results showed that the Hg0 removal efficiency for the clays was significantly enhanced by KI or KBr modification, and the KI-clays performed much better than the KBr-clays in terms of Hg0 removal under the same conditions. An increase in KI or KBr loading and adsorption temperatures improved the Hg0 removal efficiency, which indicated that chemisorption occurred. The presence of O2 and SO2 promoted Hg0 removal, whereas the presence of H2O inhibited Hg0 removal by these modified clays. The formation of I2 from the reaction (2KI + 1/2O2 ↔ I2 + K2O) was considered to be an important step in the chemisorption of Hg0 on the surfaces of the KI-clays. The lower extent of Hg0 removal exhibited by the KBr-clays than by the KI-clays was due to the difficulty of Br2 formation on the surfaces. The pseudo-second-order model was demonstrated to simulate with the removal of Hg0 by KI-clays and KBr-clays well. The KI-clays displayed much a higher of the initial adsorption rate (H) and Hg0 removal capacity (qe) than the KBr-clays under the same conditions, which demonstrated that KI-clays are more active than KBr-clays with respect to Hg0 removal.

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