Elemental mercury removal from coal-fired flue gas using recyclable magnetic Mn-Fe based attapulgite sorbent

Abstract

Magnetic manganese-iron modified attapulgite sorbents (xMnFAy) were synthesized and employed for Hg0 removal from coal-fired flue gas. The effects of calcination temperature, MnO2 loading amount, reaction temperature, as well as the individual flue gas components on Hg0 removal were investigated. The 0.1MnFA loaded with 10 wt% MnO2 and calcined at 450 °C exhibited the optimal Hg0 removal activity, above 80% Hg0 removal at a high GHSV of 4 × 105 h−1. O2 promoted Hg0 removal via recovering surface oxygen and high valence metal ions (Fe3+ and Mn4+). NO improved Hg0 capture due to the formation of adsorbed NO2 and nitrate species, which functioned as active sites for mercury oxidation. SO2 prohibited Hg0 retention because of its competitive adsorption against Hg0 for the active sites and the sulfation of the sorbent. Besides, SO2 could reduce the high valence metal ions to a lower valence, which hampers Hg0 oxidation. The presence of NO could overcome the inhibitive effect of SO2 on Hg0 removal because the adsorbed NO2 and nitrate species were still retained on the sorbent surface in the case of SO2 existence·H2O inhibited Hg0 removal because of the competitive adsorption. 0.1MnFA could maintain its good Hg0 retention ability after five regeneration cycles. This work contributes to developing the cost-effective sorbents for Hg0 removal from coal-fired flue gas, as well as maximizing the utilization of attapulgite clay.