Adsorption and Oxidation of Mercury by Montmorillonite Powder Modified with Different Copper Compounds

Abstract

In this study, montmorillonite (MT) was modified separately with CuO and CuCl2 through impregnation and then used to remove elemental mercury from simulated coal-fired flue gas. The effects of several factors, including the Cu loading amount, reaction temperature, and partial flue gas components as well as the stability of the mercury removal properties of the sorbents, were investigated. Various techniques, including Brunauer–Emmett–Teller measurements, X-ray fluorescence analysis, X-ray diffraction analysis, transmission electron microscopy, and X-ray photoelectron spectroscopy, were used to characterize the physicochemical properties of the sorbents. The obtained results showed that the sorbents with the optimal Cu loading rates, namely, 10.0% CuO/MT and 1.0% CuCl2/MT, exhibited high and stable performances, with their average Hg0 removal efficiencies being approximately 71.0 and 92.0%, respectively, at 150 °C. Moreover, the effects of the reaction temperature on the mercury removal properties of the two sorbents were different. Both O2 and NO significantly promoted the removal of elemental mercury, whereas SO2 inhibited it. The mechanisms of Hg0 capture are discussed based on the obtained results. Both the lattice oxygen (Oα) and the chemisorbed oxygen (Oβ) species contribute to the catalytic oxidation of Hg0 in the case of 10.0% CuO/MT. On the other hand, for 1.0% CuCl2/MT, the active chlorine (Cl*) species and Cu in the oxidation state (Cu2+) aid the catalytic oxidation of Hg0. Hence, 1.0% CuCl2/MT, which exhibited excellent Hg0 removal performance, can be considered a promising Hg sorbent for various applications.