Role of CuFe2O4 in elemental mercury adsorption and oxidation on modified bentonite for coal gasification

Abstract

• Roles of CuFe 2 O 4 in Hg 0 adsorption and oxidation on CuFe 2 O 4 -modified bentonite. • Hg 0 adsorption and oxidation mechanism of CuFe 2 O 4 established. • The adsorption of Hg 0 on the surface of CuFe 2 O 4 (1 1 0) have the stronger interaction. Taking spinel CuFe 2 O 4 -modified bentonite as the research object, the experimental and thermodynamic techniques were integrated to study the effect of CuFe 2 O 4 active components on removing Hg 0 in coal gasification process. Meanwhile, the density functional theory was adopted to identify the CuFe 2 O 4 ’s adsorption and oxidation mechanisms for Hg 0 . The results showed that the doping of CuFe 2 O 4 increased the active sites for adsorbing Hg 0 on the surface of bentonite and enabled bentonite with effective magnetic properties. Compared with pure bentonite, the CuFe 2 O 4 -modified one was able to convert more Hg 0 into Hg 2+ and particulate mercury[Hg(P)], which exhibited its better capacities of adsorbing and catalyzing Hg 0 . The thermodynamic simulation outcomes further verified that the bentonite adsorbent modified by CuFe 2 O 4 became more conducive to the conversion of Hg 0 to Hg 2+ . Moreover, DFT results also presented that Hg 0 was under stronger adsorption effect at the Cu-top active sites of CuFe 2 O 4 (1 1 0), which was closely related to the hybridization of orbitals between Hg and Cu atoms. The reaction of Hg 0 with O atoms followed the Markov-Mason mechanism, meaning that Hg diffusion at Fe/Cu-top site was the controlling step, HgO desorption at O-top site and hollow was the control step. The reaction of Hg 0 with active S atoms followed the two mechanisms of Eley−Riddel(E−R) and Langmuir−Hinshlwood (L−H). The energy barrier of L-H mechanism was lower than that of E-R mechanism, which was dominant in the reaction process. The excellent performance suggested that the CuFe 2 O 4 -modified bentonite was a promising sorbent for mercury removal in coal gasification.