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

Taking spinel CuFe2O4-modified bentonite as the research object, the experimental and thermodynamic techniques were integrated to study the effect of CuFe2O4 active components on removing Hg0 in coal gasification process. Meanwhile, the density functional theory was adopted to identify the CuFe2O4's adsorption and oxidation mechanisms for Hg0. The results showed that the doping of CuFe2O4 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 CuFe2O4-modified one was able to convert more Hg-0 into Hg2+ 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 CuFe2O4 became more conducive to the conversion of Hg-0 to Hg2+. Moreover, DFT results also presented that Hg-0 was under stronger adsorption effect at the Cu-top active sites of CuFe2O4(110), 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 CuFe2O4-modified bentonite was a promising sorbent for mercury removal in coal gasification.