Mechanism Study Of Mercury Species From Coal Combustion Flue Gases Adsorption On Iron Oxide Surface

Trace mercury from coal combustion as a large emission source to the atmosphere, is recognized as the direct and potential risk to both human health and environment. In recent years, researches on the mechanisms of mercury migrantion and transformation have been conducted to determine an effective and affordable sorbent for capturing mercury from combustion flue gas.Cheap fly ash has been paid more attention to reseach on adsorbent. However, evidence is insufficient to understand the mechanism of catalyzed oxidation for mercury removing. Especially, the research of metallic oxides in fly ash is still in blank field. According to this, first-principle calculations based on Density Functional Theory (DFT) were performed to investigate the binding mechanisms of mercury onα-Fe₂O₃ (001) andγ-Fe₂O₃ (001) surface. The results of geometry optimization indicate that H_g⁰ adsorption onα-Fe₂O₃ (001) perfect surface is physisorption; while weak chemisorption occurs with the energy of -47.50 kJ/mol in the present of surface oxygen vacancy. It is found that H_g⁰ adsorption onγ-Fe₂O₃ (001) perfect surface is chemisorption with the energy of -54.30 kJ/mol; however, much stronger binding occurs at oxygen vacancy surface with binding energy of -134.6 kJ/mol. Further insight into the type of bonding mechanism for Hg on theγ-Fe₂O₃ (001) surface can be obtained by analyzing the density of the states (DOS), which suggests that the presently described processes are all noncatalytic in nature. However, this is a reflection more of mercury's amalgamation ability. The oxidized forms of HgCl and HgCl₂ can be adsorbed onα-Fe₂O₃ (001) dissociatively or non-dissociatively. In the case of dissociative adsorption, a close examination of the energy diagram indicates that HgCl may be favorable for the adsorption of Cl and desorption of Hg. The dissociation of HgCl₂ with the binding of Cl and HgCl on the surface is possibly the dominant interaction pathway.Research has been made to perform theoretical calculations to obtain the details of interactions between mercury and iron oxide, which is considered as the most interesting components of fly ash. It is significant for mercury removal by fly ash widely.