Mn and Fe Modified Fly Ash As a Superior Catalyst for Elemental Mercury Capture under Air Conditions

Abstract

The objective of this study was to investigate the effects of fly ash (FA) and Mn and Fe modified FA on elemental mercury capture under air at 120 °C. X-ray fluorescence spectrometry (XRF), Brunauer–Emmett–Teller (BET) surface area, scanning electron micrographs (SEMs), X-ray diffraction (XRD), thermogravimetric (TG) analysis, and X-ray photoelectron spectroscopy (XPS) were employed to characterize the samples. The results showed that the cooperation of Mn and Fe loaded on FA improved the performance of elemental mercury capture in a laboratory packed-bed reactor. In the presence of O2, Mn(2)–Fe(3)–FA (FA modified with an Mn/Fe molar ratio of 2/3) possessed the best reactivity and its Hg0 removal efficiency stayed around 98% within 8 h. The heterogeneous mercury reaction could be speculated as: Hg0 was physically adsorbed on the cation vacancies and then was oxidized to HgO by Mn4+ and Fe3+ cations. The reduced forms of Mn3+ and Fe2+ reoxidized under air, and HgO was finally adsorbed on the surface of the catalysts.