Gas-phase elemental mercury removal from flue gas by cobalt-modified fly ash at low temperatures

Co modified fly ash (FA) prepared by the wet impregnation method was investigated for gas-phase elemental mercury capture under air at 80°C in this paper. X-ray fluorescence spectrometry, Brunauer-Emmett-Teller, scanning electron micrographs, X-ray diffraction, thermogravimetric (TG) analysis and X-ray photoelectron spectroscopy (XPS) were employed to characterize the samples. Experimental results showed that the optimal Co loading was 9 wt%, which gave a Hg(0) removal efficiency of 76% in a laboratory packed-bed reactor at low temperatures in the presence of O₂. The high removal efficiency was mainly attributed to oxidation of Hg(0) by the enrichment of well-dispersed Co₃O₄on the surface of FA. However, higher Co loading resulted in the decrease of removal efficiency due to the decline of surface area and Co₃O₄agglomeration. TG and XPS characterization indicated that Hg(0) was oxidized by Co₃O₄and some of the oxidized mercury formed recombination mercury oxide with Co₃O₄, which could either exist stably at low temperature or be desorbed from the adsorbents at higher temperature. Finally, the possible adsorption mechanisms were proposed according to the observed phenomena.