The effect of mechanical-chemical-brominated modification on physicochemical properties and mercury removal performance of coal-fired by-product

Coal combustion is one of the largest anthropogenic mercury emission source in China, while the coal-fired by-product such as fly ash (FA) and bottom ash (BA) are raw material for making mercury removal adsorbent with low-cost and high efficient and recycling. The mechanical-chemical brominated FA (FA-MC-Br) and BA (BA-MC-Br) were prepared through the omni-directional planetary ball mill. The physicochemical properties of FA, FA-MC-Br, BA, and BA-MC-Br were compared and discussed based on analyses of the X-ray photoelectron spectroscopy, Brunauer-Emmet-Teller, Scanning Electron Microscopy, and mercury temperature programmed desorption, etc. The mercury-removal ability of the four samples was estimated by fixed-bed react system which showed that the mechanical-chemical-brominated modification has no significant effect on the pore structures of FA and BA but obviously reducing their particle sizes and increase the amorphous phase on surface of FA and BA. Besides, the Fe content on the surface of BA was enhanced as well. The Br loading rate of FA-MC-Br and BA-MC-Br is 61.35% and 48.67%, respectively. The mercury removal ability of FA/BA can be significantly improved by the mechanical-chemical-brominated modification. The reaction mechanism and pathways of Hg-0 removal by FA-MC-Br and BA-MC-Br can be deduced as the following two parts: (a) HgO is adsorbed and oxidized by the active chemisorbed oxygen and Fe3+ on the surface of samples. (b) HgBr2 is generated by the reaction between the C-Br and Hg-0, which follows the Eley-Rideal mechanism.