Removal of elemental mercury in flue gas by Cu-Fe modified magnetosphere from coal combustion fly ash

Abstract

Magnetospheres (MF) obtained from fly ash by magnetic separation method has low mercury removal efficiency and weak magnetism in gas phase mercury removal. In this paper, magnetospheres were modified with Cu and Fe compounds by sol-gel method. The Hg0 removal performance of Cu-Fe modified MF were investigated in a fixed bed reactor, and the effect of calcination temperature and flue gas composition on magnetism of the modified MF were examined. The Hg0 removal efficiency of Cu(6)Fe-MF-400, which was obtained with 6 wt% Cu loading on MF, Cu:Fe atomic ratio being 1:2 and calcined at 400 °C, reaches 97% at 200 °C in the atmosphere of N2, CO2 and O2. Specific magnetic susceptibility of Cu(6)Fe-MF-400 enhances significantly from 41 to 52 cm3/g. The effect of flue gas composition on Hg0 removal indicated that HCl significantly shortens the required time to achieve 80% efficiency of Hg0 removal, while NO and SO2 prolong this required time. In the reaction temperature range of 100–350 °C, the required time decreases with the increase of temperature, and it is three seconds at temperature of 300 °C. The magnetism of Cu(6)Fe-MF is significantly weakened in atmosphere containing HCl or SO2, but strengthened in NO. Cu(6)Fe-MF still shows stable Hg0 removal efficiency and magnetism after reaction for 10 h. Cu-Fe modified not only make MF to be used for mercury control of coal-fired flue gas, but enables reuse of coal-fired waste-MF, which is in line with the principles of circular economics.