Mercury removal by Co3O4@TiO2@Fe2O3 magnetic core-shell oxygen carrier in chemical-looping combustion

Mercury pollution has received much attention due to its severe harm to human and ecological system. The major source of mercury emission is from coal combustion. In the flue gas, elemental mercury (Hg-0) is the most abundant and difficult form to be removed. In the chemical-looping combustion of coal (CLCC), oxygen carrier (OC) plays the role of oxygen storage and release, and it also has catalytic ability for Hg-0 removal. In this study, a magnetic material Co3O4@TiO2@Fe2O3 (CTF) with a core-shell structure was prepared by combining sol-gel and impregnation methods. The Co: Ti: Fe ratio was obtained as 1:2:4, which was optimized to achieve strong magnetism and catalytic ability. The Hg-0 removal efficiency increased with the increase in temperature in the temperature range of 800-900 degrees C. The mercury removal efficiency of Hg-0 + CTF + HCl was higher than that of Hg-0 + HCl, indicating that CTF promoted the conversion of Hg-0 to Hg2+/HgP. Both homogeneous and heterogeneous reaction pathways are important for Hg-0 removal. CTF promotes the oxidation of Hg-0 in HCl atmosphere by reacting with HCl to produce more Cl-2, which is more reactive towards Hg-0. Furthermore, Hg-0 is adsorbed on CTF to form adsorbed Hg-0 and HgO. Mercury on CTF is mainly desorbed in the form of HgO, which is beneficial for mercury removal. Ten redox cycles were applied on CTF, which still maintained a high Hg-0 removal efficiency and strong magnetism. CTF can be used as a recycled OC in CLCC.

Automated summary

Mercury pollution, primarily from coal combustion, poses a serious threat to both human health and ecosystems. A magnetic material, CTF, was developed to enhance the removal of elemental mercury (Hg-0) during chemical-looping combustion of coal (CLCC). Results showed that CTF promoted the conversion of Hg-0 to Hg2+/HgP in the presence of HCl, contributing to a higher mercury removal efficiency.