Removal of elemental mercury from flue gas using CuO_x and CeO₂ modified rice straw chars enhanced by ultrasound

Rice straw char (RS), a common biomass pyrolysis waste, was modified by Cu-Ce mixed oxides with ultrasound-assisted impregnation to develop a cost-effective sorbent for Hg⁰ removal from flue gas. A variety of techniques including thermogravimetric analysis, nitrogen adsorption-desorption, scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy were used to characterize the physical and chemical properties of the sorbents. The effects of ultrasound-assisted impregnation, Cu/Ce molar ratio, loading value, calcination temperature, reaction temperature and concentrations of the simulated flue gas components on Hg⁰ removal were investigated in a fixed-bed reactor. The results indicated that ultrasound-assisted impregnation promoted Hg⁰ removal. The optimal Cu/Ce molar ratio, loading value, calcination temperature and reaction temperature were 1/5, 0.18 mol/L, 260 °C and 150 °C, respectively. The presence of O₂ and NO promoted Hg⁰ removal, but H₂O and SO₂ inhibited Hg⁰ removal. The highest Hg⁰ removal efficiency obtained was 95.26%; and chemical adsorption was found to play a key role in the removal process. The results of stability and regeneration tests conducted suggest the sorbents could sustain longtime use for Hg⁰ removal.