Experimental and theoretical studies of cadmium adsorption over Fe2O3 sorbent in incineration flue gas

Abstract

Iron oxide (Fe2O3) has been used as an effective sorbent to remove various heavy metals due to its large adsorption capacity and low cost. The cadmium capture capability of Fe2O3 sorbent was investigated in the simulated flue gas at the temperatures of 700–1100 °C. Fe2O3 sorbent exhibited much better Cd adsorption capability than SiO2 and Al2O3 sorbents. The largest Cd adsorption capacity of Fe2O3 sorbent was 86.7 mg/g at 700 °C. The XPS analysis demonstrated that Fe3+ might partially participate in the cadmium adsorption process. A large quantity of CdO was generated and adsorbed on the Fe2O3 surface. The density functional theory (DFT) calculations were used to determine the active sites and the involved mechanism of different cadmium species adsorption over Fe2O3 sorbent. Cd, CdCl2, and CdO can be stably adsorbed on the Fe2O3 surface with the adsorption energies of −40.64 kJ/mol, −237.42 kJ/mol, and −375.03 kJ/mol, respectively. The results illustrate that the Fe atoms are the essential active sites for cadmium species adsorption on Fe2O3 surface. The orbital hybridization between cadmium atom and Fe site suggests that the strong interaction occurs during Cd adsorption process. Both physisorption and chemisorption mechanisms were responsible for the cadmium capture by Fe2O3 sorbent.