Effect of flue gas components on the removal of cadmium pollutants by transition metal-modified activated carbon: Density functional theory and thermodynamic study

Removal of cadmium (Cd) pollutants from waste incineration (MSW) flue gas by modified activated carbon (AC) is of great potential, yet the influence of flue gas composition on their interaction mechanism is still unclear. Thus, density functional theory and thermodynamic analyses were combined to explore the effects of typical flue gas compositions (O2, HCl, NO, SO2, CO2, and H2O) on Cd species capture over the Fe/AC and Mn/AC surfaces. All flue gas compositions inhibit the adsorption of Cd species, wherein their inhibitory effects are mainly divided into two categories, i.e., one with moderate inhibition (HCl, CO2, and H2O), and the other with significant inhibition (O2, NO, and SO2). For the first category, HCl forms new active sites after adsorption on the surface, while CO2 and H2O have weak competitiveness with Cd species, resulting in mild inhibitory effects. Nevertheless, O atoms of O2/SO2 and N atoms of NO are highly effortless to bond with Fe/Mn atoms, and strongly exclude the Cd adsorption on the active sites, greatly weakening their binding strength. According to thermodynamic analysis, the fixation of Cd species by Fe/AC and Mn/AC spontaneously proceeds with the interference of flue gas components, while the selectivity to Cd species decreases with the increased temperature. In summary, it is instrumental to adjust the operating parameters and AC injection location to attenuate the negative effects of O2, SO2, NO, and high temperature on Cd capture by Fe/AC and Mn/AC.