The role of SO₂ in arsenic removal by carbon-based sorbents: A DFT study

Carbon-based sorbents have been regarded as the promising candidates for arsenic removal from coal-fired flue gas because of their large surface area and functionality. The effect mechanism of SO2 on As2O3 adsorption over the carbon surfaces was systemically investigated by density functional theory calculations. The results show that the As2O3 molecule can be adsorbed on the carbon surfaces vertically or horizontally. The adsorption energies of As2O3 on the pure carbon surfaces range from -45.47 to -497.74 kJ/mol. When the SO2 concentration is low, the presence of SO2 can facilitate the As2O3 adsorption because of the electronic effects caused by SO2. The adsorbed SO2 can significantly decrease the level of electrostatic potential of neighbor active sites. In addition, the charge distributions of unsaturated carbon atoms are changed after SO2 adsorption, making the carbon surfaces more active for As2O3 adsorption. The enhanced charge transfer between As2O3 and the carbon surfaces with SO2 results in the stronger As2O3 adsorption. However, higher concentration of SO2 could inhibit the As2O3 adsorption because SO2 competes with As2O3 for the active adsorption sites.