Mechanism of CaO and Fe2O3 capture gaseous arsenic species in the flue gas: DFT combined thermodynamic study

In this work, the stable arsenic forms were determined based on density functional theory (DFT) combined thermodynamic system equilibrium calculation. For the stable arsenic species, the capture mechanism by CaO and Fe2O3 was studied by DFT. Trivalent arsenic(III) were the main arsenic forms in the flue gas from thermodynamic system equilibrium analysis. With H2O in the flue gas, arsenic species form was As4O6 from 700 to 1700 K and converted to AsOOH at 900 K. Without H2O in the flue gas, chain As2O3 and AsO2 was generated by As4O6 at 1200 K, and chain As2O3 decomposed to AsO2 as temperature further increased. The conversion pathways between stable arsenic species were studied as the arsenic reaction cycle. The adsorption behavior of stable arsenic species on CaO and Fe2O3 surfaces was investigated via DFT. Oxygen atoms on the CaO surface and ferric, oxygen atoms on the Fe2O3 surface were the main active adsorption sites for arsenic species. The adsorption results implied the strength of CaO and Fe2O3 capture arsenic species: chain As2O3 > AsO2 > AsOOH > As4O6. The band gap of arsenic species also confirmed this conclusion indicating high temperature was beneficial for metal oxide surface to capture arsenic species through arsenic conversion.