Study on arsenic/lead adsorption characteristics by mineral oxides in coal-fired flue gas

The As₂O₃ or PbO adsorption characteristics using typical mineral oxides as the sorbents were studied in a two-stage fixed-bed reactor under a simulated flue gas, and the density of atomic states, adsorption sites, and adsorption energy for the adsorption reaction were calculated by density functional theory (DFT). The results demonstrate that CaO has a large As₂O₃ adsorption capacity, with an arsenic adsorption capacity of 5.25 mg/g at 900 ℃, followed by Fe₂O₃, MgO, and Al₂O₃; and the adsorbed arsenic exists in the form of As³⁺ and As⁵⁺ arsenates. Kaolin and fly ash have large PbO adsorption capacities, with the maximum lead adsorption capacities of 6.69 and 2.75 mg/g, respectively, followed by SiO₂ and Al₂O₃, and the adsorption capacity for lead with the 50%SiO₂/50%Al₂O₃ mixture is higher than that with their single oxide. The oxygen atoms on the surface of the sorbents are the active sites for As₂O₃ and the unsaturated Si and Al atoms exposed on the surface of the sorbents are the active sites for PbO. In addition, the adsorption temperature and flue gas atmosphere have significant effects on the adsorption capacity and adsorption products of the sorbents.