Experimental and DFT Studies of Influence of Flue Gas Components on the Interaction between CaO and As during Sludge Combustion

The problem of As pollution emission from sludge during combustion has received widespread attention. The impact of flue gas components on the interaction with CaO and As during sludge combustion was analyzed using a series of experimental characterization methods. The strength of the activity of As 2 O 3 on the CaO(001) surface as well as on the CO 2 /SO 2 /H 2 O+CaO(001) surface with different O adsorption sites was revealed by combining with Density Functional Theory (DFT). According to the results, CO 2 in the flue gas reacted with CaO in a reversible carbonation reaction, which optimized the pore structure of the solid phase products and promoted the capture of As by CaO. SO 2 in the flue gas reacted with CaO in a sulfation reaction reaction to block the pores, which was not conducive to the capture of As by CaO. The presence of moisture led to poor pore structure collapse of the solid phase products as well as the formation of gehlenite, which reduced the enrichment of As by CaO. DFT calculations showed that the adsorption of As 2 O 3 molecules on the CO 2 +CaO(001) surface was affected by the position of the O active site, and the adsorption energy at the O C1 top site was higher than that on the clean surface, which was favorable for the stable adsorption of As 2 O 3 molecules. The existence of SO 2 decreased As 2 O 3 molecules’ adsorption energy on the CaO(001) surface, which was unfavorable for the adsorption of As 2 O 3 molecules. There were two main effects of H 2 O molecules on the adsorption of As 2 O 3 on the CaO(001) surface. One was the H 2 O molecules weakened the interaction between the As atoms and O surf atoms, which was unfavorable to the adsorption of As 2 O 3 molecules; the other was the existence of stronger adsorption of O atoms in H 2 O molecules on As atoms in As 2 O 3 molecules, which made As 2 O 3 molecules adsorbed at the top of O H0 adsorbed with adsorption energies much larger than that of clean surface, and the adsorption was more stable.