Adsorption of cadmium vapor by calcium-based adsorbents in simulated flue gas: Experimental and density functional theory studies

Calcium-based adsorbents are considered as effective high-temperature adsorbents for the removal of heavy metal in the furnace. In this work, the adsorption characteristics and reaction mechanism of calcium-based adsorbents for cadmium vapor were investigated by adsorption experiments and density functional theory (DFT) methods. The adsorption experiments showed that the adsorption performance of CaO for cadmium vapor was significantly better than Ca(OH)2, Calcite and CaSO4. The adsorption capacity of CaO adsorbent for cadmium increased firstly and then decreased with the increase of temperature. The enhanced trapping capacity of CaO for cadmium vapor with increasing temperature was associated with enhanced chemisorption, while the decrease in trapping capacity at high temperature could be attributed to adsorbent sintering. In addition, the results of DFT calculations showed that CaO had good adsorption capacity for various Cd species, and the order of the adsorption capacity was: CdO > CdCl2 > CdCl > Cd. The chemisorption mechanism dominated the adsorption of Cd species on the CaO (001) surface, and the central O site was the reactive site and electron transfer channel for the adsorption of Cd. This work provided a reference for the application of heavy metal vapor capture technology based on calcium-based minerals.