Chemically bonded zirconium oxide into CaO-based high-temperature coal-fired flue gas As2O3 absorbents for enhanced anti-sintering properties: Experimental and DFT study

CaO, as a mineral oxide adsorbent, has excellent arsenic trapping performance. Still, it has a flaw that inhibits its application: at high temperatures, CaO begins to sinter and ruduces its adsorption capacity. In this work, the anti-sintering ZrO2/CaO composite adsorbent was fabricated by the citric acid sol-gel process and applied for the first time in As2O3 adsorption studies in flue gas at 500–900 ℃. A combination of experimental and theoretical analytical methodologies was adopted to explore the influence of Zr modification on the behaviour of CaO adsorption of As2O3 and the adsorption mechanism of As2O3 on ZrO2/CaO. The experimental findings demonstrate that the introduction of ZrO2 not only significantly increases the specific surface area of the adsorbent and provides more adsorption sites, but also provides a large number of free electrons for the conversion of adsorbed oxygen in the system, which effectively promotes the reaction process of the chemical oxidation of As(III) to As(V). Furthermore, the partial CaZrO3 structure formed by chemical bonding of ZrO2 with CaO significantly improves the sintering resistance of ZrO2/CaO at high temperatures. Therefore, the adsorption capacity of the prepared ZrO2/CaO for As2O3 reaches 857.7 mg/kg at 900 ℃, which is approximately 16 times greater than that of untreated CaO. Meanwhile, the microscopic mechanism of ZrO2/CaO adsorbent was further investigated by density functional theory (DFT). The analysis revealed that the Zr site is the main active adsorption site of ZrO2/CaO. During the adsorption of arsenic, Zr undergoes strong electron-orbital hybridization with the O atoms of the system and arsenic to form a stable ZrO6 octahedral structure, which promotes the strong stability of the chemisorption system. ZrO2/CaO has remarkable arsenic trapping ability and resistance to sintering, and is a composite adsorbent material with great potential for arsenic removal.