Synthesis of A- and H-type Zeolites from Fly Ash and Their Adsorption Mechanisms for SO2, CO2, and NO
Fly ash, a byproduct of coal combustion, poses severe environmental challenges. This study synthesizes A- and H-type zeolites from fly ash via hydrothermal treatment and evaluates their adsorption performance for low-concentration acidic gases (SO2, CO2, NO) at 1000 mg/m3. The zeolites exhibited pore sizes of 3–5 nm, with specific surface areas of 18.59 m2/g (A-type) and 22.32 m2/g (H-type). At 20 °C, A-type zeolite achieved maximum saturated adsorption capacities of 1.07 mmol/g for SO2, 0.26 mmol/g for CO2, and 0.048 mmol/g for NO; H-type zeolite showed higher capacities: 1.12, 0.29, and 0.053 mmol/g, respectively. In-situ DRIFTS revealed that T–O (T=Si/Al) groups serve as key active sites, with adsorption energies for A-type zeolite calculated as -5.11 kJ/mol (SO2), -4.07 kJ/mol (CO2), and -1.41 kJ/mol (NO). Kinetic analysis indicated conformity to the Arrhenius equation. The results demonstrate that fly ash-based zeolites are promising adsorbents for acidic gas removal, with H-type outperforming A-type due to larger surface area and more silanol sites. This work provides a theoretical basis for utilizing fly ash in gas purification, contributing to the circular economy.