The Adsorption of SO₂by Zeolites Synthesized from Fly Ash

Abstract

Zeolites X, Y, and Na-P1 (90 °C) and analcime and sodalite (150 °C) were synthesized from Class F fly ash using 3 M sodium hydroxide solutions and autogenous pressures. The partially zeolitized fly ashes were dried overnight in air at room temperature and then characterized using X-ray diffraction and SEM. On occasion, a few samples were dried to constant weight for an additional 8−10 min in a microwave oven to remove bound water as well. The dried samples were evaluated for their ability to adsorb sulfur dioxide (SO2) from a simulated stack gas containing ∼2000 ppm SO2. Determinations were made in real time using a UV/vis spectrophotometer followed by a total sulfur analysis of the “loaded” samples once testing was complete. Breakthrough curves indicate that the zeolites in the samples are able to remove all of the SO2 in the simulated flue gas (zero SO2 emission) for varying periods of time, and that the actual amount of SO2 removed by the zeolite depended on the type and degree of “dryness” of the zeolite or zeolite-like material present. For example, a 7 day 150 °C cured sample containing analcime and sodalite was able to adsorb 6−7 mg of SO2 per gram of sample regardless of the source of the fly ash, whereas a 90 °C cured sample containing X, Y, and Na-P1 was significantly less efficient.