Optimization of the synthesis conditions of zeolite adsorbents derived from coal fly ash and study on their adsorption performance on benzene

Zeolite adsorbents were synthesized through an alkali fusion-hydrothermal process, using coal fly ash as a raw material. Firstly, the coal fly ash was mixed with sodium hydroxide at a mass ratio of 1∶1.2 and then roasted at 850 ℃ for 2 h to obtain the alkali-fused ash. The effects of the Si/Al molar ratio of the precursor, reaction time, temperature, and liquid/solid ratio on the structure of the zeolite adsorbents derived from coal fly ash were investigated through single-factor experiments conducted during the hydrothermal reaction. The synthesized zeolite adsorbents derived from coal fly ash were systematically characterized using X-ray diffractometer (XRD), scanning electron microscope (SEM) and specific surface area and pore size analyzer (BET). Under the optimized conditions of a Si/Al molar ratio of the precursor set at 1.5, a reaction time of 16 h, a reaction temperature of 70 ℃, and a liquid/solid ratio of 8 mL/g in hydrothermal reaction, the relative mass fraction of type X zeolite in the synthesized product was 96.3%, the specific surface area was 489.9 m2/g, and the pore volume was 0.28 cm3/g. Subsequently, the gas adsorption performance of benzene, a typical volatile organic compound, by zeolite adsorbent derived from coal fly ash was investigated and compared with commercial activated carbon. The results showed that at an initial pollutant concentration of 800 μg/L, an adsorption temperature of 100 ℃, a gas flow rate of 200 mL/min, and an adsorbent loading of 0.1 g, the zeolite adsorbents derived from coal fly ash exhibited a saturated adsorption capacity of benzene at 41.5 mg/g, which was higher compared to commercial activated carbon (31.3 mg/g). This study provides a reference for the resource utilization of coal fly ash.