Resource Recovery of Waste Fly Ash: Synthesis Of Zeolite-like Materials

Abstract

Since the main components of fly ash are SiO 2 and Al 2 O 3 , which exhibit a similar chemical structure of zeolite, fly ash was used in this study to synthesize zeolite-like materials. Different hydrothermal conditions were evaluated for achieving a maximum cation-exchange capacity of the synthesized zeolites. Experimental parameters included temperature, nature and molarity of caustic reagents, pressure, and reaction time. Tasks performed in this work included phase identification of treated fly ash by X-ray diffraction techniques, measurement of cation-exchange capacity and specific surface area of the synthesized zeolites, determination of elemental composition, and evaluation of metal adsorption onto the synthesized zeolites. Four zeolites were identified under various experimental conditions : zeolite P (2-4 N NaOH at 70-130 °C) ; analcime (2 N NaOH between 130 and 170 °C) ; hydroxy sodalite (4-10 N NaOH at 90-200 °C) ; and cancrinite (T> 200 °C). After NaOH treatment, there was a significant reduction in Si content, while Na increased as the reaction temperature or the strength of NaOH increased. The experimental conditions at 2 N NaOH, 110 °C, and 3.45 MPa for 1-day reaction resulted in treated fly ash with a cation-exchange capacity of 210 mequiv/100 g. Treated fly ash exhibited a strong affinity for Cu and Cd metal ions. At pH = 6, approximately 90% of Cu and 80% of Cd were removed by the zeolites synthesized under different conditions.