Diverse zeolites derived from a circulating fluidized bed fly ash based geopolymer for the adsorption of lead ions from wastewater

The transformation of geopolymers into zeolite materials for use as bulk-type adsorbents is an outstanding strategy for water pollution control. However, only sodium ion (Na+)-type zeolites can be typically obtained from geopolymers, which limits their variety. In this study, Li-ABW zeolite (Li-ABW), K–F zeolite (K–F), and phillipsite, were obtained via the hydrothermal transformation of a circulating fluidized bed fly ash (CFBFA)-based geopolymer using single alkali metal cations of either lithium (Li+) or potassium (K+), as well as coexisting Na+ and K+ as structure-directing agents. X-ray diffractometry and field emission scanning electron microscopy indicate that the amorphous CFBFA-based geopolymer was converted into well-defined Li-ABW zeolite, K–F zeolite, and phillipsite. The obtained zeolite products were subsequently employed as adsorbents to remove lead ions (Pb2+) from the aqueous solution, leading to adsorption capacities of 160.70, 239.50 and 252.70 mg/g for Li-ABW, K–F, and phillipsite, respectively. The kinetics of Pb2+ adsorption on the three zeolite samples fit the pseudo-second order model well, suggesting that Pb2+ adsorption on the zeolite samples occurs via chemical adsorption. The adsorption isotherms followed the Langmuir model, thereby confirming monolayer adsorption of Pb2+ on the as-synthesized zeolites. The combined results indicate that the zeolites derived from the CFBFA-based geopolymers are appropriate for Pb2+ removal from wastewater. This work provides new insights for the use of CFBFA industrial waste and the development of geopolymer-based adsorbents for the sustainable development of wastewater treatment methods. •Circulating fluidized bed fly ash-based geopolymer was converted into zeolites.•Alkali metal ions acted as directing agent on transformation processes of zeolites.•The types and structures of zeolites significantly depended on synthesis conditions.•Lead ion absorption properties on zeolites derived from the geopolymer were studied.