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 CFBFAbased 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.

Automated summary

The study successfully transformed geopolymers into zeolite materials using lithium or potassium cations, as well as structure-directing agents, to remove lead ions from aqueous solutions. The results demonstrated efficient chemical adsorption of Pb2+ onto the zeolite surfaces, confirming monolayer adsorption. This work offers new insights for sustainable wastewater treatment methods by utilizing industrial waste and developing geopolymer-based adsorbents.