Zeolite synthesis from coal fly ash and its application to heavy metals remediation from water contaminated with Pb, Cu, Zn and Ni ions

The unique properties of zeolites, such as their microporous structure and ion exchange capacity, make them a promising material for water treatment applications. This work explores the synthesis of zeolites from coal fly ash (CFA) using the microwave fusion and hydrothermal synthesis method and investigates their effectiveness in removing heavy metal ions, specifically Cu2+, Zn2+, Ni2+, and Pb2+, from an aqueous solution. Moreover, to overcome the challenge of extracting fine zeolite particles from treated water, a novel method using colloidal PVA solutions to bind magnetite nanoparticles to zeolite was used. The obtained magnetic CFA zeolite was investigated for its adsorption performance and ability to be extracted from water. The experiments included the analysis of adsorption kinetics and the determination of both zeolites adsorption capacity in single and mixed ion systems. The results obtained in this study show that the zeolite synthesized from CFA has excellent adsorption properties for the investigated metal ions. Specifically, in a single ion system, the maximum adsorption capacity of CFA-zeolite was calculated as 495 mg/g for Pb2+, 248 mg/g for Cu2+, 177 mg/g for Zn2+, and 130 mg/g for Ni2+. When tested with the same dosage of zeolite in the mixed ions system, the adsorption capacity was found to be 276 mg/g for Pb2+ and 95 mg/g for Cu2+, while Zn2+ and Ni2+ ions were not adsorbed. Furthermore, the results suggest that the magnetic zeolite composite has excellent adsorption properties. Thus, in mixed ions system its maximum adsorption capacity was found as 261 mg/g, 109 mg/g, 45 mg/g and 42 mg/g for Pb2+, Cu2+, Zn2+ and Ni2+ ions, respectively; the selectivity order of Pb2+ > Cu2+ > Zn2+ > Ni2+ was therefore established for both systems. Additionally, magnetic zeolite was shown to be easily separated from the treated solution using high intensity magnetic separation. Various surface characterization techniques were utilized to examine the zeolite's surface before and after the adsorption of metal ions, and the results suggest an ion exchange mechanism for the studied metals. Overall, this study further highlights the potential of CFA-synthesized zeolites for the removal of heavy metal pollutants from wastewater and provides insights into the mechanisms underlying their adsorption behavior. Moreover, it was demonstrated that the synthesized magnetic CFA zeolite has potential for practical water treatment applications as an effective and sustainable material for the removal of heavy metal pollutants from wastewater. Further investigations are necessary to optimize the use of CFA magnetic zeolites for practical water treatment applications.