Flyash for sustainable wastewater treatment: Origin, environmental concerns, and removal of dyes and heavy metals

Abstract The primary by‐product of coal‐burning industries and thermal power plants is flyash (FA). Heavy metals and trace elements present in the FA pose a significant disposal problem. Due to its enormous availability and favorable physicochemical properties, it has multiple applications, including environmental remediation, construction utilities and agricultural activities. The review elaborates on the origin, chemical composition, improper disposal methods, and ecological and environmental hazards of FA, focusing on the sustainable management of water pollution through adsorption. The major factors influencing adsorption and the most recent developments in FA modification techniques are also covered. Through the present application, one can deal with the concurrent problems of FA disposal and water pollution management, thereby addressing the concepts of the circular economy. Unmodified FA has adsorption capacities of 10–250 mg/g for different heavy metals and 2–100 mg/g for dyes, while modified and composite forms that contain magnetic nanoparticles, zeolites, and biochar have adsorption capacities of 1000–1500 mg/g. The adsorption efficiency increases three to six times as a result of modifications, demonstrating the potential of engineered FA‐based adsorbents in wastewater treatment. Future advancements in novel surface modification methods of FA could improve its surface area, adsorption capacity, and selectivity for various contaminants, thereby enhancing its adsorption efficiency.