Turning waste into a resource: coal fly ash as a sustainable approach for heavy metal removal in contaminated waters.

Effective, low-cost water treatment approaches are needed to address increasing heavy metal contamination, particularly in the developing world. This study evaluates the use of fly ash, a waste byproduct from coal combustion, as a sustainable adsorbent to remove cadmium (Cd2+), cobalt (Co2+), and lead (Pb2+) from aqueous solutions. Two types of fly ash sourced from different power plants in the southeastern United States were evaluated in this study: Belews Creek fly ash (BFA), which was untreated, and Wateree Station fly ash (WFA), which was processed using a proprietary carbon burnout method. The removal kinetics followed the pseudo-second order model, with equilibrium being achieved within 2 h. The experimental data best fit the Freundlich isotherm model, compared with the Linear isotherm model, suggesting that multilayer adsorption occurred on the fly ash surfaces. The results showed that Pb2+ exhibited the highest removal efficiency for each adsorbent (BFA: 99%; WFA: >99%), followed by Co2+ (BFA: 98%; WFA: 94%) and Cd2+ (BFA: 93%; WFA: 56%). Removal efficiency was influenced by pH and was negatively impacted by increasing ionic strength and total organic carbon content. The findings demonstrate that fly ash is a viable, low-cost alternative for heavy metal removal for use in resource-limited areas.