Adsorption of Se(IV) in aqueous solution by zeolites synthesized from fly ashes with different compositions

Low-calcium fly ash (LC-F) and high-calcium fly ash (HC-F) were used to synthesize corresponding zeolites (LC-Z and HC-Z), then for adsorption of Se(IV) in water. The results showed that c zeolites can effectively adsorb Se(IV). The optimal adsorption conditions were set at contact time = 360 min; pH = 2.0; the amount of adsorbent = 5.0 g·L−1; temperature = 25 °C; initial Se(IV) concentration = 10 mg·L−1. The removal efficiency of HC-Z was higher than the LC-Z after it had fully reacted because the specific surface area (SSA) of HC-Z was higher than LC-Z. The adsorption kinetics model of Se(IV) uptake by HC-Z followed the pseudo-second-order model. The Freundlich isotherm model agreed better with the equilibrium data for HC-Z and LC-Z. The maximum Se(IV) adsorption capacity was 4.16 mg/g for the HC-Z and 3.93 mg/g for the LC-Z. For the coexisting anions, barely affected Se(IV) removal, while significant affected it. Regenerated zeolites still had high capacity for Se(IV) removal. In conclusion, zeolites synthesized from fly ashes are a promising material for adsorbing Se(IV) from wastewater, and selenium-loaded zeolite has the potential to be used as a Se fertilizer to release selenium in Se-deficient areas.