Valorization of fly ash as zeolite by hydrothermal process for dyes adsorption

Abstract

Valorization of fly ash as zeolite is one of sustainable ways to reduce environmental burden. In this paper, zeolite was prepared from fly ash by hydrothermal process and applied as dyes adsorbent. In hydrothermal process, fly ash was reacted with 5 N NaOH solution using solid/liquid ratio of 1/30 for 15 hours at temperature of 85°C. Characterization of hydrothermal products consisted of X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area, and scanning electron microscope (SEM) analysis. The results indicated the formation of Na-X zeolite with higher surface area compared to raw fly ash. The obtained zeolite was applied as Eriochrome Black-T (EBT) dye adsorbent. Adsorption was conducted in batch process with variations in time and dye initial concentration. The adsorption efficiency would increase with increasing time, but after 90 minutes the adsorption efficiency would be relatively constant. The higher the dye initial concentration, the lower the adsorption efficiency. Furthermore, the study of adsorption kinetics model and adsorption isotherm model that had been carried out showed that adsorption process of EBT dye by zeolite from fly ash tended to follow pseudo-second order kinetics model and Freundlich isotherm model.