Comparison of alkali modified fly ash and alkali activated fly ash as Zn(II) ions adsorbent from aqueous solution

Fly ash which is solid waste can be used as an adsorbent for wastewater treatment. Alkali modification and alkali activation on fly ash can increase the adsorption capacity of fly ash. In this study, alkali modified fly ash and alkali activated fly ash were used as Zn(II) ions adsorbents. The effect of adsorption time and initial concentration of Zn(II) ions was studied, as well as the kinetics and isotherm adsorption. The results showed that the removal efficiency of Zn(II) ions by alkali activated fly ash is higher than that by alkali modified fly ash. The adsorptions of Zn(II) ions by alkali modified fly ash and by alkali activated fly ash have reached equilibrium after two hours. The increase of initial concentration of Zn(II) ions would decrease the removal efficiency with both alkali modified fly ash and alkali activated fly ash. Adsorptions of Zn(II) ions by both alkali modified fly ash and alkali activated fly ash tend to follow pseudo second order kinetics model and Langmuir isotherm model with maximum adsorption capacity of 62.696 mg/g and 66.667 mg/g, respectively.