Fly ash based geopolymer for heavy metal removal: A case study on copper removal

This work aims to evaluate the effectiveness of an amorphous geopolymer, synthesized from waste fly ash, as sorbent material for copper from aqueous solutions. The obtained geopolymer was found to be highly amorphous in structure due to the dissolution of fly ash glass phases. It has much higher removal efficiency compared to the raw fly ash. The removal efficiency was affected by solid/liquid ratio, temperature, reaction time, and Cu2+ initial concentration (C0). The highest Cu2+ removal capacity was obtained at pH 6. The kinetic data were found fit to the pseudo second order kinetic model. Furthermore, it was found that Langmuir model is better than Freundlich model within the temperature range (25-45 °C). The maximum sorption capacity (qm) occurred at 45 °C, reaching a value of 152 mg/g. The sorption process by the obtained geopolymer is endothermic in nature and more favorable at higher temperatures with enthalpy of adsorption of 39.49 kJ/mol. The activation energy of the sorption process at the optimum conditions was found to be 34.9 kJ/mol.