Combined removal of zinc(II) and cadmium(II) from aqueous solutions by adsorption onto high-calcium Turkish fly ash

The aim of this work is the investigation of possible use of fly ash in the removal of zinc (Zn2+) and cadmium (Cd2+) contained in aqueous solutions. Batch adsorption experiments were performed in order to evaluate the removal efficiency of lignite-based fly ash. The parameters studied include contact time, pH, temperature, initial concentration of the adsorbate and fly ash dosage. The contact time necessary to attain equilibrium was found to be two hours. Maximum adsorption occurred in the pH range of 7.0 to 7.5. The percent adsorption of Zn2+ and Cd2+ increased with an increase in concentration of Zn2+ and Cd2+, dosage of fly ash and temperature. The applicability of Langmuir isotherm suggests the formation of monolayer coverage Zn2+ and Cd2+ ions at the outer surface of the adsorbent. Thermodynamic parameters suggested the endothermic nature of the adsorption process. The fly ash was found to be an metal adsorbent as effective as activated carbon.