The use of fly ash as a low cost, environmentally friendly alternative to activated carbon for the removal of heavy metals from aqueous solutions

The objective of this study was to compare fly ash and activated carbon for their ability to remove nickel [Ni(II)] and zinc [Zn(II)] from an aqueous solution. The effects of contact time, pH, initial metal concentration and amount of adsorbent on the adsorption process at 20 ± 2 °C were studied. Batch kinetic studies showed that an equilibrium time of 1 h was required for the adsorption of Ni(II) and Zn(II) on both adsorbents. The maximum metal removal was found to be dependent on solution pH (4.0 for Ni(II) and Zn(II)). With an increase in the concentrations of these metals, the adsorption of Ni(II) and Zn(II) decreased on both of the adsorbents. The effectiveness of fly ash as an adsorbent improved with increasing calcium (CaO) content. Adsorption data in the range of pH values (3.0–8.0) using Ni(II) concentration of 25 ± 2 mg/L and Zn(II) concentration of 30 ± 2 mg/L in solution were correlated using the linear forms of the Langmuir and Freundlich equations. The fly ash was found to be a metal adsorbent as effective as activated carbon.