Removal of heavy metals from aqueous solutions by adsorption on zeolites synthesized from aluminum saline slags
Alejandro Jiménez, Raquel Trujillano, V. Rives, Miguel Á. Vicente, A. Gil
Abstract
• Faujasite and analcime zeolites were ecofriendly synthesized from aluminum salt cake. • Heavy metals (Cu, Cd, Pb) were successfully removed from aqueous solution by faujasite. • The experimental results were fitted to the pseudo-first order kinetic model. • The removal of Me 2+ is based on a cation exchange process. • Toth’s is the best model describing the adsorption of Me 2+ on faujasite. Three heavy metals (Cu 2+ , Cd 2+ and Pb 2+ ) were removed from aqueous solutions using zeolites prepared from saline slags, a very important waste generated during aluminum recycling. Zeolites were characterized by powder X-ray diffraction, thermal analysis, Fourier transform infrared spectroscopy, X-ray microfluorescence, element chemical analysis, nitrogen adsorption at −196 °C and electron microscopy. The textural and structural properties of X-type faujasite zeolite convert it in a promising adsorbent in aqueous streams. Removal of the heavy metals was evaluated in batch mode, studying the adsorbent dose, the initial concentration of the heavy metal, the selectivity of the solid in case of mixtures with various metal cations and the recyclability of the solid. The kinetic and equilibrium results were evaluated using both pseudo-first- and pseudo-second-order kinetics, and Langmuir, Freundlich and Toth equation isotherms for the equilibrium. The time needed to reach equilibrium was between 10 and 20 min. Faujasite was highly effective in removing Cu 2+ , Cd 2+ and Pb 2+ from aqueous solutions, much higher than analcime and pollucite, other two zeolites recently synthesized by us from aluminum slags, and used in this work for comparison purposes. The maximum adsorption capacity was 591 mg/g for Pb 2+ , 304 mg/g for Cu 2+ and 279 mg/g for Cd 2+ .