Synthesis and characterization of nanometric titania coated on granular alumina for arsenic removal

The adsorption process is widely used for the treatment of drinking water sources containing high levels of arsenic. The choice of the adsorbent is crucial for the efficiency of the process. Very good performances were obtained in the past by activated alumina, while more recent studies have shown that also other media such as titanium oxide can provide high removal rates. In the present work, four types of adsorbents were tested for their removal capability of pentavalent arsenic from liquid solutions. Specifically, it was investigated if modifications of activated alumina by coating with titanium oxide nanoparticles or by reducing particle size might improve their performance. The adsorbents were firstly characterized by X-ray diffraction, BET specific area measurement and SEM analysis. Then, kinetics, equilibrium isotherm experiments were conducted in batch mode at fixed pH. All the tested adsorbents showed satisfactory arsenic removal, with the best performance obtained by the mesoporous gamma-alumina which had the lowest grain size. The titanium coating did not appear to significantly improve adsorption capacity. The kinetic data were best fitted by the pseudo-second order model, while both the Freundlich and the Langmuir equations well represented the adsorption isotherm data.