Role of Modification of Natural Zeolite in Removal of Arsenic from Aqueous Solutions

The adsorption of arsenic from aqueous solution onto natural and modified zeolites was investigated. The natural zeolites were modified by ion-exchange (NH4NO3) and addition of aluminum (Al2(SO4)3). The natural and modified zeolites were characterized by XRF, XRD, N2 sorption, FTIR, NH3-TPD, zeta potential and SEM. Ion-exchange with NH4+ of NZ results in the significant exchange of most cations and an increase in surface area and pore volume of samples as well as surface acidity. While the introduction of aluminum into the zeolite increased its As (V) removal amount, it decreased its As (III) removal. Ion-exchange with NH4+ of the natural zeolite increased significantly its As(III) and As(V) adsorption capacity. The adsorption of both As(III) and As(V) with natural and modified zeolites obeys pseudo second order kinetics. The Langmuir isotherm model for all adsorbents was best fitted to the isotherm data obtained. The highest adsorption capacity for As(III) and As(V) was obtained onto the zeolite modified with ammonia and their calculated qm values are 28.7 mg/g and 36.6 mg/g, respectively. The calculated thermodynamic parameters indicated that the adsorption process was spontaneous and favorable.