Role of modification of natural zeolite in removal of manganese from aqueous solutions

The natural zeolite (NZ) was obtained from Sivas-Yavu of Turkey and modified by ion-exchange (NH4NO3), alkali treatment (NaOH) and addition of aluminum (Al-2(SO4)(3)). The natural and modified samples were characterized by XRF, XRD, N-2 sorption, FUR, NH3-TPD, particle size distribution, SEM and TGA. Ion-exchange with NH4+ of NZ results in the exchange of the Na+ and Ca2+ cations and the partial exchange of the Fe3+ and Mg2+ cations. While the treatment of the NZ with NaOH leads to insignificant change of almost all cations, it causes significant dealumination and desilication of the NZ. FUR and TGA results showed that decationization, dealumination and desilication give rise to a decrease in hydrophilic nature of NZ. However, manganese adsorption of samples enhances their hydrophilic nature. Ion exchange and aluminum introduction increase surface area and pore volume of samples as well as surface acidity, whereas alkali treatment with NaOH decreases them due to partial collapse of structure with significant desilication and dealumination. All modifications, ion exchange, alkali treatment, and aluminum introduction, increased two times the manganese adsorption capacity of natural zeolites. The Freundlich isotherm model was best fitted to the isotherm data obtained due to a heterogeneous surface existence. (C) 2014 Elsevier B.V. All rights reserved.