The modification of aluminium content of natural zeolites with different composition

Abstract

A series of natural zeolites with different compositions were modified by formation of hydrated aluminium oxide onto the zeolite structure after NaOH treatment of the natural zeolites. Natural and modified zeolites were characterized by XRD, SEM, N-2 adsorption-desorption, FTIR, zeta potential and temperature-programmed desorption of ammonia (NH3-TPD). The treatment with NaOH and then aluminium loading significantly alter zeolite characteristics depending on zeolite composition and structure. The treatment with NaOH causes significant desilication and partial dealumination of the zeolites irrespective of their compositions. The presence of quartz and feldspar phases in the zeolites increases their stability towards alkali treatment. Aluminium introduction into the zeolites treated with NaOH leads to reorganisation of zeolite structure and surface characteristics. The introduction amount of aluminium is strongly related with zeolite composition that aluminium oxide phase is detected on zeolites undergone highly desilication with NaOH treatment. Both alkali treatment and aluminium loading dramatically alter distribution of acid sites in the zeolites that while alkali treatment increases mostly strong acid sites of zeolites, aluminium loading enhances weak and medium acid sites. Enhanced aluminium content of zeolites improved its manganese adsorption capacity depending on their composition. (C) 2018 Elsevier B.V. All rights reserved.