Contents lists available at ScienceDirect Microporous and Mesoporous Materials journal homepage: www.elsevier.com/locate/micromeso Red mud as aluminium source for the synthesis of magnetic zeolite Claudia Belviso a,d,* , Anastasia Kharchenko b , Elisabetta Agostinelli c , Francesco Cavalcante a , Davide Peddis c , Gaspare Varvaro c , Nader Yaacoub e , Svetlana Mintova b a Istituto di Metodologie per l’Analisi Ambientale – CNR, Tito Scalo, PZ, 85050, Italy b Laboratoire Catalyse et Spectrochimie (LCS), ENSICAEN, Normandie Université de Caen, CNRS, Caen, 14050, France c Istituto di Struttura della Materia – CNR, Area della Ricerca di Roma1, Monterotondo Scalo, RM, 00015, Italy d Istituto di Struttura della Materia – CNR, Area di Tito Scalo, PZ, 85050, Italy e Institut des Molécules et Matériaux du Mans (IMMM) - UMR CNRS, Le Mans Cedex, 7 2085, France ARTICLE INFO Keywords: Red mud Aluminium source Zeolites Morphology Magnetic properties ABSTRACT Zeolite synthesis typically requires batch systems (precursor mixture) in which aluminate and silicate solutions are first mixed and then subjected to hydrothermal treatment. In this study, FAU and GIS types zeolite with wool ball-like morphology were synthesized using colloidal silica and red mud as an alternative aluminium source. The addition of aluminium powder to the precursor mixture composed by colloidal silica and red mud resulted in the crystallization of pure GIS-type zeolite with a cactus-like morphology. The crystalline products (GIS and FAU zeolites) were thoroughly characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and nitrogen adsorption. In addition, the magnetic properties of the zeolites were studied since the red mud used as aluminium source is mainly containing a mixture of magnetic iron-based oxides. The magnetic zeolites will be further considered for wastewater treatment, as they can be easily separated using an external magnetic field. 1. Introduction Zeolites are hydrated aluminosilicate minerals with a three-dimen- sional open structure consisting of aluminium and silicon tetrahedra linked by shared oxygen atoms. Zeolites have been synthesized using a variety of initial materials [1–13]. Some research has been focused on the use of natural minerals such as clays, pure aluminate and silica sources and waste materials mainly represented by coal and biomass ashes as well as red mud. The zeolite synthesis using natural sources is considered as not expensive process since it is using raw materials naturally available at low cost. A thermal pre-activation to convert the mineral sources into activated silica and aluminate is required prior their use in zeolite synthesis, and this significantly could reduce the economic benefits. Moreover, since the chemical composition of natural sources from different locations is not identical, the zeolite synthesis conditions need to be additionally optimized. On the other hand, during the last few years, the synthesis of zeolites using waste material has also attracted significant interest. Wastes composed by large amount of aluminosilicate and silicate phases (coal and biomass fly ash) are con- sidered as sources for zeolite syntheses. The process diverts the waste materials from disposal sites and transforms them into useful secondary products. The waste materials in some cases contain toxic elements which depend on the mode of their occurrence and could restrict them from certain applications [13]. Both FAU- and GIS- type zeolites have been prepared by direct transformation of natural sources [1,14–21], pure chemicals [22–25] and waste materials [4,26–31]. Recently alkaline pre-fusion and mi- crowave heating have been applied for the synthesis of zeolites [32–39]. Among these synthesis methods, the process requiring organic compounds as structure directing agents has been largely used mainly to direct the crystallization process of nanocrystalline and high silica zeolites [40–44]. Template-free synthesis [45–48] using pure aluminate and silicate suspensions, a seed growth approach [49], and multi-step synthesis [50–53] approaches have been wildly applied for the pre- paration of zeolites. In this study, FAU and GIS types zeolite with different morphologies using colloidal silica (Ludox HS-30) and an alternative aluminium source (red mud) were synthesized. Red mud (RM) is a waste material formed during the production of alumina when the bauxite ores are subjected to caustic leaching. It is mineralogically characterized by the presence of iron oxy-hydroxides (i.e., primarily hematite and goethite) with a minor percentage of aluminium hydroxides (i.e., boehmite). The red mud containing iron-based oxides with magnetic properties is ex- pected to induce a magnetic behavior to the final synthetic zeolites. The possible application of the magnetic zeolites will be in wastewater treatments, as they can be easily separated from the medium using an https://doi.org/10.1016/j.micromeso.2018.04.038 Received 19 December 2017; Received in revised form 16 April 2018; Accepted 24 April 2018 * Corresponding author. IMAA–CNR, Tito Scalo, Potenza, Italy. E-mail address: claudia.belviso@imaa.cnr.it (C. Belviso). Microporous and Mesoporous Materials 270 (2018) 24–29 Available online 02 May 2018 1387-1811/ © 2018 Elsevier Inc. All rights reserved. T