Synthesis of magnetic zeolite at low temperature using a waste material mixture: Fly ash and red mud

• Mixtures of hazardous residues (fly ash and red mud) were used to form zeolite.
• Magnetic zeolites were obtained without adding any extra iron oxide nanoparticles.
• Magnetic properties did not influence adsorption capacity of synthetic zeolites.
• Synthetic zeolites can be easily separated from the medium by an external magnet.

A low temperature environmentally friendly synthesis of magnetic zeolites by hydrothermal activation is reported. The novelty of the process is related to the use of a mixture of waste materials (fly ash (FA) and red mud (RM)) as precursors for the one-step synthesis (without passing through the additional synthesis of magnetic nanoparticles) of zeolites with good magnetic properties. The structural and magnetic investigation indicated that different types of zeolites were obtained for different FA/RM percentages and incubation temperatures, and all of these zeolites possess sufficiently high magnetic moments to enable their easy separation from the solution using an external magnet. Therefore, the time consuming and expensive high performance centrifugation processes, which are typically employed to recover zeolites, can be eliminated. In detail, sodalite and mixed Ti–Fe oxides formed using the 80% RM mixture, and a higher amount of A-type zeolites was observed for the 50% RM mixture. However, a mixture of A-, X- and ZK-5-type zeolites was obtained using 20% RM. The global magnetic properties of the newly formed minerals are discussed based on the magnetic properties of the precursors in which different magnetic behaviours were observed. A preliminary characterisation of the synthetic products was performed.

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