Synthetic magnetic zeolites from waste materials: fly ash and red mud

In this study, a new method is proposed to synthesise magnetic zeolites with suitable magnetic properties without the addition of iron oxide magnetic nanoparticles. The precursors employed for the synthesis are two waste materials, such as red mud (RM) and fly ash (FA), which are abundant, easy to recover and inexpensive. In addition, large amounts of FA and RM are deposited in landfills resulting in an increasing environmental problem. The two waste materials were chosen for use in this synthesis because they both contain iron-based oxides, which are the most common magnetic materials used to induce magnetic properties in zeolites. RM is a waste material formed during the production of alumina when the bauxite ores are subjected to caustic leaching. The risk associated with red mud wastes is primarily due to the cumulative contamination of land and the surrounding dwellings. RM wastes are mineralogically characterised by the presence of iron oxides (i.e., primarily hematite and goethite with a minor boehmite component), aluminium hydroxides, calcium oxides, titanium oxides, aluminosilicate minerals and sodalite occur as traces. However, the RM mineralogical composition varies due to the differences in the bauxite ores and the refining processes employed. the use of this waste material for zeolite synthesis has not been previously reported. FA is a by-product of thermal power plants and is used in concrete and cement manufacturing. FA is primarily composed of amorphous aluminosilicate and minerals, such as quartz and mullite. In addition, hematite, magnetite and carbon may also be present. More than half of fly ash is disposed of in landfills but in the last few years, much research has been focused on its use in solutions to environmental problems as well as for the synthesis of zeolites. The structural and magnetic investigation performed on the synthetic products by multidisciplinary approach indicated that different types of zeolites were obtained for different FA/RM percentages 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. This ability is even more useful taking into account the absorbance properties showed by the synthetic zeolites and determined by RO16 absorption tests. The synthetic newly-formed minerals can in fact be used to solve water pollution problems and after their action they can be easily removed from solution. The magnetic properties of the waste materials precursors is also studied.