Production and characterization of nano-magnetic material through different red mud reduction processes

Red mud (RM), is an industrial waste deriving from the production of primary aluminium, with about 200 Mtons generated annually. In this work, the reduction of RM for obtaining magnetic products with particular chemicalphysical characteristics has been explored. RM reduction was carried out in a semi-closed reducing environment at a high processing temperature (750–1100 ◦C) in the presence of carbon-rich ash (CA) resulting from a commercial pyro-gasification plant and by using an H2 atmosphere. All the materials were characterized by elemental analysis, XRD diffraction technique, SEM/EDX microscopy, thermogravimetry and infrared spectroscopy. The materials obtained under the different conditions have in common the presence of small iron-magnetic domains (with different iron oxidation states), in the order of hundreds of nanometres, and by the ferro-magnetic or paramagnetic response to an external magnetic field. In particular, the material pre-treated with HCl (enriched in iron) and reduced with H2 showed very good magnetic responses, more iron in reduced oxidative showing high ferro-magnetic responses to the external field. The synthesised materials are quite differents each states others and appear to have several potential fields of application, as sorbents for specific wastewater pollutants, as materials for CO2 capture, for catalysis and (bio)sensing applications. Nevertheless, the high interconnection between the magnetic and non-magnetic phases limit the direct separation or the iron enrichment. Further efforts should be focused on the functional studies and subsequent LCA and LCC analyses.