Valorisation of industrial iron oxide waste to produce magnetic barium hexaferrite

Abstract

Barium M-type hexagonal ferrite (BaM, BaFe12O19) is an immensely important magnetic material, which we have successfully made from the simple valorisation of Fe-rich industrial waste from steel wire drawing, with addition of BaCO3 and heating in air to 1000 degrees C. The optimum ratio of Fe. Ba (producing 86 wt% BaM) was found to be 11: 1 (non-stoichiometric), and secondary phases of alpha-Fe2O3 (non-magnetic) and ZnFe2O4 (poorly antiferromagnetic) were always present. This material consisted of small submicron platelets. A hard magnetic ferrite was produced with Ms=48.6 A m(2) kg(-1) and H-c=211.5 kA m(-1). The highest density was achieved by sintering samples with Fe: Ba ratios of 11: 1 and 12: 1 at 1200 degrees C /2 hr, with an increase in grain size up to 2 mm. The sintered 11: 1 had electrical conductivity comparable to that of commercial sintered BaM. Such materials are suitable for industrial applications as hard magnets, and EM shielding in architectural and construction materials.