Valorisation of industrial iron oxide waste to produce magnetic barium hexaferrite

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 ºC. The optimum ratio of Fe.Ba (producing 86 wt% BaM) was found to be 11:1 (non-stoichiometric), and secondary phases of α-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 m2 kg–1 and Hc=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 °C / 2 hr, with an increase in grain size up to 2 μm. 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.