Magnetic Properties of Ferrite Ceramics Made from Wastes

Abstract

Iron-rich industrial waste sludge (62 % Fe2O3) was processed to produce recycled chromatic and magnetic materials. In this paper we report on combining the waste with stoichiometric amounts of oxides, which were then fired to produce SrM hexagonal ferrite (SrFe12O19) based ceramic powders. A series of powders were made from pure oxides for comparison. All samples were fired in air at 1,050–1,150 °C, and analysed by use of XRD (X-ray diffraction) and VSM (vibrating sample magnetometry). The firing of SrM stoichiometric mixtures derived from Fe-rich waste sludge did not result in a hard SrM ferrite product, but instead resulted in strongly magnetic but soft ferrites, which were a mixture of SrM and spinel phases, along with nonmagnetic α-Fe2O3. XRD and VSM data strongly suggested that the 21 % volatile organic fraction of the waste was burnt out during firing, reducing some of the Fe3+ to form magnetite, Fe3O4, which was then oxidised on cooling in air to form maghemite, γ-Fe2O3, which is magnetically soft, with Ms and Hc values lower than those of SrM. The recycled waste magnetic materials had Ms values of 37–59 A m2 kg−1, and Hc values of 13–40 kA m−1. Thus, a highly magnetic soft-magnet ceramic is made from the simple thermal remediation of these wastes.