resumo
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 degrees 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 alpha-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, gamma-Fe2O3, which is magnetically soft, with M-s and H-c values lower than those of SrM. The recycled waste magnetic materials had M-s values of 37-59 A m(2) kg(-1), and H-c values of 13-40 kA m(-1). Thus, a highly magnetic soft-magnet ceramic is made from the simple thermal remediation of these wastes.
palavras-chave
HEXAFERRITES; PIGMENTS
categoria
Environmental Sciences & Ecology
autores
Pullar, RC; Hajjaji, W; Amaral, JS; Seabra, MP; Labrincha, JA
nossos autores
João António Labrincha Baptista
Professor Catedrático
João Cunha de Sequeira Amaral
Investigador Auxiliar
Maria Paula Seabra
Professor Auxiliar
Rob Pullar
Colaborador
Walid Hajjaji
Bolseiro de pós-DoutoramentoGrupos
G2 - Materiais Fotónicos, Eletrónicos e Magnéticos
G4 - Materiais Renováveis e Economia Circular
agradecimentos
R. C. Pullar wishes to thank the FCT Ciencia2008 programme for supporting this work. W. Hajjaji thanks FCT for the Grant SFRH/BPD/72398/2010 co-financed by Programa Operacional Potencial Humano POPH.