Characterization of magnetite in silico-aluminous fly ash by SEM, TEM, XRD, magnetic susceptibility, and Mossbauer spectroscopy

Spinel magnetite contained in a silico-aluminous fly ash (originating from la Maxe's power plant, near Metz in the east of France) issued from bituminous coal combustion has been studied by scanning and transmission electron microscopy linked with energy dispersive spectroscopy, X-ray diffraction, susceptibility measurements, and Mossbauer spectroscopy. The results show that in this magnetite Mg is strongly substituted for Fe and the chemical formula is closer to MgFe2O4 than Fe3O4. Magnetite also contains Mn, Ca, and Si elements, but at a lower proportion. The results are compatible with the chemical formula Fe2.08Mg0.75Mn0.11Ca0.04Si0.02O4 and crystallochemical formula [Fe0.922+Ca0.062+Si0.024+](letra)[Fe3+Fe0.162+Mg0.732+Mn0.112+]O-octa(4), showing the cation distribution on octahedral and tetrahedral sites of the spinel structure. The reason Mg element is not incorporated in soluble surface Salt and in glass composition of the silico-aluminous fly ashes is now understood. (C) 1999 Elsevier Science Ltd. All rights reserved.