Effect of Magnesium Substitution on Siderite Thermal Decomposition in Air Atmosphere.

Siderite is a typical iron-bearing carbonate mineral, which is characterized by thermal instability. In this study, the thermal decomposition of natural siderite with magnesium (Mg) isomorphous substitution was performed in a flowing air atmosphere. During the thermal decomposition, X-ray diffraction, Mössbauer spectroscopy, transmission electron microscope, and vibrating sample magnetometer were employed to characterize the samples. Results indicated that siderite primarily transformed into maghemite and Mg–Fe spinel in oxidation decomposition, and no magnetite was detected. The synthetic spinel phases were highly stable and difficult to oxidize even at a roasting temperature of 700 °C because of the magnesium substitution. Owing to the ferrimagnetism of maghemite and Mg–Fe spinel, the magnetism of samples significantly improved during the oxidation decomposition. [ABSTRACT FROM AUTHOR]