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, Mossbauer 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 degrees 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.