Phase Transformation of Hematite to Magnetite Under Microwave Treatment

Phase transformations of natural and synthetic hematite in aqueous Fe (II)-containing medium under the influence of microwave radiation at a temperature range from room temperature to 260°С and pressure of 6 MPa were investigated. The saturation magnetization of all initial samples was less than 1 A∙m2/kg, while the saturation magnetization of the samples after phase transformations increases significantly (i.e., up to 27 A·m2/kg). It was shown by X-ray diffraction that all samples were transformed into magnetite. Thermomagnetic curves were measured for the treated samples and Curie temperatures were determined. Curie temperatures of the samples of natural hematite were determined as 560 °C and for synthetic hematite as 559°C that are close to the Curie temperature of pure magnetite (580°C). The relatively high saturation magnetization of obtained magnetic particles makes them promising for different applications (adsorbents of radioactive waste, carriers for magnetic drug targeting, etc.). The results of this investigation could also be useful for developing new technologies for production of iron ore concentrates from the hematite-containing waste of mining and processing plants.