Synthesis and magnetic properties of magnetite prepared by chemical reduction from hematite of various particle sizes

Highlights: • Hematite of different sizes was reduced to magnetite. • CO was obtained by air blowing through a layer of carbon. • Hematite particles of 0.05–0.4 mm completely transforms. • Reduction method for magnetite manufacturing from tailings. In the process of beneficiating iron ores by the magnetic separation, particles of hematite and quartz accumulate, forming tailings that occupy large areas of agricultural lands. Such man-made deposits are quite common and contain large quantities of iron oxides such as hematite. Therefore the tailings can be used as raw material for the production of magnetite. In this work, magnetite was synthesized by hematite reduction at a temperature of 500 °C in an atmosphere of carbon monoxide. The source hematite was separated initially into ten particle size categories ranging from 0.05 to 2.5 mm. The reduction was carried out with carbon monoxide, which was synthesized by reaction of air and activated carbon at 750 °C. It was determined by X-ray diffraction analysis and magnetometry that, after reduction, samples of each particle size consisted mainly of magnetite. In addition, the magnetic properties of the resulting magnetite were noted to be somewhat different from those of natural magnetite. In particular, remanence and coercivity are higher for synthetic magnetite than for natural magnetite. The saturation magnetization of transformed samples increases to 60–80 Am²/kg, while the source hematite does not have strong magnetic properties. Hematite with a particle size from 0.05 to 0.25 mm is completely converted into magnetite, but if the size of hematite particles increases to from 0.25 to 2.5 mm, incomplete conversion of hematite to magnetite is observed. The obtained results are important for the development of technology for converting hematite to magnetite, which can, in turn, be used to beneficiate iron ores.