Interaction between iron oxides and olivine in magnetite based pellets during reduction at temperatures below 1000°C

In this work, the solid state diffusion of magnesium was studied in magnetite based pellets at temperatures between 500 and 1000°C. The samples were laboratory produced pellets with a largely exaggerated addition of olivine. The results showed that the olivine particles after oxidation had decomposed along the particle boundary and turned into magnesioferrite crystals and pyroxene/vitreous silica. Large patches of magnesioferrite rich in magnesium oxide were spread out among the haematites in the interior of the pellet. In the subsequent reduction, the haematite was converted to magnetite at 500°C. At temperatures of 800°C and above, the magnesium in the magnesioferrite diffused out to the secondarily formed magnetite and wüstite. During reduction at 600–700°C, cracks appeared along this boundary as the haematite transferred into secondary magnetite. Comparison to a commercial olivine pellet showed that the diffusion of magnesium followed the same pattern as in the laboratory pellets.