Interaction between Iron Oxides and Olivine in Magnetite Pellets during Reduction to Wustite at Temperatures of 1000–1300°C

Abstract

In this study the magnesium diffusion behaviour was studied in pellets with fine and course olivine, with and without additional fine quartzite (<20 μm) after isothermal reduction at 1000–1300°C. It was found that, by using a fine olivine (<38 μm) the whole magnesium content of the olivine was dissolved evenly in the wustite and in the slag, already at 1000°C, in agreement with the equilibrium tie-lines of the FeO–MgO–SiO₂ phase diagram. This lead the liquid slag to precipitate into fayalitic olivine and the Al, Na, K, Ca, P-content to enrich in remaining inclusions in the olivine. This crystallization did not occur in the sample with only bentonite addition, or in the sample with unreactive olivine at these temperatures. However, with further addition of fine quartzite, the slag of the sample with coarse olivine also crystallized. In the samples reduced at 1000–1100°C, magnesium gradients could be detected in the slag phase around coarse olivine particles until entering the interaction volume of an interfering particle at around ~600 μm, or occasionally at distances of more than 1 mm. For the coarse olivine the main rise in magnesium occurs at 1200°C when the olivine particle cores begin to dissolve. The dissolution of all magnesium of the 2.5% olivine addition during oxidation lead to 6.5% Mg in the crystallized slag phase. The increase in melting point resulting from this compared to fayalite with no magnesium is ~50°C, according to thermodynamic calculations.