Effect of Particle Size of MgO on the Sinter Strength before and after Reduction and Its Mechanism Analysis

It is a popular countermeasure to add MgO into sinter to cope with the use of high-Al2O3 iron ore. The effects of particle size with MgO-bearing flux on the strength of a sintered sample (Fe2O3-MgO and Fe2O3-MgO-CaO series) are discussed in the present work for the purpose of improving sinter strength before and after reduction. The experimental results show that (1) with the increase in fine light calcined magnesite (LCM) from 0 to 100%, the compressive strength with the Fe2O3-MgO series increased from 5.66 to 7.42 MPa before reduction and from 2.49 to 6.03 MPa after reduction, and the compressive strength with the Fe2O3-MgO-CaO series increased from 4.62 to 7.01 MPa before reduction and from 4.00 to 6.23 MPa after reduction. The result of the sintering pot experiment conformed with the laboratory result. In actual production, LCM with a 50% fine grind should be added into the sinter based on economic concerns and environmental protection. (2) The ball-to-ball model was introduced to explain the reason that the sample compressive strength increased with the increase in fine LCM addition before reduction. (3) To quantitatively analyze the relationship of mineralization rate and particle size with MgO-bearing flux, the mineralization reaction experiment was carried out in the study and the result was as follows: the diffusion layer thickness and diffusion rates with coarse MgO-bearing flux were 250.8 μm and 12.54 μm·min−1, respectively, and those of fine MgO-bearing flux were 397.1 μm and 19.86 μm·min−1, respectively. The experimental results also explained the reason that more fine LCM increased the compressive strength of the sample before reduction. (4) The more compact and uniform microstructures and less transformation of Fe2O3 to Fe3O4 resulted the increase in compressive strength with finer MgO-bearing flux after reduction. Based on above results, adding fine MgO-bearing flux to the sinter is effective in enhancing the sinter quality.