Effect of Particle Size on Magnetite Oxidation Behavior: A Modeling Approach Incorporating Ultra-Fine Particle Effects

Abstract Magnetite concentrates, essential for pellet production, often contain a high proportion of fine particles. These fine particles significantly influence the induration process. Understanding their oxidation behavior is crucial for optimizing pellet quality. Previous research primarily focused on magnetite particles larger than 25 µ m. This study extends the investigation to finer size fractions below 7 µ m. Isothermal oxidations were conducted on three different size fractions from two different mines, using a thermogravimetric analyzer (TGA) at 973 K and 1073 K, followed by light optical microscopy to observe the structural evolution of hematite. The oxidation of magnetite exhibits a two-step phenomenon: an initial stage characterized by a high oxidation rate, followed by a second stage where the oxidation degree increases at a constant rate. The oxidation behavior of both studied concentrates follows a consistent pattern: finer particles exhibit faster oxidation than coarser particles, resulting in a higher oxidation degree in a specific duration. Particles in the finer size range (< 7 µ m) undergo complete oxidation during the initial stage. A predictive model based on the Avrami kinetic equation was developed to assess the effect of particle size on magnetite oxidation. The model demonstrated a high validation (98 pct), indicating that particle size is a reliable predictor of magnetite oxidation behavior.