Kinetics and Mechanism of Decarburization and Melting of Direct-Reduced Iron Pellets in Slag

An experimental study was conducted to understand the decarburization and melting behavior of direct-reduced iron (DRI) pellets in SiO2-Al2O3-CaO-MgO-FeO slags with various FeO concentrations (10 to 25 wt pct) and basicities (Bs), ranging from 1.5 to 2.5. The behavior of the pellet in slag was observed using the X-ray fluoroscopy technique; the rate of decarburization was simultaneously measured with a constant volume pressure increase technique. The study shows that the decarburization of DRI in slag at 1600 °C takes place in two stages. The first stage is the reaction between the FeO and the carbon inside the pellet, which is controlled by heat transfer from the slag to the pellet; the second stage involves the decarburization reaction between the FeO in the slag and the remaining carbon in the DRI. The kinetics of this stage is determined by the mass transfer of FeO in the slag and is strongly dependent on the FeO concentration. Depending on the physicochemical properties of the slag and the rate of gas evolution, the DRI may sink through, float inside the slag, or remain on top before complete decarburization.