Developing the Oxidation Kinetic Model for Magnetite Pellet

Abstract

Oxidation is a vital phenomenon for magnetite pellets in their excursion through the furnace during induration. One of the prerequisites for magnetite pellets to achieve homogeneously structured good quality pellets is to have complete oxidation before sintering begins. Partially oxidized magnetite pellets, upon sintering, might result in inhomogeneous structured pellets which could be detrimental to pellet quality. It is necessary to understand the mechanisms responsible for magnetite oxidation, and hence, it is intended in this study to investigate experimentally as well as develop a mathematical model based on oxidation kinetics. Oxidation of pellets is largely influenced by the oxidation kinetics of particles and hence should be studied at particle as well as at pellet scale. The principles of the Grain Model have been adopted to develop the Oxidation Model at pellet scale, whereas the particles' oxidation follows the Avrami Kinetic Model. Isothermal oxidation experiments performed Thermogravimetric Analyzer showed that oxidation rate of magnetite at pellet scale contained two peaks. They were complemented well by oxidation rates predicted from the model. Further, the pellet was investigated microstructurally at pellet and particle scale to substantiate the findings from the experiments and the model. The oxidation model developed is used to predict the progression of oxidation in the magnetite pellet with respect to the reaction time at three different temperatures (873 K, 973 K, and 1073 K (600°C, 700°C, and 800°C)) and at four levels of oxygen (0.21, 0.30, 0.60, and 1.00 atm) in the oxidizing gas.

Establishing a Novel Methodology to Correlate the Macroscopic and Microscopic Degree of Sintering in Magnetite Pellets during Induration

“…This methodology of quantifying microstructural images to estimate sintering degree is a step toward understanding and monitoring the sintering behavior more comprehensively in a semi‐automated manner. This methodology can further be utilized to determine the process kinetics parameters using the isothermal power law and the Arrhenius equation, as described in previous studies . Because sintering is the last stage during the induration process, it widely determines the final properties of the pellet.…”

“…Sintering of the pellets or porous compacts is accompanied by volumetric shrinkage when the sintering is carried out at high temperatures. Optical dilatometry, which is based on the principle of light optics, was used for this purpose, as described in previous studies . In optical dilatometry, shadow images are captured continuously and subsequently used to measure the shrinkage of the pellet and the sintering degree for a given thermal profile.…”

“…The green pellet was dried in an oven at 423 K overnight prior to being mounted and polished. The sintering behavior of oxidized and non‐oxidized magnetite pellets exposed to the different thermal profiles mentioned in Table were studied previously at the macroscopic scale . Thereafter, the same pellets were investigated microscopically in this study.…”

“…The difference in sinterablity of both of these phases at high temperatures results in different sintering behavior. To account for these factors, researchers have investigated sintering macroscopically using optical dilatometry for oxidized and non‐oxidized magnetite pellets . Isothermal sintering studies have been performed to estimate the kinetic parameters and predict the respective sintering behavior.…”