Investigation of Magnetite Oxidation Kinetics at the Particle Scale
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UCTION
THE pelletization of iron-ore fines is one of the widely practiced agglomeration techniques in iron and steel making because it enables the use of a very fine concentrate. Iron-ore pellets offer several advantages over other ferrous burdens in terms of strength, reducibility and uniformity of shape (spherical), chemistry, and porosity. Magnetite pelletization provides an added benefit in terms of energy, owing to the exothermic nature of its oxidation to hematite.[1] Magnetite ore that is excavated from mines is crushed, beneficiated, and ground into fines concentrate. The concentrate is balled into green pellets with the addition of moisture and additives, such as flux and binder. Thereafter, green pellets are fired in an induration furnace to impart
T.K. SANDEEP KUMAR, C. ANDERSSON, and B. BJORKMAN are with the Lulea University of Technology (LTU), 97187 Lulea, Sweden. Contact e-mail: [email protected] N.N. VISWANATHAN is with the Indian Institute of Technology Bombay (IITB), Mumbai 400076, India. H. AHMED is with the Lulea University of Technology (LTU) and also with the Center of Metallurgical Research and Development Institute, Cairo 11421, Egypt. A. DAHLIN is with the Luossavaara-Kiirunavara Aktiebolag (LKAB), 98381 Malmberget, Sweden. Manuscript submitted February 24, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
sufficient strength and to attain the desired properties. During induration, green pellets that are laid as a packed bed undergo updraft and downdraft drying [room temperature to 523 K (250 C)] followed by oxidation [573 K to 1023 K (300 C to 750 C)] and finally sintering [> 1273 K (1000 C)].[2] The hot gases are allowed to flow in the counter-current direction across the furnace for efficient heat transfer. To achieve and enhance stability in the production of homogeneous and good-quality pellets, a model is required to predict the optimum thermal and gaseous profile for pellets during induration. Therefore, it is necessary to understand and estimate the kinetics of the phenomena involved in magnetite pellet induration. The methodology used was to investigate each of the phenomena (oxidation, sintering, and heat transfer) on a single pellet in isolation, and subsequently integrate these to develop the overall induration model. Sintering models at the single-pellet scale have already been developed on the basis of their kinetics, and have been demonstrated in previous studies.[3,4] The oxidation kinetic model for magnetite pellets has been developed in two parts. We investigated the oxidation phenomenon of magnetite concentrate from the Luossavaara-Kiirunavara Aktiebolag (LKAB) mine in Malmberget, Sweden at the particle scale; estimated the oxidation kinetics; and determined the responsible mechanisms.
The kinetics that were estimated in this study will help to establish the oxidation behavior of magnetite at the pellet scale, which will be communicated in future. From the early 1950s, several researchers have studied the oxidation of magnetite pellets and investigated the effect of different s
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