Study of the oxidation process of magnetite fluxed pellets by various methods of physical and chemical analysis

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Abstract

In order to obtain the most complete information about the processes occurring during the oxidative roasting of magnetite iron ore pellets, comprehensive studies were carried out using various methods of physicochemical analysis. To approximate the assessment of the most probable reactions occurring in pellets during oxidative heating, a thermodynamic analysis was performed. Based on the sign of the isobaric potential, determined from the equation of the isotherm of a chemical reaction, we judged the possibility of a particular chemical reaction occurring in the direction under consideration. The influence on the dissociation reaction of calcium carbonate has been established by the formation of calcium silicates and ferrites, which facilitate its occurrence, as well as the reaction of interaction of iron oxide with calcium carbonate, which, on the contrary, inhibits its occurrence. A technique has been developed for thermographic analysis of solid-gas systems filtered through a layer of granular material, which was implemented on an installation that allows experiments with pellets in a gas flow with different oxygen contents, temperatures and heat treatment durations. It has been experimentally established that decarbonization of pellets occurs most completely and quickly in an atmosphere of inert monatomic gas, as well as in a mixture of gases that do not contain carbon dioxide. The data obtained are in good agreement with the data of thermodynamic analysis. Mineralogical studies were carried out on samples of magnetite fluxed pellets in a wide temperature range. The pellets were heated in accordance with a differential heating curve to certain temperatures, and then cooled in order to fix the structure formed by the time the specified temperature was reached. The results obtained on the considered processes of magnetite oxidation, decomposition of carbonates and formation of ferrites and silicates are in fairly good agreement with the data of the thermodynamic analysis. The results obtained in this work are of particular interest to specialists involved in the development of technologies that ensure the production of pellets with high metallurgical properties.

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About the authors

B. P. Yur’ev

Federal State Autonomous Educational Institution of Higher Education “Ural Federal University named after the first President of Russia B.N.Yeltsin”

Author for correspondence.
Email: yurev-b@mail.ru
Russian Federation, Ekaterinburg

V. A. Dudko

Federal State Autonomous Educational Institution of Higher Education “Ural Federal University named after the first President of Russia B.N.Yeltsin”

Email: yurev-b@mail.ru
Russian Federation, Ekaterinburg

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Supplementary files

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2. 1. Diagram of the experimental setup: 1 – Kurnakov pyrometer, 2 – thermocouples, 3 – vessel with inert substance, 4 – reaction vessel with test sample, 5 – rheometer, 6 – resistance furnace, 7 – block.

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3. 2. The effect of the composition of the gas phase on the temperature (1) and the time interval (2) during which the maximum intensity of the decarbonization process occurs. The arrows indicate the dependence of oxygen content on the duration of heat treatment and temperature.

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4. Fig. 3. Graph of the temperature change of the sample (2) and the readings of the differential thermocouple (1) over time when heated in an air stream.

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5. Fig. 4. Microstructure of the initial (a) and annealed fluxed samples heated in an air stream to 510 (b), 580 (c) and 660 °C (d): 1 – magnetite; 2 – hematite; 3 – calcite; 4 – non-metallic minerals; 5 – pyrite Survey in reflected light with a 150x magnification microscope.

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6. 5. Microstructure of fluxed samples fired in an air stream at a temperature of 900 °C with a 10-minute exposure (a), 1000 °C with a 2-minute exposure (b), 1000 °C with a 3-minute exposure (c), 1000 °C with a 10-minute exposure (d, e) and 19 min (e): 1 – magnetite; 2 – hematite; 3 – initial non-metallic minerals; 4 – slag mass; 5 – calcium ferrites; 6 – pyrite. Shooting in reflected light with a microscope magnification of 150x (a, c, d, e); 700x with oil immersion (b).

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