Research and Development Company TOREX, Yekaterinburg, Russia¹ ; Ural Federal University named after the first President of Russia B.N. Yeltsin, Yekaterinburg, Russia²
I. S. Bersenev, Cand. Eng., Head of the Research and Analysis Department¹, Associate Prof.², e-mail: i.bersenev@torex-npvp.ru

National University of Science and Technology MISIS, Moscow, Russia
A. M. Bizhanov, Cand. Eng., Leading Expert

Research and Development Company TOREX, Yekaterinburg, Russia
E. R. Sabirov, Engineer

Ural Federal University named after the first President of Russia B.N. Yeltsin, Yekaterinburg, Russia
N. A. Spirin, Dr. Eng., Prof., Head of the Dept. of Thermal Physics and Informatics in Metallurgy

The contact surface of the solid mineral phase and gas determines the behaviour of pellets in metallurgical processes, which are determined by topochemical reactions of oxidation (in induration) and reduction (in shaft furnaces). In the present paper authors have estimated the value of the specific surface area of the pore space of fired iron ore pellets. The results of pellet sample scanning by electron microscopy and computed tomography have been used as input data, mathematical modelling (numerical simulation) - as methodology. Metallisation grade (DR) and blast furnace grade (BF) pellets have been used for the study. Their differences are in the basicity and content of total iron (DR: CaO/SiO₂=0.357 and Fe=67.2; BF: CaO/SiO₂=0.060 and Fe=64.0). The total pore area was 8.47 cm2/g and 8.81 cm²/g for BF and DR grade, respectively. This value is ~200 times lower than the specific surface area of the concentrate out of which the pellets have been produced. The most probable pore value in the iron ore pellet, which is due to the thermodynamic conditions of sintering, corresponds to an equivalent diameter of 70...90 μm. The method proposed in the paper and the results can be used in a comprehensive study of the structure of pellets and, as statistical data accumulate, will make it possible to assess the relationship between porosity and metallurgical properties - reducibility, compression strength, strength during reduction. Theoretical analysis and comparison of the characteristics of the samples has showed that from the point of view of the features of the macrostructure and the value of the specific surface area of the pores of pellets, there is no difference between the samples of DR and BF grade pellets. In this case, the behaviour of pellets during temperature-reduction treatment in a blast furnace or metallization furnace (DR module) will be determined exclusively by changes in the parameters of the microstructure, i.e. reduction of iron oxides with rearrangement of the crystal lattice, occurrence and relaxation of internal stresses etc.

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