Oxide coating mechanism during fluidized bed reduction: solid-state reaction characteristics between iron ore particles and MgO

Abstract

Experiments on the solid-state reaction between iron ore particles and MgO were performed to investigate the coating mechanism of MgO on the iron ore particles’ surface during fluidized bed reduction. MgO powders and iron ore particles were mixed and compressed into briquettes and, subsequently, roasted at different temperatures and for different time periods. A Mg-containing layer was observed on the outer edge of the iron ore particles when the roasting temperature was greater than 1173 K. The concentration of Fe in the Mg-containing layer was evenly distributed and was approximately 10wt%, regardless of the temperature change. Boundary layers of Mg and Fe were observed outside of the iron ore particles. The change in concentration of Fe in the boundary layers was simulated using a gas–solid diffusion model, and the diffusion coefficients of Fe and Mg in these layers at different temperatures were calculated. The diffusion activation energies of Fe and Mg in the boundary layers in these experiments were evaluated to be approximately 176 and 172 kJ/mol, respectively.

Keywords

fluidized beds / coating / solid reaction / ferric oxide / magnesia / diffusion coefficient

References

[1] Schenk J.L. Recent status of fluidized bed technologies for producing iron input materials for steelmaking. Particuology, 2011, 9(1): 14.

[2] Weiss B., Sturn J., Voglsam S., Strobl S., Mali H., Winter F., Schenk J. Structural and morphological changes during reduction of hematite to magnetite and wustite in hydrogen rich reduction gases under fluidised bed conditions. Ironmaking Steelmaking, 2011, 38(1): 65.

[3] Guo L., Gao H., Yu J.T., Zhang Z.L., Guo Z.C. Influence of hydrogen concentration on Fe₂O₃ particle reduction in fluidized beds under constant drag force. Int. J. Miner., Metall. Mater., 2015, 22(1): 12.

[4] Takafumi M., Hidehiro K., Masayuki H. The mechanism of defluidization of iron particles in a fluidized bed. Powder Technol., 1996, 89(3): 231.

[5] Levy E.K., Celeste B. Combined effects of mechanical and acoustic vibrations on fluidization of cohesive powders. Powder Technol., 2006, 163(1-2): 41.

[6] Zhu C., Liu G.L., Yu Q., Pfeffer R., Dave R.N., Nam C.H. Sound assisted fluidization of nanoparticle agglomerates. Powder Technol., 2004, 141(1-2): 119.

[7] Bartels M., Lin W.G., Nijenhuis J., Kapteijn F., van Ommen J.R. Agglomeration in fluidized beds at high temperatures: mechanisms, detection and prevention. Prog. Energy Combust. Sci., 2008, 34(5): 633.

[8] Shao J.H., Guo Z.C., Tang H.Q. Effect of coating MgO on sticking behavior during reduction of iron ore concentrate fines in fluidized bed. Steel Res. Int., 2012, 84(2): 111.

[9] Zhong Y.W., Wang Z., Guo Z.C., Tang H.Q. Prevention of agglomeration/defluidization in fluidized bed reduction of Fe₂O₃ by CO: the role of magnesium and calcium oxide. Powder Technol., 2013, 241, 142.

[10] Guo L., Yu J.T., Tang J.K., Lin Y.H., Guo Z.C., Tang H.Q. Influence of coating MgO on sticking and functional mechanism study during fluidized bed reduction of vanadium titano-magnetite. J. Iron Steel Res. Int., 2015, 22(6): 464.

[11] Li Q., Rudolph V., Peukert W. London-van der Waals adhesiveness of rough particles. Powder Technol., 2006, 161(3): 248.

[12] Guo L., Tang J.K., Tang H.Q., Guo Z.C. Influence of different MgO coating methods on preventing sticking during reduction of Fe₂O₃ particles in a fluidized bed. Mater. Today Proc., 2015, 2, S332.

[13] Komarneni S., Frengeau E., Breval E., Roy R. Hydrothermal preparation of ultrafine ferrites and their sintering. J. Am. Ceram. Soc., 1988, 71(1): C-26.

[14] Komarneni S., D’Arrigo M.C., Leonelli C., Pellacani G.C., Katsuki H. Microwave-hydrothermal synthesis of nanophase ferrites. J. Am. Ceram. Soc., 1998, 81(11): 3041.

[15] Zubets A.V. Mechanism of ferrite spinel formation revisited. Inorg. Mater., 2002, 38(7): 718.

[16] Moustafa S.F., Morsi M.B. The formation of Mg ferrite by mechanical alloying and sintering. Mater. Lett., 1998, 34(3-6): 241.

[17] Šepelák V., Schultze D., Krumeich F., Steinike U., Becker K.D. Mechanically induced cation redistribution in magnesium ferrite and its thermal stability. Solid State Ionics, 2001, 141-142, 677.

[18] Schmalzried H. Solid State Reactions, 1981

[19] Brown W.E., Dollimore D., Galwey A.K. Comprehensive Chemical Kinetics: Reactions in the Solid State, 1980

[20] Li J., Shen N., Wang Q., Chen S.J. Non-isothermal kinetics of the synthesis reaction of magnesium ferrite. J. Univ. Sci. Technol. Beijing, 2008, 30(9): 1029.

[21] Fukuyama H., Hossain M.K., Nagata K. Solid-state reaction kinetics of the system CaO–FeO. Metall. Mater. Trans. B, 2002, 33, 257.

[22] Hua Y.X. Introduction to Metallurgical Process Dynamics, 2004 299.

[23] Cui G.W. Defects, Diffusion and Sintering, 1990 52.

[24] Guo L., Zhong Y.W., Gao J.T., Yang Z.R., Guo Z.C. Influence of coating MgO with coprecipitation method on sticking during fluidized bed reduction of Fe₂O₃ particles. Powder Technol., 2015, 284, 210.

[25] Zhang B., Gong X.Z., Wang Z., Guo Z.C. Relation between sticking and metallic iron precipitation on the surface of Fe₂O₃ particles reduced by CO in the fluidized bed. ISIJ Int., 2011, 51(9): 1403.

[26] Zhang Q.S. Foundation of Inorganic Materials Science, 2007 236.