Abstract
During the induration of fluxed taconite pellets, alkali salts deposit on the grate support bars, causing severe corrosive degradation of these alloys. To determine the source of these deposits and to understand the mechanism by which the salts are conveyed to the grate bars, a study of the reactions between fluxed pellets and combustion gas was carried out. The study focused on the thermodynamics and kinetics of several processes associated with induration; namely, oxidation of magnetite, calcination of flux, and the formation and gaseous transport of various alkali salt species. Both theoretical and experimental techniques were used. It was concluded that the principal source of alkali salt deposits is alkali chlorides, which are present as contaminants in the flux and/or residue from contaminated washwater. The pathway from pellet to grate bar involves the following steps: evaporation of chloride salts within the pellet; diffusion of salt vapor out of the pellet, aided by the outflow of CO2 from calcination of the flux; convective transport by the combustion gas with concurrent (partial) conversion to alkali sulfates by reaction with residual SOx in the combustion gas; and condensation of salts on the grate bars.
Similar content being viewed by others
References
Alcock, C.B., and Hooper, G.W., 1959, “Measurement of vapor pressure at high temperatures by the transportation method,” in Physical Chemistry of Process Metallurgy Part I, G.R. St. Pierre, ed., Interscience, New York, pp. 325–340.
Crank, J., 1975, The Mathematics of Diffusion, 2nd Ed., Oxford University Press, pp. 96–97.
Halle, J.C., and Stern, K.H., 1980, “Vaporization and decomposition of Na2SO4 thermodynamics and kinetics,” J. Phys. Chem., 84 (13), pp. 1699–1704.
Merten, U., and Bell, W.E., 1967, “The transpiration method,” in The Characterization of High Temperature Vapors, J.L. Margrave, ed., John Wiley & Sons, pp. 91–114.
Mohanty B.P., and Shores, D.A., 1992, Handbook of Case Histories in Failure Analysis, K.A. Esaklul, ed., ASM, pp. 357–61.
Mohanty, B.P., 1994, “Role of Chlorides in High Temperature Corrosion of Fe-Cr-Ni Grate Casting Alloy During Induration of Fluxed Taconite Pellets,” Ph.D. Thesis, submitted to the University of Minnesota Graduate School, November, 155 pp.
Norman, J.H., and Winchell, P., 1970, “Vapor pressure methods,” in Physico-chemical Measurements in Metals Research, R.A. Rapp, ed., Vol. IV, pp. 131–145.
Oja, K.G., 1988, “Self-fluxed pellets,” Skillings’ Mining Review, July, pp. 4–8.
Papanastassiu, D., and Bitsianes, G., 1973, Met. Trans., 4, pp. 477–496.
Roine, A., 1993, “Outokumpu HSC Chemistry for Windows (Ver. 1.10),” Outokumpu Research Center, Finland, 72 pp.
Skillings, D.N., 1992, “North American iron ore industry review/outlook,” Skillings’ Mining Review, July, p. 16.
Szekely, J., and Themelis, N.J., 1971, Rate Phenomena in Process Metallurgy, John Wiley & Sons, pp. 400–409.
Turkdogan, E.T., 1980, Physical Chemistry of High Temperature Technology, Academic Press, New York, pp. 213–217.
Author information
Authors and Affiliations
Additional information
Nonmeeting paper 96-640.
Discussion of this peer-reviewed and approved paper is invited and must be submitted to SME prior to Feb. 28, 1998.
Rights and permissions
About this article
Cite this article
Mohanty, B.P., Shores, D.A. Liberation of alkali salts from fluxed iron ore pellets during induration. Mining, Metallurgy & Exploration 14, 17–25 (1997). https://doi.org/10.1007/BF03402774
Received:
Revised:
Published:
Issue Date:
DOI: https://doi.org/10.1007/BF03402774