The kinetics of molten iron desulfurization using magnesium vapor
- PDF / 1,740,197 Bytes
- 13 Pages / 603.28 x 783.28 pts Page_size
- 42 Downloads / 172 Views
THE work described in this paper was undertaken
to determine the kinetic mechanisms by which magnesium desulfurizes carbon-saturated iron. While there are several different commercial processes using magnesium to desulfurize iron from the blast furnace; for example Mag-Coke, salt-coated magnesium and MagLime, t fundamental studies dealing with the kinetics of the desulfurization are lacking. On the other hand, the thermodynamics of dissolution and desulfurization have been investigated by several workers. 2~ They all found that magnesium dissolves in an amount proportional to its vapor pressure (i.e., according to Henry's Law). Henry's constant, H is (0.71 +_ 0.1) • 10 -2 pct M g / k P a Mg for the conditions of the present experiments (4.4 pct C, 0.1 pct Si, 1523 K). 7 The most recent work on desulfurization 6 indicates that the experimental solubility product for magnesium sulfide precipitation is K'q = pct Mg 9 pct S = 1.8 x 10 -6 at 1533 K. In a preliminary kinetic study, 8 the present authors used a magnesium vaporizer to inject pure magnesium vapor into low-sulfur (less than 0.005 pct S) carbonsaturated iron. It was found that the magnesium dissolved readily. It was also shown that magnesium dissolution is significant in commercial processes even when desulfurization is the major overall reaction. In that paper the authors pointed out that it was difficult to extrapolate their results to the desulfurization reaction and simply assume that sulfur diffuses to the bubble interface to form magnesium sulfide while excess magnesium diffuses out into the liquid. Their reservations about such a mechanism at that time were: a) in most industrial situations, equilibrium between magnesium and sulfur is exceeded in the bulk of the G. A. IRONS is Assistant Professor, Department of Metallurgy and Materials Science, McMaster University, Hamilton, ON L8S 4L7, Canada, and R. I. L. GUTHRIE is Professor, Department of Mining and Metallurgical Engineering, McGill University,Montreal, PQ H3A 2A7, Canada. Manuscript submitted February 9, 1981.
liquid; desulfurization could therefore proceed at sites such as magnesium sulfide, b) as sulfur is surface-active, it could act as a barrier at bubble interfaces, c) oxygen and sulfur could also immobilize the bubble interface and further reduce transfer rates d) if magnesium sulfide is formed at the interface, it could remain at the interface and physically block further reaction or, alternatively it could be swept away. The present paper is aimed at identifying the importance of these various factors and isolating the controlling mechanisms. In the only other kinetic study, Nakanishi et al 9 injected magnesium granules into carbon-saturated iron. A model to predict magnesium penetration into the liquid, vaporization, and desulfurization was developed. Unfortunately those authors assumed that the solubility of magnesium in iron was too low for significant amounts to dissolve. Consequently, the rate controlling step for mass transfer was presumed to be transport of dissolved sulfur to the
Data Loading...
