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To identify the kinetic mechanism, by which magnesium desulfurizes carbon-saturated iron, dissolution of magnesium vapor into pig iron and desulfurization of pig iron by magnesium vapor have been studied by Irons and Guthrie using 60 kg of carbon-saturated iron at 1 532 K. A magnesium vaporizer was used to inject pure magnesium vapor into molten iron and the efficiency of magnesium dissolution ranged between 20 and 80 %. As for desulfurization of pig iron with magnesium vapor, they concluded that most of the desulfurization took place by precipitation on magnesium sulfide inclusions present in the bath rather than on the bubble surface. And, these particles were eliminated from the melt by bubbling or induction stirring. On the other hand, Nakanishi et al. assumed that the solubility of magnesium in molten iron was too low for significant amount of magnesium to dissolve, and most of the desulfurization took place on the bubble surface. The ratecontrolling step was the mass transfer of dissolved sulfur in the melt. Several methods have been developed for using magnesium to desulfurize hot metal from the blast furnace, such as Mag-Coke, Salt-coated magnesium and Mag-Lime. In recent years, desulfurization by injection of lime and magnesium powder into molten iron has been the subject of many investigations. Yonezawa et al. showed that with using a flux system of CaO and 10–25 % Mg powder, the desulfurization efficiency of magnesium was 10 % and the sulfur concentration reduced from 0.012 to 0.002 %. The drop in temperature during the desulfurization was only 12°C, which was obviously less than that during the desulfurization with lime injection. Aoyagi et al. reported that the desulfurization efficiency of magnesium was about 25 % and the sulfur concentration reduced to 12 ppm during the desulfurization with CaO and 10–30 % Mg powder in a torpedo car and ladle. There are the other several papers relating to the desulfurization with CaO and Mg powder. In a previous paper, a new desulfurization method of molten iron was developed by immersing a tube charged with MgO–C pellets into the melt. Heated by heat conduction from the molten iron, magnesium oxide in the pellet was reduced by carbon to produce magnesium vapor, which was injected directly into the melt together with argon carrier gas. A mathematical model of desulfurization was also developed. Since the reduction rate of magnesium oxide was slow and the magnesium partial pressure in the bubble was low, the calculated results showed that the desulfurization mainly took place on the bubble surface. The rate-controlling step changed with the progress of desulfurization during the bubble formation and ascent periods. At the beginning of the formation period, both of the mass transfer of sulfur in the melt and magnesium in the bubble should ISIJ International, Vol. 41 (2001), No. 9, pp. 965–973

Desulfurization of Molten Iron with Magnesium Vapor Produced In-situ by Aluminothermic Reduction of Magnesium Oxide.