Desulfurization of molten iron with magnesium vapor produced in-situ by carbothermic reduction of magnesium oxide

A new method of desulfurization of molten iron has been developed with magn esium vapor produced insitu by carbothermic reduction of magnesium oxide. P ellets, the main composition of which was magnesium oxide and carbon, were charged into a graphite tube. The tube was immersed into the molten iron to produce magnesium vapor. This process has been studied experimentally and theoretically. The rate of desulfurization depended mainly on the rate of reduction of mag nesium oxide. Under the present experimental conditions, the desulfurizatio n rate increased with increasing temperature and Ar carrier gas flow rate. The change in melt mass had little influence on the desulfurization efficie ncy of magnesium. The effect of pellet composition on the desulfurization h as also been investigated. A mathematical model of the desulfurization has been proposed. The calculat ed results are in good agreement with the experimental results. The rate-co ntrolling step changes with the progress of desulfurization during bubble f ormation 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 sho uld be considered as rate-controlling steps. At the end of the ascent perio d, the magnesium partial pressure in the bubble decreases close to the valu e in equilibrium with the sulfur concentration in the melt. The mass transf er of magnesium in the bubble becomes much slower than that of sulfur in th e melt and becomes the rate-controlling step. The desulfurization reaction mainly takes place on the bubble surface. The amount of desulfurization during the bubble formation period is larger than that during the bubble ascent period. Effects of pellet mass and initial s ulfur concentration on desulfurization can be reasonably explained by the p resent mathematical model.