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

Abstract

A new method of desulfurization of molten iron has been developed with magnesium vapor produced in-situ by carbothermic reduction of magnesium oxide. Pellets, 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 magnesium oxide. Under the present experimental conditions, the desulfurization rate increased with increasing temperature and Ar carrier gas flow rate. The change in melt mass had little influence on the desulfurization efficiency of magnesium. The effect of pellet composition on the desulfurization has also been investigated. A mathematical model of the desulfurization has been proposed. The calculated results are in good agreement with the experimental results. The rate-controlling step changes with the progress of desulfurization during 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 be considered as rate-controlling steps. At the end of the ascent period, the magnesium partial pressure in the bubble decreases close to the value in equilibrium with the sulfur concentration in the melt. The mass transfer of magnesium in the bubble becomes much slower than that of sulfur in the 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 sulfur concentration on desulfurization can be reasonably explained by the present mathematical model.