Attempts were made in [1, 2] to confirm that, in the desulfurization of hot iron, magnesium and sulfur react primarily in the volume of the metal. It is expedient to analyze the results on the basis of the thermodynamics and kinetics of metallurgical reactions. Well-known data on the solubility of magnesium in hot metal indicate the possibility that magnesium reacts with hot-metal impurities both at the surface of bubbles of magnesium vapor rising through the melt and in the volume of hot iron with the participation of dissolved magnesium. In desulfurization, each reaction is present; it is important to determine which is dominant in particular conditions. The first step in elucidating the reaction mechanism is to analyze the thermodynamic conditions. Magnesium has high chemical activity with respect to the oxygen and sulfur dissolved in the hot metal. Thermodynamic analysis of the conditions of oxide and sulfide formation with the participation of magnesium vapor yields temperature dependences of the equilibrium value of RTln a_(Mg) with different activities of sulfur and oxygen in the melt (Fig. 1) [3, 4]. In the reaction with dissolved magnesium, the absolute value of RTln a_(Mg) changes. However, there is no change in the relation in Fig. 1 between the activities of sulfur and oxygen at which the formation of magnesium sulfides and oxides is accompanied by the same change in energy of the system. Analysis of Fig. 1 shows that magnesium interacts preferentially with the oxygen dissolved in the metal.
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