Reaction Kinetics of Desulfurization of Molten Pig Iron Using CaO–SiO₂–Al₂O₃–Na₂O Slag Systems

Abstract

Desulfurization kinetics of molten pig iron were studied using CaO–SiO₂–Al₂O₃–Na₂O quaternary slag sys-tems at 1 350°C. The concentration of Na₂O in slag decreases with time due to evaporation. The rate of desulfurization increases by increasing the Na₂O content in slag, decreasing Al₂O₃ content, increasing the slag basicity, i.e., the ratio of CaO to SiO₂, and increasing the temperature. A mathematical model has been developed which enables the effect of decrease in Na₂O content over time to be taken into consideration. The model provides a rate equation that can represent all conceivable rate controlling steps, such as interfacial chemical reaction, mass transport in the metal phase, and in the slag phase. The apparent rate coefficient—a parameter employed in the model—was dependent on temperature and slag composition, especially Na₂O content. An equation is suggested which relates the coefficient to the sulfide capacity of slag. The activation energy of the apparent rate coefficient was found to be 127 kJ mol^-1 . It was concluded that the desulfurization of molten pig iron using the present slag system is controlled either by the interfacial chemical reaction or slag phase mass transfer.