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 systems at 1 350 degreesC. The concentration of Na2O in slag decreases with lime 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.