Effect of MnO and Substituting CaO with BaO on the Desulfurization Ability of Blast Furnace Slag

Abstract

The effect of MnO and substituting CaO with BaO on the sulfide capacity of CaO-SiO₂-MgO-Al₂O₃-BaO-MnO slag was studied at 1773 K using the gas–slag equilibration technique. The relationship between the sulfide capacity and sulfur partition ratio in equilibrium based on the present slag was discussed. The results indicate when the CaO/SiO₂ ratio and other components stay fixed; the sulfide capacity increases with MnO content increasing from 0 to 3 wt pct, which is not only due to an increase of oxygen ion activity but also to the decrease of the activity coefficient of sulfur ions. With the equal mass substitution of CaO with BaO, the free oxygen ions and corrected optical basicity decrease, and the slag structure tends to be complicated because of the compensation effect of Ba²⁺ for [AlO₄]⁵⁻ tetrahedron uniting. Furthermore, the reduced level of ${ \log }a_{{{\text{O}}^{2 - } }}$ is greater than that of $\log f_{{S^{2 - } }}$, ultimately leading to a decrease of sulfide capacity. In addition, the sulfur partition ratio is obtained from the sulfide capacity in equilibrium and shows a similar changing trend between them as a function of slag composition.