Effects of CaO Content and Magnesium Additive in Electroslag on Desulfurization of Rejected Electrolytic Manganese Metal Scrap

This study conducted high-temperature experiments and elaborated a mathematical model to study the effect of electroslag content and Mg additive on the sulfur and oxygen contents in manganese metal (MM) and MnO in slag during the remelting process. The developed mass transfer model simulated the mechanism of the slag-manganese reaction. The high-temperature experiment was realized in a MoSi2 electrical resistance furnace filled with fluid argon atmosphere at 1773 K (1500 °C) using four different types of electroslag with CaO contents ranging from 0 to 20 pct. A high-purity Mg additive was added to the molten pool as a deoxidizer. The developed mathematical model simulates the mass transfer of sulfur, oxygen, and MnO based on the two-film theory and penetration theory during the high-temperature remelting process. The results predicted by the mathematical model comply with the experimental data, indicating that the desulfurization ratio, deoxidization ratio, and MnO reduction ratio of rejected electrolytic manganese metal (EMM) scrap increase with CaO content in the electroslag. High CaO content in the slag improves the desulfurization rate by increasing the sulfur partition coefficient and overall mass transfer coefficient. The promotion of desulfurization and deoxidization of manganese metal by the Mg additive reduces the MnO content in the rejected EMM scrap. High CaO content in the slag can also promote the desulfurization reaction by increasing the deoxidation rate of manganese metal. With raising CaO content of electroslag, the activity of MnO in molten slag increases, in contrast to Al2O3 and SiO2, increasing the reduction ratio of MnO. Therefore, high CaO content in the slag increases the desulfurization and deoxidation ratios and promotes the recovery rate of rejected EMM scrap.