Effects of slag composition and additive type on desulfurization of rejected electrolytic manganese metal scrap by Na2O-containing electroslag

The recycling rate of rejected electrolytic manganese metal (EMM) scrap can be increased by inhibiting the manganese metal (MM) vaporization during the remelting process with electroslag. However, if the latter is achieved by reducing the remelting temperature, the desulfurization behavior will deteriorate. Therefore, Na2O-containing electroslag and metallic additive were used to increase the rejected EMM scrap recovery ratio. The respective high-temperature experiment was conducted in a MoSi2 electrical resistance furnace filled with fluid argon at 1673 K using five different types of electroslag with the Na2O content ranging from 5.81% to 15.71%. High-purity metallic magnesium and magnesium calcium alloy additives were used as deoxidizers. The addition of Na2O and metallic additives effectively promoted the desulfurization and deoxidization of MM. The removal of sulfur and oxygen by the interaction between Na2O-containing electroslag melt and molten MM with metallic additive was analyzed from the thermodynamic and kinetic standpoints. The effect of Na2O-containing electroslag volatilization on desulfurization and deoxidization was considered. With an increase in Na2O content in the slag, the mass loss rates of Na2O and electroslag rose, as well as the final sulfur partition ratio. If the Na2O content volatilized in the slag melt did not exceed 10.44%, the sulfur removal ratio was increased by high sulfide capacity and CaO activity in all slags due to the addition of Na2O. The rejected EMM scrap deoxidization ratio grew with the increased activity of CaO and reduced activity of Al2O3 in the molten slag, caused by the increased Na2O content in the molten slag. The addition of metallic Mg and Mg–Ca alloy indirectly promoted desulfurization and deoxidization by reducing the MnO content in the rejected EMM scrap and growing slag oxidability. The Mg–Ca alloy could also react with dissolved sulfur and oxygen, directly promoting desulfurization and deoxidization processes. The Na2O content in slag should not exceed 10.44% to ensure the high desulfurization and deoxidization abilities, fluidity and low volatilization of slag.