Physicochemical properties of MnO-based slags for the production of manganese ferroalloys

Abstract

The physicochemical properties of MnO-based slags are highly important in operation efficiency and product quality of manganese ferroalloys. Because the thermophysical properties of slags such as viscosity, electrical conductivity, and density significantly affect the process efficiency, the fundamental understanding of these properties based on the structure of molten silicates is necessitated. Thus, we investigated the structure of molten MnO-CaO-SiO2 slag using micro-Raman spectroscopy and found linear correlations between thermophysical properties and a degree of polymerization of the slag. The viscosity and the activation energy for viscous flow of the slag linearly increased with increasing degree of polymerization, whereas density and electrical conductivity linearly decreased as a degree of polymerization of silicate melts increased. The addition of CaF2 in the MnO-CaO-SiO2 slag decreased the viscosity of slags containing as high as about 10%MnO which is relatively close to SiMn slag. However, the addition of CaF2 in the 40%MnO system, which is close to FeMn slag, does not change the viscosity. This indicates that MnO is very effective network-modifier, which was confirmed by structure analysis using Raman spectroscopic method. The sulfur absorption capability, i.e. sulfide capacity of MnO-CaO-SiO2Al2O3-MgO slags was also measured by gas-slag equilibration method. The sulfide capacity increases with increasing MnO content at a fixed CaO/SiO2 ratio and increases as MnO substitutes for CaO at a fixed SiO2 content. The addition of Al2O3 and MgO does not significantly change the sulfide capacity of MnO-based slag. All these phenomena could be understood based on structure analysis using Raman spectroscopic methodology. © 2020 INFACON.All rights reserved.