An Evaluation of Thermochemical Property Models for CaO-MnO-SiO2-Al2O3-MgO Slag

The modeling of thermochemical properties is important in studying the physical behavior of slag in the operation of pyrometallurgical smelters. To study the flow of slag through a submerged-arc furnace (SAF) taphole, knowledge of thermochemical properties such as viscosity, thermal conductivity, density and heat capacity are required. In literature various models exist for silicate slags that enable thermochemical properties to be predicted as functions of chemical composition and temperature. This paper reports on the application of models in the CaO-MnO-SiO2-Al2O3-MgO slag system to be used in future CFD modeling of slag tapped from SAFs producing high-carbon ferromanganese (HCFeMn) or silicomanganese (SiMn). FactSage 6.2 is used to estimate the phase composition of slags with varying chemical composition and temperature. The dependence of thermochemical property models on chemical composition and temperature is illustrated in the form of ternary diagrams showing the predicted property values as a function of basicity (chemical composition) and temperature. Slag compositions typical of HCFeMn and SiMn processes are used. Each thermochemical property is calculated at 1400, 1500 and 1600 degrees C at a fixed weight percentage ratio Al2O3/SiO2 of 0.57 and 6% MgO. Ternary phase diagrams (1400, 1500 and 1600 degrees C) and a ternary liquidus temperature diagram are also presented for the system. Since viscosity has the most significant influence on flow behavior, results from various viscosity models have been compared with measured data. Predictions for thermal conductivity, density, and heat capacity are also discussed.