Equilibrium Content of Lanthanum in Metal under the Slag of CaO–SiO2–La2O3–15% Al2O3–8% MgO System

Abstract Thermodynamic modeling results of lanthanum equilibrium content in metal under the slag of CaO–SiO2–La2О3–Al2O3–MgO system corresponding to the chemical composition of 16 points of local simplex plan are presented using the HSC 8.03 Chemistry (Outokumpu) software package in combination with the simplex planning lattice method. In the work, slag is represented by CaO–SiO2–La2O3–15% Al2O3–8% MgO oxide system in a wide range of chemical composition for temperatures of 1550 and 1650°C, and metal contains 0.06% C, 0.25% Si, 0.05% Al (in this expression and hereinafter in mas. %). The mathematical modeling results are shown graphically in the form of composition–equilibrium content diagrams of lanthanum. There is a significant effect of slag basicity on the lanthanum equilibrium content in metal. An increase in slag basicity from 2 to 5 at a temperature of 1550°C leads to an increase in the lanthanum equilibrium content from 0.2 ppm in the region of lanthanum oxide concentration of 1–5% to 7 ppm in the region of increased concentration of lanthanum oxide to 4–7%. Hence, the increase in slag basicity favorably affects the development of lanthanum reduction. Increase in metal temperature also has positive effect on lanthanum reduction process. As temperature rises to 1650°C, the lanthanum equilibrium content in metal increases from 0.2 ppm in the region of lanthanum oxide concentration of 1–3% to 12 ppm in the region of increased concentration of lanthanum oxide to 4–7%. In diagrams of chemical composition of slag containing 56–61% CaO, 12–14% SiO2 and 4–7% La2O3 the lanthanum content in metal at level of 7–12 ppm is ensured in temperature range from 1550 to 1650°C. Therefore, a decisive role of slag basicity is confirmed, as well as the concentration of lanthanum oxide and temperature factor into the development of lanthanum reduction from slags of the studied oxide system by aluminum dissolved in metal.