Cerium Reduction by Aluminum and Calcium Carbide from Cerium-Containing Slags

Abstract—Under increasing requirements for the properties of steels, one of the ways to produce a high-quality product is microalloying with rare earth elements such as cerium, which can significantly influence the mechanical properties of steel even at low concentrations. To reduce the cost of steel, it is rational to introduce it into steel by direct reduction from oxide systems rather than by adding ferroalloys. To study this process, thermodynamic modeling of cerium reduction by aluminum and calcium carbide from slags of the CaO–SiO2–Ce2O3 system containing 15% Al2O3 and 8% MgO at temperatures of 1550 and 1650°C is carried out. The modeling is performed using the HSC 6.12 Chemistry (Outokumpu) software package based on Gibbs energy minimization using the simplex lattice planning method. The results of thermodynamic modeling are presented in the form of composition–property diagrams (equilibrium cerium content in a metal) for temperatures of 1550 and 1650°C. When metallic aluminum is used as a reducing agent, an increase in the slag basicity (CaO/SiO2) from 2 to 5 at a temperature of 1550°C leads to an increase in the equilibrium cerium content in the metal from 2 to 20 ppm in the concentration range 0–15% Ce2O3; that is, an increase in the slag basicity favorably affects the development of cerium reduction. An increase in metal temperature also exerts a positive effect on cerium reduction by aluminum. When the temperature increases to 1650°C, the equilibrium cerium content in the metal increases from 4 to 30 ppm in the concentration range 0–15% Ce2O3. The use of calcium carbide as a reducing agent leads to an increase in the cerium concentration in the metal to 30 and 40 ppm at 1550 and 1650°C, respectively, at a basicity of 5. The decisive role of slag basicity, cerium oxide concentration, and temperature factor in the development of cerium reduction by aluminum and calcium carbide has been confirmed.