Thermodynamic Assessment of the CaO-SiO 2 -Sc 2 O 3 Ternary System

Sustainable utilization of Sc 2 O 3 -containing metallurgical slag has attracted great interest in industries and the academic community in recent years. As the primary subsystem, the CaO-SiO 2 -Sc 2 O 3 ternary system plays an essential role in recovering Sc 2 O 3 from metallurgical slag. However, few thermodynamic data have been reported for Sc 2 O 3 -containing metallurgical slag systems, which greatly limits the sustainable utilization of Sc 2 O 3 . Therefore, based on the current phase diagram, thermodynamic and crystal structure data, the thermodynamic modeling of the CaO-SiO 2 , CaO-Sc 2 O 3 , and SiO 2 -Sc 2 O 3 binary systems and CaO-SiO 2 -Sc 2 O 3 ternary system. The thermodynamic parameters of CaO-SiO 2 -Sc 2 O 3 system over the whole composition range are optimized with computer coupling of phase diagrams and thermochemistry approach. The modified quasi-chemical model and polynomial expansions of the excess Gibbs energy were used to simulate the liquid slag and solid solution, respectively. The solid phases are treated as stoichiometric compounds. A thermodynamic description of the CaO-SiO 2 -Sc 2 O 3 ternary system and its Sc 2 O 3 -containing binary subsystem was given. The optimized phase diagram of the CaO-SiO 2 -Sc 2 O 3 ternary system is in good agreement with the experimental data. The thermodynamic database generated in this study can be used to predict the high-temperature metallurgical recovery of Sc 2 O 3 from calcia- and silica-containing slags.