Phase equilibria and thermodynamic properties of the Ce2O3-CaO-SiO2 quaternary system containing 5 wt% MgO at 1500–1600 °C

The sluggish advancement in technology for the recovery of rare earth elements from secondary resources can be largely attributed to an inadequate understanding of the thermodynamic properties of cerium oxide-based slag systems. This study systematically investigates the phase equilibrium of the Ce 2 O 3 -CaO-SiO 2 -5 wt% MgO quaternary system at 1500 °C and 1600 °C. High-temperature equilibrium experiments followed by rapid quenching were conducted, and phase assemblages were characterized by XRD, SEM and EPMA. For the first time, the results accurately determined the isothermal liquidus lines for the first time and identified the stable regions of key phases such as SiO 2 , Ce 2 Si 2 O 7 , CaO·2Ce 2 O 3 ·3SiO 2 , CaO·Ce 2 O 3 ·2SiO 2 , the Ce-doped dicalcium silicate (i.e., (Ca, Ce) 2 SiO 4 ), and the monticellite (i.e., CaMgSiO 4 ), as well as their coexistence relationships. Furthermore, the isothermal sections at 1500 °C and 1600 °C were constructed based on experimental data and fundamental thermodynamic principles. This study not only fills a critical gap in the thermodynamic database for rare-earth slag systems but also provides a theoretical basis for optimizing slag design and enhancing cerium recovery from waste slags.