Decomposition Model of Bastnaesite and Its Fluorine Oxygen Coupling Escape Mechanism

Nearly 90% of rare earths worldwide currently originate from bastnaesite (REFCO₃). Oxidative roasting, an effective method for the treatment of bastnaesite, has been extensively employed in industrial production practice. However, the roasting decomposition mechanism of bastnaesite at the molecular level remains controversial. In this study, two roasting atmospheres (i.e., Ar and O₂) were adopted for the treatment of the mixed rare earth concentrate in Bayan Obo. Ar-Roasting ore was skillfully treated as an intermediate and then underwent oxidation roasting. The results achieved using research methods (e.g., XRD, FT-IR, TEM, and XPS) first revealed that the oxidation roasting of bastnaesite was performed in several stages. The first stage was the thermal decomposition of bastnaesite and the oxidation of cerium (REFCO₃ → REOF + CO₂). The second stage was the escape pathway of fluorine (REOF + O₂ → RE O + O F and O F → O₂ + F₂), describing the migration rules of F and O elements and the oxidation behavior of Ce. The results of this study can provide more theoretical support and guidance for the clean extraction of bastnaesite and mixed rare earth in Bayan Obo.