Study of a Master Slag Production Based on Apatite Concentrate with the Objective of Rare Earth Element Recovery

Abstract The present study introduces a method for recovering rare earth elements (REEs) by producing a master slag derived from apatite concentrate. The process begins with dephosphorization, which effectively removes over 90% of phosphorus at approximately 2000 ℃ with a holding time of 1 h, thereby significantly increasing the REE concentration within the concentrate. The resulting dephosphorized apatite is subsequently doped with neodymium oxide (Nd 2 O 3 ) and additional compounds, following the CaO–SiO 2 –Nd 2 O 3 phase diagram to target an optimal crystal phase composition. Initial evaluations using synthetic slag helped refine process parameters, including the multistage melting and crushing necessary to retrieve homogeneity. The master slag formation and crystal growth experiments were conducted at 1500–1600 ℃ with holding times ranging from 0 to 60 min, allowing assessment of REE incorporation and crystal growth behavior. Advanced characterization techniques were used to assess slag properties and crystal structure evolution, including DTA–TGA for thermal analysis, ICP-MS for chemical composition, and XRD and SEM–EDS for phase identification. The results confirm the formation of the desired (Ca, Nd) 2 SiO 4 phase within the slag, indicating that the process stabilizes REEs and enhances their concentration in a recoverable phase. This pyrometallurgical route also avoids the production of hazardous liquid waste and enables the simultaneous removal of phosphorus as a gaseous byproduct, offering additional value in sustainable processing. This approach demonstrates a viable pathway for efficient REE extraction from apatite concentrate and shows strong potential for industrial-scale applications in REE recovery and sustainability efforts within the REE supply chain. Graphical Abstract