Sulfurization Roasting Process of Nd 2 O 3 and Synthetic NdFeO 3 with Ferric Sulfate

The environmental and economic recovery of rare-earth (RE) from NdFeB magnet waste is becoming increasingly important. In this study, the sulfurization possibility of two main RE-bearing phases of Nd 2 O 3 and NdFeO 3 in the fully oxidized NdFeB waste by ferric sulfate was evaluated. TG-DTA curves of the Nd 2 O 3 and NdFeO 3 sulfurization with 1.5 times of the theoretical Fe 2 (SO 4 ) 3 ·5H 2 O dosage showed that the temperatures range of Nd 2 (SO 4 ) 3 formation were 873 K to 963 K, and the starting temperature of Nd 2 (SO 4 ) 3 decomposition was ~ 1070 K. Specific experiments revealed by XRD and SEM-EDS analysis that Nd 2 O 3 and NdFeO 3 phases were successfully sulfated by Fe 2 (SO 4 ) 3 ·5H 2 O. The optimum roasting temperature was determined to be 973 K corresponding to the highest Nd leaching efficiency by the sulfurization of Nd 2 O 3 . At above 973 K, the decomposition of Nd 2 (SO 4 ) 3 resulted in the decrease of Nd leaching efficiency. Furthermore, the required roasting time and Fe 2 (SO 4 ) 3 ·5H 2 O dosage to obtain the same Nd leaching efficiency were different for the sulfurization of Nd 2 O 3 and NdFeO 3 at 973 K, and the sulfurization of NdFeO 3 was more difficult than that of Nd 2 O 3 . Based on the results, an innovative method for recovering RE from NdFeB magnet waste was proposed.