A Green Process for Selective REEs Recovery from Rare Earth Waste Through Mechanochemical Activation

Rare earth elements (REEs) are vital to industry development, it is important to recycle REEs from RE-contained waste; however, it still faces challenges of high acid consumption and heavy pollution. In this work, the effect of phase evolution on the leaching behavior of REEs in roasted NdFeB waste was studied and found that the insoluble phase of NdFeO3 significantly inhibited the leaching efficiency of REEs. The formation of the NdFeO3 phase reduced the leaching efficiency of REEs to about 40%, which will increase the acid consumption in the subsequent leaching process. Density functional theory calculation was used to clarify the leaching mechanism of the insoluble phase by comparing the structural stability differences between Nd2O3 and NdFeO3. Mechanical activation was an effective method to destroy the structure of the insoluble NdFeO3 phase. After mechanical activation for 4 hours, the content of the NdFeO3 phase decreased from 21.0 wt% to 3.50 wt%, and the leaching efficiency of REEs increased about twice. The present work would provide a green strategy and corresponding theoretical basis for efficiently recovering REEs from NdFeB waste.