New insight into oxidative roasting and leaching for NdFeB waste

NdFeB waste is an essential rare earth (RE) resource, which is the unique solid waste to realize large-scale RE recovery via HCl preferential dissolution method. However, the challenges of low oxidation efficiency and high acid consumption are seriously hindering RE efficient recovery. Herein, the mechanism between the phase structure transformation of roasting RE solid waste and RE elements' leaching behavior was first explored. The results showed the oxidation efficiency of NdFeB oil sludge (NOS) was improved from 2.5 % to 99.2 % with the temperature increasing. And a leaching model was proposed: Dense Layer Structure (<= 400 degrees C), Loose Layer Structure (400-600 degrees C), and RE Insoluble Structure (>= 600 degrees C). The analysis of the leaching model indicates the dense oxide layer and the RE insoluble structure (RE insoluble NdFeO3 phase and particle adhesion) will affect the leaching efficiency of RE elements. Based on the oxidation efficiency, XPS, SEM, Raman, FTIR, and EDSmapping analysis, an external oxide layer was verified on the microparticle of roasted NOS. Furthermore, the corresponding mechanism is discussed, and the improvement strategies are put forward. This study will supply a new insight into the theoretical basis for efficient and low HCl consumption recycling of NdFeB waste.

Automated summary

This study explores the mechanism between the phase structure transformation of roasted rare earth solid waste and the leaching behavior of rare earth elements. The results show improved oxidation efficiency of NdFeB oil sludge with increasing temperature. The analysis of a leaching model suggests that the dense oxide layer and the RE insoluble structure affect the leaching efficiency of RE elements. Additionally, an external oxide layer is verified on the microparticle of roasted NOS.