Innovative Application of Mechanical Activation for Rare Earth Elements Recovering: Process Optimization and Mechanism Exploration.

Quanyin Tan,Jinhui Li,Chao Deng

doi:10.1038/srep19961

Abstract

With the rapidly expanding use of fluorescent lamps (FLs) and increasing interest in conservation and sustainable utilization of critical metals such as rare earth elements (REEs), the recovering of REEs from phosphors in waste FLs is becoming a critical environmental and economic issue. To effectively recycle REEs with metallurgical methods, mechanical activation by ball milling was introduced to pretreat the waste phosphors. This current study put the emphasis on the mechanical activation and leaching processes for REEs, and explored the feasibility of the method from both theoretical and practical standpoints. Results showed physicochemical changes of structural destruction and particle size reduction after mechanical activation, leading to the easy dissolution of REEs in the activated samples. Under optimal conditions, dissolution yields of 89.4%, 93.1% and 94.6% for Tb, Eu and Y, respectively, were achieved from activated waste phosphors using hydrochloric acid as the dissolution agent. The shrinking core model proved to be the most applicable for the leaching procedure, with an apparent activation energy of 10.96 ± 2.79 kJ/mol. This novel process indicates that mechanical activation is an efficient method for recovering REEs from waste phosphors, and it has promising potential for REE recovery with low cost and high efficiency.

Highlights

With the rapidly expanding use of fluorescent lamps (FLs) and increasing interest in conservation and sustainable utilization of critical metals such as rare earth elements (REEs), the recovering of REEs from phosphors in waste FLs is becoming a critical environmental and economic issue
The chemical composition of the waste phosphors was analyzed with X-ray Fluorescence (XRF), as well as with microwave-assisted aqua regia digestion and Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES), and is presented in
The results indicate that the mechanical activation process could cause destruction of the crystal structure of the phosphors, which could be the reason for the sharp decrease in apparent activation energy, leading to the transformation of the rate-controlling step from chemical reaction to diffusion, and making the REE leaching much easier[41,42]

Summary

Innovative Application of Mechanical Activation for Rare

With the rapidly expanding use of fluorescent lamps (FLs) and increasing interest in conservation and sustainable utilization of critical metals such as rare earth elements (REEs), the recovering of REEs from phosphors in waste FLs is becoming a critical environmental and economic issue. REEs with metallurgical methods, mechanical activation by ball milling was introduced to pretreat the waste phosphors. The shrinking core model proved to be the most applicable for the leaching procedure, with an apparent activation energy of 10.96 ± 2.79 kJ/mol This novel process indicates that mechanical activation is an efficient method for recovering REEs from waste phosphors, and it has promising potential for REE recovery with low cost and high efficiency. The mechanical activation method has shown promise for recovering metal from wastes because it triggers physicochemical changes from particle comminution, new surface generation, crystalline structure defects, polymorphic transformations, and even direct reactions[28,29]. We have developed a novel process to recover REEs from waste phosphors by enhancing leaching efficiency with mechanical activation. Obtained results and findings were expected to contribute to a closed-loop process for FLs and sustainable development for REE industries

Experimental Section

Results and Discussion

Optimal level

Conclusions

Additional Information