Influence of Dysprosium Compounds on the Extraction Behavior of Dy from Nd-Dy-Fe-B Magnet Using Liquid Magnesium

Sun-Woo Nam,Do-Hyang Kim,Sang-Min Park,Myung-Suk Song,Taek-Soo Kim,Mohammad Zarar Rasheed

doi:10.3390/met11091345

Sun-Woo Nam, Do-Hyang Kim + Show 4 more

Open Access

https://doi.org/10.3390/met11091345

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Abstract

During the liquid metal extraction reaction between a Nd-Dy-Fe-B magnet and liquid Mg, Nd rapidly diffuses out of the magnet, whereas Dy is not extracted due to the reaction with the matrix and the formation of Dy2Fe17 phase. In addition, theDy2O3 phase exists at the grain boundaries. Until now, only the effect of the Dy2O3 phase on the extraction of Dy has been reported. In this study, the effect of the Dy2Fe17 phase on the extraction of Dy from the Nd-Dy-Fe-B magnet was investigated in liquid Mg. The formation of the Dy2Fe17 phase during the reaction between Mg and matrix (RE2Fe14B) was first examined using a thermodynamical approach and confirmed by microstructural analysis. It was observed that Dy extraction was dominated by Dy2Fe17 phase decomposition from 3 h to 24 h, followed by Dy2O3 phase dominant reaction with Mg. Comparing the activities of the Dy2Fe17 phase and the Dy2O3 phase, the reaction of Dy2Fe17 is dominant, as compared to the Dy2O3 phase. Finally, at 48 h, the high Dy extraction percentage of 93% was achieved. As a result, in was concluded that the Dy2Fe17 phase acts as an obstacle in the extraction of Dy. In the future, if research to control the Dy2Fe17 phase proceeds, it will be of great importance to advance the recycling of Dy.

Highlights

Rare earth (RE) permanent magnets have recently been employed in high-tech industrial applications, such as electric vehicles, renewable energy, robotics, and their utilization is increasing as the world shifts towards a green economy [1,2]
The phase transformation in the microstructures of magnets during the liquid metal extraction (LME) process is systematically investigated with increasing reaction time
The liquid Mg is diffused into the magnet area and it gradually expanded its reaction zones inside the grain boundary and matrix

Summary

Introduction

Rare earth (RE) permanent magnets have recently been employed in high-tech industrial applications, such as electric vehicles, renewable energy, robotics, and their utilization is increasing as the world shifts towards a green economy [1,2]. One of the recycling processes for recovering HREEs from EOL magnets or scraps, the pyrometallurgy method, is a potential alternative to collect REEs from Nd-Dy-Fe-B magnet [7–9]. Among these processes, liquid metal extraction (LME) is based on a selective reaction with target metals by using solvent metals, such as Mg, Ag, Bi, and Cu [10–13]. The generation and decomposition of intermediate phases are observed in detail and the Dy2 Fe17 phase is clearly identified This demonstrates that the interplay between Dy2 Fe17 and oxides affects the extraction behavior of Dy

Experimental

Results and Discussion

Conclusions