NdFeB Magnets Recycling Process: An Alternative Method to Produce Mixed Rare Earth Oxide from Scrap NdFeB Magnets

Elif Emil Kaya,Srecko Stopic,Ozan Kaya,Sebahattin Gürmen,Bernd Friedrich

doi:10.3390/met11050716

Abstract

Neodymium iron boron magnets (NdFeB) play a critical role in various technological applications due to their outstanding magnetic properties, such as high maximum energy product, high remanence and high coercivity. Production of NdFeB is expected to rise significantly in the coming years, for this reason, demand for the rare earth elements (REE) will not only remain high but it also will increase even more. The recovery of rare earth elements has become essential to satisfy this demand in recent years. In the present study rare earth elements recovery from NdFeB magnets as new promising process flowsheet is proposed as follows; (1) acid baking process is performed to decompose the NdFeB magnet to increase in the extraction efficiency for Nd, Pr, and Dy. (2) Iron was removed from the leach liquor during hydrolysis. (3) The production of REE-oxide from leach liquor using ultrasonic spray pyrolysis method. Recovery of mixed REE-oxide from NdFeB magnets via ultrasonic spray pyrolysis method between 700 °C and 1000 °C is a new innovative step in comparison to traditional combination of precipitation with sodium carbonate and thermal decomposition of rare earth carbonate at 850 °C. The synthesized mixed REE- oxide powders were characterized by X-ray diffraction analysis (XRD). Morphological properties and phase content of mixed REE- oxide were revealed by scanning electron microscopy (SEM) and Energy-dispersive X-ray (EDX) analysis. To obtain the size and particle size distribution of REE-oxide, a search algorithm based on an image-processing technique was executed in MATLAB. The obtained particles are spherical with sizes between 362 and 540 nm. The experimental values of the particle sizes of REE- oxide were compared with theoretically predicted ones.

Highlights

Rare earth elements (REEs) have a wide range of uses in technological products and applications
Various reaction temperatures from 700 ◦ C to 1000 ◦ C were tested to investigate their role on the phase formation of REOxide
The mixed REE-Oxide powders were characterized by X-ray diffraction analysis, scanning electron microscopy

Summary

Introduction

Rare earth elements (REEs) have a wide range of uses in technological products and applications. Due to the increased demand and supply risk, most REEs have been added to the list of critical metals. The production of REEs from primary resource causes environmental problems [1]. The recovery of REEs from waste materials is the most suitable strategy to find the solution of environmental problems and ensure the sustainability for production of REE raw materials in the future, according to an increased demand in industrial application. In order to produce rare earth elements oxides (REE-oxides), most researchers have studied different hydrometallurgical and pyrometallurgical strategies such as dry digestion [3], acid baking processes [4] and carbothermal reduction of ores and concentrates with subsequent leaching using strong acids [5] aiming at higher REE extractions. Demol et al [4] found that sulfation reaction of monazite with acid was virtually complete after baking at 250 ◦ C for 2 h, resulting in >90% solubilization of REEs, thorium and phosphate

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