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Abstract
Magnets containing substantial quantities of rare earth elements are currently one of the most sought-after commodities because of their strategic importance. Recycling these rare earth magnets after their life span has been identified to be a unique approach for mitigating environmental issues that originate from mining and also for sustaining natural resources. The approach is hydrometallurgical, with leaching and precipitation followed by separation and recovery of neodymium (Nd), praseodymium (Pr) and dysprosium (Dy) in the form of rare earth fluorides (REF) as the final product. The methodology is specifically comprised of sulfuric acid (H2SO4) leaching and ammonium hydroxide (NH4OH) precipitation followed by reacting the filtrate with ammonium bifluoride (NH4F·HF) to yield the REF. Additional filtering also produces ammonium sulfate ((NH4)2SO4) as a byproduct fertilizer. Quantitative and qualitative evaluations by means of XRD, ICP and TGA-DSC to determine decomposition of ammonium jarosite, which is an impurity in the recovery process were performed. Additionally, conditional and response variables were used in a surface-response model to optimize REF production from end-of-life magnets. A REF recovery of 56.2% with a REF purity of 62.4% was found to be optimal.
Highlights
Disquiet around the sustainability of rare-earth elements (REE) provisions has stimulated determination to recycle and to improve the proficiency of the materials they are used to make [1]
With their life span centered on their application, rare earth materials in hard disk drives are applied in parts such as printed circuit boards (PCB), spindles, and so on [4]
This paper presents the recycling Nd magnet scrap using a novel hydrometallurgical process involving H2 SO4 leach, NH4 O → (NH4 )Fe3 (OH) precipitation, and NH4 F·hydrofluoric acid (HF) reaction
Summary
Disquiet around the sustainability of rare-earth elements (REE) provisions has stimulated determination to recycle and to improve the proficiency of the materials they are used to make [1]. Once the materials are in solution, various processes such as precipitation, solvent extraction, and ion exchange can be used to economically produce individual REE in the required form. This paper presents the recycling Nd magnet scrap using a novel hydrometallurgical process involving H2 SO4 leach, NH4 OH precipitation, and NH4 F·HF reaction. The latter step transforms the precipitate into rare earth fluorides (REF) which should be appropriate feedstock for subsequent pyrometallurgical processing into metal in molten fluoride electrolysis [39]. The application of hydrofluoric acid (HF) was completely avoided and the process was optimized through statistical analysis and modelling
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