Evaluating organic acids as alternative leaching reagents for rare earth elements recovery from NdFeB magnets

This study proposes an advanced leaching method using organic acids to recover rare earth elements (REEs) from NdFeB permanent magnets from end-of-life computers hard disk drives (HDDs). The end-oflife HDDs were first dismantled in order to recover NdFeB magnets, which were then thermally demagnetized at 350 degrees C during 30 min before crushing in a ball mill under inert atmosphere. Scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS) analyses performed on the NdFeB magnets show the heterogeneous structure containing the major matric phase Nd2Fe14B and the REEsrich phase containing Nd and Pr oxides. Additionally, X-ray diffraction (XRD) and Moeurossbauer spectroscopy (MS) analyses on the ground NdFeB magnet show that grinding NdFeB magnets under inert atmosphere helps to minimize its oxidation. Chemical analysis shows that the composition of the ground sample is Nd: 22.8 wt%, Pr: 3.3 wt%, Dy: 1.2 wt%, Fe: 62.6 wt%, Co: 1.5 wt%, B: 0.9 wt%, Ni: 0.6 wt%. Diagrams of speciation and equilibrium phases (Eh vs. pH) were calculated to determine the predominance of the formed species in the REEs-organic acids systems. The influence of the organic acid type (acetic acid, formic acid, citric acid and tartaric acid), the acid concentration (10 vol%, up to saturation), and the solid/liquid (S/L) ratio (0.5%-10%) on NdFeB magnets leaching was investigated employing an optimal experimental design conceived by the statistical software JMP. Acetic acid (CH3COOH) shows the highest leaching performance of REEs, allowing leaching yields over 90% for Nd, Dy and Pr in the acid concentration range of 1.6-10 mol/L and the S/L ratio range of 0.5%-5% at a temperature of 60 degrees C. The results presented in this investigation suggest that REEs can be recovered from magnets of end-of-life HDDs using an eco-friendly method assisted by organic acids.(c) 2022 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights reserved.

Automated summary

This study proposes an advanced leaching method using organic acids to recover rare earth elements (REEs) from NdFeB permanent magnets from end-of-life computers hard disk drives (HDDs). Various analyses were conducted to understand the composition and structure of the NdFeB magnets. The experimental design investigated the influence of different factors on the leaching process and identified acetic acid as the most effective leaching agent.