Recovery and separation of rare earths and boron from spent Nd-Fe-B magnets

Fupeng Liu, Antti Porvali, Jin Liang Wang*, Houqing Wang, Chao Peng, Benjamin P. Wilson, Mari Lundström

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

Abstract

The environmental and economic benefits of recycling spent Nd-Fe-B magnets are becoming increasingly important. Nevertheless, the reprocessing of this type of material by conventional processes remains a challenge due to the difficulties of rare earth elements (REEs) and Fe separation, low products purity and large-scale generation of boron wastewater. This research presents an effective approach for the comprehensive recovery of REEs, iron and boron from Nd-Fe-B magnet wastes. Investigations of the initial roasting pretreatment showed it to be an effective method that aids the subsequent selective separation of REEs, with the most suitable temperature determined to be 800 °C. During the following selective hydrochloric acid pressure leaching of the roasted magnet, the addition of 2 g/L NaNO3 was found to significantly improve the separation of REEs and B from Fe. The results indicated that almost 99% of REEs and 97% of B could be extracted, whilst in contrast, less than 0.1% of iron dissolved, to leave a hematite rich residue. The extracted REEs were then directly precipitated as oxalates with >99% extraction and 99.95% purity at a value n(oxalic acid)/n(REEs) of 1, resulting in significant improvements to oxalic acid consumption and REEs product purity. In the final step, 99.5% of boron was recovered via a three-stage counter current extraction with 30% (v/v) (EHD) and 70% (v/v) sulfonated kerosene. These findings demonstrate that high recoveries of REEs, Fe and B are achievable with hydrochloric acid pressure leaching followed oxalate precipitation and boron recovery.

Original languageEnglish
Article number106097
JournalMinerals Engineering
Volume145
DOIs
Publication statusPublished - 1 Jan 2020
MoE publication typeA1 Journal article-refereed

Keywords

  • Boron
  • Hematite
  • Pressure leaching
  • Rare earth elements
  • Spent Nd-Fe-B magnets

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