Selective Leaching of Rare Earth Elements from NdFeB Sludge by Different Pretreatment Methods

Jisu Lim; SeoJin Heo; Ho-Sung Yoon; Chul-Joo Kim; Kyeong Woo Chung; Sugyeong Lee; Rina Kim

doi:10.7844/kirr.2026.35.3.35

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2026 Vol.35, Issue 3 Preview Page Next Page

Research Paper

Selective Leaching of Rare Earth Elements from NdFeB Sludge by Different Pretreatment Methods NdFeB 슬러지의 전처리 방법에 따른 희토류 선택적 침출 거동 연구

30 June 2026. pp. 35-43

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Abstract

In this study, the effect of pretreatment methods on the selective acid leaching of rare earth elements (REEs) from NdFeB sludge was investigated. A fine powdered NdFeB sludge generated during the NdFeB magnet manufacturing process primarily consisted of REEs (Nd, Pr, Dy, and Tb) and iron oxides, as analyzed by XRF and XRD. The direct acid leaching without any pretreatments using 2 M hydrochloric acid at 75℃ resulted in simultaneous dissolution of REEs (99%) and Fe (96%), indicating poor selectivity of REEs. The oxidative roasting (660℃, 3 h) led to the formation of NdFeO₃ and Fe₂O₃ phases, which suppressed both REEs and Fe leaching. In contrast, NaOH digestion (50 wt.% NaOH, 145℃, 5 h) transformed the phases into Nd(OH)₃ and Fe₃O₄, significantly enhancing REE selectivity. At mild leaching conditions (0.5 M HCl, 25℃), REE leaching exceeded 99.5% while Fe dissolution was limited to 0.53%. These results demonstrate that NaOH digestion combined with low-acid and ambient-temperature leaching enables highly selective recovery of REEs by effectively suppressing Fe dissolution.

Keywords

NdFeB sludge

rare earth elements

NaOH digestion

oxidative roasting

selective leaching

본 연구에서는 NdFeB 슬러지를 대상으로 전처리 조건 (산화배소, NaOH 침지)에 따른 희토류 (REEs)와 철의 산 침출 거동을 비교 및 분석하였다. 시료는 NdFeB 자석 가공 공정에서 발생한 미세 분말 슬러지로, XRF 및 XRD 분석 결과 Nd, Pr, Dy, Tb 등의 희토류와 Fe 산화물이 주성분으로 확인되었다. 본 시료를 전처리 없이 침출 시 염산 2 M, 온도 75℃ 조건에서 희토류 침출율 99%, 철 침출율 96%로 동반 침출되어 선택적 회수가 불가능함을 확인하였다. 전처리 방법 중 산화배소 (660℃, 3 h) 시에는 NdFeO₃ 복합 산화물과 Fe₂O₃가 형성되어 희토류 침출이 현저히 저하되는 것으로 나타났다. 반면, NaOH 침지 (50 wt.% NaOH, 145℃, 5 h) 적용 시에는 Nd(OH)₃와 Fe₃O₄ 상이 형성되었으며 염산 농도(0.5–2 M) 및 온도(25–75℃) 조건을 변화시켜 침출 실험을 수행한 결과, 0.5 M HCl, 25℃의 비교적 온건한 침출 조건 하에서 희토류 침출율 99.5% 이상, Fe 침출율 0.53%로 가장 우수한 선택성을 보였다. 본 연구를 통해 NaOH 침지 전처리와 저농도·상온 침출 조건이 Fe 침출을 효과적으로 억제하면서 NdFeB 슬러지로부터 희토류를 선택적으로 침출할 수 있음을 확인하였다.

키워드

NdFeB 슬러지

희토류

NaOH 침지

산화배소

선택적 침출

References

IEA (International Energy Agency), 2021 : The Role of Critical Minerals in Clean Energy Transitions, IEA Publications, Paris, France.

IEA (International Energy Agency), 2023 : Critical Minerals Market Review 2023, IEA Publications, Paris, France.

Yoon, H.-S., Kim, C.-J., Lee, J.-Y., et al., 2003 : Separation of Neodymium from NdFeB Permanent Magnetic Scrap, J. of Korean Inst. of Resources Recycling, 12(6), pp.57-63.

Orefice, M., Van den Bulck, A., Blanpain, B., et al., 2020 : Selective roasting of Nd–Fe–B permanent magnets as a pretreatment step for intensified leaching with an ionic liquid, Journal of Sustainable Metallurgy, 6(1), pp.91-102.

10.1007/s40831-019-00259-1

Kim, Dae-Weon, Kim, Hee-Seon, Kim, Boram, et al., 2022 : A study on the Separation/recovery of Rare Earth Elements from Waste Permanent Magnet by a Fractional Crystallization Method and Sulfuric Acid Leaching, Clean Technology, 28(2), pp.103-109.

10.7464/KSCT.2022.28.2.103

Yoon, H.-S., Kim, C.-J., Chung, K. W., et al., 2015 : The effect of grinding and roasting conditions on the selective leaching of Nd and Dy from NdFeB magnet scraps, Metals, 5(3), pp.1306-1314.

10.3390/met5031306

Zhihan, Z., Lin, Y., Xu, Y., et al., 2023 : A green process for selective rare-earth recovery from Nd-Fe-B magnets, Chemical Engineering Journal, 468, 143562.

Zhang, Y., Gu, F., Su, Z., et al., 2020 : Hydrometallurgical recovery of rare earth elements from NdFeB permanent magnet scrap: A review, Metals, 10(6), p.841.

10.3390/met10060841

Chung, K. W., Kim, C.-J., and Yoon, H.-S., 2015 : Novel extraction process of rare earth elements from NdFeB powders via alkaline treatment, Archives of Metallurgy and Materials, 60(2), pp.1301-1305.

10.1515/amm-2015-0118

Önal, M. A. R., Borra, C. R., Guo, M., et al., 2015 : Recycling of NdFeB Magnets Using Sulfation, Selective Roasting, and Water Leaching, Journal of Sustainable Metallurgy, 1(3), pp.199-215.

10.1007/s40831-015-0021-9

Information

Publisher :The Korean Institute of Resources Recycling
Publisher(Ko) :한국자원리싸이클링학회
Journal Title :Resources Recycling
Journal Title(Ko) :자원리싸이클링
Volume : 35
No :3
Pages :35-43
Received Date : 2026-05-04
Revised Date : 2026-06-12
Accepted Date : 2026-06-16
DOI :https://doi.org/10.7844/kirr.2026.35.3.35

Resources Recycling ISSN:2765-3439(Print) 2765-3447(Online) 자원리싸이클링

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