The efficient and environmentally benign separation of rare earth elements (REEs) remains a critical challenge due to their similar chemical properties and the environmental burden of conventional solvent extraction. This study addresses this challenge through the design, synthesis, and application of novel recyclable magnetic ionic liquids (MILs) for the selective separation of REEs. A series of task-specific MILs were developed by incorporating paramagnetic metal centers (e.g., Fe(III), Co(II), Mn(II)) into the anion or cation of hydrophobic ionic liquids, paired with functional groups such as diglycolamates or phosphonates known for REE complexation. These MILs combine the tunable physicochemical properties and low volatility of ionic liquids with magnetic susceptibility, allowing for facile phase separation and recovery using an external magnetic field, eliminating the need for energy-intensive centrifugation. The MILs were characterized for their magnetic properties, thermal stability, and extraction efficiency. In liquid-liquid extraction experiments, the optimal MIL, tetradecyl (trihexyl) phosphonium tris(diglycolamato)ferrate(III), demonstrated exceptional selectivity for heavy REEs (e.g., Dy³⁺, Er³⁺) over light REEs (e.g., La³⁺, Nd³⁺) from aqueous nitrate media, with separation factors (βDy/La) exceeding 150. The extraction process achieved high distribution ratios (>500 for Dy³⁺) under mild conditions (pH ~4, room temperature). Crucially, the loaded MILs could be efficiently stripped using dilute nitric acid, and the recovered MILs were successfully reused for over 10 consecutive extraction-stripping cycles with no significant loss in performance or magnetic responsiveness. This work establishes a sustainable and efficient paradigm for REE separation, integrating high selectivity, operational simplicity via magnetic handling, and excellent recyclability into a single green solvent platform, offering significant advantages over traditional molecular diluent-based processes.

Yulong Cao. Design of Recyclable Magnetic Ionic Liquids and Its Application in Green Separation of Rare Earth Elements. Academic Journal of Materials & Chemistry (2026), Vol. 7, Issue 1: 1-6. https://doi.org/10.25236/AJMC.2026.070101.

[1] Sun P, Huang K, Song W, et al. Separation of rare earths from the transition metals using a novel ionic-liquid-based aqueous two-phase system: Toward green and efficient recycling of rare earths from the NdFeB magnets[J]. Industrial & Engineering Chemistry Research, 2018, 57(49): 16934-16943.

[2] Liu Y, Chen J, Li D. Application and perspective of ionic liquids on rare earths green separation[J]. Separation science and technology, 2012, 47(2): 223-232.

[3] Miadonye A, Amadu M. Task Specific Ionic Liquids for the Recovery of Rare Earth Element Europium from Coal Ash[J]. An International Peer-reviewed and Open Access Journal for Chemistry, 2025, 17(1): 99.

[4] Vander Hoogerstraete T, Wellens S, Verachtert K, et al. Removal of transition metals from rare earths by solvent extraction with an undiluted phosphonium ionic liquid: separations relevant to rare-earth magnet recycling[J]. Green Chemistry, 2013, 15(4): 919-927.

[5] Deng W, Geng R, Hu Z, et al. Application of Ionic Liquids and Deep Eutectic Solvents as Green Solvents in the Extraction and Separation of Rare Earths[J]. Journal of Sustainable Metallurgy, 2025: 1-22.

[6] Riaño S, Binnemans K. Extraction and separation of neodymium and dysprosium from used NdFeB magnets: an application of ionic liquids in solvent extraction towards the recycling of magnets[J]. Green Chemistry, 2015, 17(5): 2931-2942.

[7] Wang K, Adidharma H, Radosz M, et al. Recovery of rare earth elements with ionic liquids[J]. Green Chemistry, 2017, 19(19): 4469-4493.

[8] Dupont D, Binnemans K. Recycling of rare earths from NdFeB magnets using a combined leaching/extraction system based on the acidity and thermomorphism of the ionic liquid [Hbet][Tf 2 N][J]. Green chemistry, 2015, 17(4): 2150-2163.

[9] Liu T, Huang C H. Sustainable extraction of rare earth elements from coal fly ash leachates using a recyclable ionic liquid[J]. npj Materials Sustainability, 2026, 4(1): 2.

[10] Alguacil F J, Robla J I, Rodriguez Largo O. Recent uses of ionic liquids in the recovery and utilization of rare earth elements[J]. Minerals, 2024, 14(7): 734.

[11] Wu J, Chen Z, Luo L, et al. Green-synthesized magnetic MnFe2O4 nanoparticles for rapid and selective extraction of rare earth elements from mining wastewater[J]. Separation and Purification Technology, 2025: 134446.

[12] Zhu M, Zhao J, Li Y, et al. An ionic liquid-based synergistic extraction strategy for rare earths[J]. Green Chemistry, 2015, 17(5): 2981-2993.

[13] Kaczorowska M A. The latest achievements of liquid membranes for rare earth elements recovery from aqueous solutions—A mini review[J]. Membranes, 2023, 13(10): 839.

[14] Do-Thanh C L, Luo H, Dai S. A perspective on task-specific ionic liquids for the separation of rare earth elements[J]. RSC Sustainability, 2023, 1(5): 1168-1176.

[15] Arrachart G, Couturier J, Dourdain S, et al. Recovery of rare earth elements (REEs) using ionic solvents[J]. Processes, 2021, 9(7): 1202.

[16] Quijada-Maldonado E, Romero J. Solvent extraction of rare-earth elements with ionic liquids: Toward a selective and sustainable extraction of these valuable elements[J]. Current Opinion in Green and Sustainable Chemistry, 2021, 27: 100428.

[17] Li X, Li Z, Orefice M, et al. Metal recovery from spent samarium–cobalt magnets using a trichloride ionic liquid[J]. ACS Sustainable Chemistry & Engineering, 2018, 7(2): 2578-2584.

[18] Önal M A R, Dewilde S, Degri M, et al. Recycling of bonded NdFeB permanent magnets using ionic liquids[J]. Green Chemistry, 2020, 22(9): 2821-2830.

[19] Vander Hoogerstraete T, Binnemans K. Highly efficient separation of rare earths from nickel and cobalt by solvent extraction with the ionic liquid trihexyl (tetradecyl) phosphonium nitrate: a process relevant to the recycling of rare earths from permanent magnets and nickel metal hydride batteries[J]. Green Chemistry, 2014, 16(3): 1594-1606.