Pyrrolidinium-Assisted Proton and Cation Exchange Enables Near-Quantitative Rare Earth Extraction from Synthetic NdFeB Leachate
Year: 2026
Type: preprint
Abstract: Diglycolamide (DGA) extractants offer strong affinity for rare-earth elements (REEs), tunable coordination, and phosphorus-free chemistry. Incomplete use of their molar capacity limits extractant utilization efficiency (EUE), while low distribution ratios (D) require larger organic-phase volumes. Ionic liquids (ILs) can stabilize DGA–REE complexes and modify extraction pathways, with proton exchange reported in some imidazolium ILs and IL-mediated cation or anion exchange in others. Combining exchange pathways within a single system could improve extraction and EUE, but this remains underexplored. Screening five ILs with N,N-dioctyldiglycolamic acid (DODGAA) identified [C2mpyrr][NTf2] as the best-performing formulation, outperforming the tested pyridinium- and imidazolium-based ILs and achieving an Nd3+ distribution ratio of approximately 7,000 at an organic-to-aqueous volume ratio of 0.1 with near-quantitative extraction. Slope analysis (~3.3), proton balance (~1 H+ per Nd3+), and aqueous 1H NMR support coupled proton and IL-cation exchange. The maximum EUE of 17.0% is comparable to several organophosphorus extractants. In synthetic NdFeB leachate, Nd3+ and Dy3+ were extracted at >99%, with low boron transfer and iron removed by hydroxide precipitation. Over five extraction–stripping cycles, the organic phase retained ~73% of its initial extraction efficiency, limited by incomplete single-stage stripping. Pyrrolidinium-assisted coupled exchange offers an efficient route to REE extraction.
Source: ChemRxiv
Institution: University of Illinois Chicago
Language: English
Subfield: Metals and Alloys
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7223159515