Recovering Rare Earth Elements from Aqueous Solution with Porous Amine–Epoxy Networks

Abstract

Recovering aqueous rare earth elements (REEs) from domestic water sources is one key strategy to diminish the U.S.'s foreign reliance of these precious commodities. Herein, we synthesized an array of porous, amine-epoxy monolith and particle REE recovery sorbents from different polyamine, namely tetraethylenepentamine, and diepoxide (E2), triepoxide (E3), and tetra-epoxide (E4) monomer combinations via a polymer-induced phase separation (PIPS) method. The polyamines provided -NH (primary amine) plus -NH (secondary amine) REE adsorption sites, which were partially reacted with C-O-C (epoxide) groups at different amine/epoxide ratios to precipitate porous materials that exhibited a wide range of apparent porosities and REE recoveries/affinities. Specifically, polymer particles (ground monoliths) were tested for their recovery of La, Nd, Eu, Dy, and Yb (Ln) species from ppm-level, model REE solutions (pH ≈ 2.4, 5.5, and 6.4) and a ppb-level, simulated acid mine drainage (AMD) solution (pH ≈ 2.6). Screening the sorbents revealed that E3/TEPA-88 (88% theoretical reaction of -NH plus -NH) recovered, overall, the highest percentage of Ln species of all particles from model 100 ppm- and 500 ppm-concentrated REE solutions. Water swelling (monoliths) and ex situ, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) (ground monoliths/particles) data revealed the high REE uptake by the optimized particles was facilitated by effective distribution of amine and hydroxyl groups within a porous, phase-separated polymer network. In situ DRIFTS results clarified that phase separation, in part, resulted from polymerization of the TEPA-E3 (N-N-diglycidyl-4-glycidyloxyaniline) species in the porogen via C-N bond formation, especially at higher temperatures. Most importantly, the E3/TEPA-88 material cyclically recovered >93% of ppb-level Ln species from AMD solution in a recovery-strip-recovery scheme, highlighting the efficacy of these materials for practical applications.

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“…Porous polymers have also been drawing attention as a new class of sorbents, owing to their strong and chemically resistant polymer network. Furthermore, the polymerization process allows the versatile functionalization of the material, depending on the monomer or cross‐linker utilized during the synthesis . Therefore, it is expected that such strategies could also be coupled and combined with some mesoporous components to build composites and/or hierarchical structures, which will eventually lead to highly efficient practical sorbents.…”

Preparation of diglycolamide polymer modified silica and its application as adsorbent for rare earth ions

“…Various adsorbent such as polymer materials [7,8], carbon materials [9,10], and silica materials [11,12] have been studied. To selectively adsorb REEs, small molecules bearing chelating groups such as β-diketone [13], EDTA [14], are often used to modify the material surface.…”

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“…Therefore, exploring new resources of the valuable rare earth elements represents an urgent research direction [8–16]. The recent efforts include the search and extraction of rare earth metals from waste streams, coals, and industrial residues [8, 10, 16–19]. Sensitive detection of the low-concentration rare earth elements in these resources is crucial for precisely evaluating the economic value of various resources.…”