1 research outputs found
Recovering Rare Earth Elements from Aqueous Solution with Porous Amine–Epoxy Networks
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<sub>2</sub> (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<sup>3+</sup>, Nd<sup>3+</sup>, Eu<sup>3+</sup>, Dy<sup>3+</sup>, and Yb<sup>3+</sup> (Ln<sup>3+</sup>) 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<sub>2</sub> plus −NH)
recovered, overall, the highest percentage of Ln<sup>3+</sup> 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 (<i>N</i>-<i>N</i>-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<sup>3+</sup> species from AMD solution
in a recovery–strip–recovery scheme, highlighting the
efficacy of these materials for practical applications