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

Walter Christopher Wilfong; Brian W Kail; Tracy L Bank; Bret H Howard; McMahan L Gray

doi:10.1021/acsami.7b03859

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

ACS Appl Mater Interfaces. 2017 May 31;9(21):18283-18294. doi: 10.1021/acsami.7b03859. Epub 2017 May 19.

Authors

Walter Christopher Wilfong^{1

2}, Brian W Kail³, Tracy L Bank³, Bret H Howard¹, McMahan L Gray¹

Affiliations

¹ U.S. Department of Energy, National Energy Technology Laboratory , 626 Cochrans Mill Road, Pittsburgh, Pennsylvania 15236, United States.
² Oak Ridge National Laboratory , P.O. Box 2008, Oak Ridge, Tennessee 37831, United States.
³ AECOM , 626 Cochrans Mill Road, Pittsburgh, Pennsylvania 15236, United States.

PMID: 28498653
DOI: 10.1021/acsami.7b03859

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 -NH₂ (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 La³⁺, Nd³⁺, Eu³⁺, Dy³⁺, and Yb³⁺ (Ln³⁺) 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 -NH₂ plus -NH) recovered, overall, the highest percentage of Ln³⁺ 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 Ln³⁺ species from AMD solution in a recovery-strip-recovery scheme, highlighting the efficacy of these materials for practical applications.

Keywords: amine; infrared spectroscopy; lanthanide; porous polymer; rare earth element; water treatment.