Stable immobilized amine sorbents for heavy metal and REE removal from industrial wastewaters†
Pollution of precious water systems with heavy metals predicates the need to eliminate them from industrial process or mining effluents prior to discharge to sustain this vital resource. Herein, we developed H2O-stable basic immobilized amine sorbents (BIAS) from a combination of N,N-diglycidyl-4-glycidyloxyaniline tri-epoxide crosslinker (E3) and polyethylenimine (PEI). Stability screening was accomplished through thermal gravimetric analysis decompositions and CO2 capture studies. Amine leach resistance of the optimized formula, PES-0.43-500 (40 wt% E3/PEI-0.43 on 500 μm SiO2) was further analyzed by CHNS analysis and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Examination of wash solution with our UV-vis/Cu2+ amine quantification technique confirmed TGA results. Sequential impregnation of SiO2 with E3/PEI was monitored in situ by DRIFTS and distinguished an interfacial, hydrogen-bonded E3–PEI⋯SiO2 layer from a bulk crosslinked E3–PEI network. Comparative adsorption tests were conducted with PES-0.43-500, S930PLUS cation exchange resin, and pine biochar for toxic (Pb, Cd, Hg, Se, Ar, Se), valuable (La through Yb REE's), and other heavy (Al, Mn, Zn, Cu, etc.) metals removal/recovery from synthetic and real solutions. High affinity of PES-0.43-500 towards Cr, As, and Se and its high Hg (99.2%) and Pb (98.2%) uptakes from a six-element mixture translated well to commercial flue gas desulfurization water discharge (FGD, pH 6.7) and Pb-spiked tap water. Near-complete recovery of all REE's from local acid mine drainage (AMD-PBG, pH 3.6) outperformed the resin and was closely mirrored during 5-cycle REE recover-strip testing with synthetic AMD (pH 2.6). Robust performance and easy scalability of green BIAS materials make them attractive for commercialization.