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To recover the lanthanides, strong acids are used to leach them from the solid waste. The composition of lanthanides in the waste varies with the geographical location from which the coal was mined. One abundant source of REEs is the fly ash and wastewater from coal-fired combustion power plants ( Binnemans et al., 2015 Dai and Finkelman, 2018 Wang et al., 2019). Such strategies may include sequestering lanthanides from recycled electronic waste (circuits, cellphones, magnets) or from industrial waste streams. Increasingly strict export controls and many countries' lack of minable repositories within their boundaries are causing them to seek alternative strategies for acquiring REEs to supply high-tech industries. Currently, China produces 75% of lanthanides and >90% of REEs worldwide. Lanthanides, which constitute the majority of the rare earth elements (REEs), are gaining increased attention worldwide due to their versatile applications in oil refining ( Kilbourn, 1986), agriculture ( Xu et al., 2002), metallurgy and alloys ( Biesiekierski et al., 2019) and in high-technology applications such as super magnets, batteries, and electronics ( Balaram, 2019). The low-temperature membrane functionalization methodology presented in this work can be used to immobilize biomolecules with even higher specificity, like engineered peptides or proteins, on membrane surfaces. The dynamic binding capacity at 50% breakthrough was independent of flowrate within the tested range. Dynamic adsorption experiments were conducted with 1 ppm La 3+ feed solutions at different flow rates using either a single membrane or three membranes in series. Lower adsorption of the higher charge density species indicates that the primary binding mode is through the amine moieties of lysine and not the carboxylic acid. Nd 3+ adsorbed to the membrane however, the fit of the Langmuir model was not significant and it adsorbed to a lower extent than La 3+ and Ce 3+. The maximum capacities modeled by the Langmuir isotherm for La 3+ and Ce 3+ were 6.11 ± 0.58 and 6.45 ± 1.29 mg/g adsorbent, respectively. Lysine-modified membranes showed negligible uptake of Na +, Ca 2+, and Mg 2+. Equilibrium adsorption experiments were performed for single specie solutions of La 3+, Ce 3+, Nd 3+, Na +, Ca 2+, and Mg 2+ at pH 5.25 ± 0.25. The degree of grafting for the p-GMA film was quantified gravimetrically and increased with increasing polymerization time. Changes in membrane surface chemistry throughout the functionalization process were monitored with Fourier Transform Infrared Spectroscopy. Then, the reactive epoxy groups of the grafted p-GMA were used for the covalent attachment of lysine molecules via a zinc perchlorate-catalyzed, epoxide ring-opening reaction at 35☌.
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In this work, membrane adsorbers were synthesized by first using ultraviolet-initiated free radical polymerization to graft a poly(glycidyl methacrylate) (p-GMA) layer to the surface of polyethersulfone membranes. Membrane adsorbers are promising separation materials to recover lanthanides from high volumes of wastewater due to their tailorable surface chemistry, high binding capacity and high throughput. Although the available lanthanide resources are enough for current levels of manufacturing, increased future demand for lanthanides will require new, efficient recovery methods to provide a sustainable supply.
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Rare-earth elements (which include all lanthanides, scandium, and yttrium) play a key role in many fields including oil refining, metallurgy, electronics manufacturing, and other high-technology applications.