Synthesis of Phosphonated Polymer Resins for the Extraction of Rare-Earth Elements

Abstract

Rare-earth elements (REEs: Y, Sc, La−Lu) are critical components in many modern technologies. With REE demand projected to increase over the next 15 years, materials capable of extracting REEs from complex solutions are needed. Solid-phase extractants can be used to capture or concentrate REEs, but this approach requires materials with high capacity for target elements. To address this challenge, we synthesized a phosphonate-containing polymer resin that is functionalized throughout the bulk and evaluated REE absorption as a function of pH and metal ion identity in both batch and flow experiments. We observed enhanced REE uptake with decreasing ionic radii, as seen in the distribution coefficients for each ion. To gain further insight, we measured REE−polymer binding thermodynamics with isothermal titration calorimetry (ITC) using a water-soluble polymer analogue, which revealed similar binding affinities (K a ) across the REE series for each ion. The combined microcalorimetry and solid-phase extraction experiments demonstrate the potential of these materials as future REE extractants.

Cryptands on a Solid Support for the Separation of Europium from Gadolinium

“…Our observed separation factor is greater than the reported separation factors of Eu III /Gd III for batch adsorption of solid−liquid extraction methods by a single-step process, 30,39,44,52 and our observed adsorption capacity is similar to that of other systems. 24,39,44,67 3.4. Adsorption Kinetic Studies.…”

“…Rare-earth element separation also was studied using phosphonate-containing polymer resin with a separation factor for Gd/Eu of 0.8. 39 The use of Cyanex 272 impregnated Amberlite XAD-7 resin in batch adsorption studies of Gd III and Eu III resulted in a Eu/Gd separation factor of 0.75. 52 However, a major limitation of these ligand-based solid-phase separation methods is a lack of the selective separation of trivalent middle rare-earth elements from each other in a single step.…”

“…Different solid-phase extractants have been studied with respect to their selectivity for rare-earth elements. − Modifications to the solid supports studied for the isolation of rare-earth elements include changing the size of the pores, degree of crosslinking, and degree of functionalization as well as selection of different ligands or functional groups to include on solid supports. ,,, Modification of solid supports with ligands is an important technique to separate rare-earth elements based on coordinating angle (bite angle), donor atoms, functional groups, cavity size, range of p K a , or denticity. ,,, With increasing specificity of the supported ligand, increased separation efficiencies become possible. Therefore, we hypothesized that 2.2.2-cryptand covalently linked to a solid support would enable the separation of lanthanides from each other as a function of size and charge because 2.2.2-cryptand preferentially binds divalent lanthanides relative to trivalent lanthanides .…”

Impedimetric sensors based on diethylphosphonate‐containing poly(arylene ether nitrile)s films for the detection of lead ions

“…Phosphates (O‐PO(OH) 2 ), 8 phosphoramides (RR′‐(PO)‐NR″ 2 ), 9 phosphonates esters (R‐PO(OR) 2 ) or phosphonic acids (R‐PO(OH) 2 ) 10–14 have gained a special interest because of their fascinating properties and potential applications in many fields. Phosphonic acids are especially useful in ion‐exchange materials, are incorporated in membranes (in paper and textile industry) for biomedical purposes, in desalination systems, 15 in proton exchange membranes for fuel cell applications 16,17 or are used to chelate rare earth elements 18 . However, the incorporation of high proportions of phosphonic acids in high performance polymers for the elaboration of sensors is still problematic, because of the low solubility of the resulting structures.…”

“…Phosphonic acids are especially useful in ion-exchange materials, are incorporated in membranes (in paper and textile industry) for biomedical purposes, in desalination systems, 15 in proton exchange membranes for fuel cell applications 16,17 or are used to chelate rare earth elements. 18 However, the incorporation of high proportions of phosphonic acids in high performance polymers for the elaboration of sensors is still problematic, because of the low solubility of the resulting structures.…”