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 (Ka) 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.