Ligand-enhanced 3D-printable natural nanomaterials for recovering rare earths from saline waste streams

Engineering the surface chemistry of nanomaterials enables diverse applications but requires a clear understanding of how functional groups interact with nanomaterials. Here, a systematic study on the ligand-matrix chemistry of naturally occurring clay-based nanomaterials is conducted to enhance the recovery of rare-earth elements (REE) over common competing salt ions. Our results reveal a clear correlation among functional groups, surface chemistry, and equilibrium adsorption capacity, where transitioning from electron-withdrawing to electron-donating groups resulted in an enhancement of equilibrium adsorption capacity (more than 9 times). The engineered particles exhibit a strong affinity for REE over competing ions found in brine and wastewater (e.g., Na⁺, Mg²⁺, and Ca²⁺), facilitating highly selective REE recovery from complex environments containing trace-level REE (exceeding 85% recovery in oilfield produced water). Furthermore, the functionalized clay nanoparticles are formulated into 3D-printable inks for fabricating porosity-controlled, customizable adsorbent prototypes, where the controlled macro-channel architecture enables improved adsorption kinetics (almost doubling the efficiency over a 24 h period) compared to chunk adsorbents of the same chemical composition without requiring external stirring, highlighting the potential for sustainable REE extraction.