Selective Recovery of Rare Earth Elements from Mine Ore by Cr-MIL Metal–Organic Frameworks

Rare earth elements (REEs) have become a strategic resource extensively used in renewable energy technologies and modern electronic devices. Depletion of natural REE-bearing mineral deposits has made selective recovery of REEs from alternative sources crucial in meeting the rising global demand. A chromium-based metal–organic framework was synthesized and modified with N-(phosphonomethyl)iminodiacetic acid (PMIDA) in this study to selectively recover REEs (europium, Eu) from chemically complex zinc ore leachate. The adsorbent was characterized and comprehensively examined for Eu uptake as a function of adsorbate concentration, contact time, and pH of the solution. Cr-MIL-PMIDA showed a maximum adsorption capacity of 69.14 mg/g at pH 5.5 while adsorption kinetics best fitted the pseudo-second-order model. Furthermore, Cr-MIL-PMIDA showed exceptional selectivity (88%) toward Eu over competing transitional metal ions (Na, Mg, Al, Ca, Mn, Fe, Ni, Cu, Co, and Zn) found in the dissolved mine ore. High selectivity toward REEs was attributed to the formation of coordinative complexes with grafted carboxylate, phosphonic, and residual amine functional groups. Cr-MIL-PMIDA demonstrated excellent structural stability over multiple regeneration cycles, highlighting its potential for industrial application for REE recovery.