Extraction of Rare Earth Elements from Organic Acid Leachate Using Formo-Phenolic-like Resins

Formo-phenolic-like resins were synthesized by replacing phenol with phloroglucinol, a biobased and biocompatible compound, and using different aldehydes, such as biomass-derived furaldehyde and glyoxal. Studies on the adsorption of rare earth elements from an aqueous organic acid solution indicate that these resins follow the Langmuir isotherm model, with maximum adsorption capacities ranging from 0.38 to 0.75 mmol/g. Adsorption was temperature-independent but strongly influenced by pH, with an up to fourfold increase between pH 2 and 5. Extraction kinetics were rapid, reaching equilibrium within two hours. Complete metal recovery was achieved within ten minutes using a 1 mol/L HCl desorption solution. Selectivity also varied with pH; glyoxal- and furfural-based resins showed superior separation performance at pH 2–3 and 3–4, respectively. The application of this method to real-world samples, including permanent magnet and red mud organic acid leachates, demonstrated effective extraction of rare earth elements and promising selectivity over iron (Fe), cobalt (Co), and nickel (Ni).