• • Fe3O4@PDAPEI achieves adsorption capacities of 168.3, 168.5, 179.7, and 180.3 mg/g for Gd3+, Nd3+, Ho3+, and Y3+, respectively, exceeding most reported magnetic REE adsorbents by a factor of 1.5–2.0, enabling efficient recovery from low-concentration mine wastewater (typically <50 mg/L REEs).
• • The adsorbent retains >90% of its initial capacity after five reuse cycles, demonstrating robust reusability essential for continuous industrial operation and reducing operational costs associated with adsorbent replacement.
• • In the presence of competing ions (Na+, Mg2+, Al3+), the adsorption capacity remains above 100 mg/g for all four REEs, indicating high selectivity that mitigates pre-treatment costs in complex wastewater matrices.
• • The adsorption mechanism involves binding to primary amines and electrostatic interactions, as confirmed by DFT calculations, zeta potential measurements, and AFM surface force measurements, providing a molecular-level foundation for designing next-generation adsorbents with tailored functional groups.