Magnetically Retrievable Core@Shell Nanocomposites for Rare Earth Element Adsorption: Experimental and Machine Learning Insights

Rare earth elements (REEs) are essential for contemporary technologies; however, their sustainable recovery from aqueous media remains challenging due to limited reserves and the environmental impacts associated with conventional extraction methods. This study presents the synthesis of magnetically retrievable core@shell nanocomposites (MRCSNs) as an efficient platform for REE adsorption from water. The MRCSNs consist of a magnetic zerovalent iron nanoparticle core, a silica shell scaffold, and surface-attached functional ligands, including 3-aminopropyltriethoxysilane (NH 2 ), 3-(2-aminoethylamino)propyltrimethoxysilane (NHNH 2 ), and trimethoxysilylpropyl ethylenediamine triacetic acid trisodium salt (EDTA). This architecture combines magnetic responsiveness with tailored chemical affinity, enabling rapid magnetic separation and selective adsorption of REEs. The nanocomposites were synthesized through a simple ambient-temperature procedure and comprehensively characterized to confirm their structure and composition. Adsorption studies demonstrated effective removal of Er 3+, La 3+, Nd 3+, Pr 3+, and Sm 3+ ions, with MRCSN-EDTA exhibiting the highest performance, achieving adsorption efficiencies of up to 82% for Er 3+ and 75% for Sm 3+ at a sorbent loading of 100 mg. Furthermore, machine learning models were integrated with experimental adsorption data in a cyclical feedback framework to predict adsorption behavior and identify key performance descriptors. The developed XGBoost models achieved an overall R 2 of approximately 0.93, identifying sorbent loading as the dominant factor governing adsorption performance, while REE atomic number served as a secondary descriptor. These results highlight the potential of integrating magnetic nanocomposites with machine learning for efficient REE adsorption.