Agro-Industrial Residues as a Unified Adsorbent Platform for the Removal of Rare Earth Elements, Transition Metals, and Organic Micropollutants from Water

Abstract Agro-industrial residues are produced in large volumes and are frequently discarded, yet they can be converted into adsorbents that address pressing water contamination problems. This Technical Note advances a unifying valorization concept by re-analyzing the reported performance of four residue-derived adsorbents prepared from orange peel, potato peel, and rice husk. Two preparation routes are compared, namely the green citric acid grafting of beta-cyclodextrin onto fruit and tuber peels, and the purification or activation of carbonaceous rice husk co-products. Across the dataset, the same logic removed cationic species (lanthanum, iron, nickel), recalcitrant organics (phenol), and emerging contaminants (perfluorosulfonic acids), with reusability through mild ultrasound or thermal desorption and effectiveness in real matrices. Matching residue and modification route to contaminant charge and hydrophobicity emerges as a practical design rule. The analysis positions agro-industrial residues as a modular, low-cost adsorbent platform for environmental remediation.