Fe2O3 and Fe2O3-Pd nanohybrids for arsenic removal: Adsorption of As(III) and As(V) from water and mine tailings

• Fe 2 O 3 -Pd improved As(III) adsorption capacity up to ∼82 mg/g, over four times higher than Fe 2 O 3. • Adsorption followed pseudo-second-order kinetics, indicating chemisorption and in situ oxidation of As(III). • Fe 2 O 3 -Pd maintained high efficiency (>95%) across pH 2–11, unlike pristine Fe 2 O 3 . • In mine tailings, Fe 2 O 3 -Pd removed 93% arsenic, outperforming Fe 2 O 3 (55%). • The material shows efficiency, selectivity, and scalability potential, suitable for arsenic remediation in real systems. Arsenic (As) contamination from mining activities threatens ecosystems and public health. In this study, iron oxide (Fe 2 O 3 ) and palladium-functionalized iron oxide (Fe 2 O 3 -Pd) nanoparticles were synthesized and evaluated as nanotechnological strategies for arsenic remediation. Characterization by scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) confirmed nanoscale size (∼8 nm) and crystalline Fe 2 O 3 phases. Batch adsorption experiments with arsenic-contaminated synthetic water were performed to define optimal conditions. The effects of pH, dosage, kinetics, and isotherm behavior were examined. Best performance was observed at pH 2.5, 20 mg of nanomaterial, and 120 min of contact. Under these conditions, Fe 2 O 3 -Pd removed ∼90% of As(III) and As(V), whereas Fe 2 O 3 reached ∼50%. Kinetic and isotherm analyses showed pseudo-second-order behavior and a better fit to the Freundlich model, suggesting multilayer adsorption on heterogeneous sites. Applicability was tested with a tailings sample from the abandoned Gringo Tichagua deposit (Melipilla, Chile). Fe 2 O 3 -Pd removed 93% of total arsenic, compared with 55% for Fe2O3, maintaining efficiency despite the matrix's complexity. This improvement is attributed to Pd-catalyzed oxidation of As(III) and the formation of stable inner-sphere complexes. Overall, Pd-functionalized iron oxides demonstrate high efficiency, selectivity, and robustness, making them optimal nanosubstrates for arsenic remediation. Environmental Implications Arsenic (As) contamination from mining residues threatens ecosystems and human health, particularly in areas with abandoned tailings. This study shows that Pd-functionalized iron oxide nanoparticles (Fe 2 O 3 -Pd) act as efficient nanoadsorbents for arsenic removal in both synthetic water and real mine tailings, reaching 93% efficiency under optimized conditions. Superior performance results from the combined effects of surface adsorption and Pd-catalyzed oxidation, enhancing reactivity, stability, and selectivity even in complex matrices. These findings highlight the potential of hybrid nanomaterials as scalable, sustainable technologies for arsenic remediation, offering practical solutions to mitigate contamination challenges in mining regions and protect water resources.