Recoverable Solvent-Treated Poultry Feathers for Multi-Metal Biosorption of Oxyanions and Cations: Experimental and Modeling Insights

• THF-treated poultry feathers achieved high removal of both cations and oxyanions. • Kinetics follow pseudo-second-order, suggesting chemisorption dominates. • Langmuir isotherm confirmed monolayer adsorption with high capacity. • Modified feathers offer a sustainable solution for multimetal water remediation. This study evaluates the biosorption potential of poultry feathers (PFs), modified using recoverable solvents (water, acetic acid, toluene, heptane, hexane, tetrahydrofuran), as biosorbents for the simultaneous removal of oxyanions (V 5+ , Cr 6+ , As 3+ ) and cations (Cd 2+ , Co 2+ , Ni 2+ ) from multi-metal simulated water. Among the test modifications, THF-treated PFs (TTPFs) achieved the highest removal efficiency. Biosorption performance was influenced by particle size (∼2 mm–fine), adsorbent dosage (0.01–0.025 g/ml), metal ion concentration (1–100 mg/L), and contact time (up to 24 h) at pH 7.5 and room temperature. FTIR confirmed the role of hydroxyl and carbonyl functional groups in metal binding, while TGA/DTG and DSC showed enhanced thermal stability and structural integrity after modification and biosorption. Kinetic data fit best to the pseudo-second order and Elovich models, indicating chemisorption as the dominant mechanism. Adsorption isotherms were described by the Langmuir model, with maximum adsorption capacities were 3.40 mg/g (V 5+ ), 2.63 mg/g (Cr 6+ ), 4.13 mg/g (As 3+ ), 4.35 mg/g (Co 2+ ), 4.78 mg/g (Ni 2+ ), and 21.40 mg/g (Cd 2+ ), all higher than untreated PFs. In multi-metal systems, competitive uptake followed the extended Langmuir isotherm, where Cd 2+ exhibited the greatest reduction in biosorption. These results demonstrate that TTPFs are a low-cost, sustainable and thermally stable biosorbent offering a practical approach for removing diverse multi-ions from contaminated water, including oil sands process-affected water.