Enhanced aqueous phosphate removal using chitosan-modified zirconium-loaded cork biochar

Abstract

Abstract The adsorption of phosphate (PO4–P) is essential for controlling and reducing eutrophication. This study reports the synthesis of a new adsorbent material: Zr(IV)-loaded chitosan-modified used cork stopper biochar composite (CS–CBC–Zr) beads. The suitability of CS–CBC–Zr beads for PO4–P removal was assessed using the batch method. The effects of various parameters were investigated, including zirconium loading level, adsorbent dosage, pH, co-anions, contact time, and the initial concentration of PO4–P. The experimental data were thoroughly analyzed using adsorption kinetic and isotherm models. Virgin beads and P-adsorbed beads were characterized using FTIR, SEM, and XPS analyses. The results demonstrated that the combination of Zr coating and CS–CBC beads exhibited superior adsorption performance compared to individual CS–CBC beads. The CS–CBC–Zr beads exhibited a maximum adsorption capacity of 33.89 mg/g, as predicted using the Langmuir–Freundlich (Sips) model. The CS–CBC–Zr beads removed PO4–P with an efficiency of 95% at an initial pollutant concentration of 50 mg/L and reached adsorption equilibrium within 120 min of contact time, outperforming some comparable adsorbents. Moreover, the beads achieved excellent PO4–P removal performance over a wide pH range of 4–10, making them highly versatile. The experiment on the effect of coexisting anions demonstrated the excellent selectivity of CS–CBC–Zr for PO4–P. Phosphate adsorption on CS–CBC–Zr fitted well with the pseudo-second-order kinetic and Sips models. Kinetic data closely fitted the pseudo-second-order model, suggesting that adsorption was primarily governed by chemisorption.