Green chitosan–starch–polyvinyl alcohol bio-composite hydrogel for zirconium capture from zircon raffinate

A novel polymer-based sorbent comprising three blended components was synthesized via aqueous mixing and ultrasonication for the efficient removal of Zr(IV) from highly acidic solutions. Characterization by FT-IR, SEM, and surface area analysis confirmed active functional groups and a mesoporous structure (16.704 m2 g⁻1, 3 nm pores). Batch studies revealed that maximum uptake (102 mg g⁻1) occurred at pH 1.25 after 120 min at 20 °C, increasing to 188 mg g⁻1 with higher initial concentrations (50–750 mg L−1). Uptake decreased at elevated temperatures (293–323 K), indicating exothermic adsorption. Kinetic analysis was consistent with adsorption involving surface interactions and was best described by the pseudo-second-order and Elovich models, while equilibrium data were better fitted by the Freundlich model, suggesting a heterogeneous adsorption surface. Thermodynamic parameters (ΔG = –18.84 to –19.60 kJ mol−1; ΔH = − 11.35 kJ mol−1; ΔS = 25.57 J mol−1 K−1) confirmed a spontaneous and exothermic process. The sorbent remained stable in acidic media up to 2 M H2SO4 and was effectively regenerated, with H2SO4 achieving the highest desorption efficiency. These findings suggest that the prepared material shows potential as an effective sorbent for Zr(IV) recovery from acidic process streams.