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.