Hydroxamic acid-functionalized chitosan hydrogel beads for sustainable and continuous gallium recovery

The sustainable recovery of gallium (Ga), a critical metal used in semiconductors, electronics, and renewable energy technologies, is increasingly important due to rising demand and limited natural reserves. Conventional methods, such as solvent extraction and ion exchange, suffer from high cost, environmental hazards, and limited recyclability. In this study, we report a novel bio-based adsorbent-hydroxamic acid-functionalized chitosan hydrogel beads (CSQ-HA)-developed by covalently grafting 4-hydroxybenzohydroxamic acid onto chitosan. The resulting material uniquely integrates strong chelation affinity for trivalent metal ions, intrinsic biodegradability, and a hydrogel bead morphology well-suited for dynamic column adsorption-offering significant advantages over conventional powder-form or unmodified chitosan adsorbents. Characterization revealed a mesoporous architecture, high surface area (1.51 m²/g), and good thermal stability. Batch adsorption studies demonstrated a high Ga(III) uptake capacity of 95.12 mg/g at an optimal pH of 4. Kinetic modeling followed the pseudo-second-order model, and equilibrium data fit both Langmuir and Freundlich isotherms, indicating a mixed monolayer-heterogeneous adsorption mechanism. The thermodynamic parameters (ΔG < 0, ΔH > 0) indicate that the adsorption process is spontaneous and endothermic over the investigated temperature range. Fixed-bed column experiments showed stable breakthrough performance modeled by the Thomas model. Remarkably, the adsorbent retained over 80 % of its initial adsorption capacity after five desorption-regeneration cycles using dilute H₂SO₄, demonstrating excellent reusability and application potential. These results confirm that CSQ-HA offers a novel, robust, and sustainable solution for selective Ga(III) recovery, with strong potential for scale-up in critical metal separation from aqueous media.