Adsorption of gallium (III) on a novel modified chitosan in strong alkaline media — Synthesis, performance and mechanisms

A glutaraldehyde and acrylic acid modified chitosan was developed and tested experimentally as a novel adsorbent for Ga(III) recovery from alkaline aqueous solutions. The adsorbent was prepared using chitosan as the main bio-based matrix, acrylic acid for grafting, and glutaraldehyde for crosslinking, and it was intentionally designed for Ga(III) recovery under the specific strong alkaline conditions as typical of industrial alumina production from bauxite. Batch adsorption experiments identified the effects of solution pH, initial Ga(III) concentration, contact time, and adsorbent dosage on the Ga(III) adsorption performance. The adsorption kinetics, isotherms, and thermodynamics were analyzed using nonlinear regression and key thermodynamic parameters (ΔG, ΔH, ΔS) were calculated. The maximum adsorption capacity of Ga(III) reached 117.1 mg/g at pH 9 with an adsorbent dosage of 1 g/L and a contact time of 250 min. The adsorption kinetic data demonstrated conformity with the pseudo-second-order kinetics and Elovich model. Thermodynamic analysis indicated that the model parameters of Ga(III) adsorption process suggest its spontaneous and endothermic character. The present study confirmed experimentally an effective and original method for enhanced Ga(III) recovery under high pH conditions using a newly developed modified chitosan adsorbent. This simpler approach avoids complicated pH adjustment in alumina production technology, which can significantly simplify the process flow and make the simultaneous recovery of gallium more economically and ecologically feasible.