Environmentally friendly chitosan-based adsorbent for gallium recovery: Modification with 3,4,5-tris ((hydroxyhydrophosphoryl)oxy) benzoate and application to waste LED chip recycling

Abstract

The researchers synthesized the novel adsorbent chitosan/3,4,5-tris (hydroxyhydrop-hosphoryl)oxy) benzoic acid derivatives PGAC using a Schiff base mechanism for adsorption of Ga³⁺. They then characterized the PGAC using various techniques, including FTIR, BET analysis, (NMR) spectroscopy (¹³C NMR, ¹H NMR) analysis, and (GC–MS). The researchers conducted batch adsorption experiments to study how well PGAC adsorbed gallium ions (Ga³⁺) from aqueous solutions. The researchers investigated the factors controlling Ga³⁺ adsorption to identify the conditions that achieved the highest adsorption efficiency: pH 3, 30-minute contact time, 0.08 g adsorbent dose, and room temperature. The adsorption kinetics conformed to the pseudo-second-order and Elovich kinetics equation. Gallium ion adsorption is a multi-stage process, including surface adsorption and intra-particle diffusion, which is confirmed by the Intra-particle Diffusion model. The adsorption isotherm followed the Langmuir model and D-R model better than the Freundlich model, and the calculated maximum Ga³⁺ adsorption capacity was 374.75  mg.g⁻¹ at 293  K. Thermodynamic studies revealed that Ga³⁺ adsorption by PGAC is endothermic. This is indicated by the positive enthalpy change (ΔH) of 10.36 kJ/mol. However, the process is also spontaneous due to the negative value of ΔG. The positive value of ΔS suggests an increase in randomness during adsorption. Finally, the researchers applied their method to recover Ga³⁺ from actual waste LED chips. They successfully recovered Ga³⁺ and characterized the obtained gallium oxide using various tools.