Eco-friendly chitosan-based composite microspheres for efficient recovery of gold from electronic waste via adsorption-reduction cascade

With the growing demand for gold, recovering it from gold-containing solutions and electronic waste has emerged as a sustainable approach to mitigate environmental pollution and resource depletion. In this context, eco-friendly materials receive increasing attention due to their sustainability, non-toxicity, biodegradability. Here, a novel environmentally friendly porous bead material, CS-Fc@CD-TU, was developed using ferrocene-modified chitosan, oxidized cyclodextrin and thiourea, combining adsorption and reduction capabilities. Despite its moderate specific surface area (44.94 m²·g^-1), CS-Fc@CD-TU exhibited exceptional Au(III) adsorption, with a maximum adsorption capacity of 722.18 mg·g^-1, following pseudo-second-order kinetic and Langmuir isotherm models. The material maintained high removal efficiency (> 94 %) across temperatures (20-50 °C), Au(III) concentrations (50-200 mg·L^-1), and pH levels (3-6), with excellent selectivity (distribution coefficient: 5.41 × 10⁴) and interferences resistance. Notably, the adsorbed gold ions were rapidly reduced in situ to Au(0) due to the presence of ferrocene groups and CN bonds, thereby releasing the occupied adsorption sites for further gold ion capture. The reduced Au(0) further grow into Au nanoparticle (6-100 nm) with 99.8 % purity after calcination. When applied to electronic waste, CS-Fc@CD-TU effectively recovered gold ions at extremely low concentrations (1.23 ppm) and demonstrated high stability and reusability, retaining >97 % removal efficiency after five cycles. These results highlight CS-Fc@CD-TU as a promising, eco-friendly adsorbent for sustainable gold recovery.