Synthesis, Process Optimization, and Statistical Analysis of Chitosan-Based Biosorbent Beads for Selective Lithium Recovery in Lithium-Ion Battery Recycling

This study explores the application of green crosslinkers for the synthesis of chitosan biosorbent beads as a novel, sustainable method for the selective recovery of metals from spent LIB cathode materials, while offering a pathway to marine waste reuse. The proposed synthesis method alleviates the limitations of powder chitosan as an adsorbent in industrial continuous systems. Two amine-based crosslinkers, L-cystine and L-arginine, were evaluated to identify an optimal crosslinking strategy. Among them, L-cystine-crosslinked chitosan beads proved to be an efficient, stable biosorbent. Crosslinking via the thiol functional group preserved active sites, improved bead integrity without mass loss, and enabled high selectivity for Co(II) and Ni(II) separation in a sulfate-citrate medium while retaining Li in solution. Optimal performance was achieved with 1% L-cystine at a dilution factor of 30, pH 4, and an adsorbent dosage of 10 g/L. Response surface modeling indicated adsorption efficiencies of 69.55% for Co(II), 31.18% for Mn(II), and 91.62% for Ni(II), with corresponding uptake capacities of 65.56 mg/g (1.11 mmol/g), 1.47 mg/g (0.03 mmol/g), and 5.92 mg/g (0.10 mmol/g), respectively, while no lithium uptake was observed. Kinetic analysis showed rapid initial adsorption, with 46% of Co(II), 32% of Mn(II), and 88% of Ni(II) adsorbed within the first 3 h. Thermodynamic evaluation revealed endothermic adsorption, with Ni(II) exhibiting the strongest driving force. Regeneration using 0.1 M EDTA over three adsorption-desorption cycles resulted in minimal capacity loss, confirming bead reusability. This work showcases a green, selective, and practically viable biosorbent system that promotes sustainable and circular economy-based LIB recycling.