Histidine-functionalized chitosan beads via sequential ionic–covalent crosslinking strategy for highly selective copper separation from battery leachate

Highly selective separation of Cu²⁺ is crucial yet challenging for the sustainable recovery of Ni, Co, Mn, and Li from spent lithium-ion batteries (SLIBs) leachate. Herein, a stable chitosan-based composite bead (CS0.5PH) was developed via an “ionic–covalent” two-step crosslinking strategy combined with histidine modification for the highly selective Cu²⁺ adsorption. CS0.5PH was shaped with sodium tripolyphosphate (STPP) and stabilized with epichlorohydrin (ECH), achieving enhanced acid resistance and cycling stability. The influence of STPP on selective adsorption was systematically examined. Subsequent histidine grafting introduced imidazole moieties, which acted synergistically with the amino groups to markedly improve Cu²⁺ selectivity. In mixed Ni²⁺, Co²⁺, and Mn²⁺ systems, selectivity coefficients ranged from 86.49 to 158.86–surpassing most reported materials. In simulated SLIBs leachate, over 99% of Cu²⁺ was preferentially removed with minimal loss of valuable metals and negligible adsorption of Li⁺. DFT calculations further confirmed the stronger binding affinity of Cu²⁺ over Ni²⁺, Co²⁺, and Mn²⁺, consistent with the experimental selectivity order. The adsorbent retained >90% of its original adsorption capacity after five regeneration cycles. Following circular economy principles, the Cu²⁺-loaded adsorbent was converted into potassium copper hexacyanoferrate (CS0.5PH–KCuFC) for highly selective Cs⁺ adsorption, enabling high-value upcycling. Thus, with its excellent Cu²⁺ selectivity and stability, the CS0.5PH adsorbent provides a sustainable pathway for resource recycling and the high-value utilization of associated wastes.