Hydroxyapatite nanowires engineered for sustainable nickel resource recovery: surface design, interfacial adsorption mechanism and performance

The escalating demand for nickel driven by electric vehicles and renewable energy storage has led to dual challenges of environmental pollution and resource sustainability. Herein, we report the synthesis of hydroxyapatite nanowires (HAPNWs) via a biomimetic solvothermal approach, positioning them as a rapid-uptake and eco-friendly adsorbent for targeted Ni2+ removal and recovery. The unique interwoven nanowire structure endowed the material with a high specific surface area (18.02 m 2 /g) and abundant mesopores, resulting in ultrafast adsorption kinetics, reaching equilibrium within only 4 min—significantly outperforming conventional adsorbents. The adsorption process, well-described by the pseudo-second-order and Langmuir models, was identified as monolayer chemisorption. A comprehensive mechanistic study, combining XPS, FT-IR, and XRD analyses, revealed that the adsorption proceeds via a synergistic effect of ion exchange (Ca 2+ /Ni 2+ ), surface complexation with phosphate/hydroxyl groups, and partial reduction. The HAPNWs exhibited exceptional selectivity for Ni 2+ over competing ions like Li + and Mg 2+ , which is crucial for treating complex waste streams such as battery recycling effluents. Furthermore, the adsorbent demonstrated excellent reusability, with a high Ni 2+ recovery efficiency of 92% using dilute HCl. This work highlights an operationally simple inorganic adsorbent emphasizing minute-scale Ni 2+ capture and acid regeneration for nickel recovery in a resource-recovery context.