Electrochemically Modified Walnut Shell‐Derived Activated Carbon: A Sustainable Alternative to Commercial Coconut‐Based Sorbents for Cobalt Recovery from Battery Recycling Solutions

ABSTRACT The sorption process of Co 2+ , a strategic metal from spent lithium‐ion batteries was investigated using modified activated carbons derived from walnut shell and coconut shell. Electrochemical modification was performed using cyclic voltammetry in 0.5 mol·L −1 HNO 3 electrolyte across two distinct potential windows, where intensive functionalization (0.8–1.5 V) increased the concentration of oxygen‐containing functional groups by 7.5 times. In static mode, the modified sorbents ACM‐C 2 and ACM‐W 2 demonstrated exceptional adsorption capacities of 48.92 and 44.90 mg·g −1 , respectively, achieving equilibrium within 4 min following pseudo‐second‐order kinetics. The study extended to dynamic column sorption using real polymetallic leach solutions containing competing ions (Ni, Mn, Li). Despite the complex matrix, the walnut‐based sorbent exhibited high mass transfer rates and a concentration factor of ∼3.0, allowing for significant volume reduction of productive solutions. Desorption studies using 0.1 M H 2 SO 4 showed high recovery efficiencies (>95%) and stable performance over five adsorption‐desorption cycles. Economic analysis confirms that electrochemically modified walnut shell‐derived carbon is a cost‐effective, sustainable alternative to commercial coconut‐based sorbents.