Adsorption Behavior and Kinetic Modeling of Cobalt Ions from Nitric Acid Medium Using Cobalt Ion-Imprinted Polymer

Efficient separation of metal ions from acidic solutions is important in environmental and industrial applications. Using a cobalt ion-imprinted polymer (Co-IIP) based on chitosan and polyacrylamide, this work examines the adsorption behavior, kinetic modeling, and thermodynamic properties of cobalt ions from a nitric acid medium. The Co-IIP was synthesized via a two-step process involving the coordination of Co2+ ions with chitosan, followed by cross-linking with epichlorohydrin and grafting with polyacrylamide under ultrasonic homogenization, ensuring enhanced porosity and binding efficiency. A nonimprinted polymer (NIP) was prepared under identical conditions for comparison. The synthesized polymers were characterized using FTIR, SEM, and TGA techniques, confirming successful cobalt imprinting, uniform porous morphology, and good thermal stability up to 250 °C. Batch adsorption experiments revealed that cobalt adsorption was highly influenced by nitric acid concentration, contact time, and pH. The ideal sorption transpired at about pH 5 as well as low nitric acid concentration (0.01 M HNO3), where the Co-IIP exhibited a maximum removal efficiency of 95% for Co2+ with a maximum adsorption capacity of 75 mg·g–1, significantly higher than the NIP and Zn2+ competitive ions. The adsorption data fit the pseudo-second-order model well, suggesting that chemical interactions at the polymer surface contribute to the overall adsorption mechanism without excluding other rate-controlling steps. After five cycles of adsorption and desorption, the Co-IIP maintained more than 80% of its original adsorption capacity, proving its excellent regeneration ability and stability. Unlike previously reported cobalt ion-imprinted or chitosan-based adsorbents, this work integrates ultrasonic-assisted grafting of polyacrylamide onto a chitosan matrix, enabling stable and selective cobalt recognition in nitric acid media. These results demonstrate the potential of cobalt ion-imprinted polymers made of chitosan and polyacrylamide as effective, reusable, and selective adsorbents for the recovery and extraction of cobalt ions from waste and nitric acid environments.