Recycling of spent LiCoO2 cathodes into layered cobalt hydroxide for oxidation processes

High-purity mixed-phase α/β-Co(OH)2 was successfully precipitated from spent Li-ion battery cathodes (LiCoO2) and characterized by XRD, FTIR, TG–DSC, and SEM–EDS. In dark conditions, suspensions containing 50 mg of Co(OH)2, 10 mM NaHCO3, and 4 mM H2O2 at pH ≈ 7 achieved complete decolorization of 10 ppm methylene blue within 50 min, following pseudo-first-order kinetics. In situ AAS measurements revealed that Co2+ concentrations remained at low micromolar levels, suggesting that the oxidative degradation was catalyzed by transiently solubilized cobalt species rather than by bulk leaching. ESI-MS and UV–Vis analyses confirmed a stepwise demethylation pathway—from methylene blue to thionine (m/z 227), and subsequently to smaller aromatic fragments (m/z 157)—approaching near-complete mineralization. This study demonstrates a light-independent advanced oxidation process that combines effective dye remediation with the sustainable recovery of cobalt from spent lithium-ion batteries.