Abstract: Staged separation of transition metals and lithium from multimetal leachates remains a key challenge in the hydrometallurgical recycling of spent NCM cathodes. Herein, an integrated strategy combining hydrated ascorbic acid-choline chloride (AA-ChCl) leaching, alkaline coprecipitation, and bubble-size-controlled CO₂ carbonation was developed for spent LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523). At a selected AA/ChCl molar ratio of 1:2, the optimized leaching conditions were obtained as water content of 50 wt%, leaching temperature of 50 ℃, liquid-to-solid ratio of 30 mL g^-1, and leaching time of 60 min. Under these conditions, the leaching efficiencies of Li, Mn, Co, and Ni reached 99.5%, 97.2%, 95.1%, and 96.2%, respectively. Water addition substantially reduced the viscosity of the AA-ChCl medium, while structural and surface analyses supported a leaching mechanism involving lattice disruption and AA-mediated reductive dissolution. Subsequent alkaline coprecipitation removed 97.1% of the total Ni, Co, and Mn from the leachate, thereby generating a Li-rich filtrate for downstream carbonation. Microbubble carbonation achieved a stage Li recovery of 94.0% within 30 min, compared with 77% and 51% under conventional- and coarse-bubble conditions, respectively. Prolonged carbonation under microbubble conditions decreased Li recovery, highlighting the importance of carbonation endpoint control. The recovered product had a Li₂CO₃-equivalent content of 95.0%. This work demonstrates an integrated low-temperature mild route for transition-metal/Li separation and subsequent lithium recovery from spent NCM cathodes.
 

Keywords: NCM523; deep eutectic solvent; reductive leaching; microbubble carbonation; lithium recovery