Efficient water-assisted precipitation of nickel, manganese, and cobalt from ethaline deep eutectic solvent

Ethaline deep eutectic solvent (DES), composed of choline chloride and ethylene glycol, is a biodegradable, selective, and particularly reusable leaching agent for spent lithium-ion battery (LIB) cathode materials such as LiCoO₂ and LiNixMnyCo₁₋ₓ₋ᵧO₂. However, for effective reuse of DES, transition metal cations must first be removed from the leachate. Conventional extraction methods, such as solvent extraction and electrodeposition, are often costly and complex. This work presents a simple, efficient, and low-cost metal recovery strategy that uses deionized water as a precipitating agent to extract valuable transition metal cations and regenerate the DES. Under optimal conditions, 94% of Ni, 98% of Mn, and 99% of Co were precipitated, while over 90% of Li remained in the solution and was subsequently recovered as Li₂CO₃ via sodium carbonate addition. The precipitation mechanism is attributed to the disproportionation of superoxide ions—generated during leaching—upon water addition, leading to a basic environment that facilitates hydroxide formation. After precipitation and water removal by heating, the DES was reused for at least three leaching cycles, showing improved performance compared to the pristine solvent. This enhancement is believed to be linked to the formation of Cl₃⁻ species during DES decomposition. • Facile and highly efficient precipitation of Ni, Co and Mn from ethaline DES • Ethaline DES can be reused after dehydration process for at least 3 times • Discovering the water-assisted precipitation mechanism using ethaline DES