Separation of Co and Mn from acetic acid leaching solution of spent lithium-ion battery by Cyanex272

Spent lithium-ion batteries (LIBs) contain large amounts of scarce metals, such as Li, Co, Al, Ni, and Mn, and are precious secondary resources. The leaching of spent LIBs using organic acids is considered to be an effective and feasible method for recovering these metals. However, the separation of Li, Co, Ni, and Mn in a solution is difficult to achieve. Using an extractant consisting of 15 % Cyanex272, 10 % tributyl phosphate, and 75 % sulfonated kerosene (v/v) and an organic to aqueous phase ratio of 1:1, over 90.13 % of Al, 95.72 % of Co, and 98.93 % of Mn were extracted. Only 2.05 % of Li and 2.68 % of Ni were co-extracted. The slope method and infrared spectra analysis showed that the extraction processes of Al, Co, and Mn with Cyanex272 follow cationic exchange mechanisms; the acetate anions introduced during the leaching participated in the extraction mechanism of Co. The thermodynamic parameters of Gibb’s free energy, enthalpy change, and entropy change for the extraction reactions were all lower than zero, indicating that the extraction reactions are exothermic and spontaneous and increase the disorder. After washing with NH₄HSO₄ 1 M, most of the Co and Mn were removed, and a negligible amount of Al was lost. By adding 2.5 times the stoichiometric amount of (NH₄)₂S₂O₈ to the washing solution and heating at 363.15 K for 40 min, 99.3 % of the Mn was precipitated as MnO₂ with a purity of 96.73 %. After removing Mn, Co²⁺ was precipitated as CoC₂O₄·2 H₂O using anhydrous oxalic acid; Co₃O₄ with a purity of 98.13 % was subsequently obtained by calcination. This study demonstrates the potential of hydrometallurgical processes for the treatment of spent LIBs and provides insights into strategies for the utilization of secondary resources.