With the development of large-scale energy storage and the electric-vehicle market, the demand for lithium-ion batteries (LIBs) is increasing, resulting in the explosive increase in spent LIBs. The cathode materials of spent LIBs contain multiple transition elements, such as lithium (Li), cobalt (Co), nickel (Ni), and manganese (Mn). The recovery of these metals has significant environmental benefits and high economic value. As a green solvent, deep eutectic solvents (DESs) show great potential in recovering valuable metal elements from spent LIBs. Here, this study proposed a new type of DES formed from betaine hydrochloride and ethylene glycol (betaine hydrochloride and ethylene glycol at a 1 : 5 molar ratio), which can efficiently leach metal elements from spent Ni–Co–Mn lithium batteries (LNCM). The leaching rates of Ni, Co, Mn, and Li can all reach 99% under the conditions of T = 140 °C, t = 10 min and no reductant. Compared with the traditional leaching process, this study provided an economical, green, and efficient approach to recover valuable metals from spent LIBs.

A scientific and rigorous study on the adsorption behavior and molecular mechanism of collector sodium oleate (NaOL) on a Ca²⁺-activated hydroxylated α-quartz surface was performed through experiments and density functional theory (DFT) simulations. The rarely reported hydroxylation behaviors of water molecules on the α-quartz (101) surface were first innovatively and systematically studied by DFT calculations. Both experimental and computational results consistently demonstrated that the adsorbed calcium species onto the hydroxylated structure can significantly enhance the adsorption of oleate ions, resulting in a higher quartz recovery. The calculated adsorption energies confirmed that the adsorbed hydrated Ca²⁺ in the form of Ca(H₂O)₃(OH)⁺ can greatly promote the adsorption of OL⁻ on hydroxylated quartz (101). In addition, Mulliken population analysis together with electron density difference analysis intuitively illustrated the process of electron transfer and the Ca-bridge phenomenon between the hydroxylated surface and OL⁻ ions. This work may offer new insights into the interaction mechanisms existing among oxidized minerals, aqueous medium, and flotation reagents.