Super concentrated HCl in a deep eutectic solvent as media for the integrated leaching and separation of metals from end-of-life lithium-ion batteries

Abstract

Recycling spent lithium-ion batteries is vital to ensure the recovery of added-value resources and minimize environmental impact. Herein, an integrated and efficient process is developed for metal recovery from spent cathode powder combining both leaching and transition metal separation in one step. A hydrophobic deep eutectic solvent (DES) is proposed as a HCl super concentrator for the one-pot leaching of cathodes from spent lithium-ion batteries and simultaneous Ni(II) precipitation. The DES composed of decanoic acid and trioctylphosphine oxide can super concentrate HCl, 2.2-folds more than the aqueous limit of 37 wt%, whilst being thermally and chemically stable under leaching conditions up to 373 K. The proposed leaching process can quantitatively extract Co(II), Mn(II) and Cu(II) from spent cathodes of laptop batteries whilst only extracting 10 % of Ni(II). The latter could be easily recovered as NiCl2·2H2O with 99 % purity through the manipulation of the coordination environment afforded by the DES relative to aqueous media. Key leaching parameters were the HCl:metal molar ratio and temperature, both having a significant impact on the leaching efficiency and its selectivity. Metal recovery was accomplished after stripping of the loaded DES solution via a straightforward sequential precipitation process, with 99 % Co(II) and 98 % Mn(II) being precipitated with 95 % and 81 % purity, respectively. The reported system presents a better atom economy compared to other DES and conventional inorganic acids, providing a new mild approach for the simultaneous leaching and separation of metals from lithium-ion batteries.