Valorization of Cobalt and Lithium from Spent Lithium-Ion Batteries via Reduction Roasting and Solvometallurgy

The economic sustainability of battery materials relies on innovative extractive strategies. Hence, the current study proposes a combined approach of reduction roasting and solvoleaching with a phosphoric acid-based extractant for recovering lithium and cobalt from spent lithium cobalt oxide (LiCoO₂) cathodes. The predissolution step involves reduction roasting at 300 °C using hydrogen peroxide to facilitate effective structural collapse and enhancing the metal dissolution efficiency. Subsequent nonaqueous leaching, or solvoleaching, achieves the dissolution of 83.2% cobalt and 91.8% lithium using 2.5 mol/L di-(2-ethylhexyl) phosphoric acid (D2EHPA) under optimized conditions (5 g/L pulp density, 600 rpm, 90 °C). Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) confirm the removal of target metals, while UV-vis spectroscopy and FTIR analysis reveal the complexation of Co-(II) as a tetrahedral coordination species, validating the reduction of Co-(III) to Co-(II) as a key dissolution mechanism. The study details the solvoleaching mechanism and emphasizes adapting a hydrometallurgical route to separate metal species completely. Metal stripping with H₂SO₄ achieves 99.4% Co and 99.8% Li recovery. Furthermore, the selective precipitation of Co²⁺ using oxalic acid was optimized through speciation modeling, ensuring a well-defined separation of cobalt and lithium at pH 2.5. Recyclability tests over five consecutive cycles confirm the efficiency of the solvent and support the integration of leaching and solvent extraction into a single, water-efficient recycling flowsheet. This approach provides a sustainable alternative to conventional aqueous-based methods. The findings demonstrate the viability of solvometallurgy for high-efficiency LIB recycling and suggest its broader potential for recovering strategic metals from secondary resources.