Recovery of cobalt sulfate from spent lithium ion batteries by reductive leaching and solvent extraction with Cyanex 272

Cobalt sulfate was recovered from crushed and screened prismatic type spent lithium ion batteries (LIBs) containing 5-20% Co, 5-7% Li, 5-10% Ni, 15% organic chemicals, and 7% plastics together with Cu, Al, Fe, and Mn. Cobalt was reductively leached from the - 16 mesh fraction in 1 h by stirring with 2 M H2SO4 and 6 vol.% H2O2, at 60 °C and 300 rpm using a solid/liquid ratio of 100 g/L to give a cobalt concentration of 28 g/L, corresponding to a leaching efficiency of > 99%. Metal ion impurities such as copper, iron, and aluminium were precipitated as hydroxides from solution by adjusting pH to 6.5. Cobalt was then selectively extracted from the purified aqueous phase by equilibrating with 50% saponified 0.4 M Cyanex 272 at an equilibrium pH ∼ 6. The McCabe-Thiele plot predicted 99.9% cobalt extraction in a 2 stage counter-current operation with A/O ratio of 1/2. Separation factors for the extraction of Co/Li and Co/Ni at pH 6 were close to 750. The stripping of the loaded organic phase with 2 M H2SO4 produced a solution of 96 g/L Co from which pure pigment grade cobalt sulfate could be recovered by evaporation/recrystallisation. Overall, 92% cobalt could be recovered from the spent lithium ion batteries.