Hydrometallurgical separation of copper and cobalt from lithium-ion batteries using aqueous two-phase systems

A new green hydrometallurgical method was developed for the selective extraction of copper and cobalt from spent lithium-ion batteries, using an aqueous two-phase system (ATPS) extraction technique. The method was optimized for the extraction of Cu(II) and Co(II), considering the influence of the following parameters: type and concentration of extractant (1-(2-pyridyl-azo)-2-naphthol (PAN), 1-nitroso-2-naphthol (1N2N), or bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272)); pH (1.00, 6.00, or 11.0); ATPS-forming electrolyte (Na2SO4 or Na3C6H5O7); tie-line length (TLL) of the system; and mass ratio of the top and bottom phases (mTP/mBP). The recovery efficiency was evaluated in terms of the extraction percentage (%E) and the separation factor (S) between copper and cobalt. The best conditions for selective extraction were achieved using an ATPS composed of L64 + Na2SO4 + H2O, with pH = 6.00, TLL = 50.3% (w/w), mTP/mBP = 1, and PAN as the extracting agent, which resulted in βCu,Co = 3.22 × 102. The method was subsequently applied to a real lithium-ion battery sample, previously leached with HCl and HNO3. Improved separation of copper and cobalt was achieved using successive extraction steps, resulting in βCu,Co = 5.40 × 105. A stripping assay was also performed, and after a single step, 70.5% of the copper was available for an electrowinning process.