MMIJ Annual Meeting

For the recycling process of Li-ion batteries (LIBs), cobalt and nickel separation is one of the critical steps given their very similar chemical behavior. Solvent extraction is one of the wider accepted methods for Co and Ni separation, especially after the introduction of highly selective extractants soluble in organic solvents. However, despite the favorable features of traditional solvent extraction, there are still some disadvantages attached to the process, as the toxic, volatile, and flammable nature of some of the organic solvents used, the large volume of extractants required and the high cost of many selective extractants with moderate efficiency. Alternatively, aqueous two-phase systems (ATPS) are gaining importance in the last years as an environmentally-safe option. These systems consist of two immiscible phases formed when certain water-soluble polymers are combined with one another or with certain inorganic salts in specific concentrations. ATPS can be used extensively for concentration, separation, and extraction of cations and anions spanning the periodic table from various salt solutions.

In this work, we studied the liquid-liquid equilibrium data for ATPS PEG 20000-Na₂SO₄ and its performance for the extraction and separation of cobalt and nickel, using 1-nitroso-2-naphtol (1N2N) as chelating agent. The effect of ATPS composition, pH and extractant was evaluated and the separation efficiency was measured by the percentage of cobalt and nickel extracted to the top phase (β_Co/Ni). The highest separation factor was obtained with 1000 mg/Kg 1N2N concentration, pH 1 and ATPS tie-line 4. At these conditions, %E_Co and %E_Ni were 96.7% and 2.7%, respectively.