Separation of cobalt and nickel in leach solutions of spent nickel-metal hydride batteries using aqueous two-phase systems (ATPS)

Abstract This paper presents the use of an aqueous two-phase system (ATPS) as an alternative to liquid–liquid solvent extraction for the selective removal of cobalt and nickel from nickel metal hydride batteries (NiMH). The optimized extraction conditions were determined with a leach liquor obtained from the NiMH battery residue as a matrix. The effect of several key variables on the metal extraction was evaluated: (i) extractant nature, (ii) pH, (iii) the ATPS-forming electrolyte, (iv) the ATPS-forming copolymer, (v) the ratio between the top and bottom phases, and (vi) liquor dilution. Process efficiency was measured by the percentage of cobalt (%E Co ) and nickel (%E Ni ) extraction and the separation factor between these metallic ions (β Co/Ni ). The highest cobalt extraction percentages were obtained for ATPS formed by L64 + Na 2 SO 4  + H 2 O at pH 5.00, using 1-nitroso 2-naphtol (1N2N) extractant and a liquor dilution factor of 35. At these conditions, %E Co and %E Ni were 99.18% and 1.29%, respectively, and β Co/Ni reached 9339 after three successive extraction steps.