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

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 (beta(Co/Ni)). The highest cobalt extraction percentages were obtained for ATPS formed by L64 + Na2SO4 + H2O 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 beta(Co/Ni) reached 9339 after three successive extraction steps.