Recovery of Nickel and Cobalt Metal Powders from the Leaching Solution of Spent Lithium-Ion Battery by Solvent Extraction and Chemical Reduction

Spent lithium-ion batteries (LIBs) contain some valuable metals. Smelting reduction of spent LIBs produces metallic alloys containing Co, Cu, Fe, Mn, and Ni. Leaching of the metallic alloys with inorganic acid solutions and subsequent separation of Cu(II), Fe(III) and Mn(II) results in a solution containing Co(II) and Ni(II). In this work, solvent extraction and chemical reduction experiments were performed to recover pure metals from this solution. Cobalt(II) was first separated from Ni(II) by solvent extraction with saponified Cyanex 272. Batch simulation experiments based on the McCabe-Thiele diagram for the extraction of Co(II) verified the complete separation of Co(II) from Ni(II). Hydrazine was then employed as a reducing agent for Co(II) and Ni(II) from the stripping solution and the raffinate, respectively. The effect of several variables on the reduction such as the molar ratio of hydrazine to metal ion, reaction time, temperature, and solution pH was investigated. It was found that the reduced metals could be dissolved owing to the oxidizing action of hydrazonium in acidic solution. Addition of NH4Cl was effective in suppressing the dissolution of the reduced metals. Especially, there was an optimum molar ratio of NH4Cl at which maximum reduction of Co(II) was obtained. The recovery percentages of Co and Ni powder were higher than 99.1% and 99.9%, respectively, and the purity of the reduced metals was higher than 99.9%.