Separation of lithium and transition metals from the leachate of spent lithium-ion battery by extraction-precipitation with p-tert-butylphenoxy acetic acid

Unlike common solvent extraction and chemical precipitation, a novel extraction-precipitation process for the separation of Li and transition metals using p-tertylphenoxyacetic acid (POAA) is developed. Extraction-precipitation method refers to a method in which the extraction-precipitant can quantitatively extract the metal ions to form solid extracted complex without the requirement of organic solvent or carrier, and the extraction-precipitant can be stripped and recycled. In this study, the extraction-precipitation mechanism and thermodynamic parameters between POAA and manganese (Mn), cobalt (Co), nickel (Ni) were analyzed. Subsequently, the equilibrium time and pH value of the separation process were optimized. Finally, the leach solution of LIB having Li, Ni, Co, Mn with concentration of 3.52 g/L, 7.93 g/L, 5.72 g/L, and 14.16 g/L, respectively, was studied for the separation at pH 4.5. The results indicate that efficient separation of Li and transition metals was possible by one-step precipitation using 0.2 mol/L POAA solution (degree of saponification = 100%) when the ratio of nPOAA/nMn+Co+Ni was 2. The separation factor for the transition metals over lithium (βCoNiMn/βLi) reached as high as 133,014. After the transition metal-loaded POAA was stripped with 2 mol/L sulfuric acid, the stripped solution could be used for the production of ternary material precursor, and the regenerated POAA could be recycled for the extraction-precipitation process. The lithium in the solution was recovered in the form of lithium carbonate (Li2CO3) with a purity level of 97.7%. This high efficiency and sustainable process based on extraction-precipitation has shown potential application for spent LIB recovery.