Recovery of transition metals (Ni, Co, and Mn) and Li from the sulfate leach solutions of spent ternary lithium-ion batteries by stepwise solvent extraction and precipitation

Abstract

Sulfate leachate from spent ternary lithium-ion batteries (LIBs) contain valuable metals, such as transition metals (Ni, Co, and Mn) and Li, and impurity metals, such as Al and Fe. Selectively separating them from solutions is necessary for their recovery. In this work, a stepwise solvent extraction and precipitation process is proposed for the selective separation and recovery of transition metals (Ni, Co, and Mn) and Li from sulfate-leaching solutions of spent ternary lithium-ion batteries. First, 100 % of the impurity metals (Al and Fe) were selectively removed from the solution through a single-stage extraction using 22.5 % (v/v) N1923 in sulfonated kerosene at an O/A ratio of 1:1 for 10 min. The losses of the transition metals (Ni, Co, and Mn) and Li were only 1.65 %. The Al and Fe in the loaded organic system was completely stripped using a 1 mol/L HNO₃ solution, followed by regeneration with sodium carbonate solution. Subsequently, the raffinate (pH = 4.46) was directly used for the co-extraction of Ni, Co, and Mn by Cyanex 272. A five-stage countercurrent extraction was performed with an organic system consisting of 1 mol/L Cyanex 272 (saponification degree: 50 %) in sulfonated kerosene, using an O/A ratio of 2.25:1. Nearly all of the Ni, Co, and Mn were extracted, while only 1.43 % Li was co-extracted. The extracted Ni, Co, and Mn in the loaded organic system were completely stripped through five-stage counter-current stripping using 1 mol/L H₂SO₄ with an O/A ratio of 5:1. During the stepwise solvent extraction process, stripped solutions of Ni, Co, Mn, and Li raffinates were sent to precipitate the pure ternary material precursors and Li₂CO₃. This study introduces a novel method for recycling spent ternary lithium-ion batteries.