Iron removal and valuable metal recovery from spent lithium-ion batteries (LIBs) using solvent extraction after bioleaching

Our study investigated the feasibility of solvent extraction for the separation of impurities, specifically aluminum (Al), copper (Cu), and iron (Fe) from simulated leachate with similar composition to real pregnant leach solution (PLS) obtained after the bioleaching of spent lithium-ion batteries (LIBs). The Fe²⁺ in the Fe-rich PLS was oxidized to Fe³⁺ by addition of H₂O₂. Subsequently, Fe³⁺, Al³⁺, Cu²⁺, and Mn²⁺ were extracted at pH 4.0 using 20 % di-(2-ethylhexyl) phosphoric acid (D2EHPA) as the extractant. At this pH, 99.99 % of Al³⁺ and Fe³⁺, 93 % of Cu²⁺, and 83 % of Mn²⁺ were successfully extracted. Co-extracted Co²⁺ was recovered through a two-stages scrubbing process, where it was replaced with Mn²⁺ using a MnSO₄ solution at an O/A ratio of 1:1. Finally, Al³⁺, Cu²⁺, and Mn²⁺ were stripped with 5 M H₂SO₄, and 99 % Fe³⁺ was separated by stripping with 100 % aqua regia. Our study presents an approach for effectively separating valuable metals and impurities, particularly Fe, by optimizing the extraction, scrubbing, and stripping stages of solvent extraction for PLS treatment. Moreover, this study emphasizes the need for further research on the pre-separation of Fe and the development of novel extractants and solvents to enhance the treatment of Fe-rich PLS after bioleaching.