Lithium recovery from weakly acidic high Na/Li ratio raffinate of spent battery recycling process by solvent extraction with P507

Lithium recovery from weakly acidic raffinate of spent LIBs by P507 was studied. • A cascade extraction process was designed for the separation of Li + /Na + . • P507 could extract 99.9% of Li + in the feed at the lower equilibrium pH of 5.96. • The stripping liquor comprising 22.2 g/L Li + and 0.11 g/L Na + was obtained. • The kinetic of Li + extraction was discussed and the control mechanism was revealed. The booming growth of electric vehicle industry contributes to sizable end-of-life lithium-ion batteries (LIBs). It is crucial to recover Li + from the high Na/Li ratio raffinate of spent LIBs for circular economy and sustainable resources. In this paper, the Li + extraction process from weakly acidic raffinate of spent LIBs by 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (P507) system was investigated. Compared with di-2-ethylhexyl phosphoric acid (P204), P507 showed better separation selectivity for Li + /Na + . The extraction parameters of saponification degree, modifying agents, phase ratio, extraction time, and loading capacity were optimized. A cascade extraction process with ten-stage extraction and eight-stage scrubbing was designed for separating Li + /Na + . It could be concluded that P507 could extract 99.9% of Li + from the feed at an equilibrium pH of 5.96, and the loaded organic phase comprising 2.55 g/L Li + and 0.02 g/L Na + was obtained. Moreover, a three-stage countercurrent stripping process was conducted with 1.75 mol/L H 2 SO 4 at an O/A ratio of 9:1. The final stripping liquor contained 22.2 g/L Li + and 0.11 g/L Na + , and a high-purity (99.5%) Li 2 CO 3 product was obtained by precipitation. Eventually, the kinetic study of Li + extraction with saponified P507 was discussed via the constant interfacial area cell method. The control mechanism was a mixing control occurring at the two-phase interface. The initial extraction rate equation of Li + could be expressed as R Li, init  = 10 –6.15 [Li + ] 0.65 [NaA] 0.95 . This research provided a novel insight into the efficient separation of Li + /Na + under weakly acidic conditions, which would benefit the potential industrial applications and environmental protection.