Phase Behavior of Saponified Cyanex 272 and Counter-Current Extraction of Co(II) from Ni-Rich Spent LIBs Leachate

Journal article, 2026

The extraction of Co from an industrially treated solution produced from spent NMC9.5.5 lithium-ion batteries was investigated using saponified Cyanex 272. The phase behavior of a NaOH (2, 5 or 10 M)–Cyanex 272–Isopar L system was studied to select suitable conditions for saponification. A Winsor II region, a monophasic microemulsion area, and a zone with a biphasic system composed of a diluent-rich and a diluent-depleted phase were identified. Both the extractant and NaOH concentration were found to impact the self-assembly of the system, whereas increasing the temperature from 21 to 40°C did not result in any noticeable macroscopic effect. 10 M NaOH solution was selected for saponification. About 95% of Co was extracted from the feed solution using 45% saponified 0.3 M Cyanex 272 in single-stage extraction (pH = 5.5 ± 0.1). The McCabe–Thiele method showed to be inaccurate in determining the number of counter-current stages when the saponified solvent was used. Two stages were instead predicted for extracting Co using a non-saponified solvent maintaining the pH equal to 5.5 in each stage. Pseudo counter-current tests were performed using both saponified and non-saponified solvents. The results showed similar Co extraction (>99%) but different pH profiles in the cascades.