High and selective separation for Co(ii), Ni(ii), Mn(ii) and other base metal ions by solvent extraction using new...

This study explores the selective separation of Co²⁺, Ni²⁺, Mn²⁺, and other associated base metal ions coexisting in primary ores and secondary resources, using a series of new tridentate amic acid extractants (L1-L5). The extractant structures, with functionalized glycine derivatives featuring varied alkyl substituents on the amide nitrogen, include: (2-(dioctylamino)-2-oxoethyl)glycine (L1), N-(2-(dioctylamino)-2-oxoethyl)-N-methylglycine (L2), N-(2-(dioctylamino)-2-oxoethyl)-N-ethylglycine (L3), N-(2-(dioctylamino)-2-oxoethyl)-N-isobutylglycine (L4), and a dihexyl analogue, (2-(dihexylamino)-2-oxoethyl)methylglycine (L5). Extraction efficiency and selectivity were systematically evaluated and optimized by varying key operational parameters such as extractant concentration, contact time, and aqueous phase pH. Mechanistic insights were obtained through slope analysis, which confirmed a predominant 2 : 1 ligand-to-metal coordination ratio and a proton-exchange extraction mechanism. Among these extractants, L2 displayed superior extraction performance, achieving rapid Co²⁺ extraction within five minutes and favourable selectivity over Ni²⁺ and Mn²⁺ ions, particularly in the pH range of 3-5. Additionally, the same extractant, L2 could be used for high separation of Ni²⁺ over Co²⁺ and Mn²⁺ after a longer period of time (24 h). The extractants demonstrated efficient metal ion recovery in acidic stripping conditions (pH < 2) without significant degradation. Recycling experiments with L2 confirmed its reusability, showing minimal loss in extraction capacity over three cycles. Structural analysis via ¹H-NMR indicated partial preservation of the extractant's integrity, with minor degradation of the N-CH₃ moiety. To assess industrial relevance, L2 was evaluated in various commercial diluents including ESCAID™ 100, ESCAID™ 110, ESCAID™ 120, and ISOPAR™ M. L2 retained good Co²⁺ selectivity across most solvent systems, reinforcing its potential application in hydrometallurgical processes. These findings establish tridentate amic acid extractants as promising candidates for efficient and selective base metal recovery from complex aqueous media. Accordingly, the study demonstrates the potential applicability of the developed extractants for the recovery of valuable metals from end-of-life cobalt-containing materials, including spent lithium-ion batteries, through integrated leaching and solvent extraction processes.