Alkali-free recovery of nickel and cobalt from spent NCM Li-ion battery hydrochloric acid leachates: A pyridine carboxamide-based solvation extraction process enabling closed-loop recycling

Solvation extraction (metal extraction via a solvation mechanism) enables the recovery of multiple metal ions (e.g., Li, Co(II), Zn, Mn(II)) from chloride solutions without alkali consumption or waste production. However, effective alkali-free Ni(II) extraction reagents are lacking, leading to obstacles throughout the recovery route. In this study, three pyridine carboxamides, namely, N-2-ethylhexylpyridine-3-formamide (MEH3), N-2-ethylhexylpyridine-4-formamide (MEH4), and N, N-bis(isooctyl)pyridine-4-carboxamide (DH4) were used to extract Ni(II) and Co(II) without pH adjustment, and the results showed that the order of extraction ability for Ni(II) is MEH3 > MEH4 > DH4. Density functional theory (DFT) calculations showed that the extraction ability of Ni(II) may be related to the binding energies of the Ni(II) complexes. The MEH3 system was selected as the optimal choice for Ni and Co recovery from the chloride leaching solutions of the NCM battery materials. Using 178.8 g/L Mn(II) as a salting-out agent, >99 % Ni(II) and 99 % Co(II) were extracted in three-stage batch continuous tests at an O/A ratio of 7:1. The concentrations of Ni(II), Co(II), Mn(II), and Cu(II) in the organic phase during the first stage were 3.9, 1.7, 1.1, and 0.3 g/L, respectively, and Ca, Mg, and Al impurities were barely extracted. Ni(II) and Co(II) were stripped using deionised water. Under an O/A of 15:1, the single-stage stripping efficiency of Ni(II) and Co(II) reached 88.5 % and 98.3 %, respectively, with concentrations reaching 47.0 and 7.5 g/L, respectively. Mn(II) and Li in the solution were co-extracted and recovered using a TBP (tributyl phosphate) /FeCl 3 extraction system. Based on these results, a closed-loop process for recovering Ni, Co, and Mn from spent NCM battery materials is proposed.