Alkali-free recovery of nickel and cobalt from spent NCM Li-ion battery hydrochloric acid leachates using a pyridinecarboxamide: continuous countercurrent extraction

Efficient and alkali-free recovery of nickel (Ni) and cobalt (Co) from spent lithium-ion batteries remains a significant challenge in chloride-based hydrometallurgy, primarily due to the poor extractability of Ni 2+ and the severe emulsification issues encountered during practical operation. To address these limitations, this study introduces a novel pyridinecarboxamide-based (PA14) extraction system, featuring an elongated alkyl side chain that substantially enhances the oil solubility of extracted metal complexes and effectively eliminates emulsification. A continuous countercurrent extraction system comprising six extraction, six scrubbing, and seven stripping stages was developed and operated for over 480 h using real industrial leach liquor from spent NCM523 cathode materials. The system achieved over 99% recovery for both Ni and Co, yielding a strip liquor with 79 g/L Ni and 32 g/L Co, which, after di-(2-ethylhexyl) phosphoric acid (D2EHPA) purification, met battery-grade impurity specifications. Systematic parameter evaluation revealed that Fe(III) is co-extracted and migrates to the product stream, necessitating upstream removal or side-stream bleeding; feed acidity must be controlled below 0.1 mol/L to prevent protonation-induced emulsification; and elevated temperatures improve phase disengagement but reduce extraction efficiency, effects that are readily compensated by multistage configuration. Notably, the PA14 extractant demonstrated exceptional long-term stability over 800 h of continuous operation, with no detectable degradation, loss of extraction capacity, or metal poisoning. This work provides a complete, practical, and sustainable engineering solution for the clean recovery of valuable metals from spent NCM batteries, overcoming the bottlenecks of both extractability and process stability that have hindered prior chloride-based approaches.