Mechanism-driven moderate alkalinity release for efficient recovery of high-purity cobalt and nickel from spent lithium-ion batteries

The saponification and extraction mechanism drives Mg(HCO3)2 as a substitution of NaOH to achieve higher separation factor and greener technique. [Display omitted] •Mechanism-driven saponifying agent tuning achieves β increase from 148.98 to 3189.95.•The extraction mechanism of nickel and cobalt has been supplied and visual.•The released alkalinity in saponification-extraction is the key factor in separation. The carbon neutralization urgently requires massive applications of energy storage materials such as lithium-ion batteries. As the critical metal for lithium-ion batteries, the sustainable utilization of nickel and cobalt still takes a long process due to the low separation factor resulting in high costs and environmental concerns, especially in spent lithium-ion batteries (LIBs). In this work, based on the further revealing whole-process mechanism of the typical saponification-extraction process, a new saponifying reagent is proposed to achieve the separation ability of a multistagecountercurrent through single-stage extraction solely along with shorter processes and less pollution. The separation factor of cobalt/nickel enhances from 148.98 to 3189.95. and the new saponification-extraction process applies in the recycling of LIBs successfully. The mechanism shows that the alkalinity introduced by saponification is the key factor affecting the separation and purity. Saponification by traditional NaOH releases all putting-in-organic-phase strong alkalinity to aqueous, providing excessive extraction capacity but hindering separation. Therefore, the mild released alkalinity tuning instructs seeking Mg(HCO3)2 as an alternative saponifying agent to achieve the balance between released alkalinity and capacity. A cleaner avenue for the high-purity recovery of cobalt and nickel is proposed by mechanism driving, which has the ideological guiding significance to other process improvements.