Abstract
The annual global volume of waste lithium-ion batteries (LIBs) has been increasing over years. Although solvent extraction method seems well developed, the separation factor between cobalt and nickel is still relatively low—only 72 when applying conventional continuous-countercurrent extraction. In this study, we improved the separation factor of cobalt and nickel by complexation-assisted solvent extraction. Before solvent extraction procedure, leaching kinetic of Li, Ni, Co and Mn was studied and can be explained by the Avrami equation. Leached residues were also investigated by SEM and XRD. Operation parameters of complexation-assisted solvent extraction were examined, including volume ratio of extractant to diluent, types of diluent, type of complexing reagent, extractant saponification percentage and volume ratio of organic phase to aqueous phase. The optimal separation factor of complexation-assisted solvent extraction could be improved to 372, which is five times that of conventional solvent extraction. The separation tendency would be interpreted by the relationship between extraction equilibrium pH and log distribution coefficient.
Highlights
Secondary lithium-ion batteries (LIBs) featuring high-energy densities and reasonable costs are widely used for energy storage in electronic devices and electric vehicles
This study investigated and optimized a continuous-countercurrent-extraction process for the separation of Mn, Co, Ni and Li from the spent nickel manganese cobalt oxide (NMC) 111 LIBs and a facile recovery technology of complexation-assisted solvent extraction for highly efficient separation of Co and Ni
The results showed that 0.1-M Na-Cyanex 272 should first be used as the extractant to separate cobalt and nickel under the optimal condition of pH 6
Summary
Secondary lithium-ion batteries (LIBs) featuring high-energy densities and reasonable costs are widely used for energy storage in electronic devices and electric vehicles. Lifetime of LIBs is only about five years, which makes high-performance methods for recycling the valuable contents in the spent NMC type LIBs a critical requirement for the industry. Cobalt is widely distributed in igneous and sedimentary rocks and present in meteorites (i.e., iron–nickel metal contains a few tenths of a percent cobalt), but cobalt reserves are very scarce. It is average content in the Earth’s crust is approximately 25–30 ppm, though widely distributed, ranks only 33rd in the order of abundance, and is less common than all other transition metals except scandium [5]. The price for cobalt (~$35,700 per ton) is comparable to lithium (~$38,100 per ton, equivalent to $6350 per ton of LiOH·H2 O), which is much more expensive than those of manganese (~$1500 per ton) and nickel (~$14,600 per ton), respectively (metal.com, June 2020)
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