Menthol:decanoic acid deep eutectic solvent for efficient separation and recovery of valuable metals from spent lithium-ion battery leach solutions

The expansion of lithium battery use is currently facing numerous problems, including ineffective disposal of spent batteries, which is a source of pollution and a waste of critical metal resources. Solvent extraction has been widely used as a primary technique for the separation of valuable metals from battery waste materials. The current research focuses on the separation and recovery of Mn, Fe, Co, Ni, and Li from mixed Spent Lithium-ion battery (LIB) waste leachate using a menthol:decanoic acid (1:1) deep eutectic solvent (DES). Spectral characterisations were performed to confirm about the DES synthesis. The thermal analysis demonstrates good thermal stability of DES with vapour pressure increasing from 0.391 Pa to 16.521 Pa upon rise in temperature from 372.15 K to 492.15 K. Optimization of extraction studies using Response Surface Methodology-Central Composite Design (RSM-CCD) depicted that with contact time of 40 min, pH of 2.73, and DES to leachate ratio of 2:1, 95.67% Co, 83.97% Ni, and 69.14% Fe were extracted into the DES phase leaving Li and Mn in raffinate. Thermodynamic studies revealed that the extraction process is exothermic and accompanied by the formation of the metal-DES complex. Extraction efficiency of DES in various diluents decreased in the order: kerosene > heptane > hexane > chloroform. As observed in regeneration experiments, the extraction efficiency of the DES gradually decreased over five extraction-stripping cycles. Upon precipitation, iron hydroxide was recovered, while Mn, Co, and Ni were recovered in oxalate form and Li as a carbonate.