Recovering Co3O4 from waste choline chloride/ethylene glycol electrolyte containing Co(II) ions along with solvent regeneration

Efficiently recovering critical metals from secondary resources is crucial to decreasing the environmental impact of mineral-resource mining and reducing production costs and process energy consumption. Herein, we propose a simple and comprehensive approach to recycle Co 3 O 4 from waste choline chloride/ethylene glycol (named Ethaline) electrolyte containing Co(II) ions along with solvent regeneration. Through the rational coordination adjustment using water, [CoCl 4 ] 2− complex in the Ethaline-based electrolyte is transformed to [CoCl 2 (H 2 O) 4 ] 0 and [CoCl 2 (H 2 O) 5 ] + to facilitate precipitation separation. Adding oxalic acid (OA) as a precipitator can reach 97.1% cobalt recovery efficiency with a high value-added Co 3 O 4 rod-like structure obtained by calcining the oxalate precipitate. In addition, the water-containing solvent can be regenerated via reduced pressure distillation with a high recovery efficiency of up to 98.0%. FT-IR and 1 H NMR characterizations verify that the regenerated Ethaline exhibits good structural stability. Impressively, the proposed recovery path shows high recovery efficiencies for both cobalt and Ethaline in various practical Co(II) ion-containing electrolytes. This study establishes a novel technical pathway for the resource utilization of metal-bearing waste Ethaline electrolytes, which shows an excellent prospect in solvent recycling after metal processing.