Highly Efficient Recovery of Cobalt-Ion Containing Waste Deep Eutectic Electrolytes: A Sustainable Solvent Extraction Approach

Abstract

Efficient recovery of metals from secondary resources is essential to address resource shortages and environmental crises. The development of a cheap, environmentally friendly, and highly efficient recovery pathway is essential for resource retrieval. In this study, we propose a high-efficiency extraction approach utilizing bis(2,4,4-trimethylpentyl) phosphonic acid (Cyanex272) to recover cobalt from waste choline chloride/ethylene glycol (Ethaline) electrolyte containing Co(II) ions. By adjusting the water content of the system to modify the ligand of Co(II) ions, combined with pH adjustment, we achieved an extraction efficiency exceeding 99.9 % for Co(II) ions. Subsequently, oxalic acid (OA) was added as a stripping agent to achieve a recovery efficiency of over 99.4 % for cobalt. The extractant can be recycled more than 15 times after stripping. Impressively, more than 98.3 % of the water-diluted Ethaline extraction raffinate was recovered through reduced pressure distillation while maintaining the structure of recovered Ethaline unchanged. This work provides an economical, efficient, and sustainable pathway for treating waste Ethaline electrolyte-containing metal ions.