A sustainable hydrometallurgical recovery strategy of critical metals from spent NCM via aspartame-assisted reductive leaching: Mechanism, stepwise recovery process and LCA.

Abstract

Inspired by the use of aspartame in sugar-free food additives, this study developed an aspartame-assisted reductive leaching process for the efficient dissolution of critical metals from spent NCM batteries. The speciation of the critical metals under different pH conditions was theoretically investigated, and the reductive leaching behavior was optimized using single-factor experiments and response surface methodology. Under optimized conditions (NCM-aspartame mass ratio 1:1.1, 65 °C, and 1.3 M H₂SO₄), the leaching efficiencies of critical metals exceeded 99%.More importantly, mechanistic investigations revealed that methanol generated during aspartame hydrolysis reduced high-valence transition-metal ions to soluble divalent species. Together with proton attack, this reduction promoted the collapse of the layered NCM structure. Leaching kinetic analysis further demonstrated that the process was controlled by surface chemical reactions. Furthermore, a stepwise recovery process was developed, in which Ni was first separated through selective chelation, Co and Mn were subsequently co-extracted, and Li was finally recovered by carbonate precipitation. The purities of all recovered products exceeded 98.5%. Besides, techno-economic analysis and life-cycle assessment demonstrated the economic feasibility and favorable environmental performance of the process, aiming to provide a sustainable hydrometallurgical strategy for the efficient recovery of critical metals from spent NCM batteries.