A Sustainable Hydrometallurgical Recovery Strategy of Critical Metals from Spent NCM via Aspartame-Assisted Reductive Leaching: Mechanism, Stepwise Recovery Process and LCA

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, the reductive leaching was also investigations revealed that methanol generated during aspartame hydrolysis reduced high-valence transition-metal to soluble divalent ions, together with proton attack, promoted the collapse of the layered NCM structure. The leaching kinetics analysis also demonstrated that the process was controlled by surface chemical reactions. Furthermore, a stepwise recovery process was then developed that Ni was firstly separated through chelation and Co and Mn were subsequently co-extracted; and lithium 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.