From Waste to Wealth: Novel Approach for Recovery of Metals from Spent Lithium-Ion Batteries Using Biological Waste

This study used tea waste (TW) as an environmentally friendly reducing agent to extract spent lithium-ion batteries in the H2SO4 solvent, thereby replacing highly explosive H2O2. The leaching parameters, including TW dosage, leaching temperature, H2SO4 concentration, leaching time, liquid-solid ratio, and stirring speed, were systematically optimized to achieve over 98% leaching efficiency of Ni, Mn, Co, and Li from the spent cathode material. The leaching kinetics study indicated that the H2SO4-TW leaching process was influenced by internal diffusion. The Box-Behnken experimental design was employed to optimize the leaching results, a proposition was made for a model that predicts the efficiencies of metal leaching. The regenerated cathode material demonstrated exceptional electrochemical performance. Contrary to the traditional biomass-reducing agents, the reduction performance of TW at low temperatures is derived from the catechins; meanwhile, at high temperatures, it is derived from the decomposition of cellulose. The oxidation process of catechins involves the oxidation of hydroxyl groups to carboxyl groups or the generation of adjacent quinone structures that form gallic acid derivatives. Using TW to extract metals from spent LIBs is an efficient, environmentally friendly, and sustainable approach to reducing the environmental impact of both waste sources.