Abstract
Waste lithium-ion batteries (LIBs) contain abundant critical metals such as lithium, nickel, cobalt, and manganese. However, industrial mixed LIB wastes, which typically consist of lithium iron phosphate (LFP) type waste combined with lithium nickel cobalt manganese oxide (NCM) type waste and are not subjected to beneficiation, often lead to simultaneous dissolution of multiple metals in conventional leaching systems, making selective separation difficult. To reduce impurity dissolution and minimize the burden of downstream extraction and purification, there is an urgent need for an efficient and economically feasible integrated recovery strategy. This study proposes a novel two-step selective leaching process for the efficient separation and recovery of lithium, nickel, cobalt, and manganese from unbeneficiated industrial-scale mixed LIB wastes dominated by LFP with minor NCM fractions. The process employs the synergistic use of a weak-acid system followed by a strong-acid system to achieve stepwise, highly selective dissolution of the target metals.
In the first step, a formic acid–hydrogen peroxide system is applied to leach lithium from the mixed material. As a weak acid, formic acid creates a mild chemical environment that enables the selective leaching of lithium without causing substantial dissolution of transition metals. Under optimized conditions, the lithium leaching efficiency exceeds 99%, while the leaching rates of nickel, cobalt, manganese, copper, aluminum, and iron remain below 1%. In the second step, the residue obtained after formic-acid leaching is further treated using a sulfuric acid–hydrogen peroxide system. The stronger acidity of sulfuric acid, combined with the reductive behavior of hydrogen peroxide, significantly enhances the dissolution of nickel, cobalt, and manganese. Under optimized conditions, the leaching efficiencies of nickel and cobalt exceed 99% and 98%, respectively, while iron remains largely in the solid phase as FePO4, confirming the excellent selectivity of this system. Overall, the two-step weak–strong acid synergistic leaching process enables efficient stepwise separation of metals and offers advantages including high selectivity, low energy consumption, environmental compatibility, and operational simplicity. This method provides a practical pathway for the green and high-value recovery of industrial mixed LIB wastes without requiring preliminary beneficiation, and establishes a robust theoretical and experimental foundation for subsequent metal separation, purification, and closed-loop recycling.