Efficient extraction of metals from industrially produced pyrolytic black powder using citric acid: Process optimization and leaching mechanism

Abstract

Full-component pyrolysis can process organic components and reduce cathode materials, making it a key focus in green recycling of lithium-ion batteries (LIBs). However, the leaching mechanism and kinetics of pyrolyzed black powder in organic acid systems remain unclear, with most research still at the laboratory stage. This study pioneers the exploration of the leaching behavior and reaction mechanism of valuable metal extraction from industrial-scale pyrolyzed black powder using citric acid. The effects of various leaching conditions on the extraction of metals were investigated by single factor experiments and response surface method. Under optimal conditions, the leaching efficiencies of Li, Ni, Co, and Mn all exceeded 97%. Kinetic analysis revealed that the leaching process was controlled by internal diffusion, with the apparent activation energies for Li, Ni, Co, and Mn being 17.89, 23.14, 20.27, and 15.21 kJ/mol, respectively. Additionally, residue characterization identified FePO4 formation as the primary inhibitor of iron dissolution.

1. Introduction

With the rapid development of portable electronic devices and electric vehicles, the demand and consumption of lithium-ion batteries (LIBs) have grown significantly [1, 2]. According to public reports, the global installed capacity of power batteries reached approximately 518 GW·h in 2022 and is expected to continue climbing in the coming decades [3]. Depending on the anode materials, LIBs can be categorized into LCO (LiCoO2), LFP (LiFePO4), LMO (LiMn2O4), NCA ((Li(Ni, Co, Al)O2) and NCM (LiNixCoyMnzO2). Among them, the cathode material constitutes over 30% of the battery cost due to its richness in high-value metal elements such as Li, Ni, and Co [4]. However, LIBs typically have a lifespan of 5−8 years [5, 6], which means that a large number of batteries will be retired in the coming decades. It is predicted that by 2040, the global recycling market for spent LIBs will exceed 1500 GW·h [3]. Spent LIBs contain abundant critical metals such as lithium, nickel, cobalt, and manganese, with their concentrations significantly higher than those found in natural ores [7, 8]. Improper handling of these batteries not only poses serious risks to the ecological environment and human health but also results in substantial resource waste. Consequently, the efficient recovery of valuable metals from spent LIBs holds immense significance in mitigating the strain on natural resources, safeguarding the environment, and enhancing economic efficiency [2, 9, 10].

Currently, hydrometallurgy has become one of the mainstream technologies for recycling spent LIBs due to its low energy consumption, high recovery efficiency and high product purity [11−13]. The traditional hydrometallurgy process usually requires manual disassembly of the spent LIBs to separate the positive and negative wafers prior to leaching [14], followed by removal of the binder (PVDF) by heat treatment or organic solvent dissolution method to strip the positive active material from the aluminum foil [15, 16]. The application of organic solvents is limited due to their high cost and environmentally unfriendly nature [17]. In contrast, heat treatment is commonly used in the industry to remove the organic matter [18], but this process fails to achieve the deconstruction of phase of the cathode material, and additional reductants need to be added to improve the leaching efficiency during the subsequent leaching process [5, 19].