Full length articleAn effective process for the recovery of valuable metals from cathode material of lithium-ion batteries by mechanochemical reduction
Graphical abstract
Introduction
Lithium-ion batteries (LIBs) are widely used in mobile phones, laptops, new energy vehicles, and other fields due to their advantages of being a clean energy, having a long service life, high energy density, and high operational safety (Chen et al., 2016; Gratz et al., 2014; Kwon and Sohn, 2020; Majeau-Bettez et al., 2011). In general, the battery lifespan is 1–3 years, and with the acceleration of electronic product updates, a large number of batteries will be scrapped in the next few years (Almeida et al., 2019; Contestabile et al., 2001; Nguyen et al., 2014). LIBs contain a variety of heavy metals, electrolytes, PVDF binder, and other harmful substances (Dhiman and Gupta, 2019; Joulié et al., 2017; Santana et al., 2017; Zeng and Li, 2014). Scientific and effective disposal of waste LIBs can reduce the environmental damage caused by the leakage of harmful substances (Golmohammadzadeh et al., 2018; Zhang et al., 2019). Meanwhile, LIBs contain a variety of valuable and scarce metals, such as Ni, Co, and Li, which have great recovery value (Ghassa et al., 2020; Peng et al., 2018; Yan et al., 2020; Yang et al., 2019). Mineral resources are extremely rare worldwide (Li et al., 2019); therefore, recycling valuable metals from waste LIBs is of great significance.
In previous research, a pretreatment process (mechanical or chemical) is commonly used for waste LIBs to improve the recovery of valuable metals in the subsequent treatment of these LIBs (Dolotko et al., 2020; Li et al., 2016, 2012; Porvali et al., 2019; Takahashi et al., 2020; Wang and Wu, 2017). Pretreatment processes mainly include dismantling, crushing, screening, a thermal treatment, mechanochemical methods, dissolution, and so on (Lv et al., 2018; Wei et al., 2018). Some of the metals, like Cu and Al, are easy to recycle via a pretreatment due to their physical properties (Wang and Wu, 2017). Pyrometallurgical (Dang et al., 2020), biohydrometallurgical (Huang et al., 2019), and hydrometallurgical methods (Golmohammadzadeh et al., 2018; Lv et al., 2018; Meshram et al., 2015; Takacova et al., 2016) are often applied to recover valuable metals from waste LIBs. The process of pyrometallurgy starts with heating at low temperatures (150–500 ℃) to remove electrolytes and organic solvent, followed by a high-temperature treatment (1400–1700 ℃) to form alloy (as Co alloy) and slag (as Li2O or Li2CO3) products for the recycling of LIBs (Assefi et al., 2020). In biohydrometallurgical process, microorganisms are applied to extract metals from e-wastes (Biswal et al., 2018). The biohydrometallurgical method is gradually being accepted for the dissolution of electronic wastes due to its low implementation costs and environmental friendliness (Erüst et al., 2013). However, application of pyrometallurgy and biohydrometallurgy is restricted. Toxic and harmful gasses are generated in the pyrometallurgical process (Kwon and Sohn, 2020), biohydrometallurgy is affected by the microbial community, resulting in high requirements for remediation conditions and a low leaching efficiency (Yao et al., 2018). Hydrometallurgy approaches are low in cost, entail little hazardous gas emissions, and feature a high extraction efficiency with a low energy consumption, which make them more popular than pyrometallurgy and biohydrometallurgy in the recycling of cathode material (Esmaeili et al., 2020; He et al., 2016; Li et al., 2012; Mylarappa et al., 2017; Qi et al., 2020; Vieceli et al., 2018). Researchers have develop many extraction systems that include l-tartaric acid (C4H6O6) and hydrogen peroxide (H2O2) (He et al., 2016; Nayl et al., 2017), l-ascorbic acid solution (Li et al., 2012), H3Cit (citric acid) and tea waste (Chen et al., 2015), and sulfuric acid (H2SO4) and sodium bisulfite (NaHSO3) (Meshram et al., 2015) for extracting valuable metals from waste LIBs.
Recently, the mechanochemical technique, as a promising approach, was applied to extract metals from waste LIBs due to its advantages, such as exhibiting a high efficiency, low energy consumption, and no secondary pollution. Lithium was selectively recovered from waste Li FE phosphate (LiFePO4) batteries through mechanochemical ball milling with NaCl (Liu et al., 2019). Mechanical activation combined with an acid leaching process (Yang et al., 2017; Guo et al., 2018) was applied to selectively extract Li, Co, and Fe from spent LIBs. Iron (Fe) powder was used as co-grinding agent for Co and Li recovery from waste LIBs via a mechanochemical reduction and acid dissolution process (Guan et al., 2017). Dolotko et al. (2020) found that metallic Co and Li derivatives could be obtained from waste LIBs by mechanochemical processing with Al powder as addictive. Wang et al. (Wang et al., 2018) confirmed that mechanochemical activation improves the leaching efficiency of Li and Co in the leaching solution due to the physicochemical structure changes of the material during mechanochemical ball milling. This previous research proved that the co-grinding additive is a critical factor in metal recovery from waste LIBs using the mechanochemical process. Thus, more highly effective additive for valuable metals from waste LIBs should be further investigated.
In this research, waste LIBs cathode material was mechanochemically ball milled with different reductive agents and then leached in diluted H2SO4 solution for the recovery of valuable metals (Li, Co, Mn, and Ni). The optimal reductive agent was determined by comparing the leaching effect of valuable metals after ball milling. The influence of various parameters such as rotational speed, milling time, and leaching condition on the valuable metals recovery from waste LIBs were investigated, and a relative leaching kinetic analysis was conducted. Furthermore, the physicochemical properties changes of the waste LIB cathode materials before and after the mechanochemical reduction were analyzed to reveal the related leaching mechanisms.
Section snippets
Materials and reagents
The LIBs cathode materials used in the experiment were provided by a waste LIB Recycling company in Guangzhou, China. The cathode material was separated from Al foil by heating at 500 ℃ for 1 h in a muffle furnace. The obtained cathode material powder was used for the mechanochemical and leaching processes. Scanning electron microscope (SEM) images of the cathode materials are shown in Fig. 1. X-ray diffraction (XRD) of waste LIBs cathode material (Fig. S1) shows that LiNi0.4Co0.3Mn0.3O2 is the
Mechanochemical reductive agent selection
Four kinds of chemical agents (Zn, Fe, NaCl, and starch (C6H10O5)n) were chosen as mechanochemical reductive agents. The reductive agents and waste LIBs cathode material (0.5: 1 mass ratio) as starting materials were co-ground for the mechanochemical reduction process at 500 rpm for 2 h. The leaching rates of metals in the cathode materials mechanochemically ball milled, with various reductive agents in H2SO4 solution, are shown in Fig. 2. When the leaching time varied within 15–120 min, the
Characterization analysis and mechanism discussion
Fig. 7 shows the surface morphologies of waste LIBs cathode material before and after mechanochemical reduction at different ball milling speeds for 120 min. The cathode material before mechanochemical ball milling consisted of relatively large and compact spherical particles. After ball milling at 200 rpm for 120 min, the surface of the particles began to become rough and finer particles appeared. When the milling speed was 300–400 rpm, the particle surfaces became rough, spherical particles
Conclusions
In this study, a mechanochemical reduction technique was proposed to enhance the leaching of valuable metals from waste LIBs in the traditional acid leaching process. It was proven that the mechanochemically ball milling of waste LIB cathode material with Zn powder effectively improved the leaching rates of valuable metals (Li, Co, Mn, and Ni), which increased from 15.2–72.0% to 91.0–99.9% at a milling speed and time of 500 rpm and 120 min, respectively. The leaching rates of Li, Ni, Co, and Mn
CRediT authorship contribution statement
Junying Xie: Writing - original draft, Investigation, Methodology, Data curation. Kaiyou Huang: Writing - original draft, Writing - review & editing, Visualization, Data curation, Software. Zhenglin Nie: Visualization, Data curation. Wenyi Yuan: Visualization. Xiaoyan Wang: Investigation, Writing - review & editing, Resources. Qingbin Song: Resources. Xihua Zhang: Investigation. Chenglong Zhang: Supervision. Jingwei Wang: Investigation. John C. Crittenden: Investigation.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
We are grateful for the financial support from National Natural Science Foundation of China (No.21876106), Gaoyuan Discipline of Shanghai-Environmental Science and Engineering (Resource Recycling Science and Engineering), and the Science and Technology Development Fund, Macau SAR (0027/2018/A).
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Junyi Xie and Kaiyou Huang have contributed equally to this manuscript.