An effective process for the recovery of valuable metals from cathode material of lithium-ion batteries by mechanochemical reduction

Highlights

• Mechanochemical reduction used to improve the recovery of valuable metals in LIBs.

• Mechanochemical reduction reduced the activation energy of Ni and Co.

• The crystal structure of cathode material was destroyed by ball milling.

• Up to 90% of valuable metals could be recovered under optimal reaction conditions.

Abstract

To improve the recovery of valuable metals (Li, Co, Ni, and Mn) from the cathode material of waste lithium-ion batteries (LIBs), a mechanochemical reduction technique is proposed in this research. The cathode material was mechanochemically ball milled with various reductive agents as a pretreatment and then subjected to a chemical leaching process for the recovery of valuable metals. The influence of mechanochemical ball milling parameters and leaching conditions on metals recovery, and the changes in physicochemical properties of cathode materials before and after mechanochemical ball milling were investigated. The results show that Zinc (Zn) powder was an effective co-grinding reagent forimproving the recovery of valuable metals from cathode materials. The crystal structure of the cathode material gradually shifted to an amorphous state with an increase in ball milling speed and time. Mn(IV) and Co(III) in the cathode material were mechanochemically reduced to Mn(III) and Co(II) after co-grinding with Zn, which was beneficial to their leaching. The activation energies of Ni and Co decreased from 30.47 KJ/mol and 31.99 KJ/mol to 5.58 KJ/mol and 7.15 KJ/mol, respectively. The leaching rates of Li, Ni, Co, and Mn increased from 72.0%, 42.5%, 31.2%, and 15.2% to 99.9%, 96.2%, 94.3%, and 91.0% under the optimum conditions of a cathode material to Zn powder mass ratio of 7:3, a rotational speed of 500 rpm, a milling time of 2 h, and a ball-to-powder mass ratio of 19: 1. This research presents a highly efficient and feasible approach for recovering valuable metals from waste LIBs.

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.