Metal extraction from spent lithium-ion batteries (LIBs) at high pulp density by environmentally friendly bioleaching process

Highlights

• Bioleaching of LIBs with high cobalt (222.5 g/kg of black mass) at high pulp densities.

• Heterogeneous LIB black mass mimicking industrial battery recycling used for bioleaching.

• High level of biogenic H₂SO₄ and Fe³⁺ ions produced in the bacterial culture used for bioleaching.

• Highest metal recovery of 94% Co and 60.3% Li obtained in 72 h at 100 g/L (S/L).

• Beneficial when scaling up the process.

Abstract

Spent lithium-ion batteries (LIBs) are more hazardous due to the presence of several toxic metals such as cobalt, lithium, nickel, manganese, etc. as well as electrolytes such as LiPF₆, LiBF₄, or LiClO₄. However, these spent LIBs are the secondary source of metals that can be extracted and reused in many ways to decrease their potential environmental risks. Metal extraction from the mixture of LiCoO₂-based spent LIBs at a high pulp density by bioleaching is challenging because of microbial inhibition due to high metal toxicity and substrate (iron) limitation. In the present study, we have investigated the bioleaching of a mixture of LiCoO₂-based LIBs at high pulp density (100 g/L) using cost-efficient autotrophic bacteria Acidithiobacillus ferrooxidans. By increasing the biogenic H₂SO₄ production in the culture media, as well as replenishing the bacterial culture for three cycles, we could recover 94% cobalt and 60% lithium in 72 h at 100 g/L pulp density. The X-ray diffraction (XRD), Scanning electron microscope (SEM), and Inductively coupled plasma - optical emission spectrometry (ICP-OES) analysis of LIB powder before and after bioleaching confirmed that more than 90% cobalt leached out from the LIB powder. This bioleaching process is an environmentally friendly way of extracting metals from the mixture of LIBs in gadgets and can be used for all types of spent LIBs.

Introduction

The increasing demand for consumer electronics such as mobile phones, tablets, laptops, electric vehicles (EV), and other devices required metals varying from gold, silver, platinum, lithium, and copper to rare earth elements for their production (Rohrig, 2015). At present, LIBs are commonly used as a powerhouse in all electronic devices and other appliances (Ra and Han, 2006; Nan et al., 2005). The LIB market is growing annually by 11%, and the value is going to hit $73 billion by 2025 (Elsa et al., 2017) with the increase in electric vehicles and stationary energy storage demand. However, the resources for the exploitable battery metals becoming scarcer, and the ore qualities are inferior (Prior et al., 2012). Using pure metals for the production of LIBs is non-renewable, and the decreasing supply of industrial grade ores increases the demand for the recycling and reuse of valuable metals present in spent LIBs. Traditional pyrometallurgical and hydrometallurgical processes are associated with high-energy input and greenhouse gas emission to extract metals from low-grade ores (Norgate et al., 2007). Stricter regulations are followed in most countries for the disposal of hazardous spent batteries containing toxic metals and electrolytes. Worldwide, now it is very challenging to manage the LIB waste (Zhang et al., 2018b).

Currently, spent LIBs are recycled using high-temperature pyrometallurgical facilities to recover valuable metals (Ebin and Isik, 2017). However, the pyrometallurgical process has more disadvantages such as high energy consumption, high capital cost, hazardous gases emissions, the cost involved in recovering elements from the slag, and loss of lithium and other components of spent LIBs during the recycling process (Sun and Qiu, 2011; Xiao et al., 2017). The hydrometallurgical process has many advantages over the pyrometallurgical process, such as high sustainability, high extraction efficiency, low energy input, and low capital cost (Weiguang et al., 2018). However, this process uses acid reagents, such as HCl, HNO₃, and H₂SO₄, as lixiviants and their disposal require additional expenditure.

Bio-hydrometallurgy offers a promising green alternative to pyrometallurgy and hydrometallurgy technologies for the recovery of metals from e-waste. In the future, biohydrometallurgy is going to play an essential role in urban mining, especially metal recovery from e-waste (Islam et al., 2020; Trivedi and Hait, 2020; Morin et al., 2006; Jain et al., 2006). Bioleaching is one of the processes under biohydrometallurgy that uses microorganisms and their metabolites to extract valuable metals from spent LIBs. Metal dissolution and recovery by microorganisms have many advantages over other recycling technologies such as environmentally safe, less harmful gases emitted, low operational costs and energy inputs (Anna et al., 2018). The bioleaching process is more environmentally friendly than other physicochemical processes because it is performed at low temperatures, requires less energy, and less toxic gas emissions. The metabolic products generated by the microorganisms for the metal dissolution are less-toxic and easier to handle, which prevent environmental contamination and processing hazards (Mahsa et al., 2019). Metal recovery from low-grade ore (Liu et al., 2017), waste printed circuit boards (PCBs) (Wu et al., 2018), sewage (Gu et al., 2017), spent catalyst (Asghari et al., 2013) and LIBs (Bahaloo-Horeha et al., 2016; Biswal et al., 2018) by microbial-mediated bioleaching process is a promising eco-friendly technology. Acidophilic iron-oxidizing and sulfur-oxidizing bacteria such as Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Leptospirillum ferrooxidans, and Sulfobacillus thermosulfidooxidans, are widely used in bioleaching processes for the metal extraction (Erüst et al., 2013). These bacteria initiate the metal dissolution process through a series of biochemical reactions by using inorganic compounds (Fe²⁺, FeS₂, and reduced S) as their primary energy source. They have been used for the removal of sulfur from solids and gases, and recovery of metals from ores, sludge, sewage, spent catalyst, printed circuit boards (PCBs) and LIBs (Zhang et al., 2018a)

Most of the previous publications regarding the bioleaching of LIBs reported were dealing with low cobalt content (Naseri et al., 2019; Biswal et al., 2018; Misrha et al., 2008) in the black mass and the batteries collected from a specific source such as coin cells (Naseri et al., 2019), mobile phones (Bahaloo-Horeha et al., 2016) and laptops (Heydarian et al., 2018). The black mass was obtained by separating the cathode and anode by manual dismantling, which is also more homogenous and easier to do bioleaching. These bioleaching processes have been performed for 10–15 days to get 80%–95% leaching at low pulp densities (5 g/L - 40 g/L). In our present study, the LiCoO₂ based spent LIBs were collected from different gadgets such as mobile phones, tablets and laptops, are also produced by various manufacturers (Cheret, 2007). The batteries were first shredded by a mechanical shredder and finely powdered together, which is more heterogeneous and reflects the realities of industrial battery recycling. Well-known A. ferrooxidans was used for bioleaching studies, which has been reported for the bioleaching of LIBs and other e-wastes (Misrha et al., 2008; Ivanus, 2010; Bajestani et al., 2014). A. ferrooxidans were chosen for bioleaching because of their ease of growth, safer to handle, and survival in extremely acidic environments by fixing CO₂ through the Calvin cycle and useing it as their sole carbon source (Zhang et al., 2018a). Bioleaching of LIBs at very high pulp density is challenging; because of microbial inhibition due to high metal toxicity and substrate (iron) limitation. Therefore, our goal is to extract valuable metals such as cobalt and lithium with high efficiency in a shorter period and to investigate the bioleaching capability of A. ferrooxidans to evaluate the leaching efficiency. We have studied the bioleaching of LiCoO₂ based spent LIBs with high cobalt content (222.5 g/kg of black mass) at very high pulp densities up to 100 g/L by replenishing three cycles of bacterial culture that produce a high concentration of biogenic sulphuric acid and ferric ions. A high concentration of biogenic sulphuric acid was produced in the culture medium by increasing the FeSO₄ level, which is the primary nutrient of A. ferrooxidans. ICP-OES was used to analyze the concentration of metals in the leached liquor; XRD and SEM-EDX were used to characterize the black mass from LIB before and after bioleaching to confirm the leaching efficiency.