PhD thesis Anna Vanderbruggen - Lithium Ion Batteries Recycling with Froth Flotation - A study on characterization and liberation strategies
Abstract and Figures
With the constant growth in portable electronic devices and the expected market growth for electric vehicles, the demand for lithium-ion batteries (LIBs) is booming. The raw materials production with a combination of mining and recycling will be essential and unavoidable to meet the upcoming demand for LIBs. Consequently, the European authority is updating the regulations demanding higher recovery efficiencies, 70 % by 2030. However, most of the state-of-the-art recycling technologies for LIBs focus on the recovery of components that have high economic value such as Co and Ni. The fine fraction resulting from the mechanical pre-treatment containing the lithium metal oxides (LMOs) and graphite particles, commonly referred to as "Black Mass" (BM), is generally used as a starting point for metals recovery by metallurgical means. Indeed, in industry, this BM is usually not further sorted and is directly fed to pyro- and/or hydrometallurgical processing routes to extract metals from LMOs, at the expense of graphite not being recovered. Recent studies, however, have convincingly illustrated that froth flotation can be applied to the BM to efficiently generate two valuable products, therefore increasing the overall efficiency of LIB recycling significantly. The work presented in this thesis aims to increase the overall materials recovery from LIBs by improving the BM beneficiation through froth flotation. The research work hereby presented offers a systematic study of the influence of the recycling pre-treatment processes on the liberation of the LIB components and the potential flotation mechanisms of active particles. The first part of this thesis is focused on the liberation analysis of the LIB components, which cannot be determined by conventional bulk characterization techniques such as X-ray fluorescence. In this thesis, a new approach for the BM characterization using automated mineralogy has been developed. With this particle-based technique, information on the chemical composition, morphology and degree of liberation of LIB components was acquired, helping to understand how the particles behaved during the process. The second part is focused on BM beneficiation on the basis of flotation. The use of flotation has recently gained interest as a method to separate LMOs and graphite particles. However, the flotation mechanisms of LMOs have not been paid sufficient attention. Therefore, this work provides the first fundamental study on the flotation mechanisms of active particles, with the aim of properly identifying the challenges to overcome in order to drive selectivity in flotation separation. To understand the flotation behavior, an industrial BM from pyrolyzed LIBs was compared to a model BM, comprising fully liberated LMOs and graphite particles. In addition, ultrafine hydrophilic particles were added to the flotation feed as an entrainment tracer, showing that the LMOs recovery in overflow products is a combination of entrainment and true flotation mechanisms. Ultimately, the findings of this thesis indicate the possibility of recovering and reusing graphite into new batteries.
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... In the LIB recycling process, heterogeneous fine powder mixtures of anode and cathode materials, called "black mass", are generated after physical/mechanical disassembly, comminution, and screening [72,73]. Separating anode graphite from cathode metal oxides from the black mass helps reuse graphite, which accounts for [15][16][17][18][19][20][21][22][23][24][25] wt.% of a LIB [70], and can simplify feed composition for subsequent hydrometallurgy and smelting operations, benefiting the extraction of critical metals like lithium, cobalt, nickel, and manganese in LIBs [74]. [73,75,76]. ...
... In practice, however, a portion of metal oxides particles were found to enter the graphite froth product. Using hydrophilic flow tracers, Vanderbruggen [73,74] showed that lithium metal oxide particles (LMOs) were transported to the froth product by a combination of entrainment and true flotation as shown in Fig. 7B. The true flotation of LMOs was caused by the organic binders used in the LIB, which rendered LMOs hydrophobic. ...
... Meanwhile, cathode powder consisting of ionic crystals with high polarity that are hydrophilic will precipitate at the bottom of the froth flotation device [10]. Chemical reagents such as collectors (which increase hydrophobicity for easier separation), frothers (which produce foam), activators (which increase the binding between collectors and desired materials), modifiers (which change the characteristics of the materials), and depressants (which stop undesirable materials from flotation) can all be added to improve the efficiency of the separation process [11,12]. ...
In this research, the primary objective is to study the recycling process of spent lithium-ion batteries (LIBs) for the recovery of valuable metals-specifically, nickel, manganese, and cobalt. This is accomplished through a comprehensive hydrometallurgical process that integrates froth flotation, acid leaching, and solvent extraction. The optimization of the flotation phase is a pivotal aspect of this study, with a focus on parameters like particle size and collector concentration. This optimization leads to a remarkable separation efficiency, evident in the recovery of 99.3% of the anode mass in the froth and 78.2% of the cathode mass in the precipitate. Notably, nickel emerges as the standout performer, with an extraordinary extraction efficiency of 99.97%. Nickel precipitates as an ammonium nickel sulfate crystals after solvent extraction due to supersaturation. These findings underscore the considerable potential of froth flotation and hydrometallurgical techniques as a sustainable, low-energy solution for recycling valuable metals sourced from spent LIBs.
Recycling is a potential solution to narrow the gap between the supply and demand of raw materials for lithium-ion batteries (LIBs). However, the efficient separation of the active components and their recovery from battery waste remains a challenge. This paper evaluates the influence of three potential routes for the liberation of LIB components (namely mechanical, thermomechanical, and electrohydraulic fragmentation) on the recovery of lithium metal oxides (LMOs) and spheroidized graphite particles using froth flotation. The products of the three liberation routes were characterized using SEM-based automated image analysis. It was found that the mechanical process enabled the delamination of active materials from the foils, which remained intact at coarser sizes along with the casing and separator. However, binder preservation hinders active material liberation, as indicated by their aggregation. The electrohydraulic fragmentation route resulted in liberated active materials with a minor impact on morphology. The coarse fractions thus produced consist of the electrode foils, casing, and separator. Notwithstanding, it has the disadvantage of forming heterogeneous agglomerates containing liberated active particles. This was attributed to the dissolution of the anode binder and its rehardening after drying, capturing previously liberated particles. Finally, the thermomechanical process showed a preferential liberation of individual anode active particles and thus was considered the preferred upstream route for flotation. However, the thermal treatment oxidized Al foils, rendering them brittle and resulting in their distribution in all size fractions. Among the three, the thermomechanical black mass showed the highest flotation selectivity due to the removal of the binder, resulting in a product recovery of 94.4% graphite in the overflow and 89.4% LMOs in the underflow product.
The zigzag (ZZ) classifier is a sorting and classification device with a wide range of applications (e.g., recycling, food industry). Due to the possible variation of geometry and process settings, the apparatus is used for various windows of operation due to the specifications of the separation (e.g., cut sizes from 100 µm to several decimetres, compact and fluffy materials as well as foils). Since the ZZ classifier gains more and more interest in recycling applications, it is discussed in this paper, with regards to its design, mode of operation, influencing parameters and the research to date. Research on the ZZ-classifier has been ongoing on for more than 50 years and can be divided into mainly experimental studies and modelling approaches.
Herein we report on an analytical study of dry‐shredded lithium‐ion battery (LIB) materials with unknown composition. Samples from an industrial recycling process were analyzed concerning the elemental composition and (organic) compound speciation. Deep understanding of the base material for LIB recycling was obtained by identification and analysis of transition metal stoichiometry, current collector metals, base electrolyte and electrolyte additive residues, aging marker molecules and polymer binder fingerprints. For reversed engineering purposes, the main electrode and electrolyte chemistries were traced back to pristine materials. Furthermore, possible lifetime application and accompanied aging was evaluated based on target analysis on characteristic molecules described in literature. With this, the reported analytics provided precious information for value estimation of the undefined spent batteries and enabled tailored recycling process deliberations. The comprehensive feedstock characterization shown in this work paves the way for targeted process control in LIB recycling processes.
The demand for lithium-ion batteries (LiBs) has increased rapidly in recent years, which has also boosted the need for battery materials. Some of these materials are already classified as critical by the European Union, including natural graphite, which is only mined in a few countries but is key in the production of battery-grade anode materials. Recycling spent LiBs can be considered a possible strategy to address the increasing demand for graphite. However, not much effort has been dedicated to the recovery of graphite, but its removal from the black mass has advantages and froth flotation has gained attention as a method to separate graphite from batteries. In this context, the main goal of this study was to evaluate the effect of the removal of graphite by froth flotation on the subsequent acid leaching of the non-floated fraction (rich in LMOs). The removal of graphite promoted a slight pre-concentration of metals in the solid samples. Additionally, the preliminary leaching results indicated a positive effect of the removal of graphite on the leaching efficiency of lithium and cobalt using sulfuric acid. On the other hand, the leaching efficiency of Mn and Ni was slightly lower after the removal of graphite and additional tests should be performed to better understand this behaviour and optimize the leaching conditions.
In order to ensure environmentally friendly mobility, electric drives are increasingly being used. As a result, the number of used lithium-ion batteries has been rising steadily for years. To ensure a closed recycling loop, these batteries must be recycled in an energy- and raw material-efficient manner. For this purpose, hydrometallurgical processes are combined with mechanical pre-treatment, including disintegration by mills, crushers and/or shears. Alternatively, electrohydraulic fragmentation (EHF) is also of great interest, as it is considered to have a selective fragmentation effect. For a better comparison, different application scenarios of EHF with other methods of mechanical process engineering for the treatment of lithium-ion batteries are investigated in the present study.
Graphite – natural or synthetic – is the most dominant active material used for LIB anodes [1] . Natural graphite, however, is considered a critical material within the EU [2] , while synthetic graphite is obtained from coke [3] – a carbon precursor produced from coal or petroleum. Therefore, efficient recycling and reuse of graphite are essential towards sustainability and resource preservation [4] .
Herein, we report a novel and highly efficient process to recover high-quality graphite from spent LIBs. Following a comprehensive physicochemical characterization of the materials obtained, we conducted an extensive electrochemical characterization in half-cells and graphite‖NMC 532 full-cells and compared the results with the data obtained for half-cells and full-cells using pristine commercial graphite. In half-cells, the recycled graphite shows remarkably high reversible specific capacities (e.g., 350 mAh g ⁻ ¹ at C/20) and very stable cycling for several hundred cycles at 1C. The graphite‖NMC 532 full-cells also show excellent cycling stability, with a capacity retention of 80% after about 1,000 cycles. Particularly, the comparison with the pristine graphite comprising full-cells reveals very comparable performance, highlighting the great promise of recycled and reused graphite as a pivotal step towards truly sustainable LIBs and the great goal of a circular economy.
References
[1] J. Asenbauer, T. Eisenmann, M. Kuenzel, A. Kazzazi, Z. Chen, and D. Bresser, “The success story of graphite as a lithium-ion anode material – fundamentals, remaining challenges, and recent developments including silicon (oxide) composites,” Sustain. Energy Fuels , 2020.
[2] Comisión Europea, European Commission, Report on Critical Raw Materials and the Circular Economy, 2018 . 2018.
[3] S. Richard, W. Ralf, H. Gerhard, P. Tobias, and W. Martin, “Performance and cost of materials for lithium-based rechargeable automotive batteries,” Nat. Energy , vol. 3, no. Li, pp. 267–278, 2018.
[4] A. Vanderbruggen, E. Gugala, R. Blannin, K. Bachmann, R. Serna-Guerrero, and M. Rudolph, “Automated mineralogy as a novel approach for the compositional and textural characterization of spent lithium-ion batteries,” Miner. Eng. , vol. 169, p. 106924, 2021.
This paper investigates one aspect of surface air nucleation in froth flotation, namely the impact of frother-type surfactants like Methyl isobutyl carbinol (MIBC). During this study, tap water was pressurized in an autoclave to produce air-oversaturated water for air nucleation precondition in flotation. Various experiments were carried out with graphite particles to investigate the influences of gas nucleation and MIBC on flotation: micro-flotation, single bubble collision experiments in hydrodynamic conditions and pickup experiments in static conditions. In addition, microscopic observations were combined with agglomeration analysis to clarify the effects of the frother MIBC on the air nucleation and agglomerate formation. The experimental results show the combination of MIBC and air nucleation can significantly increase the graphite recovery compared to using air-oversaturated water or normal tap water with MIBC alone, respectively. The analysis indicates that MIBC can improve the air nucleation probability on graphite surfaces by enhancing the stability of the air nuclei to form more micro-bubbles on the surface. Meanwhile, the surface microbubbles can collide with other particles forming coarser aggregates, improving their collision probability and with this increasing the recovery of fine particles. Furthermore, the results show that MIBC can reduce the detachment of particles from the surface of nucleation bubbles, leading to an increase in particle load of the bubble-particle aggregates in hydrodynamic conditions, improving the graphite recovery significantly.
Spent lithium-ion batteries (LIBs) contain critical raw materials that need to be recovered and recirculated into the battery supply chain. This work proposes the joint recovery of graphite and lithium metal oxides (LMOs) from pyrolyzed black mass of spent LIBs using froth flotation. Since flotation is a water-intensive process, the quality of the aqueous phase directly impacts its performance. In pursuit of an improved water-management strategy, the effect of process water recirculation on black mass flotation is also investigated. The fine fraction (<90 µm) of the black mass from pyrolyzed and crushed spent LIBs was used. After flotation, 85% of the graphite in the overflow product and 80% of the LMOs in the underflow product were recovered. After flotation with 8 wt% solids, the process water contained about 1,000 mg/L Li and accumulated up to 2,600 mg/L Li after three cycles. The flotation with process water showed no significant impact on the recovery and grade of flotation products, suggesting the feasibility of water recirculation in black mass flotation.
At the end of their efficient functionality in energy production/storage applications, spent lithium-ion batteries need to be recycled. Recycling remains the most preferred economic option with benefits such as prevention/reduction of environmental issues due to landfilling and more efficient use of natural resources. In this paper, characteristics of lithium-ion battery components before and after being spent are presented, together with highlights of various extractive options suitable for recycling. The main emphasis of this review is on the direct recycling approach, which employs the physical separation of anode and cathode materials. Since flotation is the most common processing method successfully applied to the physical separation of minerals in the mining industry, researchers have given a lot of attention to this area. The success of recycling by flotation is mainly dependent on wettability differences between the anode (hydrophobic) and cathode (hydrophilic) components. However, such components are subjected to surface modifications due to the intimate organic coating introduced in battery production. As such, the hydrophobic entities of the solid electrolyte in battery assembly, which are so essential for the electrochemical functionality of the battery during its life cycle, present main challenges on the selectivity of flotation as a recycling option. Thus, the restoration of the original hydrophobicity/hydrophilicity level of each electrode has been the main focus area for many investigations. This paper also provides an up-to-date review of proposed pretreatment options.
Lithium-ion batteries (LIBs) are widely used as a critical energy storage system for internet of things (IoT), electric vehicles (EV) and various renewable energy sources. However, the widespread use of LIBs has resulted in the significant accumulation of batteries with different chemistries in landfills. Existing methods for LIB recycling are unsustainable, non-environmentally friendly and ineffective at recycling spent LIBs with mixed chemistry. These methods are inadequate to achieve recovery and repurposing of the valuable and sometimes toxic components. This mandates an inherent need to improve the existing processes or develop a novel, sustainable, environmentally friendly and effective alternative process. In this paper, we present a comprehensive review of the current recovery technologies; demonstrating the gaps in understanding, the challenges and opportunities available in the recycling processes. This review will also examine and discuss different fundamental scientific principles and methods that can be employed to develop sustainable and effective recycling processes with an aim to facilitate the LIB recycling industry to shift towards a circular economy.