Review of Research on Li-Ion Batteries Waste Management

Rokhaya Sylla Gueye^1*, Nango Gaye¹, Mamadou Baldé¹, Adama Diedhiou¹, Ngoné Diouf¹, Seck Gorgui Awa², Idrissa Ndoye¹, Yoro Tine¹, Matar Seck¹, Djibril Fall¹, Alassane Wele¹, Mahy Diaw³

¹Laboratory of Physical, Inorganic, Organic and Therapeutic Chemistry, Faculty of Medicine, Pharmacy and Odontology, Cheikh Anta Diop Dakar University (UCAD), Dakar, Senegal.
²Gaston Berger Saint-Louis University (UGB), Saint-Louis, Senegal.
³Alioune Diop Bambey University (UADB), Bambey, Senegal.

DOI: 10.4236/ojic.2022.122002                

Abstract

Li-ion batteries (Libs) are a mature technology widely used for energy storage in various electronic devices. Nowadays, this technology has become a leading candidate for the portable electronics market and for electric vehicles due to its good performance. As a result, the demand for Libs containing critical metals, rare earth elements and precious metals is increasing day by day with the accelerated upgrades of consumer electronics, which promotes the supply risk of many mining resources. In addition, the problems associated with the production of end-of-life Lib are increasing on a global scale. Used Libs are e-waste containing significant levels of critical raw materials (such as Co, Li, Mn and Ni) along with harmful substances. Without proper management of Lib waste, these precious metals and toxic substances may end up in nature and cause environmental and public health problems. In order to preserve nature, ensure sustainable resource management and stimulate the circular economy, it has become crucial to properly manage and recycle end-of-life Li-ion batteries. By the way, conventional methods focusing on pyrometallurgical treatments combined with hydrometallurgical treatment are widely studied to recover design metals from Libs waste. It is in this context that we have conducted this bibliographic synthesis, focusing on the efficiency of the solvents employed and their competitiveness for a more environmentally friendly economic management. In this manuscript, recent leaching, solvent extraction, electrodeposition and precipitation strategies to recover precious metals from end-of-life Li-ion battery designs are reviewed and the evolution of these processes is discussed.

Keywords

Libs Waste, Leaching, Extraction Rate, Affinity, Partition Coefficient

1. Introduction

In recent decades, making certain aspects of life much easier, electronic devices that are increasingly small, manageable, portable and economical have invaded our daily lives. In fact, there has been a meteoric rise in the number of cell phones, laptops, digital devices, electric and hybrid vehicles, etc. [1] [2]. These technologies work through electrochemical systems, batteries, storing chemical energy that they reversibly restore in electrical energy during their operation. For performance reasons, improvement studies are widely carried out, leading to the development of various types of batteries such as lead acid, nickel-cadmium (Ni-Cd), nickel-metal hydride (Ni-MH), Li-ion (Libs), lithium air, etc. [3] [4] [5]. After efficiency tests, Li-ion batteries have been shown to perform better due to higher energy densities, lower self-discharge rates, higher cyclabilities and no memory effect, high capacity, etc., hence the large-scale production of Li-ion batteries for consumer electronics. According to a study, the production of Li-ion batteries increased from 500 to 700 million tons from 2000 to 2004, while the number of users exceeded 6.8 billion in 2013 [6]. Due to the accelerated upgrading of consumer electronics, we are witnessing a surge in the production of used Li-ion batteries. Based on studies of the cyclability of Li-ion batteries [7] [8] [9], results had predicted the production of waste Libs in China to be around 500,000 tons in 2020 [8].

On the other hand, a Li-ion battery is essentially composed of a negative electrode, made of LiC₆ graphite, a positive electrode, a separator and an electrolyte, made of a mixture of solvents such as DMC, DEC, EC and a lithium salt (LiPF₆) [10] [11] [12]. The positive electrodes, which have a crucial role to play on the performance of the systems, often made of metal oxide (LiMO₂), are usually composed of heavy metals (Co, Mn, Ni, etc.) in relatively high concentration [3]. Therefore, data from a statistical study showed that 4000 tons of Libs waste could contain 1100 tons of heavy metals and more than 200 tons of electrolyte constituents, which can pollute the atmosphere [6]. Therefore, improper management of used Li-ion batteries can pose a threat to the environment and public health through pollution of nature, contamination of groundwater, etc. [13].

Then, used Li-ion batteries have an added economic value due to the significant amounts of precious metals (Co, Li, Ni, Mn, Al, etc.) they contain. In addition, the critical state of their natural ores, the cost and environmental impacts of their extraction process, etc., motivate the revaluation of these technologies. Therefore, the development of an environmentally friendly and cost-effective method of processing these wastes has become a major challenge for the sustainable development of portable electronics. Cost-effective and environmentally friendly management of Libs waste, has two major advantages that are the protection of nature and public health and the development of secondary sources of Libs design raw materials. According to the literature, many processes for Li-ion battery waste recovery are developed and classified into two main families such as pyrometallurgy and hydrometallurgy [13] [14] [15]. The pyrometallurgical technique is more generally used on an industrial scale, and allows the efficient recovery of certain metals such as Ni, Co, Cu, etc. However, this method does not allow the recovery of metals such as Al and Li, which are generally found in slag [16]. Moreover, this technique consumes large amounts of energy and leads to the release of hydrogen fluoride (HF) which can pollute the atmosphere. Hydrometallurgical processes, on the other hand, are more studied in the laboratory and are more advantageous due to their low energy consumption, reduced environmental footprint, selectivity and, above all, the possibility of recovering all the design metals from a given Libs. Advances in improvement studies have led to industrial scale with the development of relevant processes [16] [17].

The hydrometallurgical treatment is quite simple and consists of a series of highly selective processes that can be divided into three main parts: leaching, extraction and purification [13] [14] [15] [16]. The hydrometallurgical treatment is usually preceded by a physical pretreatment of the system, which has as objective the separation of the electrode components and the separator for more selectivity with a lower solvent consumption.

2. Li-Ion Batteries

A Li-ion battery is a reversible electrochemical system which is able to store energy in chemical form that it restitutes in electrical energy during its operation. It is composed of two electrodes, negative and positive, insulated by an electrically insulating polymer and interconnected by a liquid electrolyte. All these components of the battery are kept in a steel and/or plastic case (Figure 1) [18].

Figure 1. Structure of a Li-ion battery.

Most commercial Libs consist of graphite at the anode and a cathode generally composed of a layer of metal oxide and lithium (LiNiO₂, LiCoO₂, LiMn₂O₄) or iron phosphate and lithium (LiFePO₄), deposited on an aluminum foil using an adhesive binder such as PVDF [19]. These are interconnected by an electrolyte solution consisting of a binary or ternary mixture of organic solvents, typically dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), in which a lithium salt such as LiPF₆, LiBF₄ or LiCiO₄ is dissolved [10] [20]. In the design of a Lib, the cathode has a composition, often mixed, in relatively high concentrations of heavy metals and varying according to the manufacturer [21]. The cathode metal composition sometimes defines the name of the battery and is responsible for its performance (energy density, working potential, etc.). The electrolyte, which ensures the transfer of Li⁺ cations from one electrode to another, plays an indispensable role in the safety of the system, facilitates operation and improves the life of the battery by its stability with the electrode components.

Despite the good use of Li-ion batteries, their heavy metal composition and the polluting nature of some of their electrolyte constituents, as well as the improper treatment of used batteries, can constitute sources of danger for public health and nature. Therefore, a cost-effective management of Li-ion battery waste, can allow the newly use of the design metals as a secondary source of metals. Proper management of Li-ion battery waste can play a vital role in the sustainable development of the electronics industry and avoid the depletion of mineral resources. Furthermore, most commercial electrolytes are composed of harmful, flammable and highly volatile components, so the disposal of used Libs or their open incineration can lead to adverse consequences [11] [22]. In view of all these threats, it is imperative for sustainable development of the electronics industry to develop a safe and economical method for the treatment of waste Libs.

With the accelerated upgrading of consumer electronics and their positive impact on our daily lives, the production of used batteries is becoming problem. In addition, considering the various threats related to the improper treatment of Libs waste, the development of a perfect management technique occupies an important place in the current research [13] [16] [23] [24].

At the present state of research, many processes, consisting of several steps, aimed at the recovery of Libs waste have been developed in various laboratories [16] [24].

3. Physical Pre-Treatment

The sample pre-treatment phase includes all the processes such as sorting, unloading, removal of crusts and heat treatment of electrodes [6] [25]. However, the most important steps are unloading, dismantling and heat treatment. After sampling, the batteries are emptied of their residual charge by means of an adapted external circuit or ionic solution such as NaCl to avoid any risk of fire or explosion. The latter are dismantled by cutting the cover and the electrodes and electronic insulation are recovered and then separated. At this level, it is often used alcoholic solvent to recover the electrolyte before heat treating the separated electrodes. The purpose of the unloading is to reduce the risks of ignition and the extraction of the electrolyte could improve the polluting character of the process and improve the efficiency of the process

4. Hydrometallurgical Treatment

Hydrometallurgy is a method of chemical treatment which aims to recover the metals present in a given sample. The principle consists in using appropriate solvents to solubilize the metallic constituents. The general procedure is subdivided into three main parts which are leaching, liquid-liquid extraction and the purification or revalorisation phase [26].

4.1. Leaching

It consists of attacking a metal or a metallic constituent by oxidizing or reducing in the presence of strong ligands capable of forming soluble and stable complexes [3] [26] - [32]. After a bibliographical study of the Libs, two types of leaching such as oxidative or alkaline leaching and reductive or acid leaching, are studied in the treatment processes by hydrometallurgy [26] [28] [33].

4.1.1. Alkaline Leaching

The selective leaching of Libs cathodes aims at attacking the aluminium metal of the cathode collector in an alkaline medium in order to solubilize it [3] [26] [27] [28]. The originality of this step is to selectively recover the aluminum from the cathodic electrical connector and possibly other metals such as iron, copper, etc. qualified as impurities to the liquid-liquid extraction [34]. Since aluminum is generally in metallic form, the solubilization of the electronic connector can be explained by an oxidation to the Al³⁺ cation and then a complexation of the present cations. Therefore, the choice of the leachant can be based on its oxidizing character and/or the coordination strength of its constituents. It is in this context that Ferreira et al. (2009) tested soda ash in a process of selective solubilization of used Libs cathodes [26]. The aim of the work was to optimize operational variables such as concentration, contact time of the reactants, L/S ratio and reaction temperature. As a result, they showed that nearly 60% of the aluminum in the connector can be solubilized when the concentration is increased to about 4 M with an L/S ratio of 10 L/Kg for one hour at a temperature of about 60˚C. Results from this work showed that the solubilization of aluminum metal is explained by its oxidation in the presence of oxygen from the air and then by the coordination of Al³⁺ cations by OH⁻ ligands in the medium (R1 and R2) [26].

$A{l}_2{O}_3+2O{H}^{-}+3H_{2}O\rightleftharpoons 2Al{\left(OH\right)}_4^{-}$ (R1)

$2A{l}_{\left(s\right)}+2O{H}^{-}+6H_{2}O\to 2Al{\left(OH\right)}_4^{-}+3H_2$ (R2)

Gaye et al. (2019) resumed the study at room temperature in an effort to improve the fitting conditions [27]. In doing so, they evaluated and optimized the variables concentration, count time, and L/S ratio. Results of this work proved respective solubilization rates of about 55% and 10% for aluminum and lithium when the study parameters were set at 4 N, L/S = 10 L/Kg for 5 h.

Other solubilization tests have been performed with soda ash and results have confirmed its good performance as a leachant [33] [34] [35] [36], which may favor its choice as a reference solvent in the selective leaching of Libs cathodes.

However, it is noted that soda solutions do not completely solubilize cathodic aluminum, which can be explained by passivation and/or precipitation of aluminum oxide in basic media [37]. Data from the literature have shown that the precipitation of aluminium oxide is favoured by the presence of CO₂, the level of OH⁻ ions, temperature, time, etc. [38] [39] [40]. In an effort to improve the design aluminum recovery rates of Libs cathodes, researchers have investigated and tested other alkaline solvents [3] [41]. As a result, Nayl et al. (2017) studied the selective leaching of cathodic and anodic Libs materials with ammonia [3]. This work allowed them to access recoveries of about 98% for Al and 65% for Cu when the experimental conditions were set to NH₄OH 4 N with L/S = 15 mL/g for one hour under 60˚C. This solubilization efficiency of Al metal can be explained by the coordination strength of the NH₃ ligand. The smaller recoveries for copper may be due to the redox potential of the Cu²⁺/Cu couple being closer to that of the oxidant, which may make the couples reactive.

4.1.2. Acid Leaching

All the metals present in Li-ion batteries are solubilized by acids. Thus, acidic solvents are used to solubilize the metals Co, Ni, Mn, Li, Al, etc. used in cathode compositions. Until today, many studies have been conducted and different organic and inorganic acids have been tested as acid leachers of Libs cathodes [13] [15] [42]. Inorganic acids such as H₂SO₄ [3] [25] [26] [36] [43] [44], HNO₃ [45], HCl [46] [47] [48] [49] [50], and H₃PO₄ [51] [52] have been widely studied and have shown great promise with solubilization rates of Li, Co, Mn, and Ni metals above 90%. Joulié et al. (2014) conducted a comparative study of the performance of HCl, H₂SO₄, and HNO₃ acids in a process to solubilize Li, Ni, Co, and Al metals from Libs cathodes [47]. Results have shown that HCl presents the best performances compared to H₂SO₄ and HNO₃, which can be explained by the presence of Cl⁻, very strong reductant towards Co(III) and Ni(III) cations (R3) contrary to $N{O}_3^{-}$ and $S{O}_4^{2-}$ anions, that have weak reducing powers.

$2LiM{O}_2+8HCl\to 2MC{l}_2+C{l}_2+2LiCl+4H_{2}O$ (R3) (with M = Ni, Co, Mn)

Despite the good results with HCl, the reduction of metal cations leads to the production and release of chlorine (Cl₂), which is very harmful to humans [53]. Since most of the metals (Mn, Co and Ni) of Libs design are more soluble with their reduced form, reducing agents are therefore studied and tested in order to improve the performance of some acids [53] [54].

According to the literature, hydrogen peroxide (H₂O₂) is widely tested with many acids in the leaching of Co, Ni and Mn metals, which are generally used in commercial Libs cathodes [3] [27] [33] [43] [55] [56]. Despite the good performance of inorganic acids associated with reducing agents, most of them, lead to the release of gaseous compounds of a polluting nature. Therefore, research is focused on other types of acids in order to improve the pollutant character of waste Libs treatment.

In this respect, many acids such as citric acid [57] [58] [59], oxalic acid [36] [60], ascorbic acid [61], DL-malic acid [62] [63], succinic acid [64], L-aspartic acid [55], L-tartaric acid [65], acetic acid [66], iminodiacetic acid [67] have been tested as cathode leachers of Libs. These types of acids have the advantage of being more environmentally friendly and are capable of solubilizing, at high levels, the design metals of Libs cathodes. Similarly, organic compounds including glucose [29] [68], ethanol [69], etc. are being studied and tested with organic acids as a reducing agent [54] [70] [71] [72]. The use of organic acids has made a significant contribution to safety in the management of waste electrical and electronic equipment in general, and of Libs waste in particular [39]. However, the use of these organic solvents often requires high concentrations, which can have economic consequences [73]. Thus, research continues in various laboratories with the objective of finding a cheap, ecological acid capable of completely solubilizing the design metals of Li-ion batteries.

4.2. Liquid - Liquid Extraction

In hydrometallurgy, solvent extraction is a process of transferring soluble metals from the aqueous phase to the organic phase by means of an organic solvent. The principle is based on the use, in appropriate proportions, of organic solvent that is weakly miscible with the aqueous phase. When the final mixture is well stirred and the metals are loaded into the organic phase, a distribution equilibrium is established between the organic and aqueous phases, characterized by a partition coefficient (D) defined as follows [9] [10] [74] [75] [76]:

$D=\frac{C_1{V}_1-C_2{V}_2}{C_2{V}_2}$ (1)

The extraction efficiency of the given solvent with respect to a metal is characterized by its extraction rate (% E), which is determined from Equation (1) below [33] [74] [77]:

$\%E=\frac{C_1{V}_1-C_2{V}_2}{C_1{V}_1}\ast 100$ (2)

In the case of a mixture of several metals, the affinity of an extractant towards the metals or the extraction selectivity of a metal in a mixture is determined according to the separation factor of these metals. This separation factor of two metals for a given solvent is determined by Equation (3) below [76].

$\beta =\frac{D_1}{D_2}$ (3)

With D the partition coefficient, % E the extraction rate, C₁ and C₂ the initial and final concentrations of a given metal in the aqueous phase, V₁ and V₂ the respective volumes of the aqueous phase before and after extraction, D₁, D₂ the distribution factors of the metals M₁ and M₂, and β the separation factor of the metal M₁ from M₂.

From a literature review, we found that many organic solvents are studied and tested in the laboratory. Organophosphorus acids such as Cyanex 272, D2EHPA and PC 88A have shown very promising performances with high extraction rates for the recovery of Co, Mn, Ni with interesting selectivity [7] [33] [77] [78] [79] [80] [81]. Table 1 below gives a presentation of chemical formulas of some well known organophosphorus solvents in the field of liquid-liquid extraction of Libs metals.

The characteristic chemical molecules of these solvents have the particularity of being able to form stable complexes that are completely insoluble in the aqueous phase, hence their good performance.

Cyanex 272 has been tested several times, for the extraction of precious metals, in the hydrometallurgical treatment of Libs wastes and the results showed an interesting affinity towards metals (Co, Mn, Ni, etc.) of cathodic design [25] [33] [35] [44] [79] [81] [82] [83]. In a process for the recovery of Co, Li, Cu and Al metals, Jha et al. (2013) conducted optimization tests of the operational variables that impact the performance of Co extraction by Cyanex 272 [83]. As a result, they obtained after 5 min, extraction rates of about 99.9% Co when the experimental conditions were increased to 15% Cyanex 272 and 3% isodecanol in kerosene and the O/A ratio was set to 1:1 (by volume) at pH equals 5. Vasilyev et al. (2019), conducted an optimization study of a process for extraction of Co, Ni, and Li metals by NH₄-Cyanex 272 from Li-ion battery leachates [79]. Other optimization work has shown that an extraction solution consisting of 1 M Cyanex 272 neutralized to 48% with ammonia and 5% TOA, can achieve nearly 99.9%

Table 1. Structure and properties of widely used extractants.

extraction of these metals with high purity rates (≤99%) for an A/O ratio equal to 1:1 for 5 min [81].

Nayl et al. (2015) also employed Cyanex 272 to recover Mn(II), Co(II), and Ni(II) cations from spent Libs mixed cathode leachates [32]. Beforehand, Cu(II), Fe(II) and Al(III), considered as impurities, are removed with 20% Acorga M5640 diluted with kerosene after 5 minutes at 30˚C. When Na-Cyanex 272 is applied after 5 minutes under 30˚C, respective extraction rates of about 91.2%, 89.3%, 95.6% are obtained for Mn(II), Co(II) and Ni(II) cations at pH 3.5, 5 and 8 respectively [32].

D2EHPA has been tested as an extractant in cathode treatment processes of waste Libs [5] [60] [78] [84] - [89]. For example, Yang et al. (2017) tested the extraction and separation of Co, Mn, Ni, and Li metals from Libs leachates [89]. After optimization tests of pH, O/A ratio, contact time, and D2EHPA concentration, extraction efficiencies up to about 100% for Mn, 99% for Co, and 85% for Ni were achieved with 40% D2EHPA, O/A ratio = 1, at pH 3.5, for 6 minutes [89]. They thus showed that the extractant has a selective affinity towards these metals (with Mn > Co > Ni > Li) and that this selectivity depends on pH. In addition, Li et al., (2018) developed a simple and effective method for manganese recovery from Libs leachates [74]. They investigated the optimization of pH, O/A ratio, contact time, and saponification rate of the extractant, and results proved high recovery rates for Mn [74]. This confirms the selective affinity of the extractant towards Mn.

Another organophosphorus such as 2-ethylhexyl phosphonic acid-mono-2-ethylhexyl ester (PC88A) has been studied and tested as an extractant of metal cations from Libs cathode leachates [85] [86] [87] [88] [89]. Yang et al. (2020) conducted an optimization study of the variables pH, O/A ratio, and concentration of PC88A in kerosene in a selective recovery study of Mn²⁺, Co²⁺, Ni²⁺, and Li⁺ cations from sulfuric leachate [89]. An extraction efficiency of 98% for Mn and 90% for Co can be obtained when the experimental conditions are set at pH = 5, O/A ratio = 2/1 for 10 minutes. Most importantly, they obtained high separation factors of Co and Mn compared to Li and Ni, found in the raffinate. These results prove an interesting extraction selectivity depending on the reaction pH value.

These works show the good performances of these extractants with selective affinities towards the metals Co, Mn, Ni and Li; D2EHPA has more affinity with Mn while Cyanex 272 and PC-88A have comparative affinities towards Co, Mn [90] [91]. These results prompted the study of their synergistic action in combinations such as Cyanex 272/PC-88A [75] [90] [92], Cyanex 272/D2EHPA [7], Cyanex 272/Cyanex 302/D2EHPA [91], Cyanex 272/Cyanex 301/D2EHPA [93], Cyanex 272/PC-88A/D2EHPA [94] [95]. Thus, results have shown that synergistic systems often have higher recovery rates with better separation for mixed leachates.

This is the case with Sarangi et al. (1999) who showed that the binary mixture Na-PC88A (0.005 M) and Na-Cyanex 272 (0.025 M) presents, under the same conditions, a better separation of Co(II) and Ni(II) from a hydrochloric acid leachate compared to the solvents Na-Cyanex, Na-PC88A, Na-D2EHPA used alone, as well as the binary mixtures of these three solvents [94].

Despite the important performance of organophosphorus solvents, the search for an extractant system that can recover cathodic design metals in a single step and with different affinities towards these metals remains a challenge. It is in this context that the family of ionic liquids is being explored and very promising studies are underway [96] [97].

4.3. Electrodeposition

Electrodeposition is an electrochemical technique for metal cations recovery or removal from leachate or effluents. The principle is based on the application of a direct current between positive and negative electrodes immersed in the electrolyte solution. When an appropriate electrodeposition potential is applied, the targeted metal cation(s) is reduced (to its metallic or metal oxide form) and deposited on the cathode. The deposit is then solubilized in an acid medium (reduced pH) for characterization and purification tests [98]. This technique is widely applied in water treatment (removal of heavy metals), industrial effluent treatment, pyrometallurgical treatment of WEEE, etc. [15] [73]. According to the literature, electrodeposition is explored by various research teams and in various laboratories during cathode treatment of used Libs [99] [100] [101] [102] [103]. Thus, it has been shown that the deposition of a given metal depends on the working potential, the nature of the electrolyte, the temperature, the pH of the medium, etc. [99] [100] [101].

Tanong et al. (2017) studied the recovery of Zn(II), Mn(II), Cd(II), and Ni(II) cations from H₂SO₄ leachates by electrodeposition [104]. The metal cations in the leachates are selectively extracted by Cyanex 272 and D2EHPA, then stripped with H₂SO₄ solution and the electrolytes are tested for electrodeposition. When an energy density of about 370 A∙m⁻² is applied at pH = 2, metallic layer deposits appear on the cathodes (made of steel) in all experiments. These deposits are subsequently solubilized by a 5% HNO₃ solution and subjected to characterization and precipitation tests.

Kim et al. (2021) studied the selective recovery of cobalt and nickel in a hydrometallurgical treatment process of Li-ion battery cathodes [98]. This work demonstrates the role played by the electrolyte on the efficiency and selectivity of metal deposition. In addition to the pH of the medium and the working potential, the use of LiCl as an electrolyte promotes the selective deposition of cobalt through the formation of the [CoCl₄]²⁻ complex by stabilizing the cationic complex [Ni(H₂O)₅Cl]⁺ [98]. Data from this experiment showed high recoveries with purities in the range of 96.4% and 94.1% for cobalt and nickel respectively.

Thus, electrodeposition is an advantageous purification process in that it reduces solvent consumption and limits the production of effluents and polluting gases [99] [100] [101]. However, this method has technical limitations in the treatment of mixtures of metals with very close redox potential [98] [104].

4.4. Chemical Precipitation

Precipitation is a process of forming insoluble end products from two or more reagents under specific conditions. After extraction or electrodeposition and subsequent stripping, the new aqueous phase is mixed with a precipitating reagent in precise proportions to precipitate metal hydroxides, sulfides or carbonates. Data from the literature have shown that this precipitation depends on many parameters, the most influential of which are the pH, contact time, nature and concentration of the reagents, temperature, etc. [33] [48] [84] [103] - [108].

Nayl et al. (2017) evaluated the impact of pH on the performance of selective precipitation of Co(II), Mn(II), Ni(II) and Li(I) cations from H₂SO₄ leachate [3]. When they employed a sodium carbonate solution, the carbonates MnCO₃, NiCO₃, CoCO₃, and Li₂CO₃ precipitated selectively when the pH was adjusted to 7.5; 9; 11 and 12, respectively. This pH-dependent selectivity of metal precipitation is confirmed by the work of Meshram et al. (2015) [109] and Natarajan et al. (2018) [110]. Furthermore, it is shown that this metal precipitation is also dependent on the reagent employed. Barik et al. (2017) demonstrated that under specific conditions, a NaClO solution results in the selective precipitation of a manganese oxide mixture from a leachate containing Mn(II), Co(II), Ni(II), Cu(II), Al(III) and Li(I) [48]. Cobalt and lithium precipitated using sodium carbonate solution while copper and aluminum precipitated using soda ash [48].

5. Conclusions

In the face of the rapid production of waste Libs and the growing demand in the portable electronics market, the economic and proper management of used Libs has become a major political and economic issue. These types of waste, if improperly treated, become a threat to public health and nature. In addition, the critical state of the ores and the economic value of the design metals make recycling a major asset for the sustainable development of consumer electronics. Nowadays, many hydrometallurgical treatment processes of Libs scrap are developed and promising results are obtained from literature data. After bibliographic synthesis, we retain that in hydrometallurgy;

Alkaline leaching can facilitate the acid leaching and liquid-liquid extraction steps by eliminating impurities such as Al, Cu, Fe, etc. and reduce the solvent consumption and minimize the number of steps. However, the solvents tested in this field lack efficiency, which calls for further studies.

Acid leaching, which is the essential step, consists in solubilizing all the metallic constituents of a given sample. Most of the inorganic acids tested release gases that can pollute the atmosphere and pose a threat to public health, while organic acids are less polluting but not too effective.

Liquid-liquid extraction and electroplating are complementary and are often confronted with a lack of selectivity in the treatment of mixed batteries. In addition, extraction can lead to the consumption of large quantities of solvent and the production of effluents.

For future studies, it would be interesting to test the use of specific oxidants of very strong complexing agents in order to improve the performance of selective leaching and the use of ionic liquids as extractants for solubilized metals.

Conflicts of Interest

The authors declare no conflicts of interest regarding the publication of this paper.

References

[1]	Zheng, X., Gao, W., Zhang, X., He, M., Lin, X., Cao, H., Zhang, Y. and Sun, Z. (2017) Spent Lithium-Ion Battery Recycling—Reductive Ammonia Leaching of Metals from Cathode Scrap by Sodium Sulphite. Waste Management, 60, 680-688. https://doi.org/10.1016/j.wasman.2016.12.007
[2]	Jha, M.K., Anjan, K., Jha, A.K., Vinay, K., Hait, J. and Pandey, B.D. (2013) Recovery of Lithium and Cobalt from Waste Lithium-Ion Batteries of Mobile Phone. Waste Management, 33, 1890-1897. https://doi.org/10.1016/j.wasman.2013.05.008
[3]	Nayl, A.A., Elkhashab, R.A., Badawy, Sayed M. and El-Khateeb, M.A. (2017) Acid Leaching of Mixed Spent Li-Ion Batteries. Arabian Journal of Chemistry, 10, S3632-S3639. https://doi.org/10.1016/j.arabjc.2014.04.001
[4]	Leridon, H. (2009) Chaire Développement Durable—Environnement, Energie et Société: Année académique 2008-2009. Lalettredu Collègede France, No. 25, 9. https://doi.org/10.4000/lettre-cdf.501
[5]	Jimenez Correa, M., Silva, F., Aliprandini, F., Moraes V., Dreisinger, D. and Espinosa, D. (2018) Separation of Copper from a Leaching Solution of Printed Circuit Boards by Using Solvent Extraction with D2EHPA. Brazilian Journal of Chemical Engineering, 35, 919-930. https://doi.org/10.1590/0104-6632.20180353s20170144
[6]	Ordoñez, J., Gago, E.J. and Girard, A. (2016) Processes and Technologies for the Recycling and Recovery of Spent Lithium-Ion Batteries. Renewable and Sustainable Energy Reviews, 60, 195-205. https://doi.org/10.1016/j.rser.2015.12.363
[7]	de Souza, M.F.A. and Mansur, M.B. (2019) Competing Solvent Extraction of Calcium And/or Nickel with CYANEX 272 And/or D2EHPA. Brazilian Journal of Chemical Engineering, 36, 541-547. https://doi.org/10.1590/0104-6632.20190361s20170527
[8]	Zeng, X., Li, J. and Ren, Y. (2012) Prediction of Various Discarded Lithium Batteries in China. 2012 IEEE International Symposium on Sustainable Systems and Technology, 16-18 May 2012, Boston, 1-4. https://doi.org/10.1109/ISSST.2012.6228021
[9]	Contestabile, M., Panero, S. and Scrosati, B. (2001) A Laboratory-Scale Lithium-Ion Battery Recycling Process. Journal of Power Sources, 92, 65-69. https://doi.org/10.1016/S0378-7753(00)00523-1
[10]	Zeng, X., Li, J. and Singh, N. (2014) Recycling of Spent Lithium-Ion Battery: A Critical Review. Critical Reviews in Environmental Science and Technology, 44, 1129-1165. https://doi.org/10.1080/10643389.2013.763578
[11]	Chagnes, A., Diaw, M., Carré, B., Willmann P. and Lemordant, D. (2005) Imidazolium-Organic Solvent Mixtures as Electrolytes for Lithium Batteries. Journal of Power Sources, 145, 82-88. https://doi.org/10.1016/j.jpowsour.2004.12.035
[12]	Taggougui, M., Diaw M., Carré, B., Willmann, P. and Lemordant, D. (2008) Solvents in Salt Electrolyte: Benefits and Possible Use as Electrolyte for Lithium-Ion Battery. Electrochimica Acta, 53, 5496-5502. https://doi.org/10.1016/j.electacta.2008.03.012
[13]	Zheng, Z., Zhu, Z., Lin X., Zhang, Y., He, Y, Cao, H. and Sun, Z. (2018) A Mini-Review on Metal Recycling from Spent Lithium Ion Batteries. Engineering, 4, 361-370. https://doi.org/10.1016/j.eng.2018.05.018
[14]	Garole, D.J., Hossain, R., Garole, V.J., Sahajwalla, V., Nerkar, J. and Dubal D.P. (2020) Recycle, Recover and Repurpose Strategy of Spent Li-Ion Batteries and Catalysts: Current Status and Future Opportunities. ChemSusChem, 13, 3079-3100. https://doi.org/10.1002/cssc.201903213
[15]	Lv, W., Wang, Z., Cao, H., Sun, Y., Zhang, Y. and Sun, Z. (2018) A Critical Review and Analysis on the Recycling of Spent Lithium-Ion Batteries. ACS Sustainable Chemistry & Engineering, 6, 1504-1521. https://doi.org/10.1021/acssuschemeng.7b03811
[16]	Meshram, P., Pandey, B.D. and Mankhand, T.R. (2014) Extraction of Lithium from Primary and Secondary Sources by Pre-Treatment, Leaching and Separation: A Comprehensive Review. Hydrometallurgy, 150, 192-208. https://doi.org/10.1016/j.hydromet.2014.10.012
[17]	Sethurajan, M. and Gaydardzhiev, S. (2021) Bioprocessing of Spent Lithium-Ion Batteries for Critical Metals Recovery—A Review. Resources, Conservation and Recycling, 165, Article ID: 105225. https://doi.org/10.1016/j.resconrec.2020.105225
[18]	Zeng, X. and Li, J. (2014) Innovative Application of Ionic Liquid to Separate Al and Cathode Materials from Spent High-Power Lithium-Ion Batteries. Journal of Hazardous Materials, 271, 50-56. https://doi.org/10.1016/j.jhazmat.2014.02.001
[19]	Diaw, M., Chagnes A., Carré, B., Willmann, P. and Lermordant, D. (2005) Mixed Ionic Liquid as Electrolyte for Lithium Batteries. Journal of Power Sources, 146, 682-684. https://doi.org/10.1016/j.jpowsour.2005.03.068
[20]	Shin, S., Kim, N., Shon, J.S., Yang, D. and Kim, Y.H. (2005) Development of a Metal Recovery Process from Li-Ion Battery Wastes. Hydrometallurgy, 79, 172-181. https://doi.org/10.1016/j.hydromet.2005.06.004
[21]	Bankole, O.E. and Lei, L. (2014) Silicon Exchange Effects of Glassware on the Recovery of LiPF6: Alternative Route to Preparation of Li2SiF6. The Journal of Solid Waste Technology and Management, No. 4, 254-259. https://doi.org/10.5276/JSWTM.2013.254
[22]	Zhang, J., Hu, J., Zhang, W., Chen, Y. and Wang, C. (2018) Efficient and Economical Recovery of Lithium, Cobalt, Nickel, Manganese from Cathode Scrap of Spent Lithium-Ion Batteries. Journal of Cleaner Production, 204, 437-446. https://doi.org/10.1016/j.jclepro.2018.09.033
[23]	Lu, Y., Han, X. and Li, Z. (2021) Enabling Intelligent Recovery of Critical Materials from Li-Ion Battery through Direct Recycling Process with Internet-of-Things. Materials, 14, Article No. 7153. https://doi.org/10.3390/ma14237153
[24]	Dorella, G. and Mansur, M.B. (2007) A Study of the Separation of Cobalt from Spent Li-Ion Battery Residues. Journal of Power Sources, 170, 210-215. https://doi.org/10.1016/j.jpowsour.2007.04.025
[25]	Chagnes, A. and Pospiech, B. (2013) A Brief Review on Hydrometallurgical Technologies for Recycling Spent Lithium-Ion Batteries. Journal of Chemical Technology & Biotechnology, 88, 1191-1199. https://doi.org/10.1002/jctb.4053
[26]	Ferreira, D.A., Padros, L.M., Majuste, D. and Mansur, M.B. (2009) Hydrometallurgical Separation of Aluminium, Cobalt, Copper and Lithium from Spent Li-Ion Batteries. Journal of Power Sources, 187, 238-246. https://doi.org/10.1016/j.jpowsour.2008.10.077
[27]	Gaye, N., Gueye, R.S., Ledauphin, J., Baldé, M., Seck, M., Wele, A. and Diaw, M. (2019) Alkaline Leaching of Metals from Cathodic Materials of Spent Lithium-Ion Batteries. Asian Journal of Applied Chemistry Research, 3, 1-7. https://doi.org/10.9734/ajacr/2019/v3i230088
[28]	Meng, Q., Zhang, Y. and Dong, P. (2017) Use of Glucose as Reductant to Recover Co from Spent Lithium Ions Batteries. Waste Management, 64, 214-218. https://doi.org/10.1016/j.wasman.2017.03.017
[29]	Meng, Q., Zhang, Y. and Dong, P. (2018) Use of Electrochemical Cathode-Reduction Method for Leaching of Cobalt from Spent Lithium-Ion Batteries. Journal of Cleaner Production, 180, 64-70. https://doi.org/10.1016/j.jclepro.2018.01.101
[30]	Lee, C.K. and Rhee, K.-I. (2003) Reductive Leaching of Cathodic Active Materials from Lithium-Ion Battery Wastes. Hydrometallurgy, 68, 5-10. https://doi.org/10.1016/S0304-386X(02)00167-6
[31]	Yang, J., Jiang, L., Liu, F., Jia, M. and Lai, Y. (2020) Reductive Acid Leaching of Valuable Metals from Spent Lithium-Ion Batteries Using Hydrazine Sulfate as Reductant. Transactions of Nonferrous Metals Society of China, 30, 2256-2264. https://doi.org/10.1016/S1003-6326(20)65376-6
[32]	Nayl, A.A., Hamed, M.M. and Rizk, S.E. (2015) Selective Extraction and Separation of Metal Values from Leach Liquor of Mixed Spent Li-Ion Batteries. Journal of the Taiwan Institute of Chemical Engineers, 55, 119-125. https://doi.org/10.1016/j.jtice.2015.04.006
[33]	Nan, J., Han, D. and Zuo, X. (2005) Recovery of Metal Values from Spent Lithium-Ion Batteries with Chemical Deposition and Solvent Extraction. Journal of Power Sources, 152, 278-284. https://doi.org/10.1016/j.jpowsour.2005.03.134
[34]	Nan, J., Han, D., Yang, M., Cui, M. and Hou, X. (2006) Recovery of Metal Values from a Mixture of Spent Lithium-Ion Batteries and Nickel-Metal Hydride Batteries. Hydrometallurgy, 84, 75-80. https://doi.org/10.1016/j.hydromet.2006.03.059
[35]	Weng, Y., Xu, S., Huang, G. and Jiang, C. (2013) Synthesis and Performance of Li[(Ni1/3Co1/3Mn1/3)1-xMgx]O2 Prepared from Spent Lithium Ion Batteries. Journal of Hazardous Materials, 246-247, 163-172. https://doi.org/10.1016/j.jhazmat.2012.12.028
[36]	Chen, L., Tang, X., Zhang, Y., Li, L., Zeng, Z. and Zhang, Y. (2011) Process for the Recovery of Cobalt Oxalate from Spent Lithium-Ion Batteries. Hydrometallurgy, 108, 80-86. https://doi.org/10.1016/j.hydromet.2011.02.010
[37]	Phambu, N. (1996) Préparation D’hydroxydes D’aluminium: Caractérisation structurale morphologique et superficielle: Application a l’étude d’une couche de passivation d’aluminium. Université Henri Poincaré - Nancy 1, Nancy.
[38]	Duan, J., Dong, P., Wang, D., Li, X., Xiao, Z., Zhang, Y. and Hu, G. (2018) A Facile Structure Design of LiNi0.90Co0.07Al0.03O2 as Advanced Cathode Materials for Lithium Ion Batteries via Carbonation Decomposition of NaAl(OH)4 Solution. Journal of Alloys and Compounds, 739, 335-344. https://doi.org/10.1016/j.jallcom.2017.12.236
[39]	Edeline, F. (1993) Elimination des Métaux lourds dans les eaux usées. tribunedel’eau, 46, 7.
[40]	Li, H., Addai, M.J., Thomas, J.C. and Gerson, A.R. (2005) The Influence of Al(III) Supersaturation and NaOH Concentration on the Rate of Crystallization of Al(OH)3 Precursorparticles from Sodium Aluminate Solutions. Journal of Colloid and Interface Science, 286, 511-519. https://doi.org/10.1016/j.jcis.2005.01.083
[41]	Bingöl, D., Canbazoglu, M. and Aydogan, S. (2005) Dissolution Kinetics of Malachite in Ammonia/Ammonium Carbonate Leaching. Hydrometallurgy, 76, 55-62. https://doi.org/10.1016/j.hydromet.2004.09.006
[42]	Zhang, X., Xie, Y., Lin, X., Li, H. and Cao, H. (2013) An Overview on the Processes and Technologies for Recycling Cathodic Active Materials from Spent Lithium-Ion Batteries. Journal of Material Cycles and Waste Management, 15, 420-430. https://doi.org/10.1007/s10163-013-0140-y
[43]	Kang, J., Senanayake, G., Sohn, J. and Shin, S.M. (2010) Recovery of Cobalt Sulfate from Spent Lithium-Ion Batteries by Reductive Leaching and Solvent Extraction with Cyanex 272. Hydrometallurgy, 100, 168-171. https://doi.org/10.1016/j.hydromet.2009.10.010
[44]	Peng, C., Hamuyuni, J., Wilson, B.P. and Lundström, M. (2018) Selective Reductive Leaching of Cobalt and Lithium from Industrially Crushed Waste Li-Ion Batteries in Sulfuric Acid System. Waste Management, 76, 582-590. https://doi.org/10.1016/j.wasman.2018.02.052
[45]	Lee, C.K. and Rhee, K.-I. (2002) Preparation of LiCoO2 from Spent Lithium-Ion Batteries. Journal of Power Sources, 109, 17-21. https://doi.org/10.1016/S0378-7753(02)00037-X
[46]	Takacova, Z., Havlik, T., Kukurugya, F. and Orac, D. (2016) Cobalt and Lithium Recovery from Active Mass of Spent Li-Ion Batteries: Theoretical and Experimental Approach. Hydrometallurgy, 163, 9-17. https://doi.org/10.1016/j.hydromet.2016.03.007
[47]	Joulié, M., Laucournet, R. and Bily, E. (2014) Hydrometallurgical Process for the Recovery of High Value Metals from Spent Lithium Nickel Cobalt Aluminum Oxide Based Lithium-Ion Batteries. Journal of Power Sources, 247, 551-555. https://doi.org/10.1016/j.jpowsour.2013.08.128
[48]	Barik, S.P., Prabaharan, G. and Kumar, L. (2017) Leaching and Separation of Co and Mn from Electrode Materials of Spent Lithium-Ion Batteries Using Hydrochloric Acid: Laboratory and Pilot Scale Study. Journal of Cleaner Production, 147, 37-43. https://doi.org/10.1016/j.jclepro.2017.01.095
[49]	Zhang, P., Yokoyama, T., Itabashi, O., Suzuki, T.M. and Inoue, K. (1998) Hydrometallurgical Process for Recovery of Metal Values from Spent Lithium-Ion Secondary Batteries. Hydrometallurgy, 47, 259-271. https://doi.org/10.1016/S0304-386X(97)00050-9
[50]	Porvali, A., Aaltonen, M., Ojanen, S., Velazquez-Martinez, O. and Eronen, E. (2019) Mechanical and Hydrometallurgical Processes in HCl Media for the Recycling of Valuable Metals from Li-Ion Battery Waste. Resources, Conservation and Recycling, 142, 257-266. https://doi.org/10.1016/j.resconrec.2018.11.023
[51]	Pinna, E.G., Ruiz, M.G., Ojeda, M.W. and Rodriguez, M.H. (2017) Cathodes of Spent Li-Ion Batteries: Dissolution with Phosphoric Acid and Recovery of Lithium and Cobalt from Leach Liquors. Hydrometallurgy, 167, 66-71. https://doi.org/10.1016/j.hydromet.2016.10.024
[52]	Chen, X., Ma, H., Luo, C. and Zhou, T. (2017) Recovery of Valuable Metals from Waste Cathode Materials of Spent Lithium-Ion Batteries Using Mild Phosphoric Acid. Journal of Hazardous Materials, 326, 77-86. https://doi.org/10.1016/j.jhazmat.2016.12.021
[53]	Xu, J., Thomas, H.R., Francis, R.W., Lum, K.R., Wang, J. and Liang, B. (2008) A Review of Processes and Technologies for the Recycling of Lithium-Ion Secondary Batteries. Journal of Power Sources, 177, 512-527. https://doi.org/10.1016/j.jpowsour.2007.11.074
[54]	Mwema, K., Mpoyo, M. and Kafumbila, M. (2002) Use of Sulphur Dioxide as Reducing Agent in Cobalt Leaching at Shituru Hydrometallurgical Plant. The Journal of South African Institute of Mining and Metallurgy, 102, 1-4.
[55]	Li, L., Dann, J.B., Zhang, X., Gaines, L., Chen, R., Wu, F. and Amine, K. (2013) Recovery of Metals from Spent Lithium-Ion Batteries with Organic Acids as Leaching Reagents and Environmental Assessment. Journal of Power Sources, 233, 180-189. https://doi.org/10.1016/j.jpowsour.2012.12.089
[56]	Baba, A.A., Ibrahim, L. Adekola, F.A., Bale, R.B., Ghost, M.K., Sheik, A., et al. (2014) Hydrometallurgical Processing of Manganese Ores: A Review. Journal of Minerals and Materials Characterization and Engineering, 2, 230-247. https://doi.org/10.4236/jmmce.2014.23028
[57]	Li, L., Ge, J., Wu, F., Chen, R., Chen, S. and Wu, B. (2010) Recovery of Cobalt and Lithium from Spent Lithium Ion Batteries Using Organic Citric Acid as Leachant. Journal of Hazardous Materials, 176, 288-293. https://doi.org/10.1016/j.jhazmat.2009.11.026
[58]	Chen, X. and Zhou, T. (2014) Hydrometallurgical Process for the Recovery of Metal Values from Spent Lithium-Ion Batteries in Citric Acid Media. Waste Management & Research, 32, 1083-1093. https://doi.org/10.1177/0734242X14557380
[59]	Chen, X., Fan, B., Xu, L., Zhou, T. and Kong, J. (2016) An Atom-Economic Process for the Recovery of High Value-Added Metals from Spent Lithium-Ion Batteries. Journal of Cleaner Production, 112, 3562-3570. https://doi.org/10.1016/j.jclepro.2015.10.132
[60]	Zeng, X. and Li, J. (2015) On the Sustainability of Cobalt Utilization in China. Resources, Conservation and Recycling, 104, 12-18. https://doi.org/10.1016/j.resconrec.2015.09.014
[61]	Li, L., Lu, J., Ren, Y., Zhang, X., Chen, R.J., Wu, F. and Amine, K. (2012) Ascorbic-Acid-Assisted Recovery of Cobalt and Lithium from Spent Li-Ion Batteries. Journal of Power Sources, 218, 21-27. https://doi.org/10.1016/j.jpowsour.2012.06.068
[62]	Sun, C., Xu, L., Chen, X., Qiu, T. and Zhou, T. (2018) Sustainable Recovery of Valuable Metals from Spent Lithium-Ion Batteries Using DL-Malic Acid: Leaching and Kinetics Aspect. Waste Management & Research, 36, 113-120. https://doi.org/10.1177/0734242X17744273
[63]	Li, L., Ge, J., Chen R., Wu, F., Chen, S. and Zhang, X. (2010) Environmental Friendly Leaching Reagent for Cobalt and Lithium Recovery from Spent Lithium-Ion Batteries. Waste Management, 30, 2615-2621. https://doi.org/10.1016/j.wasman.2010.08.008
[64]	Li, L., Qu, W., Zhang, X., Lu, J., Chen, R., Wu, F. and Amine, K. (2015) Succinic Acid-Based Leaching System: A Sustainable Process for Recovery of Valuable Metals from Spent Li-Ion Batteries. Journal of Power Sources, 282, 544-551. https://doi.org/10.1016/j.jpowsour.2015.02.073
[65]	He, L.-P., Sun, S.-Y., Mu, Y.-Y., Song, X.-F., Yu, J.-G., et al. (2017) Recovery of Lithium, Nickel, Cobalt, and Manganese from Spent Lithium-Ion Batteries Using L-Tartaric Acidas a Leachant. ACS Sustainable Chemistry & Engineering, 5, 714-721. https://doi.org/10.1021/acssuschemeng.6b02056
[66]	Golmohammadzadeh, R., Faraji, F. and Rashchi, F. (2017) Recovery of Lithium and Cobalt from Spent Lithium-Ion Batteries Using Organic Acids: Process Optimization and Kinetic Aspects. Waste Management, 64, 244-254. https://doi.org/10.1016/j.wasman.2017.03.037
[67]	Nayaka, G.P., Pai, K.V., Manjanna, J. and Keny, S.J. (2016) Use of Mild Organic Acid Reagents to Recover the Co and Li from Spent Li-Ion Batteries. Waste Management, 51, 234-238. https://doi.org/10.1016/j.wasman.2015.12.008
[68]	Pagnanelli, F., Moscardini, E., Granata, G., Cerbeli, S., Agosta, L., Fieramosca, A. and Toro, L. (2014) Acid Reducing Leaching of Cathodic Powder from Spent Lithum Ion Batteries: Glucose Oxidative Pathways and Particle Area Evolution. Journal of Industrial and Engineering Chemistry, 20, 3201-3207. https://doi.org/10.1016/j.jiec.2013.11.066
[69]	Zhao, J., Zhang, B., Xie, H., Qu, J., Qu, X., Xing, P. and Yin, H. (2020) Hydrometallurgical Recovery of Spent Cobalt-Based Lithium-Ion Battery Cathodes Using Ethanol as the Reducing Agent. Environmental Research, 181, Article ID: 108803. https://doi.org/10.1016/j.envres.2019.108803
[70]	Chen, X., Guo, C., Ma, H., Li, J., Zhou, T., Cao, L. and Kang, D. (2018) Organic Reductants Based Leaching: A Sustainable Process for the Recovery of Valuable Metals from Spent Lithium Ion Batteries. Waste Management, 75, 459-468. https://doi.org/10.1016/j.wasman.2018.01.021
[71]	Biswas, R.K., Karmakar, A.K., Kumar, S.L. and Hossain, M.N. (2015) Recovery of Manganese and Zinc from Waste Zn-C Cell Powder: Characterization and Leaching. Waste Management, 46, 529-535. https://doi.org/10.1016/j.wasman.2015.09.008
[72]	Furlani, G., Moscardini, E., Pagnanelli, F., Ferella, F., Vegliò, F. and Toro, L. (2009) Recovery of Manganese from Zinc Alkaline Batteries by Reductive Acid Leaching Using Carbohydrates as Reductant. Hydrometallurgy, 99, 115-118. https://doi.org/10.1016/j.hydromet.2009.07.005
[73]	Dalini, E.A., Karimi, Gh., Zandevakili, S. and Goodarzi, M. (2020) A Review on Environmental, Economic and Hydrometallurgical Processes of Recycling Spent Lithium-Ion Batteries. Mineral Processing and Extractive Metallurgy Review, 42, 1-22. https://doi.org/10.1080/08827508.2020.1781628
[74]	Li, J., Yang, X. and Yin, Z. (2018) Recovery of Manganese from Sulfuric Acid Leaching Liquor of Spent Lithium-Ion Batteries and Synthesis of Lithium Ion-Sieve. Journal of Environmental Chemical Engineering, 6, 6407-6413. https://doi.org/10.1016/j.jece.2018.09.044
[75]	Virolainen, S., Fallah Fini, M., Laitinen, A. and Sainio, T. (2017) Solvent Extraction Fractionation of Li-Ion Battery Leachate Containing Li, Ni, and Co. Separation and Purification Technology, 179, 274-282. https://doi.org/10.1016/j.seppur.2017.02.010
[76]	Yang, Y., Xu, S. and He, Y. (2017) Lithium Recycling and Cathode Material Regeneration from Acid Leach Liquor of Spent Lithium-Ion Battery Via Facile Co-Extraction Andco-Precipitation Processes. Waste Management, 64, 219-227. https://doi.org/10.1016/j.wasman.2017.03.018
[77]	Chen, X., Xu, B., Zhou, T., Liu, D., Hu, H. and Fan, S. (2015) Separation and Recovery of Metal Values from Leaching Liquor of Mixed-Type of Spent Lithium-Ion Batteries. Separation and Purification Technology, 144, 197-205. https://doi.org/10.1016/j.seppur.2015.02.006
[78]	Vernekar, P.V., Jagdale, Y.D., Patwardhan, A., Patwardhan, A.V., Ansari, S.A., Mohapatra, P.K. and Machandan, V.K. (2013) Transport of Cobalt(II) through a Hollow Fiber Supported Liquid Membrane Containing Di-(2-Ethylhexyl) Phosphoric Acid (D2EHPA) as the Carrier. Chemical Engineering Research and Design, 91, 141-157. https://doi.org/10.1016/j.cherd.2012.06.019
[79]	Vasilyev, F., Virolainen, S. and Sainio, T. (2019) Numerical Simulation of Counter-Current Liquid-Liquid Extraction for Recovering Co, Ni and Li from Lithium-Ion Battery Leachates of Varying Composition. Separation and Purification Technology, 210, 530-540. https://doi.org/10.1016/j.seppur.2018.08.036
[80]	Pathak, S.K., Tripathi, S.C., Singh, K.K., Mahtele, A.K. and Dwivedi, C. (2013) PC-88A—Impregnated Polymeric Beads: Preparation, Characterization and Application for Extraction of Pu(IV) from Nitric Acid Medium. Radiochimica Acta, 101, 761-771. https://doi.org/10.1524/ract.2013.2076
[81]	Mantuano, D.P. Dorella, G., Elias, R.C. and Mansur, M.B. (2006) Analysis of a Hydrometallurgical Route to Recover Base Metals from Spent Rechargeable Batteries by Liquid-Liquid Extraction with Cyanex 272. Journal of Power Sources, 159, 1510-1518. https://doi.org/10.1016/j.jpowsour.2005.12.056
[82]	Swain, B., Jeong, J., Lee, J.-C., Lee, G.-H. and Sohn, J.-S. (2007) Hydrometallurgical Process for Recovery of Cobalt from Waste Cathodic Active Material Generated During Manufacturing of Lithium Ion Batteries. Journal of Power Sources, 167, 536-544. https://doi.org/10.1016/j.jpowsour.2007.02.046
[83]	Jha, A.K., Jha, M.K., Kumari, A., Sahu, S.K., Kumar, V. and Pandey, B.D. (2013) Selective Separation and Recovery of Cobalt from Leach Liquor of Discarded Li-Ion Batteries Using Thiophosphinic Extractant. Separation and Purification Technology, 104, 160-166. https://doi.org/10.1016/j.seppur.2012.11.024
[84]	Chen, X., Chen, Y., Zhou, T., Liu, D., Hu, H. and Fan, S. (2015) Hydrometallurgical Recovery of Metal Values from Sulfuric Acid Leaching Liquor of Spent Lithium-Ion Batteries. Waste Management, 38, 349-356. https://doi.org/10.1016/j.wasman.2014.12.023
[85]	Ahn, J.-W., Ahn, H.-J. Son, S.-H. and Lee K.-W. (2012) Solvent Extraction of Ni and Li from Sulfate Leach Liquor of the Cathode Active Materials of Spent Li-Ion Batteries by PC88A. Resources Recycling, 21, 58-64. https://doi.org/10.7844/kirr.2012.21.6.58
[86]	Dinkar, A.K., Singh, S.K., Tripathi, S.C., Verma, R. and Reddy, A.V.R. (2012) Studies on the Separation and Recovery of Thorium from Nitric Acid Medium Using (2-Ethyl Hexyl) Phosphonic Acid, Mono (2-Ethyl Hexyl) Ester (PC88A)/N-Dodecane as Extractant System. Separation Science and Technology, 47, 1748-1753. https://doi.org/10.1080/01496395.2012.659786
[87]	Kumari, A., Panda, R., Jha, M.K. and Patak, D.D. (2018) Extraction of Rare Earth Metals by Organometallic Complexation Using PC88A. Comptes Rendus Chimie, 21, 1029-1034. https://doi.org/10.1016/j.crci.2018.09.005
[88]	Luo, L., Wei, J.-H., Wu, G.-Y., Toyohisa, F. and Atsushi, S. (2006) Extraction Studies of Cobalt (II) and Nickel (II) from Chloride Solution Using PC88A. Transactions of Nonferrous Metals Society of China, 16, 687-692. https://doi.org/10.1016/S1003-6326(06)60122-2
[89]	Yang, Y., Lei, S., Song, S., Sun, W. and Wang, L. (2020) Stepwise Recycling of Valuable Metals from Ni-Rich Cathode Material of Spent Lithium-Ion Batteries. Waste Management, 102, 131-138. https://doi.org/10.1016/j.wasman.2019.09.044
[90]	Wang, F., He, F., Zhao, J., Sui, N., Xu, L. and Liu, H. (2012) Extraction and Separation of Cobalt(II), Copper(II) And Manganese(II) by Cyanex272, PC-88A and Their Mixtures. Separation and Purification Technology, 93, 8-14. https://doi.org/10.1016/j.seppur.2012.03.018
[91]	Darvishi, D., Haghshenas, D.F., Alamdari, E.K., Sadrnezhaad, S.K. and Halali, M. (2005) Synergistic Effect of Cyanex 272 and Cyanex 302 on Separation of Cobalt and Nickel by D2EHPA. Hydrometallurgy, 77, 227-238. https://doi.org/10.1016/j.hydromet.2005.02.002
[92]	Zhao, J.M., Shen, X.Y., Deng, F.L., Wang, F.C., Wu, Y. and Liu, H.Z. (2011) Synergistic Extraction and Separation of Valuable Metals from Waste Cathodic Material of Lithium Ion Batteries Using Cyanex272 and PC-88A. Separation and Purification Technology, 78, 345-351. https://doi.org/10.1016/j.seppur.2010.12.024
[93]	Torkaman, R., Asadollahzadeh, M., Torab-Mostaedi, M. and Ghanadi M., (2017) Recovery of Cobalt from Spent Lithium Ion Batteries by Using Acidic and Basic Extractants in Solvent Extraction Process. SeparationandPurificationTechnology, 186, 318-325. https://doi.org/10.1016/j.seppur.2017.06.023
[94]	Sarangi, K., Reddy, B.R. and Das, R.P. (1999) Extraction Studies of Cobalt (II) And Nickel (II) from Chloride Solutions Using Na-Cyanex 272.: Separation of Co(II)/Ni(II) by the Sodium Salts of D2EHPA, PC88A and Cyanex 272 and Their Mixtures. Hydrometallurgy, 52, 253-265. https://doi.org/10.1016/S0304-386X(99)00025-0
[95]	Devi, N.B., Nathsarma, K.C. and Chakravortty, V. (1994) Sodium Salts of D2EHPA, PC-88A and Cyanex-272 and Their Mixtures as Extractants for Cobalt(II). Hydrometallurgy, 34, 331-342. https://doi.org/10.1016/0304-386X(94)90070-1
[96]	Masmoudi, A. (2020) Recyclage du lithium issu des batteries usagées par extraction liquide-liquide dans un milieu liquide ionique. Université de Strasbourg, Strasbourg.
[97]	Billy, E. (2012) Application des liquides ioniques a la valorisation des métaux précieux par une voie de chimie verte. University of Grenoble, Grenoble.
[98]	Kim, K., Raymond, D., Candeago, R. and Su, X. (2021) Selective Cobalt and Nickel Electrodeposition for Lithium-Ion Battery Recycling through Integrated Electrolyte and Interface Control. Nature Communication, 12, Article No. 6554. https://doi.org/10.1038/s41467-021-26814-7
[99]	Celante, V.G. and Freitas, M.B.J.G. (2010) Electrodeposition of Copper from Spent Li-Ion Batteries by Electrochemical Quartz Crystal Microbalance and Impedance Spectroscopy Techniques. Journal of Applied Electrochemistry, 40, 233-239. https://doi.org/10.1007/s10800-009-9996-x
[100]	Freitas, M.B.J.G. and Garcia, E.M. (2007) Electrochemical Recycling of Cobalt from Cathodes of Spent Lithium-Ion Batteries. Journal of Power Sources, 171, 953-959. https://doi.org/10.1016/j.jpowsour.2007.07.002
[101]	Garcia, E.M., Santos, J.S., Pereira E.C. and Freitas, M.B.J.G. (2008) Electrodeposition of Cobalt from Spent Li-Ion Battery Cathodes by the Electrochemistry Quartz Crystal Microbalance Technique. Journal of Power Sources, 185, 549-553. https://doi.org/10.1016/j.jpowsour.2008.07.011
[102]	Mayén-Mondragón, R., Ibanez, J., Vasquez-Medrano, R., Baeza, A. and Oropeza, M. (2008) Electrochemical Recovery of Cadmium from Simulated Waste Nickel-Cadmium Battery Solutions. Water, Air, and Soil Pollution, 194, Article No. 45. https://doi.org/10.1007/s11270-008-9697-9
[103]	Zhao, G., Xu, Z. and Sun, K. (2013) Hierarchical Porous Co3O4 Films as Cathode Catalysts of Rechargeable Li-O2 Batteries. Journal of Materials Chemistry A, 1, 12862-12867. https://doi.org/10.1039/c3ta13209a
[104]	Tanong, K., Tran, L.-H., Mercier. G. and Blais, J.-F. (2017) Recovery of Zn (II), Mn (II), Cd (II) and Ni (II) from the Unsorted Spent Batteries Using Solvent Extraction, Electrodeposition and Precipitation Methods. Journal of Cleaner Production, 148, 233-244. https://doi.org/10.1016/j.jclepro.2017.01.158
[105]	Tanong, K. (2016) Récupération par voie hydrométallurgique des métaux a partir des déchets de piles mélangées. Université Du Québec, Institut National de la Recherche Scientifique, Québec.
[106]	Myoung, J., Jung, Y., Lee, J. and Tak, Y. (2002) Cobalt Oxide Preparation from Waste LiCoO2 by Electrochemical-Hydrothermal Method. Journal of Power Sources, 112, 639-642. https://doi.org/10.1016/S0378-7753(02)00459-7
[107]	Qadir, R. and Gulshan, F. (2018) Reclamation of Lithium Cobalt Oxide from Waste Lithium Ion Batteries to Be Used as Recycled Active Cathode Materials. Materials Sciences and Applications, 9, 142-154. https://doi.org/10.4236/msa.2018.91010
[108]	Zhu, S., He, W.-Z., Li, G.-M., Zhou, X., Zhang, X.-J., Huang, J.-W., et al. (2012) Recovery of Co and Li from Spent Lithium-Ion Batteries by Combination Method of Acid Leaching and Chemical Precipitation. Transactions of Nonferrous Metals Society of China, 22, 2274-2281. https://doi.org/10.1016/S1003-6326(11)61460-X
[109]	Meshram, P., Pandey, B.G. and Mankhand, T.R. (2015) Hydrometallurgical Processing of Spent Lithium Ion Batteries (LIBs) in the Presence of a Reducing Agent with Emphasis on Kinetics of Leaching. Chemical Engineering Journal, 281, 418-427. https://doi.org/10.1016/j.cej.2015.06.071
[110]	Natarajan, S., Boricha, A.B. and Baja, H.C. (2018) Recovery of Value-Added Products from Cathode and Anode Material of Spent Lithium-Ion Batteries. Waste Management, 77, 455-465. https://doi.org/10.1016/j.wasman.2018.04.032