An Innovative Method of Leaching of Battery Masses Produced in the Processing of Li-Ion Battery Scrap

Abstract

This paper presents comparative experimental results for the single-stage and two-stage counter-current acid leaching of battery masses, with the addition of a booster, from different types of LIB waste. Three different types of battery masses were used in this research: Material I, module car; Material II, tablets and laptops; and Material III, mobile phones. These materials were obtained during the mechanical processing of Li-ion battery waste, which were dried at a temperature in the range of 80–180 °C. Leaching studies of these materials were carried out using the single-stage acid leaching method with the addition of hydrogen peroxide, and the innovative two-stage counter-current acid leaching method, also with the addition of hydrogen peroxide. The single-stage leaching of the battery mass (regardless of the composition of the material) in a 15% or 20% sulfuric acid solution with the addition of 30% H₂O₂ aqueous solution, for 2 h, with a solid-to-liquid-phase ratio of 1:5 or 1:4 at a temperature of 60 °C ensures the leaching of cobalt, nickel, copper and lithium with efficiencies above 95%. On the other hand, the use of an innovative method of two-stage counter-current leaching of the battery mass ensures the leaching of cobalt, nickel, copper and lithium at a level significantly greater than 95%, while obtaining a concentration of cobalt in the leaching solution at a level of nearly 50 g/dm³. It also reduces the leaching time of a single stage to 1 h and, importantly, reduces the amount of waste solutions and the consumption of H₂O₂ and sulfuric acid. The developed method of the two-stage counter-current leaching of battery masses is therefore characterized by high efficiency and low environmental impact, thanks to which it can be used in commercial processes for the recycling of lithium-ion batteries.

1. Introduction

The mass production of chemical lithium-ion energy sources (Li-ion batteries, LIBs) used in electric vehicles has resulted in a large stream of waste from used batteries and accumulators of various types appearing on the market. Therefore, recycling companies have often not been prepared to manage some of those new waste streams efficiently [1,2]. In addition, the latest dynamic geopolitical situation forced the industry to take very quick and radical actions to secure secondary sources of strategic metals, e.g., copper, nickel, cobalt and lithium. It resulted in high prices and a surge in interest of the metallurgical industry in the development of new processes for the recovery of secondary raw materials, often in direct cooperation with the scientific world [3,4,5].

The number of publications and technological studies presenting descriptions of processes or scientific research related directly or indirectly to the recycling of the stream of used and/or waste lithium-ion cells is very large. As described by Islam and Iyer-Raniga [6], it can be assumed that the number of publications in this area is growing exponentially. It can be noted that the articles scheduled for publication in the first half of 2023 cover very narrow problems to be solved, focusing mostly on the individual physicochemical operations which are a part of the processing and/or recycling of polymetallic chemical waste of lithium-ion energy sources (LIBs). Those publications concentrate on:

-

the management of a very complex electrolyte in terms of chemical composition [7,8];

-

the use of waste separators from used cells as ecological reducers of cathode metals for the roasting process [9];

-

the recovery of by-products of LIB hydrometallurgical processes, including graphite (C/graphite), sodium sulphate (Na₂SO₄) and lithium carbonate (Li₂CO₃) [10];

-

the selective recovery of lithium by an acid-free mechanical–chemical method [11];

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the selective leaching of nickel, cobalt, manganese, lithium and iron [12];

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or the innovative co-fusion of used Li-ion materials with copper slag [13].

Table 1 presents a list of patent applications and patents in the field related to the treatment and/or recycling of the stream of used and/or waste lithium-ion cells by pyrometallurgical, hydrometallurgical and electrometallurgical methods. The review was carried out using the desk research technique (existing sources method; secondary sources method) consisting of already existing available data from various sources, e.g., Polish Patent Office [14], European Patent Office [15], World Intellectual Property Organization [16], Google Patents [17] and Justia Patents [18].

The main conclusion that comes to mind after analyzing all the referenced documents is that the stream of waste Li-ion cells, due to the very complex chemical composition, cannot be processed with one classic pyrometallurgical or hydrometallurgical path. The desired effect of raw material recovery can only occur as a result of combining different unit processes which are used in different fields of metallurgy [2,19,20]. The hydrometallurgical stage of battery mass processing, which may or may not be preceded by thermal treatment of the substrate, usually consists of acidic or alkaline leaching of properly prepared waste (after disassembly and mechanical treatment processes). These processes should be characterized by technological and economic efficiency and the lowest impact on the environment through the use of the smallest amounts of water, chemical substances and materials, as well as energy. After the first stage of hydrometallurgical treatment, the obtained semi-finished products are processed in a series of physical and chemical operations, which lead to the separation and concentration of valuable or burdensome components between the appropriate phases, in the form of commercial products, semi-finished products for separate technological processes (pyrometallurgical and/or hydrometallurgical) or waste [21].

Many research papers have been published in which comparative studies of procedures for the effective single-stage leaching of battery masses have been presented [6]. These publications, however, most often do not include two-stage leaching methods, which, from a technological point of view (possible implementation in industrial conditions), also seems to be economically justified [10]. For example, in the publication by Jian et al. [22], a counter-current method of leaching of the cathode material from used Li-ion batteries was described, where the total efficiency of metals was 98%, 95%, 95% and 92% for Li, Co, Ni and Mn, respectively, and the acid utilization for leaching exceeded 95%.

On the other hand, a work by Meshram et al. [23] presents a two-stage process of selective leaching of waste Li-ion cathode material, during which, in the first step, the cathode powder was calcined at a temperature of 300 °C and then the material was subjected to acid leaching using sulfuric acid at a temperature of 75 °C and for 60 min. The total efficiency of recovery metals was 93%, 91%, 83% and 78% for Li, Co, Ni and Mn, respectively.

A two-step leaching process is also described in a publication from Chabhadiya et al. in which the results of the leaching of the used LiNi_xCo_yMn_zO₂ cathode material with the use of organic and mineral acids are presented [24]. A procedure of multi-stage leaching of battery masses from various types of Li-ion cells was presented in a paper by Nayl et al. [25]. Chen L. et al. [26] developed a two-stage process for the leaching of battery masses from various types of waste cells using organic acids. The process designed by the authors of this work was based on the use of formic acid and its derivatives for the leaching process.

This paper presents comparative experimental results for the single-stage and two-stage counter-current acid leaching of battery mass, with the addition of a booster, from different types of LIB waste.

Table 1. List of patent applications and patents related to the processing and/or recycling of used and/or waste lithium-ion cells by pyrometallurgical, hydrometallurgical and electrometallurgical methods.

Author	Title	Patent Application or Patent Number
Akkuuser Ltd. [27]	Battery recycling method	US 8 979 006 B2
Duesenfeld GmBH [28]	Recycling method for treating used batteries, particularly rechargeable batteries, and battery processing installation	US 2019/0260101 A1
Recupyl [29]	Method for the recycling of mixed batteries and cells comprising lithium-based anodes	EP 1733451 B1
Retriev Technology [30,31] Taxco [32]	(1) Recovery of lithium-ion batteries (2) Process for recovering and regenerating lithium cathode material from lithium-ion batteries (3) Li reclamation process	(1) 8 616 475 (2) 8 882 007 (3) 5 888 463
Umicore NV SA [33,34]	(1) Process for recycling li-ion batteries (2) Process for the recovery of lithium	(1) WO 2011/035915 A1 (2) WO 2018/184876 A1
Worcester Polytechnic Institute [35]	Method and apparatus for recycling lithium-ion batteries	US10522884B2
Commissariat a l’Energie Atomique et aux Energies Alternatives [36]	Method for recycling the electrolyte of a Li-ion battery and method for recycling Li-ion batteries	US10497993B2
Li-Cycle Corp. [37]	Process, apparatus and system for recovering materials from batteries	11077452
Lithium Inc. [38]	Lithium-ion battery recycling process	CA3076688C
SOLVAY SA [39]	A process for manufacturing nickel sulphate	WO 2021/105365 A1
Urban Mining PYT LTD [40]	Process for the recovery of cobalt, lithium and other metals from spent lithium-based batteries and other feeds	US2021079495A1
Smith W.N., Swoffer S.D. [41]	Process for recycling cobalt and nickel from lithium-ion batteries	113116208
Laucournet R., Barthelemy S., Diaferia N. [42]	Method for recycling lithium batteries and/or electrodes of such batteries	9312581
Marsh W., Rice University [43]	Recycling Li-ion batteries using green chemicals and processes	20200399737
Yi-Lung J., Jiun-Ren U.L., Je-Yuan S. [44]	Metal recovery method of wasted lithium-ion battery using sulfuric acid	TW501294B
Or PRESS FRIMET [45]	A process for recovering metals from recycled rechargeable batteries	CA3109084A1
Gagne-Bourque D.M.C, Nadeau E., Couture B. [46]	Lithium-ion battery recycling process	WO2019060996A1
Ho K.P., Wang R., Shen P. [47]	Method for recycling lithium-ion battery	US20180013181A1
JX Nippon Mining and Metals Corp. [48]	Method for recovering metals from recycled lithium-ion battery materials	JP6334450B2
Li-metal [49]	Granted patent for producing refined lithium metal from lithium carbonate	CA3179470

Table 1. List of patent applications and patents related to the processing and/or recycling of used and/or waste lithium-ion cells by pyrometallurgical, hydrometallurgical and electrometallurgical methods.

Author	Title	Patent Application or Patent Number
Akkuuser Ltd. [27]	Battery recycling method	US 8 979 006 B2
Duesenfeld GmBH [28]	Recycling method for treating used batteries, particularly rechargeable batteries, and battery processing installation	US 2019/0260101 A1
Recupyl [29]	Method for the recycling of mixed batteries and cells comprising lithium-based anodes	EP 1733451 B1
Retriev Technology [30,31] Taxco [32]	(1) Recovery of lithium-ion batteries (2) Process for recovering and regenerating lithium cathode material from lithium-ion batteries (3) Li reclamation process	(1) 8 616 475 (2) 8 882 007 (3) 5 888 463
Umicore NV SA [33,34]	(1) Process for recycling li-ion batteries (2) Process for the recovery of lithium	(1) WO 2011/035915 A1 (2) WO 2018/184876 A1
Worcester Polytechnic Institute [35]	Method and apparatus for recycling lithium-ion batteries	US10522884B2
Commissariat a l’Energie Atomique et aux Energies Alternatives [36]	Method for recycling the electrolyte of a Li-ion battery and method for recycling Li-ion batteries	US10497993B2
Li-Cycle Corp. [37]	Process, apparatus and system for recovering materials from batteries	11077452
Lithium Inc. [38]	Lithium-ion battery recycling process	CA3076688C
SOLVAY SA [39]	A process for manufacturing nickel sulphate	WO 2021/105365 A1
Urban Mining PYT LTD [40]	Process for the recovery of cobalt, lithium and other metals from spent lithium-based batteries and other feeds	US2021079495A1
Smith W.N., Swoffer S.D. [41]	Process for recycling cobalt and nickel from lithium-ion batteries	113116208
Laucournet R., Barthelemy S., Diaferia N. [42]	Method for recycling lithium batteries and/or electrodes of such batteries	9312581
Marsh W., Rice University [43]	Recycling Li-ion batteries using green chemicals and processes	20200399737
Yi-Lung J., Jiun-Ren U.L., Je-Yuan S. [44]	Metal recovery method of wasted lithium-ion battery using sulfuric acid	TW501294B
Or PRESS FRIMET [45]	A process for recovering metals from recycled rechargeable batteries	CA3109084A1
Gagne-Bourque D.M.C, Nadeau E., Couture B. [46]	Lithium-ion battery recycling process	WO2019060996A1
Ho K.P., Wang R., Shen P. [47]	Method for recycling lithium-ion battery	US20180013181A1
JX Nippon Mining and Metals Corp. [48]	Method for recovering metals from recycled lithium-ion battery materials	JP6334450B2
Li-metal [49]	Granted patent for producing refined lithium metal from lithium carbonate	CA3179470

2. Materials and Methods

2.1. Materials

Three different types of battery masses were used in this research. These materials were obtained in a procedure of mechanical processing of Li-ion battery waste and subsequently dried at temperatures in the range of 80–180 °C. Battery masses for testing were prepared by Elemental Metals Strategics Sp. z o.o. (Grodzisk Mazowiecki, Poland) [50] in cooperation with a company specializing in the construction of machines for the mechanical processing of polymetallic waste. All materials were characterized by a grain size of Ø < 1 mm, and their chemical compositions were similar to the standard Li-ion cells used on the market. The materials were as follows: Material I, module car; Material II, tablets and laptops; and Material III, mobile phones.

All analyses were performed at the Łukasiewicz Research Network-Institute of Non-Ferrous Metals, Centre of Analytical Chemistry (Gliwice, Poland). Ni, Co, Li, Mn, Cu, P, Al, Fe contents in battery masses and solutions were determined using the ICP-OES (Emission Spectrometer Optima 5300V (PerkinElmer, Waltham, MA, USA)). F and Cl content was determined using potentiometric methods. C content was determined using IR spectrometry. XRD analyses were performed at the Łukasiewicz Research Network-Institute of Non-Ferrous Metals, Centre of Functional Materials (Gliwice, Poland), based on the interpretation of diffraction patterns prepared with an XRD diffractometer Rigaku MiniFlex 600, equipped with an X-ray tube of wavelength 1.5406 Å, D/TeX silicon strip detector and 2.5″ high-resolution Soller slits on the primary and diffuse beam [51].

Analyzing the chemical compositions of the battery masses, it can be concluded that the composition of Material I differs significantly from the composition of the other materials, confirming a theory that cells from electric cars (EV) contain more nickel than cobalt, in comparison to cells from tablets, laptops and mobile phones—

Table 2. Chemical composition of the tested battery masses—Material I, Material II, Material III.

Chemical Composition (wt%)
Material	C	Co	Ni	Mn	Li	Al	Cu	P	F	Cl	Fe
I—module car	34.30	9.33	9.83	8.70	3.64	4.28	2.73	0.84	3.22	0.04	0.31
II—tablets and laptops	38.20	29.70	1.96	0.81	3.79	1.57	1.53	0.49	1.84	<0.01	0.39
III—mobile phones	39.20	27.00	2.66	1.51	3.79	1.35	1.37	0.47	2.02	<0.01	0.34

[52,53]. All materials contained a similar amount of carbon, ranging from 34.30% to 39.20%. The materials were characterized by a variable content mainly of cobalt, nickel, manganese, copper, fluorine and aluminum. Thus, the cobalt content in Material I was 9.33%, and in Materials II and III, it was between 27.00% and 29.70%. On the other hand, in the case of nickel, the highest content of 9.83% was in Material I, and in Materials II and III, the Ni content ranged from 2% to 3%. The copper content in the tested materials ranged from 1.37% to 2.73%, and the highest content was found in Material I. In the case of manganese, it was observed that a significant content of this metal was found only in Material I—8.70%. The content of fluorine, phosphorus and aluminum was also highest in Material I and amounted to 3.22%, 0.84% and 4.28%, respectively. On the other hand, the iron content for all tested materials was similar and ranged from 0.31% to 0.39%. In the case of phosphorus, the content of this component ranged from 0.97% to 1.25%. No heightened chlorine content was identified in all the analyzed battery masses. In the case of XRD analysis (Figure 1), graphite was identified in all the materials. In addition, in Material I, combinations of lithium, cobalt, manganese and other less valuable components were visible. In the case of Material II, a lithium and cobalt phase in the form of LiCoO₂ could be seen in the diffraction pattern. The same phase was identified in Material III, but a lithium-nickel phase was also visible in it. As can be seen, the battery masses used in this research were extremely diverse materials—both in terms of phase and chemical compositions. For this reason, the industrial leaching method must take into account wide fluctuations in the composition of the leaching material, which in real conditions may be as follows (amount per ton of the processed battery mass): Al—35 kg; Co—69 kg; Cu—22 kg; Fe—20 kg; Li—24 kg; Mn—29 kg; Ni—100 kg; P—6 kg; F—29 kg; and C—340 kg.

2.2. Single-Stage Acid Leaching Method with the Addition of Hydrogen Peroxide—Selection of the Leaching Agent

The tests of single-stage acid leaching with the addition of hydrogen peroxide were carried out with the use of 1 kg of the battery mass and 5 dm³ of 15% and 20% sulfuric acid solution. The material was added to the acid solution in portions over 5 min, and the leaching solution was heated to a temperature around 10 °C lower than the set temperature before leaching. Then, after reaching the set temperature, depending on the sample, 1 dm³ or 2 dm³ of 30% hydrogen peroxide was added in equal portions during 1–2 h. Initial tests were carried out at 60 °C for 2 h, with a solid-to-liquid-phase ratio of 1:5. After that, the obtained suspension was filtered using a Büchner funnel and washed with water (0.5 dm³ of water per 1 kg of the battery mass). In the case of samples with the addition of 2 dm³ of hydrogen peroxide, the battery mass was washed with an additional portion of 0.5 dm³ of water. In each test, the volume of the leaching solution was measured, in which the concentration of Co, Ni, Li, Cu, Mn, Fe, P and F ions was analyzed. The pH of the main solution after leaching was measured and the content of free sulfuric acid was determined. The leaching efficiency of individual components (L) was calculated according to the following formula:

$$L=\frac{V·C}{m·z}·100 [\mathrm{\%}]$$

(1)

where V is the volume of the solution after leaching (dm³), C is the concentration of the component in the solution after leaching (g/dm³), m is the weight of the battery mass used for testing (g) and z is the coefficient of the content of the given component in the battery mass.

2.3. Single-Stage Acid Leaching Method with the Addition of Hydrogen Peroxide—Selection of the Phase Ratio

Phase ratio selection tests for the single-stage acid leaching with the addition of hydrogen peroxide were carried out for two values of the solid-to-liquid-phase ratio—1:5 and 1:4. The experiments were performed for three materials—I, II, III. The leaching agent selected in this case was 20% aqueous solution of sulfuric acid. Thus, to 5 dm³ of sulfuric acid solution, 1.0 kg of the material was added in portions over a period of about 5 min (the leaching solution was heated to a temperature around 10 °C lower than the set temperature before leaching). Then, after reaching the set temperature, 1.0 dm³ of 30% aqueous solution of hydrogen peroxide was added in equal portions over 40 min. The tests were carried out at a temperature of 60 °C for 2 h. After that time, the obtained suspension was filtered using the Büchner funnel and washed with water (0.50 dm³ of water per 1 kg of the feed). The volume of the main solution was measured, in which the content of free sulfuric acid and the concentration of Co, Ni, Li, Cu, Mn, Fe, P, F ions were analyzed. The leaching efficiency of individual components was calculated as described in Section 2.2.

2.4. Two-Stage Counter-Current Acid Leaching Method with the Addition of Hydrogen Peroxide

The two-stage counter-current leaching tests were performed for all three materials—I, II, III—as shown in Figure 2. Thus, the experiments were carried out as follows: In the first cycle, a fresh portion of the battery mass was leached with the use of 5 dm³ of 20% sulfuric acid solution—primary leaching solution. The material in the amount of 1 kg was added to the solution in portions over a period of about 5 min (the leaching solution was heated to a temperature around 10 °C lower than the set temperature before leaching). The tests were carried out at a temperature of 60 °C, for 1 h, with a solid-to-liquid-phase ratio of 1:5. After leaching, the suspension was filtered using the Büchner funnel, which allowed for obtaining a filtrate after the first stage (directed to the recovery of valuable components) and unwashed sludge, which was sent to the second stage of leaching.

In the second stage of leaching, 20% aqueous solution of sulfuric acid was also used as the leaching agent—the primary leaching solution—but in this cycle, 30% H₂O₂ solution was added in an amount of 1 dm³. The sludge (after the first stage of leaching) was placed in a reactor with a capacity of 10 dm³ by quantitatively transferring the entire mass to a beaker, using 5 dm³ of the original leaching solution (20% sulfuric acid solution). The suspension was stirred and heated to 60 °C. After reaching the set temperature, 1 dm³ of hydrogen peroxide was added within 30–60 min. The tests were carried out at a temperature of 60 °C for 1 h. After that, the obtained suspension was filtered using the Büchner funnel and the remaining material was washed with 0.5 dm³ of water. The combined filtrate and washings after the second stage of leaching were used as the leaching solution for the next portion of the battery mass. In the first leaching stage of the next cycle, the tests were also carried out at 60 °C, for 1 h, with a solid-to-liquid-phase ratio of 1:5. After leaching, the suspension was filtered, obtaining a filtrate and an unwashed sludge, which was sent to the second stage of leaching, creating a cyclic method. For all tests, the volumes of filtrates were measured, in which the concentration of Co, Ni, Li, Cu, Mn, Fe, P and F ions was analyzed. For the solutions formed after leaching, pH was also measured and content of free sulfuric acid was determined. The leaching efficiency of the individual components was calculated as described below.

Leaching efficiency for the first stage of the first cycle:

$$W_{Me}=\frac{V_x·C_x}{Z_{Me\%}·m_y}·100\%$$

(2)

where W_Me is the leaching efficiency of individual element Me (%), V_x is the volume of the solution after the x-th leaching (dm³), C_x is the concentration of element Me in the solution after the x-th leaching (g/dm³), Z_Me% is the weight percentage of the element in the battery mass (%) and m_y is the mass of the material used in cycle x (g).

Leaching efficiency for the second stage of the first cycle:

$$W_{Me}=\frac{V_x·C_x+V_{x-1}·C_{x-1}}{Z_{Me\%}·m_y}·100\%$$

(3)

where W_Me is the leaching efficiency of individual element Me (%), V_x is the volume of the solution after the x-th leaching (dm³), C_x is the concentration of element Me in the solution after the x-th leaching (g/dm³), Z_Me% is the weight percentage of the element in the battery mass (%), m_y is the mass of the material used in cycle x (g), V_x−1 is the volume of the solution after the x − 1-th leaching (dm³) and C_x−1 is the concentration of element Me in the solution after the x − 1-th leaching (g/dm³).

Leaching efficiency for the first stage of the cycle:

$$W_{Me}=\frac{V_x·C_x-V_{x-1}·C_{x-1}}{Z_{Me\%}·m_y}·100\%$$

(4)

where W_Me is the leaching efficiency of individual element Me (%), V_x is the volume of the solution after the x-th leaching (dm³), C_x is the concentration of element Me in the solution after the x-th leaching (g/dm³), Z_Me% is the weight percentage of the element in the battery mass (%), m_y is the mass of the material used in cycle y (g), V_x−1 is the volume of the solution after the x − 1-th leaching (dm³) and C_x−1 is the concentration of element Me in the solution after the x − 1-th leaching (g/dm³).

Leaching efficiency for the second stage of the cycle:

$$W_{Me}=\frac{V_x·C_x+V_{x-1}·C_{x-1}-V_{x-2}·C_{x-2}}{Z_{Me\%}·m_y}·100\%$$

(5)

where W_Me is the leaching efficiency of individual element Me (%), V_x is the volume of the solution after the x-th leaching (dm³), C_x is the concentration of element Me in the solution after the x-th leaching (g/dm³), Z_Me% is the weight percentage of the element in the battery mass (%), m_y is the mass of the material used in cycle y (g), V_x−1 is the volume of the solution after the x − 1-th leaching (dm³), C_x−1 is the concentration of element Me in the solution after the x − 1-th leaching (g/dm³), V_x−2 is the volume of the solution after the x − 2-th leaching (dm³) and C_x−2 is the concentration of element Me in the solution after the x − 2-th leaching (g/dm³).

3. Results and Discussion

3.1. Results of the Single-Stage Acid Leaching Method with the Addition of Hydrogen Peroxide—Selection of the Leaching Agent

The results of the tests of single-stage acid leaching with the addition of hydrogen peroxide—the selection of the leaching agent—are presented in

Table 3. Results of the single-stage acid leaching with the addition of hydrogen peroxide—selection of the leaching agent.

Material	H2SO4 Concentration (%)	Volume of the Solution after Leaching (cm3)	Volume of 30% H2O2 (dm3)	pH	Free Acid Concentration (g/dm3)	Concentration of the Element in the Solution after Leaching (g/dm3)
						Co	Ni	Li	Cu	Mn	Fe	P	F
I	15	4840	1.0	1.7	5.9	14.70	15.60	5.59	3.45	12.90	0.57	1.13	4.80
	20	5700		0.5	48.5	14.90	15.70	5.67	3.98	13.20	0.50	1.06	4.30
II	15	4920		0.7	15.2	45.90	3.03	5.29	2.35	1.31	0.35	0.55	3.05
	20	5960		0.4	62.7	43.90	3.28	6.04	2.56	1.43	0.42	0.33	2.60
III	15	5300		0.7	31.0	31.10	3.80	5.02	1.91	2.19	0.51	0.65	1.65
	20	5520		0.3	86.0	36.60	4.21	5.50	2.00	2.26	0.61	0.69	2.00
I	15	5900	2.0	0.8	13.7	14.40	15.40	5.83	3.88	12.50	0.37	1.31	4.20
	20	6660		0.4	59.3	12.80	13.60	5.10	3.41	11.0	0.43	2.86	3.55
II	15	5620		0.7	7.4	34.40	2.46	5.82	1.93	1.25	0.11	0.47	2.55
	20	6040		0.4	44.6	38.20	1.81	4.90	1.37	1.24	0.43	0.65	2.45
III	15	5920		0.8	25.0	25.10	2.75	4.10	1.30	1.51	0.42	0.61	1.40
	20	5960		0.4	66.0	38.50	3.75	5.74	1.90	2.10	0.51	0.99	1.95

and described in Section 3.1.1 and Section 3.1.2.

3.1.1. Results of the Single-Stage Acid Leaching with the Addition of 1 dm³ of Hydrogen Peroxide—Selection of the Leaching Agent

The analysis of the leaching results showed that with the increase in H₂SO₄ concentration, the leaching efficiency of both nickel and cobalt clearly increased for all the tested battery masses. The obtained leaching efficiencies also depended to a large extent on the type and composition of the material fed into the leaching process. Thus, the leaching efficiencies obtained for cobalt ranged from 61.05% to 91.03%, and that for nickel ranged from 75.71% to 99.74%. The content of free acid in the solution after leaching was very diverse, but high enough to prove that an appropriate, excessive amount of leaching agent was used in all studies. The average free acid concentration was 42 g/dm³. Obtaining high concentrations of cobalt and nickel was an important element of this research due to the aspect of its implementation in industrial conditions. The highest cobalt concentrations were obtained for Materials II and III (materials with high initial Co content). These concentrations ranged from 31.10 g/dm³ to 45.90 g/dm³ of Co. In the case of nickel, the highest concentrations were obtained for Material I (material with high initial Ni content), which was about 16 g/dm³ of Ni. Also, for lithium, copper and manganese, the leaching efficiencies increased unequivocally with the increase in H₂SO₄ concentration. In the case of lithium, the concentrations in the solutions after leaching ranged from 5 g/dm³ to 6 g/dm³. The leaching efficiency of manganese varied from 72% to 100% and that of copper ranged from 61% to 100%. It should be emphasized that the lithium content was similar in each of the tested battery masses, while both the copper and manganese contents differed significantly. In the case of iron, phosphorus and fluorine, the leaching efficiencies of these components increased with increasing H₂SO₄ concentration. In the case of iron, the concentration in solutions formed after leaching ranged from 0.35 g/dm³ to 0.61 g/dm³. The leaching efficiency of phosphorus ranged from 40% to 81% and that of fluorine ranged from 43% to 84%. It should be noted that the iron content was similar in each of the tested materials, while both fluorine and phosphorus contents differed. Summing up, the applied leaching conditions resulted in the leaching of significant amounts of each of the tested components. Incredibly important is the fact that nickel and cobalt were leached from the feed with high efficiencies, confirming the results presented in a number of publications, e.g., in the work of Guimarăes et al. [54] and Peng et al. [55], in which the authors obtained over a 93% recovery of metals from battery masses using sulfuric acid. Although increasing the concentration of sulfuric acid for leaching in most cases resulted in an increase in the leaching efficiency of individual components, it also resulted in an increase in the content of free sulfuric acid in the solution formed after leaching. It is an unquestionable problem in carrying out subsequent operations aimed at the recovery of individual components in industrial conditions. For this reason, the tests were carried out using the auxiliary substance in the form of 2 dm³ of 30% aqueous solution of hydrogen peroxide.

3.1.2. Results of the Single-Stage Acid Leaching with the Addition of 2 dm³ of Hydrogen Peroxide—Selection of the Leaching Agent

From the results of the tests listed in Table 3, it can be concluded that with the use of a larger portion of the aqueous solution of hydrogen peroxide, along with the increase in concentration of H₂SO₄, there was no unequivocal increase in the leaching efficiency of both nickel and cobalt for all tested battery masses. It should be emphasized that the obtained leaching efficiencies depended to a large extent on the type and composition of the material directed to the leaching process. Thus, the leaching efficiencies obtained for cobalt ranged from 55.03% to 91.37%, and that for nickel ranged from 55.78% to 92.43%. The content of free acid in the solutions after leaching was also very diverse, but it proved that in all the studies, an appropriate, excessive amount of leaching agent was used. The average concentration of the free acid was 36 g/dm³ and was very similar to the concentration obtained in the tests using the smaller portion of hydrogen peroxide. Obtaining high concentrations of cobalt and nickel was also an important element of this research. The highest cobalt concentrations were obtained for Materials II and III (materials with high initial Co content). These concentrations ranged from 25.10 g/dm³ to 38.20 g/dm³ and were lower than those obtained with the use of the smaller portion of hydrogen peroxide. In the case of nickel, the highest concentrations were obtained for Material I (material with high initial content of Ni), which ranged from 13.60 g/dm³ to 15.40 g/dm³ and were also lower than those obtained with the addition of 1 dm³ of hydrogen peroxide. Also, in the case of lithium, copper and manganese, the leaching efficiencies of these components behaved differently with increasing H₂SO₄ concentration. For lithium, the concentrations in the solutions obtained after leaching ranged from 4 g/dm³ to 6 g/dm³ and was slightly lower than the concentrations obtained using 1 dm³ of hydrogen peroxide. The leaching efficiency of manganese ranged from 59% to 93% and that of copper ranged from 54% to 84%. It should be emphasized that these values were also lower than those obtained with the smaller portion of H₂O₂. In the case of iron, phosphorus and fluorine, the leaching efficiencies of these components in most cases increased with increasing H₂SO₄ concentration. The exception was fluorine; when leaching was carried out with Material I, the leaching efficiency decreased as the concentration of H₂SO₄ increased, but the decrease was insignificant. In the case of iron, the concentration in solutions obtained after leaching ranged from 0.37 g/dm³ to 0.51 g/dm³ and was only slightly lower than the one obtained with the smaller dose of hydrogen peroxide. The leaching efficiency of phosphorus ranged from 54% to 100% and that of fluorine ranged from 41% to 78%. In the case of phosphorus, these values were higher than those obtained for the smaller amount of H₂O₂, and slightly lower in the case of fluorine. To sum it all up, in the case of Material I, an increase in the leaching efficiencies of key components, i.e., cobalt, nickel, lithium and copper, was observed, along with an increase in the concentration of sulfuric acid with the addition of 1 dm³ of hydrogen peroxide. In the case of using 2 dm³ of hydrogen peroxide for leaching, the leaching efficiencies of the main components, i.e., Co, Ni, Li and Cu, were similarly high and amounted to 94%, 97%, 96%, >98% and 86–90%, respectively. Equally high efficiencies and a similar trend were observed for Mn, Fe, P and F. For Material II, the same behavior of increasing the leaching efficiencies of key components, i.e., cobalt, nickel, lithium and copper, with the increase in the concentration of sulfuric acid, with the addition of 1 dm³ and 2 dm³ of hydrogen peroxide, was observed. The highest leaching efficiencies for cobalt, nickel, lithium and copper were obtained using 20% sulfuric acid with 1 dm³ of hydrogen peroxide for leaching, which were 88.97%, ~100%, 96.04% and ~100%, respectively. A similar tendency was also observed in this case for Mn, Fe, P and F. Using Material III, the process was characterized by the same tendency of increasing leaching efficiencies of key components, i.e., cobalt, nickel, lithium and copper, with the increase in concentration of sulfuric acid and the addition of 1 dm³ and 2 dm³ of hydrogen peroxide. In this case, however, the highest leaching efficiencies of cobalt, nickel, lithium and copper were obtained using 20% sulfuric acid with 2 dm³ of H₂O₂, and amounted to 89.93%, ~89.73%, ~100% and 88.48%, respectively. A similar trend was observed in this case for Mn, Fe, P and F. However, this material was characterized by a low leaching efficiency of F, in comparison to the results obtained for Materials I and II, amounting to about 60%. Based on the obtained results, it was decided that further experiments to determine the optimal solid-to-liquid-phase ratio of the acid leaching process would be carried out using 20% sulfuric acid solution with the addition of 1 dm³ of hydrogen peroxide. Similar conclusions were reached by the authors of the work written by Chen and Ho [56], indicating that an effective factor supporting the acid leaching of battery masses from Li-ion cells is hydrogen peroxide in amounts similar to those presented in this work.

3.2. Results of the Single-Stage Acid Leaching Method with the Addition of Hydrogen Peroxide—Selection of the Leaching Agent

From the results of single-stage acid leach experiments with the addition of hydrogen peroxide, presented in

Table 4. Results of the single-stage acid leaching with the addition of hydrogen peroxide—selection of the phase ratio.

Material	Solid to Liquid Phase Ratio	Volume of the Solution after Leaching (cm3)	pH	Free Acid Concentration (g/dm3)	Concentration of the Element in the Solution after Leaching (g/dm3)
					Co	Ni	Li	Cu	Mn	Fe	P	F
I	1:5	5700	0.45	48.5	14.90	15.70	5.67	3.98	13.20	0.50	1.06	4.30
	1:4	1885	0.60	40.2	24.30	26.00	9.58	5.54	19.00	0.70	1.51	5.85
II	1:5	5960	0.60	62.7	43.90	3.28	6.04	2.56	1.43	0.42	0.33	2.60
	1:4	1980	0.60	65.1	63.90	4.63	8.89	3.62	1.85	0.57	0.82	3.55
III	1:5	5520	0.39	85.8	36.40	4.21	5.50	2.00	2.26	0.64	0.69	2.00
	1:4	2150	0.50	49.0	51.50	5.24	7.92	2.75	3.07	0.67	1.03	2.00

, it can be concluded that with a solid-to-liquid-phase ratio of 1:4, higher cobalt concentrations were obtained (for all three materials) in the leaching solution than using a solid-to-liquid-phase ratio of 1:5. The highest cobalt concentration of about 64 g/dm³ was obtained in the test using Material II. In the case of nickel, the highest concentration of 26 g/dm³ was obtained in the test using Material I. For all battery masses, higher concentrations were obtained for nickel with a solid-to-liquid-phase ratio of 1:4 compared to 1:5. The free acid concentration ranged from 49.00 to 85.80 g/dm³, and the pH of the tested solutions ranged from 0.45 to 0.60. For lithium, iron and manganese, the solid-to-liquid-phase ratios of 1:4 and 1:5 resulted in very similar high leaching efficiencies. The manganese leaching efficiency ranged from 82% to 100%, that of lithium ranged from 80% to 99%, and that of copper ranged from 76.50% to 99.72%. For iron, phosphorus and fluorine, the results obtained were very diverse. Therefore, the leaching efficiency for iron ranged from about 58% to 92%, that for phosphorus ranged from 40% to 94%, and that for fluorine ranged from 42% to 76%. The applied leaching conditions of the materials resulted in the leaching of significant amounts of each of the tested components, importantly with high efficiencies. Nickel and cobalt were leached from them with 74% and 87% leaching efficiencies, respectively. No significant differences were observed between the use of the 1:4 and 1:5 solid-to-liquid-phase ratios; therefore, the main criteria for choosing the appropriate conditions were the ability to obtain the highest concentrations of cobalt and nickel, the efficiency of the phase separation step and the low content of free acid obtained in the after-leaching solution. That is due to the fact that the aforementioned information will help with introducing the process to industrial conditions, based on solvent extraction processes [57], electrochemical processes [58] or selective and/or collective scrapping, allowing the recovery of valuable metals [23].

3.3. Results of the Two-Stage Counter-Current Acid Leaching with the Addition of Hydrogen Peroxide

The use of two-stage counter-current leaching resulted in obtaining high, stable, repeatable leaching efficiencies of cobalt, nickel, lithium and copper from battery masses—as shown in

Table 5. Test results of the two-stage counter-current leaching of the battery masses.

Material	Cycle	Volume of the Solution after Leaching (cm3)		pH	Concentration of the Element in the Solution after Leaching (g/dm3)
		I Stage	II Stage		Co	Ni	Li	Cu	Mn	Fe	P	F
I	1	4900	-	0.2	11.10	13.20	6.51	4.74	8.89	0.42	1.05	4.80
		-	6800	0.2	5.73	5.09	0.84	0.55	5.23	0.09	0.18	0.33
	2	6100	-	0.4	14.70	15.50	5.68	3.65	12.60	0.41	0.99	4.40
		-	6300	0.1	6.44	5.69	0.98	0.99	5.63	0.13	0.17	0.33
	3	5840	-	0.3	16.60	17.40	6.39	4.50	13.70	0.63	1.01	4.40
		-	6380	0.1	6.61	5.52	1.15	1.04	5.12	0.29	0.24	0.43
II	1	4700	-	0.1	30.00	2.73	6.32	3.00	1.26	0.50	0.50	3.14
		-	6000	0.1	24.00	0.55	1.32	0.23	0.41	0.12	0.15	0.20
	2	5510	-	0.4	47.90	2.52	5.63	1.84	1.33	0.49	0.58	2.98
		-	6240	0.1	25.80	0.97	1.49	0.52	0.57	0.16	0.20	0.22
	3	5700	-	0.5	51.60	3.34	6.67	2.41	1.46	0.52	0.55	2.76
		-	5900	0.1	21.90	1.17	1.67	0.69	0.70	0.19	0.21	0.22
III	1	4900	-	0.1	26.60	4.03	5.83	2.10	1.92	0.71	0.68	2.20
		-	6600	0.1	19.40	0.70	1.10	0.18	0.72	0.06	0.08	0.18
	2	6000	-	0.4	38.80	3.18	5.14	1.51	1.64	0.54	0.64	1.60
		-	6500	0.1	19.80	1.10	1.28	0.24	0.86	0.07	0.07	0.16
	3	5860	-	0.4	38.10	3.57	5.35	1.60	1.81	0.56	0.62	1.59
		-	6420	0.1	21.80	1.15	1.37	0.28	0.97	0.09	0.06	0.16

. In the case of Material I, the metal leaching efficiencies were above 96%, and those for Material II were slightly lower but, on average, were significantly above 90%. A similar trend was observed for Material III as for Material II. The remaining components, i.e., manganese, iron, phosphorus and fluorine, were leached at a high, stable level. Only in the case of Material III was a low fluorine efficiency observed, which did not exceed 60%. It should also be noted that in the case of cobalt, for Materials II and III, high, targeted concentrations of this metal were obtained in the solutions after leaching, ranging from 19.40 g/dm³ to 47.90 g/dm³. In the case of Material I, the concentrations of cobalt and nickel in the leaching solutions were at a similar level and amounted to about 15 g/dm³ of each of these metals.

After the analysis of the carried-out tests, it can be stated with certainty that for each tested material, in subsequent cycles of the leaching process, an increase in the amount of leached components such as cobalt, nickel, copper, lithium and manganese was observed.

3.4. Results of the Analysis of the Composition of Sludge Left after Single-Stage and Two-Stage Counter-Current Acid Leaching with the Addition of Hydrogen Peroxide

Table 6. Comparison of the results of analyses of the battery masses and sludges formed after the single-stage leaching.

Material	The Initial Weight of the Battery Mass or after-Leaching Sludge (g)	Volume of 30% H2O2 (dm3)	Composition of the Battery Mass or after-Leaching Sludge (%)
			Co	Ni	Li	Cu	Mn	Fe	P	F
I	1000	-	9.33	9.83	3.64	2.73	8.70	0.31	0.84	3.22
	431	1	0.15	0.16	0.09	0.09	0.13	0.15	0.31	2.15
	413	2	0.08	0.09	0.06	0.06	0.06	0.09	0.17	2.16
II	1000	-	29.70	1.96	3.79	1.53	0.81	0.39	0.49	1.84
	457	1	7.23	0.08	0.34	0.08	0.08	0.33	0.20	1.18
	391	2	1.42	0.05	0.12	0.11	0.01	0.21	0.20	1.33
III	1000	-	27.00	2.66	3.79	1.37	1.51	0.34	0.47	2.02
	448	1	7.06	0.14	0.42	0.08	0.07	0.08	0.09	1.36
	386	2	0.83	0.03	0.07	0.02	<0.01	0.08	0.09	1.50

presents the results of analyses of battery masses and sludges formed after the single-stage leaching with the use of 20% sulfuric acid solutions and various volumes of hydrogen peroxide.

Table 7. Comparison of the results of analyses of the battery masses and sludges formed after the two-stage counter-current leaching.

Material	The Initial Weight of the Battery Mass or after-Leaching Sludge (g)	Cycle	Composition of the Battery Mass or after-Leaching Sludge (%)
			Co	Ni	Li	Cu	Mn	Fe	P	F
I	1000	0	9.33	9.83	3.64	2.73	8.70	0.31	0.84	3.22
	422	1	0.05	0.06	0.05	0.05	0.04	0.10	0.11	2.07
	440	2	0.22	0.20	0.08	0.14	0.17	0.16	0.16	1.92
	418	3	0.22	0.21	0.08	0.10	0.16	0.14	0.14	2.01
II	1000	0	29.70	1.96	3.79	1.53	0.81	0.39	0.49	1.84
	394	1	0.37	0.02	0.05	0.05	0.01	0.11	0.17	1.33
	404	2	0.71	0.04	0.06	0.06	0.01	0.10	0.19	1.38
	405	3	0.75	0.07	0.06	0.07	0.01	0.19	0.19	1.35
III	1000	0	27.00	2.66	3.79	1.37	1.51	0.34	0.47	2.02
	381	1	0.30	0.03	0.03	0.01	0.01	0.14	0.07	1.52
	373	2	0.48	0.04	0.04	0.02	0.02	0.13	0.09	1.47
	369	3	0.33	0.03	0.03	0.01	0.01	0.08	0.08	1.49

, on the other hand, compares the results of analyses of battery masses and sludges obtained after the two-stage, counter-current leaching. Figure 3 and Figure 4 also list selected X-ray diffraction patterns of the after-leaching sludges, in the case of single-stage leaching for Materials II and III, and in the case of two-stage leaching for Materials I and III. The analysis of the obtained results of single-stage leaching showed large differences in the composition of the individual tested battery masses. In all cases, the leaching of the targeted ingredients with the higher dose of hydrogen peroxide was more effective. For Material I, the battery mass remaining after the leaching contained <0.2% of cobalt and phosphorus and <0.1% of nickel, lithium, manganese, copper and iron, and the fluorine content in the sludge did not exceed 2.2%. In the case of Materials II and III, the composition results were similar. The battery masses remaining after leaching in these two cases contained <1.5% of cobalt when using the higher dose of hydrogen peroxide, and >7% when using the lower dose of hydrogen peroxide. In the case of nickel, lithium, manganese, copper, iron and phosphorus, such large differences were not observed when using different doses of aqueous hydrogen peroxide solution. However, the fluorine content did not exceed 1.5%.

After analyzing the results, it can be concluded that for Material I, the vast majority of cobalt, nickel, lithium, copper, manganese, iron, phosphorus and fluorine was transferred into the solution after the two-stage counter-current leaching process. The battery mass remaining after the leaching contained <1% of cobalt and <0.01% of nickel, lithium, manganese and copper. In the case of iron and phosphorus, the content in the sludge did not exceed 0.2%. Fluorine, on the other hand, accounted for 1.33–1.37% of the sludge remaining after the leaching. In the case of Material II, the composition results were almost identical to those obtained in the case of Material I. However, for Material III, the battery mass remaining after the leaching contained <0.5% of cobalt and <0.005% of nickel, lithium, manganese and copper, while the iron and phosphorus amount was <0.1%. The highest content of fluorine in the sludge, nearly 1.5%, was obtained for this material. In all the diffraction patterns, the highest peak was from graphite; in each diagram, the presence of phases associated with metals, mainly with Li, was also visible.

4. Conclusions

The analysis of the presented research results allowed for the following conclusions to be drawn:

• The leaching efficiency of cobalt and other valuable components from the battery masses increases with increasing concentrations of sulfuric acid in the range from 15% to 20%, with the addition of 1 dm³ or 2 dm³ of hydrogen peroxide;
• The leaching of a 1 kg portion of the battery mass (regardless of the material composition) in the 15% or 20% sulfuric acid solution with the addition of 1 dm³ or 2 dm³ of H₂O₂, for 2 h, with a solid-to-liquid-phase ratio of 1:5 (or even 1:4) at 60 °C ensures a leaching efficiency of cobalt, nickel, copper and lithium above 95%;
• The use of the two-stage counter-current leaching of the battery mass in the selected conditions ensures the leaching efficiency of cobalt, nickel, copper and lithium at a level significantly above 95%, while obtaining the concentration of cobalt in the after-leaching solution at a level of nearly 50 g/dm³, reducing the duration of leaching in a single stage up to 1 h and, most importantly, reducing the amount of waste solutions and the consumption of H₂O₂ and sulfuric acid.

The above-mentioned data made it possible to formulate a patent application for the method of conducting the two-stage leaching process of the battery masses and to consider implementing the process of acid leaching of the battery masses in industrial conditions by Elemental Strategic Metals Ltd. (Grodzisk Mazowiecki, Poland) [59].