A sustainable process for metal recycling from spent lithium-ion batteries using ammonium chloride

Waste Management 79 (2018) 545–553

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A sustainable process for metal recycling from spent lithium-ion batteries using ammonium chloride Weiguang Lv a,b, Zhonghang Wang a, Hongbin Cao a, Xiaohong Zheng a, Wei Jin c, Yi Zhang a, Zhi Sun a,⇑ a Beijing Engineering Research Center of Process Pollution Control, Division of Environment Technology and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China b University of Chinese Academy of Sciences, Beijing 100190, China c School of Chemical and Material Engineering, Jiangnan University, Wuxi 214122, China

a r t i c l e

i n f o

Article history: Received 16 April 2018 Revised 3 August 2018 Accepted 12 August 2018

Keywords: Spent lithium ion batteries Valuable metals Sulphuric acid Ammonium chloride

a b s t r a c t In this paper, a sustainable process to recover valuable metals from spent lithium ion batteries (LIBs) in sulfuric acid using ammonium chloride as reductant was proposed and studied. Being easily reused, ammonium chloride is found to be efficient and posing minor environmental impacts during the overall process. By investigating the effects of a wide range of parameters, e.g., H2SO4 concentration, NH4Cl concentration, temperature, leaching time, and solid-to-liquid mass ratio, the leaching behaviour of Li, Ni, Co, and Mn was systematically investigated. And the leaching mechanism and kinetics were determined by mineralogically characterization of residues at various reaction times and by fitting using different kinetic models. With this research, it is possible to provide a win-win solution to improve the recycling effectiveness of spent LIBs by using waste salt that is easily reused as the reductant. Ó 2018 Elsevier Ltd. All rights reserved.

1. Introduction Rapid development of mobile phone, energy storage device and electric vehicles, leads to an ever-increasing demand of rechargeable lithium-ion batteries (Gao et al., 2017; Wu et al., 2018). Meanwhile, the amount of waste LIBs substantially climbed due to the rapid increase in the consumption of LIBs (Lv et al., 2018). Richa et al. has estimated that 0.33–4 million metric tons of LIBs are projected to enter the waste stream from electric vehicles between 2015 and 2040 (Winslow et al., 2018). The waste will lead to the issues in supply chains, resource, and environment (Mishra and Gostu, 2017). For example, some of waste LIBs are not completely discharged, which may catch fire or explode under improperly handle. Sol-vent electrolyte lithium hexafluorophosphate (LiPF6) and some of the heavy metals contained within the batteries are dangerous to leach into solution and soil (Natarajan et al., 2018; Winslow et al., 2018). Besides, LIBs contains many valuable metals such as cobalt and lithium. As a result, it is highly required to recycle spent LIBs in an environmentally friendly and economic way (Helbig et al., 2018; Lv et al., 2018; Sun et al., 2017). ⇑ Corresponding author at: Beijing Engineering Research Center of Process Pollution Control, Division of Environment Technology and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, No. 1 Beierjie, Zhongguancun, Beijing, China. E-mail address: [email protected] (Z. Sun). https://doi.org/10.1016/j.wasman.2018.08.027 0956-053X/Ó 2018 Elsevier Ltd. All rights reserved.

Nowadays, spent LIBs are usually processed by using either pyrometallurgical or hydrometallurgical methods, to recover valuable metals or other components. Pyrometallurgical methods usually carried out under harsh reaction conditions, during which toxic gases would be released and some metals like Li and Al can hardly be recovered (Li et al., 2017; Xiao et al., 2017; Zeng et al., 2014). Thus, a growing number of studies have focused on the hydrometallurgical processes, because of its high extraction efficiencies of valuable metals, especially Li, controlled environmental influence, and low energy consumption (Chagnes and Pospiech, 2013; Peng et al., 2018). A hydrometallurgical process mainly consists of leaching, purification, and fabrication procedures. In the leaching procedure, reductants are usually needed to be added into the inorganic/organic acid (Joulié et al., 2017; Meshram et al., 2015; Senc´anski et al., 2017) or ammonia-based alkaline (Ku et al., 2016; Wang et al., 2017a) leaching reagents to enhance the leaching process. The most common reductant used in experiments is H2O2, because of its lower redox potential and no introduction of impurities. However, the instability of hydrogen peroxide leads to some issues in leaching process, storage, and transport (Meng et al., 2017). Recent studies have attempted to investigate alternative reductants, like Na2S2O5 (Vieceli et al., 2018), NaHSO3 (Meshram et al., 2015), glucose (Pant and Dolker, 2016), ascorbic acid (Nayaka et al., 2018), etc. These alternatives are more stable than H2O2. However, all of these reductants cannot be directly or simply regenerated and reused. Besides, the

W. Lv et al. / Waste Management 79 (2018) 545–553

2. Material and methods 2.1. Materials and reagents The cathode scraps were supplied by a local spent LIBs recycling company (Ganzhou highpower technology Co., Ltd) in China. A complete dissolution of cathode scrap was carried out in aqua regia to determine the chemical composition using ICP-OES (iCAP 6300 Radial, Thermo Scientific). The contents of Li, Co, Ni and Mn in scrap were 6.15%, 10.70%, 26.08%, and 14.58%, respectively. The XRD patterns of the cathode scrap shown that Li(Ni0.5Co0.2Mn0.3) O2 is the major phase (Fig. 1). Sulfuric acid was used as the leaching reagent with ammonium chloride used as the reductant. All chemical reagents (H2SO4, HCl, HNO3, NH4Cl, NaOH) were of analytical

35000 Li(Ni0.5Co0.2Mn0.3)O2

(003)

30000

10000 5000 0

0

10

20

30

40

50

60

(018) (110) (113)

15000

(107)

20000

(105)

(104)

25000

(101) (006) (102)

productive processes of raw materials also need to be considered from the environmental and life cycle assessment perspective. For example, the commercial anthraquinone oxidation (AO) process for producing H2O2 generates substantial organic by-product wastes, which are necessary to remove. The separation of product from these waste organics requires high investment in equipment and high temperature (Campos-Martin et al., 2006). Fortunately, no reductant is needed when leaching with HCl, this is because that the NCM could be reduced by Cl
in this system (Takacova et al., 2016). Barik et al. (2016) used HCl as leaching reagent to recover valuable metals from spent cathode, and over 99% of Li, Co, and Mn in the cathode were extracted into the solution. Wang et al. used HCl as leaching reagent with 99% of Li, Ni, Co, and Mn leached from the mixture contained spent LiCoO2, LiMn2O4, and NCM cathode materials (Wang et al., 2009). However, when using HCl barely as the leaching reagent, the volatility and corrosion of HCl with concentration of 2–4 M should not be ignored. Therefore, to achieve a similar reaction performance, chloride components, like ammonium chloride, sodium chloride, could be introduced into non-HCl acidic systems as a reductant, without causing the above-mentioned volatility and corrosive problems. Besides, it was reported that more than 2.4 million m3 waste water containing ammonium chloride was discharged in China in 2013 (Li et al., 2016), and a lot of waste NH4Cl water produced in extracting cobalt production need to be solved through concentration and crystallization (Guideline on Available Technologies of Pollution Prevention and Control for Cobalt Smelting Industry (on Trial), 2015, Ministry of Ecology and Environment of the People’s Republic of China). If the waste ammonium chloride can be reused in industrial production, it will reduce environment pollution and increase profit. In this paper, ammonium chloride was adopted as a new reductant to achieve high leaching efficiencies of Ni, Co, Mn, and Li from the spent cathode materials in the sulfuric acid. The effect of leaching agent concentrations, reductant concentrations, solid-to-liquid mass ratio (S/L mass ratio), temperature, and leaching time on the leaching efficiencies of various valuable metals were systematically investigated. Then the leaching mechanism and kinetics were determined by mineralogically characterization of residues at various reaction times and by fitting using the unreacted contraction nuclear model. On one hand, the ammonium chloride is a stable (easy to transport and store) and cheap reductant corresponding to the H2O2. It can be obtained from factory waste, which has a huge stock and is urgent to be disposed. Therefore, this is a winwin solution. On the other hand, the recycling of chlorine during the leaching procedure was also proposed. Although, there is still a lot of work need to be done on this technology, it has great potential to be applied in the future.

Intensity

546

70

80

90

Fig. 1. XRD patterns of cathode materials.

grade from Alfa Aesar Chemical Co. Ltd and all solutions were prepared with ultrapure water (Milli-pore Milli-Q). 2.2. Leaching of cathode scraps The leaching experiments were carried out in a 250 mL roundbottom flask, equipped with condensing unit to reduce the influence from evaporation, magnetic stirrer, and a sensor based temperature controller (DF-101SZ, Gongyi, Yuhua Equipment Co., Ltd). A given mass of scraps was added to a 100 mL solution containing sulphuric acid and the reductant. The residue was dried at 80 °C in a drying cabinet (DHG-9070A, Shanghai Yiheng Equipment Co., Ltd). To investigate the leaching kinetics, 0.5 mL of liquid sample was taken out from the leachate at a certain reaction time, to get the local leaching efficiency of each metal. The leaching efficiencies of metals from the cathode scraps were determined as follows:

x ¼ C M;t  V=mM  100%

ð1Þ

where x (%) is the leaching efficiency of metal M (M = Co, Ni, Mn, Li), CM,t (g/L) is the concentration of M ions in the leachate, mM is the mass of M in the initial scraps, and V (L) is the volume of the leachate. 2.3. Characterization The cathode scrap was characterized by X-ray diffraction (X’pert PRO, PANalytical) with Cu Ka radiation and the data was collected from 5 to 90°. The concentrations of Li, Ni, Co, and Mn ions in leachate were analysed by ICP-OES (iCAP 6300 Radial, Thermo Scientific). The morphology and the surface composition of scrap were characterized using a mineral liberation analyzer (MLA 250, FEI) equipped with an energy dispersive spectrometer (EDS, EDAX GenesisSiLi) and a scanning electron microscope (SEM, Quanta 250). 3. Results and discussion 3.1. Leaching metals from spent LIBs The reaction between NCM cathode scraps and H2SO4 in the absence of reductant like NH4Cl was described as Eq. (2). The calculation demonstrates that the reaction is thermodynamically feasible. For the absence of the Gibbs free energy of NCM, the data of LiCoO2, LiNiO2 and LiMnO2 (Yokokawa et al., 1998) were used to calculate a possible range of DGh298K (Eq. (2)). The Eqs. (3)–(6)

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100

describe the reaction between cathode scraps and acid with NH4Cl.

2Li(Ni0:5 Co0:2 Mn0:3 )O2 +3H2 SO4 !Li2 SO4 +0.4CoSO4 +NiSO4 +0.6MnSO4 +3H2 O+0.5O2 " DG298 K h =
424.001 KJ/mol

ð2Þ

2LiCoO2 +4H2 SO4 +2NH4 Cl!2CoSO4 +Li2 SO4 +(NH4 )2 SO4 +Cl2 " h

þ4H2 O DG298 K =
300.246 KJ/mol

ð3Þ

2LiMnO2 +4H2 SO4 +2NH4 Cl!Li2 SO4 +2MnSO4 +Cl2 " +4H2 O+(NH4 )2 SO4

DG298 K h =
309.724 KJ/mol

2LiNiO2 +4H2 SO4 +2NH4 Cl!2NiSO4 +Li2 SO4 +(NH4 )2 SO4 +4H2 O+Cl2 " DG298 K h =
491.164 KJ/mol

80

Leaching efficiency (%)

Though the calculated values of DGh298K are negative, the leaching speed of different metals all have a low value, which can be attributed to the influence of kinetics, system complexity, side effect, etc. (Pinna et al., 2017; Takacova et al., 2016).

60

40

Li Ni Co Mn

20

ð4Þ 0 0.0

0.5

2Li(Ni0:5 Co0:2 Mn0:3 )O2 +4H2 SO4 +2NH4 Cl!Li2 SO4 +NiSO4 +0.4CoSO4 +0.6MnSO4 +4H2 O+(NH4 )2 SO4 +Cl" DG298 K h =
398.548 KJ/mol

1.0

1.5

2.0

2.5

3.0

H2SO4 concentration (mol/L)

ð5Þ

Fig. 2. Effect of H2SO4 concentration on the leaching efficiencies of metals (NH4Cl concentrarion: 0.8 mol/L, temperature: 353 K, agitation speed: 400 rpm, S/L mass ration: 100 g/L and reaction time: 60 min).

ð6Þ

Besides, the Cl2 can be converted into Cl
in a mild atmosphere through following reaction:

100







The reaction of charge from ClO to Cl could also be achieved (Belluati et al., 2007). Therefore, NH4Cl is chosen as an excellent reductant in the following experiments to reduce the usage of reductant and enhance the profile. Previous studies have found that the concentration of H2SO4 and NH4Cl played the key role in the leaching process corresponding to other conditions (Chen et al., 2018; Yang et al., 2018). The agitation speed (400–800 rpm) showed no obvious effect on leaching efficiencies (He et al., 2017). Meanwhile, a large solid-to-liquid like 100 g/L is considered to obtain a high throughput. Therefore, the order of conditions to be researched is the sulfuric acid concentration, the ammonium chloride concentration, the temperature, the leaching time and the solid-to-liquid. 3.1.1. Effect of acid concentration The effect of sulphuric acid concentration on the leaching efficiencies of Ni, Co, Mn and Li was studied in the concentration range of 0–3 mol/L, with the results presented in Fig. 2. The experiments were carried out with S/L mass ratio of 100 g/L, reaction temperature of 353 K, reaction time of 60 min, agitation speed of 400 rpm, and NH4Cl concentration of 0.8 mol/L. The result in Fig. 2 show that the leaching efficiencies of Co, Ni, Mn and Li increase sharply with increasing sulphuric acid concentration from 0 to 2.5 mol/L and then a platform appears when the sulphuric acid concentration increase further from 2.5 to 3.0 mol/L. In the correspondence of kinetics law, an increase in the H2SO4 concentration enhances the leaching rate. In consideration of the cost and efficiency, all further experiments were carried out using 2.5 mol/L sulphuric acid. 3.1.2. Effect of reductant amount With the addition of ammonia chloride, the leaching reaction of cathode scrap with sulphuric acid is described in Eq. (6). To investigate the effect of NH4Cl concentration on the leaching of different valuable metals from cathode scraps, the experiments were carried out under the conditions as follows: NH4Cl concentrations ranging from 0 to 1.2 mol/L, H2SO4 concentration of 2.5 mol/L, S/L mass ratio of 100 g/L, leaching temperature of 353 K, agitation speed of 400 rpm and reaction time of 60 min. Results presented in Fig. 3 clearly indicate that the leaching efficiencies of valuable metals

Leaching efficiency (%)

ð7Þ

Cl2 +H2 O!HClO+HCl

80

60

40

Li Ni Co Mn

20

0 0.0

0.2

0.4

0.6

0.8

1.0

NH4Cl concentration (mol/L) Fig. 3. Effect of NH4Cl concentration on the leaching efficiencies of metals (H2SO4 concentrarion: 2.5 mol/L, temperature: 353 K, agitation speed: 400 rpm, S/L mass ration: 100 g/L and reaction time: 60 min).

increase with the addition of NH4Cl. This increase tendency should be ascribable to the reducibility of Cl
in this system. As NH4Cl as a reductant helps to dissolve cobalt and nickel in LiNi0.5Co0.2Mn0.3O2, the dissolution of manganese is at the same time promoted, for the whole crystal structure is destroyed with breaking down chemical bonds between metal atoms and oxygen atom. Hence, in consideration of the cost and efficiency, 0.8 mol/L NH4Cl can be taken as the optimum value for the further experiments. 3.1.3. Effect of reaction temperature Temperature is usually a main factor that would influence the chemical reactions on both thermodynamic and kinetic aspects. The effect of temperature was investigated in the range of 293– 353 K with all other conditions maintained unchanged (reaction time 60 min, H2SO4 concentration 2.5 mol/L, NH4Cl concentration 0.8 mol/L, agitation speed 400 rpm and S/L mass ration 100 g/L). Fig. 4 shows that the leaching efficiencies of valuable metals over leaching temperatures. It can be observed that the leaching efficiencies of valuable metals are all significantly enhanced with increasing temperature from 293 to 353 K. Because, there is a

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W. Lv et al. / Waste Management 79 (2018) 545–553

100

Leaching effciency (%)

90 80 70 60

Li Ni Co Mn

50 40 30 290

300

310

320

330

340

350

leaching process. It can also be observed that almost all metals are removed from scrap to leachate, after leaching for 60 min. This might could because of the fact that the amounts of H+ and Cl
in the solution are sufficient in the initial stage of the leaching process. Then they are gradually consumed as the reaction proceeded, resulting in the decrease in reaction kinetic in the latter stages. Fig. 6 shows SEM images of residues over different leaching time in 2.5 mol/L H2SO4-0.8 mol/L NH4Cl solution at 353 K. It can be seen from Fig. 6 that along with leaching time, particle size of spherical-like crystal decreases from nearly 10 to less than 2 lm, and finally the spherical-like crystal is replaced by amorphous morphology mainly consisting of organic binder. The organic binder involved in cathode scrap has agglomerated along leaching time. Besides, the result of liner scanning is shown in Fig. S2, which gives the distribution of metal elements, indicates the decrease of Ni, Co, and Mn and increase of C in particles.

Temperature (K) Fig. 4. Effect of temperature on the leaching efficiencies of metals (H2SO4 concentration: 2.5 mol/L, NH4Cl concentration: 0.8 mol/L, agitation speed: 400 rpm, S/L mass ration: 100 g/L and reaction time: 60 min).

significant enhancement in kinetics rate to remarkably promote the leaching of valuable metals with increasing temperature. Meanwhile, the above variation could also be explained by using the E-pH diagram, as shown in Fig. S1. With the increase in temperature, the redox potential of Cl2/Cl
will decrease, and the overlap of Cl2/Cl
, MnO2/Mn2+ and Co(OH)3/Co2+ is enlarged to enhance the reduction of Co3+ and Mn4+. In consideration of the energy consumption, the temperature was set to be 353 K in the subsequent research. Supplementary data associated with this article can be found, in the online version, at https://doi.org/10.1016/j.wasman.2018.08. 027.

3.1.4. Effect of leaching time The effect of reaction time (0–120 min) on the leaching efficiencies of metals was examined under the conditions as follows: NH4Cl concentrations 0.8 mol/L, H2SO4 concentration of 2.5 mol/L, S/L mass ratio of 100 g/L, leaching temperature of 353 K, and agitation speed of 400 rpm. The result presented in Fig. 5 shows that the leaching efficiencies of Ni, Co, Mn and Li rapidly increase in the initial ten minutes and then slowly increase in the subsequent

Leaching efficiency (%)

100

80

60

40 Li Ni Co Mn

20

0

0

2

4

20

40

60

80 100 120

Time (min) Fig. 5. Effect of leaching time on the leaching efficiencies of metals (H2SO4 concentration: 2.5 mol/L, NH4Cl concentration: 0.8 mol/L, temperature: 353 K, agitation speed: 400 rpm, and S/L mass ration: 100 g/L).

3.1.5. Effect of solid-to-liquid mass ratio Effect of pulp density on the leaching efficiencies of metals was examined under the conditions as follows: H2SO4 concentration of 2.5 mol/L, NH4Cl concentrations 0.8 mol/L, reaction temperature of 353 K, and agitation speed of 400 rpm, with results shown in Fig. 7. It is obvious that S/L mass ration has a negative effect on the leaching process when it is more than 100 g/L. When it is less than 100 g/L, nearly all of Ni, Co, Mn, and Li can be leached out, whereas the leaching efficiencies drops to 75.5% for Li, 68.5% for Ni, 67.6% for Co, and 69.9% for Mn, respectively when the pulp density increase to 150 g/L. To hold a high production capacity and obtain a high economic efficiency, a 100 g/L of solid-to-liquid ratio is considered to be the optimal condition. 3.2. Leaching mechanism determination 3.2.1. The analysis of structure of leaching residues The leaching residues obtained from different leaching time under the optimal conditions were analyzed through XRD, with results summarized in Fig. 9(a). It can be seen that the intensity of characteristic peaks of NCM weaken gradually as leaching proceeds from 0 to 120 min. However, the special peaks are still found in the XRD pattern even after reacting for 120 min. And this is corresponding to the ICP result of leachate, which indicates that nearly 3–4% of Ni, Co, and Mn are still not leached. It is illustrated that the peak position of (0 0 3) has evident shift from high angle to low angle, which means the increase of c lattice parameter and the decrease of a lattice parameter. The shift supports the conclusion that the leaching of Li is quicker than other metals. The change of (0 1 8) and (1 1 0) also prove this conclusion. The analysis of leaching mechanism is shown in Fig. 8(b). Firstly, the leaching of metals from cathode scrap would destroy the crystal structure with no new phase formed, resulting in no obvious change occurred in XRD patterns of leaching residues. Secondly, with rapid extraction of lithium from crystal structure, the layer of O2
—Li+—O2
loses the lithium ions with the repulsive force of O2
—O2
increasing, leading to the increase in c lattice parameter and the decrease in a lattice parameter (Takahashi et al., 2007). Meanwhile, the remaining crystal will be easy to react with H+ and Cl
without Li+. The changes of a and c lattice parameter lead to the shift of peak position. With the dissolution of other metals, the crystal structure of NCM will be destroyed with no intermediate products. Therefore, there is no obvious shift of every peak position of NCM in the later leaching process. 3.2.2. Apparent kinetics of leaching The dissolution kinetics behaviour of Co, Ni, Mn and Li were studied at various temperatures. As shown in Fig. 5, the leaching speed is so rapid that the fast-rising period can finish in the initial

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W. Lv et al. / Waste Management 79 (2018) 545–553

(a)

(b)

(c)

(d)

Fig. 6. SEM images residues after leaching for (a) 0 min; (b) 10 min; (c) 60 min; (d) 120 min.

1
ð1
xÞ2=3 ¼ k2 t

Leaching efficiency (%)

100

1
2=3x
ð1
xÞ2=3 ¼ k3 t

80

40

Li Ni Co Mn

20

80

90

100

110

120

130

140

150

ð10Þ

where x is the leaching efficiency, k1, k2 and k3 (min
1) are the reaction rate constants and t (min) is reaction time. Table 1 summarized the fitting results by using the above three equations. It was found that the chemical reaction control model exhibits the best fitting in comparison with the other models. The apparent activation energy is calculated through the empirical Arrhenius law (Eq. (11)) and the data of the reaction rate constant and temperature obtained from Eq. (8).

60

0 70

ð9Þ

k ¼ Aexpð
Ea =RT Þ 160

S/L mass ratio (g/L) Fig. 7. Effect of S/L mass ratio on leaching of metal from NCM (523) scraps (H2SO4 concentration: 2.5 mol/L, NH4Cl concentration: 0.8 mol/L, temperature: 353 K, agitation speed: 400 rpm, and reaction time: 60 min).

ð11Þ

In Eq. (11), k is the apparent constant of different model, A is the frequency factors, T is the temperature, R is the gas constant (8.314 J K
1 mol
1) and Ea is the apparent activation energy. For the easiness of calculation, the Eq. (10) is further converted into Eq. (12).

ln k ¼ ln A
Ea =RT

ð12Þ 1/3

three to five minutes. The kinetic models including chemical reaction control (Eq. (8)), internal diffusion control model (Eq. (9)) and external diffusion model (Eq. (10)) are presented as:

1
ð1
xÞ1=3 ¼ k1 t

ð8Þ

The relevant data about the plots of 1
(1
x) = kt at different temperature were calculated using Eqs. (8) and (12). The plots of lnk vs 1/T of Li, Ni, Co and Mn (Fig. 9) illustrate that the apparent activation energies for Li, Ni, Co and Mn are 27.50 kJ/mol, 23.52 kJ/mol, 22.91 kJ/mol, and 24.12 kJ/mol, respectively. Furthermore, the chemical reaction control also illustrates the effect of

550

W. Lv et al. / Waste Management 79 (2018) 545–553

(101)

(104)

Li(Ni0.5Co0.2Mn0.3)O2

(003)

(a)

120min

(107)

(105)

Intensity

60min 30min

0

20

(018) (110)

(006) (102)

(113)

10min

40

60

3min 0min 80

16

2

18

CuK

20

(Deg.)

5 22 34 36 38 40 42 44 46 48 5055

CuK

(Deg.)

60

CuK

6 65

70

75

(Deg.)

(b)

ClH+ O2Li+ NiCoMn

Fig. 8. (a) The X-ray powder diffraction patterns of leaching residue and (b) the mechanism of H2SO4 leaching process with NH4Cl.

-1.0

-1.5

-2.0

Li Ni Co Mn

RLi2=0.997

RNi2=0.996

lnk

RCo2=0.993 R2Mn=0.997

-2.5

-3.0 0.0028

0.0030

0.0032

0.0034

1/T (K-1) Fig. 9. Arrhenius plots for leaching of Mn, Ni, Co, and Li from the cathode scrap under the surface chemical control model.

pulp density on the leaching process. Because it is a chemical control reaction, the effect of diffusion can be ignored in the initial reaction time, when the leaching reagent is abundant. However, H+ and Cl
are not abundant in the subsequent leaching process, in which the mechanism of leaching will be controlled by internal diffusion (Takacova et al., 2016). 3.3. Spent battery management The composition of waste waiting for recycling impacts our judgement in the selection of appropriate recycling methods. In order to ameliorate the pollution problem, the pretreatment methods and extraction methods are needed to be polished, in addition,

waste source management are often needed to be researched as well. Certainly, the topic of how hazards can be treated from waste LIBs have arose attentions from governmental agencies and organizations. Many efforts have been made to manage spent LIBs in parts of the world such as the European Union (EU), the United states, Japan, China, etc. However, under the current condition, the composition of waste LIBs is still complex increasing the difficulty for recycling methods (Ojanen et al., 2018; Wang et al., 2017b). The first region that pays attention to manage waste LIBs was EU. According to the Directive from EU, the obligation to manage waste LIBs belongs to manufacturers and dealers, for which all waste LIBs are needed to be recycled and classified (Zhang et al., 2018). Though the US has no federal law established to bolster waste electrical and electronic equipment recycling, yet there are some relevant bills already passed in some states in the US. In Australia, waste LIBs are not regarded as hazardous materials (Boxall et al., 2018). As for China, many active measures have been taken to treat waste LIBs, considering the fact that the production stream rapidly increased in recent years (Gu et al., 2017). It is also fortunate to see that the recycling method of waste LIBs has been modified at least. For example, the recovery rate of waste batteries has reached 95% in Sweden and 75% in Denmark (Zhang et al., 2018). However, with the development of LIBs, waste structures are growing in complexity. This raised the question of whether government should keep enforce strict laws to direct and to assist R&Ds. Besides, the public awareness of environmental protection, especially the classification of waste, is also important for the recycling of waste LIBs. As we all know, the simpler the component of waste is, the simpler the treatment technology is. The difficulty of the laboratory technology applying to the factory is usually from the complex composition. In this situation, many purification processes, which will increase the consumption of energy and the loss of valuable metals, need to be designed to remove the impurity and

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Table 1 The data of kinetic parameters during the leaching process with NH4Cl calculated using three models (Chemical control model, external diffusion model and internal diffusion model). T (k)

Li k (min
1)

Co

Ni

Mn

R2

k (min
1)

R2

k (min
1)

R2

k (min
1)

R2

Chemical reaction control 303 0.062 313 0.088 323 0.175 353 0.285

0.983 0.998 0.973 0.980

0.050 0.062 0.108 0.179

0.978 0.995 0.960 0.985

0.051 0.064 0.118 0.186

0.978 0.996 0.973 0.982

0.050 0.065 0.120 0.190

0.979 0.997 0.977 0.988

Internal diffusion control 303 0.010 313 0.019 323 0.048 353 0.084

0.850 0.921 0.985 0.981

0.007 0.011 0.024 0.040

0.749 0.923 0.982 0.963

0.006 0.010 0.021 0.038

0.852 0.932 0.989 0.968

0.007 0.011 0.025 0.042

0.850 0.919 0.980 0.959

External reaction control 303 0.113 313 0.152 323 0.288 353 0.456

0.987 0.993 0.949 0.950

0.095 0.116 0.208 0.323

0.981 0.993 0.958 0.971

0.094 0.112 0.192 0.313

0.9801 0.9891 0.945 0.967

0.093 0.117 0.211 0.330

0.982 0.994 0.962 0.975

extract pure products (Yang et al., 2017). Therefore, as the source of waste LIBs, the public has to duty to sort the waste at first before transporting out from their neighbourhood, this tends to help firms to better classify them before feeding wastes into next stage. This can be very essential to help bring up the extraction efficiency of valuable metals and to reduce the complexity of technology. 3.4. A preliminary discussion for reusing of reductant NH4Cl A flowchart of the whole technology was given in Fig. 10(a). In this technology, the waste solution will contain high concentration of Cl
, which can be reused as leaching reagent with addition of certain amount of H2SO4. Firstly, the valuable metals are leached out from cathode scrap. After that, the raffinate containing Cl
is obtained from solvent extraction. In the end, the solution from solvent extraction will be purified and regenerated by using Ca(OH)2 to remove the redundant sulphate. Meanwhile, the common extractants to separate Co and Ni are usually used in a chloride system, like the leachate from HCl leaching and the exist of Cl
can also promote the extraction of metal ions (Torkaman et al., 2017). Therefore, the existence of Cl
will not have a negative influence on the separation and purification process. The accumu-

lation of sulphate in solution needs to be considered for the common ion effect, which will reduce the solubility of valuable metal ions in solution. As a traditional technology, Ca(OH)2 is used to removed SO24 from raffinate. After that, the reductant will be reused. Fig. 10(b) shows the possible process of chlorine circulation in this leaching process. The chlorine circulation mainly depends on the self-circulation of Cl among Cl
, Cl2, and HClO. Of course, a little part of Cl2 also needs to be absorbed by alkaline solution, like ammonium hydroxide. To further identify the potential of the reusing of Cl
, NaOH is used to separate Ni, Co and Mn from leachate. After that, the concentration of Cl
in different liquid have also been analyzed through ion chromatography. The result is shown in Table 2, which

Table 2 The amount of Cl
in liquid in different process. Liquid

Cl
(g)

Before leaching (100 mL) After leaching (100 mL) After precipitation (120 mL)

2.871 2.726 2.367

Fig. 10. (a) Schematic diagram of the process to sustainably use Cl
as reductant in the leaching system, (b) schematic diagram of reaction mechanism of the sustainable utilize of Cl
.

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Table 3 The leaching efficiencies of different metals in first leaching and second leaching. Leaching efficiency, %

Li

Ni

Co

Mn

First leaching Second leaching

99.11 97.23

97.49 94.12

97.55 94.45

97.34 94.27

indicates that the Cl
is mainly lost in precipitation process. However, the remaining Cl
in solution is possible to be reused in the next leaching. 13.6 mL concentrated H2SO4 was added in the into 100 mL solution obtained from the leachate after precipitation with 0.8 g NH4Cl added. The new leaching reagent can still leach out nearly 95% of valuable metals from scraps in the second leaching process (Table 3). Therefore, the reusing of Cl
is possible. Meanwhile, the release of Cl2 is so small that it is easy to be absorbed with little pollution. 4. Conclusions A stable (easy to transport and store) and cheap reductant was adopted to enhance the recovering of recycling valuable metals from spent lithium-ion batteries cathode scraps. Meanwhile, using ammonia chloride, which has a large quantity storage waiting to be treated, is a win-win solution to improve the recycling effectiveness of spent LIBs and reduce the pollution of waste water. The following conclusions can be obtained based on the current experiments: (1) A range of relevant factors have been examined to optimize the parameters of leaching process. Under the leaching conditions of 2.5 M H2SO4, 0.8 M NH4Cl, 100 g/L, 400 rpm at 353 K, 99.11% of Li, 97.49% of Ni, 97.55% of Co, and 97.34% of Mn could be leached out within 60 min. (2) The kinetics analysis was carried out based on three common models. The results indicate that the leaching reaction of scrap with H2SO4 and NH4Cl belongs to the chemical reaction control model. Meanwhile, the leaching process of Ni, Co, Mn is similar to each other and is more difficult than Li. The change of crystal firstly occurs in the release of Li, which does not break the crystal structure, but just makes it easy to react with H+. With the dissolution of Ni, Co and Mn, the structure of crystal will be gradually destroyed. (3) Most of the Cl
in the leachate would remain in the solution after the separation and purification procedures, and has immense potential to be reused.

Acknowledgments This work was financially supported by National Key Research and Development Program of China (2017YFB0403300/ 2017YFB043305), Beijing Science and Technology Program (No. Z171100002217028), the National Natural Science Foundation of China (No. 51425405 and L1624051), and the Key Program of Chinese Academy of Science (KFZD-SW-315). References Barik, S.P., Prabaharan, G., Kumar, L., 2016. Leaching and separation of Co and Mn from electrode materials of spent lithium-ion batteries using hydrochloric acid: laboratory and pilot scale study. J. Clean. Prod. 147, 37–43. Belluati, M., Danesi, E., Petrucci, G., Rosellini, M., 2007. Chlorine dioxide disinfection technology to avoid bromate formation in desalinated seawater in potable waterworks. Desalination 203, 312–318. Boxall, N.J., Adamek, N., Cheng, K.Y., Haque, N., Bruckard, W., Kaksonen, A.H., 2018. Multistage leaching of metals from spent lithium ion battery waste using electrochemically generated acidic lixiviant. Waste Manage. 74, 435–445.

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