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Synergistic leaching of valuable metals from spent Li-ion batteries using sulfuric acid- l -ascorbic acid system
Chemical Engineering Journal 388 (2020) 124321
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Synergistic leaching of valuable metals from spent Li-ion batteries using sulfuric acid- L-ascorbic acid system
T
Dongdong Chena,b,c,d, Shuai Raob,c,d, Dongxing Wangb,c,d, Hongyang Caob,c,d, , Wuming Xiea, , Zhiqiang Liub,c,d ⁎
⁎
a
Guangzhou Key Laboratory of Environmental Catalysis and Pollution Control, Guangdong Key Laboratory of Environmental Catalysis and Health Risk Control, School of Environmental Science and Engineering, Institute of Environmental Health and Pollution Control, Guangdong University of Technology, Guangzhou 510006, China b Guangdong Research Institute of Rare Metal, Guangzhou 510650, China c Guangdong Province Key Laboratory of Rare Earth Development and Application, Guangzhou 510650, China d State Key Laboratory of Separation and Comprehensive Utilization of Rare Metals, Guangzhou 510650, China
HIGHLIGHTS
GRAPHICAL ABSTRACT
an environmentally friendly • Propose integrated flowsheet for recycling cathode materials.
analysis of metal leaching • Detailed behavior in different leaching systems. H SO –C H O system, the • Under leaching efficiency of Li, Co, Ni, and 2
4
6
8
6
Mn all exceeded 99.5%.
of Ni, 99.57% of Mn, 99.76% of • 98.96 Co, and 89.81% of Li were recovered
as C8H14N4NiO4, MnCO3, CoC2O4, and Li2CO3.
ARTICLE INFO
ABSTRACT
Keywords: Sulfuric acid L-ascorbic acid Synergistic leaching mechanism Recycling spent Li-ion batteries Precipitation-solvent extraction
With increase in the number of scrapped portable electronics and new energy powered vehicles, the production of spent Li-ion batteries (LIBs) has increased progressively each year. Harmful substances in spent LIBs can pollute the environment and threaten human health. A sustainable technology should be developed to recycle the spent LIBs. Accordingly, a new environmentally friendly hydro-metallurgical process was proposed for leaching Li, Co, Ni, and Mn from spent LIBs using sulfuric acid with L-ascorbic acid as a reductant. Over the leaching process, several parameters, including sulfuric acid and L-ascorbic acid concentrations, solid to liquid ratio, temperature and time were systematically investigated. The maximum recovery efficiencies of Li, Co, Ni, and Mn were as high as 99.69%, 99.56%, 99.60%, and 99.87% under the optimized conditions (C(H2SO4 concentration) = 1.5 mol/L, C(C6H8O6 concentration) = 0.25 mol/L, the agitation speed was 300 r/min, the liquid–solid ratio was 15 mL/g, and the temperature was 333 K for 60 min), respectively. The synergistic mechanism was analyzed by X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared spectroscopy of the structure of cathode materials, residues, and leachate. The analysis results indicate that the dissolution rate of Ni, Mn, and Co was significantly improved under the condition of adding L-ascorbic acid as a reducing agent. Finally, 98.96 of Ni, 99.57% of Mn, 99.76% of Co, and 89.81% of Li were recovered in the form of C8H14N4NiO4, MnCO3, CoC2O4, and Li2CO3 through precipitation-solvent extraction methods.
⁎
Corresponding authors at: Guangdong Research Institute of Rare Metal, Guangzhou 510650, China (H. Cao). E-mail addresses: [email protected] (H. Cao), [email protected] (W. Xie).
https://doi.org/10.1016/j.cej.2020.124321 Received 28 October 2019; Received in revised form 6 January 2020; Accepted 3 February 2020 Available online 04 February 2020 1385-8947/ © 2020 Elsevier B.V. All rights reserved.
Chemical Engineering Journal 388 (2020) 124321
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[19] [20] [21] 90% for Co, 100% for Li 94.8% (Co), 98.5% (Li) 90% for Co), 100% for Li 1.25 M C6H8O7, 1.0 vol% hydrogen peroxide, S:L = 20 g/L, agitation = 300 rpm, t = 30 min, T = 90 ℃ 1.25 mol/L C6H8O6, T = 70 ℃, t = 20 min, S:L = 25 g/L 1.5 M C4H6O5, 2.0 vol% hydrogen peroxide T = 90 ℃, t = 40 min, L/S = 50 mL/g
74.1% (Li) 94.0% (Co), 95.0% (Li) 95.0% (Co), 95.0% (Li) over 99% (Co)
LiCoO2 and Co3O4 Li1.2Co0.13Ni0.13Mn0.54O2 and LiMn2O4 LiCoO2 and Co3O4
LiCoO2(s) + LixNiyMnzCorO2(s) + 7H+ → Li+ + Co2+ + Ni2+ + Mn2+ + Co(III) precipitates + Ni(IV) precipitates + Mn(IV) precipitates (5)
C6H8O7 C6H8O6 C4H6O5
Leaching conditions
However, the dissolution of Co(III) (Co2O3), Ni(IV) (NiO2) and Mn(IV) (MnO2) as soluble salts was very difficult even in strong acids with a high potential [22,23]. Therefore, the chemical equation for the reaction of the cathode material (LiCoO2) with sulfuric acid can be expressed as Eq. (5).
Organic acid
(4)
LiFePO4 and LiMn2O4 LiCoO2 LiCoO2 LiCoO2
NiO(s) + H2SO4(aq) → NiSO4(aq) + H2O
HCl H2SO4 + H2O2 HNO3 + H2O2 H3PO4
(3)
Mineral acid
MnO(s) + H2SO4(aq) → MnSO4(aq) + H2O
Leaching substrate
(2)
Leaching system
CoO(s) + H2SO4(aq) → CoSO4(aq) + H2O
Type of acid
(1)
Table 1 A brief summary of the recovery of metals using different leaching systems.
Li2O(s) + H2SO4(aq) → Li2SO4(aq) + H2O
Leaching efficiency
Li-ion batteries (LIBs) use lithium alloys as positive materials and nonhydroelectrolyte solutions as electrolytes [1]. LIBs have the advantages of high-power densities, high-energy densities, high potentials, low self-discharge rates, long service lives, and wide operating temperature ranges [2]. Therefore, they are widely used in consumer electronics, power and energy storage industries, as well as in laptops, cell phones, cameras, audio, and video players and other portable electronic devices [3,4]. Since the 21 st century, owing to the flourishing development of clean energy, the application of LIBs has been gradually extended to automobiles, home appliances, electric bicycles, energy storage and other fields [5]. China’s LIB production reached 13.98 billion in 2018, representing an increase of 12.9% over the previous year, within this, the total installed capacity of power batteries was 56.9 GWh, with a 56.3% annual growth rate. This growth trend is likely to pose a huge challenge with respect to the disposal of waste LIBs [6]. LIBs comprise a battery case, battery cap, anode, cathode, electrolyte and separator [7]. The main component of the anode is graphite and a binder, and the cathode is composed of conductive carbon. Lithium-transition-metal oxides in cathode composites include LiCoO2, LiNiO2, LiMn2O4, and LiCoxMnyNizO2, where the contents of Co, Ni, and Li are about 5–15%, 2–7%, and 0.5–2%, respectively, while small amounts of Au, Al, Fe and other elements are present [8]. The recycle value of spent LIBs is high, and in the context of a sharp shortage of metal resources, valuable metals in LIBs (e. g., Li, Co, Ni, and Mn, etc.) have received worldwide attention as secondary recovery resources. In recent years, the recycling of graphite, valuable metals and other components in spent LIBs as secondary resources involves different processes, including pyrometallurgy, hydrometallurgy, and biometallurgy [9]. For example, a new process using MnOeSiO2eAl2O3 to recover metals from spent LIBs, and high-purity alloys were achieved, which contains Co (99.03%), Ni (99.30%), and Cu (99.30%) [10]. However, the method had the disadvantages of complicated process, high energy consumption, strict equipment requirements, and incomplete metal recovery. Several studies [11,12]. Were also conducted on extracting valuable metals using Acidithiobacillus ferrooxidans as a strain in the leaching system. Although the method was environmentally friendly and the leaching conditions were mild, the reaction rate was relatively slow and the strain was difficult to culture. On the contrary, hydrometallurgical processes have the following advantages compared with pyrometallurgy and biometallurgy, such as simple process flow, low equipment operating costs, low waste emissions and high metal recovery rates [13,14]. Mineral acid, including HCl [15], H2SO4 [16], HNO3 [17], and H3PO4 [18], is widely used as a leaching agent to recover metals, while organic acid leaching agents include C6H8O7 [19], C6H8O6 [20], and C4H6O5 [21], which are briefly summarized in Table 1. In summary, the main phases of waste cathode materials are LiCoO2 and LixNiyMnzCorO2. In the sulfuric acid leaching system, the reduced states of Li(I), Co(II), Mn(II), and Ni(II) are easily dissolved, and the reactions are represented by Eqs. (1)–(4).
6.5 mol/L HCl, T = 30 ℃, t = 60 min 2 mol/L sulfuric acid, 5 vol% hydrogen peroxide, T = 75 ℃, t = 30 min 1 mol/L nitric acid , 1.7 vol% hydrogen peroxide, T = 75 ℃, t = 60 min 0.7 mol/L phosphoric acid, T = 40 ℃, t = 60 min, 4 vol% H2O2, L/S = 20 mL/g
References
1. Introduction
[15] [16] [17] [18]
D. Chen, et al.
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However, owing to the weak reducibility of the inorganic acid and the intense reaction conditions, the leaching of the metal in the single inorganic acid system is incomplete. Therefore, several studies have chosen to add a certain amount of reducing agent during the leaching process to improve the leaching efficiency of metals. (e.g., hydrogen peroxide or Na2SO3) [24,25]. For example, a study reported that when a certain amount of reducing agent (10 vol% hydrogen peroxide) was added to the 4.0 mol/L sulfuric acid leaching system, the leaching efficiency was significantly improved, and more than 96% of Li and 95% of Co were leached [26]. In addition, Lee et al. also reported that over 95% of Li and Co was leached when a certain amount of reducing agent (1.7 vol% hydrogen peroxide) was added to the 2 mol/L nitric acid leaching system [27]. However, organic reagents are biodegradable, usually reductive and acidic, and the waste from the leaching process can be easily treated [28]. Therefore, several studies are focusing attention on the development of new leaching processes around organic reagents. For example, dissolution proceeded with a reductive-complexing mechanism, and over 95% for Co was leached with 0.4 mol/L C4H6O6 and 0.02 mol/L C6H8O6 at 80 °C for 5 h [29]. Under the conditions of the mass fraction of hydrogen peroxide = 4%, acidity of tartaric acid = 2 M, and pulp density = 17 g/L, the reaction was carried out at 333 K for 30 min, over 99.3% of Li, 99.1% of Mn, 98.6% of Co, and 99.3% of Ni were leached [30]. L-ascorbic acid is an organic acid in the body's metabolism with a weak acidity [31]. It is ionized in an aqueous solution to generate hydrogen ions. The ionization equilibrium equation of L-ascorbic acid (Fig. 1a) in aqueous solution is represented by Eqs. (6) and (7) [32]. H2C6H6O6(aq) → HC6H6O6%− + H+(pKa1 = 4.17) HC6H6O6%−
→
C6H6O62−
+H
+
Fig. 2. Metallic complexes formed with L-ascorbic acid.
The metal complex formation mechanism with dehydroascorbic acid is shown in Fig. 2. A simple thermodynamic calculation shows that C6H6O6Co was thermodynamically favorable during the leaching [35,36]. However, these studies had the following disadvantages. Firstly, they focused on the leaching mechanism of Co. Secondly, the leaching behavior of Ni and Mn was not studied in detail. Finally, not only was leaching time long, but energy consumption was also high [37,38]. In this study, an integrated technological route for recovering valuable metals from spent LIBs was proposed. Proposed biomass reducing agent (L-ascorbic acid) instead of traditional reducing agent (hydrogen peroxide), proposed a cooperative leaching mechanism of sulfuric acid and L-ascorbic acid for LiCoO2, and proposed the recovery of valuable metals (Li, Co, Ni, and Mn). The parameters affecting the leaching efficiency of valuable metals, including sulfuric acid and Lascorbic acid concentrations, liquid–solid ratio, temperature, and time have been investigated in detail. The metals and carbon of the cathode material powder and leaching residues was determined by inductively coupled plasma-atomic emission spectrometry (ICP-AES) and carbon sulfur analyzer (CS), respectively. Moreover, the reduction and leaching mechanisms are presented in detail by scanning electron microscopy (SEM), X–-ray diffraction (XRD), and Fourier-transform infrared (FT-IR) spectroscopy on the structure of cathode material, residue, and leachate.
(6)
(pKa2 = 11.57)
(7)
In addition, L-ascorbic acid is also a mild reducing agent, which can be oxidized by one electron to a radical state or doubly oxidized to the stable form called dehydroascorbic acid (C6H6O6), as shown in Fig. 1b [33]. Additionally, owing to the strong reducibility of L-ascorbic acid, Mn(IV), Ni(IV), and Co(III) are reduced to Mn(II), Ni(II), and Co(II) in aqueous solution, respectively. In a single L-ascorbic acid system, LiCoO2 dissolves to form soluble C6H6O6Li2, dehydroascorbic acid (C6H6O6) can form stable compounds C6H6O6Co and C6H6O6Mn with Co (II) and Mn (II) with the conjugate bond, which has been reported [34]. the leaching reaction was represented by Eq. (8). 4C6H8O6(aq) + 2LiCoO2(s) + 2C6H6O6Co(aq) + 4H2O
→
C6H6O6(aq)
+
C6H6O6Li2(aq) (8)
2. Experimental 2.1. Materials and reagents Experimental material spent LIBs were obtained from the Jiangmen Changsun Umicore Industry Co., Ltd., China, and were treated by discharging, dismantling, crushing, grinding, and sieving. Then, the ground samples were dry sieved using standard sieve plates and separated into different size fractions via vibration. The obtained fractions were weighed and stored for further studies. Leaching reagent, sulfuric acid (Analytical grade, Shanghai Chemical Reagent Co., Ltd.). Reducing agent, L-ascorbic acid (Analytical grade, Shanghai Chemical Reagent Co., Ltd.). Other chemical reagents were of analytical grade and all solutions were prepared using deionized water. 2.2. Metal leaching The steps of all the leaching experiments were as follows: First, 5 g of the cathode powder was transferred into the 250 mL flask before adding a certain amount of L-ascorbic acid crystal powder at a pre-determined concentration, and the sulfuric acid solution was taken according to the set liquid–solid ratio, which was fixed in the thermostat
Fig. 1. L-ascorbic acid as (a) a leaching agent and (b) a reducing agent. 3
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water bath with a digital display. After the leaching experiment was completed, the leaching residue was obtained by vacuum filtration of the slurry, and dried at 363 K for 12 h, which was characterized by ICPAES and CS analysis equipment to quantify the percentages of metals and C, respectively. The supernatant was diluted and analyzed using atomic adsorption spectroscopy (AAS, Thermo 3300). The effects of the sulfuric acid concentration (C(H2SO4), mol/L), L-ascorbic acid concentration (C(C6H8O6), mol/L), temperature (T, K), time (t, min), and liquid–solid ratio (mL/g) on the leaching efficiency of metals were investigated in detail. To eliminate the influence of the agitation speed on the experiment, all experiments were set to 300 r/min. The leaching efficiency of Mn, Ni, Li, and Co was calculated according to Eq. (9). Me
=
m1 × wt1 m2 × wt2 × 100% m1 × t1
(9)
where ηMe represented the leaching efficiency of Mn, Ni, Li, or Co; m1 and m2 represented the mass of the cathode material powder and the corresponding leaching residue, respectively; and wt1 and wt2 were the Mn, Ni, Li, or Co contents of the cathode material powder and the corresponding leaching residue, respectively.
Fig. 3. XRD patterns of cathode material powder. Table 3 The phase of cathode material powder.
2.3. Analytical method X-ray diffractometer (Bruker D8 Advance, Germany) with Cu Kα radiation scanning speed of 10° min−1 range of 5–90° was used to investigate the crystalline phases of the cathode material powders and leaching residues. ICP-AES (IRIS intrepid XSP, Thermo Electron Corporation) was used to determine the content of valuable metals in the leach residues, and CS (CS844, LECO, USA) was used to determine the carbon content in the leach residues. The morphology and crystal structure of the cathode material powder and leaching residues were analyzed by SEM, (Hitachi S-570, Japan). FT-IR spectroscopy (WQF520A, Beijing Rayleigh, China) was used to analyze the change in functional groups in the leachate between 4000 and 400 cm−1.
3.1. Characterization analysis of cathode materials The valuable metals and carbon of the cathode material powder were determined by ICP-AES and CS, respectively (Table 2). The cathode material powder contained valuable metals and carbon, including 3.86 wt% Li, 27.50 wt% Co, 1.35 wt% Ni, 2.05 wt% Mn and 29.64 wt% C. The phases of the cathode material powders were characterized by XRD (Fig. 3), and the phase composition is listed in Table 3 according to MDI Jade 5.0. The results show that LiCoO2 (01-0702685), C (01-089-8487), Li0.05Mn2O4 (01-082-0320), LiAl0.2Co0.8O2 (01-089-0912), and Li0.9Ni0.5Co0.5O2-x (00-050-0509) were the main phases of the cathode material powder. SEM images were used to characterize the morphology of the components in the cathode material (Fig. 4). The phases of LiCoO2, LixAlyCoz, C, and LixNiyMnzCorO2 had large particle sizes, particularly, LixNiyMnzCorO2 had a flocculent porous structure. The results of the color image (Fig. 4c) were consistent with the XRD results.
3.2.1. Determination of the leaching system Fig. 5 displays that the leaching efficiencies were 83.29% for Li, Table 2 The chemical composition of cathode material powder. (Mass fraction/%). Co
Ni
Mn
C
Content (wt.%)
3.86
27.50
1.35
2.05
29.64
Minor phases
cathode material powder
C, LiCoO2, Li0.05Mn2O4,
LiAl0.2Co0.8O2, Li0.9Ni0.5Co0.5O2-x
3.2.2. Effect of H2SO4 and C6H8O6 concentrations The leaching efficiency of metals in 0.25 mol/L C6H8O6 at 333 K with H2SO4 concentration (0.05–1.75 mol/L) was shown in Fig. 6a. As the concentration of sulfuric acid increased, the metal dissolution rate in the cathode material increased, and the leaching efficiency was significantly improved. When the concentration of sulfuric acid was increased to 1.5 mol/L, over 99.09% Li, 98.91% Co, 99.08% Ni, and 99.38% Mn were leached. The reason may be that the sulfuric acid concentration increased, the proportion of activated molecules did not change, the number of H + increased, and the reaction rate was accelerated. Therefore, 1.5 mol/L sulfuric acid was selected as the optimal concentration for this experiment. The effect of L-ascorbic acid concentration (0–1.25 mol/L) on metal leaching efficiency in a single factor experiment with a sulfuric acid concentration of 1.5 mol/L was shown in Fig. 6b. The increase of L-ascorbic acid concentration from 0 to 0.25 mol/L had a significant positive impact on the rate of metal dissolution, and the leaching efficiencies of Li, Co, Mn, and Ni were as high as 91.91%, 93.03%, 94.32%, and 95.27%, respectively, with 0.25 mol/
3.2. Optimal conditions for leaching experiments
Li
Major phases
68.68% for Ni, and only 47.49% for Co and 51.73% for Mn with 1.5 mol/L sulfuric acid. The reason maybe CO3O4 had a relatively stable spinel structure, and it was difficult to dissolve them even in a strong acid [39]. On the other hand, the leaching efficiency of all metals was relatively low with 0.5 mol/L L-ascorbic acid. However, upon further increasing the L-ascorbic acid concentration to 1.25 mol/L, over 98.04% Li, 97.74% Co, 94.66% Ni and 98.20% Mn were leached. Additionally, with 1.5 mol/L sulfuric acid and 0.25 mol/L L-ascorbic acid, all valuable metals were almost completely leached. The reason may be that Co(III), Ni(IV), and Mn(IV) are converted into a readily soluble reduced product under the action of L-ascorbic acid, and the assumptions are also feasible even at lower concentrations of ascorbic acid (0.25 mol/L) [40]. The results show a clear sign of synergistic effect of the two acids. The increase in Co, Mn, and Ni dissolution may be due to the reductive role of L-ascorbic acid to enhance the dissolution of LiCoO2 and LixNiyMnzCorO2 [41]. Therefore, considering the efficiency and environmental friendliness of the leaching process, it was concluded that sulfuric acid (Leaching reagent) and L-ascorbic acid (Reducing reagent) were the best leaching systems.
3. Results and discussion
Elements
sample
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Fig. 4. SEM images of cathode material powder.
production factors, other optimization experiments were performed using 1.5 mol/L sulfuric acid as the leaching system with 0.25 mol/L Lascorbic acid. 3.2.3. Effect of temperature and time Fig. 7a shows that about 88.7% Mn, 81.5% Co, and only 75.2% Ni and 78.2% Mn were leached at 303 K. As the temperature increased, the leaching efficiency of all metals was significantly improved. Then reason maybe that the temperature increased, more non-activated molecules became activated molecules, which increased the activation energy and accelerated the reaction rate. However, when the temperature was greater than 333 K, L-ascorbic acid would completely decompose and lose its reducibility [42]. Therefore, further increase in the temperature did not promote the dissolution of LiCoO2 and increased the leaching of the metal. As shown in Fig. 7b, when the reaction time was in the range of 2–80 min, the leaching efficiency of Li, Co, and Ni increased significantly. When the time was increased to 60 min, all the metal leaching efficiencies were maximized. In this leaching system, the main purpose for the addition of a small amount of L-ascorbic acid was to covert insoluble Co(III) and Mn(IV) into soluble Co 2+ and Mn 2+. In the leaching solutions, these metals were mainly present in the form of sulfates owing to a high sulfuric acid concentration. The chemical reaction of the dissolution process can be expressed as Eq. (10).
Fig. 5. Leaching efficiencies of valuable metals in various leaching systems (liquid–solid ratio = 15 mL/g, T = 333 K, t = 60 min, and stirring rate = 300 r/min).
L L-ascorbic acid. Interestingly, upon to 1.25 mol/L only slightly improved Li leaching efficiency but exerted no significant effect on the dissolution of other metals including Co and Mn. The possible reason may be that the dissolution of Li was a simple neutralization reaction. However, the dissolution of Co and Mn involved the transformation of valence state. The oxidation-redox reaction had been completed under 0.25 mol/L L-ascorbic acid. Hence, considering energy-saving, clean
LiCoO2(s) + LixNiyMnzCorO2(s) + 4H2SO4(aq) + C6H8O6(aq) → Li2SO4(aq) + CoSO4(aq) + NiSO4(aq) + MnSO4(aq) + C6H6O6(aq) + H2O (10) As such the leaching efficiency of cobalt and manganese depends on
Fig. 6. Effect of H2SO4 and C6H8O6 concentrations: (a) C(H2SO4) (mol/L), C(C6H8O6) = 0.25 mol/L, (b) C(C6H8O6) (mol/L), C(H2SO4) = 1.5 mol/L (liquid–solid ratio = 15 mL/g, T = 333 K, t = 60 min, and stirring rate = 300 r/min). 5
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Fig. 7. Effect of temperature and time: (a) Temperature (K), (b) Time (min) (C(H2SO4) = 1.5 mol/L, C(C6H8O6) = 0.25 mol/L, liquid–solid ratio = 15 mL/g, and stirring rate = 300 r/min).
the concentration of reductant used [43]. Reductant converts Co(III) or Mn(IV) to the + 2 state for effective dissolution and subsequent recovery by standard methods [27,44]. In terms of energy saving and high efficiency, other experimental temperatures were maintained at 333 K, and the reaction time was 60 min.
3.3. Characterization 3.3.1. XRD analysis Fig. 9(a–c) shows than the phases of the leaching residues, including those from the single and synergistic leaching systems were analyzed by XRD. Additionally, the phases identified according to MDI Jade 5.0 are listed in Table 4 [46]. It is clear that LiCoO2 and C as the major phases could still be observed in the sulfuric acid or L-ascorbic acid system leaching residue. Additionally, the minor phases LiAl0.2Co0.8O2 and Li0.9Ni0.5Co0.5O2-x were also observed. The main reason is that the dissolution of Co(III), Mn(IV), and Ni(IV) is insufficient in the single leaching system [47]. Fig. 9c shows than the main phase of the leaching residue was only C, and in the minor phase only Al2O3 was also observed, and the characteristic peaks of the Co(III), Mn(Ⅳ), and Ni(Ⅳ) phases completely disappeared. The XRD pattern analysis demonstrated that L-ascorbic acid positively affected the leaching process, and promoted the dissolution of particles such as LiCoO2 and LixNiyMnzCorO2 in the cathode materials.
3.2.4. Effect of liquid–solid ratio Fig. 8 shows that the leaching efficiency of all metals increased with increasing liquid–solid ratio, and the increasing trend was more significant with the liquid–solid ratio ranging from 5 mL/g to 15 mL/g. Particularly, up to 99.69% Li, 99.56% Co, 99.60% Ni, and 99.87% Mn were leached with 15 mL/g liquid–solid ratio. With the progress of the reaction, the concentration of the product increased, which affected the mass transfer coefficient and caused the leaching efficiency of the metal to decrease. However, the large liquid–solid ratio was beneficial to increase the mass transfer coefficient between the reactants and accelerating the leaching of the metal [45]. From the point of view of high efficiency and reagent savings, the optimum liquid–solid ratio in this experiment was 15 mL/g.
3.3.2. SEM analysis Fig. 10(a–f) displays the SEM background scattering image of the residue at high magnification and resolution. Through detailed analysis of the SEM, it can be concluded that the distribution of metal and carbon in the leaching residue had distinct features. Firstly, metal elements such as Li, Ni, Mn, and Co in the residue were intertwined and inlaid at similar positions, especially the Li and Co elements were completely in the same position [48]. Second, graphite carbon (C) was relatively independent at different locations, with significant gaps between the particles. As seen in Fig. 10a, a large amount of bright particles with large particle size were observed in the leaching residue, and many black C particles were interspersed between LiCoO2 and LixNiyMnzCorO2 particles with 1.5 mol/L sulfuric acid. As seen in Fig. 10b, the particle size of the LiCoO2 and LixNiyMnzCorO2 particles in the leaching residues became small with 0.25 mol/L L-ascorbic acid, indicating that some of the LiCoO2 and LixNiyMnzCorO2 had reacted. Fig. 10c shows that the brightly colored particles disappear almost completely, and the leaching residues are almost entirely composed of dark C particles, indicating that leaching of the valuable metals was relatively complete. Additionally, Fig. 10(d–f) also supports the morphological changes in LiCoO2, C, and LixNiyMnzCorO2 particles in different leaching systems. In summary, the SEM results of the leaching residue are consistent with the XRD results.
Fig. 8. Effect of liquid–solid ratio (C(H2SO4) = 1.5 mol/L, C(C6H8O6) = 0.25 mol/L, T = 333 K, t = 60 min, and stirring rate = 300 r/min).
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Fig. 9. XRD patterns of leaching residue (a) C(H2SO4) = 1.5 mol/L, (b) C(C6H8O6) = 0.25 mol/L, and (c) C(H2SO4) = 1.5 mol/L and C(C6H8O6) = 0.25 mol/L (liquid–solid ratio = 15 mL/g, T = 333 K, t = 60 min, and stirring rate = 300 r/min).
and Mn compounds in the sulfuric acid system [53,54]. Some frequency shifts can be observed in the range 1000–1200 cm−1 (as shown in the rectangular frame, from 1203.4 and 1116.6 to 1201.4 and 1108.9 cm−1), which may be due to the L-ascorbic acid facilitating the dissolution of valuable metals [55,56]. By comparing Fig. 11b and c, the telescopic vibration of CeH (2923.6 and 2925.5 cm−1) can be observed, and the appearance of a new peak at 1054.9 cm−1 can be ascribed to the deformation vibration of saturated CeH. According to the results of FT-IR, it can be concluded that the eOH, C]O, and CeH functional groups in C6H806 will promote the reduction of the oxidized metal and facilitate the formation of sulfate.
Table 4 XRD phase analysis of leaching residue. Sample
Major phases
Minor phases
Sulfuric acid leaching residue L-ascorbic acid leaching residue
C, LiCoO2 LiCoO2, C
Sulfuric acid and L-ascorbic acid leaching residue
C
Li0.09Ni1.01O2 LiAl0.2Co0.8O2, Li0.9Ni0.5Co0.5O2-x Al2O3
3.3.3. FT-IR analysis Fig. 11(a–c) shows the changes in functional group species and wavenumbers in the leachate from different leaching systems characterized by FT-IR spectroscopy. Several studies reported the use of FTIR spectroscopy to characterize changes in functional groups in the residue or leachate to reveal the metal reduction and leaching mechanism of the process in the recovery of spent LIBs by hydrometallurgical processes [49,50]. As shown in Fig. 11, the changes in the eOH bending and stretching vibrations (3469.3, 3432.7, and 3415.3 cm−1) in all leachates were observed. The results show that the type of eOH was between free and associative, and the greater the degree of molecular association, the wider the peak shape and the smaller the wave number, most likely due to the inclusion of eOH in H2O and C6H8O6 [51]. The absorption peaks at (1643.1, 1641.1, and 1643.1 cm−1) are attributed to C]O and eOH probably due to the eOH and C]O stretching vibrations in H2O and C6H8O6 [52]. Fig. 11a and c show the bends and telecast vibrations of SO42− (1201.4 and 1203.4 cm−1), SieOeSi (1120.4, 1116.6, and 1108.9 cm−1), and S]O (1054.9 cm−1) may be due to a small amount of sulfonic acid mixed in the sulfuric acid leaching system, indicating the dissolution of Li, Co,
3.4. Recovery of nickel, manganese, cobalt, and lithium As shown in Table 5, it was necessary to separate these metals from the leaching solution. Therefore, precipitation and solvent extraction methods were adopted to recover these metals. The concentrations of Li, Co, Ni, and Mn in the leaching liquid were 1.792 g/L, 12.915 g/L, 0.521 g/L, and 0.983 g/L, respectively. Firstly, dimethylglyoxime (C4H8N2O2) reagent was used to selectively precipitate nickel. The 0.05 mol/L C4H8N2O2 was used after adjusting pH of the leaching solution to 5.0, 98.96% Ni can be directly recovered as bis (dimethylglyoxime) -nickel (C8H14N4NiO4) precipitation from the leaching liquid. The loss rate of Li, Co, and Mn was < 1.5%. Secondly, the separation of manganese and cobalt was conducted by solvent extraction method using Di-(2-ethylhexyl) phosphoric acid (P204). Under the optimal extraction condition: 25% P204 + 10% octyl tributyl phosphate (TBP) + 65% sulfonated kerosene, pH = 2.2, O/A = 1: 8, t = 10 min, 99.57% Mn was extracted while losing only 0.2% Li and 0.5% Co. Then, the separation of cobalt and lithium was conducted by 7
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Fig. 10. SEM images of leaching residue (a) C(H2SO4) = 1.5 mol/L, (b) C(C6H8O6) = 0.25 mol/L, and (c) C(H2SO4) = 1.5 mol/L and C(C6H8O6) = 0.25 mol/L (liquid–solid ratio = 15 mL/g, T = 333 K, t = 40 min, and stirring rate = 300 r/min). Table 6 Concentrations of metals in the staged residual liquid (g/L). Sample
Leaching liquid After C4H8N2O2 precipitation After P204 extraction After P507 extraction After Na2CO3 precipitation Recovery efficiency (%)
Table 5 The metal content in the cathode material, leaching residue, and leaching liquid.
Cathode material (wt.%) Leaching residue (wt.%) Leaching liquid (g/L) Leaching efficiency (%)
Co
Ni
Mn
C
3.862 0.041 1.792 99.69
27.503 0.420 12.915 99.56
1.352 0.016 0.521 99.60
2.051 0.009 0.983 99.87
29.641 90.611 — —
Co
Ni
Mn
1.792 1.789 1.785 1.768 0.180 89.81
12.915 12.907 12.862 0.020 < 0.001 99.76
0.521 0.005 < 0.001 < 0.001 < 0.001 98.96
0.983 0.982 0.004 < 0.001 < 0.001 99.57
4. Conclusions In this study, a compound lixiviant system involving the synergistic use of sulfuric acid and L-ascorbic acid for recovering valuable metals from LIBs was investigated. Under the optimal leaching conditions where C(H2SO4) was 1.5 mol/L, C(C6H8O6) was 0.25 mol/L, the stirring rate was 300 r/min, the liquid–solid ratio was 15 mL/g, and the temperature was 333 K for 60 min, the leaching efficiencies of Li, Ni, Co, and Mn reached 99.69%, 99.56%, 99.60%, and 99.87%, respectively. Finally, 98.96 of Ni, 99.57% of Mn, 99.76% of Co, and 89.81% of Li were recovered in the form of C8H14N4NiO4, MnCO3, CoC2O4, and Li2CO3 through precipitation-solvent extraction methods. According to the SEM and XRD results of the residue, the major phases of the cathode materials (LiCoO2, C, Li0.05Mn2O4, LiAl0.2Co0.8O2, and Li0.9Ni0.5Co0.5O2−x) were dissolved, retaining C and Al2O3 components.
Contents of different metals Li
Li
was recovered as Li2CO3 precipitation by adjusting the pH to 14.0 with a saturated sodium carbonate solution at 90 ℃. Cobalt was recovered as CoC2O4 precipitation by adjusting the pH to 1.5 with an oxalic acid solution at 25 ℃. Manganese was recovered as MnCO3 precipitation by adjusting the pH to 9.0 with a saturated sodium carbonate solution at 25 ℃. Table 6 shows the metal concentrations in the residual liquid after each process, and the recovery efficiencies could be attained as follows: 98.96 for Ni, 99.57% for Mn, 99.76% for Co, and 89.81% for Li under optimized experimental conditions.
Fig. 11. FT-IR spectra of leachate(a) C(H2SO4) = 1.5 mol/L, (b) C(C6H8O6) = 0.25 mol/L, and (c) C(H2SO4) = 1.5 mol/L and C(C6H8O6) = 0.25 mol/L (liquid–solid ratio = 15 mL/g, T = 333 K, t = 40 min, and stirring rate = 300 r/min).
Sample
Contents of different metals (g/L)
solvent extraction method using 2-ethylhexyl dihydrogen phosphate (P507). Under the optimal extraction condition: 25% P507 + 5% TBP + 70% sulfonated kerosene, pH = 4.5, O/A = 1: 1, t = 10 min, 99.76% Co was extracted while losing only 1.6% Li. Finally, Lithium 8
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Analysis of the leach-ate by FT-IR spectroscopy indicated that L-ascorbic acid synergistically promoted the leaching of metals owing to the presence of eOH, C]O, and CeH functional groups.
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Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements The authors acknowledge the support of Special Funds of Guangdong Academy of Science (2019GDASYL-0402003, 2019GDASYL-0302011, 2019GDASYL-0104020, 2017GDASCX-0110, 2018GDASCX-0110, 2017G1FC-0007, 2018GDASCX-0938, and 2018GDASCX-0939) and the Young Scientists Fund of the National Natural Science Foundation of China (Grant No.51804083, No. 51704081, and No. 21906031), Science and Technology Planning Project of Guangdong Provincial Science and Technology Department (2017B010121005, 2017A070701022, 2017B090907026, and 2017B030314081), and Science and Technology Planning Project of Guangzhou (201904010106). References [1] X. Zhang, Y. Xie, X. Lin, H. Li, H. Cao, An overview on the processes and technologies for recycling cathodic active materials from spent lithium-ion batteries, J. Mater. Cycles Waste Manage. 15 (2013) 420–430. [2] N. Armaroli, V. Balzani, Towards an electricity-powered world, Energy Environ. Sci. 4 (2011) 3193–3222. [3] R. Yin, S. Hu, Y. Yang, Life cycle inventories of the commonly used materials for lithium-ion batteries in china, J. Cleaner Prod. 227 (2019) 960–971. [4] M. Contestabile, S. Panero, B. Scrosati, A laboratory-scale lithium-ion battery recycling process, J. Power Sour. 92 (2001) 65–69. [5] X. Zhang, Q. Xue, L. Li, E. Fan, F. Wu, R. Chen, Sustainable recycling and regeneration of cathode scraps from industrial production of lithium-ion batteries, ACS Sustain. Chem. Eng. 4 (2016) 7041–7049. [6] R.K. Nekouei, F. Pahlevani, R. Rajarao, R. Golmohammadzadeh, V. Sahajwalla, Direct transformation of waste printed circuit boards to nano-structured powders through mechanical alloying, Mater. Des. 141 (2018) 26–36. [7] E. Gratz, Q. Sa, D. Apelian, Y. Wang, A closed loop process for recycling spent lithium ion batteries, J. Power Sour. 262 (2014) 255–262. [8] N. Nitta, F. Wu, J.T. Lee, G. Yushin, Li ion battery materials: present and future, Mater. Today 18 (2014) 252–264. [9] Y.L. Yao, M.Y. Zhu, Z. Zhao, B.H. Tong, Y.P. Fan, Z.S. Hua, Hydrometallurgical processes for recycling spent lithium-ion batteries: a critical review, ACS Sustain. Chem. Eng. 6 (2018) 13611–13627. [10] S. Xiao, G. Ren, M. Xie, B. Pan, X. Xia, Recovery of valuable metals from spent lithium-ion batteries by smelting reduction process based on MnO-SiO2-Al2O3 slag system, J. Sustain. Metall. 27 (2017) 1–8. [11] G. Zeng, S. Luo, X. Deng, L. Li, C. Au, Influence of silver ions on bioleaching of cobalt from spent lithium batteries, Miner. Eng. 49 (2013) 40–44. [12] D. Mishra, D.J. Kim, D.E. Ralph, J.G. Ahn, Y.E. Rhee, Bioleaching of metals from spent lithium ion secondary batteries using acidithiobacillus ferrooxidans, Waste Manage. 28 (2008) 333–338. [13] Z.H.I. Sun, H. Cao, Y. Xiao, J. Sietsma, Y. Yang, Toward sustainability for recovery of critical metals from electronic waste: the hydrochemistry processes, ACS Sustain. Chem. Eng. 5 (2016) 21–40. [14] M.J. Kim, J.Y. Seo, Y.S. Choi, G.H. Kim, Bioleaching of spent Zn–Mn or Ni–Cd batteries by aspergillus species, Waste Manage. 51 (2016) 168–173. [15] Y. Huang, G. Han, J. Liu, W. Chai, W. Wang, S. Yang, A stepwise recovery of metals from hybrid cathodes of spent lithium–ion batteries with leaching–flotation–precipitation process, J. Power Sour. 325 (2016) 555–564. [16] B. Swain, J. Jeong, J.C. Lee, G.H. Lee, J.S. Sohn, Hydrometallurgical process for recovery of cobalt from waste cathodic active material generated during manufacturing of lithium ion batteries, J. Power Sour. 167 (2007) 536–544. [17] C.K. Lee, K.I. Rhee, Preparation of LiCoO2 from spent lithium-ion batteries, J. Power Sour. 109 (2002) 17–21. [18] X. Chen, H. Ma, C. Luo, T. Zhou, Recovery of valuable metals from waste cathode materials of spent lithium-ion batteries using mild phosphoric acid, J. Hazard. Mater. 326 (2017) 77–86. [19] L. Li, J. Ge, F. Wu, R. Chen, S. Chen, B. Wu, Recovery of cobalt and lithium from spent lithium ion batteries using organic citric acid as leachant, J. Hazard. Mater. 176 (2010) 288–293. [20] L. Li, X. Zhang, R. Chen, T. Zhao, J. Lu, F. Wu, Synthesis and electrochemical performance of cathode material Li1.2Co0.13Ni0.13Mn0.54O2 from spent lithium–ion batteries, J. Power Sour. 249 (2014) 28–34.
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Synergistic leaching of valuable metals from spent Li-ion batteries using sulfuric acid- L-ascorbic acid system
T
Dongdong Chena,b,c,d, Shuai Raob,c,d, Dongxing Wangb,c,d, Hongyang Caob,c,d, , Wuming Xiea, , Zhiqiang Liub,c,d ⁎
⁎
a
Guangzhou Key Laboratory of Environmental Catalysis and Pollution Control, Guangdong Key Laboratory of Environmental Catalysis and Health Risk Control, School of Environmental Science and Engineering, Institute of Environmental Health and Pollution Control, Guangdong University of Technology, Guangzhou 510006, China b Guangdong Research Institute of Rare Metal, Guangzhou 510650, China c Guangdong Province Key Laboratory of Rare Earth Development and Application, Guangzhou 510650, China d State Key Laboratory of Separation and Comprehensive Utilization of Rare Metals, Guangzhou 510650, China
HIGHLIGHTS
GRAPHICAL ABSTRACT
an environmentally friendly • Propose integrated flowsheet for recycling cathode materials.
analysis of metal leaching • Detailed behavior in different leaching systems. H SO –C H O system, the • Under leaching efficiency of Li, Co, Ni, and 2
4
6
8
6
Mn all exceeded 99.5%.
of Ni, 99.57% of Mn, 99.76% of • 98.96 Co, and 89.81% of Li were recovered
as C8H14N4NiO4, MnCO3, CoC2O4, and Li2CO3.
ARTICLE INFO
ABSTRACT
Keywords: Sulfuric acid L-ascorbic acid Synergistic leaching mechanism Recycling spent Li-ion batteries Precipitation-solvent extraction
With increase in the number of scrapped portable electronics and new energy powered vehicles, the production of spent Li-ion batteries (LIBs) has increased progressively each year. Harmful substances in spent LIBs can pollute the environment and threaten human health. A sustainable technology should be developed to recycle the spent LIBs. Accordingly, a new environmentally friendly hydro-metallurgical process was proposed for leaching Li, Co, Ni, and Mn from spent LIBs using sulfuric acid with L-ascorbic acid as a reductant. Over the leaching process, several parameters, including sulfuric acid and L-ascorbic acid concentrations, solid to liquid ratio, temperature and time were systematically investigated. The maximum recovery efficiencies of Li, Co, Ni, and Mn were as high as 99.69%, 99.56%, 99.60%, and 99.87% under the optimized conditions (C(H2SO4 concentration) = 1.5 mol/L, C(C6H8O6 concentration) = 0.25 mol/L, the agitation speed was 300 r/min, the liquid–solid ratio was 15 mL/g, and the temperature was 333 K for 60 min), respectively. The synergistic mechanism was analyzed by X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared spectroscopy of the structure of cathode materials, residues, and leachate. The analysis results indicate that the dissolution rate of Ni, Mn, and Co was significantly improved under the condition of adding L-ascorbic acid as a reducing agent. Finally, 98.96 of Ni, 99.57% of Mn, 99.76% of Co, and 89.81% of Li were recovered in the form of C8H14N4NiO4, MnCO3, CoC2O4, and Li2CO3 through precipitation-solvent extraction methods.
⁎
Corresponding authors at: Guangdong Research Institute of Rare Metal, Guangzhou 510650, China (H. Cao). E-mail addresses: [email protected] (H. Cao), [email protected] (W. Xie).
https://doi.org/10.1016/j.cej.2020.124321 Received 28 October 2019; Received in revised form 6 January 2020; Accepted 3 February 2020 Available online 04 February 2020 1385-8947/ © 2020 Elsevier B.V. All rights reserved.
Chemical Engineering Journal 388 (2020) 124321
2
[19] [20] [21] 90% for Co, 100% for Li 94.8% (Co), 98.5% (Li) 90% for Co), 100% for Li 1.25 M C6H8O7, 1.0 vol% hydrogen peroxide, S:L = 20 g/L, agitation = 300 rpm, t = 30 min, T = 90 ℃ 1.25 mol/L C6H8O6, T = 70 ℃, t = 20 min, S:L = 25 g/L 1.5 M C4H6O5, 2.0 vol% hydrogen peroxide T = 90 ℃, t = 40 min, L/S = 50 mL/g
74.1% (Li) 94.0% (Co), 95.0% (Li) 95.0% (Co), 95.0% (Li) over 99% (Co)
LiCoO2 and Co3O4 Li1.2Co0.13Ni0.13Mn0.54O2 and LiMn2O4 LiCoO2 and Co3O4
LiCoO2(s) + LixNiyMnzCorO2(s) + 7H+ → Li+ + Co2+ + Ni2+ + Mn2+ + Co(III) precipitates + Ni(IV) precipitates + Mn(IV) precipitates (5)
C6H8O7 C6H8O6 C4H6O5
Leaching conditions
However, the dissolution of Co(III) (Co2O3), Ni(IV) (NiO2) and Mn(IV) (MnO2) as soluble salts was very difficult even in strong acids with a high potential [22,23]. Therefore, the chemical equation for the reaction of the cathode material (LiCoO2) with sulfuric acid can be expressed as Eq. (5).
Organic acid
(4)
LiFePO4 and LiMn2O4 LiCoO2 LiCoO2 LiCoO2
NiO(s) + H2SO4(aq) → NiSO4(aq) + H2O
HCl H2SO4 + H2O2 HNO3 + H2O2 H3PO4
(3)
Mineral acid
MnO(s) + H2SO4(aq) → MnSO4(aq) + H2O
Leaching substrate
(2)
Leaching system
CoO(s) + H2SO4(aq) → CoSO4(aq) + H2O
Type of acid
(1)
Table 1 A brief summary of the recovery of metals using different leaching systems.
Li2O(s) + H2SO4(aq) → Li2SO4(aq) + H2O
Leaching efficiency
Li-ion batteries (LIBs) use lithium alloys as positive materials and nonhydroelectrolyte solutions as electrolytes [1]. LIBs have the advantages of high-power densities, high-energy densities, high potentials, low self-discharge rates, long service lives, and wide operating temperature ranges [2]. Therefore, they are widely used in consumer electronics, power and energy storage industries, as well as in laptops, cell phones, cameras, audio, and video players and other portable electronic devices [3,4]. Since the 21 st century, owing to the flourishing development of clean energy, the application of LIBs has been gradually extended to automobiles, home appliances, electric bicycles, energy storage and other fields [5]. China’s LIB production reached 13.98 billion in 2018, representing an increase of 12.9% over the previous year, within this, the total installed capacity of power batteries was 56.9 GWh, with a 56.3% annual growth rate. This growth trend is likely to pose a huge challenge with respect to the disposal of waste LIBs [6]. LIBs comprise a battery case, battery cap, anode, cathode, electrolyte and separator [7]. The main component of the anode is graphite and a binder, and the cathode is composed of conductive carbon. Lithium-transition-metal oxides in cathode composites include LiCoO2, LiNiO2, LiMn2O4, and LiCoxMnyNizO2, where the contents of Co, Ni, and Li are about 5–15%, 2–7%, and 0.5–2%, respectively, while small amounts of Au, Al, Fe and other elements are present [8]. The recycle value of spent LIBs is high, and in the context of a sharp shortage of metal resources, valuable metals in LIBs (e. g., Li, Co, Ni, and Mn, etc.) have received worldwide attention as secondary recovery resources. In recent years, the recycling of graphite, valuable metals and other components in spent LIBs as secondary resources involves different processes, including pyrometallurgy, hydrometallurgy, and biometallurgy [9]. For example, a new process using MnOeSiO2eAl2O3 to recover metals from spent LIBs, and high-purity alloys were achieved, which contains Co (99.03%), Ni (99.30%), and Cu (99.30%) [10]. However, the method had the disadvantages of complicated process, high energy consumption, strict equipment requirements, and incomplete metal recovery. Several studies [11,12]. Were also conducted on extracting valuable metals using Acidithiobacillus ferrooxidans as a strain in the leaching system. Although the method was environmentally friendly and the leaching conditions were mild, the reaction rate was relatively slow and the strain was difficult to culture. On the contrary, hydrometallurgical processes have the following advantages compared with pyrometallurgy and biometallurgy, such as simple process flow, low equipment operating costs, low waste emissions and high metal recovery rates [13,14]. Mineral acid, including HCl [15], H2SO4 [16], HNO3 [17], and H3PO4 [18], is widely used as a leaching agent to recover metals, while organic acid leaching agents include C6H8O7 [19], C6H8O6 [20], and C4H6O5 [21], which are briefly summarized in Table 1. In summary, the main phases of waste cathode materials are LiCoO2 and LixNiyMnzCorO2. In the sulfuric acid leaching system, the reduced states of Li(I), Co(II), Mn(II), and Ni(II) are easily dissolved, and the reactions are represented by Eqs. (1)–(4).
6.5 mol/L HCl, T = 30 ℃, t = 60 min 2 mol/L sulfuric acid, 5 vol% hydrogen peroxide, T = 75 ℃, t = 30 min 1 mol/L nitric acid , 1.7 vol% hydrogen peroxide, T = 75 ℃, t = 60 min 0.7 mol/L phosphoric acid, T = 40 ℃, t = 60 min, 4 vol% H2O2, L/S = 20 mL/g
References
1. Introduction
[15] [16] [17] [18]
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However, owing to the weak reducibility of the inorganic acid and the intense reaction conditions, the leaching of the metal in the single inorganic acid system is incomplete. Therefore, several studies have chosen to add a certain amount of reducing agent during the leaching process to improve the leaching efficiency of metals. (e.g., hydrogen peroxide or Na2SO3) [24,25]. For example, a study reported that when a certain amount of reducing agent (10 vol% hydrogen peroxide) was added to the 4.0 mol/L sulfuric acid leaching system, the leaching efficiency was significantly improved, and more than 96% of Li and 95% of Co were leached [26]. In addition, Lee et al. also reported that over 95% of Li and Co was leached when a certain amount of reducing agent (1.7 vol% hydrogen peroxide) was added to the 2 mol/L nitric acid leaching system [27]. However, organic reagents are biodegradable, usually reductive and acidic, and the waste from the leaching process can be easily treated [28]. Therefore, several studies are focusing attention on the development of new leaching processes around organic reagents. For example, dissolution proceeded with a reductive-complexing mechanism, and over 95% for Co was leached with 0.4 mol/L C4H6O6 and 0.02 mol/L C6H8O6 at 80 °C for 5 h [29]. Under the conditions of the mass fraction of hydrogen peroxide = 4%, acidity of tartaric acid = 2 M, and pulp density = 17 g/L, the reaction was carried out at 333 K for 30 min, over 99.3% of Li, 99.1% of Mn, 98.6% of Co, and 99.3% of Ni were leached [30]. L-ascorbic acid is an organic acid in the body's metabolism with a weak acidity [31]. It is ionized in an aqueous solution to generate hydrogen ions. The ionization equilibrium equation of L-ascorbic acid (Fig. 1a) in aqueous solution is represented by Eqs. (6) and (7) [32]. H2C6H6O6(aq) → HC6H6O6%− + H+(pKa1 = 4.17) HC6H6O6%−
→
C6H6O62−
+H
+
Fig. 2. Metallic complexes formed with L-ascorbic acid.
The metal complex formation mechanism with dehydroascorbic acid is shown in Fig. 2. A simple thermodynamic calculation shows that C6H6O6Co was thermodynamically favorable during the leaching [35,36]. However, these studies had the following disadvantages. Firstly, they focused on the leaching mechanism of Co. Secondly, the leaching behavior of Ni and Mn was not studied in detail. Finally, not only was leaching time long, but energy consumption was also high [37,38]. In this study, an integrated technological route for recovering valuable metals from spent LIBs was proposed. Proposed biomass reducing agent (L-ascorbic acid) instead of traditional reducing agent (hydrogen peroxide), proposed a cooperative leaching mechanism of sulfuric acid and L-ascorbic acid for LiCoO2, and proposed the recovery of valuable metals (Li, Co, Ni, and Mn). The parameters affecting the leaching efficiency of valuable metals, including sulfuric acid and Lascorbic acid concentrations, liquid–solid ratio, temperature, and time have been investigated in detail. The metals and carbon of the cathode material powder and leaching residues was determined by inductively coupled plasma-atomic emission spectrometry (ICP-AES) and carbon sulfur analyzer (CS), respectively. Moreover, the reduction and leaching mechanisms are presented in detail by scanning electron microscopy (SEM), X–-ray diffraction (XRD), and Fourier-transform infrared (FT-IR) spectroscopy on the structure of cathode material, residue, and leachate.
(6)
(pKa2 = 11.57)
(7)
In addition, L-ascorbic acid is also a mild reducing agent, which can be oxidized by one electron to a radical state or doubly oxidized to the stable form called dehydroascorbic acid (C6H6O6), as shown in Fig. 1b [33]. Additionally, owing to the strong reducibility of L-ascorbic acid, Mn(IV), Ni(IV), and Co(III) are reduced to Mn(II), Ni(II), and Co(II) in aqueous solution, respectively. In a single L-ascorbic acid system, LiCoO2 dissolves to form soluble C6H6O6Li2, dehydroascorbic acid (C6H6O6) can form stable compounds C6H6O6Co and C6H6O6Mn with Co (II) and Mn (II) with the conjugate bond, which has been reported [34]. the leaching reaction was represented by Eq. (8). 4C6H8O6(aq) + 2LiCoO2(s) + 2C6H6O6Co(aq) + 4H2O
→
C6H6O6(aq)
+
C6H6O6Li2(aq) (8)
2. Experimental 2.1. Materials and reagents Experimental material spent LIBs were obtained from the Jiangmen Changsun Umicore Industry Co., Ltd., China, and were treated by discharging, dismantling, crushing, grinding, and sieving. Then, the ground samples were dry sieved using standard sieve plates and separated into different size fractions via vibration. The obtained fractions were weighed and stored for further studies. Leaching reagent, sulfuric acid (Analytical grade, Shanghai Chemical Reagent Co., Ltd.). Reducing agent, L-ascorbic acid (Analytical grade, Shanghai Chemical Reagent Co., Ltd.). Other chemical reagents were of analytical grade and all solutions were prepared using deionized water. 2.2. Metal leaching The steps of all the leaching experiments were as follows: First, 5 g of the cathode powder was transferred into the 250 mL flask before adding a certain amount of L-ascorbic acid crystal powder at a pre-determined concentration, and the sulfuric acid solution was taken according to the set liquid–solid ratio, which was fixed in the thermostat
Fig. 1. L-ascorbic acid as (a) a leaching agent and (b) a reducing agent. 3
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water bath with a digital display. After the leaching experiment was completed, the leaching residue was obtained by vacuum filtration of the slurry, and dried at 363 K for 12 h, which was characterized by ICPAES and CS analysis equipment to quantify the percentages of metals and C, respectively. The supernatant was diluted and analyzed using atomic adsorption spectroscopy (AAS, Thermo 3300). The effects of the sulfuric acid concentration (C(H2SO4), mol/L), L-ascorbic acid concentration (C(C6H8O6), mol/L), temperature (T, K), time (t, min), and liquid–solid ratio (mL/g) on the leaching efficiency of metals were investigated in detail. To eliminate the influence of the agitation speed on the experiment, all experiments were set to 300 r/min. The leaching efficiency of Mn, Ni, Li, and Co was calculated according to Eq. (9). Me
=
m1 × wt1 m2 × wt2 × 100% m1 × t1
(9)
where ηMe represented the leaching efficiency of Mn, Ni, Li, or Co; m1 and m2 represented the mass of the cathode material powder and the corresponding leaching residue, respectively; and wt1 and wt2 were the Mn, Ni, Li, or Co contents of the cathode material powder and the corresponding leaching residue, respectively.
Fig. 3. XRD patterns of cathode material powder. Table 3 The phase of cathode material powder.
2.3. Analytical method X-ray diffractometer (Bruker D8 Advance, Germany) with Cu Kα radiation scanning speed of 10° min−1 range of 5–90° was used to investigate the crystalline phases of the cathode material powders and leaching residues. ICP-AES (IRIS intrepid XSP, Thermo Electron Corporation) was used to determine the content of valuable metals in the leach residues, and CS (CS844, LECO, USA) was used to determine the carbon content in the leach residues. The morphology and crystal structure of the cathode material powder and leaching residues were analyzed by SEM, (Hitachi S-570, Japan). FT-IR spectroscopy (WQF520A, Beijing Rayleigh, China) was used to analyze the change in functional groups in the leachate between 4000 and 400 cm−1.
3.1. Characterization analysis of cathode materials The valuable metals and carbon of the cathode material powder were determined by ICP-AES and CS, respectively (Table 2). The cathode material powder contained valuable metals and carbon, including 3.86 wt% Li, 27.50 wt% Co, 1.35 wt% Ni, 2.05 wt% Mn and 29.64 wt% C. The phases of the cathode material powders were characterized by XRD (Fig. 3), and the phase composition is listed in Table 3 according to MDI Jade 5.0. The results show that LiCoO2 (01-0702685), C (01-089-8487), Li0.05Mn2O4 (01-082-0320), LiAl0.2Co0.8O2 (01-089-0912), and Li0.9Ni0.5Co0.5O2-x (00-050-0509) were the main phases of the cathode material powder. SEM images were used to characterize the morphology of the components in the cathode material (Fig. 4). The phases of LiCoO2, LixAlyCoz, C, and LixNiyMnzCorO2 had large particle sizes, particularly, LixNiyMnzCorO2 had a flocculent porous structure. The results of the color image (Fig. 4c) were consistent with the XRD results.
3.2.1. Determination of the leaching system Fig. 5 displays that the leaching efficiencies were 83.29% for Li, Table 2 The chemical composition of cathode material powder. (Mass fraction/%). Co
Ni
Mn
C
Content (wt.%)
3.86
27.50
1.35
2.05
29.64
Minor phases
cathode material powder
C, LiCoO2, Li0.05Mn2O4,
LiAl0.2Co0.8O2, Li0.9Ni0.5Co0.5O2-x
3.2.2. Effect of H2SO4 and C6H8O6 concentrations The leaching efficiency of metals in 0.25 mol/L C6H8O6 at 333 K with H2SO4 concentration (0.05–1.75 mol/L) was shown in Fig. 6a. As the concentration of sulfuric acid increased, the metal dissolution rate in the cathode material increased, and the leaching efficiency was significantly improved. When the concentration of sulfuric acid was increased to 1.5 mol/L, over 99.09% Li, 98.91% Co, 99.08% Ni, and 99.38% Mn were leached. The reason may be that the sulfuric acid concentration increased, the proportion of activated molecules did not change, the number of H + increased, and the reaction rate was accelerated. Therefore, 1.5 mol/L sulfuric acid was selected as the optimal concentration for this experiment. The effect of L-ascorbic acid concentration (0–1.25 mol/L) on metal leaching efficiency in a single factor experiment with a sulfuric acid concentration of 1.5 mol/L was shown in Fig. 6b. The increase of L-ascorbic acid concentration from 0 to 0.25 mol/L had a significant positive impact on the rate of metal dissolution, and the leaching efficiencies of Li, Co, Mn, and Ni were as high as 91.91%, 93.03%, 94.32%, and 95.27%, respectively, with 0.25 mol/
3.2. Optimal conditions for leaching experiments
Li
Major phases
68.68% for Ni, and only 47.49% for Co and 51.73% for Mn with 1.5 mol/L sulfuric acid. The reason maybe CO3O4 had a relatively stable spinel structure, and it was difficult to dissolve them even in a strong acid [39]. On the other hand, the leaching efficiency of all metals was relatively low with 0.5 mol/L L-ascorbic acid. However, upon further increasing the L-ascorbic acid concentration to 1.25 mol/L, over 98.04% Li, 97.74% Co, 94.66% Ni and 98.20% Mn were leached. Additionally, with 1.5 mol/L sulfuric acid and 0.25 mol/L L-ascorbic acid, all valuable metals were almost completely leached. The reason may be that Co(III), Ni(IV), and Mn(IV) are converted into a readily soluble reduced product under the action of L-ascorbic acid, and the assumptions are also feasible even at lower concentrations of ascorbic acid (0.25 mol/L) [40]. The results show a clear sign of synergistic effect of the two acids. The increase in Co, Mn, and Ni dissolution may be due to the reductive role of L-ascorbic acid to enhance the dissolution of LiCoO2 and LixNiyMnzCorO2 [41]. Therefore, considering the efficiency and environmental friendliness of the leaching process, it was concluded that sulfuric acid (Leaching reagent) and L-ascorbic acid (Reducing reagent) were the best leaching systems.
3. Results and discussion
Elements
sample
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Fig. 4. SEM images of cathode material powder.
production factors, other optimization experiments were performed using 1.5 mol/L sulfuric acid as the leaching system with 0.25 mol/L Lascorbic acid. 3.2.3. Effect of temperature and time Fig. 7a shows that about 88.7% Mn, 81.5% Co, and only 75.2% Ni and 78.2% Mn were leached at 303 K. As the temperature increased, the leaching efficiency of all metals was significantly improved. Then reason maybe that the temperature increased, more non-activated molecules became activated molecules, which increased the activation energy and accelerated the reaction rate. However, when the temperature was greater than 333 K, L-ascorbic acid would completely decompose and lose its reducibility [42]. Therefore, further increase in the temperature did not promote the dissolution of LiCoO2 and increased the leaching of the metal. As shown in Fig. 7b, when the reaction time was in the range of 2–80 min, the leaching efficiency of Li, Co, and Ni increased significantly. When the time was increased to 60 min, all the metal leaching efficiencies were maximized. In this leaching system, the main purpose for the addition of a small amount of L-ascorbic acid was to covert insoluble Co(III) and Mn(IV) into soluble Co 2+ and Mn 2+. In the leaching solutions, these metals were mainly present in the form of sulfates owing to a high sulfuric acid concentration. The chemical reaction of the dissolution process can be expressed as Eq. (10).
Fig. 5. Leaching efficiencies of valuable metals in various leaching systems (liquid–solid ratio = 15 mL/g, T = 333 K, t = 60 min, and stirring rate = 300 r/min).
L L-ascorbic acid. Interestingly, upon to 1.25 mol/L only slightly improved Li leaching efficiency but exerted no significant effect on the dissolution of other metals including Co and Mn. The possible reason may be that the dissolution of Li was a simple neutralization reaction. However, the dissolution of Co and Mn involved the transformation of valence state. The oxidation-redox reaction had been completed under 0.25 mol/L L-ascorbic acid. Hence, considering energy-saving, clean
LiCoO2(s) + LixNiyMnzCorO2(s) + 4H2SO4(aq) + C6H8O6(aq) → Li2SO4(aq) + CoSO4(aq) + NiSO4(aq) + MnSO4(aq) + C6H6O6(aq) + H2O (10) As such the leaching efficiency of cobalt and manganese depends on
Fig. 6. Effect of H2SO4 and C6H8O6 concentrations: (a) C(H2SO4) (mol/L), C(C6H8O6) = 0.25 mol/L, (b) C(C6H8O6) (mol/L), C(H2SO4) = 1.5 mol/L (liquid–solid ratio = 15 mL/g, T = 333 K, t = 60 min, and stirring rate = 300 r/min). 5
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Fig. 7. Effect of temperature and time: (a) Temperature (K), (b) Time (min) (C(H2SO4) = 1.5 mol/L, C(C6H8O6) = 0.25 mol/L, liquid–solid ratio = 15 mL/g, and stirring rate = 300 r/min).
the concentration of reductant used [43]. Reductant converts Co(III) or Mn(IV) to the + 2 state for effective dissolution and subsequent recovery by standard methods [27,44]. In terms of energy saving and high efficiency, other experimental temperatures were maintained at 333 K, and the reaction time was 60 min.
3.3. Characterization 3.3.1. XRD analysis Fig. 9(a–c) shows than the phases of the leaching residues, including those from the single and synergistic leaching systems were analyzed by XRD. Additionally, the phases identified according to MDI Jade 5.0 are listed in Table 4 [46]. It is clear that LiCoO2 and C as the major phases could still be observed in the sulfuric acid or L-ascorbic acid system leaching residue. Additionally, the minor phases LiAl0.2Co0.8O2 and Li0.9Ni0.5Co0.5O2-x were also observed. The main reason is that the dissolution of Co(III), Mn(IV), and Ni(IV) is insufficient in the single leaching system [47]. Fig. 9c shows than the main phase of the leaching residue was only C, and in the minor phase only Al2O3 was also observed, and the characteristic peaks of the Co(III), Mn(Ⅳ), and Ni(Ⅳ) phases completely disappeared. The XRD pattern analysis demonstrated that L-ascorbic acid positively affected the leaching process, and promoted the dissolution of particles such as LiCoO2 and LixNiyMnzCorO2 in the cathode materials.
3.2.4. Effect of liquid–solid ratio Fig. 8 shows that the leaching efficiency of all metals increased with increasing liquid–solid ratio, and the increasing trend was more significant with the liquid–solid ratio ranging from 5 mL/g to 15 mL/g. Particularly, up to 99.69% Li, 99.56% Co, 99.60% Ni, and 99.87% Mn were leached with 15 mL/g liquid–solid ratio. With the progress of the reaction, the concentration of the product increased, which affected the mass transfer coefficient and caused the leaching efficiency of the metal to decrease. However, the large liquid–solid ratio was beneficial to increase the mass transfer coefficient between the reactants and accelerating the leaching of the metal [45]. From the point of view of high efficiency and reagent savings, the optimum liquid–solid ratio in this experiment was 15 mL/g.
3.3.2. SEM analysis Fig. 10(a–f) displays the SEM background scattering image of the residue at high magnification and resolution. Through detailed analysis of the SEM, it can be concluded that the distribution of metal and carbon in the leaching residue had distinct features. Firstly, metal elements such as Li, Ni, Mn, and Co in the residue were intertwined and inlaid at similar positions, especially the Li and Co elements were completely in the same position [48]. Second, graphite carbon (C) was relatively independent at different locations, with significant gaps between the particles. As seen in Fig. 10a, a large amount of bright particles with large particle size were observed in the leaching residue, and many black C particles were interspersed between LiCoO2 and LixNiyMnzCorO2 particles with 1.5 mol/L sulfuric acid. As seen in Fig. 10b, the particle size of the LiCoO2 and LixNiyMnzCorO2 particles in the leaching residues became small with 0.25 mol/L L-ascorbic acid, indicating that some of the LiCoO2 and LixNiyMnzCorO2 had reacted. Fig. 10c shows that the brightly colored particles disappear almost completely, and the leaching residues are almost entirely composed of dark C particles, indicating that leaching of the valuable metals was relatively complete. Additionally, Fig. 10(d–f) also supports the morphological changes in LiCoO2, C, and LixNiyMnzCorO2 particles in different leaching systems. In summary, the SEM results of the leaching residue are consistent with the XRD results.
Fig. 8. Effect of liquid–solid ratio (C(H2SO4) = 1.5 mol/L, C(C6H8O6) = 0.25 mol/L, T = 333 K, t = 60 min, and stirring rate = 300 r/min).
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Fig. 9. XRD patterns of leaching residue (a) C(H2SO4) = 1.5 mol/L, (b) C(C6H8O6) = 0.25 mol/L, and (c) C(H2SO4) = 1.5 mol/L and C(C6H8O6) = 0.25 mol/L (liquid–solid ratio = 15 mL/g, T = 333 K, t = 60 min, and stirring rate = 300 r/min).
and Mn compounds in the sulfuric acid system [53,54]. Some frequency shifts can be observed in the range 1000–1200 cm−1 (as shown in the rectangular frame, from 1203.4 and 1116.6 to 1201.4 and 1108.9 cm−1), which may be due to the L-ascorbic acid facilitating the dissolution of valuable metals [55,56]. By comparing Fig. 11b and c, the telescopic vibration of CeH (2923.6 and 2925.5 cm−1) can be observed, and the appearance of a new peak at 1054.9 cm−1 can be ascribed to the deformation vibration of saturated CeH. According to the results of FT-IR, it can be concluded that the eOH, C]O, and CeH functional groups in C6H806 will promote the reduction of the oxidized metal and facilitate the formation of sulfate.
Table 4 XRD phase analysis of leaching residue. Sample
Major phases
Minor phases
Sulfuric acid leaching residue L-ascorbic acid leaching residue
C, LiCoO2 LiCoO2, C
Sulfuric acid and L-ascorbic acid leaching residue
C
Li0.09Ni1.01O2 LiAl0.2Co0.8O2, Li0.9Ni0.5Co0.5O2-x Al2O3
3.3.3. FT-IR analysis Fig. 11(a–c) shows the changes in functional group species and wavenumbers in the leachate from different leaching systems characterized by FT-IR spectroscopy. Several studies reported the use of FTIR spectroscopy to characterize changes in functional groups in the residue or leachate to reveal the metal reduction and leaching mechanism of the process in the recovery of spent LIBs by hydrometallurgical processes [49,50]. As shown in Fig. 11, the changes in the eOH bending and stretching vibrations (3469.3, 3432.7, and 3415.3 cm−1) in all leachates were observed. The results show that the type of eOH was between free and associative, and the greater the degree of molecular association, the wider the peak shape and the smaller the wave number, most likely due to the inclusion of eOH in H2O and C6H8O6 [51]. The absorption peaks at (1643.1, 1641.1, and 1643.1 cm−1) are attributed to C]O and eOH probably due to the eOH and C]O stretching vibrations in H2O and C6H8O6 [52]. Fig. 11a and c show the bends and telecast vibrations of SO42− (1201.4 and 1203.4 cm−1), SieOeSi (1120.4, 1116.6, and 1108.9 cm−1), and S]O (1054.9 cm−1) may be due to a small amount of sulfonic acid mixed in the sulfuric acid leaching system, indicating the dissolution of Li, Co,
3.4. Recovery of nickel, manganese, cobalt, and lithium As shown in Table 5, it was necessary to separate these metals from the leaching solution. Therefore, precipitation and solvent extraction methods were adopted to recover these metals. The concentrations of Li, Co, Ni, and Mn in the leaching liquid were 1.792 g/L, 12.915 g/L, 0.521 g/L, and 0.983 g/L, respectively. Firstly, dimethylglyoxime (C4H8N2O2) reagent was used to selectively precipitate nickel. The 0.05 mol/L C4H8N2O2 was used after adjusting pH of the leaching solution to 5.0, 98.96% Ni can be directly recovered as bis (dimethylglyoxime) -nickel (C8H14N4NiO4) precipitation from the leaching liquid. The loss rate of Li, Co, and Mn was < 1.5%. Secondly, the separation of manganese and cobalt was conducted by solvent extraction method using Di-(2-ethylhexyl) phosphoric acid (P204). Under the optimal extraction condition: 25% P204 + 10% octyl tributyl phosphate (TBP) + 65% sulfonated kerosene, pH = 2.2, O/A = 1: 8, t = 10 min, 99.57% Mn was extracted while losing only 0.2% Li and 0.5% Co. Then, the separation of cobalt and lithium was conducted by 7
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Fig. 10. SEM images of leaching residue (a) C(H2SO4) = 1.5 mol/L, (b) C(C6H8O6) = 0.25 mol/L, and (c) C(H2SO4) = 1.5 mol/L and C(C6H8O6) = 0.25 mol/L (liquid–solid ratio = 15 mL/g, T = 333 K, t = 40 min, and stirring rate = 300 r/min). Table 6 Concentrations of metals in the staged residual liquid (g/L). Sample
Leaching liquid After C4H8N2O2 precipitation After P204 extraction After P507 extraction After Na2CO3 precipitation Recovery efficiency (%)
Table 5 The metal content in the cathode material, leaching residue, and leaching liquid.
Cathode material (wt.%) Leaching residue (wt.%) Leaching liquid (g/L) Leaching efficiency (%)
Co
Ni
Mn
C
3.862 0.041 1.792 99.69
27.503 0.420 12.915 99.56
1.352 0.016 0.521 99.60
2.051 0.009 0.983 99.87
29.641 90.611 — —
Co
Ni
Mn
1.792 1.789 1.785 1.768 0.180 89.81
12.915 12.907 12.862 0.020 < 0.001 99.76
0.521 0.005 < 0.001 < 0.001 < 0.001 98.96
0.983 0.982 0.004 < 0.001 < 0.001 99.57
4. Conclusions In this study, a compound lixiviant system involving the synergistic use of sulfuric acid and L-ascorbic acid for recovering valuable metals from LIBs was investigated. Under the optimal leaching conditions where C(H2SO4) was 1.5 mol/L, C(C6H8O6) was 0.25 mol/L, the stirring rate was 300 r/min, the liquid–solid ratio was 15 mL/g, and the temperature was 333 K for 60 min, the leaching efficiencies of Li, Ni, Co, and Mn reached 99.69%, 99.56%, 99.60%, and 99.87%, respectively. Finally, 98.96 of Ni, 99.57% of Mn, 99.76% of Co, and 89.81% of Li were recovered in the form of C8H14N4NiO4, MnCO3, CoC2O4, and Li2CO3 through precipitation-solvent extraction methods. According to the SEM and XRD results of the residue, the major phases of the cathode materials (LiCoO2, C, Li0.05Mn2O4, LiAl0.2Co0.8O2, and Li0.9Ni0.5Co0.5O2−x) were dissolved, retaining C and Al2O3 components.
Contents of different metals Li
Li
was recovered as Li2CO3 precipitation by adjusting the pH to 14.0 with a saturated sodium carbonate solution at 90 ℃. Cobalt was recovered as CoC2O4 precipitation by adjusting the pH to 1.5 with an oxalic acid solution at 25 ℃. Manganese was recovered as MnCO3 precipitation by adjusting the pH to 9.0 with a saturated sodium carbonate solution at 25 ℃. Table 6 shows the metal concentrations in the residual liquid after each process, and the recovery efficiencies could be attained as follows: 98.96 for Ni, 99.57% for Mn, 99.76% for Co, and 89.81% for Li under optimized experimental conditions.
Fig. 11. FT-IR spectra of leachate(a) C(H2SO4) = 1.5 mol/L, (b) C(C6H8O6) = 0.25 mol/L, and (c) C(H2SO4) = 1.5 mol/L and C(C6H8O6) = 0.25 mol/L (liquid–solid ratio = 15 mL/g, T = 333 K, t = 40 min, and stirring rate = 300 r/min).
Sample
Contents of different metals (g/L)
solvent extraction method using 2-ethylhexyl dihydrogen phosphate (P507). Under the optimal extraction condition: 25% P507 + 5% TBP + 70% sulfonated kerosene, pH = 4.5, O/A = 1: 1, t = 10 min, 99.76% Co was extracted while losing only 1.6% Li. Finally, Lithium 8
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Analysis of the leach-ate by FT-IR spectroscopy indicated that L-ascorbic acid synergistically promoted the leaching of metals owing to the presence of eOH, C]O, and CeH functional groups.
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Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements The authors acknowledge the support of Special Funds of Guangdong Academy of Science (2019GDASYL-0402003, 2019GDASYL-0302011, 2019GDASYL-0104020, 2017GDASCX-0110, 2018GDASCX-0110, 2017G1FC-0007, 2018GDASCX-0938, and 2018GDASCX-0939) and the Young Scientists Fund of the National Natural Science Foundation of China (Grant No.51804083, No. 51704081, and No. 21906031), Science and Technology Planning Project of Guangdong Provincial Science and Technology Department (2017B010121005, 2017A070701022, 2017B090907026, and 2017B030314081), and Science and Technology Planning Project of Guangzhou (201904010106). References [1] X. Zhang, Y. Xie, X. Lin, H. Li, H. Cao, An overview on the processes and technologies for recycling cathodic active materials from spent lithium-ion batteries, J. Mater. Cycles Waste Manage. 15 (2013) 420–430. [2] N. Armaroli, V. Balzani, Towards an electricity-powered world, Energy Environ. Sci. 4 (2011) 3193–3222. [3] R. Yin, S. Hu, Y. Yang, Life cycle inventories of the commonly used materials for lithium-ion batteries in china, J. Cleaner Prod. 227 (2019) 960–971. [4] M. Contestabile, S. Panero, B. Scrosati, A laboratory-scale lithium-ion battery recycling process, J. Power Sour. 92 (2001) 65–69. [5] X. Zhang, Q. Xue, L. Li, E. Fan, F. Wu, R. Chen, Sustainable recycling and regeneration of cathode scraps from industrial production of lithium-ion batteries, ACS Sustain. Chem. Eng. 4 (2016) 7041–7049. [6] R.K. Nekouei, F. Pahlevani, R. Rajarao, R. Golmohammadzadeh, V. Sahajwalla, Direct transformation of waste printed circuit boards to nano-structured powders through mechanical alloying, Mater. Des. 141 (2018) 26–36. [7] E. Gratz, Q. Sa, D. Apelian, Y. Wang, A closed loop process for recycling spent lithium ion batteries, J. Power Sour. 262 (2014) 255–262. [8] N. Nitta, F. Wu, J.T. Lee, G. Yushin, Li ion battery materials: present and future, Mater. Today 18 (2014) 252–264. [9] Y.L. Yao, M.Y. Zhu, Z. Zhao, B.H. Tong, Y.P. Fan, Z.S. Hua, Hydrometallurgical processes for recycling spent lithium-ion batteries: a critical review, ACS Sustain. Chem. Eng. 6 (2018) 13611–13627. [10] S. Xiao, G. Ren, M. Xie, B. Pan, X. Xia, Recovery of valuable metals from spent lithium-ion batteries by smelting reduction process based on MnO-SiO2-Al2O3 slag system, J. Sustain. Metall. 27 (2017) 1–8. [11] G. Zeng, S. Luo, X. Deng, L. Li, C. Au, Influence of silver ions on bioleaching of cobalt from spent lithium batteries, Miner. Eng. 49 (2013) 40–44. [12] D. Mishra, D.J. Kim, D.E. Ralph, J.G. Ahn, Y.E. Rhee, Bioleaching of metals from spent lithium ion secondary batteries using acidithiobacillus ferrooxidans, Waste Manage. 28 (2008) 333–338. [13] Z.H.I. Sun, H. Cao, Y. Xiao, J. Sietsma, Y. Yang, Toward sustainability for recovery of critical metals from electronic waste: the hydrochemistry processes, ACS Sustain. Chem. Eng. 5 (2016) 21–40. [14] M.J. Kim, J.Y. Seo, Y.S. Choi, G.H. Kim, Bioleaching of spent Zn–Mn or Ni–Cd batteries by aspergillus species, Waste Manage. 51 (2016) 168–173. [15] Y. Huang, G. Han, J. Liu, W. Chai, W. Wang, S. Yang, A stepwise recovery of metals from hybrid cathodes of spent lithium–ion batteries with leaching–flotation–precipitation process, J. Power Sour. 325 (2016) 555–564. [16] B. Swain, J. Jeong, J.C. Lee, G.H. Lee, J.S. Sohn, Hydrometallurgical process for recovery of cobalt from waste cathodic active material generated during manufacturing of lithium ion batteries, J. Power Sour. 167 (2007) 536–544. [17] C.K. Lee, K.I. Rhee, Preparation of LiCoO2 from spent lithium-ion batteries, J. Power Sour. 109 (2002) 17–21. [18] X. Chen, H. Ma, C. Luo, T. Zhou, Recovery of valuable metals from waste cathode materials of spent lithium-ion batteries using mild phosphoric acid, J. Hazard. Mater. 326 (2017) 77–86. [19] L. Li, J. Ge, F. Wu, R. Chen, S. Chen, B. Wu, Recovery of cobalt and lithium from spent lithium ion batteries using organic citric acid as leachant, J. Hazard. Mater. 176 (2010) 288–293. [20] L. Li, X. Zhang, R. Chen, T. Zhao, J. Lu, F. Wu, Synthesis and electrochemical performance of cathode material Li1.2Co0.13Ni0.13Mn0.54O2 from spent lithium–ion batteries, J. Power Sour. 249 (2014) 28–34.
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