A stepwise recovery of metals from hybrid cathodes of spent Li-ion batteries with leaching-flotation-precipitation process

Journal of Power Sources 325 (2016) 555e564

Contents lists available at ScienceDirect

Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour

A stepwise recovery of metals from hybrid cathodes of spent Li-ion batteries with leaching-flotation-precipitation process Yanfang Huang, Guihong Han*, Jiongtian Liu**, Wencui Chai, Wenjuan Wang, Shuzhen Yang, Shengpeng Su School of Chemical Engineering and Energy, Zhengzhou University, 450001, Zhengzhou, PR China

h i g h l i g h t s

g r a p h i c a l a b s t r a c t


A leaching-flotation-precipitation process is adopted to recycle metals from cathode.
Li/Fe/Mn ions are released from the cathode using HCl assisted with H2O2.
Fe3þ ions are selectively recovered as FeCl3 from the leachate in the flotation step.
Mn2þ/Mn3þ and Liþ ions are precipitated and separated as MnO2/Mn2O3 and Li3PO4.
The final products could be a source for cathode materials of Li-ion battery.

a r t i c l e i n f o

a b s t r a c t

Article history: Received 3 April 2016 Received in revised form 31 May 2016 Accepted 15 June 2016 Available online 21 June 2016

The recovering of valuable metals in spent lithium-ion battery cathodes brings about economic and environmental benefits. A stepwise leaching-flotation-precipitation process is adopted to separate and recover Li/Fe/Mn from the mixed types of cathode materials (hybrid wastes of LiFePO4 and LiMn2O4). The optimal operating conditions for the stepwise recovery process are determined and analyzed by factorial design, thermodynamics calculation, XRD and SEM characterization in this study. First, Li/Fe/Mn ions are released from the cathode using HCl assisted with H2O2 in the acid leaching step. The leachability of metals follows the series Li > Fe > Mn in the acidic environment. Then Fe3þ ions are selectively floated and recovered as FeCl3 from the leachate in the flotation step. Finally, Mn2þ/Mn3þ and Liþ ions are sequentially precipitated and separated as MnO2/Mn2O3 and Li3PO4 using saturated KMnO4 solution and hot saturated Na3PO4 solution, respectively. Under the optimized and advisable conditions, the total recovery of Li, Fe and Mn is respectively 80.93 ± 0.16%, 85.40 ± 0.12% and 81.02 ± 0.08%. The purity for lithium, ferrum and manganese compounds is respectively 99.32 ± 0.07%, 97.91 ± 0.05% and 98.73 ± 0.05%. This stepwise process could provide an alternative way for the effective separation and recovery of metal values from spent Li-ion battery cathodes in industry. © 2016 Elsevier B.V. All rights reserved.

Keywords: Spent Li-ion battery Cathode recycling Metal recovery Acid leaching Flotation Precipitation

1. Introduction * Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (G. Han), [email protected] (J. Liu). http://dx.doi.org/10.1016/j.jpowsour.2016.06.072 0378-7753/© 2016 Elsevier B.V. All rights reserved.

Today lithium ion batteries are the major power supply for

556

Y. Huang et al. / Journal of Power Sources 325 (2016) 555e564

portable electronics and electric vehicles [1,2]. The annual consumption of lithium ion batteries is increased to 6 billion cells in 2015 [3]. The life span of lithium ion batteries is approximately 2e3 years depending on the usage and their quality. The increased reliance of lithium ion batteries in electronic equipment leads to a lot of spent batteries being disposed to the landfills [4]. Spent lithium ion batteries contain organic electrolytes and metals such as ferrum, titanium, aluminum, nickel, cobalt, copper, and lithium [5e8]. The improperly disposing of spent batteries particularly is easy to cause serious environmental problems, such as soil and underground water contamination [7,8]. In order to seeking an approach for recycle and utilization of spent lithium ion batteries, hence, a worldwide study is underway. The recycling technology of spent lithium ion batteries mainly includes two categories: physical technologies and chemical technologies [9]. Physical processes as pre-treatment steps mainly involve dismantling, crushing, and sieving. Subsequently, the separated electrode powders are further treated to separate the valuable components through a series of chemical processes [9e11]. The recycling of valuable metals in spent batteries can not only save limited metal reserves, but also reduces environmental pollution. Among the components of lithium ion batteries, the active cathode materials that contain Li and other metals are the most valuable for recycling [6,10]. Some processes have been developed for recycling metals from the cathode materials. In the recycling of cathodes, metal components are generally first dissolved into the solution, followed by recovering metal ions from the leachate in different steps [12,13]. Acids such as dilute H2SO4, HNO3 and HCl, are usually employed to dissolve metal ions from the cathode [14e17]. The dissolved metal ions are then separated and recovered by various processes such as chemical precipitation, solvent extraction, and electrochemical process [17e19]. Among these recovering techniques, chemical precipitation is generally used. However, it is not easy to control the target metal to be recovered from the precipitation process. The major reason is that the target metal compound is prone to co-precipitate with other metal salts [20]. This leads to a more-complicated process that is required to further separate the mixed-metal compounds. Many techniques have already been studied to recover precious metals (including Co, Ni and Cu., et al.) from the cathode of spent lithium-ion batteries [8,19,20]. However, the main recycling routes were focused on a relatively simple spent cathode material. The preparation technologies of lithium ion batteries could change their composition elements, meaning that their electrode materials would certainly be changed continually. Nowadays, the prevalent cathode materials (LiCoO2 and LiCoxNi1-xO2) are being replaced by some inexpensive Fe/Mn-containing compounds such as LiFePO4, LiNi1/3Mn1/3Co1/3O2 and LiMn2O4 [21e25]. Low-cost metals (Fe/Mn or Li) in spent cathode materials are less important than the precious metals. They can still lead to enormous waste of metal resources and serious environmental risk because of the increasing accumulation of quantity and the improper disposal with a mixing manner in China [2]. Therefore, it is very important to explore new processes to meet the requirements of metals recovering from these kinds of complicated waste cathodes in the future. The studies of technologies for recycling spent lithium ion batteries are required to be consequently be updated with the rapid development of new kinds of cathode materials. The current recycling process developed for spent lithium ion batteries is very specific, meaning that the process may not be applicable, even if the same cathode materials, but with a different composition. In this study, a leaching-flotation-precipitation recovery process was investigated to separate and recover Fe/Mn/Li metals from the mixed types of waste cathode materials (hybrid powders of LiFePO4 and LiMn2O4) after the pretreatment of spent lithium-ion batteries

(including discharging, dismantling, peeling off aluminum foil and grinding of waste cathode active materials). This work is to illustrate how the stepwise recovery technique can be used to design the process and determine the optimal operating conditions of the recycling process for the cathode materials. 2. Experimental 2.1. Materials and reagents The hybrid cathode powder was supplied by a local e-waste collection center, China. The chemical composition of the powder is given in Table 1. It shows the presence of 33.45 ± 0.15% Mn along with 4.35 ± 0.05% Li, 17.18 ± 0.12% Fe and 9.36 ± 0.07 P (analyzed by ICP-OES). The powder was analyzed for the phase identification by XRD (Bruker D8 Discover, Germany). The XRD analysis in Fig. 1 shows the presence of LiFePO4, LiMn2O4 and graphite as the major constituents in the material. The graphite was expected to be from conductive carbon black and PVDF binder (the important components in Li-ion battery) [26]. The particle size of the cathode powder was determined by the optical microscope equipped with statistical analysis software (ZEISS Axio Scope. A1, Germany). The particle size is found to be < 40 mm and 80% of size distribution being <15 mm. Hydrochloric acid (HCl, 20 wt% concentration) and hydrogen peroxide (H2O2, 30.0 wt% concentration) as leaching reagents, were purchased from Tianjin Aokatet Chemical Co., Ltd., China. Betainium bis(trifluoromethylsulfonyl)imide (ionic liquid structure precipitant), n-butyl xanthate (collector) and a-Terpineol (frother) were used as flotation reagents, which were purchased from Sinopharm chemical reagent Co., Ltd., China. Potassium permanganate and sodium phosphate (obtained from Tianjin Aokatet Chemical Co., Ltd., China) were used as metal-precipitators. All reagents were of analytical grade and were used without further purification. 2.2. Stepwise leaching-flotation-precipitation process The schematic diagram of stepwise recovering of valuable metals from the cathode powder is plotted in Fig. 2. It can be seen from Fig. 2 that, the stepwise recovery of valuable metals can be divided into acid leaching, ion flotation and precipitation steps. First, ferrum, manganese and lithium are leached from the cathode powder using HCl assisted with H2O2. Ferrum can be selectively floated by Hbet][Tf2N] as [Fe(bet)n][(Tf2N)3] and nbutyl xanthate, respectively. The final output of ferrum is FeCl3. Subsequently, manganese is precipitated by KMnO4 as MnO2/ Mn2O3. Finally, the leaching liquor is treated with sodiumphosphate (Na3PO4) solution to precipitate and recover lithium as Li3PO4. 2.2.1. Leaching step The leaching experiments were done to determine the optimum leaching efficiency of metals. The cathode powder was leached in a 1000 mL three-necked glass flask equipped with a magnetic stirrer, a digital controller unit and a thermostat used for controlling the reaction temperature. In addition, the reactor was provided for a reflux condenser preventing from HCl evaporation, which was Table 1 Chemical composition of the hybrid cathode powder. Elements

Li

Fe

Mn

P

Wt %

4.35 ± 0.05

17.18 ± 0.12

33.45 ± 0.15

9.36 ± 0.07

Y. Huang et al. / Journal of Power Sources 325 (2016) 555e564

557

stirring with a required agitation speed. The schematic diagram of flotation step had been previously described in detail [27]. The recovery of metal ðRM Þ from the leachate was calculated by the following Equation (2).


RM ¼

1

Cf $Vf Ce $Vl

  100%

(2)

where M refers to metal ions, Ce and Cf are the concentrations of metal ions in the leachate before and after flotation step (mol/L); Ve and Vf is respectively leachate volume before and after flotation (L).

Fig. 1. XRD pattern of the hybrid cathode powder.

bathed in water bath, changing the leaching temperature (30e60  C) and time (0.5e2 h). A measured amount of spent cathode powder in different concentrations of HCl, H2O2 and different solid to liquid ratios was input and bathed in the reactor under the required conditions. The leaching efficiency of metal ðEM Þ was calculated by the following Eq. (1).

EM ¼

C1 $V1  100% W$m

(1)

where C1, V1, W and m refer to the concentration of metal ions in the leachate (mol/L), leachate volume (L), the weight of cathode powder and the content of metal (mol/g) in the powder, respectively. 2.2.2. Flotation step The flotation experiments were carried out to determine the optimum recovery of ferrum. In the flotation step, each batch a 0.5 L of leachate was first introduced into the flotation apparatus. [Hbet] [Tf2N], n-butyl xanthate and a-Terpineol were then successively added to the leachate. During this step, the leachate was kept

2.2.3. Precipitation steps The precipitation experiments were conducted to determine the optimum recovery of manganese and lithium. In the precipitation steps, the solution pH was adjusted with 2.0 M NaOH in a 500 mL glass beaker equipped with a magnetic stirrer. The pH meter (PHS3D, 2000) was used for pH monitoring and regulating. Then a saturated solution of KMnO4 was added to precipitate Mn2þ/Mn3þ. The resulting MnO2/Mn2O3 was washed with pure water to remove the soluble salts and dried at 105  C for 2 h. After the precipitation of manganese, hot saturated Na3PO4 with a high temperature (90  C) was added to precipitate and recover Liþ as Li3PO4. In order to wash off NaCl and furthest reduce the loss of lithium, hot deionized water (~100  C) was used to wash off the impurity ions entrained. The Li3PO4 product was then dried at 60  C for 4 h in vacuum drying oven. The precipitation efficiency PM can be calculated according to Eq. (3):

PM ¼

1

Cf $VP CP $VP’

!  100%

(3)

where PM is the metal precipitation efficiency; Cf and Cp are the concentrations of metals in the solution before and after

Fig. 2. Schematic diagram of the stepwise recovery of valuable metals from the cathode powder.

558

Y. Huang et al. / Journal of Power Sources 325 (2016) 555e564

Fig. 4. Effects of amount of H2O2 on the leaching efficiency of Li, Fe and Mn.

2.4. Metal elements determination The concentration of metal ions was determined by inductively coupled plasma-atomic emission spectrometry (ICP-OES, PerkinElmer Optima 7300 V, America). 2.5. Data acquisition and analysis To avoid random errors, three parallel experiments were conducted during the whole leaching-flotation-precipitation operations. Statistical analysis including the analysis of variance was treated with Originpro v8.0 software. 3. Results and discussion 3.1. Extraction of Mn2þ/Mn3þ, Fe3þ and Liþ with acid leaching

Fig. 3. EhepH diagrams for LieH2O, FeeH2O and MneH2O systems. (soluble species concentration (except Hþ) ¼ 1.0 M at 298 K and 1 atm pressure).

precipitation (mol/L), respectively; Vp and V’p refer to the volumes of the liquor before and after precipitation (L), respectively. 2.3. Material characterization X-ray diffraction (XRD) testing was carried out using an X-ray diffractometer (Bruker D8 Discover, Germany) equipped with a graphite monochromatized Cu-Ka radiation source (l ¼ 1.5406 Å). The sample was scanned at a scan rate of 0.05 s1 in a 2q ranges from 10 to 90 . Scanning electron microscopy (SEM) analysis was conducted by a JSM-7500F (JEOL, Japan) equipped with an energy dispersive spectrometer (EDS).

Aiming at studying the extraction behavior of Li, Fe and Mn during acid leaching, the thermodynamic aspects particularly the stability regions of different phases of metals in the aqueous solutions was calculated using HSC 6.0 software. The EhepH diagram of LieH2O system is shown in Fig. 3(a). It can be seen that the domain of LiOH and Liþ phases is within the stability region of water, Li can thus be disolved in whole acidic and alkaline region. In the EhepH diagram of FeeH2O system, Fig. 3(b) shows that Fe(III) phase does not dissolve even in strong acid until redox potential reached to þ0.75 V. Fe(II) can be solubilized in acid as its stability region extends till pH 6.9. This region is easy to achieve under the normal leaching conditions. Fe(II) present as LiFePO4 in the cathode material, therefore, can dissolve in hydrochloric acid [17,28]. In the EhepH diagram of MneH2O system, Fig. 3(c) demonstrates that manganese (II) can be disolved in acidic region. Aiming at dissolving Mn(IV) phase which is a part of LiMn2O4 (a spinel structure-containing Mn3þ and Mn4þ) in the spent cathode [29], a very strong reducing condition and strong acid solutions are needed to form soluble Mn(II) phase. Mn(IV) can be solubilized as Mn(II) through the formation of an intermediate Mn(III) phase (Mn2O3). Former literature had revealed that low recovery of Mn from spent cathode is attributed to its higher valence states (Mn4þ) [5,30]. Hence, the leachability of Mn was expected to be improved in the presence of a reductant such as H2O2 in this work. The related reactions between H2O2 and metal ions in the acid leaching are expressed as Eq. (4) and Eq. (5) [31].

Y. Huang et al. / Journal of Power Sources 325 (2016) 555e564

559

Table 2 Four-factor four-level L16(45) orthogonal design and the leaching efficiency of Li, Fe and Mn in acid leaching. Factors

Temperature

Time

Units

(oC)

(h)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

30 30 30 30 40 40 40 40 50 50 50 50 60 60 60 60

0.5 1.0 1.5 2.0 0.5 1.0 1.5 2.0 0.5 1.0 1.5 2.0 0.5 1.0 1.5 2.0

Li leaching efficiency Average rejection rate for all factors Li 75.95 K

82.55

83.55

83.75

F value Temperature

85.25

85.20

84.72

85.50

Time

2.652

90.65

87.28

87.30

86.85

Solid-liquid ratio

1.668

91.32

88.15

87.60

87.08

Agitation intensity

1.000

18.46

1 Li K2 Li K3 Li K4 RLi 1

15.38

Fe leaching efficiency Average rejection rate for all factors Fe 72.58 K 1 Fe K2 Fe K3 Fe K4 Fe R1

1 Mn

Mn K3 Mn K4 RMn 1

1:2 1:3 1:4 1:5 1:3 1:2 1:5 1:4 1:4 1:5 1:2 1:3 1:5 1:4 1:3 1:2

4.050

Agitation intensity

Leaching efficiency (%)

(r/min)

ELi

400 600 800 1000 800 1000 400 600 1000 800 600 400 600 400 1000 800

65.81 74.13 81.22 83.71 84.37 84.91 85.63 86.25 89.32 90.34 91.96 91.17 90.81 92.50 90.42 91.61

EFe ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.12 0.13 0.12 0.15 0.14 0.12 0.16 0.10 0.12 0.15 0.24 0.15 0.17 0.14 0.15 0.15

63.22 70.21 75.62 80.73 82.90 83.11 85.33 86.75 85.92 86.43 87.37 86.23 86.70 88.11 88.74 89.16

EMn ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.13 0.17 0.12 0.14 0.24 0.23 0.12 0.15 0.15 0.20 0.21 0.12 0.15 0.15 0.24 0.12

57.91 65.35 69.82 77.29 81.45 83.62 83.91 84.54 83.72 85.55 84.83 82.73 83.35 85.25 84.94 88.61

80.70

F value Temperature

84.50

82.10

82.15

82.88

Time

2.534

86.45

84.22

84.08

83.50

Solid-liquid ratio

1.287

88.15

85.68

84.78

84.60

Agitation intensity

1.000

20.96

6.000

4.100

3.900

76.58

78.72

77.42

F value Temperature

83.35

79.98

78.65

79.55

Time

2.267

84.18

80.85

80.80

81.32

Solid-liquid ratio

1.386

85.50

83.25

82.48

82.35

Agitation intensity

1.000

17.88

6.675

0.22 0.13 0.17 0.22 0.12 0.13 0.12 0.23 0.14 0.12 0.19 0.12 0.13 0.05 0.09 0.15

3.325

80.68

15.58

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

21.56

79.68

Mn leaching efficiency Average rejection rate for all factors Mn 67.62 K K2

5.600

Solid-liquid ratio

3.825

4.925

Note: The amounts of HCl and H2O2 keep a constant as 6.5 mol L1 and 5% vol%, respectively.

MnO2 þ H2O2 þ 2Hþ ¼ Mn2þ þ O2[ þ 2H2O

(4)

2Fe2þ þ H2O2 þ 2Hþ ¼ 2Fe3þ þ 2H2O

(5)

The effects of amount of H2O2 on the leaching efficiency of Li, Fe and Mn are displayed in Fig. 4. As seen from Fig. 4, the leaching efficiency of Li, Fe and Mn obviously increases with the increase of amount of H2O2. It is noteworthy that the leaching efficiency of Mn is enhanced from 23.87 ± 0.13% to 67.81 ± 0.15% when the amount of H2O2 is increased from 6 to 18 vol%. Comparatively, the effect of amount of H2O2 on the leaching efficiency of Mn is not very obvious when amount of H2O2 exceeds 15 vol%. Combined with the EhepH diagrams of metaleH2O system, Fig. 4 confirms that the leachability of metals follows the series Li > Fe > Mn in the acidic region. The extraction of metals with acid leaching can be affected by multiple factors. A four-factor four-level L16(45) orthogonal design table was designed in this study. The factors are the reaction temperature, time, agitation intensity and solid-liquid ratio. The leaching efficiency of Li, Fe and Mn is respectively listed in Table 2. As listed in Table 2, the leaching efficiency of Li is from 65.81 ± 0.12% to 92.50 ± 0.14%. The leaching efficiency of Mn varies

from 57.91 ± 0.22% to 88.61 ± 0.15%, and Fe leaching can reach Fe 89.16 ± 0.12%. The maximum differences ðRLi 1 ; R1 Þ in Li and Fe leaching process increase in order of agitation intensity < solidliquid ratio < reaction time < extracting temperature. The maximum difference RMn increase in order of solid-liquid 1 ratio < agitation intensity < reaction time < extracting temperature. It shows an increase in dissolution of Li, Fe and Mn, depending mainly on the leaching temperature considering the differences in the F values. In the presence of amount of H2O2 of 15% vol%, the optimized conditions for were obtained according to the four-factor four-level L16(45) orthogonal design as follows: 60  C, leaching time of 2.0 h, solid-liquid ratio of 1:5 and agitation intensity of 1000 r/min. In that case, the leaching efficiency of Li, Fe and Mn is respectively 92.15 ± 0.25%, 91.73 ± 0.17% and 89.95 ± 0.11%. The concentrations of metal ions in the leachate under the optimized acid leaching step are given in Table 3. The X-ray diffraction pattern of the cathode after acid leaching under the optimized conditions is presented in Fig. 5. Meantime, the comparison of surface morphology of the cathode before and after acid leaching was determined by SEM observations (as shown in Fig. 6).

560

Y. Huang et al. / Journal of Power Sources 325 (2016) 555e564

Table 3 The concentrations of metal ions in the leachate under the optimized acid leaching step. Temperature

Time

(oC)

(h)

60

2.0

Solid-liquid ratio

1:5

Agitation intensity

Metal ions in leachate (g/L)

(r/min)

Li

Fe

Mn

1000

4.00 ± 0.03

15.76 ± 0.05

30.09 ± 0.06

3.3. Separation selectively of Mn2þ/Mn3þ and Liþ with precipitation A solution mainly consisting of Liþ of 3.75 ± 0.05 g/L and Mn2þ/3þ of 28.45 ± 0.05 g/L was used for the following precipitation separation step. The precipitation and separation of manganese was carried out by drop-wise adding saturated KMnO4 solution to the liquor. The main reaction between KMnO4 and Mn2þ can be given as Eq. (7) and Eq. (8) [18,32]. 2KMnO4 þ 3Mn2þ þ 2H2O ¼ 5MnO2Y þ 2Kþ þ 4Hþ

(7)

KMnO4 þ 4Mn2þ þ 10H2O ¼ 5MnO(OH) þ Kþ þ 15Hþ

(8)

Fig. 5. XRD pattern of the cathode after acid leaching.

Fig. 5 demonstrates that the main phase of the leached cathode residue is graphite. As seen from Fig. 6(a), the origin cathode powder is irregular particle with relatively smooth surface. The surface of the leached residue becomes coarser as shown in Fig. 6(b). And the particle size of the cathode residue becomes smaller. As revealed in Fig. 6(c), the elements that hold their composition are mainly carbon, phosphorus and chlorine, with small amounts of Fe and Mn. The results in Figs. 5 and 6 confirm that the metals in the cathode had been extracted in the acid leaching step, leaving trace amounts of metals in the residue. 3.2. Recovery of Fe3þ from leachate with ion flotation A leachate with Liþ of 4.00 ± 0.03 g/L, Fe3þ of 15.76 ± 0.05 g/L and Mn2þ/3þ of 30.09 ± 0.06 g/L was obtained for the following flotation step. Also, a four-factor four-level L16(45) orthogonal design table was designed for flotation step. The factors are the dosage of precipitating reagent, dosage of collector, flotation pH and agitation intensity. The recovery of Fe3þ in flotation process is listed in Table 4. As given in Table 4, the recovery of Fe is from 54.21 ± 0.13% to 92.73 ± 0.13%. The maximum differences (RFe 2 ) in Fe recovery follow the descending order: dosage of precipitating reagent > dosage of collector > flotation pH > agitation intensity. It shows an increase in the recovery of Fe depending mainly on the dosage of precipitating reagent. Based on the orthogonal design, the optimized level for Fe recovery under the flotation step can be found in Table 4. In that case, the recovery of Fe reaches 93.10 ± 0.15%. The concentrations of metal ions in the solution under the optimized flotation step are given in Table 5. In this flotation step, Fe3þ was recovered by Hbet][Tf2N] as [Fe(bet)n][(Tf2N)3]. The reaction between [Hbet][Tf2N] and Fe3þ can be expressed by the following Eq. (6) [27].

  Fe3þ þ 3½Hbet½Tf 2 N ¼ FeðbetÞn ½Tf 2 N3 Y þ ð3  nÞHðbetÞþ þ nH þ (6) During reagent recycling process with adding HCl, ½FeðbetÞn ½Tf 2 N3  was then turned into [Hbet][Tf2N] and FeCl3. [Hbet][Tf2N] can be reused in the flotation step. And FeCl3 was considered as the final product of Fe.

Precipitator dosage and equilibrium pH are the main factors influencing the precipitation step [5,33,34]. The effects of amount of KMnO4 and equilibrium pH on the precipitation efficiency of manganese are depicted in Fig. 7. Fig. 7(a) shows that, the precipitation efficiency of manganese increases with the increase of amount of KMnO4. Approximately 95.27 ± 0.28% manganese is precipitated when the amount of KMnO4 comes to 0.35 mol L1. And only about 5% lithium is lost in that case. Therefore, KMnO4 amount of 0.35 mol L1 is treated as the advisable KMnO4 dosage. As seen from Fig. 7(b), the precipitation efficiency of manganese increases when equilibrium pH is smaller than 2.0. The precipitation efficiency of manganese declines with the increase of equilibrium pH when the equilibrium pH is larger than 2.0. This phenomenon may be attributed to incomplete oxidizing precipitation of Mn(II) to Mn(IV) and the generation of intermediate MnO(OH) as reflected in Eq. (8). Based on the results in Fig. 7, the advisable precipitation conditions of manganese are equilibrium pH of 2.0 and KMnO4 amount of 0.35 mol L1 under which about 95.27 ± 0.28% Mn2þ/Mn3þ can be selectively precipitated and separated. For the recovery of lithium, saturated sodium phosphate (Na3PO4) was used to precipitate lithium as lithium phosphate (Li3PO4). The main reaction between Na3PO4 and Liþ can be given as Eq. (9) [35]. 3Liþ þ PO3 4 ¼ Li3PO4Y

(9)

The effects of amount of Na3PO4 and equilibrium pH on the precipitation efficiency of lithium are depicted in Fig. 8. It can be seen from Fig. 8(a), the precipitation efficiency of lithium also increases with increasing the amount of Na3PO4. The precipitation efficiency of lithium cannot be further obviously enhanced when the amount of Na3PO4 exceeds 0.20 mol L1. Therefore, Na3PO4 amount of 0.20 mol L1 is treated as the advisable Na3PO4 dosage. About 93.68 ± 0.35% lithium is precipitated when the amount of Na3PO4 is 0.20 mol L1. As described in Fig. 8(b), the precipitation efficiency of lithium keeps increasing when equilibrium pH is enhanced. And the precipitation efficiency of lithium is not obviously increased when equilibrium pH is above 7.5. It can be concluded from Fig. 8 that, the advisable precipitation conditions of lithium are equilibrium pH of 7.0 and Na3PO4 amount of 0.20 mol L1 under which about 93.68 ± 0.35% Liþ is precipitated. Saturated sodium carbonate (Na2CO3) was also used to precipitate lithium. Comparatively, the precipitation efficiency of Na2CO3

Y. Huang et al. / Journal of Power Sources 325 (2016) 555e564

561

Fig. 6. SEM observations for surface morphology of the cathode before and after acid leaching (a) Surface morphology of the origin cathode (20,000); (b) Surface morphology of the leached residue (1,00,000); and (c) EDS analysis for the assigned zone of (b).

(about 85%) is much smaller than that of using saturated Na3PO4 due to its higher solubility than Li3PO4 [18,35]. 3.4. Total recovery of metals and purity analysis of final products The optimized and advisable conditions for the stepwise leaching-flotation-precipitation process are concluded based on the results obtained from the above separate steps. The total recovery of metals using this stepwise process is calculated, and the results are listed in Table 6. As shown in Table 6, the total recovery of Li, Fe and Mn is respectively 80.93 ± 0.16%, 85.40 ± 0.12% and

81.02 ± 0.08%. Comparatively, the recovery of metals using this process is higher than those obtained with other processes [5,13,26]. Table 7 shows the results of the purity analysis of final products. As seen from the above results, relatively pure metal products with little impurities can be obtained when this recovery process is adopted. The purities for the compounds of lithium, ferrum and manganese are 99.32 ± 0.07%, 97.91 ± 0.05% and 98.73 ± 0.05%, respectively. Meantime, the average particle size of FeCl3, MnO2/ Mn2O3 and Li3PO4 is respectively <20 mm, <40 mm and <40 mm (determined by optical microscope equipped with statistical

562

Y. Huang et al. / Journal of Power Sources 325 (2016) 555e564

Table 4 Four-factor four-level L16(45) orthogonal design and the recovery of Fe3þ in flotation process. Factors

Dosage of precipitating reagent

Dosage of collector

Units

(g/L)

(g/L)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

5 5 5 5 7 7 7 7 9 9 9 9 12 12 12 12

Flotation pH

3 5 7 9 3 5 7 9 3 5 7 9 3 5 7 9

Fe Recovery Average rejection rate for all factors Fe 64.64 K’1 Fe 75.77 K’2 Fe 85.94 K’3 Fe 89.00 K’4 24.36 RFe

0.5 1.0 1.5 2.0 1.0 0.5 2.0 1.5 1.5 2.0 0.5 1.0 2.0 1.5 1.0 0.5

Fe recovery (%)

(r/min)

RFe

500 700 900 1200 900 1200 500 700 1200 900 700 500 700 500 1200 900

54.21 63.37 67.41 73.59 65.78 75.83 81.67 79.81 82.78 87.99 85.76 87.23 86.44 92.73 90.57 86.29

72.30

75.52

78.96

79.98

76.74

78.84

81.35

80.68

76.87

81.73

82.42

80.69

9.428

2

Agitation intensity

6.901

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.13 0.15 0.11 0.05 0.14 0.14 0.13 0.12 0.08 0.15 0.02 0.13 0.15 0.13 0.15 0.12

The optimized level Dosage of precipitating reagent: 12 g/L Dosage of collector: 9 g/L Flotation pH: 2.0 Agitation intensity: 1200 r/min

3.825

Table 5 The concentrations of metal ions in the solution under the optimized flotation step. Dosage of precipitating reagent

Dosage of collector

(g/L)

(g/L)

12

9

Flotation pH

2.0

analysis software). These final products can be employed as raw materials for new cathode materials of lithium-ion batteries or other fields. 3.5. Economic and environmental prospective of the integrated process There are previous studies on the recovering of lithium or manganese, ferrum from lithium ion batteries by the traditional acid leaching and followed precipitation processes [18,36]. However, it is very difficult to simultaneously extract the target metals. And it is hard to achieve the separation and purification of final

Agitation intensity

Metal ions in solution (g/L)

(r/min)

Li

Fe

Mn

1200

3.75 ± 0.05

1.134 ± 0.02

28.45 ± 0.05

metal products during the precipitation process [36]. Therefore, the total recovery of metal using previous routes is generally not very satisfying. And those proposed techniques are relatively difficult to be operated and scaled up in industry. Comparatively, the development of our integrated process route is one of the most important discoveries that can immediately be adapted to an industrial scale. From the perspective of reagent cost and product value, the economic prospective of the integrated process is given in Table 8. Table 8 shows that the recovering of metals in spent lithium-ion battery cathodes using leaching-flotation-precipitation process can bring about obvious economic benefits. In conclusion, this stepwise recovery process shows the merits by the following: (1) The acid

Fig. 7. Effects of amount of KMnO4 and equilibrium pH on the precipitation efficiency of manganese.

Y. Huang et al. / Journal of Power Sources 325 (2016) 555e564

563

Fig. 8. Effects of amount of Na3PO4 and equilibrium pH on the precipitation efficiency of lithium.

Table 6 Total recoveries of metals under the optimized process. Elements

Leaching efficiency (%)

Flotation recovery (%)

Precipitation efficiency (%)

Total recovery (%)

Li Fe Mn

92.15 ± 0.05% 91.73 ± 0.04% 89.95 ± 0.05%

93.75 ± 0.04% 93.10 ± 0.05% 94.55 ± 0.05%

93.68 ± 0.35% e 95.27 ± 0.28%

80.93 ± 0.16% 85.40 ± 0.12% 81.02 ± 0.08%

Note: Total recovery refers to the product of leaching efficiency, flotation recovery and precipitation efficiency.

Table 7 Purity analysis of the final products under the optimized process. Elements

Final products

Purity

FeCl3

MnO2/Mn2O3

Li3PO4

97.91 ± 0.05%

98.73 ± 0.05%

99.32 ± 0.07%

recovery of Fe, Mn and Li from mixed type cathodes of spent Li-ion battery is proposed in this work. For the first step, metals are extracted from the cathode using HCl of 6.5 mol L1. With the assistance of amount of H2O2 of 15% vol%, the optimized conditions obtained with L16(45) orthogonal design are as follows: 60  C, leaching time of 2.0 h, S/L of 1:5 and agitation intensity of 1000 r/

Table 8 The economic prospective of the integrated process. Reagent cost ($/t)

Final product benefit ($/t)

HCl

H2O2

[Hbet][Tf2N]

n-butyl xanthate

KMnO4

Na3PO4

FeCl3

MnO2

Li3PO4

100e120

150e200

5000e6000

1300e1400

2200e2300

1000e1100

2000e3000

7000e8000

50,000e55,000

Note: [Hbet][Tf2N] can be prepared by the authors, and it is fully reused. Therefore, the cost should be cut down in the practical operations.

leaching process proposed in this work promises high extraction capability toward Li/Fe/Mn, and only a small quantity of residue can be released to environment; (2) All reagents used have already been widely used and well marketed in many countries, and the relatively expensive flotation reagent can be fully reused; (3) The optimal equilibrium pH range for each of the leaching, flotation or precipitation process increases in a stepwise direction, revealing that unnecessary back and forth pH adjustments will be avoided and large amounts of alkali or acid will be saved; (4) Especially for lithium recovery, it will relieve the shortage and excessive depletion of lithium resources with the increasing utilization of Li-ion battery; (5) It specifies an effective way for the recycling of Fe and Mn in Li-ion battery, since the valuable Ni or Co could be replaced by these low-cost metals in the future. It has been examined that our recycling process can work effectively for spent lithium ion batteries in a hydrometallurgical plant in China.

min. The leaching efficiency of Li, Fe and Mn are 92.15 ± 0.25%, 91.73 ± 0.17% and 89.95 ± 0.11%, respectively. For the second step, Fe ions are selectively separated and recovered by ion floatation. The optimized conditions for Fe recovery in the flotation step are advised as follows: precipitating reagent of 12 g/L, collector of 9 g/L, flotation pH 2.0 and agitation intensity of 1200 r/min. For the third step, Mn and Li ions are selectively precipitated by KMnO4 and Na3PO4, respectively. The advisable precipitation conditions of Mn are equilibrium pH of 2.0 and KMnO4 amount of 0.35 mol L1. The suitable precipitation conditions of Li are equilibrium pH of 7.0 and Na3PO4 amount of 0.20 mol L1. The total recoveries of Li, Fe and Mn are 80.93 ± 0.16%, 85.40 ± 0.12% and 81.02 ± 0.08%, respectively. These metal products (FeCl3, MnO2/Mn2O3 and Na3PO4) could be a source for cathode materials of new batteries or other chemical reagents. The recovering of metals in spent lithium-ion battery cathodes with this stepwise process brings about remarkable economic and environmental benefits.

4. Conclusions Acknowledgments Abandon of valuable metals contained in the cathode materials of spent Li-ion battery causes the waste of resources and environmental problems. A stepwise process with three steps for the

The authors acknowledge the financial supports of the National Science Fund for Young Scholars of China (Nos.51404213 and

564

Y. Huang et al. / Journal of Power Sources 325 (2016) 555e564

51404214) and the Development Fund for Outstanding Young Teachers of Zhengzhou University (No.1421324065).

[19]

References [20] [1] T. Georgi-Maschler, B. Friedrich, R. Weyhe, H. Heegn, M. Rutz, Development of a recycling process for Li-ion batteries, J. Power Sources 207 (2012) 173e182. [2] X. Zeng, J. Li, L. Liu, Solving spent lithium-ion battery problems in China: opportunities and challenges, Renew. Sust. Energ Rev. 52 (2015) 1759e1767. [3] X.L. Zeng, J.H. Li, Spent rechargeable lithium batteries in e-waste: composition and its implications, Front. Env. Sci. Eng. 8 (2014) 792e796. [4] J.J. Jiang, X.X. Zeng, J.H. Li, Feasibility analysis of recycling and disposal of spent lithium-ion batteries in china, Appl. Mech. Mater. 768 (2015) 622e626. [5] S.H. Joo, D. j. Shin, C. Oh, J.P. Wang, G. Senanayake, S.M. Shin, Selective extraction and separation of nickel from cobalt, manganese and lithium in pretreated leach liquors of ternary cathode material of spent lithium-ion batteries using synergism caused by Versatic 10 acid and LIX 84-I, Hydrometallurgy 159 (2016) 65e74. [6] X.C. Wen, J. Tang, T. Zhou, H. Duan, Y. Chen, J. Wang, Recovery of Ti and Li from spent lithium titanate cathodes by a hydrometallurgical process, Hydrometallurgy 147b (2014) 210e216. [7] L.P. He, S.Y. Sun, X.F. Song, J.G. Yu, Recovery of cathode materials and Al from spent lithium-ion batteries by ultrasonic cleaning, Waste Manage 46 (2015) 523e528. [8] L. Yang, G. Xi, Y. Xi, Recovery of Co, Mn, Ni, and Li from spent lithium ion batteries for the preparation of LiNixCoyMnzO2 cathode materials, Ceram. Int. 41 (2015) 11498e11503. [9] J. Xu, H.R. Thomas, R.W. Francis, K.R. Lum, J. Wang, B. Liang, A review of processes and technologies for the recycling of lithium-ion secondary batteries, J. Power Sources 177 (2008) 512e527. [10] 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) 288e293. [11] L. Li, J.B. Dunn, X.X. Zhang, L. Gaines, R.J. Chen, F. Wu, K. Amine, Recovery of metals from spent lithium-ion batteries with organic acids as leaching reagents and environmental assessment, J. Power Sources 233 (2013) 180e189. [12] G.P. Nayaka, J. Manjanna, K.V. Pai, R. Vadavi, S.J. Keny, V.S. Tripathi, Recovery of valuable metal ions from the spent lithium-ion battery using aqueous mixture of mild organic acids as alternative to mineral acids, Hydrometallurgy 151 (2015) 73e77. [13] Rong-Chi Wang, Yu-Chuan Lin, She-Huang Wu, A novel recovery process of metal values from the cathode active materials of the lithium-ion secondary batteries, Hydrometallurgy 99 (2009) 194e201. [14] P. Meshram, B.D. Pandey, T.R. Mankhand, Recovery of valuable metals from cathodic active material of spent lithium ion batteries: leaching and kinetic aspects, Waste Manage 45 (2015) 306e313. [15] X. Zeng, J. Li, B. Shen, Novel approach to recover cobalt and lithium from spent lithium-ion battery using oxalic acid, J. Hazard. Mater. 295 (2015) 112e118. [16] S.H. Joo, D. Shin, C. Oh, J.P. Wang, S.M. Shin, Extraction of manganese by alkyl monocarboxylic acid in a mixed extractant from a leaching solution of spent lithium-ion battery ternary cathodic material, J. Power Sources 305 (2016) 175e181. [17] M.A.H. Shuva, A.S.W. Kurny, Dissolution kinetics of cathode of spent lithium ion battery in hydrochloric acid solutions, J. Instit. E India Ser. D. 94 (2013) 13e16. [18] X. Chen, B. Xu, T. Zhou, D. Liu, H. Hu, S. Fan, Separation and recovery of metal

[21]

[22]

[23]

[24]

[25] [26]

[27]

[28]

[29] [30]

[31]

[32]

[33]

[34] [35]

[36]

values from leaching liquor of mixed-type of spent lithium-ion batteries, Sep. Purif. Technol. 144 (2015) 197e205. A.A. Nayl, M.M. Hamed, S.E. Rizk, Selective extraction and separation of metal values from leach liquor of mixed spent Li-ion batteries, J. Taiwan Instit. Chem. E 55 (2015) 119e125. X. Zhang, H. Cao, Y. Xie, P. Ning, H. An, H. You, F. Nawaz, A closed-loop process for recycling LiNi1/3Co1/3Mn1/3O2 from the cathode scraps of lithium-ion batteries: process optimization and kinetics analysis, Sep. Purif. Technol. 150 (2015) 186e195. J. Li, G. Wang, Z. Xu, Environmentally-friendly oxygen-free roasting/wet magnetic separation technology for in situ recycling cobalt, lithium carbonate and graphite from spent LiCoO2/graphite lithium batteries, J. Hazard. Mater. 302 (2016) 97e104. L. Li, L. Zhai, X. Zhang, J. Lu, R. Chen, F. Wu, K. Amine, Recovery of valuable metals from spent lithium-ion batteries by ultrasonic-assisted leaching process, J. Power Sources 262 (2014) 380e385. X. Zeng, J. Li, Innovative application of ionic liquid to separate Al and cathode materials from spent high-power lithium-ion batteries, J. Hazard. Mater. 271 (2014) 50e56. X. Chen, C. Luo, J. Zhang, J. Kong, T. Zhou, Sustainable recovery of metals from spent lithium-ion batteries: a green process, ACS Sustain. Chem. Eng. 3 (2015) 3104e3113. T. Trager, B. Friedrich, R. Weyhe, Recovery concept of value metals from automotive lithium-ion batteries, Chem. Ing. Technol. 87 (2015) 1550e1557. C. Hanisch, T. Loellhoeffel, J. Diekmann, K.J. Markley, W. Haselrieder, A. Kwade, Recycling of lithium-ion batteries: a novel method to separate coating and foil of electrodes, J. Clean. Prod. 108 (2015) 301e311. Y.F. Huang, W.C. Chai, G.H. Han, W.J. Wang, S.Z. Yang, J.T. Liu, A perspective of stepwise utilisation of Bayer red mud: step twodextracting and recovering Ti from Ti-enriched tailing with acid leaching and precipitate flotation, J. Hazard. Mater. 307 (2016) 318e327. W.I.F. David, M.M. Thackeray, L.A. De Picciotto, J.B. Goodenough, Structure refinement of the spinel-related phases Li2Mn2O4 and Li0.2Mn2O4, J. Solid State Chem. 67 (1987) 316e323. X.L. Zeng, J.H. Li, N. Singh, Recycling of spent lithium-ion battery: a critical review, Crit. Rev. Env. Sci. Tec. 44 (2014) 1129e1165. P. Meshram, B.D. Pandey, T.R. Mankhand, Hydrometallurgical processing of spent lithium ion batteries (LIBs) in the presence of a reducing agent with emphasis on kinetics of leaching, Chem. Eng. J. 281 (2015) 418e427. X. Chen, Y. Chen, T. Zhou, D. Liu, H. Hu, S. Fan, Hydrometallurgical recovery of metal values from sulfuric acid leaching liquor of spent lithium-ion batteries, Waste Manage 38 (2015) 349e356. X. Chen, B. Fan, L. Xu, T. Zhou, J. Kong, An atom-economic process for the recovery of high value-added metals from spent lithium-ion batteries, J. Clean. Prod. 112 (2016) 3562e3570. S. Liang, K.Q. Qiu, Vacuum pyrolysis and hydrometallurgical process for the recovery of valuable metals from spent lithium-ion batteries, J. Hazard. Mater. 194 (2011) 378e384. J. Li, P. Shi, Z. Wang, Y. Chen, C.C. Chang, A combined recovery process of metals in spent lithium-ion batteries, Chemosphere 77 (2009) 1132e1136. rio, Metal separation from K. Provazi, B.A. Campos, D.C.R. Espinosa, J.A.S. Teno mixed types of batteries using selective precipitation and liquideliquid extraction techniques, Waste Manage 31 (2011) 59e64. G. Cai, K.Y. Fung, K.M. Ng, Process development for the recycle of spent lithium ion Batteries by chemical precipitation, Ind. Eng. Chem. Res. 53 (2014) 18245e18259.