Separation of lithium and cobalt from waste lithium-ion batteries via bipolar membrane electrodialysis coupled with chelation

Accepted Manuscript Separation of lithium and cobalt from waste lithium-ion batteries via bipolar membrane electrodialysis coupled with chelation Atsushi Iizuka, Yasunobu Yamashita, Hiroki Nagasawa, Akihiro Yamasaki, Yukio Yanagisawa PII: DOI: Reference:

S1383-5866(13)00220-7 http://dx.doi.org/10.1016/j.seppur.2013.04.014 SEPPUR 11150

To appear in:

Separation and Purification Technology

Received Date: Revised Date: Accepted Date:

6 March 2013 9 April 2013 11 April 2013

Please cite this article as: A. Iizuka, Y. Yamashita, H. Nagasawa, A. Yamasaki, Y. Yanagisawa, Separation of lithium and cobalt from waste lithium-ion batteries via bipolar membrane electrodialysis coupled with chelation, Separation and Purification Technology (2013), doi: http://dx.doi.org/10.1016/j.seppur.2013.04.014

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Separation of lithium and cobalt from waste lithium-ion batteries via bipolar membrane electrodialysis coupled with chelation Atsushi Iizukaa,*, Yasunobu Yamashitab, Hiroki Nagasawac, Akihiro Yamasakid, Yukio Yanagisawac a

Research Center for Sustainable Science and Engineering, Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Sendai, Miyagi 980-8577, Japan b Department of Chemical System Engineering, Faculty of Engineering, The University of Tokyo, 7-3-1 Hongo Bunkyo-ku, Tokyo 113-8656, Japan c Department of Environment Systems, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha Kashiwa, Chiba 277-8563, Japan d Department of Materials and Life Science, Faculty of Science and Technology, Seikei University, 3-3-1 Kichijoji-kitamachi, Musashino, Tokyo 180-8633, Japan *

Corresponding Author: E-mail: [email protected], Phone: +81-022-217-5214

Abstract A new type of process for separating metals in solution, based on bipolar membrane electrodialysis coupled with metal-ion chelation, is proposed. The method was applied to a mixed solution of lithium and cobalt, as in the recycling of waste lithium-ion batteries. When a chelating agent, ethylenediaminetetraacetic acid (EDTA), was added to a mixed solution of lithium ions and cobalt ions, almost all the cobalt ions were chelated by EDTA to form anions, whereas lithium ions were hardly chelated, at pH > 4. Electrodialysis of the feed solution was conducted using a three-cell-type electrodialysis system, with a unit consisting of two ion-exchange membranes and a bipolar membrane. Lithium was transported to the lithium recovery cell and cobalt was transported to the cobalt recovery cell, using an applied electric field. The selectivity for each metal in the recovery cell was about 99%. The effects of initial EDTA concentration and pH were examined. Absorption of metal ions in the ion-exchange membranes was observed; this can be avoided by using a continuous semi-batch operation.

Keywords: Bipolar membrane electrodialysis, Cobalt, Lithium, Separation, Chelate

Abbreviations EDTA: ethylenediaminetetraacetic acid; BPM: bipolar membrane; AEM: anionexchange membrane; CEM: cation-exchange membrane CEM

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1. Introduction We propose a new type of process for separating metals in solution, based on bipolar membrane electrodialysis coupled with metal-ion chelation. The method was applied to a mixed solution of lithium and cobalt, which simulates the solutions generated in the recycling of waste lithium-ion batteries. Lithium-ion batteries are used for various applications such as cellular phones and personal computers because of their high energy density, high stability in charge– discharge cycles, low self-discharging, and low memory effects [1–3]. It is predicted that lithium-ion batteries will be used as power sources for electric vehicles in the near future [4,5]. With the expansion of the market for lithium-ion batteries, the amount of waste lithium-ion batteries will increase. Considering the scarcity of lithium and cobalt resources, effective recycling and recovery processes for lithium and cobalt from waste lithium-ion batteries are required. Various processes for recycling lithium-ion batteries have been proposed, including hydrometallurgical processes [1, 2, 6–11], pyrometallurgical processes [12– 16], and hydro-pyrometallurgical processes [12, 17–20]. The hydrometallurgical recycling of lithium-ion batteries generally consists of four steps: 1. Pretreatment of the waste lithium-ion battery, i.e., deactivation, crushing of the battery to a powder, and physical separation; 2. Dissolution of metals in acids; 3. Separation or fractional recovery of each metal; and 4. Recovery of metals by electrolysis, precipitation, or crystallization. In the third step, separation of metals from solutions is performed using solvent extraction methods, in which an extraction reagent that is highly selective for a target metal ion is used. Solvent extraction is a costly and energy-intensive process. This is mainly because a large amount of waste solvent, which is not easily recycled or reused, is generated in the solvent extraction process. In addition, highly selective reagents for complex formation with target metals are sometimes expensive, and this also increases the recovery costs. Lithium cobalt oxide (LiCoO2) is widely used as a cathode material in lithium-ion batteries [2, 4, 16, 20, 21]. In the recycling of lithium-ion batteries, the cathode is separated from the battery body by dissolution in an acid such as nitric acid after removal of carbon, the anode material, and the electrolyte solution. 2. Principle of cobalt and lithium recovery by electrodialysis The proposed method for separating cobalt and lithium in a mixed solution consists of two steps. In the first step, a chelating agent such as ethylenediaminetetraacetic acid (EDTA) is added to a mixed solution containing lithium and cobalt via electrodialysis. EDTA is dissociated in the following four steps, depending on the ambient pH: [22] H4Y H+ + H3Y−; H3Y− H+ + H2Y2−; H2Y2− H+ + H1Y3−; H1Y3− H+ + Y4−;

K1 = 1.02 × 10−2 K2 = 2.14 × 10−3 K3 = 6.92 × 10−7 K4 = 5.50 × 10−11

2

where H4Y denotes EDTA without proton dissociation. Figure 1 shows the equilibrium ratios of various forms of dissociated EDTA as a function of ambient pH, calculated on the basis of the above EDTA dissociation constants. When the pH is 1, about 90% of EDTA in the solution exists in the nonionic form, H4Y, without dissociation, and only 10% of the EDTA is dissociated to the univalent anion, H3Y−. On increasing the pH, the ratio of dissociated EDTA to multivalent anions such as H2Y2−, H1Y3−, and Y4− increases. When the ambient pH is greater than 12, almost 100% of the EDTA is dissociated to the tetravalent anion, Y4−, in the aqueous phase.

1.0

Fraction [-]

0.8 0.6

[Y]4[H Y]3[H 2Y]2-

0.4

[H 3Y][H 4Y]

0.2 0.0 2

4

6

8 pH [-]

10

12

14

Fig. 1. Ratios of forms of EDTA as a function of ambient pH in aqueous solution.

The chelating equilibrium of EDTA with metal ions can be calculated based on the dissociation constants and chelate formation constants of the metal ions. Figure 2 shows the ratios of metal ions, cobalt and lithium, chelated by EDTA as a function of ambient pH. The ratio of cobalt ions chelated by EDTA increases with increasing pH, and the ratio reaches about 100% when the pH is greater than 4. The valence of the chelated ions depends on the pH, reflecting the dissociated forms of EDTA, i.e., monovalent cation, CoH3Y+ (chelated by H3Y−); neutral, CoH2Y (chelated by H2Y2−); monovalent anion, CoHY− (chelated by HY3−); and bivalent anion, CoY2− (chelated by Y4−). At pH > 12, all the cobalt ions will be chelated by EDTA in the form of a bivalent anion, CoY2−. In contrast, almost negligible quantities of lithium ions are chelated by EDTA at pH < 8. When EDTA is added to a mixed solution containing cobalt and lithium ions at pH > 4, all the cobalt ions will be chelated, but the lithium ions will remain in solution as cations. In addition, when the pH is greater than 8, almost all the cobalt ions will form negative ions (CoHY− or CoY2−), whereas the lithium ions will exist as positive 3

monovalent ions, Li+. Separation of mixtures of anions and cations can be achieved by electrodialysis as a result of these charge differences.

R atio of ED TA com plex [-]

1.0 C o-ED TA Li-ED TA

0.8 0.6 0.4 0.2 0.0 2

4

6

8 pH [-]

10

12

14

Fig. 2. Effect of pH on chelation equilibrium of EDTA with cobalt and lithium.

Figure 3 shows the principle of the lithium and cobalt separation process based on the chelating equilibrium with EDTA. The electrodialysis unit consists of three cells divided by two bipolar membranes (BPM), one anion-exchange membrane (AEM), and one cation-exchange membrane (CEM). The feed solution is introduced to the feed cell, which is divided by two ion-exchange membranes. The cobalt recovery cell is divided by a bipolar membrane and an anion-exchange membrane located at the anode side of the feed cell, where an electrolyte solution is supplied. The lithium recovery cell is divided by a cation-exchange membrane and a bipolar membrane located at the cathode side of the cell, where an electrolyte solution is supplied. The electrodialysis unit consists of these three types of cell and several units are stacked together to form the electrodialysis equipment. At the ends of the stack, two electrode cells, i.e., an anode cell and a cathode cell, are installed. Electrolyte solutions are provided in the electrode cells, and this is where electrolysis takes place. When the pH is greater than 8, almost all the cobalt ions are chelated by EDTA to form bivalent anions, CoY2−, in the feed solution, whereas a negligible proportion of the lithium ions are chelated, and almost all the lithium ions exist as cations in the feed solution. Because of the electric potential applied to the cell, lithium ions will be transported toward the cobalt recovery cell located at the cathode side, through the cation-exchange membrane, whereas chelated cobalt ions will be transported to the lithium recovery cell through the anion-exchange membrane. In the cobalt recovery cell, protons will be provided from the anode side of the bipolar membrane. Cobalt ions 4

chelated by EDTA will therefore be transferred to the cobalt recovery cell, and recovered. In contrast, lithium ions will be transferred to the lithium recovery cell, where hydroxide ions will be transported from the cathode side of the bipolar membrane. Without BPM, only concentration of feed solution can be achieved, however, by utilizing BPM, separation of metal ions can be achieved. The above concept can be widely applied to mixtures of metal ions that have large differences between their chelating equilibrium constants. In previous researches, the use of EDTA to enhance the separation of lithium and cobalt in an extraction process [23], the use of EDTA to enhance the separation of nickel from cobalt [24], and the use of electrodialysis for the recovery of lithium from aqueous solutions [25] were reported. However, separation of lithium and cobalt via bipolar membrane electrodialysis coupled with EDTA has not been reported yet.

Fig. 3. Principle of method for separation of cobalt and lithium based on electrodialysis.

3. Experimental apparatus and method Figure 4 shows the experimental apparatus for the separation of lithium and cobalt mixtures by electrodialysis. The electrodialysis equipment (Type FIV-0) was purchased from the Asahi Glass Company (AGC) Ltd., Japan. The effective membrane area was 117.5 cm2. The gap between the membranes was 0.75 mm. A titanium/platinum electrode was used as the cathode, and an SUS316 plate was used as the anode. The electrodialysis stack consisted of five units of three cells: feed, lithium recovery, and cobalt recovery cells. The cation- and anion-exchange membranes were supplied by AGC (Selemion CMV and Selemion AMV, respectively). Neosepta BP-1E (ASTOM Ltd., Japan) was

5

used as the bipolar membrane. The specifications of the ion-exchange membranes are summarized in Table 1. In Table 2, the basic initial conditions for the feed solution are summarized. The feed solution was prepared from reagent-grade lithium nitrate, cobalt nitrate, and EDTA-2Na salt (Wako Pure Chemical Industries, Japan) dissolved in ion-exchanged water. Sodium hydroxide (special grade, Wako Pure Chemical Industries) was added to the feed solution to control the initial pH at 7.0. As a result, the feed solution contained three types of metal ion: lithium, cobalt, and sodium. Note that chelation of sodium ions with EDTA is negligible at pH < 7. It has been reported that 99.9% of lithium and cobalt ions in powdered LiCoO2 can be extracted by 1 M of nitric acid with 0.8vol% of H2O2 at 75oC after 30 min extraction (S/L = 20 g/L)[26]. The lithium and cobalt concentration in the feed solution used in the study was almost equivalent to those in ten times dilution of the extracted solution. Dilute nitric acid (0.01 M) was supplied to the cobalt and lithium recovery cells. Sodium sulfate solution (0.1 M, special grade, Wako Pure Chemical Industries) was supplied to both electrode cells. The feed solution, lithium recovery solution, and cobalt recovery solution were supplied to the appropriate cells using a liquid tube pump from a tank, with the flow rate set at 0.375 L min−1, and circulated to a tank. The electrodialysis was carried out at a constant electric potential of 20 V with a direct-current power supply. The solution in each flow was sampled for a given interval during the experiments. The metal concentrations in the solutions were measured using inductively coupled plasma atomic-emission spectroscopy (Thermo Jarrell Ash).

6

Fig. 4. Schematic diagram of experimental apparatus for electrodialysis: 1) electrode rinsing solution tank; 2) feed solution tank; 3) lithium recovery solution tank; 4) cobalt recovery solution tank; 5) electrodialysis cell; 6) direct-current power unit; and 7) tube pump. Table 1 Properties of Selemion membranes (AMV and CMV). 3

Apparent density [g/cm ] 2

Effective area [cm ] Water content [%] thickness [mm] Ion exchange capacity [meq/g]

0.95 116 20 0.14 2.0

Table 2 Basic initial conditions of feed solution. Component Concentration [M] Li+ 0.02 2+ Co 0.02 NO30.06 EDTA 0.02 Na+ 0.08 Initial pH 7.0

4. Results and discussion Results using basic initial conditions Figure 5 shows the changes in pH with time in each cell during the electrodialysis. The initial pH values in the cobalt and lithium recovery cells were 2. A rapid increase in the pH in the lithium recovery cell was observed, because hydroxide ions were supplied from the bipolar membrane. After 5 min, the pH in the lithium recovery cell was almost constant, at about 12.5. In contrast, the pH in the cobalt recovery cell gradually decreased with time. This is because of supply of protons generated by the bipolar membrane, but the pH was buffered by EDTA transported from the feed side in the form of chelated ions. In the feed cell, the pH decreased in the initial stage, and became almost constant after 20 min. This can be also explained by the buffering effect of EDTA. Figure 6 shows the current and voltage changes with time during the electrodialysis. The current decreased rapidly as electrodialysis proceeded, especially up to 15 min, and almost no current was observed after 45 min. This is because the feed solution was deionized by the electrodialysis. Figure 7 shows the changes in the total volume of the solution circulating in each cell with time. The volume of solution circulating in the lithium recovery cell slightly increased, and that in the cobalt recovery cell obviously increased with time, whereas that in the feed cell decreased. The increases in the volume in the cobalt and lithium recovery cells were almost equivalent to the decrease in the volume in the feed cell. This result indicates

7

that water flow driven by the electro-osmosis took place from the feed cell to the lithium and cobalt recovery cells during electrodialysis. Furthermore, water flow driven by the osmotic pressure also took place from the feed cell to the cobalt recovery cell. Because of the solution volume variations, the transport of metals through the membranes should be evaluated from the net amounts transported, not from the concentration changes in the cells. Figure 8(a) shows the changes in the amounts of lithium and cobalt in the feed cell with time. The amounts of both lithium and cobalt in the feed cell decreased rapidly with time, and became almost zero after 45 min of electrodialysis. The decrease in the amount of lithium was greater than that of cobalt. The metals in the feed cell were almost completely removed by electrodialysis in 45 min. This result is consistent with the current changes shown in Figure 6. Figure 8(b) shows the changes with time in the amounts of metals in the lithium recovery cell. The amount of lithium increased with time, whereas that of cobalt was almost zero during the experiment. The ratio of lithium in the lithium recovery cell was about 99%, demonstrating that lithium is exclusively recovered in the lithium recovery cell. Figure 8(c) shows the changes with time in the amounts of metals in the cobalt recovery cell. The amount of cobalt increased with time, whereas that of lithium was almost zero up to 45 min. The cobalt selectivity in the cobalt recovery cell was 99%. These results show that cobalt and lithium in the feed solution were separated into the two recovery cells with a high selectivity of 99%. However, the increases in the amounts of metals in the recovery cells were lower than the decreases in the amounts of metals in the feed cell. This discrepancy can be attributed to the absorption of metal ions on the ion-exchange membranes during transport.

14 12

pH [-]

10

Feed cell Co recovery cell Li recovery cell

8 6 4 2 0

10

20

30

40

50

Time [min]

Fig. 5. Changes in pH with time in each cell during electrodialysis.

8

2.0

15

1.5

10

Voltage drop Current

5

1.0

Current [A]

Voltage drop [V]

20

0.5

0 0

10

20

30

40

0.0 50

Time [min]

Fig. 6. Changes with time in current and voltage during electrodialysis.

800

Volume [mL]

600

400

200

Feed cell Co recovery cell Li recovery cell

0 0

10

20

30

40

50

Time [min]

Fig. 7. Volume changes with time for each cell.

9

10

(a) Feed Cell

Amount of metal [mmol]

8

Li Co

6

4

2

0 0

10

20 30 Time [min]

40

50

10

(b) Li Recovery Cell

Amount of metal [mmol]

8 Li Co

6

4

2

0 0

10

20 30 Time [min]

40

50

10

(c) Co Recovery Cell

Amount of metal [mmol]

8 Li Co

6

4

2

0 0

10

20 30 Time [min]

40

50

Fig. 8. Changes with time in amounts of lithium and cobalt in each cell: (a) feed cell, (b) lithium recovery cell, and (c) cobalt recovery cell.

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Effects of operating parameters The separation performances of the present system could be affected by various parameters such as the initial EDTA concentration and the initial pH of the feed solution. Table 3 shows the experimental conditions used to examine the effect of EDTA concentration. The concentration of EDTA was set in the range 0.01 to 0.03 M, which corresponds to a concentration ratio of EDTA to cobalt of 0.5 to 1.5. The initial pH was set at 7.0, and was adjusted by adding sodium hydroxide to the feed solution. This adjustment resulted in an increase in the amount of sodium ions in the feed solution. Figure 9 shows the changes in pH with time in each cell. The pH changes in the lithium and cobalt recovery cells were both almost unaffected by the EDTA concentration. A gradual decrease in the pH of the feed solution was observed for all EDTA concentrations, and the final pH was in the range 4–5, which corresponds to the pH range where almost all cobalt ions are chelated by EDTA. Figure 10 shows the changes with time in the liquid volumes in the cells. Electro-osmosis was observed for all EDTA concentrations, and was highest for an EDTA concentration of 0.02 M, which is the stoichiometric concentration with cobalt ions in the solution. Figure 11 shows the changes with time in the amounts of lithium in the feed cell, in the lithium recovery cell, and in the cobalt recovery cell for different initial EDTA concentrations. The decrease in the amount of lithium in the feed cell decreased with increasing EDTA concentration. However, the effect of EDTA concentration on the increase in the amount of lithium in the lithium recovery cell was less significant than the effect of EDTA on the decrease in the amount of lithium in the feed cell. The transport of lithium ions to the cobalt recovery cell was almost negligible for all EDTA concentrations; the lithium selectivity was more than 95%. Because lithium ions do not form chelates with EDTA, the transport of lithium ions takes place as a result of the potential difference. In the present case, the transport of sodium ions would compete with that of lithium ions. The amount of sodium ions in the feed cell is set higher for the case with a higher initial EDTA concentration to adjust the initial pH of the feed solution to 7. The decrease in the amount of lithium ions in the feed cell could be reduced by increasing the concentrations of sodium ions. The observed gap between the decrease in the amount of lithium in the feed cell and the increase in the amount of lithium in the recovery cell can be attributed to absorption of lithium ions in the cation-exchange membrane. When the EDTA concentration was low, i.e., a lower sodium concentration, a higher amount of lithium would be removed from the feed cell, but some of it would be captured by the cation-exchange membrane; the effect of EDTA concentration on the lithium recovery cell would be less significant than that of the decrease in the amount in the feed cell. Figure 12 shows the changes with time in the amount of cobalt in each cell during the electrodialysis experiments. The amount of cobalt in the feed cell decreased with time, and the decrease was lower at higher EDTA concentrations. The leakage of cobalt into the lithium recovery cell was almost negligible, as shown in Figure 12(b). However, the increase in the amount of cobalt in the cobalt recovery cell was highest for an initial EDTA concentration of 0.02 M, and lowest for an EDTA concentration of 0.03 M. The effect of EDTA could be explained as follows. When the EDTA concentration was 0.01 M, which is half of the initial concentration of cobalt ions, half of the cobalt ions would be chelated by EDTA. With increasing EDTA concentration, the ratio of chelated cobalt ions would increase and the transport of chelated cobalt ions

11

would be enhanced, as shown in Figure 12, up to an EDTA concentration of 0.02 M. When the EDTA concentration was 0.01 M, cobalt ions (Co2+) would be also removed by the absorption in CEM. When the concentration of EDTA was 0.03 M, where excess EDTA was added, the transport of excess EDTA would compete with that of EDTA–Co ions. This is the reason for the decrease in the cobalt recovery rate for 0.03 M EDTA. Table 3 Experimental conditions for investigating effect of EDTA concentration. Component Concentration [M] Li+ 0.02 Co2+ 0.02 0.06 NO3EDTA 0.01 0.02 0.03 Na+ 0.04 0.08 0.11 Initial pH 7.0

14 12 Feed Co

10 8 pH (-)

Li

0.01 M 0.02 M 0.03 M

6 4 2 0 0

10

20

30

40

50

60

Time (min)

Fig. 9. Changes with time in pH in cells during electrodialysis experiments; effect of EDTA concentration.

12

700

Volume [mL]

600 500 Feed Co

400

Li

0.01 M 0.02 M 0.03 M

300 200 0

10

20

30 40 Time [min]

50

60

Fig. 10 Changes with time in volumes in cells during electrodialysis experiments; effect of EDTA concentration.

13

10

(a)

Li in Feed [mmol]

8

0.01 M 0.02 M 0.03 M

6

4

2

0 0

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30 40 Time [min]

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Li in Li recovery cell [mmol]

10 0.01 M 0.02 M 0.03 M

8

(b)

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2

0 0

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20

30 Time [min]

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50

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50

60

Li in Co recovery cell [mmol]

10 0.01 M 0.02 M 0.03 M

8

(c)

6

4

2

0 0

10

20

30 Time [min]

40

Fig. 11. Changes with time in amounts of lithium; effect of EDTA concentration: (a) feed cell, (b) lithium recovery cell, and (c) cobalt recovery cell. 14

10

(a) Co in Feed [mmol]

8 0.01 M 0.02 M 0.03 M

6

4

2

0 0

10

20

30 40 Time [min]

50

60

Co in Li recovery cell [mmol]

10 0.01 M 0.02 M 0.03 M

8

(b)

6

4

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0 0

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30 Time [min]

40

50

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Co in Co recovery cell [mmol]

10

(c) 8 0.01 M 0.02 M 0.03 M

6

4

2

0 0

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30 Time [min]

40

50

60

Fig. 12. Changes with time in amounts of cobalt; effect of EDTA concentration: (a) feed cell, (b) lithium recovery cell, and (c) cobalt recovery cell. 15

The effect of initial pH on the metal recovery performances was investigated. The experimental conditions are summarized in Table 4. The initial pH was changed in the range 4–12 by changing the amount of sodium hydroxide solution in the feed solution. The initial concentration of EDTA was set at 0.02 M, which is stoichiometric with the cobalt ions in the feed solution. Figure 13 shows the pH changes in the solution in each cell for different initial pH conditions. The pH in the feed cell changed toward a pH of about 4 with time, irrespective of the initial pH of the feed solution. This indicates that most of the cobalt ions were chelated during the electrodialysis experiments. In contrast, the pH in the lithium recovery and cobalt recovery cells quickly changed to pH 12 and pH 2, respectively, after starting the experiment, as a result of formation and transport of protons and hydroxide ions in the bipolar membranes. Figure 14 show the changes with time in the amounts of lithium in the feed cell, the lithium recovery cell, and the cobalt recovery cell for different initial pH values. A higher decrease in the amount of lithium in the feed cell was observed when the initial pH was 4. This can be explained by a lower concentration of sodium ions, which would compete with lithium ions. The transport of lithium ions to the cobalt recovery cell was almost negligible for all the initial pH conditions. Figure 15 shows the changes with time in the amounts of cobalt in each cell during the electrodialysis experiments. A higher decrease in the amount of cobalt in the feed cell was observed under lower initial pH conditions. This can be explained by lower concentrations of hydroxide ions, which would compete with cobalt ions. The transport of cobalt ions to the lithium recovery cell was almost negligible for all the initial pH conditions.

Table 4 Experimental conditions for investigating effect of initial pH. Component Concentration [M] + Li 0.02 Co2+ 0.02 NO30.06 EDTA 0.02 Na+ 0.04 0.08 0.12 Initial pH 7.0

16

14 12

pH [-]

10

Feed C o pH 4 pH 7 pH 12

8 6

Li

4 2 0 0

10

20 30 Tim e [m in]

40

50

Fig. 13. Changes with time in pH in cells during electrodialysis experiments; effect of initial pH in feed cell.

17

10

(a)

Li in Feed [mmol]

8 pH 4 pH 7 pH 12

6

4

2

0 0

10

20

30 40 Time [min]

50

60

Li in Li recovery cell [mmol]

10

(b)

pH 4 pH 7 pH 12

8

6

4

2

0 0

10

20

30 40 Time [min]

50

60

Li in Co recovery cell [mmol]

10 pH 4 pH 7 pH 12

8

(c)

6

4

2

0 0

10

20

30 Time [min]

40

50

60

Fig. 14. Changes with time in amounts of lithium in cells; effect of initial pH: (a) feed cell, (b) lithium recovery cell, (c) cobalt recovery cell.

18

10

(a)

Co in Feed [mmol]

8 pH 4 pH 7 pH 12

6

4

2

0 0

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30 40 Time [min]

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Co in Li recovery cell [mmol]

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(b)

pH 4 pH 7 pH 12

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6

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Co in Co recovery cell [mmol]

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(c)

pH 4 pH 7 pH 12

8

6

4

2

0 0

10

20

30 Time [min]

40

50

60

Fig. 15. Changes with time in amounts of cobalt in cells; effect of initial pH: (a) feed cell, (b) lithium recovery cell, and (c) cobalt recovery cell.

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Semi-batch experimental study Because significant amounts of cobalt and lithium in the feed solution were captured and stabilized in the ion-exchange membranes, the recovery rates of these metals using the present method were reduced. To improve the recovery rates, a semibatch experiment was conducted. In this trial, the feed solution was fed to the feed cell and circulated for 30 min, and then fresh feed solution was fed to the feed cell. This change of feed solution was repeated five times every 30 min up to 150 min. In contrast, the solutions introduced to the metal recovery cells were not changed for 150 min. The other conditions are shown in Table 5. The concentrations of metals in the feed cell decreased with time to almost zero after 30 min of operation (Figure 16 (a)). As the number of cycles increased, the removal rate of metal ions in the feed solution was almost unchanged. However, the amount of lithium ions in the lithium recovery cell and that of cobalt in the cobalt recovery cell increased linearly with operating time (Figure 16 (b), (c)). The final concentrations in the metal recovery cells were higher than those in the fresh feed cells. This result indicates that not only can lithium and cobalt in the feed solution be separated by the present system, but concentration of the metals can be achieved using a semi-batch operation. However, from the material balance calculations, the amount of cobalt absorbed in the anion-exchange membrane was saturated after 60 min of operation, and about 50% of cobalt ions supplied would be captured in the anionexchange membrane. The absorption ratio of lithium in the cation-exchange membrane was much lower, at about 20%. Table 5 Initial composition of feed solution for semi-batch experiment. Component Concentration [M] Li+ 0.02 Co2+ 0.02 NO30.06 EDTA 0.02 Na+ 0.08 Initial pH 7.0

20

A m ount of Liand C o [m m ol]

10 (a)

Li Co

8 6 4 2 0 0

30

60 90 Tim e [m in]

120

150

A m ount of Liand C o [m m ol]

40 (b) 30

20

10

Li Co

0 0

30

60 90 Tim e [m in]

120

150

A m ount of Liand C o [m m ol]

40 (c)

Li Co

30

20

10

0 0

30

60 90 Tim e [m in]

120

150

Fig. 16. Changes with time in amounts of lithium and cobalt in cells; (a) feed cell, (b) lithium recovery cell, and (c) cobalt recovery cell.

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5. Conclusion The following conclusions can be drawn from the experimental investigations in this study. Equimolar mixtures of cobalt and lithium ions can be separated using a bipolar membrane electrodialysis method with EDTA chelation; the selectivities for lithium and cobalt in the metal recovery cells were 99%. The lithium recovery rates were higher when the initial concentration of EDTA and the pH were low. The cobalt recovery rates were higher under low initial pH and equimolar EDTA conditions. This is mainly the result of the transport of coexisting ions that would compete with the lithium and cobalt ions. Some proportion of the metals supplied in the feed cell were absorbed and captured in the ion-exchange membranes. The recovery rate can be improved by using a semi-batch-type operation. References 1. P. Zhang, T. Yokoyama, O. Itabashi, T. Suzuki, K. Inoue, Hydrometallurgical process for recovery values from spent lithium-ion secondary batteries, Hydrometallurgy. 47, (1998) 259-271. 2. J. Lin, C. Fan, I. Chang, J. Shiu, Clean process of recovering metals from waste Lithium ion batteries, US patent 6514311B1, (2003). 3. J. Dewulf, G. Van Der Vorst, K. Denturck, H. Langenhovea, W. Ghyootb, K. Vandeputte, Recycling rechargeable lithium ion batteries: Critical analysis of natural resource savings. Resources, Conservation and Recycling. 54, (2010) 229– 234. 4. S. Inagaki, S., Current status and future perspective of lithium ion batteries materials (in Japanese), Aluminium, 17, (2010) 1-4. 5. K. Utsumi, Lithium ion batteries for next generation automobile (in Japanese), Aluminium, 17, (2010) 5-7. 6. W. Maclaughlin, Method for neutralization of hazardous materials, US Patent 5345033, (1994). 7. W. Maclaughlin, T. Adams, Lithium reclamation process, US patent 5888463, (1999). 8. F. Tedjar, J. Foudraz, Method for the mixed recycling of lithium-based anode batteries and cells, US Patent 7820317B2, (2010). 9. S. Kawakami, Method for recovering lithium cell materials, US patent 5882811, (1999). 10. M. Lain, Recycling lithium ion cells and batteries. J. power sources. 97-98, (2001) 736-738. 11. D. Mishra, D. Kim, D. Ralph, J. Ahn, Y. Rhee, Bioleaching of metals from spent lithium ion secondary batteries using Acidithiobacillus ferrooxidans. Waste Manage. 28, (2008) 333–338.

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