Application of heterogeneous ion exchange membranes for simultaneous separation and recovery of lithium and boron from aqueous solution with bipolar membrane electrodialysis (EDBM)

Desalination 479 (2020) 114313

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Application of heterogeneous ion exchange membranes for simultaneous separation and recovery of lithium and boron from aqueous solution with bipolar membrane electrodialysis (EDBM)

T

Deniz İpekçia,d, Nalan Kabaya, , Samuel Bunania,b,e, Esra Altıoka, Müşerref Ardab, Kazuharu Yoshizukac, Syouhei Nishihamac ⁎

a

Ege University, Chemical Engineering Department, 35100 Izmir, Turkey Ege University, Chemistry Department, 35100 Izmir, Turkey The University of Kitakyushu, Department of Chemical Engineering, Kitakyushu, Japan d Süleyman Demirel University, Chemical Engineering Department, Isparta, Turkey e University of Burundi, Department of Chemistry, Bujumbura, Burundi b c

GRAPHICAL ABSTRACT

ARTICLE INFO

ABSTRACT

Keywords: Electromembrane processes Boron Lithium Heterogeneous ion exchange membrane Simultaneous separation and recovery

In this study, heterogeneous ion exchange membranes were tested for separation and recovery of boron and lithium from aqueous solutions with bipolar membrane electrodialysis (EDBM). The results indicated that separation efficiencies and recoveries of both boron and lithium were strongly influenced by the acid and base solutions employed in acid and base cells, flow rate of sample solution and electrical potential applied. It was concluded that separation efficiencies and recoveries of boron and lithium were improved with an increase in the flow rate of sample solution. The highest separation efficiencies were 93% and 69% for lithium and boron, respectively at 50 L/h of sample solution flow rate. The highest recoveries of lithium and boron were achieved as 57% and 41%, respectively at this condition. When electrical potential increased from 15 V to 25 V, boron and lithium separation efficiencies and recoveries obtained were higher. At 30 V of electrical potential, pH of sample solution decreased because of the proton leakage into the sample cell. Since anionic borate ions in sample solution cell were considered to be converted to neutral boric acid, this situation resulted in lower separation efficiencies and recovery of boron from sample solution. By applying optimal process conditions (25 V and 50 L/h of sample solution flow rate), 59% of boron recovery and 73% of lithium recovery were obtained in acid and base cells, respectively.

⁎

Corresponding author. E-mail address: [email protected] (N. Kabay).

https://doi.org/10.1016/j.desal.2020.114313 Received 8 September 2019; Received in revised form 28 December 2019; Accepted 6 January 2020 0011-9164/ © 2020 Elsevier B.V. All rights reserved.

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1. Introduction

was < 10 mg/L while final boron concentration in the concentrate cell was found as 10 g/L. They also proposed three steps to concentrate boric acid. Iizuka et al. investigated simultaneous separation and recovery of lithium by EDBM through chelation by EDTA [29]. They separated mixtures of cobalt and lithium with this method and they obtained a highly selective enrichment for cobalt and lithium in recovery cell. Ji et al. studied on lithium recovery by using ED method with monovalent selective ion exchange membrane to determine applicability of ED for elimination of magnesium and lithium from salt lakes. They found that applied voltage is an important factor for this process [30]. In our previous studies, simultaneous separation and recoveries of boron and lithium from aqueous solutions by EDBM method using homogeneous ion exchange membranes were reported [15,31–33]. In the present study, application of heterogeneous ion exchange membranes was investigated for simultaneous separation and recovery of boron and lithium from aqueous solutions by EDBM method.

Boron is generally found as boric acid, borates or borosilicates in nature [1]. A small increase in boron concentration can cause boron toxicity for some plants even though boron is an important for plants because it is one of the essential elements for the plant cell wall. Boron tolerance limits are varied according to plant species. Therefore, elimination of excess boron from water is important in terms of agricultural irrigation [2,3]. Boron is not only a micronutrient for various plants but it is also an important element in various industries [4]. Boron compounds are used for manufacturing glass and ceramic, production of detergents, other cleaning products, fertilizers, and for metallurgy [5]. Lithium has also wide application areas in industry as an important element. Lithium compounds are utilized as pharmaceutical, refrigerant, special alloy and catalyst [6]. Most importantly, lithium is used in lithium-ion batteries as an energy source since lithium is lightest metal and has high energy density. Lithium ion batteries constitute 37% of rechargeable battery market. It was predicted that lithium demand will increase in the near future to be used for next generation technologies [7,8]. Boron can be found in seawater at a concentration of 4–5 mg/L [9]. Moreover, ground waters also contain trace amounts of boron and lithium [10,11]. Concentration of boron in groundwater can be up to 100 mg/L while lithium concentration in groundwater changed between 10 and 15 mg/L [10,11]. Extraction of lithium from seawater can be also favorable because seawater contains 0.1–0.2 mg/L of lithium. Several methods were applied for elimination of boron and lithium from aqueous solutions. Ion exchange, adsorption-membrane filtration hybrid process, adsorption, electrocoagulation, pressure driven membrane processes, and electromembrane processes were utilized for separation of boron and lithium from aqueous media [12–18]. Electrodialysis (ED) is an environmentally friendly process used for desalination of saline water [19]. This process includes anion and cation exchange membranes. Electrical potential difference between cathode and anode is the main driving force for ED [20,21]. Main application areas for ED are production of process and drinking waters from brackish water, minimization of industrial effluents, production of salt and recovery of valuable compounds [22]. ED and modified ED processes have a small share in membrane market but they have stable share in desalination plants [23]. Ion exchange membranes have important roles in separation by electromembrane processes [24]. They are not categorized according to only their fixed charged groups, but also classified as homogeneous and heterogeneous ion exchange membranes. While charged groups are chemically binded to polymer matrix in homogeneous membranes, they are physically mixed with the matrix in heterogeneous type ion exchange membranes. Heterogeneous ion exchange membranes are less preferred than homogenous ones due to high energy consumption in ED operations [25,26]. EDBM method is an integration of ion exchange membranes with bipolar membranes in an ED stack. Bipolar membranes are special kinds of ion exchange membranes that are constituted of cation and anion exchange membranes combined with a hydrophilic layer between them. During an EDBM operation, water molecules in hydrophilic layer of bipolar membranes dissociate into H+ and OH– ions by electrical potential applied as driving force. Anions that pass through the anion exchange membrane combine with hydrogen ions coming from bipolar membranes. Simultaneously, cations transported through the cation exchange membrane react with hydroxyl ions coming from bipolar membranes. Thus, acid and base solutions are produced in acid and base cells by EDBM operation [23]. Turek et al. used ED method for elimination of boron from aqueous solution. They achieved a maximum boron removal as 97% by using homogeneous ion exchange membranes [27]. Noguchi et al. used multistep EDBM in order to separate and recover boron from aqueous solution [28]. They reported that final boron concentration in diluate

2. Experimental Mega EDR-Z-FULL-V4 type lab-scale ED system was used to conduct EDBM experiments. This system includes 10 anion exchange membranes, 11 cation exchange membranes and 10 bipolar membranes. Properties of heterogeneous ion exchange membranes involved in ED system are given in Table 1. The flow scheme of Mega EDR-Z-FULL-V4 type ED system was shown in Fig. 1. The sample solution (2 L) was prepared from Li2B4O7.5H2O to carry out the experiments. This model solution contains 812 ± 56.15 mg B/L and 256 ± 33.11 mg Li/L. In acid and base cells, 500 mL of 0.003 M HCl and 500 mL of 0.003 M NaOH solutions were used, respectively. A 0.1 M NaOH solution (250 mL) was employed in the electrode cell. In our experiments, firstly sample solution was fed to ED stack without applying any electrical potential in order to control the circulation of feed solution in the ED stack. System performance was assessed by calculating removal efficiencies (S, %), percent recoveries of lithium and boron in acid and base cells (β, %), mass flux (J, mol/m2s), mass transfer coefficient (k, m/s), and specific power consumption (ESPC, kWh/m3) by applying following equations [16]:

S (%) =

=

Crt n

Ci

100(C0 C0

C)

(1)

100

(2)

J = kC

(3)

J = (V/A)dC/dt

(4)

ln(C/Co) =

(5)

k (A/V)t

Table 1 Characteristics of membranes in EDBM system. Ion exchange membrane Ion exchange group Matrix Ion exchange capacity (meq/g) Thickness (mm) Dry Swelled Electrical resistance (ohm-cm2) Changes during swelling (%) Thickness Length Width Weight

2

Cation exchange −

Anion exchange

R SO3 Polyethylene 2.2

R−(CH3)3N+ Polyethylene 1.8

< 0.45 < 0.70 <8

< 0.45 < 0.75 < 7.5

<3 <4 < 65 < 60

<3 <4 < 65 < 65

−

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Fig. 1. A flow sheet of EDBM system.

ESPC =

E

t 0

50 L/h of flow rate (Table 2). However, recoveries were lower when feed flow rate of sample solution was 30 L/h (Table 2, Figs. 2b and 3b). Maximum recoveries of lithium and boron were found as 57% and 41%, respectively at this condition as summarized in Table 2. Decreasing flow rate of sample solution led to an increase in sample solution contact time with membranes and this situation might probably result in partial adsorption of borate and lithium ions on the membrane surface. Bearing in mind the results obtained at a flow rate of 30 L/h, it was considered that experimental period should be increased at low flow rates. Since optimum flow rate of sample solution was determined as 50 L/h, all tests after this step were conducted at 50 L/h of flow rate.

Idt

V

(6)

The concentration of boron in samples was analyzed by Azomethine-H method using Jasco V-530 model UV/Vis spectrophotometer while lithium concentration was determined by atomic absorption spectrometer using Shimadzu AA7000 model AAS. 3. Results and discussion 3.1. Influence of sample solution flow rate The influence of feed flow rate on separation performance of Mega EDR-Z-FULL-V4 type ED system having heterogeneous Ralex ion exchange membranes for removal and recovery of boron and lithium from aqueous solution was investigated. For this, two different sample solution flow rates of 30 L/h and 50 L/h were tested. For EDBM tests, 0.003 M HCl and 0.003 M NaOH solutions were employed in acid and base cells, respectively, taking into consideration our previous studies. When it compared to our earlier studies carried out by homogeneous ion exchange membranes, in this case the tests were carried out using lower initial acid and base concentrations in acid and base cells. However, as evidenced by Rubinstein et al., electrolyte concentrations near the conductive areas of homogeneous membranes are higher than those obtained by heterogeneous membranes because of the fact that local current density is higher than homogenous ones for heterogeneous ion exchange membranes [34]. Therefore, low initial acid and base concentrations in acid and base cells were chosen this time. A 15 V of electrical potential was applied to EDBM stack while lithium and boron concentrations were kept constant as 256 ± 33.11 mg/L and 812 ± 56.15 mg/L, respectively in the feed solution for each test. According to the results, it was obtained that there was no valuable difference for separation efficiencies of lithium and boron at 30 L/h and 50 L/h of feed flow rates as shown in Figs. 2a and 3a. Maximum separations of lithium and boron were 93% and 69%, respectively at

3.2. Influence of electrical potential applied For these tests, 0.003 M HCl and 0.003 M NaOH solutions in acid and base cells were used. The studies were performed using electrical potentials of 15, 20, 25 and 30 V. As it can be seen from Figs. 4a and 5a, when electrical potential applied was high, separation rates of lithium and boron from the sample solution increased. The maximum removal of lithium was 93% when electrical potential was 15 V. Maximum removal of lithium was 99% at 20 V and 30 V (Table 2 and Fig. 4a). As depicted in Table 2, maximum boron removal was 69% under 15 V of electrical potential. It was seen that if electrical potential increased, separation rate of boron became faster (Fig. 5a). When 25 V and 30 V of electrical potentials were applied, boron removal reached 74% at both electrical potentials at the end of two-hour test (Table 2). Recovery of lithium was higher than boron recovery and it increased more rapidly with increasing electrical potential (Fig. 4b and Table 2). Maximum recoveries of lithium were 57%, 66%, 73%, and 74% when electrical potentials applied were 15, 20, 25 and 30 V, respectively (Table 2). Parsa et al. observed the similar phenomenon while they were working on recovery of lithium from lithium bromide solution that contains sodium by ED method. The authors applied 3 V, 5 V, and 7 V of 3

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electrical potentials to sample solution and 1.5%, 4.5% and 14% of lithium recoveries were obtained, respectively [35]. In terms of boron recoveries, increasing electrical potential from 15 V to 25 V resulted in an increased boron recovery in acid cell (Fig. 5b). Additionally, the recovery of boron at a potential of 30 V was higher than that at 25 V before 70 min. However, when the experiment was carried out for 70 min, the recovery rate of boron by applying a potential of 25 V was higher than that of at 30 V. The possible reason of this situation is that when 30 V of electrical potential was applied to system, removal rate of borate ions increased. This might cause to an increase in boron concentrations accumulated on anion exchange membrane surfaces due to the fact that partial adsorption of borate ions on the membrane surface increased after 70 min. This was resulted in decreasing recovery rate of borate ions after 70 min. On the other hand, separation of boron was achieved rapidly at 30 V but pH value of the sample solution showed a faster decline at this voltage than at electrical potentials lower than 30 V as seen in Fig. 6. It was considered that borate ions in the sample cell were converted into boric acid in molecular form at 30 V of electrical potential applied. Since boric acid is not charged, it cannot be transferred to the acid cell easily. Therefore, it was concluded that pH is another important factor on recovery of boron. The main reason of the decrease in pH of the sample solution is considered to be proton leakage from acid cell to the sample cell at especially when a high electrical potential applied to EDBM stack. This situation was considered not to be related with using homogeneous or heterogeneous ion exchange membranes. According to the obtained results here and in the literature, it was considered that proton leakage can occur while using both homogeneous and heterogeneous ion exchange membranes in EDBM stack [15,35]. This problem might be solved by changing the membrane stack configuration. According to the obtained results in this study, maximum boron recovery was 59% at 25 V while maximum lithium recovery was 73% at 25 V of electrical potential applied. Since there was no significant difference in boron and lithium recoveries when electrical potential was increased to 30 V, optimum electrical potential was accepted as 25 V (Table 2). Bunani et al. observed similar results while working with PC-Cell EDBM system having homogeneous ion exchange membranes [15]. The authors performed their EDBM tests using electrical potentials in a range of 10–18 V and obtained that pH of sample solution showed a faster decline at 18 V. They found that maximum removals of boron from sample cell were around 62%, 74%, 75% and 75% at 10 V, 13 V, 15 V, and 18 V, respectively. Respective maximum boron recoveries were found as 29%, 60%, 64%, and 53% at 10 V, 13 V, 15 V and 18 V with PC-Cell EDBM system having homogeneous ion exchange membranes [15]. Bunani et al. used also Astom Acilyzer EDBM system having homogeneous Neosepta membranes [31]. The separation performance of EDBM process was found to be influenced by the electrical potential applied [31]. It was reported that applying an electrical potential which is higher than the optimum value did not significantly increase the system performance. It was concluded that an electrical voltage between 28 and 30 V was enough to achieve a > 94% of separation efficiency for both boron and lithium. Applying an electrical potential which is > 30 V resulted in deviation of linearity between separation and voltage applied. Similar trend was also seen for recovery data [36]. Separations and recoveries of lithium and boron could not be achieved as equal even at optimum electrical potential. As explained before, the reason of this situation could be due to partial adsorptions of boron and lithium on membrane surfaces. This problem might be solved by increasing experimental period but this situation may be led to a slight increase in cost of BMED. In the literature, it was stated that using heterogeneous ion exchange membranes in ED processes often requires more electrical consumption than by using homogeneous ion exchange membranes. Additionally, it is well-known that heterogeneous ion

300 (a)

250

CLi (mg/L)

200 150 100 30 L/h

50

50 L/h 0 0

40

80

120

Time (min) 700 30 L/h

CLi (mg/L)

600

50 L/h

500 400 300 200 100

(b)

0 0

40

80

120

Time (min)

CB (mg/L)

Fig. 2. Removal of lithium from sample compartment at different feed flow rates (a); recovery of lithium in base compartment at different feed flow rates (b).

900 800 700 600 500 400 300 200 100 0

(a)

30 L/h 50 L/h 0

40

80 Time (min)

120

CB (mg/L)

1600 1400

30 L/h

1200

50 L/h

1000 800 600 400 200 (b)

0 0

40

80 Time (min)

120

Fig. 3. Removal of boron from sample compartment at different feed flow rates (a); recovery of boron in acid compartment at different feed flow rates (b).

4

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Table 2 Experimental results obtained with EDBM system having heterogeneous ion exchange membranesa. SPC (kWh/m3)

Acid and base solutions in acid and base cells

Electrical potential (V)

Flow rate (L/h)

pH

RB (%)

RLi (%)

0.003 M HCl 0.003 M NaOH 0.003 M HCl 0.003 M NaOH 0.003 M HCl 0.003 M NaOH 0.003 M HCl 0.003 M NaOH 0.003 M HCl 0.003 M NaOH 0.003 M H3BO3 0.003 M LiOH

15

30

9.19 ± 0.07

62

88

21

30

3.23

15

50

9.19 ± 0.07

69

93

41

57

1.98

20

50

9.19 ± 0.07

72

99

55

66

3.21

25

50

9.19 ± 0.07

74

99

59

73

4.11

30

50

9.19 ± 0.07

74

99

50

74

5.66

25

50

9.19 ± 0.07

77

99

51

72

4.40

a

Li (%)

B (%)

Sample solution (2 L): 812 ± 56.15 mg B/L and 256 ± 33.11 mg Li/L.

300 15 V 250

20 V 25 V

CB (mg/L)

CLi (mg/L)

200

30 V

150 100 50 (a)

900 800 700 600 500 400 300 200 100 0

0

15 V 20 V 25 V 30 V 0

0

20

40

60 80 Time (min)

100

(b)

CB (mg/L)

700 600 500 400

15 V 20 V 25 V 30 V

300 200 100

20

40

120

800

CLi (mg/L)

(a)

2000 1800 1600 1400 1200 1000 800 600 400 200 0

60 80 Time (min)

100

120

15 V 20 V 25 V 30 V

(b)

0

20

40

60

80

100

120

0 0

20

40

60 80 Time (min)

100

Time (min)

120

Fig. 5. Removal of boron from sample compartment at different electrical potentials (a); recovery of boron in acid compartment at different electrical potentials (b).

Fig. 4. Removal of lithium from sample compartment at different electrical potentials (a); recovery of lithium in base compartment at different electrical potentials (b).

10.00 9.00 pH of the sample solution

exchange membranes are less expensive than homogenous ones [37,38]. In our previous study [33], the highest removal efficiencies and recoveries of boron were 86.9% and 49.8%, respectively at optimum conditions (0.05 M HCl and 0.05 M NaOH in acid and base cells, respectively at 30 V of electrical potential) while working with homogenous Neosepta ion exchange membranes. The highest removal efficiencies and recoveries of lithium were also found as 94.7% and 62.0%, at optimum conditions. Compared with our previous study carried out with homogenous ion exchange membranes, optimum initial acid and base concentrations in acid and base cells and optimum electrical potentials employed in this study were lower while working with heterogeneous ion exchange membranes. Additionally, recoveries of lithium and boron were higher at optimum experimental conditions with heterogeneous ion exchange membranes. Removal efficiency of boron was higher while removal

8.00 7.00 6.00 5.00 4.00 15 V

3.00

20 V

2.00 25 V

1.00 30 V

0.00 0

20

40

60 80 Time (min)

100

120

Fig. 6. pH of the sample solution at various electrical potentials.

5

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0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10

3.5 30 L/h 50 L/h

3

ESPC (kWh/m3)

In (CLi/CLi0)

D. İpekçi, et al.

2.5 2 1.5 1

0.003 M HCl-0.003 M NaOH

0.5

0.003 M H3BO3-0.003 M LiOH

0

0

20

40

60

80

100

120

0

40

80

120

Time (min)

Time (min)

Fig. 9. SPC values calculated at two different flow rates.

Fig. 7. Linearization of lithium separation data for different acid and base solutions used in acid and base compartments.

0

6.00 ESPC (kWh/m3)

5.00 In(CB/CB0)

-1

-2

4.00 3.00 120

2.00

90

1.00 0.00

0.003 M HCl-0.003 M NaOH

60 15 20

0.003 M H3BO3-0.003 M LiOH 0

20

40

60 Time (min)

80

100

30

25 Electrical Potential (V)

-3 120

30

Fig. 10. SPC values vs.time plots obtained at different electrical potentials.

Fig. 8. Linearization of boron separation data for different acid and base solutions used in acid and base compartments.

5.00 4.50

efficiency of lithium was lower at optimum experimental conditions with homogeneous ion exchange membranes [32].

ESPC (kWh/m3)

4.00

3.3. Influence of acid/base solutions used in acid/base recovery cells Influence of types of acid and base solutions employed in acid and base cells was examined while HCl and NaOH solutions were changed with H3BO3 and LiOH solutions in acid and base cells, respectively. Main goal of this change is to prevent extra purification step to acquire H3BO3 and LiOH as acid and base products after EDBM process. These tests were performed under 25 V of electrical potential. For this, 0.003 M H3BO3–0.003 M LiOH and 0.003 M HCl-0.003 M NaOH solutions were used in acid and base cells. Linearized plots of lithium and boron separations versus time as a function of different acid and base solutions in acid and base cells were shown in Figs. 7 and 8, respectively. The small differences between data points in linearization graphs for lithium and boron at these two conditions were considered to be stemmed from small difference in separations of lithium and boron. When linearized graphs of lithium and boron separations were compared with literature, it can be clearly seen that much better linear relationships were obtained with homogeneous Neosepta ion exchange membranes [31]. Since homogeneous ion exchange membranes are thinner than heterogeneous ion exchange

3.50 3.00 2.50 2.00 1.50 1.00

0.003 M HCl-0.003 M NaOH

0.50

0.003 M H3BO3-0.003 M LiOH

0.00 0

40

80

120

Time (min) Fig. 11. SPC values calculated for different acid and base solutions used in acid and base compartments.

membranes, such result was considered to be reasonable. Thus, it can be considered that the concentration profile becomes a function of both time and membrane thickness. Mass transfer coefficients of lithium and boron were calculated using the data obtained by different acid and base solutions in acid and base cells. The results were given in Table 3 briefly. Mass transfer coefficients of boron and lithium did not change significantly in two

Table 3 Mass transfer coefficients of boron and lithium calculated for different acid and base solutions used in acid and base cells. Acid-base solutions in acid-base chambers

Electrical potential (V)

Flow rate (L/h)

pH

kB*105 (m/s)

kLi*105 (m/s)

0.003 M HCl-0.003 M NaOH 0.003 M H3BO3–0.003 M LiOH

25 25

50 50

9.19 ± 0.07 9.19 ± 0.07

0.63 0.63

3.13 3.14

6

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Table 4 Separation and recovery of lithium from aqueous solutions by using different methods. Method

Operating conditions

Feed solution

Efficiency

ED EDBM

2V 26 V

βLi = 22.2% [39] Desorption rate = 70% [40]

EEDBMa NF HCDIb

15 V 298 K, 3.5 MPa 2 V, 25 °C

EDBM

30 V, 01 M HCl-0.1 M NaOH, Neosepta CMB, AHA BP-1E membranes

37.7 μ g/L Li in HCl 6 g of LiMn2O4 dissolved in 500 mg/L of LiCl 879 mg Li/L MgCl2·6H2O (58.0 g/L); LiCl (1.25 g/L) Geothermal water containing 15.7 mg Li/L Model solution containing 340 mg Li/L

EDBM

15 V, 0.5 L sample solution 3 mM HCl-3 mM NaOH PC SK-PC Acid 60, PC-bip membranes 30 V, 2 L sample solution 5 mM HCl-5 mM NaOH 3 mM HCl-3 mM NaOH 25 V, 50 L/h of sample solution flow rate

EDBM This study a b

Production of Li2CO3 (95% purity) [41] 99% yield of lithium [42] SLi = 73% [10]

Model Solution containing 250 mg Li/L

SLi = 97.8% βLi = 20.0% [31] SLi = 99.6% βLi = 88.3% [15]

Model solution containing 340 mg Li/L Model solution containing 256 ± 33.11 mg Li/L

SLi = 94.7 βLi = 62.0% [32] SLi = 99.0% βLi = 73.0%

EEDBM is electro-electrodialysis with bipolar membrane. Hybrid capacitive deionization method.

Table 5 Separation and recovery of boron from aqueous solutions by using different methods. Method

Operating conditions

Feed solution

Efficiencya

RO

TFN membrane, 55 bar TFC membrane, 55 bar 250 mL solution/mL resin pH = 9, 75 °C-80 °C 17.4 mA/cm2, pH = 6.3, room temperature First stage RO: 69 atm Second stage RO: 68 atm 30 V, Neosepta CMB, AHA membranes

Model solution including 5 mg/L H3BO3

SB = 99.2%

20 V, 4 cell Neosepta CMX, AMX membranes, Purolite CT175Purolite A500TL 15 V, 0.5 L sample solution 3 mM HCl-3 mM NaOH PC SK-PC Acid 60, PC-bip membranes 30 V, 2 L sample solution 5 mM HCl-5 mM NaOH 3 mM HCl3 mM NaOH 25 V, 50 L/h of sample solution flow rate

RO permeate of geothermal water containing 3.98–5.36 mg B/L

Ion Exchange Electrocoagulation ED-RO integrated system

EDBM EDI EDBM EDBM This study

a

SB = 82.3% [43] Geothermal water including 19 mg/L boron

SB = 99% [44]

10.4 mg/L H3BO3 solution Mixed solution containing 132 mg B/lt

SB = 99.7% [45] 3.9 kg/h H3BO3(s) produced [46]

Model Solution containing 1000 mg B/L

SB = 97.8% βB = 39.1% [31] Product water < 0.20 mg B/L SB = 95.3% [47] SB = 72.3% βB = 70.8% [15] SB = 86.9% βB = 50.0% [32] SB = 74.0% βB = 59.0%

Model Solution containing 850 mg B/L Model solution containing 1000 mg B/L Model solution containing 812 ± 56.15 mg B/L

SB: Separation of boron; βB: Recovery of boron.

different cases since separation rates of boron and lithium were also not influenced when different acid and base solutions were employed in acid and base cells. On the other hand, mass transfer coefficients of boron calculated were lower than those of lithium. This result was in good agreement with separation data obtained for boron, lithium (Figs. 7 and 8), and also with literature data [31].

consumption by pumping the sample solution also. The ESPC values were estimated as 3.23 kWh/m3 and 1.98 kWh/m3 at the end of 2 h for 30 L/h and 50 L/h of feed flow rates, respectively. It was concluded that ESPC required for ion transfer from the membranes decreased when the flow rate of the feed solution was increased. An increase in flow rate of the sample solution resulted in the reduction of partial adsorption of ions on the membrane, thus transfer of ions through membranes was carried out easily. ESPC increased with increasing applied electrical potential as it was expected. Compared to our previous study [33] carried out with homogeneous ion exchange membranes, energy consumption obtained with heterogeneous ion exchange membranes employed in this study was found less at optimum experimental conditions. It was determined that ESPC values can be lower while working with heterogeneous ion exchange membranes, if more boron and lithium are recovered at low electrical potentials by using low concentrations of acid and base solutions in acid and base cells. At 25 V when 0.003 M HCl and 0.003 M

3.4. Specific power consumption (ESPC) Specific power consumptions (ESPC) were calculated for two different feed flow rates, different applied electrical potentials, and different acid/base solutions employed in acid and base recovery cells. As shown in Fig. 9, ESPC decreased with increasing feed flow rate. However, in this case, it would not be right to do the cost analysis based solely on ESPC due to electrical energy consumed by ion transport. Increasing flow rate of the solution led to an increase in electrical 7

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NaOH solutions were used in acid and base cells, respectively, ESPC value calculated was 4.11 kWh/m3 at the end of the process (Fig. 10 and Table 2). Using H3BO3 and LiOH solutions instead of HCl and NaOH solutions in acid and base cells, respectively under the constant electrical potential (25 V) resulted in a slight increase in ESPC value calculated for EDBM system with heterogeneous membranes (Fig. 11). In our previous study performed with homogenous Neosepta ion exchange membranes, when H3BO3 and LiOH solutions were used in acid and base cells, similar result was obtained. On the other hand, using H3BO3 and LiOH solutions in acid and base cells with higher concentrations is needed in case of EDBM system having homogeneous ion exchange membranes [32]. According to the results obtained in this study, using less concentration of H3BO3 and LiOH solutions in acid and base cells was adequate while using heterogeneous ion exchange membranes.

interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgement This work was supported by bilateral TÜBİTAK-JSPS project between Turkey and Japan by TÜBİTAK (Project No. 214M360). The authors would like to thank TÜBİTAK, Turkey and JSPS, Japan for their financial supports. References [1] M. Tagliabue, P.A. Reverberi, R. Bagatin, Boron removal from water: needs, challenges and perspectives, J. Clean. Prod. 77 (2014) 56–64. [2] N. Kabay, E. Güler, M. Bryjak, Boron in seawater and methods for its separation, Desalination 261 (2010) 212–217. [3] A.M. Wimmer, T. Eichert, Review: mechanisms for boron deficiency-mediated changes in plant water relations, Plant Sci. 203-204 (2013) 25–32. [4] P.Y. Tang, L. Luo, Z. Thong, T.S. Chung, Recent advances in membrane materials and technologies for boron removal, J. Membr. Sci. 541 (2017) 434–446. [5] C. Neal, J.R. Williams, J.M. Bowes, C.M. Harras, M. Neal, P. Rowland, H. Wickham, S. 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4. Conclusions The results of separation and recovery of lithium and boron by EDBM method employed in this study and other methods were compared in Tables 4 and 5. In the view of removal efficiency and recovery of lithium from aqueous solution, promising results were obtained in this study when compared to other methods given in the literature. When removal efficiency and recovery of boron from aqueous solutions were compared, it was seen that percent recovery of boron was highly competitive although removal efficiency of boron was not so high. It was concluded that heterogeneous ion exchange membranes employed in EDBM system can be also used for simultaneous separation and recovery of boron and lithium from aqueous solutions. Author statement Deniz İpekçi: Data collection, calculations, writing. Nalan Kabay: Coordinating the research work, supervising, reviewing and editing. Samuel Bunani: Assisting in the laboratory work. Esra Altıok: Lithium analyses. Müşerref Arda: Evaluating analytical measurement results. Kazuharu Yoshizuka: partnership in international research project, data evaluation. Syouhei Nishihama: partnership in international research project, data evaluation. Nomenclature Co C Crt n E I V J t A k

Concentration of species at beginning of the process in sample chamber (lithium and boron) (mg/L) Concentration of boron or lithium in sample solution at the end of 2 h of experimental time (mg/L) Concentration of species in acid and base chambers at the end of 2 h experimental time (mg/L) Proportion of sample solution volume at the beginning to acid /base solutions volume at the beginning in acid and base chambers Electrical potential (V) Electrical current (A) Volume of the sample solution (m3) Mass flux (mol/m2s) time (s) Effective membrane area (m2) Mass transfer coefficient of boron or lithium (m/s)

Declaration of competing interest The authors declare that they have no known competing financial 8

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