Production of Lithium Hydroxide from Lake Brines through Electro

Article pubs.acs.org/IECR

Production of Lithium Hydroxide from Lake Brines through Electro− Electrodialysis with Bipolar Membranes (EEDBM) Chenxiao Jiang, Yaoming Wang, Qiuyue Wang, Hongyan Feng, and Tongwen Xu* Laboratory of Functional Membranes, School of Chemistry and Material Science, University of Science and Technology of China, Hefei 230026, China ABSTRACT: To investigate the feasibility of a novel method to produce LiOH from lithium contained brine, A lab-scale electro−electrodialysis with bipolar membrane (EEDBM) was installed with an arrangement of bipolar membrane−cation exchange membrane−bipolar membrane−cation exchange membrane in series. Conventional electrodialysis (CED) stack configured with repeat-arranged five cation exchange membranes and four anion exchange membranes was installed as a pretreatment process. After preconcentrating and precipitating brine with CED and Na2CO3, a high purity of ca. 98% Li2CO3 powder was obtained. The influence of current density and feed concentration on the production of LiOH was investigated. EEDBM Process cost is estimated to 2.59 $/kg at current density of 30 mA/cm2 and feed concentration of 0.18 M. It can be inferred that lower energy consumption would be obtained at the case of scaling up. Considering the environmental aspects, the corporate process for LiOH production is also mutually beneficial.

1. INTRODUCTION Lithium compounds are finding a commercial increase in production of glass and ceramic, air conditioning refrigeration systems, primary and second batteries, and nuclear energy production. However, most of them require high quality with low level of impurities. Lithium is often recovered from lithium minerals and nature brines.1−3 However, brine generally has low concentration of lithium. For example, the brine of Zabuye Lake in China contains only about 800−1500 ppm of lithium.3 Lithium hydroxide is a widely used raw material in industry. It has been used as lithium-based lubricant greases due to its high resistance to temperature and production of inks, principle chemical absorbent used as a carbon dioxide scrubber material in shuttle spacecraft,4 lithium ion and lithium polymer chargeable and dischargeable batteries.5,6 The basic process to produce lithium hydroxide is via an aqueous causticization reaction between lime (Ca(OH)2) and Li2CO3, as shown in eqs 1 and 2. These processes produce approximately 3% lithium hydroxide aqueous solution, from which lithium hydroxide is obtained through concentrating and crystallization. Battery application typically requires high levels of lithium hydroxide with trace sodium, calcium, and chlorides. It is very difficult to obtain lithium hydroxide with low calcium level when using calcium-based compound such as lime. Additional purification step will increases manufacture time and cost.7 Moreover, these processes often produce voluminous precipitates of CaCO3 which is a pollutant to the environment and it would induce large loss of Li+, due to its low yield of lithium hydroxide in water. CaO + H 2O → Ca(OH)2 + heat

(1)

Ca(OH)2 + Li 2CO3 → 2LiOH (aq) + CaCO3

(2)

usually composed of repeated arranged monopolar membrane alternatively between two parallel electrodes that divide stack into unit of dilute or concentrate compartment. Under reverse current bias, corresponding ions will migrate from dilute compartment to concentrate compartment across corresponding membrane. As aforementioned, low concentration of lithium brine, which was previously purified to remove magnesium and calcium, will be concentrated and then used to extract lithium as Li2CO3 form by adding of Na2CO3. It will significantly reduce process cost and time to extract lithium from lake brines. Electrolysis with ion exchange membrane has been introduced to produce high purity lithium hydroxide with LiCl, Li2SO4, or Li2CO3.16,17 Normally, the electrolysis stack contains only one sheet cation exchange membrane between two inert electrodes; it is hard to produce sufficient lithium hydroxide to meet growing demand of market even though the setup is scaled up. Thus, a bipolar membrane is introduced into electrolysis stack to configure electro−electrodialysis bipolar membrane (EEDBM) stack for producing lithium hydroxide in this work. A bipolar membrane is composed from an anion exchange layer, cation exchange layer, and a thin hydrophilic polymer interlayer between them. It can dissociate water into H+ and OH− under bias of potential gradient at the junction, which can be further used as the sources of acids and bases for cleaning production and environmental protection,18 such as fuel-gas desulfurizing agents regeneration,19 CO2 gas treatment,20−22 biotechnology,23−25 chemical industry,26−28 and organic acid production.29−33 Under specific configuration of EEDBM stack, purified Li2CO3 feed solution from CED stack is pumped into the feed compartment, Li+ will migrate through

Conventional electrodialysis (CED) is a cost-effective process that has been widely used in the field of water treatment,8−11 purification of biological solution,12 and demineralization of mixed feed.13−15 Electrodialysis stacks are © 2014 American Chemical Society

Received: Revised: Accepted: Published: 6103

December March 12, March 14, March 14,

21, 2013 2014 2014 2014

dx.doi.org/10.1021/ie404334s | Ind. Eng. Chem. Res. 2014, 53, 6103−6112

Industrial & Engineering Chemistry Research

Article

Table 1. Types of Membranes and Their Properties membrane type

thickness (μm)

IECa (meq·g−1)

area resistanceb (Ω·cm2)

water uptakec (%)

transport no. (%)

JAM-II-05 JCM-II-05 Neosepta CMX Neosepta BP-1

160−230 160−230 164 200−350

1.8−2.2 2.0−2.9 1.62

4−8 1−3 2.91

24−30 35−43 18 23

90−95 95−99 98 >98

IEC was determined by titration in meq·g−1 in Cl− and Na+ form for AEM and CEM, respectively. bMembrane area resistance was measured in 0.1 M NaCl @T = 25 °C. cWater uptake/swelling degree were determined by equation of gH2O/gdry.

a

Figure 1. Schematic diagrams and configuration of CED and EEDBM stack for producing lithium hydroxide.

cation-exchange membrane and combine with OH− to form LiOH in base and cathode compartments. Compared with a single EDBM, EEDBM will not only maximize process capacity but also increase current efficiency, since it can fully utilize OH− produced from cathode reaction. In this work, the EEDBM process, which combines electrolysis with bipolar membrane electrodialysis, is initiated to produce LiOH at base and cathode compartments. Effect of current density and feed concentration on the production of LiOH will be discussed, and to evaluate feasibility of this novel process, energy consumption and current efficiency will be calculated as well.

Sinopharm Chemical reagent Co., Ltd. The lithium brine was simulated by dissolving LiCl, MgCl2, and CaCl2 into deionized water as the standard of Zabuye Lake in China.3 Pretreatment by CED followed Precipitation. A CED stack with an effective membrane area of 99 cm2 was used for preconcentrating low lithium-contained brine to produce Li2CO3. It was composed of four dilute compartments and four concentrated compartments through an alternatively arrangement of five cation exchange membranes and four anion exchange membranes between two electrodes. Two neighboring membranes were separated by a plexiglas spacer and a silicon rubber (total thickness of 1 mm). An additional cation exchange membrane was placed adjacent to anode to block the transportation of chloride ion (which can form hazardous gases and cause the damage of electrodes). Na2SO4 (0.3 M) was used as supporting electrolyte for both anode and cathode compartments. Constant voltage (10/15 V) was used for the CED process. Before the CED process, Ca2+ and Mg2+ were removed by adding Na2CO3 in a stoichiometric amount. Then, Li2CO3 was obtained from the concentrated brine by precipitation with stoichiometric Li2CO3. The precipitation process was operated on magnetic stirrer; Li2CO3 was extracted by suction filtration and dried in oven at 60 °C. It should be noted that, for the high quality requirement, fractional crystallization was used to

2. EXPERIMENTAL SECTION Materials. The ion-exchange membranes used for CED stack were JAM-II-05 (anion exchange membrane, Beijing Tingrun Membrane Technology Development Co. Ltd., China), and JCM-II-05 (cation exchange membrane, ibid). Those for EEDBM stack were Neosepta CMX (cation exchange membrane, Tokuyama Co., Japan), and Neosepta BP-1 (bipolar membrane, Tokuyama Co., Japan). Main properties of the membranes were listed in Table 1. The used reagents such as LiCl, MgCl2, CaCl2, LiNO3, LiOH, Na2SO4, and HCl are all as received and purchased from 6104



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Figure 2. Current−time curves during the CED process at constant voltages of 10 and 15 V. Flow rate is 22 L/h.

Figure 3. Conductivity−time curves for dilute and concentrate compartments during CED process at constant voltages of 10 and 15 V. Flow rate is 22 L/h.

remove Na+, Cl−, as well as residual Ca2+/Mg2+. Conductivity was recorded with conductivity meter (DDS-307 PHSJ-3F, Shanghai INESA & Scientific Instrument Co. Ltd.). Each element was determined by ICP (Optima 7300DV, inductively coupled plasma emission spectrometer). Production of Lithium Hydroxide Using EEDBM. Labscale EEDBM stack with an effective membrane area of 7.07 cm2 was used to produce LiOH. It comprised of (1) a cathode and an anode; (2) alternatively arranged two cation-exchange membranes and two bipolar membranes that divide the stack into five compartments with a silicon rubber (total thickness of 1 mm), named as anode, feed, base-1, acid, cathode (base-2), alternatively. Lithium hydroxide solution (0.1 and 0.3 M) was supplied into the base-1 and cathode compartments while lithium nitrate (0.3 M) was filled with anode compartment. The feed and acid compartments were filled with different concentrations of Li2CO3. A series of constant current−density values (20−60 mA/cm2) were used for EEDBM process. A pH change in the acid and feed compartments was online-recorded through a pH meter (PHSJ-3F, Shanghai INESA & Scientific Instrument Co. Ltd.). Lithium hydroxide in base-1 and cathode compartments was sampled every 10 min and titrated afterward with standard HCl using an automatic potentiometric titrator.

The electrodes for CED and EEDBM stacks were all made of titanium coated with ruthenium and connected to a direct CC/ CV current power supply (WYL1703, Hangzhou Siling Electrical Instrument Ltd.). The voltage drop across the stack was directly read from indicators on the power supply. Each chamber was connected to a glass beaker, which allows for the circulation of external solutions by submersible pumps (AP1000, Zhongshan Zhenghua Electronics Co. Ltd., China, with the maximal flow rate of 22 L/h). Before the experiment, each chamber was circulated for 30 min to eliminate the visible bubbles. Experiment was performed at constant voltage for CED and constant current for EEDBM coupled process. The corporate CED and EEDBM stacks for producing lithium hydroxide from simulated Zabuye Lake brine are schematically shown in Figure 1. Calculation of Current Efficiency and Energy Consumption for EEDBM Stack. Current efficiency η (%) is calculated as following equation29

η=

(Ct − C0)VF NIt

(3)

Where η is current efficiency; Ct and C0 (mol/L) are the concentration of lithium hydroxide in base compartment at time t and 0 respectively; V (mL) is the volume of base 6105



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3.2. Production of Lithium Hydroxide Using EEDBM. 3.2.1. Effect of Current Density. Current density has a great influence on the production yield and capacity for EDBM process based on our previous investigation.19 A series of constant currents (20, 30, 40, 50, 60 mA/cm2) was applied to investigate the effect of current density in treating Li2CO3 feed with EEDBM stack. The feed and acid compartments were filled with 0.09 M Li2CO3. Figure 4 shows the effect of current density on the voltage drop across the EEDBM stack. These voltage drops follow the current density order of 60 > 50 > 40 > 30 > 20 mA/cm2. Generally, the voltage drop mainly includes Donnan potential at all solution−membrane interfaces and diffusion potentials, both in the cation-exchange membrane and in the solution, as well as the voltage drop across the bipolar membrane.35 The water dissociation rate is proportional to applied current density. When current was applied at glavanostatic condition, the cell voltage drops would remain approximately constant, which indicates a constant dissociation of water at the interface of the bipolar membrane, as water dissociation mainly occurs in the depletion layer and the dissociated ions removed from this region are replenished by following water dissociation equilibrium as follows.36

compartment; F is the Faraday constant (96500 C); I is the constant current used to the stack; N is repeating unit of the stack; t (min) is test time. The energy consumption (kWh/kg) was calculated as the following equation:29 E=

∫0

t

UI dt ΔCtVM

(4)

where E (kWh/kg) is energy consumption; U (V) is the voltage drop across EEDBM stack; I (A) is the current applied; Ct is the net increased concentration of lithium hydroxide in base compartment at certain period; V is the volume of base circulate in base compartment (200 mL); M is the molar mass of lithium hydroxide (23.94).

3. RESULT AND DISCUSSION 3.1. Preconcentration of Lithium Brine through CED. The electrodialysis process was operated at constant voltage with flow rate of 22 L/h, the maximum flow rate of the used immersible pump. Considering the limiting current density of monopolar membrane, the CED stack was run at constant voltage (thus current was changed) of 10 and 15 V. As can be seen from Figure 2, current decreases gradually with time, and the difference between curves of 15 and 10 V is not significant. It is attributed to the decrease of salt concentration in dilute compartment with time, since the resistance of stack is mainly summed by compartment resistance, membrane resistance, and electrode resistance.34 The dilute compartment resistance is gradually increased with time. The conductivity there decreases to 70 μs/cm, which is lower than that of tap water (140 μs/cm) at the end of the experiment (Figure 3). In the concentrate compartment, the conductivity increases to the highest value of 8610 μs/cm, eight times higher than initial conductivity of salt brine. Table 2 shows the ions content in lake brine before and after pretreatment. It can be observed that lithium increases from

k1

H 2O XooY H+ + OH− k −1

The water dissociation is accelerated by electric field according to the second Wien effect. The water dissociation constant k1 is influenced by a strong electric field E, while the recombination rate k−1 is not.37,38 For further comparison, the measured lithium hydroxide yield as a function of time for constant current density of 20, 30, 40, 50, 60 mA/cm2 was shown in Figure 5. The production rates of lithium hydroxide can be determined from the slope of those lines. Obviously, such yield rate was significantly influenced by the current density. The concentration of lithium hydroxide increases with current density at same time intervals for both base-1 and base-2 compartments. However, a slight fluctuation exists in base-2 compartment due to the H2 production from electrolysis reaction. Figure 6 shows pH change throughout experiment in feed and acid compartments, respectively. Typically, pH decreases gradually with time. The slope of the line, that is, the pH decreasing rate, varies with current density: the higher the current density, the quicker the rate decreased. This is because high current density enhances the water dissociation. The produced H+ speed up the exchange with Li+, which then constantly migrate from feed and acid compartments to the corresponding base-1 and base-2 compartments. Figure 7 shows energy consumption and current efficiency at the different current densities. It can be observed that energy consumption increases with the current density. A great part of total current energy transforms to Joules of heat, and this phenomenon is more obvious with the increase of current density.21 Energy consumption increases with the current density, but current efficiency has no regular trend. Instead, it fluctuates with the current density and shows highest value at 60 mA/cm 2 . The trend can be understood by the permselectivity of ion exchange membrane because its selectivity for counterions decreases gradually with the increase of current density. Furthermore, a high current density leads to shorter transition time (tc) of corresponding ions (Li+, OH−). Additionally, these two ions approach to combine with each

Table 2. Ions Composition in Salt Brine before and after CED Pretreatment Li+ (mg/L)

Na+ (mg/L)

Ca2+ (mg/L)

Mg2+ (mg/L)

879 3157 3485

0 7379 7319

0.76 5.53 5.29

21 97.71 37.32

raw solution 10 V 15 V

879 mg/L to 3157 mg/L for 10 V and to 3485 mg/L for 15 V. The lithium content was improved to a level of preferably ca. 2.8−6.0% by weight. Such concentration can satisfy the precipitation of lithium in Li2CO3 form.7 As shown in Table 3, sodium content decreases from 3.14% to 1.98% by a secondary crystallization process and the purity of Li2CO3 powder increases from 90.33% to 95.30%, simultaneously. All other elements such as Ca2+, Mg2+, and Cl− were reduced to a desirable percentage by fractional crystallization, and we can infer that high purity Li2CO3 will be obtained by this method. Table 3. Content of Elements in Li2CO3 Powder

primary secondary

Li+ (%)

Na+ (%)

Ca2+ (%)

Mg2+ (%)

Cl− (%)

CO32− (%)

Li2CO3 (%)

16.9 18.43

3.14 1.98

0.03 0.02

0.66 0.09

0.11 0.05

78.81 79.43

90.33 95.30

(5)

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Figure 4. Voltage drop across EEDBM stack vs time at current density of 20−60 mA/cm2, and other conditions are flow rate of 22 L/h, feed concentration of 0.09 M.

Figure 5. Concentration of the produced lithium hydroxide in base-1 and base-2 compartments vs time at current density of 20−60 mA/cm2, and other conditions are flow rate of 22 L/h, feed concentration of 0.09 M.

Figure 6. pH changes for feed and acid compartments vs time at current density of 20−60 mA/cm2; other conditions are flow rate of 22 L/h and feed concentration of 0.09 M.

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this reason, voltage drop across stack is inversely proportional to the feed concentration. Moreover, current that converts to heat decreases correspondingly with the rising of feed concentration. Thus, it can be predicted that energy consumption will be decreased at higher feed concentration, as will be discussed later. Figure 9 shows the measured lithium hydroxide yield as a function of time at constant current density of 30 mA/cm2 and different feed concentrations. From the slope of lines, the production rates of lithium hydroxide can be determined. It indicates that the concentration of lithium hydroxide increases with the increase of current density at the same time intervals in both base-1 and base-2 compartments. Obviously, the magnitude of feed concentration has insignificant effect on the production of lithium hydroxide in base-1 compartment, but it has a great influence on the base-2 compartment. As the existence of H2 in the base-2 compartment is due to the electrolysis reaction, the slope of those curves change irregularly, but the lithium hydroxide yield increases. It suggests that, at the same operation conditions, a high concentration of lithium hydroxide in the base-2 compartment can be achieved by increasing the Li2CO3 concentration in feed and acid compartments. As observed in Figure 9, at 90 min, a maximum concentration of lithium hydroxide as high as 0.0599 and 0.0562 M in base-1 and base-2 compartments was obtained for 0.09 M feed. In comparison with conventional lime precipitation process to produce LiOH (shown as eqs 1 and 2), the new process can produce more lithium hydroxide of high purity. Furthermore, it would also eliminate discharge of solid waste to great extent since the precipitation process is avoided. Figure 10 shows the measured pH values in feed and acid compartments as a function of time at constant current density of 30 mA/cm2 and different feed concentrations. The color of data points represents pH of the feed and acid solution. As low solubility of Li2CO3 at ambient temperature, buffer ability of Li2CO3 solution is not enough to maintain solution pH value. So when a constant current density is applied, pH of acid and feed compartments will be significantly influenced as water dissociation at the interface of bipolar membrane. Li + constantly migrates from feed and acid compartments to base-1 and base-2 compartments until the depletion of Li2CO3

Figure 7. Current efficiency and energy consumption vs current density; other conditions are flow rate of 22 L/h and feed concentration of 0.09 M.

other to form lithium hydroxide instead of migrating toward the adjacent compartment. These factors co-induce the fluctuation consequence for current efficiency. 3.2.2. Effect of Feed Concentration on the Production of Lithium Hydroxide. Constant current experiments were performed under steady state to explore the effect of feed concentration on the production of lithium hydroxide. The experiments were investigated with feed of 0.054, 0.09, and 0.18 M Li2CO3. Figure 8 shows the effect of feed concentration on the voltage drops across the EEDBM stack. Obviously, at galvanostatic condition, stack voltage drop is approximately constant for 0.18 M feed, but it slightly increases for other two feeds, which indicates steady water dissociation at the interface of the bipolar membrane. The magnitude of voltage drop follows the order 0.054 M > 0.09 M > 0.18 M. Typically, voltage drop mainly includes Donnan potential, as aforementioned.35 At a constant value of 30 mA/cm2, the solution resistance increased dramatically when the feed concentration decreased. As a result, the contribution of Donnan potential at solution−membrane interface is significantly decreased. For

Figure 8. Voltage drop across EEDBM stack vs time at feed concentrations of 0.054−0.18 M, and other conditions are flow rate of 22 L/h and constant current density of 30 mA/cm2. 6108



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Figure 9. Concentration of the produced lithium hydroxide in base-1 and base-2 compartments vs time at feed concentrations of 0.054−0.18 M, and other conditions are flow rate of 22 L/h and constant current density of 30 mA/cm2.

Figure 10. pH changes for feed and acid compartments vs time at feed concentrations of 0.054−0.18 M; other conditions are flow rate of 22 L/h and constant current density of 30 mA/cm2.

2H 2O + Li 2CO3 ↔ H 2CO3 + 2LiOH

in feed and acid solution. As observed in Figure 10, pH values in feed and acid compartments decrease gradually with time for 0.18 M feed solution at a fixed current density. However, for 0.054 and 0.09 M feed experiment, pH decrease is approximately constant before pH 9.0, and then decreases sharply to 7.41 and 7.6 at of 50 and 70 min, respectively. It may be ascribed to the buffer effect of CO32− ions. As well-known, protons that generated from bipolar membrane would react with CO32− by two steps (c.f. equations 6−8): H+ combine with CO32− ions to form HCO3− and then further form H2CO3, since pKa1 of H2CO3 (6.38) is much smaller than pKa2 of HCO3− (10.33). Normally, pH of bicarbonate salt is 8.31− 9.0, it equals to the inflection point of pH curves for 0.054 and 0.09 M feed solution perfectly as shown in Figure 10. Moreover, pH eventually decreases to 9.86 for 0.18 M feed. With an increase in CO32− concentration, much more H+ is needed for stoichiometric reaction with CO32− before inflection point and thus more time is needed to reach inflection point. H+ + CO32 − → HCO3−

(6)

H+ + HCO3− → H 2CO3

(7)

(8)

Figure 11 shows energy consumption and current efficiency with respect to the feed concentration of Li2CO3. When feed concentration increases, the energy consumption decreases dramatically. Due to the low solubility of Li2CO3 in water (concentration of saturated solution is 0.18 M at ambient temperature), the conductivity of feed and acid solution are relatively low compared to the electrode rinse solution (0.3 M). So conductivity of feed and acid compartments significantly influences energy consumption that reflects a decreased trend of voltage drop with feed concentration in EEDBM stack. With the decreases of Li2CO3 concentration, energy consumption for LiOH production increases correspondingly. A great part of current energy transforms to Joule heat for 0.09 and 0.054 M feed, and this phenomenon is much obvious with the decrease of feed concentration.21 However, current efficiencies are in the range 91.8−94.2%, indicating a high utilization of current. We can conclude that the influence of feed concentration on current efficiency is negligible but it has a great effect on energy consumption. Low energy consumption and high current efficiency would be achieved by applying 0.18 M feed at current density of 30 mA/cm2. 6109



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3.3. Process Cost. Process cost varies with processing capacity, thus it is evaluated on the basis of lab-scale setup. As described before, the total processes for extracting lithium include pretreatment steps such as CED concentration, precipitation, crystallization process, and EEDBM. Generally, crystallization process shares only about 0.25−0.3% fraction while CED process cost accounts for ca. 10−40% according to the concentration of the treated brine. Due to the high price of bipolar membranes, EEDBM is mainly responsible for the total cost. For simplification, this work mainly focuses on the possibility of LiOH production using EEDBM process and the cost was estimated according to EEDBM using the reported calculation method.34,39 By the consideration of shadow effect, effective membrane area of the stack is a little less than that of practical use. Thus, a coefficient of β (0.7) was introduced to estimate the membrane price. As can be seen from Table 4, all the runs at different current densities and feed concentrations have different EEDBM process cost. They all fall into the range 2.56−4.03 $/kg for the production of lithium hydroxide (95%) with lab-scale setup. Specifically, for 0.09 M feed with 30 mA/ cm2 experiment, it has the lowest EEDBM process cost of 2.56

Figure 11. Current efficiency and energy consumption vs feed concentration; other conditions are flow rate of 22 L/h and constant current density of 30 mA/cm2.

Table 4. Estimation of EEDBM Process Cost BP-C-BP-C 1

2

Operation Condition repeat unit 1 1 current density (mA/cm2) 20 30 experiment time (min) 60 60 effective membrane area (cm2) 7.07 7.07 practical membrane used (cm2)a 10.01 10.01 LiNO3 concn. (mol/L) 0.3 0.3 fluid flow speed (L/h) 22 22 Li2CO3 concn. (mol/L) 0.09 0.09 LiOH concn. (mol/L) 0.029 0.039 current efficiency (%) 94.6 89.9 Energy Cost energy consumption (KWh/kg) 6.66 10.82 process capacity (kg/year) 2.08 2.82 electricity charge ($/kWh) 0.1 0.1 energy cost for LiOH ($/kg) 0.67 1.08 energy cost for peripheral equipment ($/kg × 10−2) 3.35 5.4 total energy cost ($/kg) 0.7 1.13 Investment Cost membrane lifetime and amortization of the peripheral equipment (year) 3 3 monopolar membrane price ($/m2)b 135 135 bipolar membrane price ($/m2)b 1350 1350 membrane cost ($) 2.97 2.97 stack cost ($)c 4.46 4.46 peripheral equipment cost ($)d 6.69 6.69 total investment cost ($)e 11.15 11.15 amortization ($/year)f 3.72 3.72 interest ($/year)g 0.3 0.3 maintenance ($/year)h 1.11 1.11 total fixed cost ($/year) 5.13 5.13 total fixed cost ($/kg) 2.47 1.82 EEDBM process cost ($/kg) 3.17 2.95

3

4

5

6

7

8

1 40 60 7.07 10.01 0.3 22 0.09 0.057 93.0

1 50 60 7.07 10.01 0.3 22 0.09 0.062 89.5

1 60 60 7.07 10.01 0.3 22 0.09 0.078 95.7

1 30 90 7.07 10.01 0.3 22 0.05 0.058 94.2

1 30 90 7.07 10.01 0.3 22 0.09 0.058 93.1

1 30 90 7.07 10.01 0.3 22 0.18 0.062 98.9

12.40 4.07 0.1 1.24 6.2 1.3

16.06 4.47 0.1 1.61 8.05 1.69

17.89 5.56 0.1 1.79 8.95 1.88

20.37 2.72 0.1 2.04 10.2 2.14

14.61 2.70 0.1 1.46 7.3 1.53

7.94 2.92 0.1 0.79 3.95 0.83

3 135 1350 2.97 4.46 6.69 11.15 3.72 0.3 1.11 5.13 1.26 2.56

3 135 1350 2.97 4.46 6.69 11.15 3.72 0.3 1.11 5.13 1.15 2.84

3 135 1350 2.97 4.46 6.69 11.15 3.72 0.3 1.11 5.13 0.92 2.8

3 135 1350 2.97 4.46 6.69 11.15 3.72 0.3 1.11 5.13 1.89 4.03

3 135 1350 2.97 4.46 6.69 11.15 3.72 0.3 1.11 5.13 1.9 3.43

3 135 1350 2.97 4.46 6.69 11.15 3.72 0.3 1.11 5.13 1.76 2.59

a

An introduced coefficient b (0.7) for scale corrections. bCurrent selling price of membrane available on the market. cCalculated by membrane cost multiplied by 1.5. dCalculated by stack cost multiplied by 1.5. eEquals to peripheral equipment cost added by stack cost. fCalculated by total investment cost divided by 3 years. gCalculated by amortization for three years with lending rates of 8.1%. hMaintenance mainly accounts for 10% of the total investment; Much more detail work is available in refs 34 and 39. 6110



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$/kg which has considered depreciation of equipment (containing electrode price, land cost, pumps cost, etc.). Therefore, EEDBM is a considerably competitive process beyond traditional one. Compared with the current market price of lithium hydroxide (14.67 $/kg) in China, it has huge popularizing potential and competitive strength. It should be noted that the EEDBM process cost would be further reduced if pilot- or industry-scale plant is utilized. Other cost factors such as experiment operation cost, and fixed investment will decrease, since energy cost decreases with the augmentation of production capacity.40

4. CONCLUSION Novel EEDBM process was initiated for the production of lithium hydroxide from simulated lake brines. CED was used for pretreatment, and lithium was extracted as Li2CO3 form with purity of 95% and then lithium hydroxide solution with purity of ca. 95% was obtained through a lab scale EEDBM stack. The influence of parameters such as current density, feed concentration was investigated. Moreover, to evaluate performance of the process, an EEDBM process cost that takes into consideration of energy cost and investment cost was estimated. The EEDBM process cost is roughly 2.59 $/kg at a current density of 30 mA/cm2 and a feed concentration of 0.18 M. The results indicate that high current efficiency and low energy consumption were obtained at saturated Li2CO3 solution. Compared with conventional electrolysis and causticization reaction process, EEDBM provides an environmental-friendly and cost-effective process for producing LiOH from CED pretreated Lake Brine. It can not only significantly increase the process capacity via introducing of two pieces of bipolar membrane and one piece of cation exchange membrane compared to electrolysis process but also avoids the use of lime which likely decreases the purity of lithium hydroxide and causes environmental problem.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +86-551-360-1587. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research is supported in part by the National Natural Science Foundation of China (Nos. 21025626, 21206155, 21206154), National High Technology Research and Development Program 863 (No. 2012AA03A608). We also would like to thank to Erigene Bakangura and M.D. Masem Hossain for their English reading of this manuscript.

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REFERENCES

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Production of Lithium Hydroxide from Lake Brines through Electro

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