Article pubs.acs.org/IECR
Systemic and Direct Production of Battery-Grade Lithium Carbonate from a Saline Lake Zhenhua Xu, Haijun Zhang, Ruiyuan Wang, Wenjun Gui, Guofeng Liu, and Ying Yang* Key Laboratory of Nonferrous Metals Chemistry and Resources Utilization of Gansu Province, Lanzhou University, Lanzhou 730000, P. R. China ABSTRACT: A process was developed to produce battery-grade lithium carbonate from the Damxungcuo saline lake, Tibet. A two-stage Li2CO3 precipitation was adopted in a hydrometallurgical process to remove impurities. First, industrial grade Li2CO3 was obtained by removing Fe3+, Mg2+, and Ca2+ from a liquor containing lithium. Second, industrial grade Li2CO3 was treated by CO2 to get the more soluble bicarbonates. EDTA-Li (lithium 2-carboxyhydrazine-1,1,2-tricarboxylate) was added to chelate Ca2+ and Mg2+. The decomposition of LiHCO3 produced insoluble Li2CO3 at 85 °C. The final precipitation yielded a high purity (99.6%) and homogeneous Li2CO3. Some factors affecting the production efficiency were investigated. The results showed that an L/S mass ratio of 30:1 favored the formation of a Li2CO3 slurry; a molar ratio of EDTA-Li to (Ca+Mg) 1.05:1 and hot water washing precipitate (L/S mass ratio 1:1) promoted ions removal; a cyclic use of filtrate improved the recovery of lithium. anions to be removed, such as Cl−, SO42−, were considered in the washing process. Figure 1 outlined the major steps involved in the production of industrial grade Li2CO3. The production of battery-grade Li2CO3 by using EDTA-Li to remove impurities was shown in Figure 2. As shown in Figure 2, the high purity of Li2CO3 benefited from the use of EDTA-Li to remove of Mg2+, Ca2+, and Fe3+ ions, and this process could promote the recovery of lithium through the reuse of filtrate. Compared with other studies on the recovery of lithium recently, EDTA-Li is first used to produce battery-grade Li2CO3. The as-formed Li2CO3 shows a higher purity (99.6%) with ion impurity content lower than the national standard. To find out the optimal condition for the preparation of battery-grade Li2CO3, the effect of different variables on the Li2CO3 production efficiency was evaluated. Some factors such as liquid-to-solid mass ratio, (Ca +Mg) to EDTA-Li molar ratio, and reuse of the filtrate were investigated.
1. INTRODUCTION Lithium is the lightest metal that could float on oil. And being so light, lithium is the most energy dense of battery materials, meaning it stores the most energy for a given weight.1,2 This property of high energy density and excellent electrochemical reactivity has thus brought it to be very widely used in various electronic devices, especially in portable electronic devices.3 The words “lithium” and “battery” are almost synonymous this soft metal is in all our smartphones, tablets, and laptops. Additionally, lithium compounds and minerals have attracted much attention for their applications in ceramics, glass, aluminum, lubrication industries, and pharmaceuticals.4,5 Reports indicate that the global consumed amount of lithium related products for batteries has been increasing by more than 20% per year during the past several years.6−8 Most lithium products are currently produced from brine sources.9,10 China has been the second biggest Li-rich resource in the world, and 26.9% of Chinese lithium resources are in Damxung Tibet and Jabu Qinghai.11 Table 1 shows that the Damxungcuo saline lake contains a high level of Li/Mg concentration ratios (Li+, 0.36 g/L; Mg2+, 0.81g/L), unlike brines in other countries.12 But it is difficult to recover lithium from a saline lake because of preferential magnesium extraction.13 Recent research has focused on Li recovery from salt-lake brine using methods such as the precipitation method,14,15 calcination,16 solar evaporation,17 membrane extraction,18 and adsorption.19,20 Most of the products obtained from these methods are industrial grade Li2CO3 (Table 2). Moreover, few industrial applications could be found in China.21 Therefore, the recovery of lithium from the Chinese saline lake is a problem to be urgently solved . In this paper, a hydrometallurgical process is proposed to overcome the difficult production of battery-grade Li2CO3 from Damxungcuo saline lake brine. First, industrial grade Li2CO3 was obtained by using a precipitation method to remove impurities. Second, industrial grade Li2CO3 was treated by CO2 to get the bicarbonates solution; EDTA-Li was added to solution to remove Mg2+, Ca2+, Fe3+ ions. Compounds with © 2014 American Chemical Society
2. EXPERIMENTAL SECTION 2.1. Materials. Approximately 50 kg solid for the experimental testwork was obtained by evaporation of saline lake. The concentration of Li+ determined by ICP−AES is 11.6% (wt %). All of the glassware used in the following procedures were cleaned by sonication for 15 min in purified water. All chemicals used in the study were analytical grade. 2.2. Analysis. The ion concentrations of filtrate and residues were determined by ICP −AES (IRS ER/S TJA Co., Ltd., US). Thermogravimetric analysis (TG-DTA) was carried out with a STA PT1600 thermal balance. The morphology of Li2CO3 was observed by scanning electronic microscope (SEM, 1.0 nm, 15Kv, Electron Optics Co., Japan). The structures were Received: Revised: Accepted: Published: 16502
July 9, 2014 September 23, 2014 September 26, 2014 September 26, 2014 dx.doi.org/10.1021/ie502749n | Ind. Eng. Chem. Res. 2014, 53, 16502−16507
Industrial & Engineering Chemistry Research
Article
Table 1. Main Compositions of the Damxungcuo Saline Lake observation data 2011-5-19 Li+
air
humidity
brine
brine depth
salinity
pH
density
volume
weight
T/°C
%
T/°C
cm
%
18 °C
g cm−2
L
kg
Na+
18.0 K+
20.5 Cl−
18.4 SO42−
8.7 CO32−
(g/L)
(g/L)
(g/L)
(g/L)
(g/L)
(g/L)
0.360
54.13
7.32
67.67
7.08
10.80
13.6 HCO3−
9.50 Mg2+
1.104 B4O72−
55.32
61.07 mineralization
(g/L)
(g/L)
(g/L)
(g/L)
0.00
0.81
2.91
151.08
Table 2. Experimental Profiles and Results of Several Published Studies on Recovery of Lithium raw material J. W. An et al. Hydrometallurgy 117−118 64−70 Q. X. Yan et al. Int. J. Mineral Process. 110−111 1−5 V. T. Luong et al. Hydrometallurgy 141 8−16 Z. Y. Zhou et al. Ind. Eng. Chem. Res. 51 12926−12932 Yan et al. Hydrometallurgy 121−124 54−59
solar brine, Uyuni Lepidolite, JiangXi,China MQAM mine, Korea Zabuye Saline lake, China Lepidolite, JiangXi, China
production of Li2CO3 (wt %)
extraction of Li (%)
99.55 91.61 85 93 98.88
method precipitation sulfation roasting and water washing iron sulfate raosting extraction with extractant defluorination and autocluve
Figure 2. Flowsheet developed for the recovery of battery-grade Li2CO3 from the Damxungcuo saline lake.
precipitation in each step were determined by ICP-AES. A 600 mL portion of hot water (80 °C) was added to the wash solid (20.06g), 2.5 mL of H2SO4 (98%) was used to dissolve the solid in 200 mL of distilled water. Sample amounts of 8.91 g and 1.38 g of Li2CO3 are obtained from 200 mL of acid dissolving solution and 600 mL of washing water, respectively. Second, battery-grade Li2CO3 was produced by using EDTALi to remove Ca2+, Mg2+, and Fe3+. EDTA-Li was obtained by mixing 36 mL of LiOH (10%) and 14.6 g of EDTA in 110 mL of distilled water at 60 °C. The molar ratio of Li to EDTA was 3:1. The concentration of EDTA-Li was as follows.
Figure 1. Flowsheet developed for the recovery of industrial grade Li2CO3 from the Damxungcuo saline lake.
determined by X-ray diffraction analysis (X′PertPRO Panalytical, NL). 2.3. Methods. Table 3 shows the values of the national standard of Li2CO3 in China. First, the preparation of industrial grade Li2CO3 was carried out using the following method. The precipitation of Fe, Mg, and Ca was conducted at room temperature (18−20 °C) using various reactors incorporating different speed modes of stirring. Hot water (80 °C) was added to wash solid Li2CO3 and H2SO4 to dissolve solid in distilled water. Different precipitants such as lime milk, NaOH, and oxalic acid were added in solid to avoid the dilution of the solution and quantities were decided by the pH value. After Fe3+, Mg2+, and Ca2+ were removed, the clean brine and washing water were subjected to carbonation to precipitate Li2CO3 using Na2CO3. The contents of major impurities in the
C(EDTA − Li) = 14.6 g/(292 g/mol × 0.146 L) = 0.34 mol/L
At room temperature, CO2 was bubbled directly into the Li2CO3 slurry for 3 h to ensure that all industrial grade Li2CO3 was converted to soluble LiHCO3. LiHCO3 solution after adding EDTA-Li was stirred for 10 min, LiHCO3 decomposed to Li2CO3 when the solution was heated to 85 °C. The operation conditions for the preparation of Li2CO3 slurry was as follows: At room temperature, Li2CO3 was soaked in water for 10 min, then CO2 (99%) was bubbled into the slurry (130 mL, 450 mL, 500 mL) for 3 h by treating 13.15 g, 15.1 g, and 16503
dx.doi.org/10.1021/ie502749n | Ind. Eng. Chem. Res. 2014, 53, 16502−16507
Industrial & Engineering Chemistry Research
Article
Table 3. Industrial Grade and Battery-Grade Li2CO3 in China (China’s National Standard, GB/T11075-2006, YS/T582-2006) impurity content (wt %) ≤ index Li2CO3
purity ≥
particle size ≤
moisture content ≤
Na
K
Ca
Mg
Fe
Mn, Ni, Pb, Al, Cl, SO4
Industrial grade Battery grade
99% 99.50%
600um 6um
0.60% 0.40%
0.111 0.025
0.053 0.001
0.025 0.005
0.1 0.01
0.005 0.002
0.5 0.1
5 g of industrial grade Li2CO3, respectively. The remainder was treated with 20 g of industrial grade Li2CO3 under the optimal conditions. The recovery of EDTA was conducted by adding H2SO4 to adjust the pH to 2, and EDTA could be recycled. EDTA could be used repeatedly with no obvious decrease of uptake after regeneration by inorganic acid. H2SO4 was added to the 500 mL filtrate (EDTA, 28.58 g) to adjust the pH to 2. A 26 g sample of EDTA was recycled, and the recovery of EDTA was 91%.
3. RESULTS AND DISCUSSION 3.1. Preparation of Industrial Grade Li2CO3. The reactions were presented as follows to describe the flowsheets. 2FeSO4 + H 2SO4 + H 2O2 = Fe2(SO4 )3 + 2H 2O
(1)
3Ca(OH)2 + Fe2(SO4 )3 = 2Fe(OH)3 ↓ + 3CaSO4
(2)
3NaOH + MgSO4 = Mg(OH)2 ↓ + Na 2SO4
(3)
Figure 3. Solubility of lithium salts are given in grams per 100 g of water (g/100 g) (Wikipedia, http://en.wikipedia.org/wiki/Solubility_ table#L).
CaSO4 + Ca(OH)2 + 2H 2C2O4 = 2CaC2O4 ↓ + H 2SO4 + H 2O
(4)
Li 2SO4 + Na 2CO3 = Li 2CO3 ↓ + Na 2SO4
(5)
Li 2CO3 + CO2 + H 2O = 2LiHCO3
(6)
M(SO4 )n + Na 2CO3 → M(CO3)n + M(OH)2n + Na 2SO4 (7)
M(CO3)n + CO2 + H 2O → M(HCO3)2n
(8)
EDTA‐Li + M(HCO3)2n → EDTA‐M + LiHCO3
(9) (10)
Figure 4. Effect of pH on the solubility of calcium oxalate. (Lange’s Handbook of Chemistry).
The Li+ ions were soluble and stable over a wide range of pH values, whereas precipitation of Fe(OH)3, Mg(OH)2, and CaC2O4 could be separated (eq 2, 3 and 4). Continuous pH value changes were conducted to remove impurities. As seen in Figure 3, the solubility of LiOH, LiCl, and LiNO3 increased with the increase of temperature, indicating that hot water washing was an effective means of recovering lithium. In the meantime, soluble ions such as Na+, K+, Cl−, and SO42−, could be removed as far as possible. It was proposed that lime milk be used to adjust the pH value to 4 to remove Fe3+ and Fe2+ (adding H2O2 to oxidize Fe2+), according to Ksp[Fe(OH)3] = 4 × 10−38 (Lange’s Handbook of Chemistry22). The use of NaOH changed the pH to 12 to precipitate Mg as Mg(OH)2. The separation of Mg(OH)2 was difficult because of the nanosize crystal. This could be solved by a static settlement at 80 °C for 12 h, and then the large size of Mg(OH)2 could be separated by filtering. The solubility of CaC2O4 changing with pH was seen in Figure 4. The Ca2+ (including that added from
lime milk) removal was carried out by adjusting the pH value to 4.6 using oxalic acid. Meanwhile, boron was enriched by calcium and magnesium precipitation, and boron presented as byproducts before Li2CO3 could be recovered.23 A total of 8.91 g and 1.38 g of Li2CO3 are obtained from the acid dissolving solution and washing water, respectively. The recovery of Li is around 84%, and the remaining 16% could be recovered by reusing the filtrate, which will be investigated in our future work. Table 4 shows that the loss of Li is minimal when the lithium contents of the precipitations are 0.22%, 0.17%, and 0.014%, respectively. The conventional process of precipitation can yield industrial grade Li2CO3, but a deep treatment is necessary to obtain battery-grade Li2CO3. 3.2. Effect of Liquid-to-Solid Mass Ratio on the Preparation of Li2CO3 Slurry. The liquid-to-solid mass ratios of 10:1, 20:1, 30:1, 50:1, and 100:1 on the preparation of Li2CO3 slurry were investigated. As seen in Figure 5, the liquidto-solid mass ratio has a slight effect on the process, and all precipitations give battery-grade Li2CO3. When the ratio is 10,
85 ° C
2LiHCO3 ⎯⎯⎯⎯→ Li 2CO3 + CO2 + H 2O (M = Ca 2 +, Mg 2 +, Fe3 +)
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dx.doi.org/10.1021/ie502749n | Ind. Eng. Chem. Res. 2014, 53, 16502−16507
Industrial & Engineering Chemistry Research
Article
Table 4. Chemical Composition of Precipitation (in wt %) component
B
Ca
Fe
K
Li
Mg
Na
Fe(OH)3 Mg(OH)2 CaC2O4 Li2CO3
0.0088 0.69 0.0007 0.03
0.18 0.058 25.34 0.025
3.07 0.0042 0.0037 0.0021
1.52 0.0077 0.0011 0.11
0.22 0.17 0.014 18.64
0.94 35.01 0.17 1.12
1.1 0.92 0.34 0.111
Cu, Mn, Ni, Pb, Zn < < <
