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Study of lithium exploitation from carbonate subtype and sulfate type salt-lakes of Tibet
Hydrometallurgy 149 (2014) 143–147
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Study of lithium exploitation from carbonate subtype and sulfate type salt-lakes of Tibet Chengcai Zhu a,b, Yaping Dong a, Zeng Yun c, Yong Hao c, Chun Wang a,b, Naijin Dong a,b, Wu Li a,⁎ a b c
Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, PR China Graduate University of Chinese Academy of Sciences, Beijing 100049, PR China Tibetan Guoneng Mining Development Co., Ltd, Lhasa 850000, PR China
a r t i c l e
i n f o
Article history: Received 9 December 2013 Received in revised form 20 June 2014 Accepted 10 July 2014 Available online 2 August 2014 Keywords: Salt-lakes Carbonate subtype Sulfate type Lithium carbonate Lithium
a b s t r a c t A novel process for extracting lithium from carbonate subtype and sulfate type salt-lakes of Tibet by making full use of local resources and energy was developed. In this research, we extract lithium from carbonate subtype and sulfate type salt-lakes of Tibet through following three steps: carbonate enriched brine was prepared via freezing content is 60.76 g/L); lithium enriched brine was obtained by and evaporating of carbonate type brine (CO2− 3 mixing sulfate-type brine and frozen carbonate-type brine (Li+ content is 12.56 g/L); and lithium carbonate with a purity of 97.49% and a lithium yield of 54.85% was precipitated by mixing the lithium enriched brine and carbonate enriched brine. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Lithium, as the lightest metal, was used widely in batteries, lubricants, ceramics, glass, polymers and other areas due to its unique electrochemical reactivity as well as other properties. The worldwide consumption of lithium in 2013 is expected to be approximately 30,000 tons, increasing by 6% from that of 2012(Suzette, 2014). The demand of lithium (lithium carbonate equivalent) is forecast to increase by approximately 60% from 102,000 tonnes to 162,000 tonnes in the next five years (Hykawy, 2010). Lithium resources of the world have been mined from two distinct sources—continental brines and hard rock ore. By the USGS (Suzette, 2014) data, the total lithium resources in the world are estimated to be about 39.5 million tonnes, of which 60% belongs to the brine of salt-lakes; others belong to pegmatite minerals. Compared with spodumene, lepidolite and other solid lithium minerals, lithium extraction from brine is cheap (Helvaci, 2004). The main producers of lithium products from brine are SQM (Chili, Salar de Atacama deposit), FMC (Argentina, Hombre Muerto), Chemetall Foote Corp (Chili, Salar de Atacama deposit; United States, Silver Peak salt-lake) and Tibet Lithium New Technology Development Co (China, Zabuye Salt-lake)(Naumov and Naumova, 2010). Lithium resources of Tibet are rich; thus it is of great significance to extract lithium from the salt lakes of Tibet. To extract lithium from brine, many methods, such as lithium coprecipitation, organic solvents extraction, ion exchange extraction ⁎ Corresponding author.
http://dx.doi.org/10.1016/j.hydromet.2014.07.006 0304-386X/© 2014 Elsevier B.V. All rights reserved.
and adsorption, are developed (Hamzaoui et al., 2008). At present, the separation of magnesium and lithium from sulfate type salt-lake containing high ratio of magnesium to lithium is still an international technical problem in the development of salt-lake brine. In addition, lithium can't be enriched highly with increasing of the concentration of carbonate ions because of lower solubility of lithium carbonate in water during exploiting lithium from carbonate subtype salt-lakes. Many techniques, such as precipitation method, solvent extraction and ion-exchange, are developed to separate magnesium from lithium-containing salines (An et al., 2012). Precipitation methods are using NaOH, ammonia, carbonate and oxalate to separate Mg from lithium-containing saline. Xu et al. (2009) developed a two-step of magnesium precipitation salt lake brine with high ratio of magnesium to lithium using ammonia and ammonium bicarbonate respectively. In the first step, ammonia is used to adjust pH of brine and react with Mg to form insoluble magnesium hydroxide. Then residual magnesium is precipitated with ammonium bicarbonate as basic magnesium carbonate. After precipitating, about 98% of Mg is separated from brine. Tran et al. (2013) separated magnesium and calcium from Salar de Uyuni brine by using oxalic acid. After precipitating, the magnesium recovery is high than 95% and the losses of K and Li are up to 35% from the original brine. Telzhensky et al. (2011) separated Mg from seawater using nanofiltration membranes DS-5 DL with Mg recovery of 64% and a new solution containing 3.5 g/L Mg. The representative carbonate-subtype salt-lakes are Searles Lake of USA and Zabuye Salt Lake of China. Lithium crystallized as NaLi2PO4 during evaporation process of Searles Lake. Then Li2CO3 was obtained
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C. Zhu et al. / Hydrometallurgy 149 (2014) 143–147
after flotation, acidulation using H2SO4 and precipitation using Na2CO3 (Liu, 1987). The ratio of Mg/Li of Zabuye Salt Lake is about zero and Li2CO3 is almost saturated from original salt lake. Thus, Zhao et al. (2004) obtained Li2CO3 directly with lithium yield of 22.16% from Zabuye Salt Lake by heating brine in salar pond. More than two hundred of carbonate subtype and sulfate type saltlakes containing lithium resources were found on North Tibet Plateau of China. However, the bad natural environment of this area, such as higher altitude (4500 m in average), lower average temperature (−25 °C in winter), worse transportation condition, less energy sources and so on, makes the exploration of salt-lake resources much more difficult. Our purpose in this work is to obtain lithium carbonate from Tibet carbonate subtype and sulfate type salt-lakes by using local lowertemperature and solar energy. The technology used in this paper is simple, effective and pollution-free. 2. Experimental 2.1. Materials and analyses Pre-freezing brine (Brine A), which has been evaporated until lithium carbonate being saturated, was taken from Jiezechaka Salt Lake (47.28 L). Frozen brine (Brine B) was then evaporated from Brine A in cold bath. Sulfate type brine (Brine C), which has been evaporated until bischofite being saturated, was sampled from Longmucuo Salt Lake (1.90 L). Lithium enriched brine (Brine D) was prepared by blending Brine A and Brine E. Melted solution frozen from Brine A was concentrated for carbonate enriched brine (Brine E). The analytical methods were based on those given by the Analysis Group, Qinghai Institute of Salt-Lakes, Chinese Academy of Sciences (Zhai et al., 1988). Contents of lithium of the brines were analyzed by atomic absorption spectroscopy (AAnalyst 800, PE of USA) while others were analyzed by chemical analysis methods. K+ was analyzed using the gravimetric method, with a precision of 0.1%; Ca2 + and Mg2 + were analyzed by disodium ethylenediamine tetraacetate (EDTA) voluwas analyzed metric titration method, with a precision of 0.1%; SO2− 4 by the gravimetric method, using barium chloride, with a precision of 0.1%; Cl− was analyzed by the silver nitrate volumetric titration method, with a precision of 0.1%; the concentrations of CO23 − and HCO− 3 were determined by titration with 0.1 mol/L HCl, using methyl orange and phenolphthalein as the double indicator, with a precision of 0.3%; the borate ion concentration was evaluated by titration with 0.05 mol/L NaOH, in the presence of mannitol, with phenolphthalein as the indicator, with a precision of 0.3%. The compositions of brines are shown in Table 1. X-ray diffraction (XRD, PANalytical X'Pert PRO diffractometer with Cu Kα radiation, λ = 0.15406 nm) was used to identify the components of reaction sediments and crystallized salts. All chemicals used in the study were of analytical grade. 2.2. Experimental techniques Fig. 1 outlines the major steps involved in the experiments. Lithium was extracted through three steps: carbonate enriched brine was prepared via freezing and evaporating of carbonate type brine; lithium enriched brine was prepared by mixing sulfate-type brine and frozen
Fig. 1. Flowsheet for the extraction of lithium from carbonate subtype and sulfate type salt-lakes.
carbonate-type brine; and lithium carbonate was prepared by mixing the high concentrations of carbonate and lithium brines at room temperature. 2.2.1. Carbonate enriched brine Pre-freezing brine (Brine A) in which lithium carbonate is saturated was sampled from Tibet carbonate subtype brine (47.28 L). Brine A brine was frozen at different temperature (− 20 °C and − 10 °C) and kept under isothermal condition for 72 h. Then it was separated quickly by vacuum filtration to obtain 21.8 kg frozen salt enriched with ions of carbonate, sodium and sulfate and 31.44 L Frozen brine (Brine B). The frozen salts composed of mirabilite (Na2SO4·10H2O) and natron (Na2CO3·7H2O) are melted into solution enriched with ions of carbonate, sodium and sulfate ions at room temperature (~20 °C). Then the solution was evaporated to carbonate enriched brine (Brine E). Frozen brine (Brine B) was evaporated and reacted with sulfate type brine before saturation of lithium carbonate to prepare lithium enriched brine (Brine D). 2.2.2. Lithium enriched brine Sulfate type brine (Brine C) in which carnallite is saturated was sampled from Tibet sulfate type brine (1.90 L). Lithium enriched brine (Brine D) was prepared by mixing and evaporating Brine B and Brine E. Sulfate type brine and frozen brine were blended quickly with molar 2+ +Ca2+) being 1.3:1 and 1.1:1 for 0.5 h respectiveratio of CO2− 3 : (Mg ly, and then ripened for 9 days at 22 °C. The mixtures were separated by centrifuge separation to get solid magnesium carbonate and solution containing magnesium and carbonate with lower concentration. Then solution was evaporated to Brine D.
Table 1 Compositions of the brines used in experiments (g/L). Brine
K+
Ca2+
Mg2+
SO2− 4
Cl−
B2O3
CO2− 3
HCO− 3
Li+
Na+
Pre-freezing brine (A) Frozen brine (B) Sulfate type brine (C) Lithium enriched brine (D) Carbonate enriched brine (E)
34.42 44.35 2.45 60.50 45.33
b0.05 b0.05 b0.05 b0.05 b0.05
0.07 0.04 99.38 0.32 b0.05
43.42 2.27 32.10 25.72 56.02
164.92 202.16 278.52 199.22 150.61
9.27 4.90 16.98 32.03 19.86
22.66 7.55 b0.05 b0.05 60.76
7.97 12.63 b0.05 7.52 b0.05
1.76 2.41 3.66 12.56 1.28
121.73 108.36 b0.05 66.07 131.74
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2.2.3. Lithium carbonate Lithium enriched brine (2 L) and carbonate enriched brine (2.55 L) + being 1.37:1 for were mixed slowly with a molar ratio of CO2− 3 :2Li 2 h and then ripened for 24 h at 22 °C. The mixtures were separated by centrifuge separation to get solid lithium carbonate and solution with saturated lithium carbonate. 3. Results and discussion 3.1. Freeze of carbonate subtype brine Brine A was frozen in cold bath at −10 °C and −20 °C respectively. − 2− After being frozen and separated, frozen proportion of SO2− 4 , CO3 , Cl and Na+ of Brine A frozen at − 10 °C were 83.92%, 2.64%, 6.19% and 2− − + 14.03% respectively. But the proportion of SO2− 4 , CO3 , Cl and Na frozen at − 20 °C were 95.49%, 75.13%, 35.38% and 55.33% respectively. Compositions of the Brine A were simplified and most of SO24 − and were frozen out being frozen at −20 °C. It's depicted that lower CO2− 3 temperature is better to improve freezing efficiency of SO24 −, CO23 −, Cl− and Na+. 3.2. Preparation of carbonate enriched brine The frozen salts composed of mirabilite (Na2SO4·10H2O) and natron (Na2CO3·7H2O) are melted into solution in which carbonate, sodium and sulfate ions are enriched at room temperature (~20 °C). Concentra2− tions of SO2− 4 and CO3 of solution were 93.99 g/L and 54.76 g/L. Sulfate salts will be precipitated out if this solution was used to prepare lithium carbonate. Metastable phase diagram of Na+, K+//Cl−, SO24 −, CO2− 3 — H2O at 25 °C (Fang and Niu, 1991; John, 1929) was employed to guide and explain the evaporation–crystallization path and carbonate-enrich behavior of the solution melted from frozen salt. As shown in Figs. 2 and 3, phase points passed through phase fields of Na2SO4 and NaK3(SO4)2 successively. In this evaporating process, concentration of was reduced from 93.99 g/L to 20.12 g/L gradually. However, the SO2− 4 concentration of CO23 − rose first and then fell down after reaching at the point of maximum (125.0 g/L). Solid salts of halite (NaCl), borax(Na2B4O7·10H2O), burkeite (Na6CO3(SO4)2), sodium sulfate (Na2SO4) and aphthitalite (NaK3(SO4)2) were crystallized during evaporation process from L1 to L3 while halite (NaCl) and aphthitalite (NaK3(SO4)2) crystallized during process from L4 to L9. However, the evaporation, concentration and crystallization behavior of the solution are different from those of metastable phase diagram of Na+, K+//Cl−,
2− Fig. 2. Metastable phase diagram of Na+, K+//Cl−, SO2− 4 , CO3 —H2O at 25 °C and the evaporation–crystallization path of the solution melted from frozen salt.
Fig. 3. Relation between evaporation rate and concentrations of SO2− and CO2− of the 4 3 solution melted from frozen salt.
2− SO2− 4 , CO3 —H2O at 25 °C because of temperature difference of dayand-night during evaporating (about 5 °C). In this research, we used of 60.76 g/L and SO2− of 36.02 the brine with concentration of CO2− 3 4 g/L and lithium enriched brine to prepare lithium carbonate.
3.3. Preparation of lithium enriched brine The mass ratio of magnesium to lithium is reduced after mixing sulfate type brine and frozen carbonate subtype brine. Lithium can be 2+ +Ca2+) enriched effectively under proper molar ratio of CO2− 3 :(Mg of the mixture. As shown in Fig. 4, concentration of lithium can be enriched more than 12 g/L while the molar ratio is 1.1:1. However, it's hard to for lithium to be enriched more than 8 g/L while the molar ratio is 1.3:1 because of growing concentration of CO2− 3 during evaporation. It's proved that the molar ratio of CO23 −:(Mg2++ Ca2+) as 1.1:1 is proper for increasing of lithium concentration. After mixing, concentration of magnesium was reduced from 99.38 g/L to 2.69 g/L while carbonate was from 20.18 g/L to 1.50 g/L. Needle-like magnesium carbonate hydrate (MgCO3·3H2O) with fewer impurities of sodium
2+ Fig. 4. Lithium enriching process at different molar ratios of CO2− +Ca2+). 3 :(Mg
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C. Zhu et al. / Hydrometallurgy 149 (2014) 143–147
Fig. 5. XRD patterns of magnesium carbonate hydrate.
chloride (Fig. 5) was synthesized after ripening the reaction mixtures for 9 days at 22 °C. This special morphology of magnesium carbonate hydrate is better for separation of the mixtures. The mixtures were separated easily by using centrifuge separation. Solid of magnesium carbonate and solution with lower concentrations of magnesium and carbonate were obtained. Lithium can be concentrated to 12.56 g/L by evaporating the solution. The reduction of magnesium and carbonate was beneficial for enrichment of lithium. 3.4. Precipitation of lithium carbonate High reaction temperature and concentrations of carbonate and lithium (An et al., 2012) are better for the yield of lithium during precipitation of lithium carbonate. However, higher transport costs and lack of source energy have limited the exploration of lithium from carbonate subtype brine of Tibet. In this paper, lithium carbonate was obtained using lithium enriched brine and carbonate enriched brine prepared in these experiments at room temperature (22 °C). The content of Li2CO3 and the yield of lithium are 84.81% and 54.84%, respectively, in the raw precipitated lithium carbonate salts (unwashed by dilute water) with few contaminations of K+, Na+, B2O3, Cl− and SO24 −. As XRD analysis showed (Fig. 6), the salts are composed of Li2CO3, KCl
and Na2B4O7·5H2O. After washing the salts with distilled water at 20 °C, the content of Li2CO3 increases from 84.81% to 97.49%. 4. Conclusions A novel technique was developed to extract lithium from carbonate subtype and sulfate type salt-lakes of Tibet. Three stages were employed to prepare lithium enriched brine (Li+ content is 12.56 g/L), carbonate enriched brine (CO23 − content is 60.76 g/L) and lithium carbonate. Lithium carbonate salts with the content of Li2CO3 being 97.49% and the yield of lithium being 54.84% were produced by blending lithium enriched brine and carbonate enriched brine. Acknowledgments This work was supported by the National Natural Science Fund projects of China (grant no. 41273032 and No.41073050). References Hamzaoui, A.H., Jamoussi, B., M'Nif, A., 2008. Lithium recovery from highly concentrated solutions: response surface methodology (RSM) process parameters optimization. Hydrometallurgy 90 (1), 1–7.
Fig. 6. XRD patterns of lithium carbonate.
C. Zhu et al. / Hydrometallurgy 149 (2014) 143–147 Zhai, Z.X., Cheng, Z.B.,Hu, F., et al., 1988. Workbook of Identification and Analysis Method of Salt Minerals. Chemical Industry Press, Beijing (in Chinese). Helvaci, C., 2004. Presence and distribution of lithium in borate deposits and some recent lake waters of West-Central Turkey. Int. Geol. Rev. 46 (2), 177–190. Hykawy, J., 2010. Looking at lithium: discussing market demand for lithium in electronics. Mater. World Ceram. Lith. 18 (5), 34–35. Suzette, M.K., 2014. Mineral commodity summaries (USGS) 2014. http://minerals.usgs. gov/minerals/pubs/mcs/2014/mcs2014.pdf. Naumov, A.V., Naumova, M.A., 2010. Modern state of the world lithium market. Russ. J. Nonferr. Met. 51 (4), 324–330. Xu, H., Xu, L., Chen, B.Z., Shi, X.C., et al., 2009. Separating technique for magnesium and lithium from high Mg/Li ratio salt lake brine. J. Cent. South Univ. 40 (1), 36–40. Tran, K.T., Luong, T.V., An, J.W., et al., 2013. Recovery of magnesium from Uyuni salar brine as high purity magnesium oxalate. Hydrometallurgy 138, 93–99.
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Telzhensky, M., Birnhack, L., Lehmann, O., et al., 2011. Selective separation of seawater Mg2+ ions for use in downstream water treatment processes. Chem. Eng. J. 175, 136–143. Liu, L.Y., 1987. Comprehensive utilization of Searles Lake resources. Cons. Util. Miner. Resour. 04, 28–30. Zhao, Y.Y., Zheng, M.P., Pu, L.Z., et al., 2004. Study on salt pan technology of lithium salt extracting from carbonate-type saline lakes, Tibet. Sea-Lake. Salt. Chem. Ind. 34 (2), 1–6 (in Chinese with English abstract). John, E.T., 1929. The industrial development of Searles Lake Brines. The Chemical Catalog Company, New York. 2− Fang, C.H.,Niu, Z.D., 1991. Metastable phase diagram study of Na+, K+//Cl−, SO2− 4 , CO3 — H2O at 25 °C. Acta. Chim. Sinica 49 (11), 1062–1070. An, J.W., Kang, D.J., Tran, K.T., et al., 2012. Recovery of lithium from Uyuni salar brine. Hydrometallurgy 117–118, 64–70.
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Hydrometallurgy journal homepage: www.elsevier.com/locate/hydromet
Study of lithium exploitation from carbonate subtype and sulfate type salt-lakes of Tibet Chengcai Zhu a,b, Yaping Dong a, Zeng Yun c, Yong Hao c, Chun Wang a,b, Naijin Dong a,b, Wu Li a,⁎ a b c
Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, PR China Graduate University of Chinese Academy of Sciences, Beijing 100049, PR China Tibetan Guoneng Mining Development Co., Ltd, Lhasa 850000, PR China
a r t i c l e
i n f o
Article history: Received 9 December 2013 Received in revised form 20 June 2014 Accepted 10 July 2014 Available online 2 August 2014 Keywords: Salt-lakes Carbonate subtype Sulfate type Lithium carbonate Lithium
a b s t r a c t A novel process for extracting lithium from carbonate subtype and sulfate type salt-lakes of Tibet by making full use of local resources and energy was developed. In this research, we extract lithium from carbonate subtype and sulfate type salt-lakes of Tibet through following three steps: carbonate enriched brine was prepared via freezing content is 60.76 g/L); lithium enriched brine was obtained by and evaporating of carbonate type brine (CO2− 3 mixing sulfate-type brine and frozen carbonate-type brine (Li+ content is 12.56 g/L); and lithium carbonate with a purity of 97.49% and a lithium yield of 54.85% was precipitated by mixing the lithium enriched brine and carbonate enriched brine. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Lithium, as the lightest metal, was used widely in batteries, lubricants, ceramics, glass, polymers and other areas due to its unique electrochemical reactivity as well as other properties. The worldwide consumption of lithium in 2013 is expected to be approximately 30,000 tons, increasing by 6% from that of 2012(Suzette, 2014). The demand of lithium (lithium carbonate equivalent) is forecast to increase by approximately 60% from 102,000 tonnes to 162,000 tonnes in the next five years (Hykawy, 2010). Lithium resources of the world have been mined from two distinct sources—continental brines and hard rock ore. By the USGS (Suzette, 2014) data, the total lithium resources in the world are estimated to be about 39.5 million tonnes, of which 60% belongs to the brine of salt-lakes; others belong to pegmatite minerals. Compared with spodumene, lepidolite and other solid lithium minerals, lithium extraction from brine is cheap (Helvaci, 2004). The main producers of lithium products from brine are SQM (Chili, Salar de Atacama deposit), FMC (Argentina, Hombre Muerto), Chemetall Foote Corp (Chili, Salar de Atacama deposit; United States, Silver Peak salt-lake) and Tibet Lithium New Technology Development Co (China, Zabuye Salt-lake)(Naumov and Naumova, 2010). Lithium resources of Tibet are rich; thus it is of great significance to extract lithium from the salt lakes of Tibet. To extract lithium from brine, many methods, such as lithium coprecipitation, organic solvents extraction, ion exchange extraction ⁎ Corresponding author.
http://dx.doi.org/10.1016/j.hydromet.2014.07.006 0304-386X/© 2014 Elsevier B.V. All rights reserved.
and adsorption, are developed (Hamzaoui et al., 2008). At present, the separation of magnesium and lithium from sulfate type salt-lake containing high ratio of magnesium to lithium is still an international technical problem in the development of salt-lake brine. In addition, lithium can't be enriched highly with increasing of the concentration of carbonate ions because of lower solubility of lithium carbonate in water during exploiting lithium from carbonate subtype salt-lakes. Many techniques, such as precipitation method, solvent extraction and ion-exchange, are developed to separate magnesium from lithium-containing salines (An et al., 2012). Precipitation methods are using NaOH, ammonia, carbonate and oxalate to separate Mg from lithium-containing saline. Xu et al. (2009) developed a two-step of magnesium precipitation salt lake brine with high ratio of magnesium to lithium using ammonia and ammonium bicarbonate respectively. In the first step, ammonia is used to adjust pH of brine and react with Mg to form insoluble magnesium hydroxide. Then residual magnesium is precipitated with ammonium bicarbonate as basic magnesium carbonate. After precipitating, about 98% of Mg is separated from brine. Tran et al. (2013) separated magnesium and calcium from Salar de Uyuni brine by using oxalic acid. After precipitating, the magnesium recovery is high than 95% and the losses of K and Li are up to 35% from the original brine. Telzhensky et al. (2011) separated Mg from seawater using nanofiltration membranes DS-5 DL with Mg recovery of 64% and a new solution containing 3.5 g/L Mg. The representative carbonate-subtype salt-lakes are Searles Lake of USA and Zabuye Salt Lake of China. Lithium crystallized as NaLi2PO4 during evaporation process of Searles Lake. Then Li2CO3 was obtained
144
C. Zhu et al. / Hydrometallurgy 149 (2014) 143–147
after flotation, acidulation using H2SO4 and precipitation using Na2CO3 (Liu, 1987). The ratio of Mg/Li of Zabuye Salt Lake is about zero and Li2CO3 is almost saturated from original salt lake. Thus, Zhao et al. (2004) obtained Li2CO3 directly with lithium yield of 22.16% from Zabuye Salt Lake by heating brine in salar pond. More than two hundred of carbonate subtype and sulfate type saltlakes containing lithium resources were found on North Tibet Plateau of China. However, the bad natural environment of this area, such as higher altitude (4500 m in average), lower average temperature (−25 °C in winter), worse transportation condition, less energy sources and so on, makes the exploration of salt-lake resources much more difficult. Our purpose in this work is to obtain lithium carbonate from Tibet carbonate subtype and sulfate type salt-lakes by using local lowertemperature and solar energy. The technology used in this paper is simple, effective and pollution-free. 2. Experimental 2.1. Materials and analyses Pre-freezing brine (Brine A), which has been evaporated until lithium carbonate being saturated, was taken from Jiezechaka Salt Lake (47.28 L). Frozen brine (Brine B) was then evaporated from Brine A in cold bath. Sulfate type brine (Brine C), which has been evaporated until bischofite being saturated, was sampled from Longmucuo Salt Lake (1.90 L). Lithium enriched brine (Brine D) was prepared by blending Brine A and Brine E. Melted solution frozen from Brine A was concentrated for carbonate enriched brine (Brine E). The analytical methods were based on those given by the Analysis Group, Qinghai Institute of Salt-Lakes, Chinese Academy of Sciences (Zhai et al., 1988). Contents of lithium of the brines were analyzed by atomic absorption spectroscopy (AAnalyst 800, PE of USA) while others were analyzed by chemical analysis methods. K+ was analyzed using the gravimetric method, with a precision of 0.1%; Ca2 + and Mg2 + were analyzed by disodium ethylenediamine tetraacetate (EDTA) voluwas analyzed metric titration method, with a precision of 0.1%; SO2− 4 by the gravimetric method, using barium chloride, with a precision of 0.1%; Cl− was analyzed by the silver nitrate volumetric titration method, with a precision of 0.1%; the concentrations of CO23 − and HCO− 3 were determined by titration with 0.1 mol/L HCl, using methyl orange and phenolphthalein as the double indicator, with a precision of 0.3%; the borate ion concentration was evaluated by titration with 0.05 mol/L NaOH, in the presence of mannitol, with phenolphthalein as the indicator, with a precision of 0.3%. The compositions of brines are shown in Table 1. X-ray diffraction (XRD, PANalytical X'Pert PRO diffractometer with Cu Kα radiation, λ = 0.15406 nm) was used to identify the components of reaction sediments and crystallized salts. All chemicals used in the study were of analytical grade. 2.2. Experimental techniques Fig. 1 outlines the major steps involved in the experiments. Lithium was extracted through three steps: carbonate enriched brine was prepared via freezing and evaporating of carbonate type brine; lithium enriched brine was prepared by mixing sulfate-type brine and frozen
Fig. 1. Flowsheet for the extraction of lithium from carbonate subtype and sulfate type salt-lakes.
carbonate-type brine; and lithium carbonate was prepared by mixing the high concentrations of carbonate and lithium brines at room temperature. 2.2.1. Carbonate enriched brine Pre-freezing brine (Brine A) in which lithium carbonate is saturated was sampled from Tibet carbonate subtype brine (47.28 L). Brine A brine was frozen at different temperature (− 20 °C and − 10 °C) and kept under isothermal condition for 72 h. Then it was separated quickly by vacuum filtration to obtain 21.8 kg frozen salt enriched with ions of carbonate, sodium and sulfate and 31.44 L Frozen brine (Brine B). The frozen salts composed of mirabilite (Na2SO4·10H2O) and natron (Na2CO3·7H2O) are melted into solution enriched with ions of carbonate, sodium and sulfate ions at room temperature (~20 °C). Then the solution was evaporated to carbonate enriched brine (Brine E). Frozen brine (Brine B) was evaporated and reacted with sulfate type brine before saturation of lithium carbonate to prepare lithium enriched brine (Brine D). 2.2.2. Lithium enriched brine Sulfate type brine (Brine C) in which carnallite is saturated was sampled from Tibet sulfate type brine (1.90 L). Lithium enriched brine (Brine D) was prepared by mixing and evaporating Brine B and Brine E. Sulfate type brine and frozen brine were blended quickly with molar 2+ +Ca2+) being 1.3:1 and 1.1:1 for 0.5 h respectiveratio of CO2− 3 : (Mg ly, and then ripened for 9 days at 22 °C. The mixtures were separated by centrifuge separation to get solid magnesium carbonate and solution containing magnesium and carbonate with lower concentration. Then solution was evaporated to Brine D.
Table 1 Compositions of the brines used in experiments (g/L). Brine
K+
Ca2+
Mg2+
SO2− 4
Cl−
B2O3
CO2− 3
HCO− 3
Li+
Na+
Pre-freezing brine (A) Frozen brine (B) Sulfate type brine (C) Lithium enriched brine (D) Carbonate enriched brine (E)
34.42 44.35 2.45 60.50 45.33
b0.05 b0.05 b0.05 b0.05 b0.05
0.07 0.04 99.38 0.32 b0.05
43.42 2.27 32.10 25.72 56.02
164.92 202.16 278.52 199.22 150.61
9.27 4.90 16.98 32.03 19.86
22.66 7.55 b0.05 b0.05 60.76
7.97 12.63 b0.05 7.52 b0.05
1.76 2.41 3.66 12.56 1.28
121.73 108.36 b0.05 66.07 131.74
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2.2.3. Lithium carbonate Lithium enriched brine (2 L) and carbonate enriched brine (2.55 L) + being 1.37:1 for were mixed slowly with a molar ratio of CO2− 3 :2Li 2 h and then ripened for 24 h at 22 °C. The mixtures were separated by centrifuge separation to get solid lithium carbonate and solution with saturated lithium carbonate. 3. Results and discussion 3.1. Freeze of carbonate subtype brine Brine A was frozen in cold bath at −10 °C and −20 °C respectively. − 2− After being frozen and separated, frozen proportion of SO2− 4 , CO3 , Cl and Na+ of Brine A frozen at − 10 °C were 83.92%, 2.64%, 6.19% and 2− − + 14.03% respectively. But the proportion of SO2− 4 , CO3 , Cl and Na frozen at − 20 °C were 95.49%, 75.13%, 35.38% and 55.33% respectively. Compositions of the Brine A were simplified and most of SO24 − and were frozen out being frozen at −20 °C. It's depicted that lower CO2− 3 temperature is better to improve freezing efficiency of SO24 −, CO23 −, Cl− and Na+. 3.2. Preparation of carbonate enriched brine The frozen salts composed of mirabilite (Na2SO4·10H2O) and natron (Na2CO3·7H2O) are melted into solution in which carbonate, sodium and sulfate ions are enriched at room temperature (~20 °C). Concentra2− tions of SO2− 4 and CO3 of solution were 93.99 g/L and 54.76 g/L. Sulfate salts will be precipitated out if this solution was used to prepare lithium carbonate. Metastable phase diagram of Na+, K+//Cl−, SO24 −, CO2− 3 — H2O at 25 °C (Fang and Niu, 1991; John, 1929) was employed to guide and explain the evaporation–crystallization path and carbonate-enrich behavior of the solution melted from frozen salt. As shown in Figs. 2 and 3, phase points passed through phase fields of Na2SO4 and NaK3(SO4)2 successively. In this evaporating process, concentration of was reduced from 93.99 g/L to 20.12 g/L gradually. However, the SO2− 4 concentration of CO23 − rose first and then fell down after reaching at the point of maximum (125.0 g/L). Solid salts of halite (NaCl), borax(Na2B4O7·10H2O), burkeite (Na6CO3(SO4)2), sodium sulfate (Na2SO4) and aphthitalite (NaK3(SO4)2) were crystallized during evaporation process from L1 to L3 while halite (NaCl) and aphthitalite (NaK3(SO4)2) crystallized during process from L4 to L9. However, the evaporation, concentration and crystallization behavior of the solution are different from those of metastable phase diagram of Na+, K+//Cl−,
2− Fig. 2. Metastable phase diagram of Na+, K+//Cl−, SO2− 4 , CO3 —H2O at 25 °C and the evaporation–crystallization path of the solution melted from frozen salt.
Fig. 3. Relation between evaporation rate and concentrations of SO2− and CO2− of the 4 3 solution melted from frozen salt.
2− SO2− 4 , CO3 —H2O at 25 °C because of temperature difference of dayand-night during evaporating (about 5 °C). In this research, we used of 60.76 g/L and SO2− of 36.02 the brine with concentration of CO2− 3 4 g/L and lithium enriched brine to prepare lithium carbonate.
3.3. Preparation of lithium enriched brine The mass ratio of magnesium to lithium is reduced after mixing sulfate type brine and frozen carbonate subtype brine. Lithium can be 2+ +Ca2+) enriched effectively under proper molar ratio of CO2− 3 :(Mg of the mixture. As shown in Fig. 4, concentration of lithium can be enriched more than 12 g/L while the molar ratio is 1.1:1. However, it's hard to for lithium to be enriched more than 8 g/L while the molar ratio is 1.3:1 because of growing concentration of CO2− 3 during evaporation. It's proved that the molar ratio of CO23 −:(Mg2++ Ca2+) as 1.1:1 is proper for increasing of lithium concentration. After mixing, concentration of magnesium was reduced from 99.38 g/L to 2.69 g/L while carbonate was from 20.18 g/L to 1.50 g/L. Needle-like magnesium carbonate hydrate (MgCO3·3H2O) with fewer impurities of sodium
2+ Fig. 4. Lithium enriching process at different molar ratios of CO2− +Ca2+). 3 :(Mg
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Fig. 5. XRD patterns of magnesium carbonate hydrate.
chloride (Fig. 5) was synthesized after ripening the reaction mixtures for 9 days at 22 °C. This special morphology of magnesium carbonate hydrate is better for separation of the mixtures. The mixtures were separated easily by using centrifuge separation. Solid of magnesium carbonate and solution with lower concentrations of magnesium and carbonate were obtained. Lithium can be concentrated to 12.56 g/L by evaporating the solution. The reduction of magnesium and carbonate was beneficial for enrichment of lithium. 3.4. Precipitation of lithium carbonate High reaction temperature and concentrations of carbonate and lithium (An et al., 2012) are better for the yield of lithium during precipitation of lithium carbonate. However, higher transport costs and lack of source energy have limited the exploration of lithium from carbonate subtype brine of Tibet. In this paper, lithium carbonate was obtained using lithium enriched brine and carbonate enriched brine prepared in these experiments at room temperature (22 °C). The content of Li2CO3 and the yield of lithium are 84.81% and 54.84%, respectively, in the raw precipitated lithium carbonate salts (unwashed by dilute water) with few contaminations of K+, Na+, B2O3, Cl− and SO24 −. As XRD analysis showed (Fig. 6), the salts are composed of Li2CO3, KCl
and Na2B4O7·5H2O. After washing the salts with distilled water at 20 °C, the content of Li2CO3 increases from 84.81% to 97.49%. 4. Conclusions A novel technique was developed to extract lithium from carbonate subtype and sulfate type salt-lakes of Tibet. Three stages were employed to prepare lithium enriched brine (Li+ content is 12.56 g/L), carbonate enriched brine (CO23 − content is 60.76 g/L) and lithium carbonate. Lithium carbonate salts with the content of Li2CO3 being 97.49% and the yield of lithium being 54.84% were produced by blending lithium enriched brine and carbonate enriched brine. Acknowledgments This work was supported by the National Natural Science Fund projects of China (grant no. 41273032 and No.41073050). References Hamzaoui, A.H., Jamoussi, B., M'Nif, A., 2008. Lithium recovery from highly concentrated solutions: response surface methodology (RSM) process parameters optimization. Hydrometallurgy 90 (1), 1–7.
Fig. 6. XRD patterns of lithium carbonate.
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