Lithium recovery from the mother liquor obtained in the process of

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Lithium recovery from the mother liquor obtained in the process of Li2CO3 production Junfeng Wang, Shicheng Yang, Ruibing Bai, Yongmei Chen, and Suojiang Zhang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b05495 • Publication Date (Web): 02 Jan 2019 Downloaded from http://pubs.acs.org on January 8, 2019

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Industrial & Engineering Chemistry Research

Lithium recovery from the mother liquor obtained in the process of Li2CO3 production Junfeng Wanga, Shicheng Yangb, Ruibing Baia, Yongmei Chenb, Suojiang Zhanga* a

State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, PR China b

*

Beijing University of Chemical Technology, Beijing 100190, PR China

Corresponding Author: Tel.: +86 10 82627080. Fax: +86 10 82627080. E-mail: [email protected].

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Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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ABSTRACT: It is important to find an effective way to separate lithium from the mother liquor obtained by the reaction of lithium chloride/lithium sulfate and sodium carbonate. A synergistic solvent extraction system containing 1-phenyl-3-heptyl-1,3-propanedione (PHPD) and liquid mixture of trialkyl-phosphine oxides (Cyanex923) to separate lithium from the system of Li++Na++Cl-+CO32-+H2O was developed. The pH of aqueous solution showed an important effect on the lithium extraction. At pH 13.06, PHPD alone showed a high extractability of lithium, but the addition of Cyanex923 led to a high separation ability of lithium over sodium due to the synergistic extraction effect. For a single extraction, the extraction percentage of lithium was 97.83% from the solution with 1.39 g·L-1 Li and 68.97 g·L-1 Na using the extraction system containing 0.4 mol·L-1 PHPD and 0.2 mol·L-1 Cyanex923 at the A/O ratio of 1:1, initial aqueous pH of 13.06 and 293.15 K, and the separation factor of lithium over sodium reached 475.06. Based on the McCabe-Thiele diagram of lithium extraction, two stages need to be used to achieve the complete extraction of lithium with an A/O ratio of 1.8. The extracted lithium species obtained by the slope analysis method were LiES and LiES2, where E and S represent the deprotonated PHPD and Cyanex923, respectively. The electrospray ionization mass spectra (ESI-MS) further confirmed that another two main Li adducts existing in the organic phase were LiE and LiE(H2O). The extracted lithium could be completely stripped from the loaded organic solution with hydrochloride of 0.5 mol·L-1 at an A/O ratio of 1:1. All of these will provide a theoretical basis for lithium separation from the mother liquor obtained during the process of lithium carbonate production.

KEYWORDS: Lithium separation; Solvent extraction; Mother liquor; β-diketone; Mechanisms.


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1. INTRODUCTION In recent years, lithium carbonate (Li2CO3) is not only the starting material for the industrial production of both inorganic and organic lithium compounds,1-5 but also used to fabricate materials in lithium ion batteries because of its simple form and stability.6 Li2CO3 can be produced by the reaction of purified LiCl or Li2SO4 solution with soda ash. The purified solutions can be obtained from the mineral sources or brines containing lithium by different methods, such as chemical precipitation,7,8 calcination,9 adsorption,10,11 membrane separation12,13 and solvent extraction.14,15 For example, the precipitation method was developed to separate lithium from salt lakes of Atacama (Chile), Hombre Muerto (Argentina) and Silver peak (U.S.) with a low Mg/Li ratio.16-17 The calcination method has been used by Qinghai CITIC Guoan Science and Technology Development Co. Ltd in China to produce the purified LiCl solution from West Taijinar salt lake with a relatively higher Mg/Li ratio.18 However, during the process of Li2CO3 production using the purified lithium solution as raw material and sodium carbonate as precipitant, a large amount of mother liquor with high Na/Li ratio is generated.19 According to the compositions of mother liquor provided by Qinghai CITIC Guoan Science and Technology Development Co. Ltd in China, the concentrations of lithium and sodium are in the range of 1.4-2.0 g·L-1 and 55-62 g·L-1, respectively. It is estimated that about 25 m3 mother liquor of high Na/Li ratio is generated for one ton of Li2CO3 manufactured by using the purified LiCl aqueous solution as raw material.20 As of now, the mother liquor was not recycled and directly discharged back into the saline lakes. Therefore, it is necessary to find an effective method to implement the effective utilization of lithium in the mother liquor from the economic and environmental point of view. In our previous work, the phase equilibrium of Li2CO3+NaCl+Na2SO4+H2O system over the temperature range from 283.15 K to 363.15 K was investigated, and the thermodynamic model for this system was developed. Based on these, the route of Li2CO3 crystallization was designed. Unfortunately, only about 50% lithium can be recycled from the mother liquor using this route.20 Some researchers found that the method of synergistic solvent extraction showed a great potential for separating of lithium from the alkali aqueous solution with high sodium concentration. Among the extractants studied, β-diketones 3 Environment ACS Paragon Plus


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might be the most suitable for the recovery of Li from the high Na concentration solution. Some extraction systems containing β-diketones have been developed,21-29 especially a combination of β-diketones (such as methoxy-l,3-diketones (MODKs), benzoyltrifluoroacetone (HBTA), thenoyl trifluoroacetone (HTTA) and α-acetyl-m-dodecylacetophenone (Lix54)) and trialkyl-phosphine oxides (such as tributyl-phosphine oxide (TBP), tri-n-octyl-phosphine oxide (TOPO) and liquid mixture of four trialkyl-phosphine oxides (Cyanex923)). For example, Marinkina et al.21 found that the extraction system containing MODKs and TBP showed the good extractability of lithium from the system of Li++Na++K++OH-+H2O. Zhang et al.22 investigated the extraction behavior of lithium in aqueous carbonate media using the synergistic extraction system containing HBTA and TOPO, finding that lithium extraction could be 95% by two stage countercurrent extraction. Healy23 found that the extraction system containing HTTA and TOPO gave great synergistic effect on lithium separation from the aqueous solution of Li++Na++NO3-+HCO3-+H2O. Pranolo et al.24 investigated the lithium extraction ability from the system of Li++Na++Cl-+H2O with the extraction system containing Lix54 and Cyanex923, finding that the lithium extraction and the separation factor of lithium to sodium reached 96.3% and 1123 at the optimal parameters, respectively. In addition, they found that Lix54 alone cannot extract lithium and sodium. Another kind of β-diketones, 1-phenyl-3-heptyl-1,3-propanedione (PHPD), is the main component of some extractants.30 Some researchers found that PHPD alone showed the high separation ability of metal ions from alkaline aqueous solution. For example, Fu et al.31 used PHPD in kerosene to extract copper from synthetic NH4Cl solution, finding that the extraction percentage of copper was 95.35% at an A/O ratio of 2:1 and copper extraction could be achieved using two counter-counter stages. Therefore, the pure compound, PHPD, was selected to separate lithium from the system of Li++Na++Cl-+CO32-+H2O system obtained from the process of Li2CO3 production in this work. In addition, Cyanex923 was chosen to be synergist because it is completely miscible with all common hydrocarbon diluents even at very low ambient temperatures. The objective of this research is to determine the compositions of the adduct complexes of extractant and synergist with lithium, which can provide the fundamental basis for predict and design of Li extraction process. The effect of different parameters on extractive separation of lithium 4 Environment ACS Paragon Plus

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are investigated, and then the extractive separation route of lithium from the solution with high sodium concentration is developed according to the optimal parameters. 2. EXPERIMENTAL 2.1. Experimental Materials The extractants, 1-phenyl-3-heptyl-1,3-propanedione (PHPD, 98% purity) and Cyanex923 (93% purity) were kindly donated by Shanghai Rare-earth Chemical Co., Ltd, China and Shanghai Institute of Organic Chemistry, China, respectively, and were used without further purification. The kerosene oil used as the diluent was supplied by Shanghai Aladdin Biochemical Technology Co., Ltd., China. Lithium carbonate (99.99%, Sinopharm Chemical Reagent Co., Ltd., high purity), sodium chloride (99.0%, Sinopharm Chemical Reagent Co., Ltd., analytical grade) and sodium hydroxide (98.0%, Tianjin Kermel Chemical Reagent Co., Ltd., analytical grade) were used without further purification in the experiments. High-purity Milli-Q water (resistivity > 18.2 MΩ·cm and conductivity < 0.1μS·cm-1) was used to prepare all aqueous solutions. 2.2. Solution Preparation The solution of the organic phase was prepared by diluting PHPD and Cyanex923 in kerosene. Two kinds of aqueous solutions, i.e. Feed 1 and Feed 2, were prepared by dissolving lithium carbonate and sodium chloride in high-purity Milli-Q water. Feed 1 was used to optimize extraction system, and the concentrations of Li and Na are 1.39 g·L-1 and 68.97 g·L-1, respectively. Feed 2 was used for theoretical study, and the concentrations of Li and Na are 0.15 g·L-1 and 2.0 g·L-1, respectively. The stripping solutions were prepared by diluting sodium hydroxide in high-purity water. All qualities were weighed by a METTLER analytical balance accurate to ±0.0001 g. The standard deviations of the concentrations were calculated and corresponded to an experimental uncertainty of 0.003. 2.3. Solvent Extraction Procedure Extraction experiments were carried out in 20 mL flasks. A certain volume of aqueous solution of known composition was poured into the flasks, which were equipped with a magnetic stirrer and sealed with a screwed cap. The pH of the aqueous phase was adjusted by adding 1 mol·L-1 NaOH solution. The 5 Environment ACS Paragon Plus


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flasks were firstly immersed in a temperature-controlled water bath. The aqueous solution was stirred for about 20 min to establish the temperature equilibrium. Then a certain volume of organic phase was added to the aqueous solution and was continuously stirred for another 30 min which was the standard equilibrium time used in this work. After the equilibrium was attained, stirring was stopped and the mixture was centrifuged at 4000 rpm for 5 min. Subsequently, the aqueous phase was carefully removed and its equilibrium pH was measured. Finally, the contents of Li+ and Na+ in aqueous phase were determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). And, the concentrations of Li+ and Na+ in the organic phase can be calculated based on the mass balance. According to the data obtained, the extraction percentages of Li+ and Na+, ELi(%) and ENa(%),were determined using the following equations: ‫୐ܧ‬୧ ሺΨሻ ൌ ‫୒ܧ‬ୟ ሺΨሻ ൌ

஼೔ǡై౟ ൈ௏೔ǡఽ ି஼೐ǡై౟ ൈ௏೐ǡఽ ஼೔ǡై౟ ൈ௏೔ǡఽ

ൈ ͳͲͲΨ

஼೔ǡొ౗ ൈ௏೔ǡఽ ି஼೐ǡొ౗ ൈ௏೐ǡఽ ஼೔ǡొ౗ ൈ௏೔ǡఽ

ൈ ͳͲͲΨ

(1) (2)

where c denotes the concentration of metal ions (g·L-1), V denotes the volume of aqueous phase (L), the subscript A denotes aqueous phase, and the subscript i and e denote the initial and equilibrated concentrations of metal ions in aqueous solution, respectively. The extraction mechanism of the extraction system containing PHPD and Cyanex923 was investigated by the electrospray ionization mass spectra. For stripping experiments, the loaded organic phase was scrubbed with the dilute hydrochloric acid solution. The organic phase was then washed thoroughly with distilled water and dried for reuse in the next cycle. All experiments were made at least three times, and the results were averaged. For each experiment, concentrations of Li+ and Na+ were repeatedly analyzed 5 times using ICP-AES, and the average value was recorded to reduce random errors. 2.4. Stripping Procedure of the Loaded Organic Solution A certain volume of loaded organic solution of known composition was poured into the flasks. Then the flasks were immersed in a temperature-controlled water bath, and was stirred for about 20 min to establish the temperature equilibrium. Then the same volume of stripping phase was added to the organic 6 Environment ACS Paragon Plus

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solution and was continuously stirred for another 30 min. Subsequently, the mixture was centrifuged and the stripping phase was carefully removed. Finally, the concentrations of Li+ and Na+ in stripping phase were determined by ICP-AES, and those in the organic phase can be calculated based on the mass balance. On the basis of these data obtained, the stripping percentages of Li+ and Na+ were obtained. 2.5. Apparatus and Measurements The concentrations of lithium and sodium in aqueous phase were determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES, Thermal Fisher ICAP 6300, USA). The pH values of the aqueous phase were measured using a pH meter (Rex PHS-3C, China). The electrospray ionization mass spectra (ESI-MS) of extractants and lithium adducts were acquired by a Waters/Micromass ZQ mass spectrometer (Manchester, UK) equipped with a Harvard Apparatus syringe pump. All samples were prepared in acetonitrile. Mass spectra were acquired in the positive ion detection modes with unit mass resolution at a step of 1 m/z unit. The mass range for ESI experiments was from m/z = 100 to m/z = 1400. 3. RESULTS AND DISCUSSION 3.1. Extraction Equilibrium and Chemical Reaction In this work, the extraction system containing PHPD, Cyanex923 and kerosene is selected to recover lithium from mother liquor of high sodium to lithium ratio, which was obtained from the lithium carbonate production process. This kind of β-diketone extractant, PHPD, can promote the extraction reaction of lithium because PHPD has a donor group capable of formation of bidentate chelate compounds with the extracted metal.32 Cyanex923 can be completely miscible with common hydrocarbon diluents even at very low ambient temperatures. To understand the behaviors of extraction equilibrium for the system studied in this work, the complexes of PHPD and Cyanex923 with lithium need to be determined. In the aqueous phase studied in this work, the ion species include Li+, LiCO3-, Na+, CO32-, HCO3-, Cl-, OH- and H+. During the extraction process, the dissociation reaction of LiCO3- and other chemical reactions in aqueous solution with high pH value are shown as follows: (3) (4) 7 Environment ACS Paragon Plus


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(5) (6) where K1 and K2 denote the disassociation constant of LiCO3 and the association constant of LiOH, -

respectively. K3 and K4 denote the equilibrium constants of H2O and LiCO3-, respectively. The concentration of Li+ in the aqueous solution is equal to the sum of the free Li+ concentration and the associated Li-bearing species (LiCO3- and LiOH) concentration, and is expressed as follows: (7) On the basis of the liquid-liquid extraction characteristics, the extraction reactions in this system are put forward as follows: (8) (9) where HE and S denote PHPD and Cyanex923, respectively. The subscript a and b are the stoichiometric coefficients of HE and S in the complex of lithium, respectively. The subscript c and d are the stoichiometric coefficients of HE and S in the complex of sodium, respectively. Ke,Li and Ke,Nadenote the extraction equilibrium constants of lithium and sodium at a certain temperature, respectively. Based on Eqs. (7) - (9), the extraction equilibrium constants of lithium and sodium at a certain temperature can be expressed by Eqs. (10) and (11), respectively.

(10) (11) where the subscript O denotes the organic phase. For the liquid-liquid extraction system, the distribution coefficients of lithium and sodium, DLi and DNa, can be expressed as follows: (12) (13) Based on Eqs. (10) - (13), Eqs. (14) and (15) can be derived.


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(14) (15) 3.2. Optimization of the Extraction System 3.2.1. Effect of Extraction Time To investigate the effect of extraction time on the Li extraction, the initial extraction experiments of Li+ and Na+ were conducted using the system containing 0.4 mol·L-1 PHPD and 0.2 mol·L-1 Cyanex923 at an A/O ratio of 1:1, 293.15 K and initial pH 13.06. Fig. 1 shows the relationship of Li+ and Na+ extraction percentage with the extraction time. It was clear that the Li+ extraction percentage can reached 95.3% in 2 min, and then slowly increased to 96.57% at the extraction time of 10 min. However, the extraction percentage of Na+ reached 12.01% in 0.5 min, and then decreased to about 8.99% after 10 min. The decrease in Na+ extraction percentage might be attributed to the crowding effect of Li+. It can be concluded from the experimental results that extraction time of 30 min was sufficient to reach the extraction equilibrium, and was used in the following investigations. 3.2.2. Effect of pH Value The effect of initial aqueous pH on the extraction percentages and distribution coefficients of Li+ and Na+ in the absence and the presence of Cyanex923 at an A/O ratio of 1:1, extraction time of 30 min and 293.15 K was investigated. The initial pH of aqueous solution varied from 10.68 to 13.34. Figs. 2(a) and 2(b) show the extraction percentages and distribution coefficients of Li+ and Na+ as a function of the initial aqueous pH using the extraction system containing 0.4 mol·L-1 PHPD and 0.2 mol·L-1 Cyanex923 as well as 0.6 mol·L-1 PHPD and 0 mol·L-1 Cyanex923, respectively. It was obvious that the extraction percentages of Li+ and Na+ showed hardly changes with pH as the initial aqueous pH was less than 12. With the further increase of initial aqueous pH to 13.06, an increase in extraction was appreciable for Li+ but not so much for Na+. For the extraction system of 0.4 mol·L-1 PHPD and 0.2 mol·L-1 Cyanex923, the separation factor of Li+ over Na+ which was calculated according to Eq. (16), reached 475.06, as shown in Fig. 2(a).



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(16) where βLi/Na is the separation factor of Li+ over Na+. However, a further increase in initial aqueous pH led to the decrease of Li+ and Na+ extractability. This result might be attributed to the fact that the extraction reagent, PHPD, has a slightly aqueous solubility, especially in the higher pH value.33 Therefore, it could be concluded from these experimental results that the optimum aqueous pH for Li+ extraction is 13.06, which facilitated the high Li+ extractability and selectivity. It also can be seen from Fig. 2(b) that PHPD alone could extract Li+ and Na+. At an initial aqueous pH of 13.06, the extraction percentage of Li using PHPD alone as extractant reached 96.95%, which was only little lower than the value of 97.83% for the extraction system containing PHPD and Cyanex923. In addition, it was found from the experimental results that Cyanex923 alone hardly extracted Li and Na, which was agreement with the result reported by Pranolo et al..24 Fu et al.31 extracted nickel using the extraction system of PHPD in kerosene, finding that the extraction percentage of nickel could reach 98.53% at the equilibrium pH of 7.7. However, Kunugita et al.34 found that another β-diketone extractant, Lix54, could only extract little Li and almost no Na even at a higher equilibrium pH. This might be due to the fact that alkyl substituent in β-diketone might has a hinder effect on the extraction behavior of metal. The more the number or longer of alkyl groups bonded to the α-carbon of the carbonyl group (shown as C* in Fig. 3), stronger the hinder effect on metal extraction.31 In addition, the experimental results showed that the equilibrium aqueous pH was in the range of 9.99-12.76, indicating that the equilibrium aqueous pH was always lower than the initial aqueous pH of 10.68-13.34. For β-diketones, there are two main kinds of molecules: the enol form and the keto form,31 as shown in Fig. 3. During the extraction process, some hydrogen ions in enol molecules moved from the organic phase to the aqueous phase through the ion exchange with metal ions, thus leading to a decrease in the equilibrium pH of aqueous phase. Therefore, the Li+ extraction can be enhanced by the increase of the alkali concentration in the aqueous phase during the extraction process, as shown in Figs. 2(a) and 2(b). For the system of Li++Na++Cl-+CO32-+H2O with Li+ concentration of 1.39 g·L-1 and Na+ 10 Environment ACS Paragon Plus

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concentration of 68.97 g·L-1 studied in this work, its initial aqueous pH was about 10.68, which was only a little lower than the optimum value of 13.06. Therefore, this kind of alkali extraction system containing β-diketone was suitable for the separation of Li+ from the alkali mother liquor obtained from the process of lithium carbonate production from the economic point of view. 3.2.3. Effect of PHPD/Cyanex93 Mole Ratio As it can be seen from Figs. 2(a) and 2(b) that the addition of Cyanex923 led to a higher selectivity of Li+ to Na+. Thus, in this work, the extraction system of PHPD and Cyanex923 was selected to do the following investigations. The effect of PHPD/Cyanex923 mole ratio on the extraction of Li+ and Na+ was studied in the range 0-5 while keeping the concentration of extractants to 0.6 mol·L-1, the initial aqueous pH of 13.06, A/O ratio of 1:1, extraction time of 30 min and 293.15 K. As shown in Fig. 4, the extraction percentage of Li+ increased from 1.17 to 97.83% over the PHPD/Cyanex923 mole ratio range from 0 to 2, and then decreased to 94.16% at the PHPD/Cyanex923 mole ratio of 5. However, the extraction percentage of Na+ increased from 0.85% to 12.75% over the PHPD/Cyanex923 mole ratio range from 0 to 4, and then decreased to 10.17% at the PHPD/Cyanex923 mole ratio of 5. The separation factor for Li+ over Na+ increased from 1.38 to 475.06 (as shown in Supporting Information Table S1) with an increase in the PHPD/Cyanex923 mole ratio from 0 to 2 and decreased thereafter with a further increase in the PHPD/Cyanex923 mole ratio. Therefore, the optimum parameter for the PADK/Cyanex923 mole ratio was 2 at the PHPD concentration of 0.4 mol·L-1. 3.2.4. Effect of A/O Volume Ratio To study the effects of the A/O volume ratio on the Li+ extraction with the extraction system containing 0.4 mol·L-1 PHPD and 0.2 mol·L-1 Cyanex923, the O/A phase ratio was varied from 1/2 to 10/1. The initial aqueous pH, extraction time, temperature and stirring speed were kept constant at 13.06, 30 min and 293.15 K, respectively. It was obvious from Supporting Information Table S2 that the separation factor of Li+ over Na+ decreased from 680.13 to 15.31 over the O/A phase ratio range from 1/2 to 10/1. The McCabe-Thiele diagram was constructed in Fig. 5. Two theoretical extraction stages for Li+ extraction are needed at an A/O ratio of 1.8/1. Decreasing the A/O ratio caused a decrease in the number 11 Environment ACS Paragon Plus


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of stages for Li+ extraction. Only one theoretical extraction stage is needed for Li+ extraction at an A/O ratio of 1/1. 0.03 g·L-1 Li and 62.99 g·L-1 Na were left in the raffinate and the loaded organic phase contained 1.36 g·L-1 Li and 5.98 g·L-1 Na. The mass ratio of Na+ to Li+ decreased from 49.62 to 4.40. Li+ in the loaded organic solution can be stripped by the hydrochloride acid solution and will be introduced in the section of 3.5. 3.3. Extraction Mechanisms The number of PHPD and Cyanex923 molecules involved in the extraction was firstly determined by the slope analysis method. To keep the concentrations of PHPD and Cyanex923 in the loaded organic phase close to those in the fresh organic phase, the extracted Li+ and Na+ concentrations should be very low. Therefore, the aqueous solution containing 0.15 g·L-1 Li and 2.0 g·L-1 Na was used, and initial aqueous pH, extraction time, temperature, as well as A/O ratio were kept constant at 12.30, 30 min, 298.15 K, and 1:1, respectively. At the constant Cyanex923 concentration of 0.2 mol·L-1, the effect of PHPD concentration on Li+ extraction was investigated, and the PHPD concentration was varied from 0.1 to 0.5 mol·L-1. Based on Eq. (14), the dependence of difference (log(DLi) - pH) between the logarithmic value of the lithium distribution ratio (log(DLi)) and the equilibrium aqueous pH against logarithmic value of concentration of PHPD in organic phase (log[PHPD]) was shown in Fig. 6. It can be seen that an increase in the concentration of PHPD resulted in the increase of lithium distribution ratio. The plot of log(DLi) pH as a function of log[PHPD] was found to be a straight line with a slope of 0.9530 and a correlation coefficient of 0.9995, indicating that one PHPD molecule involved in the lithium extraction process of one single Li+. Also, the organic system containing 0.4 mol·L-1 PHPD was used for the concentration of Cyanex923 dependence study. Fig. 7 plots the variation in the difference between log(DLi) and the equilibrium aqueous pH as a function of the logarithmic value of the Cyanex923 concentration in the organic phase (log[Cyanex923]). This result revealed that an increase in the concentration of Cyanex923 resulted in the increase of lithium distribution ratio. A linear relationship between log(DLi) - pH and log[Cyanex923]


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was obtained with a slope of 1.6179 and a correlation coefficient of 0.9995, suggesting that not just one Cyanex923 molecule involved in the extraction process of one single Li+. Based on the stoichiometric relations obtained above, the lithium extraction reactions with PHPD and Cyanex923 extractants could be expressed as in Eqs. (17) and (18). Two types of adduct complexes, LiES and LiES2, where E denoted the deprotonated PHPD, were formed in the Li+ extraction process. (17) (18) Based on the β-diketones extractants, Li extraction mechanisms have been studied by some researchers. For example, Kunugita et al.34 studied the separation of Li+ from the system of Li++Na++SO42-+H2O using Lix54 and TOPO. They found that the structure of lithium adduct formed in the organic phase was LiR(TOPO)1.3 (R represents the deprotonated Lix54 extractant). Pranolo et al.24 investigated the extraction of Li+ and Na+ in the aqueous system of Li++Na++Cl-+H2O using Lix54 and Cyanex923, finding that lithium adduct formed in the organic phase was LiRS on the basis of the slope analysis method. Healy23 found the Li adduct formed was Li(TTA)(TOPO)2 when HTTA and TOPO extractants were used to extract lithium from seawater. These results suggested that, except for the hinder effect of long alkyl substituents in β-diketone, the properties of aqueous solution might have an effect on the structure of lithium adduct formed in the organic solution. In addition, the synergistic effect of the neutral ligand Cyanex923 in the solvent extraction of Li+ can be confirmed by EMI-MS spectrometer, which has been used to identify metal-ligand complexes.35 Fig. 8 showed ESI-MS spectra of pure PHPD extractant, the extracted Li species in the absence and presence of Cyanex923. It was clear that the two ion peaks (m/z = 247.2 and 261.2) representing the protonated species of PHPD extractant and other weak fragments peaks were exhibited in Fig. 8(a). When PHPD alone was used to extract Li+, several other signals at m/z = 253.2, 267.2 and 271.2 were seen in Fig. 8(b), suggesting that two types of Li adducts, LiE and LiE(H2O), were present in the organic phase. With the further addition of Cyanex923, except that the m/z signals for Cyanex923 can be clearly seen in Fig. 8(c), those for Li adducts (LiES and LiES2) appeared. Due to the low content of Cyanex923 trimer, the adduct 13 Environment ACS Paragon Plus


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complex, LiES3 was not found in Fig. 8(c). This result was in accordance with that obtained in the experiments (as shown in Fig. 7). The structures of Li adducts should be in the form of a six-numbered ring due to the fact that the hydrogen connected to the two oxygen atoms in PHPD was replaced with Li during the extraction process, as shown in Fig. 3. 3.4. Determination of Thermodynamic Parameters The effect of temperature on the Li+ extraction from the system containing 0.15 g·L-1 Li and 2.0 g·L1

Na using 0.4 mol·L-1 and 0.2 mol·L-1 in kerosene was studied. Initial aqueous pH, extraction time and

A/O ratio were kept constant at 12.50, 30 min and 1:1, respectively. Supporting Information Table S3 listed the equilibrium aqueous pH, lithium extraction percentage and distribution coefficient at different temperature. It can be seen that an increase in temperature resulted in the decrease of lithium extraction percentage, as well as a slight change in the equilibrium aqueous pH. The dependence of difference between log(DLi) and equilibrium aqueous pH against 1/T was shown in Fig. 9. A straight line with a slope of 0.4414 and a correlation coefficient of 0.9229 was obtained. Based on the slope, the change in enthalpy (ΔH) during lithium extraction process can be calculated by the following van't Hoff equation: (19) where R is the gas constant (8.314 J·mol-1·K-1), T is the temperature (K) and C denotes the integral constant for the system. ΔH calculated was -8.45 KJ·mol-1, suggesting that the extraction process was exothermically driven in the extraction system of PHPD + Cyanex923 + kerosene. 3.5. Stripping of Lithium from the Loaded Organic The lithium in the loaded organic phases containing 1.39 g·L-1 Li was stripped with different concentrations of HCl solution at an A/O ratio of 1:1 and 298.15 K. During the stripping process of lithium and sodium, the pH of aqueous solution increased obviously. This could be attributed to the fact that hydrogen ions in the aqueous phase displaced Li and Na in the loaded organic phase, thus resulting in the decrease of H+ concentration in the stripping solution. Fig. 10 shows the extraction and stripping process of Li+. Supporting Information Table S4 listed the stripping percentages of lithium and sodium at different HCl concentration. It was clear that stripping efficiency of sodium was much higher than that of lithium. 14 Environment ACS Paragon Plus

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The stripping percentage of sodium increased greatly from 20.49% to 99.17% with an increase in HCl concentration from 0.01 to 0.20 mol·L-1 in the stripping solutions. However, the stripping percentage of Li only reached 23.88% at the HCl concentration of 0.2 mol·L-1. With the further increase of HCl concentration to 0.5 mol·L-1, the Li stripping percentage attained 99.45%. Based on these results, 40% sodium in the loaded organic phase could be firstly scrubbed using the HCl solution of 0.20 mol·L-1, and then the HCl solution of 0.5 mol·L-1 was used to scrub Li and the rest of Na in organic phase. 3.6. Application of the Route of Two Extraction Stages To validate the McCabe-Thiele result obtained above, a two stages counter-counter extraction was undertaken using the mother liquor provided by Qinghai CITIC Guoan Science and Technology Development Co. Ltd in China with the extraction system containing 0.4 mol·L-1 PHPD and 0.2 mol·L-1 Cyanex923 at the initial aqueous pH of 13.06, O/A ratio of 1.8:1, extraction time of 30 min and 293.15 K. Supporting Information Table S5 listed the compositions of the mother liquor. The equilibrium concentrations of Li+ and Na+ in the aqueous and organic phases after each extraction stage are shown in Fig. 11. The final raffinate (Raffinate II) contained 0.02 g·L-1 Li and 61.21 g·L-1 Na. The recovery of Li+ into the organic phase was up to 98.55%. Practically, the LiCl aqueous solution with higher purity could be obtained by additional extraction stages. These results indicated that the extraction system containing PHPD and Cyanex923 was very promising for separating lithium from the alkali solution with high sodium concentration. 5. CONCLUSIONS The extraction of lithium and its separation from the Li++Na++Cl-+CO32-+H2O system were studied with the extraction system containing PHPD and Cyanex923. The pH of aqueous solution had an important effect on the separation of lithium from this system. At initial aqueous pH of 13.06, the lithium extraction percentage was more than 97% with the extraction system consisting of 0.4 mol·L-1 PHPD and 0.2 mol·L-1 Cyanex923 in kerosene at an A/O ratio of 1:1 and 293.15 K. The separation factor of lithium over sodium was 495.06 with the solution containing 1.39 g·L-1 Li and 69.87 g·L-1 Na, indicating that high separation ability from sodium at high sodium concentration. On the basis of the McCabe-Thiele 15 Environment ACS Paragon Plus


Page 16 of 27

results of lithium extraction, two theoretical extraction stages were required at an A/O ratio of 1.8. By a combination of experiments (the slope analysis) and characterizations (EMI-MS spectra), Li adducts were found to be LiE, LiE(H2O), LiES, and LiES, where E and S denote the deprotonated PHPD and Cyanex923, respectively. Finally, a two-stage counter-counter extraction was validated to separate lithium from the mother liquor kindly donated by Qinghai CITIC Guoan Science and Technology Development Co. Ltd in China. ASSOCIATED CONTENT Supporting Information Table S1 listing effect of mole ratio of PHPD to Cyanex923 on Li and Na extraction percentage (%) and separation factor (βLi/Na) at an A/O ratio of 1:1, 293.15 K and initial pH 13.06. Table S2 listing effect of A/O ratio on Li and Na extraction and separation factor (βLi/Na) with extraction system containing 0.4 mol·L-1 PHPD and 0.2 mol·L-1 Cyanex923 at 293.15 K and initial pH 13.06. Table S3 listing effect of temperature on Li extraction percentage (%) and distribution coefficient (DLi) with extraction system containing 0.4 mol·L-1 PHPD and 0.2 mol·L-1 Cyanex923 at an A/O ratio of 1:1, extraction time of 30 min and initial pH 12.50. Table S4 listing effect of HCl concentration on stripping of Li and Na loaded in organic phase at an A/O ratio of 1:1 and 298.15 K. Table S5 listing Compositions of mother liquor. This materials is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author *Suojiang Zhang. E-mail: [email protected]. Phone: +86 10 82627080. Fax: +86 10 82627080. Author Contributions The paper was written through contributions of all authors. All authors have given approval to the final version of the paper. Junfeng Wang designed the experiments and wrote the paper. Shicheng Yang and Ruibing Bai executed experiments. Yongmei Chen gave some good suggestions about the experiments. Suojiang Zhang guided the project and revised the paper. Notes 16 Environment ACS Paragon Plus

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The authors declare no competing financial interest. ACKNOWLEDGEMENTS This work was supported by the National Natural Science Foundation of China (U1407111), the Fund of State Key Laboratory of Multiphase Complex Systems (MPCS-2017-A-08), Key Program of National

Natural

Science

Foundation

of

China

(91434203)

and

Key Research Program of Frontier Sciences CAS (QYZDY-SSW-JSC011). REFERENCES [1] Gao, Y. X.; Wang, X. P.; Wang, W. G.; et al. Synthesis, Ionic Conductivity, and Chemical Compatibility of Garnetlike Lithium Ionic Conductors Li5La3Bi2O12. Solid State Ionics 2010, 181, 1415-1419. [2] Kokal, I.; Ramanujachary, K. V.; Notten, P. H. L.; Hintzen, H. T. Sol–gel Synthesis and Lithium Ion Conduction Properties of Garnet-type Li6BaLa2Ta2O12. Materials Research Bulletin 2012, 47, 1932-1935. [3] Kokal, I.; Somer, M.; Notten, P. H. L.; Hintzen, H. T. Sol-gel Synthesis and Lithium Ion Conductivity of Li7La3Zr2O12 with a Garnet-related Type Structure. Solid State Ionics 2011, 185, 42-46. [4] Wang, R.; Yu, X. Q.; Bai, J. M.; et al. Electrochemical Decomposition of Li2CO3 in NiO–Li2CO3 Nanocomposite Thin Film and Powder Electrodes. Journal of Power Sources 2012, 218, 113-118. [5] Zhou, X. Y.; Chen, M. M.; Bai, H. L.; et al. Preparation and Electrochemical Properties of Spinel LiMn2O4 Prepared by Solid-state Combustion Synthesis. Vacuum 2014, 99, 49-55. [6] Wanger, T. C. The Lithium Future—Resources, Recycling, and the Environment. Conservation Letters 2011, 4, 202206. [7] Kesler, S. E.; Gruber, P. W.; Medina, P. A.; et al. Global Lithium Resources: Relative Importance of Pegmatite, Brine and Other Deposits. Ore. Geol. Rev. 2012, 48, 55–69. [8] Turek, M.; Gnot, W. Precipitation of Magnesium Hydroxide from Brine. Ind. Eng. Chem. Res. 1995, 34, 244–250. [9] Cui, X. Q.; Cheng, F. Q.; Zhang, A. H.; et al. Application of Continuous Acidolysis in TiO2 Production by Sulfuric Acid Process. Inorganic Chemical Industry 2012, 44, 33-35. [10] Zhu, G. R.; Wang, P.; Qi, P. F.; et al. Adsorption and Desorption Properties of Li+ on PVC-H1.6Mn1.6O4 Lithium Ion-sieve Membrane. Chem. Eng. J. 2014, 235, 340–348. [11] Xiao, J. L.; Sun, S. Y.; Song, X. F.; et al. Lithium Ion Recovery from Brine Using Granulated Polyacrylamide– MnO2 Ion-sieve. Chem. Eng. J. 2015, 279, 659–666. [12] Somrani, A.; Hamzaoui, A. H.; Pontie, M. Study on Lithium Separation from Salt Lake Brines by Nanoﬁltration (NF) and Low Pressure Reverse Osmosis (LPRO). Desalination 2013, 317, 184–192. [13] Ji, Z. Y.; Chen, Q. B.; Yuan, J. S.; et al. Preliminary Study on Recovering Lithium from High Mg2+/Li+ Ratio Brines by Electrodialysis. Separation and Purification Technology 2017, 172, 168–177. [14] Zhou, Z. Y.; Qin, W.; Fei, W. Y.; et al. A Study on Stoichiometry of Complexes of Tributyl Phosphate and Methyl Isobutyl Ketone with Lithium in the Presence of FeCl3. Chin. J. Chem. Eng. 2012, 20, 36–39.



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[15] Shi, C. L.; Jia, Y. Z.; Zhang, C.; et al. Extraction of Lithium from Salt Lake Brine Using Room Temperature Ionic Liquid in Tributyl Phosphate. Fusion. Eng. Des. 2015, 90, 1–6. [16] Grosjean, C.; Miranda, P. H.; Perrin, M.; et al. Assessment of World Lithium Resources and Consequences of Their Geographic Distribution on the Expected Development of the Electric Vehicle Industry. Renew. Sustain. Energy Rev. 2012, 16, 1735–1744. [17] Tran, K. T.; Luong, T. V.; An, J. W.; et al. Recovery of Magnesium from Uyuni Salar Brine as High Purity Magnesium Oxalate. Hydrometallurgy 2013, 138, 93–99. [18] Wu, X. W.; Zhu, H. L. Preparation of High Purity Magnesium Peroxide by Magnesia and Ammonium Salt Solutions. Guangdong Chemical Industry 2011, 39, 64-65. [19] G.W. Liu, Z.R. Li, J. Li, et al. A method for recovery lithium from mother liquor. CN104030322A, 2014. [20] Wang, J. F.; Wu, X. W.; Zhang, S. J. Development of the Thermodynamic Model for Li2CO3-NaCl-Na2SO4-H2O System and Its Application. Journal of Chemical Thermodynamics 2018, 123, 62–73. [21] Marinkina, G. A.; Zanina, A. S.; Shergina, S. I.; et al. Bulletin of the Russian Academy of Sciences Division of Chemical Science 1992, 41, 1015-1020. [22] Zhang, L. C.; Li, L. J.; Shi, D.; et al. Selective Extraction of Lithium from Alkaline Brine Using HBTA-TOPO Synergistic Extraction System. Separation and Purification Technology 2017, 188, 167–173. [23] Healy, T.V. Synergism in the Solvent Extraction of Alkali Metal Ions by Thenoyl Trifluoracetone. J. Inorg. Nucl. Chem. 1968, 30, 1025–1036. [24] Pranolo, Y.; Zhu, Z. W.; Cheng, C.Y. Separation of Lithium from Sodium in Chloride Solutions Using SSX Systems with LIX 54 and Cyanex 923. Hydrometallurgy 2015, 154, 33–39. [25] Ishimori, K.; Imura, H. The Synergistic Selective Extraction of Lithium(1) with 2-thenoyltrifluoroacetone and 1,10Phenanthroline Derivatives. Solvent Extr. Res. Dev. 2002, 9, 13–25. [26] Kim, Y. S.; In, G.; Choi, J. M. Chemical Equilibrium and Synergism for Solvent Extraction of Trace Lithium with Thenoyltrifluoroacetone in the Presence of Trioctylphosphine Oxide. Bull. Korean Chem. Soc. 2013, 24, 1495–1500. [27] Kinugasa, T.; Nishibara, H.; Murao, Y.; et al. Equilibrium and Kinetics of Lithium Extraction by a Mixture of Lix54 and TOPO. J. Chem. Eng. Jpn. 1994, 27, 815–818. [28] Zhou, Z. Y.; Liang, S. K.; Qin, W.; et al. Extraction Equilibria of Lithium with Tributyl Phosphate, Diisobutyl ketone, Acetophenone, Methyl Isobutyl Ketone, and 2-heptanone in Kerosene and FeCl3. Ind. Eng. Chem. Res. 2013, 52, 7912–7917. [29] Xiang, W.; Liang, S. K.; Zhou, Z.Y.; et al. Lithium Recovery from Salt Lake Brine by Counter-current Extraction Using Tributyl Phosphate/FeCl3 in Methyl Isobutyl Ketone. Hydrometallurgy 2017, 171, 27–32. [30] Mickler, W.; Uhlemann, E.; Herzschuh, R. The Characterization of the Active Components in Commerical β– Diketone-type Extractants Lix 54 and MX 80A. Separation Science and Technology 1992, 27, 1171-1179. [31] Fu, W.; Chen, Q. Y.; Hu, H. P.; et al. Solvent Extraction of Copper from Ammoniacal Chloride Solutions by Sterically Hindered β-diketone Extractants. Separation and Purification Technology 2011, 80, 52–58. [32] Chekmarev, A. M.; Kondralyeva, E. S.; Kolesnikov, V. A.; Gubin, A. F. Extractant Selection for Copper(II) Ion Extraction. Doklady Chemistry 2015, 464, 221-225. [33] Seeley, F. G.; Baldwin, W. H. Extraction of Lithium from Neutral Salt Solutions with Fluorinated β-diketones. Journal of Inorganic and Nuclear Chemistry 1976, 38, 1049-1052.


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[34] Kunugita, E.; Kim, J. H.; Komsawa, I. Extraction and Separation of Lithium and Sodium by Solvent Extraction with. β-diketone and Neutral Ligand. Kagaku Kogaku Ronbunshu 1989, 15, 504–510. [35] Boda, A.; Ali, S. M.; Rao, H.; Ghosh, S. K. Ab Initio and Density Functional Theoretical Design and Screening of Model Crown Ether Based Ligand (host) for Extraction of Lithium Metal Ion (guest): Effect of Donor and Electronic Induction. Journal of Molecular Modeling 2012, 18, 3507-3522.



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Figure Legends Figure 1. Effect of extraction time on the extraction of Li and Na by the system containing 0.4 mol·L-1 PHPD and 0.2 mol·L-1 Cyanex923 at an A/O ratio of 1:1, 293.15 K and initial pH 13.06.. Figure 2. Effect of initial pH value on the extraction of Li and Na by the extraction system containing 0.4 mol·L-1 PHPD and 0.2 mol·L-1 Cyanex923 (a) as well as 0.6 mol·L-1 PHPD and 0 mol·L-1 Cyanex923 (b) at an A/O ratio of 1:1, extraction time of 30 min and 293.15 K. Figure 3. Chemical structures of PHPD in the keto and enol forms. Figure 4. Effect of mole ratio of PHPD to Cyanex923 on the extraction of Li and Na at an A/O ratio of 1:1, extraction time of 30 min, 293.15 K and initial pH 13.06. Figure 5. McCabe-Thiele plot for the extraction of Li by the system containing 0.4 mol·L-1 PHPD and 0.2 mol·L-1 Cyanex923 at A/O ratio range from 1:2 to 10:1, Li concentration of 1.39 g·L-1, Na concentration of 68.97 g·L-1, initial pH value of 13.06, 293.15 K and extraction time of 30 min. Figure 6. Effect of PHPD concenration on Li extraction at a constant Cyanex923 concentration of 0.2 mol·L-1, Li concentration of 0.15 g·L-1, Na concentration of 2.0 g·L-1, A/O ratio of 1:1, initial pH value of 12.3, 298.15 K and extraction time of 30 min. Figure 7. Effect of Cyanex923 concenration on Li extraction at a constant PHPD concentration of 0.4 mol·L-1, Li concentration of 0.15 g·L-1, Na concentration of 2.0 g·L-1, A/O ratio of 1:1, initial pH value of 12.3, 298.15 K and extraction time of 30 min. Figure 8. ESI-MS spectra of pure PHPD (a), the extracted Li species by PHPD in the absence (b) and presence of Cyanex923 (c) using positive ion mode. Figure 9. Effect of temperature on the extraction of Li by the system containing 0.4 mol·L-1 PHPD and 0.2 mol·L-1 Cyanex923 at an A/O ratio of 1:1, Li concentration of 0.15 g·L-1, Na concentration of 2.0 g·L1

, extraction time of 30 min and initial pH 12.3.

Figure 10. Two-stage counter-current simulation study for extraction of lithium and sodium by the system containing 0.4 mol·L-1 PHPD and 0.2 mol·L-1 Cyanex923 at A/O ratio of 1.8:1, Li concentration of 1.39 g·L-1, Na concentration of 68.97 g·L-1, initial pH value of 13.06, 293.15 K and extraction time of 30 min.


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Extraction percentage (%)

100

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

80 Li extraction

60

Na extraction 40 20 0

0

300

600 900 1200 Extraction time (s)

1500

1800

Figure 1. Effect of extraction time on the extraction of Li and Na by the system containing 0.4 mol·L-1 PHPD and 0.2 mol·L-1 Cyanex923 at an A/O ratio of 1:1, 293.15 K and initial pH 13.06.

Figure 2. Effect of initial pH value on the extraction of Li and Na by the extraction system containing 0.4 mol·L-1 PHPD and 0.2 mol·L-1 Cyanex923 (a) as well as 0.6 mol·L-1 PHPD and 0 mol·L-1 Cyanex923 (b) at an A/O ratio of 1:1, extraction time of 30 min and 293.15 K.



Figure 3. Chemical structures of PHPD in the keto and enol forms.

Extraction percentage (%)

100 80

Li extraction 60 Na extraction Li distribution coefficient Na distribution coefficient

60

40

40

20

20

Distribution coefficient

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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0 0

0

1 2 3 4 Mole ratio of PHPD to Cyanex923

5

Figure 4. Effect of mole ratio of PHPD to Cyanex923 on the extraction of Li and Na at an A/O ratio of 1:1, extraction time of 30 min, 293.15 K and initial pH 13.06.


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3

A/O=2:1

A/O=10:1

A/O=1.8:1 Two stages

2

[Li]org (g/L)

A/O=5:1

Feed concentration of Li, 1.39 g/L

A/O=3:1

A/O=1:1

1 A/O=1:2 A/O=1:1 One stage

0 0.0

0.5

[Li]aq (g/L)

1.0

1.5

Figure 5. McCabe-Thiele plot for the extraction of Li by the system containing 0.4 mol·L-1 PHPD and 0.2 mol·L-1 Cyanex923 at A/O ratio range from 1:2 to 10:1, Li concentration of 1.39 g·L-1, Na concentration of 68.97 g·L-1, initial pH value of 13.06, 293.15 K and extraction time of 30 min.

-9.4

Log(DLi)-pH

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


-9.6

y = 0.9530x - 9.1021 2 R = 0.9995

-9.8

-10.0

-10.2

-1.0

-0.8

-0.6

-0.4

-0.2

Log[PHPD]

Figure 6. Effect of PHPD concenration on Li extraction at a constant Cyanex923 concentration of 0.2 mol·L-1, Li concentration of 0.15 g·L-1, Na concentration of 2.0 g·L-1, A/O ratio of 1:1, initial pH value of 12.3, 298.15 K and extraction time of 30 min.

ACS Paragon Plus Environment

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-9.0 -9.2

Log(DLi)-pH

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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-9.4 -9.6

y = 1.6179x - 8.3284 2 R = 0.9995

-9.8

-10.0 -10.2

-1.0

-0.9

-0.8

-0.7

-0.6

-0.5

Log[Cyanex923]

Figure 7. Effect of Cyanex923 concenration on Li extraction at a constant PHPD concentration of 0.4 mol·L-1, Li concentration of 0.15 g·L-1, Na concentration of 2.0 g·L-1, A/O ratio of 1:1, initial pH value of 12.3, 298.15 K and extraction time of 30 min.


24

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Figure 8. ESI-MS spectra of pure PHPD (a), the extracted Li species by PHPD in the absence (b) and presence of Cyanex923 (c) using positive ion mode.


25


1.3 1.2

y = 0.4414x - 0.3532 2 R =0.9229

1.1

Log(DLi)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1.0 0.9 0.8

2.9

3.0

3.1 3.2 -1 1000/T (K )

3.3

3.4

Figure 9. Effect of temperature on the extraction of Li by the system containing 0.4 mol·L-1 PHPD and 0.2 mol·L-1 Cyanex923 at an A/O ratio of 1:1, Li concentration of 0.15 g·L-1, Na concentration of 2.0 g·L-1, extraction time of 30 min and initial pH 12.3.

Fig. 10. Lithium extraction and stripping process of Li+ with PHPD and Cyanex923 extractants.


26

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Loaded organic solution II Li (g·L-1)

Loaded organic solution I

2.47

0.00

1.60

Na (g·L-1) 13.97

0.00

7.18 First stage

1.39 68.97

Aqueous solution

Fresh organic solution

Second stage 0.50 64.98 Raffinate I

0.02 61.21

Raffinate II

Figure 11. Two-stage counter-current simulation study for extraction of lithium and sodium by the system containing 0.4 mol·L-1 PHPD and 0.2 mol·L-1 Cyanex923 at A/O ratio of 1.8:1, Li concentration of 1.39 g·L-1, Na concentration of 68.97 g·L-1, initial pH value of 13.06, 293.15 K and extraction time of 30 min.


27

Lithium recovery from the mother liquor obtained in the process of

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