Solvent extraction of lithium from aqueous solution using an ammonium ionic liquid

Article abstract of DOI:10.1016/j.molliq.2020.112756

A new functionalized ionic liquid (FIL), tetrabutylammonium 2-ethylhexyl hydrogen-2-ethylhexylphosphonate ([N₄₄₄₄][EHEHP]), was prepared and used in the extraction of lithium ion from aqueous solution. The factors affecting the extraction efficiencies, such as aqueous acidity, extractant concentration and temperature, were optimized. The mechanism involved in the extraction system was analyzed by slope analysis and FT-IR data. According to the Van't Hoff equation, the thermodynamic functions of the extraction reaction in ionic liquid system were obtained. Liquid/liquid extraction tests indicated that the ionic liquid system exhibited better selectivity towards lithium ions in the solution containing alkali metal ions. In addition, the quantitative stripping of lithium ions from the loaded ionic liquid phase was carried out and the effect of hydrochloric acid concentration on stripping rate was investigated in detail.

Full text of DOI:10.1016/j.molliq.2020.112756

Journal Pre-proof
Solvent extraction of lithium from aqueous solution using an
ammonium ionic liquid
Chenglong Shi, Hongxia Li, Bing Liu, Yaru Qin, Guixiu Song
PII:
S0167-7322(19)35537-0
DOI:
https://doi.org/10.1016/j.molliq.2020.112756
MOLLIQ 112756
Reference:
To appear in:
Journal of Molecular Liquids
Received date:
Revised date:
Accepted date:
7 October 2019
16 February 2020
19 February 2020
Please cite this article as: C. Shi, H. Li, B. Liu, et al., Solvent extraction of lithium from
aqueous solution using an ammonium ionic liquid, Journal of Molecular Liquids(2020),
https://doi.org/10.1016/j.molliq.2020.112756
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Solvent extraction of lithium from aqueous solution using a
ammnoium ionic liquid
a
a
b,c
a
a
Chenglong Shi , Hongxia Li , Bing Liu , Yaru Qin *, Guixiu Song
a
College of Chemistry and Chemical Engineering, Qinghai Nationalities University, 810007,
Xining, China.
b
Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Lake Resources,
Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, 810008, Qinghai, China.
c
University of Chinese Academy of Sciences, 100049, Beijing, China
Abstract
A new functionalized ionic liquid (FIL), tetrabutylammonium 2-ethylhexyl
hydrogen-2-ethylhexylphosphonate ([N4444][EHEHP]), was prepared and used in the
extraction of lithium ion from aqueous solution. The factors affecting the extraction
efficiencies, such as aqueous acidity, extractant concentration and temperature, were
optimized. The mechanism involved in the extraction system was analyzed by slope
analysis and FT-IR data. According to the Van’t Hoff equation, the thermodynamic
functions of the extraction reaction in ionic liquid system were obtained. Liquid/liquid
extraction tests indicated that the ionic liquid system exhibited better selectivity
towards lithium ions in the solution containing alkali metal ions. In addition, the
quantitative stripping of lithium ions from the loaded ionic liquid phase was carried
out and the effect of hydrochloric acid concentration on stripping rate was
investigated in detail.
Keywords: Lithium, Solvent extraction, Ionic liquids.
1
. Introduction
Ionic liquids (ILs) are organic salts molten at temperatures lower than 373 K [1].
Usually they are made up of a bulky, asymmetric organic cation, and an inorganic or
organic anion. ILs are attracting increasing attention in various fields because they
have some unique characteristics such as negligible vapor pressures, nonflammability,
high polarity, high thermal stability and tunable properties [2-7]. Earlier studies on the
extraction of metal ions with ILs made use of hydrophobic ILs containing
imidazolium cations and fluorinated anions and the ILs was only used as a solvent for
a molecular extractant [8-13]. These ionic liquids are usually involved in the
extraction reaction by cation exchange. Although the extraction efficiency can be
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increased, the ILs cations are lost to the aqueous solution. This not only contaminates
the aqueous solution, but also decreases the stability of the organic phase. When the
cationic or anionic part of the ILs tethered covalently with an organic functional
moiety, they are known as functionalized ionic liquids (FILs). Due to the presence of
coordinating groups, these FILs can be used as extractants for metal ions and not just
diluents in extraction systems. FILs are enjoying a strong interest as novel extractants
for solvent extraction of metal ions [14-17]. For example, Shen et al. [18] synthesized
a
new
FIL
trialkylmethylammonium
di-(2-ethylhexyl)orthophosphinate
(
[A336][P507]) and studied the extraction behavior of mid-heavy rare earth metals
REs). The [A336][P507] showed high extractability towards mid-heavy REs from
(
the simulated leach liquor. Dong et al. [19] reported the extraction of Y(III) using FIL
trihexyl(tetradecyl)-phosphonium] [sec-octylphenoxy acetate] ([P6,6,6,14][SOPAA]).
[
The extractability and selectivity of [P6,6,6,14][SOPAA] for Y(III) are pronouncedly
better than those of acidic extractant HSOPAA. The extraction mechanism and
stripping
property
of
bifunctional
ionic
liquid
[methyltrioctyl
ammonium][sec-octylphenoxy acetic acid] ([N1888][CA12]) for yttrium separation
were investigated by Wang et al. [20]. Yttrium product with a purity of 99.1 mol.%
was obtained via 13 stages of extraction section, 8 stages of scrubbing section and 5
stages of stripping section.
Lithium is currently a very important metal, largely as a result of its crucial role
in energy production and storage, especially in the areas of Li ion battery technology
and nuclear power [21-24]. Liquid-liquid extraction is an efficient and economical
method for the separation of lithium ions from aqueous solutions. The extractants
mainly includes alcohols, ketones, crown ethers, organophosphorus compounds and
the like. Among them, the tributyl phosphate (TBP) is a popular neutral
organophosphorus extractant with high selectivity to lithium ions. For example, the
extraction of lithium by TBP-kerosene-FeCl extraction system was reported by Sun
3
et al. [25]. Under the optimal conditions, the single-stage extraction efficiency of
lithium reached 88%. The extraction behavior of lithium ions using TBP in methyl
isobutyl ketone (MIBK) with FeCl was reported by Zhou et al. [26]. It was found that
3
this extraction system can effectively extract lithium ions. In a follow-up study, the
reaction mechanisms were proposed and the extracted species were ascertained based
on the experimental data [27]. The formed complex was found to be LiFeCl ·2MIBK.
4
Though conventional extraction systems could obtain a satisfied separation, most of
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them must be used under strongly acidic conditions to avoid the hydrolysis of ferric
ions in the aqueous phase. These systems often suffered from emulsification,
equipment corrosion and other problems[28].
In view of this, the present study deals with the extraction behavior of lithium
ions using
a
novel FIL, namely tetrabutylammonium 2-ethylhexyl
hydrogen-2-ethylhexylphosphonate ([N4444][EHEHP]). The ionic liquid is made up of
a hydrophobic organic cation, and a long chain anion. There is a metal-coordinating
group attached to the anion and the FIL could be used as a extractant. Ion association
other than ion exchange may occur in this new extraction system. It was therefore
envisaged that the loss of ILs to the aqueous phase would be reduced significantly,
which was favorable for recycle utilization of the ionic liquid. The effects of various
parameters such as aqueous acidity, concentration of ionic liquid and temperature on
the extraction of lithium ions was studied. The extraction behavior of [N4444][EHEHP]
is compared with that of the molecular extractant HEHEHP. The stripping of lithium
ions from the loaded organic phase was also investigated.
2
. Experimental
2
.1. Reagents
The chemicals, tetrabutylammonium chloride ([N4444][Cl]), barium chloride,
cesium chloride, and silver nitrate, were procured from Sigma–Aldrich. The
-ethylhexyl hydrogen-2-ethylhexylphosphonate (HEHEHP) was procured from J&K
2
Scientific Ltd. The lithium chloride, sodium hydroxide, sodium chloride and
dichloromethane were procured from Aladdin Industrial Corporation. All reagents
used in this study were of AR grade.
2
.2. Instruments
NMR spectra were measured on an Inova-400 spectrometer (Agilent, USA) at
5°C. The metal contents of the aqueous phase were determined by inductively
2
coupled plasma emission spectrometer (ICAP 6300, Thermo Fisher Scientific). The
concentration of metal ions in the organic phase was obtained by mass balance.
Fourier transform infrared spectroscopy (FTIR) measurements were performed with a
Nexus 870 FTIR Spectrometer (Thermo Nicolet Corporation, USA).
2
.3. Synthesis of FIL
Firstly, the tetrabutylammonium chloride was dissolved in dichloromethane. The
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solution of [N4444][Cl] in dichloromethane and sodium hydroxide solution were
−
−
thoroughly shaken and mixed. Ion exchange will occur between [OH] and [Cl] and
[
N4444][OH] was obtained. In order to verify the completeness of the ion exchange
−
reaction, the acidified silver nitrate solution was used to test the [Cl] in the aqueous
phase after the reaction. Then, an acid-base neutralization reaction was carried out
between 2-ethylhexyl
hydrogen-2-ethylhexylphosphonate (HEHEHP) and
[
N4444][OH]. After rotary evaporation, stripping and drying, the [N4444][EHEHP] was
finally obtained. It was observed that the resulting [N4444][EHEHP] was a pale yellow
viscous liquid. Fig. 1 showed the structure of HEHEHP, [N4444][Cl] and
[
N4444][EHEHP]. The [N4444][EHEHP] was characterized by NMR spectrometer, and
1
13
the data of H NMR and C NMR were given below.
1
[
N4444][EHEHP]. H NMR (300 MHz, CDCl ): 0.95-1.03 (12H, 4CH ), 1.14-1.18
3
3
(
12H, 4CH ), 1.24 (2H, PCH ), 1.42-1.61(32H, 16CH ), 1.793 (2H, 2CH), 3.419 (8H,
3 2 2
1
3
4
1
NCH ), 3.61 (2H, OCH ); C NMR (CDCl , ppm): 10.41 (4CH ), 11.72(1CH ),
2 2 3 3 3
3.64 (1CH ), 14.10(2CH ), 19.58 (4CH ), 23.14(PCH ), 23.23 (1CH ), 24.30
3
3
2
2
2
(
1CH ), 26.71(4CH ), 28.81 (1CH ), 29.11 (1CH ), 30.15 (1CH ), 31.30(1CH ),
2 2 2 2 2 2
3
2.03(1CH ), 33.95(1CH ), 34.96(1CH), 41.42(1CH), 57.96(4NCH ), 66.79 (OCH ).
2 2 2 2
Fig. 1. Chemical structure of the [N4444][EHEHP], [N4444][Cl] and HEHEHP.
2
.4. Extraction experiments
The FIL in this paper was viscous, hence, the organic phase was prepared by
dissolving FIL in dichloroethane. The extraction experiments were performed by
contacting 2.5 mL of aqueous phase and 5 mL of organic phase in separatory funnels.
+
−1
The concentration of Li in aqueous phase is 0.5 g·L . The two-phase system was
fully shaken for 30 minutes with the help of a mechanical shaker. The aqueous phase
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was removed and properly diluted. The metal contents of the aqueous phase were
determined by ICAP. The lithium ions were back-extracted from loaded organic phase
with dilute hydrochloric acid. The stripping efficiency was calculated by measuring
the concentration of lithium ions in the stripping acid. The extraction efficiency (E)
and distribution ratio (D) were defined as followed:
[
Li]org
Vaq
C - Ce
o
D =
=

(1)
(2)
[
Li]aq
Ce
Vorg
C - C
o
e
E(%) =
100
Co
where C and C represent initial and equilibrated concentrations of metal ions in
o
e
aqueous phase, respectively. V and V (mL) represent the volume of the aqueous
aq
org
phase and organic phase, respectively.
3
. Results and Discussion
.1. Effect of hydrochloric acid concentration
3
95
90
85
80
75
70
65
60
8
6
4
2
0
[
N4444][EHEHP]
HEHEHP
0
.0
0.1
0.2
0.3
0.4
0.5
-
1
[HCl], mol L
+
Fig. 2. Effect of aqueous acidity on extraction efficiency of lithium. Aqueous phase: [Li ] = 0.5
−
1
−1
g·L and [HCl] = 0-0.5 mol·L ; temperature = 293 K.
+
Fig. 2 illustrated the extraction behavior of FIL and HEHEHP for Li as a
+
function of aqueous acidity. Notably, quantitative extraction of Li was achieved over
the whole pH range. When the hydrochloric acid was not added to the aqueous phase,
the percentage extraction of lithium at equilibrium amounted to 94.61% with FIL.
Increasing HCl concentration was not conducive to the extraction of lithium, and the
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−
1
extraction efficiency in 0.5 mol·L HCl decreased to 64.50%. Obviously, the
presence of HCl in the aqueous phase inhibited the lithium trapping by
[
N4444][EHEHP]. The decrease in extraction efficiency could be attributed to the
+
+
stronger coordination ability between H and the extractant than that between Li and
+
the extractant. With the H concentration in the aqueous phase increased, the amount
+
of extractant combined with H was also increased. This resulted in a reduced
+
probability of coordination between the extractant and Li , which decreased the
+
extraction efficiency of Li . For comparison purposes, the extraction behavior of the
acidic extractant HEHEHP was also investigated. As can be seen from Fig. 2, the
+
extraction efficiency of Li by acidic extractant was very low, usually less than 10%.
This could be explained by the lack of inner synergism in HEHEHP. There existed an
inner synergism between the anion and cation of FIL, resulting in a higher extraction
efficiency for the metal ions[29,30].
3
.2. Extraction mechanism
In solvent extraction, the slope analysis method was usually used to determine
the mechanism of the extraction system. By plotting logD as a function of
log[extractant], the slope of the line was obtained after fitting. And the slope indicated
the number of molecules of the extractant in the complex formed in the organic phase.
+
Since FIL contained functional groups that could coordinate with Li , the extraction
+
of Li in this system may be realized by ion association rather than ion exchange. The
extraction reaction equation, from available literature on analogous extraction systems
+
[
19], could be expressed by Eq. (3). The concentration of Li in aqueous phase is 0.5
−
1
g·L and the concentration of FIL in the organic phase was adjusted by using
dichloroethane as a diluent. Fig. 3 showed the effect of the [N4444][EHEHP]
concentration on the distribution coefficients of lithium ions at a phase ratio (O/A) of
2
.
+
aq)
-
Li( +n[N4444][EHEHP](org) +Cl LiCln[N4444][EHEHP](org)
(3)
(aq)
The distribution ratio (D ) was equal to the ratio of the total concentration of
Li
lithium ions in organic phase to its total concentration in the aqueous phase.
According to the Eq. (3), the D and reaction equilibrium constant (K) can be
Li
calculated as:
-
log D = log K + n log[N4444
•
EHEHP](org) + log[Cl ]
(4)
Li
(aq)
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As can be seen from Fig. 3, the D increased with increasing the concentration
Li
of FIL. A straight line with a slope of 1.16 was obtained by linear regression analysis
of the extraction data. This showed that around one molecule of FIL was required to
+
coordinated with one molecule of Li into the organic phase. This may be due to the
large volume of the ionic liquid and steric hindrance, so that the complex formed by
+
−
one molecule of FIL and Li was more stable. The plot of logD versus log[Cl ] was
Li
−
also recorded (Fig.4). It was found that the plot of logD versus log[Cl ] produced a
Li
straight line with a slope of 1.19, suggesting that only one chloride ion was included
in the complex. In present system, therefore, a plausible mechanism of lithium
extraction by the FIL dissolved in dichloroethane was considered to progress as Eq.
(5).
+
aq)
-
Li( +[N4444][EHEHP](org) +Cl LiCl[N4444][EHEHP](org)
(5)
(aq)
1
1
0
0
0
.2
.0
.8
.6
.4
Slope = 1.16
2
R = 0.97
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.1
log [N4444·EHEHP](org)
+
-1
Fig. 3. Plot of log D as a function of log [N4444·EHEHP](org). Aqueous phase: [Li ] = 0.5 g·L ;
Li
temperature = 293 K; organic phase: varying concentrations of [N4444][EHEHP] in dichloroethane.
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0
0
0
0
0
.8
.6
.4
.2
.0
Slope = 1.19
2
R = 0.9906
-0.2
-1.9
-1.8
-1.7
-1.6
-1.5
-1.4
-1.3
-1.2
-1.1
-
log [Cl ]
−
−
−1
Fig. 4. Plot of log D as a function of log [Cl ]. Aqueous phase: [Cl ] = 0.51 - 2.55 g·L ; organic
Li
phase: [N4444][EHEHP] in dichloroethane; temperature = 293 K; phase ratio O/A = 2.
a
1
380
1
463
2
874
1047
1
186
2
930
b
1
380
2
960
874
930
1463
2
1164
1
047
2
2
960
000
3
2500
2000
1500
1000
500
-
1
Wavelength, cm
Fig. 5. FTIR analysis of the organic phase.
The organic phases were characterized by an infrared spectrometer. Fig. 5 (a) and
Fig. 5 (b) were the infrared spectra of the organic phase before and after extraction,
respectively. The results showed that the characteristic peaks of most of the functional
groups in FIL did not change after lithium extraction. For example, the peaks at 2960,
−
1
2
874, 1463 and 1380 cm were considered to be the stretching vibration and
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+
deformation vibration of -CH groups in [N ] cations. In the spectra of loaded
3
4444
organic phase (Fig. 5b), the typical peaks of -CH groups still remained compared
3
–
with the net organic phase (Fig. 5a). Furthermore, The [EHEHP] anions of FIL gave
−
1
a symmetrical stretching vibration for the P-O-C bond at 1047 cm , which was
unchanged after extraction. Another important functional group of FIL was the P=O
−
1
group. Its characteristic absorption peak occurred at 1186 cm . After extraction, the
−1
+
corresponding peak was shift to 1164 cm , indicating that P=O and Li interacted
during the extraction process. The electron density of P=O groups decreased, causing
the characteristic peak of P=O groups to move to a low wave number.
3
.3. Determination of thermodynamic parameters
To investigate the effect of temperature on the extraction behavior of Li ,
+
extraction studies were performed at various temperatures in the range of 293–333 K
using [N4444][EHEHP] / dichloroethane. As can be seen from Fig. 6, the extraction
efficiency of lithium ion decreased significantly with the increase of temperature. At
2
93 K, the single-stage extraction efficiency of lithium ion was 94.64%. When the
temperature was raised to 333 K, the extraction efficiency of lithium ions decreased to
8
3
6.09%. At the same time, the distribution ratio of lithium ions decreased from 8.83 to
.10. The reason why the extraction efficiency of lithium ions decreased may be that
the high temperature increased motion of molecules, which made the stability of the
complex formed between lithium ion and the extractant decrease. According to the
Vant Hoff’s equation, a relationship between the enthalpy change (ΔH°), the
distribution ratio of lithium ions, and the temperature can be obtained, and the
equation is shown in Eq. (6). It can be seen that there is a linear relationship between
logD and the extraction temperature. When logD is plotted against 1000/T, the slope
of the line is -ΔH°/2.303R. The variation of log D as a function of reciprocal
temperature was shown in Fig. 7. It can be seen from Fig. 7 that there is a good linear
relationship between the distribution ratio and the reciprocal temperature. The slope
of the fitted curve was 1.11, and the enthalpy of the extraction reaction was calculated
−
1
to be -21.25 kJ·mol . The change in enthalpy of extraction was negative, which
indicated that the extraction of lithium ions was exothermic. An increase in
temperature at constant pressure will shift the equilibrium (Eq. 5) to the left, so the
extraction efficiency of lithium ions decreased.
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o


log D H

(6)
(1 T) 2.303R
The relationship between the Gibbs energy change(ΔG°), the entropy (ΔS°), and
the temperature can be expressed as follows:
o
ΔG =-2.303RT logK
(7)
(8)
o
o
ΔH - ΔG
o
ΔS =
T
The value of log K can be obtained from the intercept of the line in Fig. 3.
According to Eq. (7), the Gibbs free energy of the extraction system was calculated to
−1
be -5.89 kJ·mol . The value of Gibbs free energy was negative, indicating that the
extraction reaction of lithium ion was spontaneous. By substituting the values of the
enthalpy change and the Gibbs free energy into Eq. (8), the entropy change of the
extraction reaction can be calculated at a fixed temperature. At 293 K, the entropy
−
1
−1
change of the extraction reaction was -52.42 J·K ·mol , which indicated that the
extraction was ordered in nature. The possible reason was that the butyl chains in
ionic liquid became more crowded and the degrees of freedom were decreased when
the extractant was complexed with lithium ions[31].
1
1
8
6
4
2
0
2
96
94
92
90
88
86
84
0
E%
D
290
300
310
320
330
340
Temperature, K
+
−1
Fig. 6. Effect of temperature on extraction efficiency of lithium. Aqueous phase: [Li ] = 0.5 g·L ;
organic phase: [N4444][EHEHP] in dichloroethane; temperature = 293–333 K.
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1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
Slope = 1.11
2
R = 0.99
3.0
3.1
3.2
3.3
3.4
-
1
1
000/T, K
+
+
−1
Fig. 7. Plot of log D versus 1000/T for Li extraction. Aqueous phase: [Li ] = 0.5 g·L ; organic
phase: [N4444][EHEHP] in dichloroethane; temperature = 293–333 K.
3
.4. Extraction of lithium ions from multi-metal-ion solutions
9
8
7
6
5
4
3
2
1
0
Li
Na
K
Rb
Cs
Fig. 8. Extraction efficiencies of several alkali metal ions with [N4444][EHEHP] in dichloroethane.
+
+
+
+
+
−1
Aqueous phase: [Li ] = [Na ] = [K ] = [Rb ] = [Cs ] = 0.5 g·L ; organic phase: [N4444][EHEHP]
in dichloroethane; phase ratio O/A=1/1; temperature = 293 K.
A competitive extraction of alkali metal ions by FIL in dichloroethane was
carried out to assess the selectivity of the present system. The distribution ratios are
plotted in Fig. 8. The lithium ions are effectively extracted under the extraction
conditions. However, the ionic liquid system had very low distribution coefficients for
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the other alkali metal ions. The possible reason for this selectivity could be that the
+
+
+
+
cation [Li ] has higher surface charge density than other alkali metals (Na , K , Rb
+
and Cs ) due to its smaller ionic radius. So the higher stability of the complexes
formed from [N4444][EHEHP] with lithium ions. The results clearly showed that the
ionic liquid system was found to be highly selective for the extraction of lithium in
the solution containing alkali metal ions.
3
.5. Stripping experiments
In traditional neutral phosphonium extraction systems, the back extraction of
lithium ions from the loaded organic phase was usually carried out concentrated
hydrochloric acid，which may cause serious equipment corrosion. For example, Zhang
et al. [32] reported the extraction behavior of lithium ions with
HBTA-TOPO-kerosene system. The lithium ions was stripped from the loaded
−
1
organic phase by 3.0 mol·L HCl solution. Shi et al. [33] studied the lithium ions
−
1
extraction process using TBP - kerosene - FeCl system. The 6.0 mol·L HCl solution
3
was chosen as the stripping agent, and the stripping efficiency of lithium ions was
close to 100% at a phase ratio of 10/1 through a four – stage stripping process. In the
present study, the effect of hydrochloric acid concentrations were experimentally
−
1
studied in the range of 0.0 to 2.0 mol L and the results were presented in Fig. 9. As
shown in Fig. 9, the stripping efficiency of lithium ions initially increased with an
increase in hydrochloric acid concentration. About 99.37% of the loaded lithium ions
−
1
could be recovered using hydrochloric acid concentration above 0.5 mol·L in a
single contact. And further increase in hydrochloric acid concentration may result in
no significant variation in the stripping efficiency. From the results obtained, the 0.5
−
1
mol·L hydrochloric acid was a suitable choice for recovering lithium ion from the
organic phase. In the ionic liquid extraction system, the lower concentration of
hydrochloric acid was used as the stripping agent, which was beneficial to reduce the
corrosion of the equipment.
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100
80
60
40
20
0
0
.0
0.5
1.0
1.5
2.0
-
1
[HCl], mol· L
Fig. 9. Stripping effect of different concentrations of hydrochloric acid on lithium ions in organic
−
1
phase. Temperature = 293 K; [HCl] = 0-2.0 mol L ; phase volume ratio = 1.
4
. Conclusions
A new FIL, [N4444][EHEHP], was prepared and studied for the extraction of
lithium ions from aqueous solution. The ionic liquid [N4444][EHEHP] shown stronger
extractabilities in comparison to its acidic extractant HEHEHP. The mechanism
involved in the extraction system was analyzed by slope analysis and FT-IR data,
which indicated the interaction of one molecule of ionic liquid with each lithium ion
through phosphate groups. The effect of temperature on the extraction of lithium ions
was studied and it was found to be exothermic, spontaneous and ordered in nature.
During the extraction of lithium ions from a mixed solution containing several alkali
metal ions, the ionic liquid system exhibited better selectivity towards lithium ions.
Quantitative stripping of lithium ions from the loaded ionic liquid phase was achieved
−
1
with 0.5 mol·L hydrochloric acid. The present study highlighted the potential of FIL
as an extractant for the extraction of valuable metal ions.
Acknowledgments
The authors are grateful for the financial aids from Natural Science Foundation
of Qinghai Province (No. 2018-ZJ-950Q) and Natural Science Foundation of Qinghai
Nationalities University (No. 2017XJG01 and No. 2019XJG04).
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CRediT author statement
Chenglong Shi: Formal analysis, Writing - Original Draft, Funding acquisition.
Hongxia Li: Methodology, Formal analysis. Bing Liu: Investigation, Resources.
Yaru Qin: Conceptualization, Resources, Writing - Review & Editing, Supervision.
Guixiu Song: Investigation, Formal analysis.
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Declaration of interests
☑
The authors declare that they have no known competing financial interests or personal
relationships that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which may be
considered as potential competing interests:
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Highlights:
1
. A new functionalized ionic liquid was successfully synthesized and used for
lithium extraction.
2
3
. Nature of extracted species was found out to be 1:1.
. The ionic liquid system exhibited better selectivity towards lithium ions in the
solution containing alkali metal ions.
18