(Thanh Tuan Tran)
1
(Man Seung Lee)
1*
Copyright © 2020 The Korean Institute of Metals and Materials
Key words(Korean)
ionic liquids, solvent extraction, hydrometallurgy, aliquat336
1. Introduction
Liquid-liquid extraction is a chemical technique which utilizes the distribution of
solutes between two immiscible liquid phases [1]. The technique is employed in hydrometallurgy for the extraction and purification
of metals. However, choosing suitable extractants that have both good performance
and environmental friendliness is a challenging task.
Today, commercial extractants and their mixtures are widely employed to separate metal
ions from diverse aqueous media. In metal processing industries, when the metal ions
exist in cationic form in aqueous solution, organophosphorous acids are frequently
employed, such as Cyanex272 (bis(2,4,4-trimethylpentyl)phosphinic acid), D2EHPA (di-(2-ethylhexyl)phosphoric
acid), Cyanex301 (bis(2,4,4-trimethylpentyl)dithiophosphinic acid) [2-4]. However, the use of these acidic extractants to extract metal ions from weak acidic
solutions results in a decrease in equilibrium pH, which reduces the effectiveness
of the extraction. Saponification of these acidic extractants by NH3 and NaOH generates effluents which contain the corresponding ammonia-nitrogen and
Na+, leading to environmental issues [5, 6]. Although neutral extractants avoid the disadvantages of acidic extractants, their
selectivity for metal extraction is lower than that of organophosphorus acids [7]. Thus, a new extraction system is needed to circumvent the disadvantages of the
organophosphorous acids in metal processing.
Ionic liquids (ILs) are organic salts with a melting point below 100 °C. ILs have
specific properties including thermal stability, low flammability and negligible vapor
pressure [8]. In particular, their physicochemical properties can be controlled by changing discrete
cations and anions, which gives them more flexibility and a wider selection of properties
[9]. For instance, changing the viscosity or enhancing the ionic exchange characteristics
of ILs can be performed by either increasing or decreasing alkyl groups in the molecular
components, or by replacing other ionic components.
The use of imidazolium, ammonium, or phosphonium ILs for the separation of metal ions
has recently been reported [10-13]. However, the use of hydrophilic ILs often results in the loss of IL components
during the extraction, which requires regeneration of the ILs [14]. Moreover, ILs containing fluoride can also be hydrolyzed, producing toxic and corrosive
chemicals such as HF, POF3, H2PO3F, and HPO2F2 [15, 16]. Therefore, the ILs most desirable for extracting metals are composed of non-fluorinated
anions and functional cations, such as tricaprylmethylammonium chloride (Aliquat 336,
[A336][Cl]) and tri(hexyl)tetradecylphosphonium chloride (Cysphos IL 101) [17, 18]. Many bi-functional ionic liquids (bif-IL) have been developed based on Aliquat336
or Cysphos IL 101, including [A336][P204], [A336][P507], [A336][C272], [A336][C302],
[A366][CA-12], [A336][CA-100], TOMAS, Cysphos 104 and Cysphos 167. These bif-ILs can
extract metal ions as well as hydrogen ions, which is of great importance for controlling
the equilibrium pH [19-25]. However, these bif-ILs are often very viscous and thus require the use of diluents
or other extractants as a modifier.
Mixtures of solvating extractants such as TBP or TOPO and other extractants have been
employed for the synergistic extraction of metal ions and to prevent the formation
of a third phase [26-28]. Adding solvating extractants to ionic liquids can also result in synergisms which
enhance metal extraction. To the best of our knowledge, the interaction between bif-IL
and neutral extractants has not yet been analyzed.
In this work a bif-IL synthesized using Aliquat336 and Cyanex272 was selected, and
the effect of adding TBP to this bif-IL was investigated. The interactions between
the mixtures were analyzed by FT-IR. Then, the extraction behavior of Co(II) and Ni(II)
in HCl solutions with bif-IL and its mixture with TBP was investigated.
Since the concentration of HCl acid significantly affects the formation of chloride
complexes of metal ions, the extraction behavior of the two metal ions using these
extractants was investigated in strong and weak acidic media, corresponding to 1.0×10-4 and 6.8 mol·L-1 HCl. The extracted metal species in the loaded organic phase were identified by UV/VIS
spectra. Based on these results, the role of TBP in the extraction of Co(II) and Ni(II)
by the bif-IL is discussed.
2. Experimental
2.1 Reagents and Chemicals
The extractants such as Aliquat336 (N-Methyl-N, N, N-trioctylammonium chloride, BASF
Co., 93%), Cyanex272 (bis(2,4,4-trimethylpentyl)phosphinic acid, Cytec Inc., 85%)
and TBP (tributylphosphate) were used without any purification. The structure and
properties of these extractants are presented in Table 1. Kerosene (Samchun Pure Chemical Co.) was used as a diluent and all the other chemicals
used were of analytical grade.
The synthetic solutions of Co(II) and Ni (II) were prepared by dissolving appropriate
amounts of CoCl2. 6H2O (Junsei Chemical Co., ≥ 97%) and NiCl2. 6H2O (Yakuri Pure Chemical Co., Japan, ≥ 96%) in acid solutions. The concentration of
metal ions was approximately 500 mg·L-1. The acidity of the solution was adjusted by adding doubly distilled water to concentrated
HCl (Daejung Co., 35%).
ALiCY (N-Methyl-N, N, N-trioctylammonium bis(2,4,4-trimethylpentyl)phosphinate, R4NA) was prepared by mixing an equimolar concentration of Aliquat336 (R4NCl) and Cyanex272 (HA) in kerosene according to the method reported in the paper
[29].
2.2 Extraction procedure
The extraction experiments were carried out by mixing equal volumes of aqueous and
organic phase (each 15 mL) in a screw cap bottle for 30 minutes using a Burrell wrist
action shaker (model 75, USA) at ambient temperature (22 ± 1 °C). The shaken solutions
were allowed to stand in a glass separatory funnel for phase separation. The concentration
of hydrogen ions in the aqueous phases before and after extraction was determined
by Orion Star thermal scientific pH meter (model A221, USA) and the volumetric titration
method [30].
2.3 Analytical methods
Fourier transform infrared spectrometers (FT-IR-Vertex 80 V, Bruker, Germany) were
employed to analyze the formation of ALiCY, and interactions between individual extractants
in the mixtures before and after extraction. The infrared spectra were taken in the
range of 4000-550 cm-1. However, the spectra were mainly analyzed in the range of 1600-600 cm-1, where most of the significant changes occurred. The loaded organic phases were analyzed
spectrophotometrically using UV/VIS (UV-1800, Shimadzu, Japan).
The concentration of nickel and cobalt ions in the aqueous phases before and after
extraction was determined by ICPOES (Inductively coupled plasma-optical emission spectrometry,
Spectro Arcos). Extraction percentage (%E) was calculated from the concentration of
metal ions in the aqueous phases before [M]i and after [M]*(aq) extraction: %E
=
(
(
[
M
]
i
-
[
M
]
(
a
q
)
*
)
[
M
]
i
)
×
100
, assuming that there was no change in the volume of the two phases after extraction.
The distribution ratio D, was calculated from the relation:
D
=
(
(
[
M
]
i
-
[
M
]
(
a
q
)
*
)
[
M
]
(
a
q
)
*
)
The separation factor, SFCo/Ni, between Co(II) and Ni(II) was defined by the following equation:
S
F
=
D
C
o
D
N
i
3. Results and Discussion
3.1. Analysis of the formation of ALiCY by FT-IR
In order to identify the formation of bif-IL, the FT-IR spectra of ALiCY (R4NA) was compared with that of Aliquat336 (ALiCl, R4NCl) and Cyanex272 (HCY, HA). The concentration of the analysts was fixed at 0.1 mol·L-1. The frequencies of the characteristic stretching vibrational bands of these extractants
in kerosene are presented in Fig 1 and Table 2.
It has been reported that the -OH stretching vibration bands of Cyanex272 in nonpolar
diluents would be present in the region 2700-1700 cm-1 because of intermolecular hydrogen bonding in the dimeric form [31]. However, this band was not observed in any of the spectra in the present work,
which matches other reported results [32]. The characteristic stretching vibrational bands of Cyanex272 for P=O and P-O groups
were at 1170.4 cm-1 and at 959.6 cm-1. The characteristic peaks of C-N and C-H in Aliquat 336 at 1378.5 and 1459.2 cm-1 were overlapped by the C-H stretching vibrations of kerosene. Therefore, the spectra
were analyzed to detect any change in the characteristic bands of P=O and P-O groups.
Comparing the spectra of ALiCY to that of Cyanex272, there was a significant shift
in the positions of the characteristic stretching vibrational bands of the P=O and
P-O groups, namely from 1170.4 cm-1 (P=O group) and 959.6 cm-1 (P-O group) of Cyanex272 to 1143.7 cm-1 (P=O group) and 1023.6 cm-1 (P-O groups) of ALiCY, respectively. Besides that, the increasing intensity of the
peaks, which could be due to the interaction between Aliquat336 cation (R4N+) and Cyanex272 anion (A-), also indicated the successful synthesis of bif-IL.
3.2 Effect of hydrochloric acid concentration on the Co(II) and Ni(II) extraction
by ALiCY
The extraction of Co(II) and Ni(II) by 0.1 mol·L-1 ALiCY was investigated using two hydrochloric acid solutions, of 1.0×10-4 and 6.8 mol·L-1. In these experiments, the concentration of Co(II) and Ni(II) was fixed at 500 mg·L-1. The extraction percentages of Co(II) and Ni(II) in the 1.0×10-4 mol·L-1 HCl were 57.4 and 36.8%, while that of Co (II) at 6.8 mol·L-1 HCl was 51.1% and no Ni(II) was extracted at all.
When the hydrochloric acid concentration is 1.0×10-4 mol·L-1, both Co(II) and Ni(II) exist in cationic forms (e.g Co(H2O)6]2+, [Co(H2O)5Cl]+, and [Ni(H2O)6]2+). Unlike Ni(II), Co(II) has a strong tendency to form complexes with chloride ions.
Cobalt ions in the concentrated HCl (6.8 mol·L-1) favor the formation of chlorocomplexes with a tetrahedral configuration, like CoCl3- and CoCl42-, while nickel ions tend to exhibit an octahedral form (e.g., Ni(H2O)5Cl+, Ni(H2O)4Cl2) [13]. Moreover, it has been reported that the cation of Aliquat336 forms R4N+ [HCoCl4]- species when the HCl concentration is higher than 5 mol·L-1 [33, 34]. The fact that no nickel was extracted from the 6.8 mol·L-1 HCl solution indicates that the interaction between nickel ions and the anion of
Cyanex272 under this condition is weak, and thus ALiCY extracted only anionic complexes
of Co(II). These results agree well with the reported data [13]. In addition, the extraction of hydrogen ions by ALiCY was also observed. The variation
in the concentration of hydrogen ions is presented in Table 3.
Accordingly, the solvent extraction of Co(II) and Ni(II) by ALiCY at the two HCl concentrations
could be represented as:
In the 1.0×10-4 mol·L-1 HCl concentration:
where Me2+ are Co(II) and Ni(II) ions.
In the 6.8 mol·L-1 HCl concentration:
Our results clearly indicated that ALiCY can act as a cation extractant at low HCl
concentration, while it acts as an anion extractant in strong HCl solution. In these
experiments, the formation of a third phase was observed. Therefore, TBP was added
to the ALiCY in order to prevent the formation of a third phase, and the effect of
TBP addition on the extraction of Co(II) and Ni(II) was investigated.
3.3 Effect of TBP addition to ALiCY on the extraction of Co(II) and Ni(II)
In order to investigate the effect of adding TBP to ALiCY on the extraction of Co(II)
and Ni(II), the concentration of TBP in 0.1 mol·L-1. ALiCY was varied from 0.02 to 0.2 mol·L-1. These mixtures were contacted with the aqueous solutions of 1.0×10-4 and 6.8 mol·L-1 HCl. The results (see Fig 2) showed that there was no noticeable change in the extraction of the metals in the
1.0×10-4mol·L-1 HCl, since the TBP concentration in the mixture varied. Specifically, the extraction
percentage from the mixtures was between 52.2 and 59.4% for Co(II) and between 30.8
and 39.1% for Ni(II). Since TBP would not extract Co(II) and Ni(II) from the 1.0×10-4mol·L-1 HCl solution, the addition of TBP to ALiCY had little effect on the extraction characteristics
of ALiCY. However, it is noteworthy that no third phase was formed in the presence
of TBP in this work.
The reaction by ALiCY in 1.0×10-4 mol·L-1 HCl could be the same as the Co(II) and Ni(II) extraction. Therefore, the effect
of the mixture of ALiCY and TBP on the Co(II), Ni(II) and H+ extraction reaction can
be proposed as:
where Me2+ are Co2+ and Ni2+ ions.
Fig 3 shows the effect of the addition of variable amounts of TBP to 0.1 M ALiCY, on the
extraction of Co(II) and Ni(II) from the 6.8 mol·L-1 HCl solution. As the TBP concentration increased to 0.2 mol·L-1, the extraction percentage of Co(II) decreased from 48.8 to 34.0%, while the extraction
of Ni(II) increased from 1.5 to 2.4%. The decrease in the extraction of Co(II) by
ALiCY in the presence of TBP at this HCl concentration could be attributed to the
interaction between the R4N+ and the polar P=O groups of the TBP. This interaction may compete with the interaction
between R4N+ and anionic cobalt complexes, leading to a decrease in Co(II) extraction as TBP concentration
increased.
The anion of Cyanex 272, A-, acts as a base and thus can extract hydrogen ions from aqueous solution, resulting
in a decrease in the equilibrium concentration of hydrogen ions at both HCl concentrations,
as shown in Table 3. The HA molecules extracted into the organic phase could interact with TBP through
hydrogen bonds [35]. A small extraction of Ni(II) from the 6.8 mol·L-1 HCl solution might be ascribed to the fact that TBP can extract electrically neutral
Ni(II) species under this condition.
The solvent extraction of Co(II) and Ni(II) by mixtures of ALiCY and TBP can be proposed
as
On the other hand, in the strong acid medium Co(II) ions were selectively extracted
over Ni(II) by the mixture of ALiCY and TBP, which was not observed for the weak case.
This can be confirmed by comparing the separation factors of Co(II) and Ni(II) for
each HCl solution (see in Table 4). However, when TBP concentration was increased in the mixture, it led to a decrease
in the separation factor between the two metals in the strong acid medium, because
the extraction percentage of Co(II) decreased. The addition of TBP to ALiCY affected
the extraction of Co(II) and Ni(II) and the effect was more pronounced in the stronger
HCl solution.
The interaction between ALiCY and TBP was further elucidated by the FT-IR and UV/VIS
analyses.
3.4 Analysis of the interaction between ALiCY and TBP by FT-IR before and after the
extraction of Co(II) and Ni (II)
3.4.1 FT-IR of the mixtures of ALiCY and TBP before extraction
TBP contains polar functional groups of high nucleophilicity –P=O, which could be
responsible for the interaction with other molecules. The characteristic bands observed
in the spectra of organophosphorous acid esters result from P=O and P-O-C stretching
vibrations. Aliphatic phosphine oxides absorb in the 1150–1100 cm−1 region and the phosphate esters absorb in the 1299–1250 cm−1 region [36]. Thus, the FT-IR spectrum in the 1600–600 cm−1 region should be useful in identifying the possible interactions between TBP and
ALiCY.
The FT-IR spectra of ALiCY, TBP and their mixture at equimolar ratios were analyzed.
The concentration of all the extractants was fixed at 0.1 mol·L-1. The spectra data are presented in Fig 4 and Table 5. The results in Fig 4 show that shifts in peak position did not occur when single extractants were mixed
with each other, except for a slight shift in the peak of the P=O groups from 1143.7
cm-1 to 1151.9 cm-1. Such changes may be ascribed to the formation of hydrogen bonding by dipole-dipole
attraction between the P=O groups of TBP, and the hydrogen atoms in the methyl group
of the R4N+ ions, which affects the electrostatic interaction between R4N+ and A- ion pairs. This led to a shift in the P=O band of the A- anion in the mixture. It might be said that the interaction between ALiCY and TPB
was not strong enough to lead to a shift in other peaks.
The effect of TBP concentration on the interaction was also considered by changing
the concentration from 0.02 to 0.2 mol·L-1 in the mixture (Fig 5). As TBP concentration increased in the mixture with ALiCY, an increase in the intensity
of peaks at 1027.9 cm-1 (P-O group) and 1271 cm-1 (P=O group) was observed. However, there was no change in the intensity of the peak
of the P=O group of the A- anion at 1151.9 cm-1. This also further supports the above comments about the weak interaction between
ALiCY and TBP.
3.4.2 FT-IR of the mixtures of ALiCY and TBP after extraction at several HCl concentrations
The organic phases after extraction in the 1.0×10-4 mol·L-1 HCl were analyzed by FT-IR. The spectral data in Fig 6 indicates that the shift in the characteristic peaks of P=O (at 1151.9 cm-1) and the P=O (at 1272.4 cm-1) groups did not occur in the TBP concentration range, meaning there was little difference
in the FT-IR of the organic phase between before and after extraction (see Fig 5). This shows that the extraction of Co(II) and Ni(II) from a weak acidic medium did
not affect the interaction between the mixtures. The results agree well with the proposed
reaction (Eq. 5) which describes the role of Cynex272 anions during the extraction of Co(II) and
Ni(II) from a weak acid medium.
Fig 7 shows the spectra of the mixtures after the extraction of Co(II) and Ni(II) from
the 6.8 mol·L-1 HCl solution. The peak of the P-O-H groups reappeared at 958.5 cm-1, similar to that of Cyanex272. This indicated that A- ions in the mixture reacted with hydrogen ions in the aqueous phase to form HA, namely,
the P-O-H group. In addition, a change in the peaks of the P-O-H groups and P=O groups
(at 1153.5 cm-1) of the Cyanex272 anion, and in the peaks of the P=O groups (at 1272.0 cm-1) of TBP were observed. This indicates that the interaction between HA and TBP occurs
through hydrogen bonding. Compared to the spectra of Cyanex272, the bonds in the mixture
were not clear. These FT-IR data support the occurrence of Eqs. (6) and (7), indicating that the extraction behavior of the mixture of ALi-D2 and TBP considerably
depends on interaction between the R4N+ cations and meal ions. Competition between the metal complex ions and TBP molecules
in the interaction with R4N+ cations could explain the decrease in the extraction percentage of Co(II) when the
concentration of TBP in the mixture was increased.
3.5 UV/VIS Spectra Analysis
The coordination of Ni(II) and Co(II) complexes formed in the presence of chloride
ions can be determined by UV/Vis spectra of the organic phase. It was reported that
the Ni(II) complexes appear with two bands between 600 and 800 cm-1 for the octahedral configurations (e.g., [Ni(H2O)6]2+ and [Ni(H2O)5Cl]+) and double bands at 650 – 750 cm-1 for NiCl4- in trioctylamine chloride after extraction by Cyphos 101 and Cyphos 104 [13, 37, 38]. In Fig 8a), the UV/Vis confirmed that peaks between 590 and 640 cm-1 correspond to Ni(II) octahedral complexes and no peaks were observed for NiCl42- in the organic phase. Therefore, this agrees well with the extraction data, that
the percentage of Ni(II) extraction was negligible at this condition. As TBP concentration
increased in the mixtures, there was no observed difference in the absorbance of the
mixtures, indicating that TBP did not affect the extraction of Co(II) and Ni(II).
These results also agree well with the results in Fig 6.
The spectra in Fig 8a and Fig 8b show a shift in the configuration of the Co(II) complex, from octahedral (peak at
550 nm) to tetrahedral (700 nm, broad signal), as HCl concentration varied from 1.0×10-4 to 6.8 mol·L-1. The predominant extracted species of Co(II) in the organic phase was CoCl42- [13, 38]. FT-IR and UV/VIS data supports that Eqs. (3) and (4) are responsible for the extraction of Co(II) from 6.8 mol·L-1 HCl solution. On the other hand, no Ni(II) complexes were observed under this experimental
condition, indicating that Ni(II) was not extracted from the 6.8 mol·L-1 HCl solution.
4. Conclusions
The extraction of Co(II) and Ni(II) from two HCl concentrations (1.0×10-4 and 6.8 mol·L-1) was investigated by employing an ionic liquid (ALiCY) and its mixture with TBP.
In the extraction with ALiCY, both Co(II) and Ni(II) were extracted from the 1.0×10-4 mol·L-1 HCl, while only Co(II) was extracted from the 6.8 mol·L-1 HCl, and thus separation of the two metal ions was possible. These extraction data
indicate that ALiCY acts as a cation extractant in a weak HCl solution but an anion
extractant in a concentrated HCl solution. The advantage of employing ALiCY over single
Cyanex272 lies in its ability to extract hydrogen ions from the aqueous, which is
of great importance in controlling the equilibrium pH.
The effect of adding TBP to ALiCY on the extraction of the two metal ions was found
to depend on HCl concentration. The addition of TBP to ALiCY resulted in a decrease
in the extraction percentage of Co(II) from the 6.8 mol·L-1 HCl solution, while its effect was negligible from the 1.0×10-4 mol·L-1 HCl. FT-IR data showed that solvation of R4N+ by the TBP molecules was responsible for the decrease in the extraction of Co(II)
from the 6.8 mol·L-1 HCl. In addition, the hydrogen bond between TBP and Cyanex 272 was also observed.
The TBP effect in the 1.0×10-4 mol·L-1 HCl was attributed to the weak interaction between the anion of Cyanex 272 and TBP.
UV/VIS spectra in loaded organic showed that a tetrahedral Co(II) chloride complex
was extracted from the 6.8 mol·L-1 HCl solution, while hexahedral Ni(II) was extracted from the 1.0×10-4 mol·L-1 HCl.
Acknowledgements
This study was supported by a grant from the Korean Research Foundation (2018R1D1A1BO7044951)
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Figures and Tables
Fig. 1.
FT-IR of Aliquat336 (ALiCl), Cyanex272 (HCY) and ALiCY in kerosene. Concentration
of extractants was fixed 0.1 mol·L-1
Fig. 2.
Extraction percentage of Co(II), Ni(II) by the mixture of ALiCY and TBP at 1.0×10-4 mol·L-1 HCl. The concentration of ALiCY in the mixture was fixed at 0.1 mol·L-1.
Fig. 3.
Extraction percentage of Co(II), Ni(II) by the mixture of ALiCY and TBP at 6.8 mol·L-1 HCl. The concentration of ALiCY in the mixture was fixed at 0.1 mol·L-1
Fig. 4.
FT-IR of TBP, ALiCY and the mixture of ALiCY and TBP in kerosene.
Fig. 5.
FT-IR of the mixture of 0.1 mol·L-1 ALiCY and various concentration of TBP (from 0.02 to 0.2 mol·L-1) in kerosene.
Fig. 6.
FT-IR spectra of loaded organic phase after extraction from Co(II) and Ni(II) solution
at 1.0×10-4 mol·L-1
Fig. 7.
FT-IR spectra of organic phase after extraction from Co(II) and Ni(II) solution at
6.8 mol·L-1 HCl
Fig. 8.
UV/VIS spectra of organic phase after extraction with aqueous phase at 1×10-4 mol·L-1 (a) and 6.8 mol·L-1 (b)
Table 1.
Properties and chemical structures of the extractants
|
Extractant
|
Chemical formula/molar mass (g·mol-1)
|
Density (g·cm-3)
|
Viscosity (mPa·s)
|
Solubility in water (mg·L-1)
|
Structure
|
|
TBP
|
C12H27O4P
|
0.979
|
-
|
0.4 at 25℃
|
|
|
266.32
|
|
Aliquat336 (ALiCl)
|
C25H54ClN
|
0.884 at 25℃
|
1500 at 30℃
|
0.12 at 30℃
|
|
|
404.16
|
|
Cyanex272 (HCY) pKa = 6.37
|
C16H35O2P
|
0.920 at 24℃
|
14.2 at 25℃
|
38 at 25℃
|
|
|
290.43
|
|
ALiCY
|
C41H88NO2P
|
-
|
-
|
-
|
|
|
658.14
|
Table 2.
Frequencies of characteristic vibrational bands of individual extractants in kerosene.
|
Extractants
|
P=O
|
P-O-H or P-O
|
C-N and C-H overlapped
|
|
ALiCl
|
-
|
-
|
1378.5 and 1459.2
|
|
HCY
|
1170.4
|
959.6
|
|
ALiCY
|
1143.7
|
1023.6
|
Table 3.
The concentration of hydrogen ion in the aqueous phase after the extraction with the
organic phase
|
The concentration of TBP in the mixture (mol·L-1)
|
0.00
|
0.02
|
0.05
|
0.10
|
0.20
|
|
pH = 4 (1.0×10-4 mol·L-1)
|
7.35
|
7.18
|
7.22
|
7.34
|
7.34
|
|
[HCl] = 6.8 mol·L-1 |
6.11
|
6.25
|
6.25
|
6.25
|
6.25
|
Table 4.
Separation factor (SF) between Co(II) and Ni(II) in HCl solutions extracted by the
mixture of ALiCY and TBP
|
The concentration of TBP in the mixture (mol·L-1)
|
0.02
|
0.05
|
0.10
|
0.20
|
|
SFco/Ni at pH = 4
|
2.7
|
2.3
|
2.5
|
2.1
|
|
SFCo/Ni at [HCl] = 6.8 mol·L-1 |
39.3
|
56.0
|
26.7
|
28.3
|
Table 5.
Frequencies of characteristic vibrational bands of individual extractants in kerosene.
(Concentrations of extractants were fixed 0.1 mol·L-1).
|
Extractants
|
P=O
|
P-O-H or P-O
|
|
ALiCY
|
1143.7
|
1027.9
|
|
TPB
|
1027.9
|
1274.2
|
|
ALiCY - TBP
|
1151.9
|
1274.2
|