Ionic-Liquid-Type Imidazolium Gemini Surfactant Based Water-in-Oil

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Ionic-Liquid-Type Imidazolium Gemini Surfactant Based Water-in-Oil Microemulsion for Extraction of Gold from Hydrochloric Acid Medium Shubin Wang,† Yan Zheng,† Hong Zhang,† Yan Yan,† Xia Xin,*,‡ and Yanzhao Yang*,† †

Key Laboratory for Special Functional Aggregate Materials of Education Ministry, School of Chemistry and Chemical Engineering and ‡National Engineering Technology Research Center For Colloidal Materials, Shandong University, Jinan, 250100, PR China ABSTRACT: A microemulsion with hydrochloric acid solution as the polar phase, n-heptane as the continuous phase, [C14-4-C14im]Br2 as an ionic-liquidtype imidazolium gemini surfactant and extractant, and n-amyl alcohol as cosurfactant was studied on Au(III) extraction. Compared to its corresponding monomer [C14-mim]Br-based microemulsion for Au(III) extraction, the [C14-4C14im]Br2-based microemulsion system showed excellent extractability of Au(III). The anion-exchange mechanism of Au(III) extraction was confirmed by the slope method and spectrum analysis (UV−vis, FT-IR, and 1H NMR). Main influence factors such as phase ratio, extraction equilibrium time, amyl alcohol volume fraction, and the concentration of ionic liquid on the extraction efficiency (E%) were explored. Moreover, [C14-4-C14im]Br2-based water-in-oil microemulsion had high selectivity over a multimetal ion solution (Co (II), Cu(II), Fe(III), Ni(II), Sn(IV), and Al(III)). Therefore, it is indicated that [C14-4-C14im]Br2-based microemulsion provides an effective and potential approach for the separation and purification of Au(III) from HCl solution.

1. INTRODUCTION Gold is an important metal as well as an indispensable and nonsubstitutable strategic resource and has many applications in industry, electronic products, jewelry, and medicine and plays an important role in national economy.1,2 Because of the high value and the increasing demand for gold, the recovery of gold from secondary sources (such as waste catalysts, mobile phones, and computer circuit boards) has been greatly encouraged.3,4 In a wide variety of recovery methods, solvent extraction is one of the efficient techniques to separate and preconcentrate gold. However, extractants, e.g., amide derivatives,5,6 calixarene derivatives,7,8 and sulfur-containing reagents,9 are limited in terms of their selectivity and toxicity.10 Consequently, a “greener” extractant is required,11 and the use of ionic liquids (ILs) as alternatives to traditional extractant could overcome this disadvantage.12,13 ILs with a low melting temperature are composed of organic cations and organic or inorganic anions.14−16 ILs are environmentally benign substances17 with some specific properties, e.g., low steam pressure,18 nonflammable,19 good thermal stability,20 and wide electrochemical window.21 Moreover, ILs have been extensively explored as alternatives to conventional organic solvents for liquid−liquid extraction of various metallic ions. Davis and co-workers have discovered that ILs could be used for the construction of microemulsions and showed several superior properties for extraction.22 The nanometer-sized spherical or bicontinuous structure of a microemulsion can be regarded as “pools”, which provide a microenvironment for the extraction and separation.23 ILs have been widely applied to the construction of microemulsions for over 10 years.24 The © XXXX American Chemical Society

significance is that ILs-based microemulsions can expand potential application of ILs as solvents, reaction, and extraction media.25 However, with respect to green chemistry, ILs constitute polar or apolar component in the traditional ILs-based microemulsion studies.26 Furthermore, critical studies revealed that most the ILs are often viscous, which limits the potential development of ILs-based microemulsion. Thus, a new type of ILs should be synthesized that can regulate their properties for better use.27 Among various kinds of ILs, surface-active ILs (SAILs), which referred to the ILs containing long alkyl chains which exhibit amphiphilic character, have emerged as a novel kind of amphiphiles.28 Ionic liquid-type imidazolium gemini surfactant consists of anion and doubly charged cation that is composed of two singly charged cations linked by an alkyl chain.29−31 Compared to the corresponding monomeric cationic ILs, IL-type imidazolium gemini surfactants possess a better biocompatibility, lower critical micellar concentrations, wider liquid range, and higher thermal stability;32−35 therefore, they are widely used in various fields, e.g., DNA genetics,36,37 enzymatic catalysis,38 and metal nanoparticles.39,40 Besides, ILtype imidazolium gemini surfactant could act as surfactant for the construction of microemulsion and shows several advantages. First, the doubly broad imidazolium heads show a high capacity for solutes. Second, the attraction between the Received: October 31, 2015 Revised: February 23, 2016 Accepted: February 25, 2016

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DOI: 10.1021/acs.iecr.5b04115 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research

other metal ions (Co(II), Cu(II), Fe(III), Ni(II), Sn(IV), and Al(III)) were determined by an inductively coupled plasma atomic emission spectrometer (IRIS Intrepid II XSP, Thermo Electron Corp., Boston, MA, USA). The samples ([C14-4C14im]Br2 and [C14-4-C14im]Br2−Au(III)) were analyzed by UV spectrophotometry (UV-9000, Shanghai Metash Instruments Co., Ltd., Shanghai, China), FT-IR (Tensor27, Bruker Corporation, Karlsruhe, Germany), and 1H NMR (AV300, Bruker Corporation, Karlsruhe, Germany). 2.3. Microemulsion Preparation. [C14-4-C14im]Br2 was added into the mixture of n-heptane and n-amyl alcohol (nheptane 14 mL, n-amyl alcohol 6 mL); subsequently, the organic phase was diluted gradually by 1 mol L−1 HCl solution until the aqueous phase arose. The [C14-4-C14im]Br2/nheptane/n-amyl alcohol/HCl microemulsion system was wellprepared.

cosurfactants and imidazolium ring could facilitate the stability of liquid film, which prevents the leakage of solutes. The abovementioned studies suggest that both SAILs and microemulsion can achieve a win-win situation by the former acting as surfactant. Thus, in our work, a new IL-type imidazolium gemini surfactant ([C14-4-C14im]Br2) was used for the construction of the water-in-oil (W/O) microemulsion and applied for extraction of Au(III) first. In the [C14-4-C14im]Br2/nheptane/n-amyl alcohol/hydrochloric acid W/O microemulsion system, [C14-4-C14im]Br2 bore the double functions of surfactant and extractant. For comparison, [C14-4-C14im]Br2’s corresponding monomer ([C14-mim]Br)-based microemulsion for Au(III) extraction was also studied. The mechanism and behavior of the Au(III) extraction by the [C14-4-C14im]Br2/nheptane/n-amyl alcohol/HCl microemulsion system has been explored systematically by considering main influence factors, e.g. phase ratio, extraction equilibrium time, amyl alcohol volume fraction, and the concentration of IL.

3. RESULTS AND DISCUSSION 3.1. Conductivity Properties of the [C14-4-C14im]Br2/nHeptane/n-Amyl Alcohol/HCl Microemulsion System. To investigate the different types of self-assembling microstructures, conductivity measurement was employed. HCl solution (1 mol L−1) was added dropwise into the organic phase including 4 mmol L−1 [C14-4-C14im]Br2 or [C14mim]Br until the aqueous phase arose obviously. The conductivity value (κ) of the microemulsion was determined in this process of dilution and plotted versus aqueous weight (Waq). As shown in Figure 1, the κ/Waq curve could be obviously divided into three

2. EXPERIMENTAL SECTION 2.1. Reagents and Materials. 1-Tetradecyl-3-methylimidazolium bromide, [C14mim]Br (>99%) was purchased from Lanzhou Greenchem ILs, LICP, CAS (Lanzhou, China). The cationic imidazolium gemini surfactant ([C14-4-C14im]Br2) was synthesized according to the procedure described in refs 41 and 42. The structure of [C14-4-C14im]Br2 and [C14mim]Br are shown in Scheme 1. Both n-amyl alcohol and n-heptane (both Scheme 1. Chemical Structures of [C14-4-C14im]Br2 and [C14-mim]Br

analytical-reagent-grade) were obtained from Damao Chemical Reagent Tianjin Corp (Tianjin, China). Gold solution was prepared by dissolving metal chlorides in hydrochloric acid solution (HAuCl4·4H2O, Sinopharm Chemical Reagent Beijing Co., Ltd., Beijing, China). CoCl 2 ·6H 2 O, CuCl 2 ·6H 2 O, FeCl3.6H2O, NiCl2·6H2O, SnCl4·5H2O, and AlCl3, were procured from Kermel Chemical Reagent Tianjin Co., Ltd. (Tianjin, China). These metal chloride salts were added to the hydrochloric acid to prepare mixed solution. All of the reagents and materials were used as received. In all the experiments, distilled water was used to prepare the aqueous solution. 2.2. Analytical Techniques. A conductivity analyzer (DDS-307, Precision & Scientific Instrument Shanghai Co.,Ltd., Shanghai, China) was used to measure the electrical conductivities of the microemulsion. A high performance stability analy (Turbiscan Lab, Formulaction Inc., France) was employed to determine the stability of microemulsion using back scattering. The concentration of Au(III) before and after extraction was measured by an atomic absorption spectrophotometer (3150, Precision & Scientific Instrument Shang-hai Co., Ltd., Shanghai, China). The concentrations of

Figure 1. Electric conductivity κ of microemulsion as a function of aqueous weight Waq; both the initial concentrations of [C14-4C14im]Br2 and [C14mim]Br were 4 mmol L−1.

regions. In the range of low aqueous content, the microstructure was W/O,43 and a small amplitude increase in conductivity values κ could be registered. This phenomenon was explained in terms of its discrete droplets. The subsequent addition of HCl solution led to a linear increase of the conductivity value κ, which could be associated with the formation of bicontinuous microstructure.43 In this region, organic phase and aqueous phase coexisted. Finally, a twophase system was emerging; the curve at high aqueous content showed a region of constant κ. This behavior could be explained by the fact that the IL under these experimental B


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Figure 2. Electric conductivity κ of microemulsion as a function of aqueous weight, Waq. (A) Initial concentration of [C14-4-C14im]Br2 ranges from 1 to 8 mmol L−1 ; (B) initial volume fraction of n-amyl alcohol ranges from 25 to 35%.

conditions was not sufficient for the formation of an oil-inwater microstructure.44 Moreover, compared to the [C14mim]Br/n-heptane/n-amyl alcohol/HCl microemulsion system, [C14-4-C14im]Br2/n-heptane/n-amyl alcohol/HCl microemulsion system had better water-solubilization ability. It demonstrated that for cationic IL the surface activity of gemini cationic IL was higher than that of the corresponding monomeric cationic IL; therefore, the interfacial film of the microemulsion with [C14-4-C14im]Br2 possessed a higher stabilization. In addition, the [C14-4C14im]Br2/n-heptane/n-amyl alcohol/HCl microemulsion system showed a higher conductivity value, which might be related to more electric charge around [C14-4-C14im]Br2. In addition, the influence of the concentration of [C14-4C14im]Br2 and the volume fraction of n-amyl alcohol (n-amyl alcohol volume/aqueous volume) on microstructure were also investigated. Figure 2A shows that the water-solubilization capacity and conductivity κ increased with the concentration of [C14-4-C14im]Br2. Figure 2B shows the influence of the volume fraction of n-amyl alcohol on the conductivity, and it can be seen that the water-solubilization capacity is positive. This is due to the fact that cosurfactants could facilitate the stability of liquid film which prevents the leakage of HCl solution. 3.2. Stability of the [C14-4-C14im]Br2/n-Heptane/nAmyl Alcohol/HCl Microemulsion System. Microemulsion might become unstable because of various causes (lack of surfactant to cover the interface, attractive forces, etc.). Herein, Turbiscan stability index (TSI)45 was employed for the measurements of microemulsion stability. TSI values were calculated with the special computer program using the equation: TSI =

∑

Figure 3. TSI values of microemulsions as a function of aging time; the aging time is 360 min.

6 months. The low TSI and long aging time under these experimental conditions are sufficient for the demonstration of [C14-4-C14im]Br2/n-heptane/n-amyl alcohol/HCl microemusion stability. 3.3. Spectra Analysis. UV−vis measurements were employed to analyze the [C14-4-C14im]Br2−Au(III) complex. As shown in Figure 4, there were two ultraviolet absorption peaks (λmax = 247 and 322 nm) shown by the complexes in chloroform. The [C14-4-C14im]Br2−Au(III) complexes absorption peak at 247 nm belongs to [C14-4-C14im] and is due to the ultraviolet absorption of purified [C14-4-C14im]Br2 in chloroform at 242 nm. The absorption peak at 322 nm belongs to [AuCl4] and is due to the ultraviolet absorption of HAuCl4 in HCl solution at 313 nm; the peak shift was caused by a change in solvent (HCl solution → chloroform). Thus, the results indicated that the complexes consists of [C14-4-C14im] and [AuCl4]. FT-IR measurements were employed to analyze the interaction between [C14-4-C14im] and [AuCl4]. The FT-IR spectra of [C14-4-C14im]Br2−Au(III) complex and [C14-4C14im]Br2 are shown in Figure 5. The vibration bands are as follows: ring O−H stretch, 3473 cm−1; ring C−H stretch, 3131 cm−1, 3069 cm−1; aliphatic C−H stretch, 2917 and 2849 cm−1; ring CC stretch, 1617 cm−1; ring CN stretch, 1562 cm−1; MeC−H deformation, 1468 cm−1; and ring C−H deformation in plane, 1159 cm−1. The ring O−H stretch is exhibited clearly and can be associated with the samples containing trace

∑h |scani(h) − scani − 1(h)| H

(1)

where scani(h) is the ith scan light intensity on every sample height (h), Scani−1(h) is the (i − 1)th (previous one) scan light intensity on every sample height (h), and H is the selected height. At a given aging time, the higher the TSI, the worse the stability of the sample. The TSI were determined and plotted versus time (min), as shown in Figure 3. The [C14mim]Br/nheptane/n-amyl alcohol/HCl microemulsion system took 250 min to achieve a TSI of 1, which stably existed for 6 months, whereas the [C14-4-C14im]Br2/n-heptane/n-amyl alcohol/HCl microemulsion system took 360 min. On the basis of this result, it can be determined that the latter could exist stably for at least C


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Figure 4. UV−vis spectra of [C14-4-C14im]Br2−Au(III) complexes, ionic liquid [C14-4-C14im]Br2, and HAuCl4: (a) 4.86 × 10−4 mol L−1 [C14-4-C14im]Br2−Au(III) complexes in chloroform, (b) 4.86 × 10−4 mol L−1 HAuCl4 in HCl solution (1 mol L−1), and (c) 2.43 × 10−4 mol L−1 [C14-4-C14im]Br2 in chloroform.

Figure 6. 1H NMR spectra of [C14-4-C14im]Br2 and [C14-4C14im]Br2−Au(III) complexes.

indicated that the structure of [C14-4-C14im]2+ has no changes. Moreover, the closer the hydrogen atoms to the nitrogen atom in the imidazole ring, the larger the chemical shifts. These results demonstrated that the electrostatic interaction between AuCl4− and the cationic headgroup of [C14-4-C14im]Br2 is strong. The results of 1H NMR also agree with the UV−vis spectrum and FT-IR spectrum. Slope method was employed to investigate the extraction proportionalities of the extraction reaction. It is reasonable to hypothesize that one AuCl4− can combine with n[C14-4C14im]Br2; the reaction equations can be written as AuCl4 −aq + n[C14 ‐4‐C14im]2 +

or

⇋ AuCl4 −·n[C14 ‐4‐C14 im]2 +or (2)

The equilibrium constant is K= Figure 5. Infrared spectra of [C14-4-C14im]Br2-Au(III) complexes and ionic liquid [C14-4-C14im]Br2.

[AuCl4 −·n(C14 ‐4‐C14im)2 + ]or [AuCl4 −]aq [(C14 ‐4‐C14im)2 + ]nor

(3)

and the distribution ratio is D=

amounts of adsorbed water. Before, during, and after the extraction process, the aliphatic C−H stretch peaks do not shift obviously because of the weak interaction between alkyl side chain and [AuCl4]. By contrast, the ring C−H stretch peaks exhibit an obvious shift (43 cm−1). The results indicated that the interaction between imidazole ring and [AuCl4] was strong, and this strong interaction was attributed to the electrostatic interaction. Complementary to this, 1H NMR measurement was also employed to get more information about the molecular structure of [C14-4-C14im]Br2−Au(III) complex. The 1H NMR spectra of [C14-4-C14im]Br2−Au(III) and [C14-4C14im]Br2 in CDCl3 are shown in Figure 6. The chemical shifts of hydrogen atoms nearest to the nitrogen atom changed the most: A−A′ 10.215 → 8.959, B−B′ 7.980 → 7.623, and C− C′ 7.193 → 7.260. The chemical shifts of hydrogen atoms farther from the nitrogen atom change less: D−D′ 4.583 → 4.437, E−E′ 4.249 → 4.213, and F−F′ 2.231 → 2.259. The chemical shifts of hydrogen atoms farthest to the nitrogen atom change the least: G−G′1.910 → 1.935, H−H′ 1.253 → 1.244, and I−I′ 0.879 → 0.880. The 1H NMR spectra showed that every hydrogen nuclei remained the one-to-one correspondence relationship before and after the Au(III) loading, which

[AuCl4 −·n(C14 ‐4‐C14im)2 + ]or [AuCl4 −]aq

(4)

Substituting eq 3 into eq 4, the distribution ratio can be written as D=

K[AuCl4 −]aq [(C14 ‐4‐C14im)2 + ]nor [AuCl4 −]aq

(5)

Equation 6 was obtained by taking the natural log of both sides of eq 5: ⎛ [AuCl4 −]aq ⎞ ⎟⎟ + n lg [(C14 ‐4‐C14 im)2 + ]or lg D = lg K + lg⎜⎜ − ⎝ [AuCl4 ]aq ⎠ (6)

where lg K and lg ([AuCl−4]aq/[AuCl−4]aq) were constants for the constant of temperature. The lg D versus lg [C14-4C14im]Br2 curve is shown in Figure 7. The slope of this straight line (R2 = 0.99) is 0.503, which is close to 0.5. This result indicates that one [C14-4-C14im]Br2 can combine two AuCl−4, forming one complex that can transfer to the organic phase. 3.4. Extraction Mechanism Analysis. The mechanism of extraction can be speculated according to the results mentioned D


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or

+ 2AuCl4 −aq

⇋ [C14 ‐4‐C14im][AuCl4]2 or + 2Br −aq

(7)

3.5. Extraction Behaviors. The extraction behaviors were investigated to establish optimum extraction conditions with the experiment of the aqueous phase of 0.05 g L−1 Au(III) in 1 mol L−1 HCl solution, as shown in Figure 8. The extraction equilibrium was soon achieved and 5 min is sufficient for the extraction (Figure 8A). Figure 8B shows the effect of the phase ratio (aqueous phase volume/microemulsion phase volume, R) on extraction efficiency; the zone of nonlinearity of sharply decreasing extraction efficiency (E%) could be correlated to the decrease in the number of effective extraction groups. In addition, the [C14-4-C14im]Br2/n-heptane/n-amyl alcohol/HCl microemulsion system showed a higher extraction efficiency (E %) compared with that of the [C14mim]Br/n-heptane/n-amyl alcohol/HCl microemulsion system. As shown in Figure 8C, the decrease in extraction efficiency (E%) could be explained by the fact that the n-amyl alcohol combined with the headgroup of [C14-4-C14im]Br2 and that then the [C14-4-C14im]Br2 lost the activity of extraction.23 Of note is the fact that low n-amyl alcohol volume fraction was not sufficient for the formation of a stable microemulsion. Therefore, considering both stability and extractability, the volume fraction of n-amyl alcohol was set at 30%. Both extraction efficiency (E%) and distribution ratio (D) increase as the concentration of [C14-4-C14im]Br2 increases. Under optimum conditions, the distribution ratio (D) can reach more than 3000, as shown in Figure 8D. Figure 9 shows the influence of HCl concentration in aqueous phase on the extraction efficiency (E%) of Au(III) by

Figure 7. Slope method for the [C14-4-C14im]Br2/n-heptane/n-amyl alcohol/HCl microemulsion system.

above. First, the UV−vis spectra indicated that the [C14-4C14im]Br2−Au(III) complex consists of [C14-4-C14im] and [AuCl4]. Second, FT-IR spectra indicated that the interaction between imidazole ring and [AuCl4] was very strong, which attributed to the electrostatic interaction. Third, the 1H NMR spectra verified the correctness of the two former methods. Fourth, the result of extraction proportionality indicates that the proportion of AuCl4− and [C14-4-C14im]2+ is 2:1. Extraction of Au(III) can be regarded as a transfer process of Au(III) from the aqueous phase to the microemulsion phase; therefore, combined with the above conclusions, the anion-exchange mechanism is represented in eq 7:

Figure 8. (A) Effect of extraction equilibrium time on extraction efficiency, (B) effect of phase ratio, R, on extraction efficiency, (C) effect of amyl alcohol volume fraction on extraction efficiency, and (D) effect of the concentration of ionic liquid on extraction efficiency and distribution ratio. E


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second zone of the curve was varied only slightly, which could be associated with the dominant position of anion exchange theory. 3.6. Selective Extraction. It is well-known that impurity of a metal element (e.g., copper, iron, or aluminum) might interfere with gold(III)-selective recovery from secondary resources.10 Considerable efforts have been devoted to the selectivity of gold(III)-selective extraction. Figure11 shows the

Figure 9. Influence of HCl concentration on extraction efficiency.

[C14-4-C14im]Br2/n-heptane/n-amyl alcohol/HCl microemulsion system. In the range of low HCl concentration (0.1−1 mol L−1), an decrease in extraction efficiency (E%) could be registered until a minimum is reached. After this point, a second zone (1−5 mol L−1) of linearity of increasing extraction efficiency (E%) could be registered. On the one hand, an increase in the concentration of HCl may increase the ionic strength. High ionic strength can increase the extraction efficiency (E%).46 On the other hand, according to the previous extraction mechanism, the reaction between HCl and [C14-4C14im]Br2 can be expressed by the following equations: [C14 ‐4‐C14im]Br2

or

⇋ [C14 ‐4‐C14 im]2 +or + 2Br −aq

[C14 ‐4‐C14 im]2 +or + 2Cl−aq ⇋ [C14‐4‐C14 im]Cl2

or

Figure 11. Extraction behavior of gold(III) from multimetal solution.

extraction behavior of multiple metal ions (Co(II), Cu(II), Fe(III), Ni(II), Sn(IV), and Al(III)), and the concentration of each metal ion was all 0.05g L−1 in hydrochloric acid (1 mol L−1) media. Under the uniform experimental condition, gold(III) is mainly extracted with the extraction efficiency of 99.55%, whereas the extraction efficiency for other metal ions were as follows: 4.05% for Co(II), 4.95% for Cu(II), 6.78% for Fe(III), 4.68% for Ni(II), 6.05% for Sn(IV), and 2.56% for Al(III). These results indicate that high selectivity for Au(III) extraction can be achieved by [C14-4-C14im]Br2/n-heptane/n-amyl alcohol/HCl microemulsion system. 3.7. Recovery of Gold by Reductive Stripping. In the present study, two methods have been employed to the stripping of gold. For the first one, black gold particles were obtained by mixing hydrazine hydrate (0.5 mol L−1) and the gold-loaded microemulsion phase. The Au(III) content was determined by atomic absorption spectrometry (AAS), and there is hardly any Au(III) left in the microemulsion phase after

(8) (9)

Equations 8 and 9 indicate that an increase in the concentration of HCl may decrease the extraction efficiency (E%). The behavior of this curve could be explained by the fact that both anion exchange and ionic strength had influence on extraction efficiency (E%): For the first zone (0.1−1 mol L−1), the hydrochloric acid concentration was low, and the influence of anion exchange dominated. For the second zone (1−5 mol L−1), the hydrochloric acid concentration was high, and the influence of ionic strength dominated. To reinforce this interpretation, the influence of NaCl concentration on the extraction efficiency was additionally performed. Figure 10A showed the same trend as that in Figure 9, which verified the correctness of anion exchange/ionic strength theory. Figure 10B showed the influence of NaBr concentration on extraction efficiency. It could be seen that the

Figure 10. Influence of (A) NaCl and (B) NaBr concentration on extraction efficiency. F


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(7) Zaghbani, A.; Tayeb, R.; Dhahbi, M.; Hidalgo, M.; Vocanson, F.; Bonnamour, I.; Seta, P.; Fontàs, C. Selective thiacalix[4]arene bearing three amide groups as ionophore of binary Pd(II) and Au(III) extraction by a supported liquid membrane system. Sep. Purif. Technol. 2007, 57, 374. (8) Fontàs, C.; Antico, E.; Vocanson, F.; Lamartine, R.; Seta, P. Efficient thiacalix[4]arenes for the extraction and separation of Au(III), Pd(II) and Pt(IV) metal ions from acidic media incorporated in membranes and solid phases. Sep. Purif. Technol. 2007, 54, 322. (9) Núnez, M. E.; Rodríguez de San Miguel, E. R.; Mercader-Trejo, F. M.; Aguilar, J. C.; de Gyves, J. Selective ω-thiocaprolactam-based recovery of Au(III) from chloride media in solvent extraction and polymer inclusion membrane systems. Sep. Purif. Technol. 2006, 51, 57. (10) Lu, W. J.; Lu, Y. M.; Liu, F.; Shang, K.; Wang, W.; Yang, Y. Z. Extraction of gold(III) from hydrochloric acid solutions by CTAB/nheptane/iso-amyl alcohol/Na2SO3 microemulsion. J. Hazard. Mater. 2011, 186, 2166. (11) Qiu, Z.; Texter, J. Ionic liquids in microemulsions. Curr. Opin. Colloid Interface Sci. 2008, 13, 252. (12) Huddleston, G. J.; Willauer, H. D.; Swatloski, R. P.; Visser, A. E.; Rogers, R. D. Chem. Commun. 1998, 1765. (13) Horváth, I. T.; Anastas, P. T. Innovations and Green Chemistry. Chem. Rev. 2007, 107, 2169. (14) Rogers, R. D.; Seddon, K. R. Ionic Liquids: Industrial Applications for Green Chemistry; American Chemical Society: Washington, DC, 2002. (15) Sheldon, R. A. Green solvents for sustainable organic synthesis: state of the art. Green Chem. 2005, 7, 267. (16) Plechkova, N. V.; Seddon, K. R. Applications of ionic liquids in the chemical industry. Chem. Soc. Rev. 2008, 37, 123. (17) Liu, S.; Xiao, J. Toward green catalytic synthesistransition metal-catalyzed reactions in non-conventional media. J. Mol. Catal. A: Chem. 2007, 270, 1. (18) Deetlefs, M.; Seddon, K. R. Ionic liquids: fact and fiction. Chim. Oggi-Chem. Today 2006, 24, 16. (19) Stark, A.; Seddon, K. R. Ionic liquids. In Kirk-Othmer Encyclopedia of Chemical Technology; Seidel, A, Ed.; Wiley: Hoboken, NJ, 2007; pp 836. (20) Zhang, S.; Sun, N.; He, X.; Lu, X.; Zhang, X. Physical properties of ionic liquids: database and evaluation. J. Phys. Chem. Ref. Data 2006, 35, 1475. (21) Armand, M.; Endres, F.; MacFarlane, D. R.; Ohno, H.; Scrosati, B. Ionic-liquid materials for the electrochemical challenges of the future. Nat. Mater. 2009, 8, 621. (22) Merrigan, T. L.; Bates, E. D.; Dorman, S. C.; Davis, J. H., Jr. New fluorous ionic liquids function as surfactants in conventional room-temperature ionic liquids. Chem. Commun. 2000, 2051. (23) Liu, F.; Yang, Y. Z.; Lu, Y. M.; Shang, K.; Lu, W. J.; Zhao, X. D. Extraction of germanium by the AOT microemulsion with N235 system. Ind. Eng. Chem. Res. 2010, 49, 10005. (24) Plechkova, N. V.; Seddon, K. S. Ionic liquids: “designer” solvents for green chemistry. In Methods and Reagents for Green Chemistry: An Introduction; Tundo, P, Perosa, A, Zecchini, F, Eds.; Wiley: New York, 2007; p 105. (25) Chen, Y. J.; Zhuo, K. L.; Chen, J.; Bai, G. G. Volumetric and viscosity properties of dicationic ionic liquids in (glucose + water) solutions at T = 298.15 K. J. Chem. Thermodyn. 2015, 86, 13. (26) Zhang, Z.; Yang, L.; Luo, S.; Tian, M.; Tachibana, K.; Kamijima, K. Ionic liquids based on aliphatic tetraalkylammonium dications and TFSI anion as potential electrolytes. J. Power Sources 2007, 167, 217. (27) Anderson, J. L.; Ding, R.; Ellern, A.; Armstrong, D. W. Structure and properties of high stability geminal dicationic ionic liquids. J. Am. Chem. Soc. 2005, 127, 593. (28) Gong, Y. J.; Hu, Q. Z.; Cheng, N.; Wang, T.; Xu, W. W.; Bi, Y. H.; Yu, L. Fabrication of pH- and temperature-directed supramolecular materials from 1D fibers to exclusively 2D planar structures using an ionic self-assembly approach. J. Mater. Chem. C 2015, 3, 3273. (29) Moumene, T.; Belarbi, E. H.; Haddad, B.; Villemin, D.; Abbas, O.; Khelifa, B.; Bresson, S. Study of imidazolium dicationic ionic

the stripping process. The second method was that of goldloaded microemulsion phase mixed with an equal volume of H2C2O4 aqueous solution (1.5 mol L−1). The hybrid system was maintained at 80 °C for 4 h. Afterward, the metallic gold gradually subsided. The results of AAS showed that Au(III) is completely reduced to Au by gold precipitation. In other words, gold stripping by the two methods were simple and effective.

4. CONCLUSIONS A [C14-4-C14im]Br2/n-heptane/n-amyl alcohol/HCl microemulsion system was constructed and characterized by conductivity and TSI values; IL-type imidazolium gemini surfactant [C14-4-C14im]Br2 was used in dual roles as surfactant and extractant. Next, the anion-exchange mechanism was confirmed by the method of slope and spectrum analysis (UV−vis, FT-IR, and 1HNMR). Extraction behaviors were influenced obviously by various experimental conditions. In contrast to the [C14mim]Br-based microemulsion system, the [C14-4-C14im]Br2-based microemulsion system showed a higher extraction efficiency. Under the uniform conditions, the [C14-4C14im]Br2/ n-heptane/n-amyl alcohol/HCl microemulsion system shows a high selectivity for Au(III) over base metals ions (Co(II), Cu(II), Fe(III), Ni(II), Sn(IV), and Al(III)). In addition, multiple simple and effective methods were devoted to gold(III) stripping. It can be rationally envisioned that sophisticated gold(III) extraction may be achieved when more versatile IL-type imidazolium gemini surfactant based microemulsions are rationally utilized.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. Phone: +86-531-88363597. Fax: +86-531-88361008. *E-mail: [email protected]. Phone: +86-531-88362988. Fax: +86-531-88361008. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge the financial support from the National Natural Science Foundation of China (21476129 and 21203109) and Ji’nan Youth Science and Technology Star Program (2013040).

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REFERENCES

(1) Tong, Y.; Yang, H. X.; Li, J.; Yang, Y. Z. Extraction of Au(III) by ionic liquid from hydrochloric acid medium. Sep. Purif. Technol. 2013, 120, 367. (2) Tong, Y.; Han, L.; Yang, Y. Z. Microemulsion Extraction of Gold(III) from Hydrochloric Acid Medium Using Ionic Liquid as Surfactant and Extractant. Ind. Eng. Chem. Res. 2012, 51, 16438. (3) Parajuli, D.; Hirota, K.; Inoue, K. Trimethylamine-modified lignophenol for the recovery of precious metals. Ind. Eng. Chem. Res. 2009, 48, 10163. (4) Ha, V. H.; Lee, J.; Jeong, J.; Hai, H. T.; Jha, M. K. Thiosulfate leaching of gold from waste mobile phones. J. Hazard. Mater. 2010, 178, 1115. (5) Martınez, S.; Sastre, A. M.; Alguacil, F. J. Solvent extraction of gold III by the chloride salt of the tertiary amine Hostarex A327. Estimation of the interaction coefficient between AuCl4− and H+. Hydrometallurgy 1999, 52, 63. (6) Narita, H.; Tanaka, M.; Morisaku, K.; Abe, T. Extraction of gold (III) in hydrochloric acid solution using monoamide compounds. Hydrometallurgy 2006, 81, 153. G


Article

Industrial & Engineering Chemistry Research liquids by Raman and FTIR spectroscopies: The effect of the nature of the anion. J. Mol. Struct. 2015, 1083, 179. (30) Gao, Y.; Li, N.; Hilfert, L.; Zhang, S.; Zheng, L.; Yu, L. Temperature-inducedmicrostructural changes in ionic liquid-based microemulsions. Langmuir 2009, 25, 1360. (31) Eastoe, J.; Gold, S.; Rogers, S. E.; Paul, A.; Welton, T.; Heenan, R. K.; Grillo, I. Ionic liquid-in-oil microemulsions. J. Am. Chem. Soc. 2005, 127, 7302. (32) Gao, H.; Li, J.; Han, B.; Chen, W.; Zhang, J.; Zhang, R.; Yan, D. Microemulsions with ionic liquid polar domains. Phys. Chem. Chem. Phys. 2004, 6, 2914. (33) Greaves, T. L.; Drummond, C. J. Ionic liquids as amphiphile selfassembly media. Chem. Soc. Rev. 2008, 37, 1709. (34) Jadhav, A. H.; Kim, H.; Hwang, I. T. Efficient selective dehydration of fructose and sucrose into 5-hydroxymethylfurfural (HMF) using dicationic room temperature ionic liquids as a catalyst. Catal. Commun. 2012, 21, 96. (35) Pal, A.; Datta, S.; Aswal, V. K.; Bhattacharya, S. Small-Angle Neutron-Scattering Studies of Mixed Micellar Structures Made of Dimeric Surfactants Having Imidazolium and Ammonium Headgroups. J. Phys. Chem. B 2012, 116, 13239. (36) Kumar, K.; Barrán-Berdón, A. L.; Datta, S.; Muñoz-Ú beda, M.; Aicart-Ramos, C.; Kondaiah, P.; Junquera, E.; Bhattacharya, S.; Aicart, E. A delocalizable cationic headgroup together with an oligooxyethylene spacer in gemini cationic lipids improves their biological activity as vectors of plasmid DNA. J. Mater. Chem. B 2015, 3, 1495. (37) Misra, S. K.; Muñoz-Ú beda, M.; Datta, S.; Barrán-Berdón, A. L.; Aicart-Ramos, C.; Castro-Hartmann, P.; Kondaiah, P.; Junquera, E.; Bhattacharya, S.; Aicart, E. Effects of a Delocalizable Cation on the Headgroup of Gemini Lipids on the Lipoplex-Type Nanoaggregates Directly Formed from Plasmid DNA. Biomacromolecules 2013, 14, 3951. (38) Adak, S.; Datta, S.; Bhattacharya, S.; Banerjee, R. Imidazolium based ionic liquid type surfactant improves activity and thermal stability of lipase of Rhizopus oryzae. J. Mol. Catal. B: Enzym. 2015, 119, 12. (39) Datta, S.; Biswas, J.; Bhattacharya, S. How does spacer length of imidazolium gemini surfactants control the fabrication of 2D-Langmuir films of silver-nanoparticles at the air−water interface? J. Colloid Interface Sci. 2014, 430, 85. (40) Bhattacharya, S.; Srivastava, A. Synthesis and Characterization of Novel Cationic Lipid and Cholesterol-Coated Gold Nanoparticles and Their Interactions with Dipalmitoylphosphatidylcholine Membranes. Langmuir 2003, 19, 4439. (41) Ao, M. Q.; Xu, G. Y.; Zhu, Y. Y.; Bai, Y. Synthesis and properties of ionic liquid-type Gemini imidazolium surfactants. J. Colloid Interface Sci. 2008, 326, 490. (42) Ao, M. Q.; Huang, P. P.; Xu, G. Y.; Yang, X. D.; Wang, Y. J. Aggregation and thermodynamic properties of ionic liquid-type gemini imidazolium surfactants with different spacer length. Colloid Polym. Sci. 2009, 287, 395. (43) Li, X.; He, G.; Zheng, W.; Xiao, G. Study on conductivity property and microstructure of TritonX-100/alkanol/n-heptane/water microemulsion. Colloids Surf., A 2010, 360, 150. (44) Murashova, N. M.; Levchishin, S. Yu.; Yurtov, E. V. Effect of Bis-(2-ethylhexyl)Phosphoric Acid on Sodium Bis-(2-ethylhexyl)Phosphate Microemulsion for Selective Extraction of Non-Ferrous Metals. J. Surfactants Deterg. 2014, 17, 1249. (45) Lesaint, C.; Glomm, W. R.; Lundgaard, L. E.; Sjöblom, J. Dehydration efficiency of AC electrical fields on water-in-model-oil emulsions. Colloids Surf., A 2009, 352, 63. (46) Nazal, M. K.; Albayyari, M. A.; Khalili, F. I. Effect of high ionic strength on the extraction of uranium(VI) ions. J. Saudi Chem. Soc. 2014, 18, 59.

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Ionic-Liquid-Type Imidazolium Gemini Surfactant Based Water-in-Oil

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