Extraction of Germanium by the AOT Microemulsion with N235 System

Sep 28, 2010 - Zhenning Lou , Xurui Cui , Shuqin Zhang , Xiaodong Feng , Weijun Shan , Ying Xiong ... Jing Yang , Xidan Zhao , Yanzhao Yang. Separatio...
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Ind. Eng. Chem. Res. 2010, 49, 10005–10008

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Extraction of Germanium by the AOT Microemulsion with N235 System Fei Liu, Yanzhao Yang,* Yanmin Lu, Kai Shang, Wenjuan Lu, and Xidan Zhao Key Laboratory for Special Functional Aggregated Materials of Education Ministry, School of Chemistry and Chemical Engineering, Shandong UniVersity, Jinan 250100, China

The extraction of germanium to a W/O microemulsion by the combination with an anionic surfactant and an amine extractant was studied. In the AOT/n-butanol/n-heptane/Na2SO4/N235 system, AOT was used as an anionic surfactant to form a microemulsion in n-heptane, n-butanol was injected in the microemulsion as a cosurfactant to enhance the stability, and N235 was a typical extractant in the system. The microemulsion system without N235 showed poor extractability and stability. However, by adding N235, the extraction efficiency (E%) can be more than 99%, and the stability of the microemulsion extremely enhanced. The influences of the concentration of cosurfactant, temperature, pH of the feed solution, and composition of the feed solution on the extraction efficiency (E%) were verified. 1. Introduction The separation of germanium has attracted much more attention because of its increasingly important role in industry, such as in catalysts, infrared, fiber optics and semiconductor devices. During World War II, germanium was investigated intensively for its use in rectifying microwaves for radar applications.1 At present, tannin precipitation process is the most used process in the conventional germanium recovery.2,3 Considering that the tannin is expensive, solvent extraction was studied for reducing the cost. There are some extractants used in the solvent extraction of germanium: oxine derivatives (KELEX100), a-hydroxyoximes (LIX63), and hydroxamic acid (YW100). These three extractants have high selectivity in the process of extracting germanium from the zinc plant residues, under proper conditions. KELEX100 and LIX63 require severe conditions, such as the high concentration of extractant and the strong acidity. YW100, a hydroxamic acid with 5-9 carbon atoms, is used successfully to extract germanium. However, it cannot be recycled because of its high solubility in water. Therefore, the high cost of production is the main problem in this process.4-6 Microemulsions, which have unique properties as separation media such as the nanometer-sized spherical or bicontinuous structure, the rapid coalescence and reseparation dynamics of the structure and the enhanced solubilization capacity, is defined as a system formed by the dispersion of microdroplets of two immiscible liquids, stabilized by an interfacial membrane formed by the surfactant and cosurfactant. They are thermodynamically stable, homogeneous, and optically isotropic solutions. There are four types of microemulsion systems called Winsor I, Winsor II, Winsor III, and Winsor IV. Generally speaking, only the Winsor II microemulsion, which is oil continuous, can be used to separate material from aqueous phase. The extraction of metal ions using W/O microemulsion coexisting with a water phase is often very effective to accelerate extraction and improve on extractability. The enormous rise of the microinterfacial surface area in the microemulsion phase and the participation of the microemulsion globules to transport metal ions from the aqueous phase to the organic phase are the prime motivators to accelerate extraction. The electrostatic attraction between the headgroup of surfactant and metal ions is the driving force of the extraction process.7-11 * To whom correspondence should be addressed. E-mail: yzhyang@ sdu.edu.cn.

The purpose of the present work is to investigate the possibility of germanium ions’ removal from aqueous solutions by Winsor II systems with extractant N235 (Figure 1), which is an amine extractant. On the basis of our experiments, we found that adding N235 into the microemulsion system had some advantages: when the N235 used in the ordinary solvent extraction, the feed solution must be strong acid (pH e1.2) to obtain high extraction efficiency. When the microemulsion without extractant used to extract germanium, the pH value of feed solution must be lower than 2 to keep the stability and maximum extraction efficiency. However, the microemulsion system with N235 had a great extractability when the pH value of feed solution was 1-12. N235 improved the stability of microemulsion system, and the extractability was enhanced, too. The system showed good application properties to extract germanium and solve the problem of the severe conditions needed in solvent extraction for germanium extraction. 2. Experimental Section 2.1. Reagents and Instruments. The chemicals used in the experiments were all analytical grade except N235. AOT, bis (2-ethylhexyl) sulfosuccinate sodium salt, purchased from Alfa Aesar China. N235, which was purchased from Chinese Academy of Sciences, was acidulated with 0.25 mol/L H2SO4. Tartaric acid was purchased form Tianjin kemiou factory. The other regents, n-heptane, n-butanol, sodium sulfate, and germanium dioxide were purchased form China National Pharmaceutical Industry Corporation. Vibrator (Yancheng Science Instrument Factory, Jiangsu Province), with a vibration frequency of 275 ( 5 min-1, and a

Figure 1. Structure of N235.

10.1021/ie100963t  2010 American Chemical Society Published on Web 09/28/2010

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Table 1. Extraction Efficiency (E%) of Germanium as the Function of AOT Concentrationa AOT/mol/L

0.11

0.22

0.34

0.60

0.65

E%

60%

61.6%

62.1%

63.5%

appear crystal liquid

Oil phase, Cn-butanol ) 7.7 mol/L; Cn-heptane ) 2 mol/L; inner aqueous is deionized water. Feed solution: CGe (IV) ) 0.1 g/L; pH 2. a

temperature controlling precision of (1 K. UV grating spectrophotometer 754 Type (Shanghai Third Analysis Instrument Factory). 2.2. Procedure. In the following studies, unless stated specially, the temperature was generally maintained at 298 ( 1 K. The organic phase was prepared by injecting AOT, Na2SO4 solution, n-butanol, and/or N235 in n-heptane. Tartaric acid and GeO2 were dissolved in the deionized water to prepare the feed solution, which contained 0.1 g/L germanium, the pH of the feed solution was adjusted by NaOH pellet and H2SO4 solution. The procedure of metal extraction into microemulsion system is, in principle, the same as for ordinary solvent extraction experiment. The organic phase was used to extract an equal volume of the feed solution. The two phases shook mechanically for 10 min (10 min is the required time to reach equilibrium). Afterward, the mixture was kept under rest for phase separation (microemulsion and aqueous phase). After extraction, the aqueous phase was collected and the germanium concentration in aqueous solution was measured by spectrophotometry and the germanium concentration in organic solution was calculated by mass balance. 2.3. Theory. The reaction between germanium, tartaric acid and N235, can be expressed by the following equations: 3C4O6H6 + GeO2 · H2O h H2Ge(C4O6H4)3 + 3H2O

(1) R3N(o) + H2SO4(a) h [R3NH]+[HSO4](o) 2[R3NH]+[HSO4](o) + [H2Ge(C4O6H4)3](a) h 2[R3NH]+ 2 [Ge(C4O6H4)3](o) + 2H2SO4(a)

(2)

(3)

in which R3N represents the N235 and the indexes (o) and (a) refer to organic and aqueous phases, respectively. The GeO2 react with tartaric acid to form the complex H2Ge(C4O6H4)3, which combined with the acidulated N235 on the external aqueous/organic interface to form the binary complex [R3NH]+2[Ge(C4O6H4)3]2-, then the binary complex diffuses to the inner organic/aqueous interface. 3. Result and Discussion 3.1. Microemulsion without N235 Extraction of Ge(IV). The extraction behavior of Ge(IV) by the AOT microemulsion without N235 was examined. Table 1 shows the effect of AOT concentration at pH 2 on the extraction behavior of Ge(IV). It was found that the extractability of Ge(IV) was reinforced with AOT concentration increasing. However, when the concentration of AOT was more than 0.65 (mol/L), the liquid crystal phase was formed, which could not used to extract metals because of its high viscosity. When the inner phase changed to be Na2SO4 solution, the stability of microemulsion was strengthened, after adjusted the conditions, the maximum value (68.8%) of germanium extraction efficiency (E%) was obtained. The organic phase without N235 showed poor extractability, and the microemulsion was easily emulsified in the extraction procedure. By adding butanol (g70%), the stability of AOT-

Figure 2. Extraction efficiency (E%) of germanium as the function of n-butanol concentration. Oil phase: CAOT ) 12%; CN235 ) 30%; inner aqueous is 0.07 mol/L Na2SO4 solution. Feed solution: CGe(IV) ) 0.1 g/L; ntartaric acid/nGe(IV) ) 3; pH 6.

based microemulsion system was enhanced but the extractability was still poor. 3.2. Microemulsion with Acidulated N235 Extraction of Ge(IV). By adding only a small amount of acidulated N235, the microemulsion was greatly stabilized and extremely enhanced extractability. The amount of butanol injected in the microemulsion was greatly decreased without the system emulsified. Adding some organics, such as acidulated N235, into the microemulsion could enhance the stability. It might because that the H+ of acidulated N235 can be combined with the alkyl chains and those of AOT by the hydrophobic interaction, which can contribute to the reinforcement of the AOT microemulsion. However, a further study is necessary for a complete understanding. 3.2.1. Effect of n-Butanol Concentration. The cosurfactant is a nonionic molecule that combine with surfactant to neutralize the repulsive effect among the surfactant polar heads. Most of surfactants need cosurfactant to form microemulsion but some branched surfactants have no use for cosurfactants, such as AOT, which has two tail groups could contribute to the preservation of the negative interfacial curvature without alcohol. In the system used in the germanium extraction, an amount of n-butanol was injected in the organic, or the system was not stable enough to extract metals. The effects of the various concentration of n-butanol on the germanium extraction efficiency (E%) were investigated, which can be seen in Figure 2. The germanium extraction efficiency (E%) reduced as the concentration of n-butanol increased, when the n-butanol concentration was greater than 40%, the germanium extraction yield was almost constant. This result may be explained by the combination between n-butanol and AOT, which made some of AOT lose their activity. The third phase appeared when the n-butanol concentration less than 10%, so the extraction yield of germanium was decreasing. 3.2.2. Effect of the pH of the Feed Solution. With the purpose of investigating the influence of the extraction pH on the germanium extraction, experimental runs were conducted in the pH range between 1 and 12. The obtained result was showed in Figure 3. According to the previous transport mechanism (eqs 1-3), Ge(IV) extraction is highly dependent on the external pH. When there were too much hydrogen ions, which could combined with HSO4-, the reverse reaction of eq 3 would be promoted, which was inimical to the germanium extraction. Also, tartaric acid is a weak acid, strong acid environment obstructed the hydrolysis of tartaric acid, which was inimical to the process of eq 1. So, the higher the external phase pH value is, the higher the germanium extraction efficiency (E%) is. When there were too much hydroxyl ions,

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Figure 3. Extraction efficiency (E%) of germanium as the function of pH value of feed solution. Oil phase: CAOT ) 12%; CN235 ) 30%; Cn-butanol ) 10%; inner aqueous is 0.07 mol/L Na2SO4 solution. Feed solution: CGe(IV) ) 0.1 g/L; ntartaric acid/nGe(IV) ) 3.

Figure 4. Extraction efficiency (E%) of germanium (use N235 and n-heptane) as the function of pH value of feed solution. Oil phase: CN235 ) 50%, n-heptane used as the solvent. Feed solution: CGe(IV) ) 0.1 g/L; ntartaric acid/nGe(IV) ) 3. Voil phase:Vfeed solution ) 1.

[R3NH]+[HSO4]-, which is the reactant of eq 3, might reacted with hydroxyl ions (eq 4), so the production of eq 3 was reduced. For this reason, when pH > 7, the germanium extraction efficiency (E%) was reduced slightly. On the basis of these results, an external phase pH value of 6 was regarded as the best choice. [R3NH]+[HSO4](o) + 2NaOH(a) h R3N(o) + NaSO4(a) + 2H2O(a) (4)

As the external pH value between 0.5 and 2, the extraction of germanium with the mixture of N235 and n-heptane was investigated. The result, which is shown in Figure 4, indicated that the germanium extraction efficiency (E%) was first increased then decreased as the increasing of the pH value. However, the scope of proper pH value was quite limited, and the germanium extraction efficiency (E%) was much lower. 3.2.3. Effect of the Concentration of Tartaric Acid in the Feed Solution. The tartaric acid used in the experiment was combined with GeO2 to form the complex H2Ge(C4O6H4)3 (eq 1). As shown in the Figure 5, the concentration of tartaric acid also effected the germanium extraction. The germanium extraction efficiency (E%) was 70% without tartaric acid, which was almost equal to the germanium extraction efficiency (E%) using the AOT microemulsion without extractant. When the value of ntartaric acid/nGe(IV) was greater than 3, the germanium extraction efficiency (E%) was constant, which was consistent with the reaction equation (eq 1). On the basis of the experiment data, the value of ntartaric acid/nGe(IV) was fixed at 3. 3.2.4. Effect of Temperature. The temperature was an important influencing factor in the extraction procedure. In the

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Figure 5. Extraction efficiency (E%) of germanium as the function of the value of ntartaric acid/nGe(IV) in the feed solution. Oil phase: CAOT ) 12%; CN235 ) 30%; Cn-butanol ) 10%; inner aqueous is 0.07 mol/L Na2SO4 solution. Feed solution: CGe(IV) ) 0.1 g/L; pH 6.

Figure 6. Influence of T to the partition coefficients of the Ge(IV) between the organic and aqueous phases. Oil phase: CAOT ) 12%; CN235 ) 30%; Cn-butanol ) 10%; inner aqueous is 0.07 mol/L Na2SO4 solution. Feed solution: CGe(IV) ) 0.1 g/L; ntartaric acid/nGe(IV) ) 3; pH 6.

Figure 6, it could be noted that: the partition coefficients of the Ge(IV) between the organic and aqueous phases (D) was decreased with the temperature increased from 283.15 to 323.15 K, this phenomenon can be explained that the extraction is an exothermic nature and lower temperature favor the metal extraction. The enthalpic change (∆rHοm) can be calculated from the slope of the linear equation between ln D and 1/T (eq 5).12

[ ( )] ∂ ln D 1 ∂ T

)

-∆rHοm R

(5)

P

D is the partition coefficient of Ge(IV) between the organic and aqueous phases, T (K) is the temperature, and R is the gas ο ) -16.11 kJ/mol. It can be known that the constant. ∆rHm extraction process is a spontaneously exothermic process. 4. Conclusions Important conclusions could be drawn from this work, all related to the germanium extraction process using microemulsions with/without the N235 as the carrier. The study of germanium extraction by microemulsions showed that this system is very efficient, and the extraction yield could be higher than 99%. The microemulsion system without extractant used in the extraction showed poor extractability and the microemulsion was easily emulsified. When the extractant (N235) was injected in the microemulsion, the extractability was greatly improved, and the microemulsion was much more stable. The microemul-

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sion with extractant (N235) was maintaining high extractability (above 97%) in a considerable pH range (1-12). The system consists only extractant and organic solvent showed poor extractability, and the pH range was small (0.5-2), when the pH value was more than 2, the system was easily emulsified or showed very poor extractability (E% < 30%). Acknowledgment The authors acknowledge financial support for this work from The National Natural Science Foundation of China (No. 20876089), Natural Science Foundation of Shandong province (Grant no. Y2007B05), and Key Technologies R&D Programme of China (NO. 2007BAD87B05). Literature Cited (1) Liang, D. Q.; Wang, J. K.; Wang, Y. H. Behavior of Tannins in Germanium Recovery by Tannin Process. Hydrometallurgy 2008, 93, 140. (2) Kul, M.; Topkaya, Y. Recovery of Germanium and Other Valuable Metals from Zinc Plant Residues. Hydrometallurgy 2008, 92, 87. (3) Sargar, B. M.; Anuse, M. A. Solvent Extraction Separation of Germanium(IV) with N-n-Octylaniline As an Extractant. J. Anal. Chem. 2005, 60, 404.

(4) Tang, S. F.; Zhou, C. S.; Jiang, X. Y.; Zhao, C. L. Extraction Separation of Germanium with Hydroxamic Acid HGS98. J. Cent. South UniV. Technol. 2000, 7, 40. (5) Vlasta, V.; Iva, J.; Biserka, T. Extraction and Separation of Germanium(IV) with 4-Pyridone Derivatives. Croat. Chem. Acta. 2001, 74, 467. (6) Wang, J. D.; Chen, J. Y. SolVent Extraction Manual; Chemical Industry Press: Beijing, 2001; 664-667. (7) Hitoshi, W. Microemulsions in Separation Sciences. J. Chromatogr. A 1997, 780, 93. (8) Paul, B. K.; Moulik, S. P. Microemulsions: an overview. J. Disper. Sci. Technol. 1997, 18, 301. (9) Moulik, S. P.; Paul, B. K. Structure, Dynamics and Transport, Properties of Microemulsions. AdV. Colloid Interface Sci. 1998, 78, 99. (10) Klier, J.; Tucker, C. J.; Kalantar, T. H.; Green, D. P. Properties, and Applications of Microemulsions. AdV. Mater. 2000, 12, 1751. (11) Yang, Y. Z.; Zhu, T.; Xia, C. B.; Xin, X. M.; Liu, L.; Liu, Z. Y. Study on the Extraction of Cobalt and Nickel from NH4SCN Solution by Winsor II Microemulsion System. Sep. Purif. Technol. 2008, 60, 174. (12) Pei, Y. C.; Wang, J. J.; Wu, K.; Xuan, X. P.; Lu, X. J. Ionic LiquidBased Aqueous Two-Phase Extraction of Selected Proteins. Sep. Purif. Technol. 2009, 64, 288.

ReceiVed for reView April 26, 2010 ReVised manuscript receiVed September 10, 2010 Accepted September 12, 2010 IE100963T