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Separation and preconcentration of trace indium(III) from environmental samples with nanometer-size titanium dioxide
Hydrometallurgy 95 (2009) 92–95
Contents lists available at ScienceDirect
Hydrometallurgy j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / h yd r o m e t
Separation and preconcentration of trace indium(III) from environmental samples with nanometer-size titanium dioxide Lei Zhang ⁎, Yingnan Wang, Xingjia Guo, Zhu Yuan, Zhongyuan Zhao College of Chemistry, Liaoning University, Shenyang 110036, PR China
A R T I C L E
I N F O
Available online 8 May 2008 Keywords: Nanometer TiO2 Indium Preconcentration Yellow red soil Ultrasonic
A B S T R A C T This work assesses the potential of an adsorptive material, nanometer TiO2, for the separation and preconcentration of trace indium ions from various aqueous media. The adsorption behavior of nanometer TiO2 for indium ions was investigated. It was found that the adsorption percentage of the indium ions was more than 96% in pH 3.5–4.0, and the desorption percentage of In(III) ions was more than 99% in pH ≤ 1.5. Good relative standard deviate (1.5%) and lower analytical detection limit (0.45 µg•mL− 1) were obtained. The adsorption equilibrium was well described by the Langmuir isotherm model with monolayer adsorption capacity of 4566 µg g− 1 (25 °C). The accuracy of the method is confirmed by analyzing the certified reference material (GBW-07405, GBW07406). The results demonstrated good agreement with the certified values. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Indium is a crystalline, very soft, ductile, and malleable metal that retains its high plastic properties at cryogenic temperatures. It generally increases the strength, corrosion resistance, and hardness of an alloy system, when indium is added. It is also used in electrical contacts, liquid crystal displays, low-pressure sodium lamps, alkaline dry batteries, and semiconductors (Watanabe et al., 2002). Indium is widely spread in nature, generally in very low concentrations. The direct determination of extremely low concentrations is limited with not only low sensitivity, but also matrix interference. For this reason, the preliminary separation and preconcentration of trace indium from matrix is often required. The most widely used techniques for the separation and preconcentration of trace indium include liquid–liquid extraction (Gupta et al., 2004), ionexchange (Taher, 2000) and solid–liquid separation (Zhang et al., 2004; Fortes and Benedetto, 1998). Recently, solid-phase extraction has achieved an increasing application because of its simple procedure, higher preconcentration factor, rapid phase separation and combination with different detection techniques. The main requirements with respect to substances to be used as solid-phase extractants are as follows (Rodriguez et al., 1992; Leanne and Gayle, 2003): possibility of extracting a large number of elements over a wide pH range, fast and quantitative adsorption and elution, high capacity and accessibility. Numerous substances have been proposed and applied as solid-phase extractants (such as modified silica (Syouhei et al., 1998; Fortes et al., 2003) and alumina (Liang et al., 2003), magnesia (Alguacil, 1999) active carbon (Demeestere et al., 2003) and cellulose (Prestidge et al., 2004)). ⁎ Corresponding author. Tel.: +86 24 62207816; fax: +86 24 62202380. E-mail address: [email protected] (L. Zhang). 0304-386X/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.hydromet.2008.05.001
Nano material is one of functional materials, which has attracted much attention due to its special properties (Zhang et al., 2003; Liang et al., 2001), and is also known as ultra-fine particles. Most of atoms on the surface of the nanoparticles are unsaturated and can easily bind with other atoms. Consequently, nanometer material can adsorb selectively metal ions, and has a quite high adsorption capacity. The aim of this work is to investigate the adsorption characteristics of indium ions on nanometer TiO2 and the conditions for preconcentration of trace indium using nano-TiO2. This method was successfully applied to the determination of indium ions in geological standard samples. 2. Experimental method 2.1. Apparatus Cary 5000 UV–Vis–NIR spectrophotometer (VARIAN) was used for the determination of indium ions. A Mettler Toledo 320-S pH meter (Mettler Toledo Instruments (Shanghai) Co. LTD) was used to measure the pH of solutions. KQ-100 Controllable Serial-Ultrasonics apparatus (Kunshan apparatus company, China) was adopted to disperse the solution of nano-TiO2, operating at an ultrasonic frequency of 20– 80 kHz and output power of 0–50 W through manual adjustment. A model TDL80-2B centrifugal machine (Shanghai Anting Scientific Instrument Co., China) was used throughout. 2.2. Reagent and solution Nano-TiO2 (anatase) that was used as adsorbent in this study was provided from Zhoushanmingri Nanometer Material Co.(China), and its particle size is about 20–30 nm.
L. Zhang et al. / Hydrometallurgy 95 (2009) 92–95 Table 1 Studies on the effect of different nano-materials on adsorption behaviour of indium ions Sorbent
Adsorption efficiency (%)
Nano-TiO2 (anatase, 20–50 nm) Nano-TiO2 (rutile, 20–50 nm) Nano-SiO2 (particle diameter 20–50 nm)
96.3 77.2 56.2
The certified reference material yellow red soil (GBW07405 and GBW07406) used in this experiment, was provided by State Technology Supervision Administration. Stock solution of In (III) (1 mg mL− 1) was prepared by tepidly dissolving 0.2500 g pure indium (99.999%) with 50 mL 1 + 1 hydrochloric acid. After it got cool, it was moved to 250 mL flask. After that, it was diluted with doubly distilled water to maintain a constant volume. All of the reagents, including salicyl fluorescence ketone (SAF, 0.05%), bromize16-alkyl-3-methyl ammonium (CTMAB, 0.5%), polyvinyl alcohol (PVD, 2%), acetic acid-acetic ammonium buffer solution, hydrochloric acid (1 + 1), hydrochloric acid (0.1 mol L− 1), ammonia (25%), hydrogen peroxide (30%), sodium hydroxide (1%) were all analytical grade. Doubly distilled water was used in the experiment. EDTA-triethanolamine-NaOH solution: 10.0 g EDTA, 50 mL triethanolamine (98%) and 25.0 g sodium hydroxide were dissolved in a 1000 mL flask with doubly distilled water. The stock solutions of the various metal ions (mg mL− 1) were prepared with their nitrate or chloride salts (≥99.99%) and used to investigate the possible effects of interfering ions. 2.3. Experimental procedure 2.3.1. Determination of In (III) Some volumes of In (III) standard solution were put into 25 mL volumetric flasks, 0.2 mL 2% PVA, 0.3 mL 0.05% SAF, 1.5 mL 0.5% CTMAB and 1.5 mL pH 5.5 HAc-NH4Ac buffer solution were added to the volumetric flasks. Double-distilled water was put into the solutions to prepare desired volumes and shaken up. After 30 min, absorbency was determined by using UV–Vis–NIR Spectrometer at wavelength of 568 nm, and the content of the In (III) was calculated. 2.3.2. Sample preparation Portions (1.0000 g) of GBW-07405 or, GBW07406 were transferred into corundum crucibles, and 2.0 g of sodium peroxide were added into every corundum crucible. After stirring to make them uniform, then putting a layer of sodium peroxide (about 1.0 g) on the top of each sample, heated about 6–7 min at 750 °C. After cooling to room temperature, transferred them into 250 mL beakers containing some EDTA-triethanolamine-NaOH solution, then adding 2.50 mL of magnesium salt solution (10.0 mg MgO/mL) and 2 mL of hydrogen peroxide, heated to boil and kept 15 min. Took them down, then added 1 mL of hydrogen peroxide to dissolve brick red cuprous oxide which maybe exist. After cooling 30 min, samples were filtrated with alkali-resisting middle speed filter paper. The deposition was washed seven times with 1% sodium hydroxide solution and then washed three times with doubly distilled water. Put the filter paper with deposition into the initial beaker, then added 0.1 mol L− 1 tepid hydrochloric acid and stirred to dissolve the deposition. 10 min later, the deposition had been dissolved completely, and was transferred into 100 mL volumetric flask, washing initial beaker and filter paper clean, diluting to scale. pH value was adjusted to 3.5 with hydrochloric acid and ammonia for determination of In(III). 2.3.3. Adsorption and desorption The adsorption experiments were carried out in a series of 50 mL Erlenmeyer flasks containing 100 mg nano-TiO2 and 15 mL of 10 mg L− 1 indium solution at the desired pH. If necessary, an appropriate HCl or ammonia solution was used to adjust the pH of the solution after addition of nano-TiO2. After ultrasonic dispersion for 2 min and static adsorption for 10 min, the two phases were separated by centrifuging
93
at 4000 rpm for 5 min. The amount of In(III) adsorbed per gram of nano-TiO2 was determined by using the supernatant. The adsorbed indium ions were desorbed from solid phase into aqueous medium by 2.0 mL of 1.0 mol L− 1 hydrochloric acid eluent solution. The adsorption percentage was calculated based on the following equation, η¼
ðC0 −C ÞV 100k C0 V
ð1Þ
η was the adsorption percentage of indium; C0 was the initial content of In (III) in aqueous solution with the unit of μg mL− 1; C was the equilibrant content of In (III) in aqueous solution; V was the volume of the solution with the unit of L. The adsorption capacity for nano-TiO2 particles were calculated based on the following equation, ðC0 −C ÞV ð2Þ W where q was the adsorption capacity for nano-TiO2 particles with the unit of μg g− 1; C0 was the initial content of In (III) in aqueous solution with the unit of μg mL− 1; C was the equilibrant content of In (III) in aqueous solution; V was the volume of the solution with the unit of L; W was the mass of added sorbent with the unit of g. Adsorption isotherm studies were carried out with different initial concentrations of In(III) while maintaining the sorbent dosage at constant level in the range 0–50 °C. q¼
3. Results and discussion 3.1. Selection of sorbent The effect of different sorbents on the adsorption behaviour for the In (III) in aqueous solution was studied and shown in Table 1. It was found that the nano-TiO2 (anatase) was the best sorbent. 3.2. Effect of pH In this study, knowledge of pH was important because the pH of solution influences the distribution of active sites on the surface of nanoTiO2. At the higher pH, the OH− on the surface of nano-TiO2 provides the ability of binding cations. The decrease of pH leads to the neutralization of surface charge, and OH− is displaced from the surface. When the surface of nano-TiO2 carries positive charges, it begins to adsorb anions. Therefore, the effect of the initial pH on the adsorption of In (III) ions was investigated in the pH range of 1–5 by using 0.1 g of nano-TiO2 at a fixed concentration of In (III) ions as 10 µg mL− 1. The variation of adsorption percentage with the pH of solution is shown in Fig. 1.
Fig.1. Effect of pH on the adsorption of the In3+ (10 µg mL− 1) on nano-TiO2. 100 mg of nanoTiO2; CIn(III)10 µg mL− 1; V 15 mL; ultrasonic dispersed 1.5 min; temperature 25± 0.1 °C.
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L. Zhang et al. / Hydrometallurgy 95 (2009) 92–95
Fig. 1 shows the effect of pH on the adsorption of In (III) by nanoTiO2, which indicates that the recovery of indium increases with increasing pH from 1 to 4. The effect of pH on In(III) adsorption can be explained by the following reasons. The surface charge is neutral at isoelectric point (IEP), which pHIEP value is 6.8 for nano-TiO2. The surface of sorbent carries positive charges at pH value lower than IEP, which enhances electrostatic force of attraction with InCl−4 (In the studied system, the main chemical species of indium in solutions is InCl−4 (Chung et al., 2003)). As a result, the process of sorption takes place more easily in pH 2–3.5, so the adsorption percentage of In(III) was higher. In pH b 2, there is a balance reaction: H+ + InCl−4 ⇄ HInCl4, the main chemical species of In(III) is HInCl4 (Hasegawa et al., 1980; Akçay, 2004; Reddy and Reddy, 1985), so the adsorption percentage of In(III) was lower. Therefore, pH 3.5 was chosen for adsorption of In(III) in the experiment. 3.3. Desorption and enrichment factor It is found from Fig. 1 that the adsorption of In(III) at pH b 1.5 could be negligible. For this reason, various concentration HCl were studied for the elution of retained In(III) from nano-TiO2. The results obtained indicated that 1.2 mol L− 1 HCl was sufficient for complete elution. The effect of eluent volume on the recovery of analytes was also studied by keeping the HCl concentration of 1.2 mol L− 1, it was found that with 1.0 mL HCl quantitative recoveries (N95%) could be obtained. Therefore, the volume of 1.0 m L eluent was used in following experiments. The influence of the sample volume on recoveries of indium was also examined. For this purpose, indium was preconcentrated from volumes of 10, 20, 25, 50 and 100 mL of sample solution containing 150 μg indium by applying the procedure mentioned above. The maximum sample volume can be up to 25 mL with the 95% recovery and the enrichment factor was 25 with 1.0 mL HCl elution (Mizuike, 1983). 3.4. Comparison different adsorption behaviors The comparison adsorption behavior was made, based on the method stated above. It was shown that for the experiments carried out for over five times, the oscillation average adsorption percentage was 92.3%, the average adsorption percentage of ultrasonic oscillation for 1.5 min was more than 96.0%, and the static average adsorption percentage was 87.7% after 60 min. The effect of oscillation adsorption was larger than static adsorption, and the ultrasonic adsorption was the most significant. It was also shown that In (III) ions could be adsorbed fast and quantitively by nano-TiO2. Therefore, ultrasonic adsorption was used in this study, the reason of which may be that it can be carried out easily.
Table 2 Related coefficient and experimental parameters of Langmuir isotherms T/°C
Langmuir equation Ce/q = 1/Kqm + Ce/qm
K (mL/μg)
qm (μg/g)
r2
0 25 50
Ce/q = 0.000257Ce + 0.000284 Ce/q = 0.000208 Ce + 0.000236 Ce/q = 0.000154 Ce + 0.000244
0.9049 0.8814 0.6311
3891 4566 6494
0.998 0.998 0.999
Nano-TiO2 particles were small in diameter, thus surface area rate was large, surface energy increased and the adsorption capacity increased. Particles could be gathered, forming secondary particles due to the huge surface energy. As a result, it was difficult to make use of the special high adsorption. So ultrasonic adsorption was used in this study, which resulted from the huge energy and pressure of gas bubbles in ultrasonic cavitation process. The vibration wave could make the gathered nano-particles disperse and the efficient surface area increase. The adsorption ability increased, so did the adsorption percentage. 3.5. Adorption isotherm and adsorption capacity The adsorption behaviour of the nano-TiO2 was determined by studying the amount of adsorbed indium as a function of indium concentration. For this purpose, 10 mL In (III) ions solutions with different concentrations were added to a series of 50 mL conical flasks with stoppers, the pH of which was adjusted to 3.5. Nano-TiO2 (0.1 g) particles were added and then adsorption experiments were conducted at 0 °C, 25 °C and 50 °C, respectively. The profile of adsorption isotherm of nano-TiO2 for In (III) ions is shown in Fig. 2. There was a gradual increase of adsorption for In(III) ions until the equilibrium was attained. Adsorption isotherm is important to describe how solutes interact with the sorbent. The data of the isotherm reveal that the adsorption processes conform to Langmuir model. In Fig. 2, the graph shows an excellent fit to data in concentration interval studied in all cases for the Langmuir model. A modified Langmuir equation conformed to this kind of adsorption isotherm as represented below: Ce =q ¼ 1=Kqm þ Ce =qm Here, Ce is equilibrium concentration of the indium (III) ion in solution (µg mL− 1); q is the amount of indium (III) adsorbed per unit weight of nano-TiO2 at equilibrium concentration (µg g− 1); qm is the maximum monolayer adsorption capacity (µg g− 1); K is the Langmuir constant related to the affinity of binding sites(mg L − 1). A plot of Ce/q versus Ce, the sorption parameters qm and K evaluated from the slope and intercept. The maximum adsorption capacity of indium (III) on nano-TiO2 was from 3891 µg g− 1 to 6494 µg g− 1 for the temperature range of 0–50 °C (Table 2).
Table 3 Tolerance limits for coexisting ions in adsorption of the studied elements
Fig. 2. Adsorption isotherm of In3+ on nano-TiO2. Temperature, 0 °C, 25 °C, 50 °C; pH: 3.5; V 15 mL; static time 20 min, 100 mg of nano-TiO2; the initial In(III) concentration range was 15–60 mg L− 1.
Interfering ion
Maximum allowable volume (mg)
Interfering ion
Maximum allowable volume (mg)
Ga2+ Mo6+ Sb5+ Tl+ Pb2+ Zn2+ Fe3+ Mn2+ Ba2+ Na+
0.065 0.230 0.230 0.170 2.500 2.100 1.000 1.000 0.300 0.100
Ge4+ Al3+ Cu2+ Ni2+ Se4+ Co3+ Cd2+ Mg2+ Cr3+ Cl−
1.950 0.002 0.010 1.000 0.140 1.800 0.750 100 0.120 10
There were some white deposits for Ti4+, Sn4+, As3+, Te4+ at the pH of 3.5 and so they did not have influence.
L. Zhang et al. / Hydrometallurgy 95 (2009) 92–95 Table 4 Analytical result of In(III) ions in standard reference material(n = 7) P
Sample
Added (μg·g− 1)
Reference value(μg·g− 1)
Found xFt psffiffiNffi (μg·g− 1)
GBW07405 GBW07406
– 4.0
4.1 ± 0.6 0.84 ± 0.20
4.16 ± 0.42 5.01 ± 0.57
95
In (III) at certain pH, high precision and concentration factor and low detection limit. Moreover, the effects of coexisting interfering ions in the determination of In (III) could be eliminated by the selective adsorption, elution and sample preparation. So this method can be applied to detect In (III) in soil or other environmental samples.
Indicates that model parameters are statistically significant (t-test) at 95% confidence level.
Acknowledgements 3.6. Interference effects Some experiments were carried out in order to examine the effects of common coexisting ions on the adsorption of the studied ions on nanometer TiO2. The effects of potential interferences occurring in geological samples on the determination of indium were investigated using the optimized preconcentration procedure. Metal ions were added individually to a solution as their nitrate or nitrate or chloride salts, the proposed preconcentration method was applied. The tolerance of the coexisting ions is given in Table 3. Except Al3+ and Cu2+, other species almost didn't have effect and the allowable amount for these species were large. 3.7. Detection limits and precision From measurements made under the optimum conditions described above, the calibration graph was linear in the range 0.3– 20 µg /25 mL. The calibration equation is A = 0.0101 + 0.0633C with a correlation coefficient of 0.9993. Where C is the concentration of indium (μg/25 mL), and A is the absorbance. The detection limit (evaluated as concentration corresponding to three times the standard deviation of 11 runs of blank solution) of this method for In(III) is 0.45 µg mL− 1, and the relative standard deviation (RSDs) 1.5% (n = 11, C = 15 µg /mL). 3.8. Sorbent reuse The stability and potential regeneration of nano-TiO2 were investigated. Nano-TiO2 was rinsed to neutrality and dried, then be used to adsorb In(III) ions again. The experimental results showed there was not obvious decrease in the recoveries for In(III) ions(93.9%) after at least 7 adsorption/desorption cycles. 3.9. Analytical application Since it was found that the proposed preconcentration method was useful for the preconcentration of trace indium, the method was applied to the determination of indium (total indium) in soil reference material (GBW07405, GBW07406) to evaluate the accuracy of the developed procedure. Indium concentration found as mean of seven determinations at 95% confidence level was 4.16 ± 0.42, 1.01 ± 0.57 (which had been subtracted the added amount 4.0), respectively. It was found that there is no significant difference between results found by the proposed method and certified value (4.1 ± 0.6, 0.84 ± 0.2) according to the t- test. It can be concluded that there is no systematic error in the determination at 95% confidence level. The results are shown in Table 4. As can be seen, the results agree with the certified values. 4. Conclusions This method was suitable for the preconcentration and direct determination of In (III) in soil with a high selective adsorbability for
The authors greatly acknowledge the Education Department of Liaoning Province Science Foundation (No. 20060363 and No. 2007T053) of China for financial support. The authors also thank our colleagues and other students participating in this work. References Akçay, Mehmet, 2004. Characterization and determination of the thermodynamic and kinetic properties of p-CP adsorption onto organophilic bentonite from aqueous solution. Journal of Colloid and Interface Science, 280, pp. 299–304. Alguacil, F.J., 1999. Solvent extraction of indium by LIX 973N. Hydrometallurgy 51, 97–102. Chung, Nguyen Huu, Nishimoto, Jun, Kato, Osamu, Tabata, Masaaki, 2003. Selective extraction of thallium in the presence of gallium, indium, bismuth and antimony by salting-out of an aqueous mixture of 2-propanol. Analytica Chimica Acta 477, 243–249. Demeestere, Kristof, Dewulf, Jo, Van Langenhove, Herman, Sercu, Bram, 2003. Gassolidad sorption of selectedvolatile organic compounds on titanium dioxide Degussa P25. Chemical Engineering Science 58, 2255–2267. Fortes, M.C.B., Benedetto, J.S., 1998. Separation of indium and iron by solvent extraction. Minerals Engineering 11 (5), 447–457. Fortes, M.C.B., Martins, A.H., Benedetto, J.S., 2003. Indium adsorption onto ion exchange polymeric resins. Minerals Engineering 16, 659–663. Gupta, Bina, Deep, Akash, Malik, Poonma, 2004. Liquid–liquid extraction and recovery of indium using Cyanex 923. Analytica Chimica Acta 513, 463–471. Hasegawa, Yuko, Shimada, Toshiaki, Niitsu, Masaru, 1980. Solvent extraction of 3B group metal ions from hydrochloric acid with trioctylphosphine oxide. Journal of Inorganic & Nuclear Chemistry 42, 1487–1489. Leanne Britcher, A., Gayle Morris, E., 2003. Sodium stearate adsorption onto titania pigment. Journal of Colloid and Interface Science 268, 293–300. Liang, P., Qin, Y.Ch., Hu, B., Peng, T.Y., Jiang, Z.Ch., 2001. Nanometer-size itanium dioxide microcolumn on-line preconcentration of trace metals and their determination by inductively coupled plasma atomic emission spectrometry in water. Analytica Chimica Acta 440, 207–213. Liang, P., Shi, a, T.Q., Lu, a, H.B., Jiang, Z.Ch., Hu, B., 2003. Speciation of Cr(III) and Cr(VI) by nanometer titanium dioxide micro-column and inductively coupled plasma atomic emission spectrometry. Spectrochimica Acta Part B 58, 1709–1714. Mizuike, A., 1983. Springer-Verlag, Berlin, p 6. Prestidge, Clive A., Barnes, Timothy, Simovic, Spomenka, 2004. Polymer and particle adsorption at the PDMS droplet-water interface. Advances in Colloid and Interface Science 108, 105–118. Reddy, A.S., Reddy, M.L.P., 1985. Solvent extraction separation of T1/I/ from T1/III/ with sulphoxides. Journal of Radioanalytical and Nuclear Chemistry 94, 259–264. Rodriguez, M., Cote, G., Bauer, D., 1992. Recovery of indium from mixed hydrochloric acid-sulfuric acid media by solvent extraction with cyanex 301. Solvent Extraction and Ion Exchange 10 (5), 811–823. Syouhei, Nishihama, Akira, Hino, Takayuki, Hirai, 1998. Extraction and separation of gallium and indium from aqueous chloride solution using several organophorus compounds as extractants. Journal of Chemical Engineering of Japan 31 (5), 818–825. Taher, Mohammad Ali, 2000. Differential pulse polarography determination of indium after column preconcentration with [1-(2-pyridylazo)-2-naphthol]-naphthalene adsorbent or its complex on microcrystalline naphthalene. Talanta 52, 301–309. Watanabe, A., Niino, H., Yabe, A., 2002. Low temperature growth of metal oxide thin films by metallorgranic laser photolysis. Applied Surface Science 186 (1–4), 173–178. Zhang, X.Y., Yin, G.Y., Hu, Z.G., 2003. Extraction and separation of gallium, indium and thallium with several carboxylic acids from chloride media. Talanta 59, 905–912. Zhang, X.Y., Lou, X.D., Yin, G.Y., Zhang, Y.J., 2004. Extraction and separation of Ga(III) and Tl(I) or In(III) and Tl(I) fromchloride media with CA-12 in sulphonating kerosene. Rare Metals 23 (1), 6–9.
Contents lists available at ScienceDirect
Hydrometallurgy j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / h yd r o m e t
Separation and preconcentration of trace indium(III) from environmental samples with nanometer-size titanium dioxide Lei Zhang ⁎, Yingnan Wang, Xingjia Guo, Zhu Yuan, Zhongyuan Zhao College of Chemistry, Liaoning University, Shenyang 110036, PR China
A R T I C L E
I N F O
Available online 8 May 2008 Keywords: Nanometer TiO2 Indium Preconcentration Yellow red soil Ultrasonic
A B S T R A C T This work assesses the potential of an adsorptive material, nanometer TiO2, for the separation and preconcentration of trace indium ions from various aqueous media. The adsorption behavior of nanometer TiO2 for indium ions was investigated. It was found that the adsorption percentage of the indium ions was more than 96% in pH 3.5–4.0, and the desorption percentage of In(III) ions was more than 99% in pH ≤ 1.5. Good relative standard deviate (1.5%) and lower analytical detection limit (0.45 µg•mL− 1) were obtained. The adsorption equilibrium was well described by the Langmuir isotherm model with monolayer adsorption capacity of 4566 µg g− 1 (25 °C). The accuracy of the method is confirmed by analyzing the certified reference material (GBW-07405, GBW07406). The results demonstrated good agreement with the certified values. © 2008 Elsevier B.V. All rights reserved.
1. Introduction Indium is a crystalline, very soft, ductile, and malleable metal that retains its high plastic properties at cryogenic temperatures. It generally increases the strength, corrosion resistance, and hardness of an alloy system, when indium is added. It is also used in electrical contacts, liquid crystal displays, low-pressure sodium lamps, alkaline dry batteries, and semiconductors (Watanabe et al., 2002). Indium is widely spread in nature, generally in very low concentrations. The direct determination of extremely low concentrations is limited with not only low sensitivity, but also matrix interference. For this reason, the preliminary separation and preconcentration of trace indium from matrix is often required. The most widely used techniques for the separation and preconcentration of trace indium include liquid–liquid extraction (Gupta et al., 2004), ionexchange (Taher, 2000) and solid–liquid separation (Zhang et al., 2004; Fortes and Benedetto, 1998). Recently, solid-phase extraction has achieved an increasing application because of its simple procedure, higher preconcentration factor, rapid phase separation and combination with different detection techniques. The main requirements with respect to substances to be used as solid-phase extractants are as follows (Rodriguez et al., 1992; Leanne and Gayle, 2003): possibility of extracting a large number of elements over a wide pH range, fast and quantitative adsorption and elution, high capacity and accessibility. Numerous substances have been proposed and applied as solid-phase extractants (such as modified silica (Syouhei et al., 1998; Fortes et al., 2003) and alumina (Liang et al., 2003), magnesia (Alguacil, 1999) active carbon (Demeestere et al., 2003) and cellulose (Prestidge et al., 2004)). ⁎ Corresponding author. Tel.: +86 24 62207816; fax: +86 24 62202380. E-mail address: [email protected] (L. Zhang). 0304-386X/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.hydromet.2008.05.001
Nano material is one of functional materials, which has attracted much attention due to its special properties (Zhang et al., 2003; Liang et al., 2001), and is also known as ultra-fine particles. Most of atoms on the surface of the nanoparticles are unsaturated and can easily bind with other atoms. Consequently, nanometer material can adsorb selectively metal ions, and has a quite high adsorption capacity. The aim of this work is to investigate the adsorption characteristics of indium ions on nanometer TiO2 and the conditions for preconcentration of trace indium using nano-TiO2. This method was successfully applied to the determination of indium ions in geological standard samples. 2. Experimental method 2.1. Apparatus Cary 5000 UV–Vis–NIR spectrophotometer (VARIAN) was used for the determination of indium ions. A Mettler Toledo 320-S pH meter (Mettler Toledo Instruments (Shanghai) Co. LTD) was used to measure the pH of solutions. KQ-100 Controllable Serial-Ultrasonics apparatus (Kunshan apparatus company, China) was adopted to disperse the solution of nano-TiO2, operating at an ultrasonic frequency of 20– 80 kHz and output power of 0–50 W through manual adjustment. A model TDL80-2B centrifugal machine (Shanghai Anting Scientific Instrument Co., China) was used throughout. 2.2. Reagent and solution Nano-TiO2 (anatase) that was used as adsorbent in this study was provided from Zhoushanmingri Nanometer Material Co.(China), and its particle size is about 20–30 nm.
L. Zhang et al. / Hydrometallurgy 95 (2009) 92–95 Table 1 Studies on the effect of different nano-materials on adsorption behaviour of indium ions Sorbent
Adsorption efficiency (%)
Nano-TiO2 (anatase, 20–50 nm) Nano-TiO2 (rutile, 20–50 nm) Nano-SiO2 (particle diameter 20–50 nm)
96.3 77.2 56.2
The certified reference material yellow red soil (GBW07405 and GBW07406) used in this experiment, was provided by State Technology Supervision Administration. Stock solution of In (III) (1 mg mL− 1) was prepared by tepidly dissolving 0.2500 g pure indium (99.999%) with 50 mL 1 + 1 hydrochloric acid. After it got cool, it was moved to 250 mL flask. After that, it was diluted with doubly distilled water to maintain a constant volume. All of the reagents, including salicyl fluorescence ketone (SAF, 0.05%), bromize16-alkyl-3-methyl ammonium (CTMAB, 0.5%), polyvinyl alcohol (PVD, 2%), acetic acid-acetic ammonium buffer solution, hydrochloric acid (1 + 1), hydrochloric acid (0.1 mol L− 1), ammonia (25%), hydrogen peroxide (30%), sodium hydroxide (1%) were all analytical grade. Doubly distilled water was used in the experiment. EDTA-triethanolamine-NaOH solution: 10.0 g EDTA, 50 mL triethanolamine (98%) and 25.0 g sodium hydroxide were dissolved in a 1000 mL flask with doubly distilled water. The stock solutions of the various metal ions (mg mL− 1) were prepared with their nitrate or chloride salts (≥99.99%) and used to investigate the possible effects of interfering ions. 2.3. Experimental procedure 2.3.1. Determination of In (III) Some volumes of In (III) standard solution were put into 25 mL volumetric flasks, 0.2 mL 2% PVA, 0.3 mL 0.05% SAF, 1.5 mL 0.5% CTMAB and 1.5 mL pH 5.5 HAc-NH4Ac buffer solution were added to the volumetric flasks. Double-distilled water was put into the solutions to prepare desired volumes and shaken up. After 30 min, absorbency was determined by using UV–Vis–NIR Spectrometer at wavelength of 568 nm, and the content of the In (III) was calculated. 2.3.2. Sample preparation Portions (1.0000 g) of GBW-07405 or, GBW07406 were transferred into corundum crucibles, and 2.0 g of sodium peroxide were added into every corundum crucible. After stirring to make them uniform, then putting a layer of sodium peroxide (about 1.0 g) on the top of each sample, heated about 6–7 min at 750 °C. After cooling to room temperature, transferred them into 250 mL beakers containing some EDTA-triethanolamine-NaOH solution, then adding 2.50 mL of magnesium salt solution (10.0 mg MgO/mL) and 2 mL of hydrogen peroxide, heated to boil and kept 15 min. Took them down, then added 1 mL of hydrogen peroxide to dissolve brick red cuprous oxide which maybe exist. After cooling 30 min, samples were filtrated with alkali-resisting middle speed filter paper. The deposition was washed seven times with 1% sodium hydroxide solution and then washed three times with doubly distilled water. Put the filter paper with deposition into the initial beaker, then added 0.1 mol L− 1 tepid hydrochloric acid and stirred to dissolve the deposition. 10 min later, the deposition had been dissolved completely, and was transferred into 100 mL volumetric flask, washing initial beaker and filter paper clean, diluting to scale. pH value was adjusted to 3.5 with hydrochloric acid and ammonia for determination of In(III). 2.3.3. Adsorption and desorption The adsorption experiments were carried out in a series of 50 mL Erlenmeyer flasks containing 100 mg nano-TiO2 and 15 mL of 10 mg L− 1 indium solution at the desired pH. If necessary, an appropriate HCl or ammonia solution was used to adjust the pH of the solution after addition of nano-TiO2. After ultrasonic dispersion for 2 min and static adsorption for 10 min, the two phases were separated by centrifuging
93
at 4000 rpm for 5 min. The amount of In(III) adsorbed per gram of nano-TiO2 was determined by using the supernatant. The adsorbed indium ions were desorbed from solid phase into aqueous medium by 2.0 mL of 1.0 mol L− 1 hydrochloric acid eluent solution. The adsorption percentage was calculated based on the following equation, η¼
ðC0 −C ÞV 100k C0 V
ð1Þ
η was the adsorption percentage of indium; C0 was the initial content of In (III) in aqueous solution with the unit of μg mL− 1; C was the equilibrant content of In (III) in aqueous solution; V was the volume of the solution with the unit of L. The adsorption capacity for nano-TiO2 particles were calculated based on the following equation, ðC0 −C ÞV ð2Þ W where q was the adsorption capacity for nano-TiO2 particles with the unit of μg g− 1; C0 was the initial content of In (III) in aqueous solution with the unit of μg mL− 1; C was the equilibrant content of In (III) in aqueous solution; V was the volume of the solution with the unit of L; W was the mass of added sorbent with the unit of g. Adsorption isotherm studies were carried out with different initial concentrations of In(III) while maintaining the sorbent dosage at constant level in the range 0–50 °C. q¼
3. Results and discussion 3.1. Selection of sorbent The effect of different sorbents on the adsorption behaviour for the In (III) in aqueous solution was studied and shown in Table 1. It was found that the nano-TiO2 (anatase) was the best sorbent. 3.2. Effect of pH In this study, knowledge of pH was important because the pH of solution influences the distribution of active sites on the surface of nanoTiO2. At the higher pH, the OH− on the surface of nano-TiO2 provides the ability of binding cations. The decrease of pH leads to the neutralization of surface charge, and OH− is displaced from the surface. When the surface of nano-TiO2 carries positive charges, it begins to adsorb anions. Therefore, the effect of the initial pH on the adsorption of In (III) ions was investigated in the pH range of 1–5 by using 0.1 g of nano-TiO2 at a fixed concentration of In (III) ions as 10 µg mL− 1. The variation of adsorption percentage with the pH of solution is shown in Fig. 1.
Fig.1. Effect of pH on the adsorption of the In3+ (10 µg mL− 1) on nano-TiO2. 100 mg of nanoTiO2; CIn(III)10 µg mL− 1; V 15 mL; ultrasonic dispersed 1.5 min; temperature 25± 0.1 °C.
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L. Zhang et al. / Hydrometallurgy 95 (2009) 92–95
Fig. 1 shows the effect of pH on the adsorption of In (III) by nanoTiO2, which indicates that the recovery of indium increases with increasing pH from 1 to 4. The effect of pH on In(III) adsorption can be explained by the following reasons. The surface charge is neutral at isoelectric point (IEP), which pHIEP value is 6.8 for nano-TiO2. The surface of sorbent carries positive charges at pH value lower than IEP, which enhances electrostatic force of attraction with InCl−4 (In the studied system, the main chemical species of indium in solutions is InCl−4 (Chung et al., 2003)). As a result, the process of sorption takes place more easily in pH 2–3.5, so the adsorption percentage of In(III) was higher. In pH b 2, there is a balance reaction: H+ + InCl−4 ⇄ HInCl4, the main chemical species of In(III) is HInCl4 (Hasegawa et al., 1980; Akçay, 2004; Reddy and Reddy, 1985), so the adsorption percentage of In(III) was lower. Therefore, pH 3.5 was chosen for adsorption of In(III) in the experiment. 3.3. Desorption and enrichment factor It is found from Fig. 1 that the adsorption of In(III) at pH b 1.5 could be negligible. For this reason, various concentration HCl were studied for the elution of retained In(III) from nano-TiO2. The results obtained indicated that 1.2 mol L− 1 HCl was sufficient for complete elution. The effect of eluent volume on the recovery of analytes was also studied by keeping the HCl concentration of 1.2 mol L− 1, it was found that with 1.0 mL HCl quantitative recoveries (N95%) could be obtained. Therefore, the volume of 1.0 m L eluent was used in following experiments. The influence of the sample volume on recoveries of indium was also examined. For this purpose, indium was preconcentrated from volumes of 10, 20, 25, 50 and 100 mL of sample solution containing 150 μg indium by applying the procedure mentioned above. The maximum sample volume can be up to 25 mL with the 95% recovery and the enrichment factor was 25 with 1.0 mL HCl elution (Mizuike, 1983). 3.4. Comparison different adsorption behaviors The comparison adsorption behavior was made, based on the method stated above. It was shown that for the experiments carried out for over five times, the oscillation average adsorption percentage was 92.3%, the average adsorption percentage of ultrasonic oscillation for 1.5 min was more than 96.0%, and the static average adsorption percentage was 87.7% after 60 min. The effect of oscillation adsorption was larger than static adsorption, and the ultrasonic adsorption was the most significant. It was also shown that In (III) ions could be adsorbed fast and quantitively by nano-TiO2. Therefore, ultrasonic adsorption was used in this study, the reason of which may be that it can be carried out easily.
Table 2 Related coefficient and experimental parameters of Langmuir isotherms T/°C
Langmuir equation Ce/q = 1/Kqm + Ce/qm
K (mL/μg)
qm (μg/g)
r2
0 25 50
Ce/q = 0.000257Ce + 0.000284 Ce/q = 0.000208 Ce + 0.000236 Ce/q = 0.000154 Ce + 0.000244
0.9049 0.8814 0.6311
3891 4566 6494
0.998 0.998 0.999
Nano-TiO2 particles were small in diameter, thus surface area rate was large, surface energy increased and the adsorption capacity increased. Particles could be gathered, forming secondary particles due to the huge surface energy. As a result, it was difficult to make use of the special high adsorption. So ultrasonic adsorption was used in this study, which resulted from the huge energy and pressure of gas bubbles in ultrasonic cavitation process. The vibration wave could make the gathered nano-particles disperse and the efficient surface area increase. The adsorption ability increased, so did the adsorption percentage. 3.5. Adorption isotherm and adsorption capacity The adsorption behaviour of the nano-TiO2 was determined by studying the amount of adsorbed indium as a function of indium concentration. For this purpose, 10 mL In (III) ions solutions with different concentrations were added to a series of 50 mL conical flasks with stoppers, the pH of which was adjusted to 3.5. Nano-TiO2 (0.1 g) particles were added and then adsorption experiments were conducted at 0 °C, 25 °C and 50 °C, respectively. The profile of adsorption isotherm of nano-TiO2 for In (III) ions is shown in Fig. 2. There was a gradual increase of adsorption for In(III) ions until the equilibrium was attained. Adsorption isotherm is important to describe how solutes interact with the sorbent. The data of the isotherm reveal that the adsorption processes conform to Langmuir model. In Fig. 2, the graph shows an excellent fit to data in concentration interval studied in all cases for the Langmuir model. A modified Langmuir equation conformed to this kind of adsorption isotherm as represented below: Ce =q ¼ 1=Kqm þ Ce =qm Here, Ce is equilibrium concentration of the indium (III) ion in solution (µg mL− 1); q is the amount of indium (III) adsorbed per unit weight of nano-TiO2 at equilibrium concentration (µg g− 1); qm is the maximum monolayer adsorption capacity (µg g− 1); K is the Langmuir constant related to the affinity of binding sites(mg L − 1). A plot of Ce/q versus Ce, the sorption parameters qm and K evaluated from the slope and intercept. The maximum adsorption capacity of indium (III) on nano-TiO2 was from 3891 µg g− 1 to 6494 µg g− 1 for the temperature range of 0–50 °C (Table 2).
Table 3 Tolerance limits for coexisting ions in adsorption of the studied elements
Fig. 2. Adsorption isotherm of In3+ on nano-TiO2. Temperature, 0 °C, 25 °C, 50 °C; pH: 3.5; V 15 mL; static time 20 min, 100 mg of nano-TiO2; the initial In(III) concentration range was 15–60 mg L− 1.
Interfering ion
Maximum allowable volume (mg)
Interfering ion
Maximum allowable volume (mg)
Ga2+ Mo6+ Sb5+ Tl+ Pb2+ Zn2+ Fe3+ Mn2+ Ba2+ Na+
0.065 0.230 0.230 0.170 2.500 2.100 1.000 1.000 0.300 0.100
Ge4+ Al3+ Cu2+ Ni2+ Se4+ Co3+ Cd2+ Mg2+ Cr3+ Cl−
1.950 0.002 0.010 1.000 0.140 1.800 0.750 100 0.120 10
There were some white deposits for Ti4+, Sn4+, As3+, Te4+ at the pH of 3.5 and so they did not have influence.
L. Zhang et al. / Hydrometallurgy 95 (2009) 92–95 Table 4 Analytical result of In(III) ions in standard reference material(n = 7) P
Sample
Added (μg·g− 1)
Reference value(μg·g− 1)
Found xFt psffiffiNffi (μg·g− 1)
GBW07405 GBW07406
– 4.0
4.1 ± 0.6 0.84 ± 0.20
4.16 ± 0.42 5.01 ± 0.57
95
In (III) at certain pH, high precision and concentration factor and low detection limit. Moreover, the effects of coexisting interfering ions in the determination of In (III) could be eliminated by the selective adsorption, elution and sample preparation. So this method can be applied to detect In (III) in soil or other environmental samples.
Indicates that model parameters are statistically significant (t-test) at 95% confidence level.
Acknowledgements 3.6. Interference effects Some experiments were carried out in order to examine the effects of common coexisting ions on the adsorption of the studied ions on nanometer TiO2. The effects of potential interferences occurring in geological samples on the determination of indium were investigated using the optimized preconcentration procedure. Metal ions were added individually to a solution as their nitrate or nitrate or chloride salts, the proposed preconcentration method was applied. The tolerance of the coexisting ions is given in Table 3. Except Al3+ and Cu2+, other species almost didn't have effect and the allowable amount for these species were large. 3.7. Detection limits and precision From measurements made under the optimum conditions described above, the calibration graph was linear in the range 0.3– 20 µg /25 mL. The calibration equation is A = 0.0101 + 0.0633C with a correlation coefficient of 0.9993. Where C is the concentration of indium (μg/25 mL), and A is the absorbance. The detection limit (evaluated as concentration corresponding to three times the standard deviation of 11 runs of blank solution) of this method for In(III) is 0.45 µg mL− 1, and the relative standard deviation (RSDs) 1.5% (n = 11, C = 15 µg /mL). 3.8. Sorbent reuse The stability and potential regeneration of nano-TiO2 were investigated. Nano-TiO2 was rinsed to neutrality and dried, then be used to adsorb In(III) ions again. The experimental results showed there was not obvious decrease in the recoveries for In(III) ions(93.9%) after at least 7 adsorption/desorption cycles. 3.9. Analytical application Since it was found that the proposed preconcentration method was useful for the preconcentration of trace indium, the method was applied to the determination of indium (total indium) in soil reference material (GBW07405, GBW07406) to evaluate the accuracy of the developed procedure. Indium concentration found as mean of seven determinations at 95% confidence level was 4.16 ± 0.42, 1.01 ± 0.57 (which had been subtracted the added amount 4.0), respectively. It was found that there is no significant difference between results found by the proposed method and certified value (4.1 ± 0.6, 0.84 ± 0.2) according to the t- test. It can be concluded that there is no systematic error in the determination at 95% confidence level. The results are shown in Table 4. As can be seen, the results agree with the certified values. 4. Conclusions This method was suitable for the preconcentration and direct determination of In (III) in soil with a high selective adsorbability for
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