- Email: [email protected]
Recovery of tellurium from chloride media using tri-iso-octylamine
Separation and Purification Technology 40 (2004) 177–182
Recovery of tellurium from chloride media using tri-iso-octylamine Dilip Kumar Mandal∗ , Badal Bhattacharya, Raj Dulal Das School of Material Science and Technology, Department of Metallurgical Engineering, Jadavpur University, Kolkata 700 032, India Received in revised form 19 February 2004; accepted 20 February 2004
Abstract For the purpose of developing the extraction of tellurium, we have investigated the extraction using the chloride salt of tri-iso-octylamine (TIOA) in xylene. Experimental data have been analyzed graphically and numerically to determine the stoichiometry of the extraction species. It is found that the extraction reaction is exothermic (H = −51.49 KJ/mol). Tellurium was extracted according to the following the reaction: 2[R3 N+ HCl− ]org + [TeCl6 2− ]aq = [(R3 N+ H)2 TeCl6 2− ]org + 2[Cl− ]aq . The extraction of tellurium proceeds through an ion-association mechanism and the extracted species is [(R3 N+ H)2 TeCl6 2− ]. The distribution constants and thermodynamic functions; enthalpy (H), entropy (S), and free energy (G) in the extraction of tellurium with TIOA have been evaluated. © 2004 Elsevier B.V. All rights reserved. Keywords: Tellurium; Extraction; TIOA; Thermodynamic parameters; Xylene
1. Introduction The solid tellurium is a p-type semiconductor and it has wide applications in electronic industry. It is also used in glass and ceramic industry. Tellurium is used as an alloy with cast iron, copper and stainless steel and when added to lead, prevents corrosion. It is developed specifically for use in professional audio CD recorders as it allows more than 1000 erase/record cycles. The highly sensitive silver–indium–antimony–tellurium phase-change material employed in the recording layer ensures the optimum performance in a wide range of recorders and players. Tellurium is widely distributed in various environmental samples in trace amounts. It is classified as both essential micronutrients for many animals as well as toxic at elevated levels. It can be considered either as an impurity in a number of processes or as a toxic element that needs to be eliminated. The preparation and application of a coated-graphite tellurium(IV) ion-selective electrode, based on the TeCl6 2− acts as an anion-exchange resin fixed in a poly(vinyl chloride) matrix, are described. The influence of HCl and
∗
Corresponding author. Tel.: +91-9830549072. E-mail address: dilip [email protected] (D.K. Mandal).
1383-5866/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.seppur.2004.02.008
interference ions were investigated. The electrode showed a near-Nernstian slope of 30 ± 2 mV per decade over a tellurium(IV) ion concentration range of 3 × 10−4 to 10−2 mol/dm3 and a response time of 30 s in 6 mol/dm3 hydrochloric acid solution. Na+ , K+ , and Ca2+ did not interfere, but other ions, such as Bi3+ , Cd2+ , Fe3+ , Ga3+ , Sb3+ , ClO4 − , PO4 3− , and SO4 2− , caused interference. The electrode was successfully used to determine the concentration of tellurium in Bi2 Te3 and CdTe after the separation of tellurium from bismuth or cadmium by the hydroxide precipitation method in the presence of EDTA as a masking reagent for bismuth and cadmium [1]. A method for the determination of indium and tellurium in geological reference materials is presented. A sample of 0.01–1.0 g, containing less than 50 g of Bi, Pb, or Sn and 100 g of Cu, was decomposed with aquaregia and HF. The contents were then evaporated to dryness. The residue was dissolved by heating with diluted HCl, and centrifuged to remove any undissolved material. After the addition of sulphamic acid, potassium iodide–ascorbic acid, and palladium solutions to the supernatant, indium and tellurium were extracted into 0.5–1.0 ml of MIBK containing 5% trioctylmethylammonium chloride, and determined by graphite-furnace atomic absorption spectrometer. Although interference from most elements could be minimized by the addition of palladium
178
D.K. Mandal et al. / Separation and Purification Technology 40 (2004) 177–182
as a matrix modifier, a large amount of Bi, Pb, Sn, and Cu suppressed the indium and/or tellurium absorbance. The relative standard deviation was smaller than 10% for a content larger than 3 ng of indium and tellurium, and the limit of detection for both elements was 0.2 ng/g for a 1 g sample. Various geological sample were analyzed for determination of indium and tellurium by this method [2]. A waste minimization hydrometallurgical process with near zero-discharge was developed for the treatment of cemented tellurium from copper refining [3]. Shibasaki et al. [4] suggested the fixed bed type reactor in cementation to improve the recovery of tellurium. Recovery of tellurium from cemented tellurium was practiced using various processes, which was and revived by Hoffmann [5]. The recycling of tellurium from thin-film photovoltaic device has been studied by sulfuric acid leaching in presence hydrogen peroxide [6]. The mechanism of tellurium separation from selenium in HCl media by solvent extraction with tri-n-butyl phosphate in kerosene was studied in a batch-stirred glass cell. The dependence of extraction on acid, metal concentration, extractant concentration and extraction temperature were also studied [7]. Mass transfer of tellurium between an aqueous and organic phase was investigated in a modification Lewis cell. The organic phase was composed of tri-n-butyl phosphate in kerosene. The transfer rate of tellurium from aqueous to the organic phase was very fast [8]. Mass transfer of tellurium between an aqueous and organic phase was investigated in a modification Lewis cell. The organic phase was composed of tri-n-butyl phosphate as an extractant in de-aromatized kerosene at varying volume ratio [9]. The conventional pyrometallurgical method of extraction of the tellurium needs high-energy consumption and also gives low efficiency. Besides, the tellurium is recovered mainly from anode slime obtained during electro-refining of copper by alkali fusion technique. Separation of this element from complex sulfide matrix is very difficult. With this aim a simple method has been developed for extraction and separation of tellurium with tri-iso-octylamine (TIOA). The extraction of metals such as chromium from various acidic media using high molecular weight tri-iso-octylamine has been reported in literatures [10–12]. But there are no data available in the literature on the use of the tertiary amine TIOA for the extraction of tellurium. Thus, in the present work, the concentration dependency of the equilibrium distribution of the tellurium between hydrochloric acid solutions and the chloride salt of the tertiary amine TIOA in xylene has been studied.
lurium was prepared by dissolving 1.737 g of sodium telluride (Na2 TeO3 ) (BDH Chemicals Ltd., Poole, England) in 1 M hydrochloride acid and diluted to 1000 ml with double distilled water [13]. All organic and inorganic reagents used in this study are of analytical grade. 2.2. Methods Diluting a measured volume of the amine with xylene makes the preparation of organic solution. Extractions have been carried out by following procedure: equal volumes of aqueous and organic phases of known concentrations are placed in a (1 l) five-neck flat bottom flask using a mechanical stirrer at 1000 ± 10 rpm. A Beckman thermometer to maintain uniform temperature ±1 ◦ C controls the temperature of the flask. After separating the phases, the tellurium concentrations in the aqueous have been determined with Perkin-Elmer flame atomic absorption spectrometer (Model 2380) equipped with Perkin-Elmer hydride generating system (Model MHS-10) and deuterium background corrector was used to record the absorption signals of all measurements. The areas of the peak values were considered for signal processing. Electrode less discharge lamp (EDL) of tellurium generator was used with wavelength setting of 214.3 nm. The tellurium concentrations in the organic phase have been calculated from the difference between the tellurium concentration in the aqueous phase before and after the extraction. All the instruments used for the investigation were calibrated using standard quality assurances practices. The relative standard deviations of the experimental results remained within 1.5%. The Perkin-Elmer AAS (model no. 2380) was pre calibrated before using unknown sample.
3. Results and discussion 3.1. Effect of contact time The extraction of tellurium was carried out by shaking at 30 ◦ C, for different lengths of time, with aqueous solution of 0.078 mmol/dm3 tellurium and organic solution of 33.9× 10−3 M of TIOA in xylene at O/A ratio of 1. It is observed from Fig. 1, that tellurium was completely extracted within 90 s of shaking time. A clear phase separation within 2 min is also observed. A shaking time of 2 min was taken for the extraction of tellurium in all experiments which followed. 3.2. Effect of the initial concentration of the extractant
2. Experimental 2.1. Materials The tri-iso-octylamine (Alamine 308), was supplied by Henkel Corporation, USA. The extractant was used without any further purification. Standard stock solutions of tel-
The effect of extractant (TIOA) concentration in the extraction of tellurium has been studied. Fig. 2a shows an increase in extraction of tellurium as the extractant concentration is increased. The results indicated that the optimum concentration of TIOA was 33.9 × 10−3 M for nearly complete extraction of tellurium by single stage operation.
D.K. Mandal et al. / Separation and Purification Technology 40 (2004) 177–182
Extraction equilibrium (Kex ) [(R3 N+ H)n TeCl6 2− ]org [Cl− ]naq = [TeCl6 2− ]aq [R3 N+ HCl− ]norg
120 100 % Extraction
179
80 60
Distribution constant (KD ) =
40 20
Kex =
Therefore,
0 0
25
50
75
100
125
(2)
[(R3 N+ H)n TeCl6 2− ]org [TeCl6 2− ]aq
KD [Cl− ]naq
(3)
(4)
[R3 N+ HCl− ]norg
For constant [Cl− ]
Time (Second)
Fig. 1. Plot of % extraction vs. time (s). Initial tellurium concentration 0.078 × 10−3 mmol/dm3 . Organic phase: 33.9 × 10−3 M TIOA in xylene. O/A ratio 1.
log KD = n log[R3 N+ HCl− ]org + constant
(5)
3.3. Effect of temperature From this experiment it was also observed that two amine ligands react with one tellurium ion by the plot of log KD versus log[R3 N+ HCl− ], with slope 1.99, which is very close to 2 (Fig. 2b), from the following equations: [TeCl6 2− ]aq + n[R3 N+ HCl− ]org = [(R3 N+ H)n TeCl6 2− ]org + n[Cl− ]aq
(1)
The effect of temperature on the extraction of tellurium by the chloride salt of tri-iso-octalamine in xylene has been studied from an aqueous phase of 0.078 mmol/dm3 tellurium in 2.5 M HCl. The result shows that there is a decrease in tellurium extraction as the experimental temperature increased (Fig. 3a). The van’t Hoff equation shows the change of the distribution constant (KD ) with temperature
120
12 0 10 0 % Extraction
100
%Extraction
80
60 40
80 60 40 20 0 280
20
(a)
0 0
0.01
0.02
(a)
0.03
0.04
0.05
0.06
0.07
290
300
310
320
330
340
Temperature(K)
1.5
[TIOA] (M) 4
1 log K D
3 2
slope = 1.99
log KD
s lope = 2.69 0.5
1 0
0 3
-1 -3
(b)
-2.5
-2
-1.5
-1
-0.5
0
(b)
3.2
3.4
3.6
[1/T] K-1
log[R 3NH +Cl -]
Fig. 2. (a) Plot of % extraction vs. [TIOA] (M). Initial tellurium concentration 0.078 × 10−3 mmol/dm3 . O/A ratio 1. (b) Plot of log KD vs. log[log[R3 NH+ Cl− ]. Initial tellurium concentration 0.078 × 10−3 mmol/dm3 . O/A ratio 1.
Fig. 3. (a) Plot of % extraction vs. temperature (K). Initial tellurium concentration 0.078 × 10−3 mmol/dm3 . Organic phase: 33.9 × 10−3 M TIOA in xylene. O/A ratio 1. (b) Plot of log KD vs. [1/T] (K−1 ). Initial tellurium concentration 0.078 × 10−3 mmol/dm3 . Organic phase: 33.9 × 10−3 M TIOA in xylene. O/A ratio 1.
180
D.K. Mandal et al. / Separation and Purification Technology 40 (2004) 177–182
Table 1 Effect of temperature on extraction of tellurium
120
log KD
G (kJ/mol)
S (JK−1 mol−1 )
283 293 303 313 323 333
1.38 0.95 0.72 0.45 0.19 0.03
−7.48 −5.32 −4.18 −2.69 −1.17 −0.19
−0.156 −0.156 −0.156 −0.156 −0.156 −0.154
100 % Extraction
Temperature (K)
80 60 40 20
Initial tellurium concentration 0.078 × 10−3 mmol/dm3 . Organic phase: 33.9 × 10−3 M TIOA in xylene. O/A ratio 1.
0 0
D(log KD ) −H = D(1/T) 2.303R
(6)
(a)
4
6
8
HCl (M)
G = −2.303RT log KD
(7)
H − G T
(8)
The negative values of free energy imply that the reaction is spontaneous. The negative enthalpy value indicates that the extraction of tellurium with TIOA in xylene is favorable at low temperature (Table 1). 3.4. The effect of acid and chloride salt The extraction were carried out at 30 ◦ C, varying the tellurium ion concentration in aqueous phase and using various concentration of HCl. Fig. 4a shows that the distribution constant (KD ) of tellurium reaches a maximum at high acid concentrations. There is a difference in the behavior of this extraction system with the tellurium used, for each HCl acid concentration; the distribution constant (KD ) increases as the initial concentration of tellurium is decreased (Fig. 4b). This behavior may be explained from the following set of equations: TeCl6 2− + [2(R3 N+ HCl− )]org = [(R3 N+ H)2 TeCl2− 6 ]org + 2Cl−
(9)
In order to achieve this exchange, the amine is first converted to the appropriate amine salt to provide an anion to exchange with the metal species [R3 N]org + HCl = [R3 N+ HCl− ]org
(10)
This shows the acidification of amine extractant to form an amine salt or ion pair [R3 N+ HCl− ] in organic phase. Therefore, extraction of tellurium from chloride system undergoes ion-association mechanism [14]. It was observed that in the ion-association extraction system, high concentrations of electrolyte like MgCl2 and
Distribution ConstantKD
5
The plot of log KD versus 1/T (Fig. 3b) is linear and with slope 2.69 and the enthalpy change (H) of the reaction was −51.49 KJ/mol, which means it is an exothermic reaction. The free energy change (G) and entropy (S) were calculated by the following equations:
S =
2
3 0.078 mmole/dm3
2 0.156 mmole/dm3
1 0 0.5
(b)
.039 mmole/dm3
4
1
1.5
2
2.5
HCl (M)
Fig. 4. (a) Plot of % extraction vs. HCl (M), Initial metal concentration 0.078 × 10−3 mmol/dm3 tellurium. Organic phase: 33.9 × 10−3 M TIOA in xylene. O/A ratio 1. (b) Plot of distribution constants (KD ) vs. HCl (M). Initial tellurium concentrations 0.039 × 10−3 , 0.078 × 10−3 , and 0.156 × 10−3 mmol/dm3 . Organic phase: 33.9 × 10−3 M TIOA in xylene. O/A ratio 1.
ZnCl2 are effective is increasing the extent of extraction. The addition of such salts, referred to as salting-out reagents, serves two purposes. The first and more obvious is to aid the direct formation of the complex by the mass action effect—the formation of a chloro complex. It is promoted by increasing the concentration of chloride ion. Secondly, as the salt concentration increases, the concentration of ‘free’ water decreases because the ions require a certain amount of water for hydration. This decreases the solubility of complex [(R3 N+ H)2 TeCl6 2− ] in aqueous phase. 3.5. Influence of carbon chain of amine extractant Tellurium extraction with amine is influenced by the nature of the carbon chain as well as the number of carbon atoms in the chain. Experiments were conducted with number of tertiary amines, where the carbon chain length was varied. For all the amines of 33.9 × 10−3 mmol/dm3 solution was prepared with xylene as solvent. The result, shown in Table 2 indicates a sharp increases in extraction with the increase of carbon chain length. Extraction of tellurium remained constant with amines having carbon chain length from C8 to C12 . From Table 2, it is also observed that with tri-iso-octylamine and trilaurylamine, the extraction of
D.K. Mandal et al. / Separation and Purification Technology 40 (2004) 177–182
181
Table 2 Effect of carbon chain of amine extractant on the extraction of tellurium
Table 4 Effect of Acids on extraction of tellurium
Tertiary amine
% Extraction of tellurium
Acids
Concentration (M)
%Extraction
Tributylamine Trihexlamine Methyldi-n-octylamine Tricaprylamine Trilaurylamine Tri-iso-octylamine
70.4 85.6 94.5 97.8 98.9 99.5
H2 SO4
0.5 1.0 2.0 3.0
99.5 98.5 97.8 94.5
HNO3
0.01 0.02 0.05 2.5
93.2 84.5 72.5 50.5
HClO4
0.01 0.02 0.05 0.10
89.5 72.2 42.5 26.2
Initial tellurium concentration 0.078 × 10−3 mmol/dm3 . Organic phase: 33.9 × 10−3 M of various tertiary amines in xylene. O/A ratio 1.
tellurium is quantitative. Although the extraction was almost quantitative with trilaurylamine, but phase separation was not clear as observed with tri-iso-octylamine. 3.6. Effect of diluents The extraction of tellurium was carried out with 33.9 × 10−3 mmol/dm3 of TIOA in different diluents. From the results given in Table 3, it is clear that effective extraction occurred in xylene followed by methyl isobutyl ketone. Though extraction was effective in methyl isobutyl ketone but clear phase separation was much slower compared to xylene. Moreover, the solubility of methyl isobutyl ketone increases with increase in acidity. Xylene was found to be the most suitable solvent for extraction of tellurium. It is so, because better extraction and clear phase separation took place in xylene within 2 min. 3.7. Effect of acids on extraction The effect of sulfuric, nitric, and perchloric acids on the tellurium extractions were investigated. The results are shown in Table 4. Sulfuric acid above 2 M reduced the extraction. Nitric and perchloric acids interfered even at the concentration of 0.01 M. This is due to salt effect of various ions. Salt effects generally decreases the metal extraction by amine in the order ClO4 − > NO3 − > SO4 − .
Initial tellurium concentration 0.078 × 10−3 mmol/dm3 . Organic phase: 33.9 × 10−3 M TIOA in xylene. O/A ratio 1.
reduction of absorption signal was observed for nitric acid as stripping agent with concentration range of 0.5–1.0 M. Suppression of signals were found to enhance with increase in acid concentration. Similar suppression of absorption signals were also observed for sulfuric acid, but less pronounced than for nitric acid. With salt solutions the recoveries of tellurium was observed in the range of 90–92%. The organic phase was vigorously shaken with different concentrations of hydrochloric acid (0.05–2.0 M) and then left for clear phase separation. The results obtained have indicated that the recovery of tellurium is quantitative while shaking the organic phase with 0.08 M solution (Fig. 5). This is due to the fact that in ion-association system, where high acid concentration acid concentrations are required for metal extraction; stripping with water or very low acid concentration usually results in stripping of metal from organic phase [15]. For all experiments, a 0.1 M HCl solution was used as stripping agent. The optimum contact time for stripping was 2 min. 3.9. The effect of diverse ions The effect of diverse ions on the recovery of 1000 g tellurium was investigated by adding 100–500-fold known
3.8. Effect of stripping agents Tellurium extracted into organic phase (TIOA in xylene) was stripped with different strengths of stripping agents. A
120
Solvents
% Extraction of tellurium
Chloroform Toluene Kerosene Carbontetrachloride Methyl isobutylkotone Xylene
30.5 71.4 78.2 85.0 95.5 99.5
Initial tellurium concentration 0.078 × 10−3 mmol/dm3 . Organic phase: 33.9 × 10−3 M TIOA in xylene. O/A ratio 1.
% Recovery
100
Table 3 Effect of solvent on the extraction of tellurium
80 60 40 20 0 0.04
0.06
0.08 HCl (M)
0.1
0.12
Fig. 5. Plot of % recovery vs. HCl (M). Initial tellurium concentration 0.078 × 10−3 mmol/dm3 . O/A ratio 1.
182
D.K. Mandal et al. / Separation and Purification Technology 40 (2004) 177–182
Table 5 Effect of diverse ions on extraction of tellurium Ions
Added as
Taken (g)
Cu2+
CuSO4 ·5H2 O CdCl2 AlCl3 CrCl3 HgCl2 NaAsO2 KCl NaCl MgCl2 CaCl2 ·2H2 O NaSbO2 SnCl2 ·2H2 O PbCl2 ·2H2 O ZrOCl2 ·8H2 O TiCl4 ·4H2 O FeCl3 ·6H2 O BaCl2 ·2H2 O SrCl2 ·2H2 O CoCl2 MnCl2 ·4H2 O NiCl2 ·6H2 O ZnSO4 ·7H2 O
1000 500 2000 500 200 400 1000 1000 1000 1000 400 500 500 500 500 2000 1000 1000 1000 1000 1000 1000
Cd2+ Al3+ Cr3+ Hg2+ As3+ K+ Na+ Mg2+ Ca2+ Sb3+ Sn2+ Pd2+ Zr4+ Ti4+ Fe3+ Ba2+ Sr2+ Co2+ Mn2+ Ni2+ Zn2+
Initial tellurium concentration 0.078 × 10−3 mmol/dm3 . Organic phase: 33.9 × 10−3 M TIOA in xylene. O/A ratio 1.
amounts of each ionic species to be examined. The amount of each ionic species added to investigate the effect of interfering foreign ions is presented in Table 5. The error of recovery of tellurium in presence of following ions was not more than ±1.5%. 4. Conclusion From the above results, it is observed that tellurium is extracted with tri-iso-octylamine in xylene as a moderator by a ion-association mechanism. The extracted species in the organic phase is [(R3 N+ H)2 TeCl6 2− ]. The thermodynamic functions; enthalpy (H), entropy (S), and free energy (G) in the extraction of tellurium with tri-iso-octlyamine have been evaluated. The extraction reaction is an exother-
mic process with the extraction percentage decreasing with increasing of temperature. Another important feature of the proposed method is that extraction of tellurium using 33.9× 10−3 M TIOA, in xylene from aqueous phase has resulted in 99% recovery in 2 min.
Acknowledgements The authors thank Henkel Corporation, USA for sending the reagent TIOA and also the Department of Metallurgical Engineering, Jadavpur University for extending laboratory facilities. Authors are thankful to Ms. Kasturi Mitra for her contribution.
References [1] N. Yoshikuni, S. Nishiumi, K. Oguma, Jpn. Soc. Anal. Chem. 49 (10) (2000) (Review). [2] S. Terashima, Jpn. Soc. Anal. Chem. 49 (10) (2000) (Review). [3] K.I. Rhee, C.K. Lee, Y.C. Ha, G.J. Jeong, H.S. Kim, H.J. Sohn, Hydrometallugy 53 (1999) 89. [4] T. Shibasaki, K. Abe, H. Takeuchi, Hydrometallugy 59 (1992) 399. [5] E. Hoffmann, J. Met., Miner. Mater. Soc. 41 (7) (1989) 33. [6] W. Trolley, R. Swarup, The Minerals, Metals & Materials Society, AIME, Warrendale, PA, 1995, p. 503. [7] M.R. Chowdhury, S.K. Sanyal, Hydrometallugy 32 (1993) 189. [8] M.R. Chowdhury, S. Datta, S.K. Sanyal, Hydrometallugy 43 (1996) 175. [9] M.R. Chowdhury, S. Datta, S.K. Sanyal, Hydrometallugy 42 (1996) 115. [10] Y.H. Huang, C.Y. Chen, J.F. Kuo, Hydrometallurgy 28 (1992) 297. [11] Y.H. Huang, C.Y. Chen, J.F. Kuo, Bull. Chem. Soc. Jpn. 64 (1991) 3059. [12] Y.H. Huang, C.Y. Chen, J.F. Kuo, Chem. Eng. J. Jpn. 24 (1990) 149. [13] Analytical Methods for Atomic Absorptions for Spectrophotometric, Perkin-Elmer, Norwalk, Connecticut, USA, 1982. [14] G.M. Ritcey, A.W. Ashbrook, Solvent Extraction: Principles and Application to Process Metallurgy, Part I, Elsevier, Amsterdam, 1984 (Chapter 3). [15] G.M. Ritcey, A.W. Ashbrook, Solvent Extraction: Principles and Application to Process Metallurgy, Part I, Elsevier, Amsterdam, 1984 (Chapter 2).
Recovery of tellurium from chloride media using tri-iso-octylamine Dilip Kumar Mandal∗ , Badal Bhattacharya, Raj Dulal Das School of Material Science and Technology, Department of Metallurgical Engineering, Jadavpur University, Kolkata 700 032, India Received in revised form 19 February 2004; accepted 20 February 2004
Abstract For the purpose of developing the extraction of tellurium, we have investigated the extraction using the chloride salt of tri-iso-octylamine (TIOA) in xylene. Experimental data have been analyzed graphically and numerically to determine the stoichiometry of the extraction species. It is found that the extraction reaction is exothermic (H = −51.49 KJ/mol). Tellurium was extracted according to the following the reaction: 2[R3 N+ HCl− ]org + [TeCl6 2− ]aq = [(R3 N+ H)2 TeCl6 2− ]org + 2[Cl− ]aq . The extraction of tellurium proceeds through an ion-association mechanism and the extracted species is [(R3 N+ H)2 TeCl6 2− ]. The distribution constants and thermodynamic functions; enthalpy (H), entropy (S), and free energy (G) in the extraction of tellurium with TIOA have been evaluated. © 2004 Elsevier B.V. All rights reserved. Keywords: Tellurium; Extraction; TIOA; Thermodynamic parameters; Xylene
1. Introduction The solid tellurium is a p-type semiconductor and it has wide applications in electronic industry. It is also used in glass and ceramic industry. Tellurium is used as an alloy with cast iron, copper and stainless steel and when added to lead, prevents corrosion. It is developed specifically for use in professional audio CD recorders as it allows more than 1000 erase/record cycles. The highly sensitive silver–indium–antimony–tellurium phase-change material employed in the recording layer ensures the optimum performance in a wide range of recorders and players. Tellurium is widely distributed in various environmental samples in trace amounts. It is classified as both essential micronutrients for many animals as well as toxic at elevated levels. It can be considered either as an impurity in a number of processes or as a toxic element that needs to be eliminated. The preparation and application of a coated-graphite tellurium(IV) ion-selective electrode, based on the TeCl6 2− acts as an anion-exchange resin fixed in a poly(vinyl chloride) matrix, are described. The influence of HCl and
∗
Corresponding author. Tel.: +91-9830549072. E-mail address: dilip [email protected] (D.K. Mandal).
1383-5866/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.seppur.2004.02.008
interference ions were investigated. The electrode showed a near-Nernstian slope of 30 ± 2 mV per decade over a tellurium(IV) ion concentration range of 3 × 10−4 to 10−2 mol/dm3 and a response time of 30 s in 6 mol/dm3 hydrochloric acid solution. Na+ , K+ , and Ca2+ did not interfere, but other ions, such as Bi3+ , Cd2+ , Fe3+ , Ga3+ , Sb3+ , ClO4 − , PO4 3− , and SO4 2− , caused interference. The electrode was successfully used to determine the concentration of tellurium in Bi2 Te3 and CdTe after the separation of tellurium from bismuth or cadmium by the hydroxide precipitation method in the presence of EDTA as a masking reagent for bismuth and cadmium [1]. A method for the determination of indium and tellurium in geological reference materials is presented. A sample of 0.01–1.0 g, containing less than 50 g of Bi, Pb, or Sn and 100 g of Cu, was decomposed with aquaregia and HF. The contents were then evaporated to dryness. The residue was dissolved by heating with diluted HCl, and centrifuged to remove any undissolved material. After the addition of sulphamic acid, potassium iodide–ascorbic acid, and palladium solutions to the supernatant, indium and tellurium were extracted into 0.5–1.0 ml of MIBK containing 5% trioctylmethylammonium chloride, and determined by graphite-furnace atomic absorption spectrometer. Although interference from most elements could be minimized by the addition of palladium
178
D.K. Mandal et al. / Separation and Purification Technology 40 (2004) 177–182
as a matrix modifier, a large amount of Bi, Pb, Sn, and Cu suppressed the indium and/or tellurium absorbance. The relative standard deviation was smaller than 10% for a content larger than 3 ng of indium and tellurium, and the limit of detection for both elements was 0.2 ng/g for a 1 g sample. Various geological sample were analyzed for determination of indium and tellurium by this method [2]. A waste minimization hydrometallurgical process with near zero-discharge was developed for the treatment of cemented tellurium from copper refining [3]. Shibasaki et al. [4] suggested the fixed bed type reactor in cementation to improve the recovery of tellurium. Recovery of tellurium from cemented tellurium was practiced using various processes, which was and revived by Hoffmann [5]. The recycling of tellurium from thin-film photovoltaic device has been studied by sulfuric acid leaching in presence hydrogen peroxide [6]. The mechanism of tellurium separation from selenium in HCl media by solvent extraction with tri-n-butyl phosphate in kerosene was studied in a batch-stirred glass cell. The dependence of extraction on acid, metal concentration, extractant concentration and extraction temperature were also studied [7]. Mass transfer of tellurium between an aqueous and organic phase was investigated in a modification Lewis cell. The organic phase was composed of tri-n-butyl phosphate in kerosene. The transfer rate of tellurium from aqueous to the organic phase was very fast [8]. Mass transfer of tellurium between an aqueous and organic phase was investigated in a modification Lewis cell. The organic phase was composed of tri-n-butyl phosphate as an extractant in de-aromatized kerosene at varying volume ratio [9]. The conventional pyrometallurgical method of extraction of the tellurium needs high-energy consumption and also gives low efficiency. Besides, the tellurium is recovered mainly from anode slime obtained during electro-refining of copper by alkali fusion technique. Separation of this element from complex sulfide matrix is very difficult. With this aim a simple method has been developed for extraction and separation of tellurium with tri-iso-octylamine (TIOA). The extraction of metals such as chromium from various acidic media using high molecular weight tri-iso-octylamine has been reported in literatures [10–12]. But there are no data available in the literature on the use of the tertiary amine TIOA for the extraction of tellurium. Thus, in the present work, the concentration dependency of the equilibrium distribution of the tellurium between hydrochloric acid solutions and the chloride salt of the tertiary amine TIOA in xylene has been studied.
lurium was prepared by dissolving 1.737 g of sodium telluride (Na2 TeO3 ) (BDH Chemicals Ltd., Poole, England) in 1 M hydrochloride acid and diluted to 1000 ml with double distilled water [13]. All organic and inorganic reagents used in this study are of analytical grade. 2.2. Methods Diluting a measured volume of the amine with xylene makes the preparation of organic solution. Extractions have been carried out by following procedure: equal volumes of aqueous and organic phases of known concentrations are placed in a (1 l) five-neck flat bottom flask using a mechanical stirrer at 1000 ± 10 rpm. A Beckman thermometer to maintain uniform temperature ±1 ◦ C controls the temperature of the flask. After separating the phases, the tellurium concentrations in the aqueous have been determined with Perkin-Elmer flame atomic absorption spectrometer (Model 2380) equipped with Perkin-Elmer hydride generating system (Model MHS-10) and deuterium background corrector was used to record the absorption signals of all measurements. The areas of the peak values were considered for signal processing. Electrode less discharge lamp (EDL) of tellurium generator was used with wavelength setting of 214.3 nm. The tellurium concentrations in the organic phase have been calculated from the difference between the tellurium concentration in the aqueous phase before and after the extraction. All the instruments used for the investigation were calibrated using standard quality assurances practices. The relative standard deviations of the experimental results remained within 1.5%. The Perkin-Elmer AAS (model no. 2380) was pre calibrated before using unknown sample.
3. Results and discussion 3.1. Effect of contact time The extraction of tellurium was carried out by shaking at 30 ◦ C, for different lengths of time, with aqueous solution of 0.078 mmol/dm3 tellurium and organic solution of 33.9× 10−3 M of TIOA in xylene at O/A ratio of 1. It is observed from Fig. 1, that tellurium was completely extracted within 90 s of shaking time. A clear phase separation within 2 min is also observed. A shaking time of 2 min was taken for the extraction of tellurium in all experiments which followed. 3.2. Effect of the initial concentration of the extractant
2. Experimental 2.1. Materials The tri-iso-octylamine (Alamine 308), was supplied by Henkel Corporation, USA. The extractant was used without any further purification. Standard stock solutions of tel-
The effect of extractant (TIOA) concentration in the extraction of tellurium has been studied. Fig. 2a shows an increase in extraction of tellurium as the extractant concentration is increased. The results indicated that the optimum concentration of TIOA was 33.9 × 10−3 M for nearly complete extraction of tellurium by single stage operation.
D.K. Mandal et al. / Separation and Purification Technology 40 (2004) 177–182
Extraction equilibrium (Kex ) [(R3 N+ H)n TeCl6 2− ]org [Cl− ]naq = [TeCl6 2− ]aq [R3 N+ HCl− ]norg
120 100 % Extraction
179
80 60
Distribution constant (KD ) =
40 20
Kex =
Therefore,
0 0
25
50
75
100
125
(2)
[(R3 N+ H)n TeCl6 2− ]org [TeCl6 2− ]aq
KD [Cl− ]naq
(3)
(4)
[R3 N+ HCl− ]norg
For constant [Cl− ]
Time (Second)
Fig. 1. Plot of % extraction vs. time (s). Initial tellurium concentration 0.078 × 10−3 mmol/dm3 . Organic phase: 33.9 × 10−3 M TIOA in xylene. O/A ratio 1.
log KD = n log[R3 N+ HCl− ]org + constant
(5)
3.3. Effect of temperature From this experiment it was also observed that two amine ligands react with one tellurium ion by the plot of log KD versus log[R3 N+ HCl− ], with slope 1.99, which is very close to 2 (Fig. 2b), from the following equations: [TeCl6 2− ]aq + n[R3 N+ HCl− ]org = [(R3 N+ H)n TeCl6 2− ]org + n[Cl− ]aq
(1)
The effect of temperature on the extraction of tellurium by the chloride salt of tri-iso-octalamine in xylene has been studied from an aqueous phase of 0.078 mmol/dm3 tellurium in 2.5 M HCl. The result shows that there is a decrease in tellurium extraction as the experimental temperature increased (Fig. 3a). The van’t Hoff equation shows the change of the distribution constant (KD ) with temperature
120
12 0 10 0 % Extraction
100
%Extraction
80
60 40
80 60 40 20 0 280
20
(a)
0 0
0.01
0.02
(a)
0.03
0.04
0.05
0.06
0.07
290
300
310
320
330
340
Temperature(K)
1.5
[TIOA] (M) 4
1 log K D
3 2
slope = 1.99
log KD
s lope = 2.69 0.5
1 0
0 3
-1 -3
(b)
-2.5
-2
-1.5
-1
-0.5
0
(b)
3.2
3.4
3.6
[1/T] K-1
log[R 3NH +Cl -]
Fig. 2. (a) Plot of % extraction vs. [TIOA] (M). Initial tellurium concentration 0.078 × 10−3 mmol/dm3 . O/A ratio 1. (b) Plot of log KD vs. log[log[R3 NH+ Cl− ]. Initial tellurium concentration 0.078 × 10−3 mmol/dm3 . O/A ratio 1.
Fig. 3. (a) Plot of % extraction vs. temperature (K). Initial tellurium concentration 0.078 × 10−3 mmol/dm3 . Organic phase: 33.9 × 10−3 M TIOA in xylene. O/A ratio 1. (b) Plot of log KD vs. [1/T] (K−1 ). Initial tellurium concentration 0.078 × 10−3 mmol/dm3 . Organic phase: 33.9 × 10−3 M TIOA in xylene. O/A ratio 1.
180
D.K. Mandal et al. / Separation and Purification Technology 40 (2004) 177–182
Table 1 Effect of temperature on extraction of tellurium
120
log KD
G (kJ/mol)
S (JK−1 mol−1 )
283 293 303 313 323 333
1.38 0.95 0.72 0.45 0.19 0.03
−7.48 −5.32 −4.18 −2.69 −1.17 −0.19
−0.156 −0.156 −0.156 −0.156 −0.156 −0.154
100 % Extraction
Temperature (K)
80 60 40 20
Initial tellurium concentration 0.078 × 10−3 mmol/dm3 . Organic phase: 33.9 × 10−3 M TIOA in xylene. O/A ratio 1.
0 0
D(log KD ) −H = D(1/T) 2.303R
(6)
(a)
4
6
8
HCl (M)
G = −2.303RT log KD
(7)
H − G T
(8)
The negative values of free energy imply that the reaction is spontaneous. The negative enthalpy value indicates that the extraction of tellurium with TIOA in xylene is favorable at low temperature (Table 1). 3.4. The effect of acid and chloride salt The extraction were carried out at 30 ◦ C, varying the tellurium ion concentration in aqueous phase and using various concentration of HCl. Fig. 4a shows that the distribution constant (KD ) of tellurium reaches a maximum at high acid concentrations. There is a difference in the behavior of this extraction system with the tellurium used, for each HCl acid concentration; the distribution constant (KD ) increases as the initial concentration of tellurium is decreased (Fig. 4b). This behavior may be explained from the following set of equations: TeCl6 2− + [2(R3 N+ HCl− )]org = [(R3 N+ H)2 TeCl2− 6 ]org + 2Cl−
(9)
In order to achieve this exchange, the amine is first converted to the appropriate amine salt to provide an anion to exchange with the metal species [R3 N]org + HCl = [R3 N+ HCl− ]org
(10)
This shows the acidification of amine extractant to form an amine salt or ion pair [R3 N+ HCl− ] in organic phase. Therefore, extraction of tellurium from chloride system undergoes ion-association mechanism [14]. It was observed that in the ion-association extraction system, high concentrations of electrolyte like MgCl2 and
Distribution ConstantKD
5
The plot of log KD versus 1/T (Fig. 3b) is linear and with slope 2.69 and the enthalpy change (H) of the reaction was −51.49 KJ/mol, which means it is an exothermic reaction. The free energy change (G) and entropy (S) were calculated by the following equations:
S =
2
3 0.078 mmole/dm3
2 0.156 mmole/dm3
1 0 0.5
(b)
.039 mmole/dm3
4
1
1.5
2
2.5
HCl (M)
Fig. 4. (a) Plot of % extraction vs. HCl (M), Initial metal concentration 0.078 × 10−3 mmol/dm3 tellurium. Organic phase: 33.9 × 10−3 M TIOA in xylene. O/A ratio 1. (b) Plot of distribution constants (KD ) vs. HCl (M). Initial tellurium concentrations 0.039 × 10−3 , 0.078 × 10−3 , and 0.156 × 10−3 mmol/dm3 . Organic phase: 33.9 × 10−3 M TIOA in xylene. O/A ratio 1.
ZnCl2 are effective is increasing the extent of extraction. The addition of such salts, referred to as salting-out reagents, serves two purposes. The first and more obvious is to aid the direct formation of the complex by the mass action effect—the formation of a chloro complex. It is promoted by increasing the concentration of chloride ion. Secondly, as the salt concentration increases, the concentration of ‘free’ water decreases because the ions require a certain amount of water for hydration. This decreases the solubility of complex [(R3 N+ H)2 TeCl6 2− ] in aqueous phase. 3.5. Influence of carbon chain of amine extractant Tellurium extraction with amine is influenced by the nature of the carbon chain as well as the number of carbon atoms in the chain. Experiments were conducted with number of tertiary amines, where the carbon chain length was varied. For all the amines of 33.9 × 10−3 mmol/dm3 solution was prepared with xylene as solvent. The result, shown in Table 2 indicates a sharp increases in extraction with the increase of carbon chain length. Extraction of tellurium remained constant with amines having carbon chain length from C8 to C12 . From Table 2, it is also observed that with tri-iso-octylamine and trilaurylamine, the extraction of
D.K. Mandal et al. / Separation and Purification Technology 40 (2004) 177–182
181
Table 2 Effect of carbon chain of amine extractant on the extraction of tellurium
Table 4 Effect of Acids on extraction of tellurium
Tertiary amine
% Extraction of tellurium
Acids
Concentration (M)
%Extraction
Tributylamine Trihexlamine Methyldi-n-octylamine Tricaprylamine Trilaurylamine Tri-iso-octylamine
70.4 85.6 94.5 97.8 98.9 99.5
H2 SO4
0.5 1.0 2.0 3.0
99.5 98.5 97.8 94.5
HNO3
0.01 0.02 0.05 2.5
93.2 84.5 72.5 50.5
HClO4
0.01 0.02 0.05 0.10
89.5 72.2 42.5 26.2
Initial tellurium concentration 0.078 × 10−3 mmol/dm3 . Organic phase: 33.9 × 10−3 M of various tertiary amines in xylene. O/A ratio 1.
tellurium is quantitative. Although the extraction was almost quantitative with trilaurylamine, but phase separation was not clear as observed with tri-iso-octylamine. 3.6. Effect of diluents The extraction of tellurium was carried out with 33.9 × 10−3 mmol/dm3 of TIOA in different diluents. From the results given in Table 3, it is clear that effective extraction occurred in xylene followed by methyl isobutyl ketone. Though extraction was effective in methyl isobutyl ketone but clear phase separation was much slower compared to xylene. Moreover, the solubility of methyl isobutyl ketone increases with increase in acidity. Xylene was found to be the most suitable solvent for extraction of tellurium. It is so, because better extraction and clear phase separation took place in xylene within 2 min. 3.7. Effect of acids on extraction The effect of sulfuric, nitric, and perchloric acids on the tellurium extractions were investigated. The results are shown in Table 4. Sulfuric acid above 2 M reduced the extraction. Nitric and perchloric acids interfered even at the concentration of 0.01 M. This is due to salt effect of various ions. Salt effects generally decreases the metal extraction by amine in the order ClO4 − > NO3 − > SO4 − .
Initial tellurium concentration 0.078 × 10−3 mmol/dm3 . Organic phase: 33.9 × 10−3 M TIOA in xylene. O/A ratio 1.
reduction of absorption signal was observed for nitric acid as stripping agent with concentration range of 0.5–1.0 M. Suppression of signals were found to enhance with increase in acid concentration. Similar suppression of absorption signals were also observed for sulfuric acid, but less pronounced than for nitric acid. With salt solutions the recoveries of tellurium was observed in the range of 90–92%. The organic phase was vigorously shaken with different concentrations of hydrochloric acid (0.05–2.0 M) and then left for clear phase separation. The results obtained have indicated that the recovery of tellurium is quantitative while shaking the organic phase with 0.08 M solution (Fig. 5). This is due to the fact that in ion-association system, where high acid concentration acid concentrations are required for metal extraction; stripping with water or very low acid concentration usually results in stripping of metal from organic phase [15]. For all experiments, a 0.1 M HCl solution was used as stripping agent. The optimum contact time for stripping was 2 min. 3.9. The effect of diverse ions The effect of diverse ions on the recovery of 1000 g tellurium was investigated by adding 100–500-fold known
3.8. Effect of stripping agents Tellurium extracted into organic phase (TIOA in xylene) was stripped with different strengths of stripping agents. A
120
Solvents
% Extraction of tellurium
Chloroform Toluene Kerosene Carbontetrachloride Methyl isobutylkotone Xylene
30.5 71.4 78.2 85.0 95.5 99.5
Initial tellurium concentration 0.078 × 10−3 mmol/dm3 . Organic phase: 33.9 × 10−3 M TIOA in xylene. O/A ratio 1.
% Recovery
100
Table 3 Effect of solvent on the extraction of tellurium
80 60 40 20 0 0.04
0.06
0.08 HCl (M)
0.1
0.12
Fig. 5. Plot of % recovery vs. HCl (M). Initial tellurium concentration 0.078 × 10−3 mmol/dm3 . O/A ratio 1.
182
D.K. Mandal et al. / Separation and Purification Technology 40 (2004) 177–182
Table 5 Effect of diverse ions on extraction of tellurium Ions
Added as
Taken (g)
Cu2+
CuSO4 ·5H2 O CdCl2 AlCl3 CrCl3 HgCl2 NaAsO2 KCl NaCl MgCl2 CaCl2 ·2H2 O NaSbO2 SnCl2 ·2H2 O PbCl2 ·2H2 O ZrOCl2 ·8H2 O TiCl4 ·4H2 O FeCl3 ·6H2 O BaCl2 ·2H2 O SrCl2 ·2H2 O CoCl2 MnCl2 ·4H2 O NiCl2 ·6H2 O ZnSO4 ·7H2 O
1000 500 2000 500 200 400 1000 1000 1000 1000 400 500 500 500 500 2000 1000 1000 1000 1000 1000 1000
Cd2+ Al3+ Cr3+ Hg2+ As3+ K+ Na+ Mg2+ Ca2+ Sb3+ Sn2+ Pd2+ Zr4+ Ti4+ Fe3+ Ba2+ Sr2+ Co2+ Mn2+ Ni2+ Zn2+
Initial tellurium concentration 0.078 × 10−3 mmol/dm3 . Organic phase: 33.9 × 10−3 M TIOA in xylene. O/A ratio 1.
amounts of each ionic species to be examined. The amount of each ionic species added to investigate the effect of interfering foreign ions is presented in Table 5. The error of recovery of tellurium in presence of following ions was not more than ±1.5%. 4. Conclusion From the above results, it is observed that tellurium is extracted with tri-iso-octylamine in xylene as a moderator by a ion-association mechanism. The extracted species in the organic phase is [(R3 N+ H)2 TeCl6 2− ]. The thermodynamic functions; enthalpy (H), entropy (S), and free energy (G) in the extraction of tellurium with tri-iso-octlyamine have been evaluated. The extraction reaction is an exother-
mic process with the extraction percentage decreasing with increasing of temperature. Another important feature of the proposed method is that extraction of tellurium using 33.9× 10−3 M TIOA, in xylene from aqueous phase has resulted in 99% recovery in 2 min.
Acknowledgements The authors thank Henkel Corporation, USA for sending the reagent TIOA and also the Department of Metallurgical Engineering, Jadavpur University for extending laboratory facilities. Authors are thankful to Ms. Kasturi Mitra for her contribution.
References [1] N. Yoshikuni, S. Nishiumi, K. Oguma, Jpn. Soc. Anal. Chem. 49 (10) (2000) (Review). [2] S. Terashima, Jpn. Soc. Anal. Chem. 49 (10) (2000) (Review). [3] K.I. Rhee, C.K. Lee, Y.C. Ha, G.J. Jeong, H.S. Kim, H.J. Sohn, Hydrometallugy 53 (1999) 89. [4] T. Shibasaki, K. Abe, H. Takeuchi, Hydrometallugy 59 (1992) 399. [5] E. Hoffmann, J. Met., Miner. Mater. Soc. 41 (7) (1989) 33. [6] W. Trolley, R. Swarup, The Minerals, Metals & Materials Society, AIME, Warrendale, PA, 1995, p. 503. [7] M.R. Chowdhury, S.K. Sanyal, Hydrometallugy 32 (1993) 189. [8] M.R. Chowdhury, S. Datta, S.K. Sanyal, Hydrometallugy 43 (1996) 175. [9] M.R. Chowdhury, S. Datta, S.K. Sanyal, Hydrometallugy 42 (1996) 115. [10] Y.H. Huang, C.Y. Chen, J.F. Kuo, Hydrometallurgy 28 (1992) 297. [11] Y.H. Huang, C.Y. Chen, J.F. Kuo, Bull. Chem. Soc. Jpn. 64 (1991) 3059. [12] Y.H. Huang, C.Y. Chen, J.F. Kuo, Chem. Eng. J. Jpn. 24 (1990) 149. [13] Analytical Methods for Atomic Absorptions for Spectrophotometric, Perkin-Elmer, Norwalk, Connecticut, USA, 1982. [14] G.M. Ritcey, A.W. Ashbrook, Solvent Extraction: Principles and Application to Process Metallurgy, Part I, Elsevier, Amsterdam, 1984 (Chapter 3). [15] G.M. Ritcey, A.W. Ashbrook, Solvent Extraction: Principles and Application to Process Metallurgy, Part I, Elsevier, Amsterdam, 1984 (Chapter 2).