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Extraction of chromium (VI) from multicomponent acidic solutions by emulsion liquid membranes using TOPO as extractant
Journal of Hazardous Materials 167 (2009) 1141–1147
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Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat
Extraction of chromium (VI) from multicomponent acidic solutions by emulsion liquid membranes using TOPO as extractant Recep Ali Kumbasar ∗ Department of Chemistry, Faculty of Science, Sakarya University, 54100 Adapazarı, Turkey
a r t i c l e
i n f o
Article history: Received 24 May 2008 Received in revised form 7 November 2008 Accepted 28 January 2009 Available online 6 February 2009 Keywords: Acidic solution Chromium (VI) Extraction Emulsion liquid membrane Trioctylphosphine oxide
a b s t r a c t Experimental results for the extraction of chromium (VI) from multicomponent acidic solutions by emulsion liquid membrane (ELM) using trioctylphosphine oxide (TOPO) as extractant are presented. The membrane phase consists of kerosene as diluent, TOPO as extractant, ECA 4360J (a nonionic polyamine) as surfactant and (NH4 )2 CO3 solution as stripping phase. Effects of various parameters such as mixing speed, type and concentration of stripping solution, surfactant and extractant concentrations, and volume ratio of the membrane phase to internal stripping phase on Cr (VI) extraction were studied and optimum conditions were determined. Results show that with proper adjustment of experimental conditions for the extraction of Cr (VI) can be enhanced to a great extent. This study also examined the effects of concentrations of acid and metal ions in the feed phase for the extraction of Cr (VI) ions. The results also showed that by appropriate selection of the extraction and stability conditions, nearly all of the Cr (VI) ions (100–500 mg/L) present in the acidic feed solution containing 1000 mg/L from each of Cu (II), Zn (II), Co (II), Ni (II) and Cd (II) ions were extracted within a few minutes. Concentration variations of Cr (VI) and other ions in the acidic solutions were determined by atomic absorption spectrophotometry. © 2009 Elsevier B.V. All rights reserved.
1. Introduction The removal of toxic metals from industrial wastewater is a major concern. Hexavalent chromium receives particular attention because of its high toxicity and numerous industrial applications (electroplating, metal finishing, and corrosion inhibition). Plating baths in the electroplating process contain 100–200 g/L of hexavalent chromium, and they can be polluted by metallic cations (i.e., Fe3+ , Cr3+ , Ni2+ ; concentrations of which change between 1 and 10 g/L) and by anions (nitrates, chlorides, phosphates, and sulfates). Concentration of Cr (VI) in the rinsing waters used after chromium plating need to reduce from 100–500 to <1 mg/L before discharge to the environment [1]. The treatment of electroplating effluents generally consists in a reduction of Cr (VI) to Cr (III) with a chemical reducing agent such as ferrous sulfate, sulfur dioxide, or sodium bisulfite, and then precipitation of the trivalent chromium as hydrated oxides. Other recycling processes involve anionic-exchange resins which are used to remove chromate or dichromate followed by elution with NaOH solution, and reverse osmosis. These techniques are costly and produce additional sludges. The possibility of recovering and concentrating of Cr (VI) for reuse makes very
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attractive the techniques of solvent extraction and liquid membrane [1,2]. Solvent extraction technology has been widely used for the recovery and/or removal of heavy metals in hydrometallurgy. A limitation in traditional solvent extraction is that a large inventory of solvent is required, especially when processing dilute solutions [3,4]. ELM systems have now become an alternative metal separation technique from dilute solutions. This technique offers advantages over conventional solvent extraction. Because, conventional solvent extraction requires larger volumes of solvent and associated equipment, and therefore becomes inefficient when the metal ion concentration in the effluent stream is low [5]. Particularly, a ELM process has sufficient ability to selectively separate metals from aqueous solutions using a double W/O/W emulsion stabilized by the use of suitable surfactants, with a reduced amount of organic solvent and greater extraction. First study on the industrial applications of ELM was made by Li et al. [6,7]. They are normally credited with this invention. Many investigators have studied the practical operation of ELM and the mechanisms that regulate the transport of metals through them, a process that would be regulated by a diffusive phenomenon of mass transfer with a chemical reaction. The ELM method would have the ability to remove and concentrate selectively or collectively, depending on the extractants chosen, the low metal contents present in these residual aqueous solutions, in a continuous and fast process, using a thin liquid membrane that has a large inter-
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facial area and needs only a very small volume of organic solvent [8–11]. In the present work, in order to have a better understanding of the dynamics of ELM technique, the major parameters influencing to selective extraction and concentration of chromium (VI) by ELM process from the acidic feed solutions containing Co, Ni, Cd, Zn, and Cu ions were experimentally studied and the optimum conditions were determined.
extraction experiments were carried out batchwise at the ambient temperature of 20 ± 1 ◦ C. All aqueous solutions were prepared using deionised water.
2. Experimental
The extraction reactions of Cr (VI) are quite complicated. Because, the forms of Cr (VI) in aqueous solutions vary with the concentration of Cr (VI) and solution pH. Very few researchers have taken account of the various forms of Cr (VI) in the analysis of extraction mechanisms. Recently, Huang et al. [12] have established the equilibria for the solvent extraction of Cr (VI) between aqueous solution (pH 2–4) and kerosene containing TOPO (Fig. 1a), considering the presence of various forms of Cr (VI) species in aqueous phase and the influence of solution ionic strength for equilibrium constants. The equilibria for the extraction of HCrO4 − and Cr2 O7 2− with TOPO could be expressed through the formation of the species H2 CrO4 ·(TOPO)(org) and H2 Cr2 O7 ·(TOPO)3(org) . The chromate ions may exist in the aqueous phase in different ionic forms (HCrO4 − , CrO4 2− , HCr2 O7 − , Cr2 O7 2− ). Any of these forms will predominate to other forms of chromium depending on total amount of chromium and pH of the aqueous phase. CrO4 2− anion prevails in basic or slightly acidic solution while Cr2 O7 2− anions dominate in acidic aqueous solution. Moreover, Cr2 O7 2− convert into HCrO4 − anions in acidic aqueous solution at a total Cr (VI) concentration lower than (1.26–1.74) × 10−2 mol/L [13]. Thus, in this study, chromate ions will exist as HCrO4 − in the multicomponent acidic solution at low initial concentration (100–500 mg/L) of Cr (VI). The reaction for the extraction of HCrO4 − with TOPO (Fig. 1b) from aqueous solutions could be expressed by the following equations [2]:
2.1. Materials The liquid membrane solution is composed of a surfactant, an extractant, and a diluent. The surfactant is a nonionic polyamine which is commercially known as ECA 4360J. The mobile carrier or extractant is TOPO which is purchased from Merck, Germany. A commercial kerosene (TUPRAS Oil Company, Turkey) was used as diluents. Commercial kerosene is a complex mixture of aliphatic origin and also contains aromatics about 15% (w/w). ECA 4360J is the products of ExxonMobil, that was used directly as received from the manufacturer. Hydrochloric acid, (NH4 )2 CO3 , Na2 CO3 , NaOH, K2 Cr2 O7 and all other chemicals used such as CuCl2 ·2H2 O, ZnCl2 , CoCl2 ·6H2 O, NiCl2 ·6H2 O and CdCl2 ·2.5H2 O were purchased from Fluka and were used directly as received from the manufacturer. 2.2. Membrane preparation In 250 mL beaker, a 30 mL portion of TOPO and ECA 4360J in kerosene are emulsified at mixing speed of 1800 rpm by a variable speed mixer. 18 mL of 0.5 M (NH4 )2 CO3 solution was used as stripping solution. Stripping solution was added dropwise to the stirred membrane solution. The solution is stirred continuously for 20 min to obtain emulsion liquid membrane.
3. Results and discussion 3.1. Extraction and stripping mechanisms of Cr (VI) in acidic aqueous solution
2.3. Feed solution preparation
HCrO4(aq) − + H+ (aq) + TOPO(org) ⇔ H2 CrO4 TOPO(org)
Stock solutions of other metals were prepared from their salts above mentioned. Acidic feed solutions were prepared by the addition of hydrochloric acid solution into aqueous solution containing appropriate amount cobalt, nickel, cadmium, zinc, copper, and chromium (VI) ions. Unless otherwise stated, metal ion and acid concentrations of this acidic feed solutions are 100 mg/L Cr (VI), 1000 mg/L Co, Ni, Cd, Zn, Cu, and 0.1 M HCl, respectively.
The complex formed as above diffuses through the membrane toward the stripping side, then in the presence of (NH4 )2 CO3 there, the following reaction (Fig. 1b) is expected to take place at the membrane face on the stripping solution side:
(1)
H2 CrO4 TOPO(org) + (NH4 )2 CO3(aq) ⇔ TOPO(org) + (NH4 )2 CrO4(aq) + CO2(aq) + H2 O(aq)
(2)
2.4. Experimental method 3.2. Effect of acid type in feed solution In 600 mL beaker, the ELM prepared (membrane solution and stripping solution) was added to 250 mL of the multicomponent acidic solution. The contents were stirred by a variable speed mixer equipped with a turbine-type impeller at the speed of 250 rpm for extraction time of 10 min. To determine the important variables governing the permeation of chromium (VI) from acidic feed solution, extractant and surfactant concentrations, mixing speed, acid and chromium concentrations of the feed solution, phase ratio, and type and concentration of stripping solution were varied to observe their effect on Cr (VI) separation. At the end of each run, the emulsion was recovered and subsequently broken into its constituents using a high voltage splitter with niobium electrodes.
Type and concentration of acid used in the multicomponent acidic solution are parameters influencing the extraction efficiency. Therefore, the extraction of Cr (VI) ions by ELM process was studied to be used three different acid in the multicomponent acidic solution and the result obtained were shown in Fig. 2. As seen in Fig. 2, the highest extraction efficiency was obtained with hydrochloric acid. Moreover, it was observed that ELM was more stable in feed solution of hydrochloric acid during process time. Therefore, hydrochloric acid was accepted as the best acid and was selected further studies. 3.3. Effect of acid concentration or pH in feed solution
2.5. Analytical method The uptake of metal ions was monitored by removing samples of the feed solution periodically for analysis. Atomic absorption spectrophotometry (Shimadzu AA-6701F model, Tokyo, Japan) was used for metals’ (Cr (VI), Co, Ni, Cd, Zn, Cu) determinations. All the
The effect of acid concentration of the multicomponent acidic solution on the extraction of Cr (VI) ions through TOPO–ECA 4360Jkerosene-based membrane was represented in Fig. 3. It can be inferred from Fig. 3 that the extraction efficiency of Cr (VI) was maximum around 0.5 M HCl (pH ≈ 0.3). Above and below this pH the
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Fig. 1. (a) Structure of TOPO and (b) extraction and stripping of Cr (VI) by ELM using TOPO as extractant from the multicomponent acidic solutions.
extraction decreased. From the results, it is clear that an decrease in hydrogen ion concentration causes a decrease in the rate of association of Cr (VI) with TOPO. After reaching a maximum value the extraction decreases with the increase in acid concentration. This can be explained as follows [14]:
al. [15] during extraction of Cr (VI) from sulfuric acid solutions with Aliquat 336.
HCrO4 − + H+ → H2 CrO4
As the extraction step occurs in the interface between the multicomponent acidic solution and the ELM, the extraction of Cr (VI) necessarily requires a simultaneous back-extraction step at the opposite side of the membrane. In the back-extraction stage, the extractant is regenerated and Cr (VI) is stripped. The literature contains many options for accomplishing the stripping of Cr (VI) complex, among them, solutions of NH4 OH, ammonium salts as sulfate or nitrate, NaOH, Na2 CO3 , (NH4 )2 CO3 and some mixtures of these compounds have been used. From among this stripping solutions, NaOH, Na2 CO3 and (NH4 )2 CO3 solutions were used as stripping solution in the present work. As seen from Fig. 4, emul-
(3)
The increase in proton concentration or the decrease of pH in the feed solution will form a species like H2 CrO4 which may not ionize completely at a higher acid concentration or a lower pH to form a complex with TOPO according to Eq. (2). Hence the extraction of Cr (VI) will decrease, and thereby the extraction efficiency decreases with the increase in acid concentration. Actually, from the literature, the extraction of Cr (VI) ions increase with the increase in protons concentration or the decrease in pH up to a limit value. After reaching a maximum value the extraction decrease with the decrease in pH. Similar results were also observed by Strzelbicki et
Fig. 2. Effect of acid type in feed solution on the extraction rate of Cr (ECA 4360J: 6%; TOPO: 3%; kerosene: 91%; stripping solution: 18 mL 0.5 M (NH4 )2 CO3 ; Cr2 O7 − concentration of feed solution: 100 mg/L; mixing speed of feed solution: 250 rpm; phase ratio: 3/5; treatment ratio: 250/48; C: Cr (VI) concentration in the feed phase at any time, C0 : initial Cr (VI) concentration in the feed phase; C/C0 : dimensionless Cr (VI) concentration in the feed phase at any time).
3.4. Effect of type of stripping solution
Fig. 3. Effect of acid concentration in feed solution on the extraction rate of Cr (ECA 4360J: 6%; TOPO: 3%; kerosene: 91%; stripping solution: 18 mL 0.5 M (NH4 )2 CO3 ; Cr2 O7 − concentration of feed solution: 100 mg/L; mixing speed of feed solution: 250 rpm; phase ratio: 3/5; treatment ratio: 250/48).
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Fig. 4. Effect of type of stripping solution on the extraction rate of Cr (ECA 4360J: 6%; TOPO: 3%; kerosene: 91%; acid concentration of feed solution: 0.1 M HCl; Cr2 O7 − concentration of feed solution: 100 mg/L; mixing speed of feed solution: 250 rpm; phase ratio: 3/5; treatment ratio: 250/48).
Fig. 6. Effect of mixing speed in feed solution on the extraction rate of Cr (ECA 4360J: 6%; TOPO: 3%; kerosene: 91%; stripping solution: 18 mL 0.5 M (NH4 )2 CO3 ; acid concentration of feed solution: 0.1 M HCl; Cr2 O7 − concentration of feed solution: 100 mg/L; phase ratio: 3/5; treatment ratio: 250/48).
sions formed with NaOH and Na2 CO3 stripping solutions were instable to the end of process time and therefore extraction efficiencies also decreased. On the other hand, stability of emulsion containing (NH4 )2 CO3 stripping solution was protected during process time and the highest extraction efficiency was obtained with this stripping solution.
3.6. Effect of mixing speed in feed solution
3.5. Effect of concentration of stripping solution The effect of (NH4 )2 CO3 concentration in the stripping solution on the extraction efficiency of Cr (VI) was also investigated in the range of 0.1–1 M and the results was shown in Fig. 5. From Fig. 5, it was found that maximum extraction of Cr (VI) occurred at 0.5 M (NH4 )2 CO3 concentration. In addition from Fig. 5, it can be seen that there was very slight increase in extraction rates with an increase of stripping solution concentration from 0.1 to 0.5 M. But above this concentration, emulsion was unstable due to interaction of stripping solution with surfactant and hence the extraction efficiency also decreased.
Fig. 5. Effect of concentration of stripping solution on the extraction rate of Cr (ECA 4360J: 6%; TOPO: 3%; kerosene: 91%; acid concentration of feed solution: 0.1 M HCl; Cr2 O7 − concentration of feed solution: 100 mg/L; mixing speed of feed solution: 250 rpm; phase ratio: 3/5; treatment ratio: 250/48).
The effect of mixing speed in the multicomponent acidic solutions was studied in the range of 200–350 rpm in order to obtain optimal mixing speed that allows effective extraction of Cr (VI) in emulsion liquid membrane process. The effect of mixing speed on the rate of extraction was shown in Fig. 6. Within the first 2 min, as seen from Fig. 6, the extraction efficiency of Cr (VI) increased with increasing of mixing speed. But after this minute, extraction efficiency decreased at mixing speed of 350 rpm and the highest extraction efficiency at the end of tenth minute was obtained with mixing speed of 325 rpm. According to Hirato et al. [16], by increasing the mixing speed, the size of the emulsion globule dispersed in the external phase decreases, and as a result the extraction rate increases. At the same time, the rate of the breakdown of the emulsion increases. Therefore, at speeds above 325 rpm, leakage of chromium (VI) might be started due to shearing of emulsion, which ultimately resulted in a gradual depletion in extraction and stripping. Thus, as the highest extraction efficiency at the end of tenth minute was obtained with mixing speed of 325 rpm, this speed was accepted as the best speed.
Fig. 7. Effect of extractant concentration on the extraction rate of Cr (ECA 4360J: 6%; kerosene: 88–92%; stripping solution: 18 mL 0.5 M (NH4 )2 CO3 ; acid concentration of feed solution: 0.1 M HCl; Cr2 O7 − concentration of feed solution: 100 mg/L; mixing speed of feed solution: 250 rpm; phase ratio: 3/5; treatment ratio: 250/48).
R. Ali Kumbasar / Journal of Hazardous Materials 167 (2009) 1141–1147
Fig. 8. Effect of surfactant concentration on the extraction rate of Cr (TOPO: 3%; kerosene: 91–96%; stripping solution: 18 mL 0.5 M (NH4 )2 CO3 ; acid concentration of feed solution: 0.1 M HCl; Cr2 O7 − concentration of feed solution: 100 mg/L; mixing speed of feed solution: 250 rpm; phase ratio: 3/5; treatment ratio: 250/48).
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Fig. 9. Effect of phase ratio on the extraction rate of Cr (ECA 4360J: 6%; TOPO: 3%; kerosene: 91%; stripping solution: 18 mL 0.5 M (NH4 )2 CO3 ; acid concentration of feed solution: 0.1 M HCl; Cr2 O7 − concentration of feed solution: 100 mg/L; mixing speed of feed solution: 250 rpm; treatment ratio: 250/48). Table 1 Optimum conditions.
3.7. Effect of extractant concentration Extractant concentration in the membrane phase plays a vital role in the overall extraction behaviour of ELM systems. To study this effect, the extractant concentration in the ELMs was varied in the range of 2–6% in the membrane phase. The results obtained were shown in Fig. 7. It can be seen that an increase in extractant concentration from 2% to 6% leads to an increase in extraction efficiency. But after sixth minute, with increasing of extractant concentration from 4% to 6% does not show significant change in the extraction efficiency of chromium (VI). It is due to the access of free extractant in membrane phase. Under the present extractant concentration, the free extractant is considered to be enough for forward extraction. Further increase in the extractant concentration leads to the decrease in the stripping reaction rate. This is because the chromium (VI) remains in the complex form (in the membrane phase) without getting stripped which in its turn affected the final recovery by the emulsion liquid membrane process. Similar results were obtained by Othman et al. [17]. Therefore, extractant concentration of 4% was considered to be sufficed for Cr (VI) extraction and was accepted as the best extractant concentration.
Parameter
Value
Surfactant (ECA 4360J) Extractant (TOPO) Diluent (kerosene) Type and concentration of the stripping solution Cr (IV) concentration in the feed solution Acid type and concentration of the feed solution Mixing speed Phase ratio Treatment ratio
2% 4% 92% 18 mL 0.5 M (NH4 )2 CO3 100–500 mg/L 0.5 M HCl 325 rpm 3/5 250/48
3.9. Effect of phase ratio The effect of the phase ratio (the stripping phase/membrance phase, Vs/Vm) on the extraction rate, by maintaining membrane volume constant, is depicted in Fig. 9. As seen in Fig. 9, emulsions formed in the ratios of 4/5 and 5/5 were not stable during 10 min; therefore the extraction efficiencies obtained with the ratios of 4/5 and 5/5 were lower. For the volume ratios of 2/5 and 3/5, the extraction rate increased with increasing ratio of the stripping phase/membrance phase. Because, walls of membrane globules formed with the volume ratio of 3/5 are thinner than that of 2/5.
3.8. Effect of surfactant concentration Influence of surfactant concentration in the membrane phase of the emulsion on the extraction rates was investigated at five ECA 4360J concentration levels from 1% to 6%. Emulsion formed with 1% ECA 4360J was not stable during 10 min. Except for 1% ECA 4360J, decreasing the surfactant concentration from 6% to 2% resulted in only a slightly increase in the extraction efficiency of chromium (VI) as shown in Fig. 8. As ECA 4360J concentration increases, the decrease in the rates of extraction could be attributed to a number of possible factors caused by high interfacial occupancy of the surfactant that includes decrease in rate of Cr (VI) complexation at the membrane phase–feed phase interface, increase in interfacial viscosity and decrease in movement of inner droplets within the emulsion globule and so on [18]. With 1 wt% ECA 4360J, although the extraction rate was higher than in the other cases in the first 2 min, the emulsion was less stable under the experimental conditions. Thus, 2% ECA 4360J was selected as the best surfactant concentration.
Fig. 10. Effect of chromium (VI) concentration on the extraction rate of chromium (VI) at optimum condition.
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Table 2 Experimental results in the optimum conditions. Initial concentration in the feed solution
500 mg/L Cr (VI) 1000 mg/L Co 1000 mg/L Ni 1000 mg/L Cd 1000 mg/L Zn 1000 mg/L Cu
Separation factors, ˇij
Extraction (%) 2 min
4 min
6 min
10 min
2 min
4 min
6 min
10 min
84.0 0.5 0.3 1.0 1.5 0.5
97.0 0.8 0.5 2.0 3.0 0.9
99.0 1.1 0.7 5.0 7.0 1.5
99.0 1.5 1.0 12.0 17.1 1.8
– 169 280 84 56 168
– 121 194 48 32 107
– 90 141 20 14 66
– 66 99 8 6 55
Consequently, the best extraction efficiency was obtained with the volume ratio of 3/5. Therefore, the volume ratio of 3/5 was selected as the best volume ratio.
percentages of extraction of metal ions during 10 min were shown in Table 2. 3.12. Membrane selectivity
3.10. Effect of Cr (VI) concentration on the extraction rate of chromium (VI) at the optimum conditions The effect of initial Cr (VI) concentration on the extraction efficiency of chromium (VI) at the optimum conditions (Table 1) was shown in Fig. 10. The chromium (VI) concentration in the multicomponent acidic solution was varied from 100 to 500 mg/L. The results showed that it was possible to extract 99% of chromium (VI) after contact time of 10 min. As can be seen from Fig. 10, the concentration of chromium (VI) in the multicomponent acidic solutions containing 100, 300, and 500 mg/L Cr (VI) at the optimum conditions was reduced to 1.0 mg/L within 10 min. On the other hand, concentration of chromium (VI) in the stripping solutions increased from zero to 1368, 4136, and 6862 mg/L within 10 min, respectively.
The separation factors ˇij of chromium (VI) with respect to the other ions that exist in the solutions are given in Table 2. The separation factor ˇij is given as follows: ˇij =
(Ci /Cj )strip (Ci /Cj )feed,o
(4)
where Ci and Cj are the concentrations of i and j components in the stripping and initial feed solutions. At the end of one experiment, in 10 min, liquid membrane selectivity of chromium (VI) with respect to cobalt, nickel and copper ions are high. The separation factors for chromium (VI) are shown in Table 2. As seen in Table 2, the separation factors in tenth minute compared reasonably well, except for zinc and cadmium. 4. Conclusions
3.11. Extraction of chromium (VI) and other ions at optimum conditions The effect of optimum conditions (Table 1) on the extraction efficiencies of chromium (VI) and other ions from the multicomponent acidic solution was shown in Fig. 11. From Fig. 11, it was observed that 99% extraction of chromium (VI) was achieved within 10 min, and the emulsion stability was also maintained during this period. Again, as seen from Fig. 11, the concentrations of copper, cobalt, and nickel ions during 10 min and of zinc and cadmium ions in the first 4 min almost remain fairly steady. But after the fourth minute, due to the decreasing of chromium (VI) concentration in the feed solution, cadmium and zinc were extracted into the stripping solution at the highest ratio, as compared to the other metal ions. The
An ELM process using TOPO to extract chromium (VI) from the multicomponent acid solution has been investigated. From this study the following conclusions can be drawn: 1. The optimum conditions were determined experimentally as stated above. 2. At the optimum conditions, at fourth minute, chromium (VI) was extracted with an extraction efficiency of about 97%. The liquid membrane selectivity was higher within the first 4 min. But after the fourth minute, due to the decreasing of chromium (VI) concentration in the feed solution, cadmium and zinc were extracted into the stripping solution at the highest ratio, as compared to the other metal ions. 3. The experimental results obtained showed the validity of the ELM method. 4. Cr (VI) concentration could be increased about 13 times in one stage, and using more stages the concentration of Cr (VI) could be further improved. 5. The reduced of solvent amount required for selective separation and concentration of toxic chromium metal, account for the promising performance of this technology in practical applications. Acknowledgements The author wish to express his sincere gratitude to the State Planning Organization of Turkiye (DPT), that supported this work, and Mehmet Yilmaz, coordinator of BAPK in Sakarya University. References
Fig. 11. Extraction of chromium (VI) and other ions at optimum condition.
[1] A. Zouhri, B. Ernst, M. Burgard, Bulk liquid membrane for the recovery of chromium(VI) from a hydrochloric acid medium using dicyclohexano-18crown-6 as extractant-carrier, Sep. Sci. Technol. 34 (1999) 1891–1905.
R. Ali Kumbasar / Journal of Hazardous Materials 167 (2009) 1141–1147 [2] T.-C. Huang, C.-C. Huang, D.-H. Chen, Thermodynamic equilibria of the extraction of chromium(vi) with tri-n-octylphosphine oxide from aqueous solutions, Solv. Extr. Ion Exch. 15 (1997) 837–862. [3] C. Basualto, M. Poblete, J. Marchese, A. Ochoa, A. Acosta, J. Sapaga, F. Valenzuela, Extraction of cadmium from aqueous solutions by emulsion liquid membranes using a stirred transfer cell contactor, J. Braz. Chem. Soc. 17 (2006) 1347–1354. [4] P.R. Danesi, Separation of metal species by supported liquid membranes, Sep. Sci. Technol. 19 (1984) 857–909. [5] P.R. Danesi, C. Clanetti, Permeation of metal ions through a series of two complementary supported liquid membranes, J. Membr. Sci. 20 (1984) 201– 213. [6] N.N. Li, Separating hydrocarbons with liquid membranes, U.S. Patent 3,410,794 (1968). [7] N.N. Li, R.P. Chan, A.L. Shrier, Liquid membrane process fort the separation of aqueous mixtures, U.S. Patent 3,779,907 (1973). [8] N. Alizadeh, S. Salimi, A. Jabbari, Transport study of palladium through a bulk liquid membrane using hexadecylpyridinium as carrier, Sep. Purif. Technol. 28 (2002) 173–180. [9] P. Kulkarni, Recovery of uranium(VI) from acidic wastes using tri-noctylphosphine oxide and sodium carbonate based liquid membranes, Chem. Eng. J. 92 (2003) 209–214. [10] P. Pal, S. Datta, P. Bhattacharya, Multi-enzyme immobilization in eco-friendly emulsion liquid membrane reactor—a new approach to membrane formulation, Sep. Purif. Technol. 27 (2002) 145–154.
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[11] J.B. Wright, D.N. Nilsen, G. Hundley, G.J. Galvan, Field test of liquid emulsion membrane technique for copper recovery from mine solutions, Miner. Eng. 8 (1995) 549–556. [12] T.-C. Huang, C.-C. Huang, D.-H. Chen, Extraction equilibria of chromium(vi) from sulfuric acid solutions with tri-n-octylphosphine oxide, J. Chem. Technol. Biotechnol. 73 (1998) 43–53. [13] A. Bhowal, S. Datta, Studies on transport mechanism of Cr(VI) extraction from an acidic solutions using liquid surfactant membranes, J. Membr. Sci. 188 (2001) 1–8. [14] C.F. Baes Jr., R.E. Mesmer, The Hydrolysis of Cations, Wiley-Inter-science, New York, 1976. [15] J. Strzelbicki, W.A. Charewicz, A. Mackiewicz, Permeation of chromium(VI) and rhenium(VII) oxyanions through liquid organic membranes facilitated by quaternary ammonium chlorides, Sep. Sci. Technol. 19 (1984) 321–336. [16] T. Hirato, I. Kishigami, Y. Awakura, H. Majima, Concentration of uranyl sulfate solution by an emulsion-type liquid membrane process, Hydrometallurgy 26 (1991) 19–33. [17] N. Othman, H. Mat, M. Goto, Separation of silver from photographic wastes by emulsion liquid membrane system, J. Membr. Sci. 282 (2006) 171–177. [18] L. Yang, Y. Zhang, Z. Guo, X. Gao, H. Takeuchi, Uranium(VI) extraction by liquid surfactant membrane with N-alkylcaprolactams as a carrier, Sep. Purif. Technol. 47 (2005) 88–94.
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Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat
Extraction of chromium (VI) from multicomponent acidic solutions by emulsion liquid membranes using TOPO as extractant Recep Ali Kumbasar ∗ Department of Chemistry, Faculty of Science, Sakarya University, 54100 Adapazarı, Turkey
a r t i c l e
i n f o
Article history: Received 24 May 2008 Received in revised form 7 November 2008 Accepted 28 January 2009 Available online 6 February 2009 Keywords: Acidic solution Chromium (VI) Extraction Emulsion liquid membrane Trioctylphosphine oxide
a b s t r a c t Experimental results for the extraction of chromium (VI) from multicomponent acidic solutions by emulsion liquid membrane (ELM) using trioctylphosphine oxide (TOPO) as extractant are presented. The membrane phase consists of kerosene as diluent, TOPO as extractant, ECA 4360J (a nonionic polyamine) as surfactant and (NH4 )2 CO3 solution as stripping phase. Effects of various parameters such as mixing speed, type and concentration of stripping solution, surfactant and extractant concentrations, and volume ratio of the membrane phase to internal stripping phase on Cr (VI) extraction were studied and optimum conditions were determined. Results show that with proper adjustment of experimental conditions for the extraction of Cr (VI) can be enhanced to a great extent. This study also examined the effects of concentrations of acid and metal ions in the feed phase for the extraction of Cr (VI) ions. The results also showed that by appropriate selection of the extraction and stability conditions, nearly all of the Cr (VI) ions (100–500 mg/L) present in the acidic feed solution containing 1000 mg/L from each of Cu (II), Zn (II), Co (II), Ni (II) and Cd (II) ions were extracted within a few minutes. Concentration variations of Cr (VI) and other ions in the acidic solutions were determined by atomic absorption spectrophotometry. © 2009 Elsevier B.V. All rights reserved.
1. Introduction The removal of toxic metals from industrial wastewater is a major concern. Hexavalent chromium receives particular attention because of its high toxicity and numerous industrial applications (electroplating, metal finishing, and corrosion inhibition). Plating baths in the electroplating process contain 100–200 g/L of hexavalent chromium, and they can be polluted by metallic cations (i.e., Fe3+ , Cr3+ , Ni2+ ; concentrations of which change between 1 and 10 g/L) and by anions (nitrates, chlorides, phosphates, and sulfates). Concentration of Cr (VI) in the rinsing waters used after chromium plating need to reduce from 100–500 to <1 mg/L before discharge to the environment [1]. The treatment of electroplating effluents generally consists in a reduction of Cr (VI) to Cr (III) with a chemical reducing agent such as ferrous sulfate, sulfur dioxide, or sodium bisulfite, and then precipitation of the trivalent chromium as hydrated oxides. Other recycling processes involve anionic-exchange resins which are used to remove chromate or dichromate followed by elution with NaOH solution, and reverse osmosis. These techniques are costly and produce additional sludges. The possibility of recovering and concentrating of Cr (VI) for reuse makes very
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attractive the techniques of solvent extraction and liquid membrane [1,2]. Solvent extraction technology has been widely used for the recovery and/or removal of heavy metals in hydrometallurgy. A limitation in traditional solvent extraction is that a large inventory of solvent is required, especially when processing dilute solutions [3,4]. ELM systems have now become an alternative metal separation technique from dilute solutions. This technique offers advantages over conventional solvent extraction. Because, conventional solvent extraction requires larger volumes of solvent and associated equipment, and therefore becomes inefficient when the metal ion concentration in the effluent stream is low [5]. Particularly, a ELM process has sufficient ability to selectively separate metals from aqueous solutions using a double W/O/W emulsion stabilized by the use of suitable surfactants, with a reduced amount of organic solvent and greater extraction. First study on the industrial applications of ELM was made by Li et al. [6,7]. They are normally credited with this invention. Many investigators have studied the practical operation of ELM and the mechanisms that regulate the transport of metals through them, a process that would be regulated by a diffusive phenomenon of mass transfer with a chemical reaction. The ELM method would have the ability to remove and concentrate selectively or collectively, depending on the extractants chosen, the low metal contents present in these residual aqueous solutions, in a continuous and fast process, using a thin liquid membrane that has a large inter-
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facial area and needs only a very small volume of organic solvent [8–11]. In the present work, in order to have a better understanding of the dynamics of ELM technique, the major parameters influencing to selective extraction and concentration of chromium (VI) by ELM process from the acidic feed solutions containing Co, Ni, Cd, Zn, and Cu ions were experimentally studied and the optimum conditions were determined.
extraction experiments were carried out batchwise at the ambient temperature of 20 ± 1 ◦ C. All aqueous solutions were prepared using deionised water.
2. Experimental
The extraction reactions of Cr (VI) are quite complicated. Because, the forms of Cr (VI) in aqueous solutions vary with the concentration of Cr (VI) and solution pH. Very few researchers have taken account of the various forms of Cr (VI) in the analysis of extraction mechanisms. Recently, Huang et al. [12] have established the equilibria for the solvent extraction of Cr (VI) between aqueous solution (pH 2–4) and kerosene containing TOPO (Fig. 1a), considering the presence of various forms of Cr (VI) species in aqueous phase and the influence of solution ionic strength for equilibrium constants. The equilibria for the extraction of HCrO4 − and Cr2 O7 2− with TOPO could be expressed through the formation of the species H2 CrO4 ·(TOPO)(org) and H2 Cr2 O7 ·(TOPO)3(org) . The chromate ions may exist in the aqueous phase in different ionic forms (HCrO4 − , CrO4 2− , HCr2 O7 − , Cr2 O7 2− ). Any of these forms will predominate to other forms of chromium depending on total amount of chromium and pH of the aqueous phase. CrO4 2− anion prevails in basic or slightly acidic solution while Cr2 O7 2− anions dominate in acidic aqueous solution. Moreover, Cr2 O7 2− convert into HCrO4 − anions in acidic aqueous solution at a total Cr (VI) concentration lower than (1.26–1.74) × 10−2 mol/L [13]. Thus, in this study, chromate ions will exist as HCrO4 − in the multicomponent acidic solution at low initial concentration (100–500 mg/L) of Cr (VI). The reaction for the extraction of HCrO4 − with TOPO (Fig. 1b) from aqueous solutions could be expressed by the following equations [2]:
2.1. Materials The liquid membrane solution is composed of a surfactant, an extractant, and a diluent. The surfactant is a nonionic polyamine which is commercially known as ECA 4360J. The mobile carrier or extractant is TOPO which is purchased from Merck, Germany. A commercial kerosene (TUPRAS Oil Company, Turkey) was used as diluents. Commercial kerosene is a complex mixture of aliphatic origin and also contains aromatics about 15% (w/w). ECA 4360J is the products of ExxonMobil, that was used directly as received from the manufacturer. Hydrochloric acid, (NH4 )2 CO3 , Na2 CO3 , NaOH, K2 Cr2 O7 and all other chemicals used such as CuCl2 ·2H2 O, ZnCl2 , CoCl2 ·6H2 O, NiCl2 ·6H2 O and CdCl2 ·2.5H2 O were purchased from Fluka and were used directly as received from the manufacturer. 2.2. Membrane preparation In 250 mL beaker, a 30 mL portion of TOPO and ECA 4360J in kerosene are emulsified at mixing speed of 1800 rpm by a variable speed mixer. 18 mL of 0.5 M (NH4 )2 CO3 solution was used as stripping solution. Stripping solution was added dropwise to the stirred membrane solution. The solution is stirred continuously for 20 min to obtain emulsion liquid membrane.
3. Results and discussion 3.1. Extraction and stripping mechanisms of Cr (VI) in acidic aqueous solution
2.3. Feed solution preparation
HCrO4(aq) − + H+ (aq) + TOPO(org) ⇔ H2 CrO4 TOPO(org)
Stock solutions of other metals were prepared from their salts above mentioned. Acidic feed solutions were prepared by the addition of hydrochloric acid solution into aqueous solution containing appropriate amount cobalt, nickel, cadmium, zinc, copper, and chromium (VI) ions. Unless otherwise stated, metal ion and acid concentrations of this acidic feed solutions are 100 mg/L Cr (VI), 1000 mg/L Co, Ni, Cd, Zn, Cu, and 0.1 M HCl, respectively.
The complex formed as above diffuses through the membrane toward the stripping side, then in the presence of (NH4 )2 CO3 there, the following reaction (Fig. 1b) is expected to take place at the membrane face on the stripping solution side:
(1)
H2 CrO4 TOPO(org) + (NH4 )2 CO3(aq) ⇔ TOPO(org) + (NH4 )2 CrO4(aq) + CO2(aq) + H2 O(aq)
(2)
2.4. Experimental method 3.2. Effect of acid type in feed solution In 600 mL beaker, the ELM prepared (membrane solution and stripping solution) was added to 250 mL of the multicomponent acidic solution. The contents were stirred by a variable speed mixer equipped with a turbine-type impeller at the speed of 250 rpm for extraction time of 10 min. To determine the important variables governing the permeation of chromium (VI) from acidic feed solution, extractant and surfactant concentrations, mixing speed, acid and chromium concentrations of the feed solution, phase ratio, and type and concentration of stripping solution were varied to observe their effect on Cr (VI) separation. At the end of each run, the emulsion was recovered and subsequently broken into its constituents using a high voltage splitter with niobium electrodes.
Type and concentration of acid used in the multicomponent acidic solution are parameters influencing the extraction efficiency. Therefore, the extraction of Cr (VI) ions by ELM process was studied to be used three different acid in the multicomponent acidic solution and the result obtained were shown in Fig. 2. As seen in Fig. 2, the highest extraction efficiency was obtained with hydrochloric acid. Moreover, it was observed that ELM was more stable in feed solution of hydrochloric acid during process time. Therefore, hydrochloric acid was accepted as the best acid and was selected further studies. 3.3. Effect of acid concentration or pH in feed solution
2.5. Analytical method The uptake of metal ions was monitored by removing samples of the feed solution periodically for analysis. Atomic absorption spectrophotometry (Shimadzu AA-6701F model, Tokyo, Japan) was used for metals’ (Cr (VI), Co, Ni, Cd, Zn, Cu) determinations. All the
The effect of acid concentration of the multicomponent acidic solution on the extraction of Cr (VI) ions through TOPO–ECA 4360Jkerosene-based membrane was represented in Fig. 3. It can be inferred from Fig. 3 that the extraction efficiency of Cr (VI) was maximum around 0.5 M HCl (pH ≈ 0.3). Above and below this pH the
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Fig. 1. (a) Structure of TOPO and (b) extraction and stripping of Cr (VI) by ELM using TOPO as extractant from the multicomponent acidic solutions.
extraction decreased. From the results, it is clear that an decrease in hydrogen ion concentration causes a decrease in the rate of association of Cr (VI) with TOPO. After reaching a maximum value the extraction decreases with the increase in acid concentration. This can be explained as follows [14]:
al. [15] during extraction of Cr (VI) from sulfuric acid solutions with Aliquat 336.
HCrO4 − + H+ → H2 CrO4
As the extraction step occurs in the interface between the multicomponent acidic solution and the ELM, the extraction of Cr (VI) necessarily requires a simultaneous back-extraction step at the opposite side of the membrane. In the back-extraction stage, the extractant is regenerated and Cr (VI) is stripped. The literature contains many options for accomplishing the stripping of Cr (VI) complex, among them, solutions of NH4 OH, ammonium salts as sulfate or nitrate, NaOH, Na2 CO3 , (NH4 )2 CO3 and some mixtures of these compounds have been used. From among this stripping solutions, NaOH, Na2 CO3 and (NH4 )2 CO3 solutions were used as stripping solution in the present work. As seen from Fig. 4, emul-
(3)
The increase in proton concentration or the decrease of pH in the feed solution will form a species like H2 CrO4 which may not ionize completely at a higher acid concentration or a lower pH to form a complex with TOPO according to Eq. (2). Hence the extraction of Cr (VI) will decrease, and thereby the extraction efficiency decreases with the increase in acid concentration. Actually, from the literature, the extraction of Cr (VI) ions increase with the increase in protons concentration or the decrease in pH up to a limit value. After reaching a maximum value the extraction decrease with the decrease in pH. Similar results were also observed by Strzelbicki et
Fig. 2. Effect of acid type in feed solution on the extraction rate of Cr (ECA 4360J: 6%; TOPO: 3%; kerosene: 91%; stripping solution: 18 mL 0.5 M (NH4 )2 CO3 ; Cr2 O7 − concentration of feed solution: 100 mg/L; mixing speed of feed solution: 250 rpm; phase ratio: 3/5; treatment ratio: 250/48; C: Cr (VI) concentration in the feed phase at any time, C0 : initial Cr (VI) concentration in the feed phase; C/C0 : dimensionless Cr (VI) concentration in the feed phase at any time).
3.4. Effect of type of stripping solution
Fig. 3. Effect of acid concentration in feed solution on the extraction rate of Cr (ECA 4360J: 6%; TOPO: 3%; kerosene: 91%; stripping solution: 18 mL 0.5 M (NH4 )2 CO3 ; Cr2 O7 − concentration of feed solution: 100 mg/L; mixing speed of feed solution: 250 rpm; phase ratio: 3/5; treatment ratio: 250/48).
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Fig. 4. Effect of type of stripping solution on the extraction rate of Cr (ECA 4360J: 6%; TOPO: 3%; kerosene: 91%; acid concentration of feed solution: 0.1 M HCl; Cr2 O7 − concentration of feed solution: 100 mg/L; mixing speed of feed solution: 250 rpm; phase ratio: 3/5; treatment ratio: 250/48).
Fig. 6. Effect of mixing speed in feed solution on the extraction rate of Cr (ECA 4360J: 6%; TOPO: 3%; kerosene: 91%; stripping solution: 18 mL 0.5 M (NH4 )2 CO3 ; acid concentration of feed solution: 0.1 M HCl; Cr2 O7 − concentration of feed solution: 100 mg/L; phase ratio: 3/5; treatment ratio: 250/48).
sions formed with NaOH and Na2 CO3 stripping solutions were instable to the end of process time and therefore extraction efficiencies also decreased. On the other hand, stability of emulsion containing (NH4 )2 CO3 stripping solution was protected during process time and the highest extraction efficiency was obtained with this stripping solution.
3.6. Effect of mixing speed in feed solution
3.5. Effect of concentration of stripping solution The effect of (NH4 )2 CO3 concentration in the stripping solution on the extraction efficiency of Cr (VI) was also investigated in the range of 0.1–1 M and the results was shown in Fig. 5. From Fig. 5, it was found that maximum extraction of Cr (VI) occurred at 0.5 M (NH4 )2 CO3 concentration. In addition from Fig. 5, it can be seen that there was very slight increase in extraction rates with an increase of stripping solution concentration from 0.1 to 0.5 M. But above this concentration, emulsion was unstable due to interaction of stripping solution with surfactant and hence the extraction efficiency also decreased.
Fig. 5. Effect of concentration of stripping solution on the extraction rate of Cr (ECA 4360J: 6%; TOPO: 3%; kerosene: 91%; acid concentration of feed solution: 0.1 M HCl; Cr2 O7 − concentration of feed solution: 100 mg/L; mixing speed of feed solution: 250 rpm; phase ratio: 3/5; treatment ratio: 250/48).
The effect of mixing speed in the multicomponent acidic solutions was studied in the range of 200–350 rpm in order to obtain optimal mixing speed that allows effective extraction of Cr (VI) in emulsion liquid membrane process. The effect of mixing speed on the rate of extraction was shown in Fig. 6. Within the first 2 min, as seen from Fig. 6, the extraction efficiency of Cr (VI) increased with increasing of mixing speed. But after this minute, extraction efficiency decreased at mixing speed of 350 rpm and the highest extraction efficiency at the end of tenth minute was obtained with mixing speed of 325 rpm. According to Hirato et al. [16], by increasing the mixing speed, the size of the emulsion globule dispersed in the external phase decreases, and as a result the extraction rate increases. At the same time, the rate of the breakdown of the emulsion increases. Therefore, at speeds above 325 rpm, leakage of chromium (VI) might be started due to shearing of emulsion, which ultimately resulted in a gradual depletion in extraction and stripping. Thus, as the highest extraction efficiency at the end of tenth minute was obtained with mixing speed of 325 rpm, this speed was accepted as the best speed.
Fig. 7. Effect of extractant concentration on the extraction rate of Cr (ECA 4360J: 6%; kerosene: 88–92%; stripping solution: 18 mL 0.5 M (NH4 )2 CO3 ; acid concentration of feed solution: 0.1 M HCl; Cr2 O7 − concentration of feed solution: 100 mg/L; mixing speed of feed solution: 250 rpm; phase ratio: 3/5; treatment ratio: 250/48).
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Fig. 8. Effect of surfactant concentration on the extraction rate of Cr (TOPO: 3%; kerosene: 91–96%; stripping solution: 18 mL 0.5 M (NH4 )2 CO3 ; acid concentration of feed solution: 0.1 M HCl; Cr2 O7 − concentration of feed solution: 100 mg/L; mixing speed of feed solution: 250 rpm; phase ratio: 3/5; treatment ratio: 250/48).
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Fig. 9. Effect of phase ratio on the extraction rate of Cr (ECA 4360J: 6%; TOPO: 3%; kerosene: 91%; stripping solution: 18 mL 0.5 M (NH4 )2 CO3 ; acid concentration of feed solution: 0.1 M HCl; Cr2 O7 − concentration of feed solution: 100 mg/L; mixing speed of feed solution: 250 rpm; treatment ratio: 250/48). Table 1 Optimum conditions.
3.7. Effect of extractant concentration Extractant concentration in the membrane phase plays a vital role in the overall extraction behaviour of ELM systems. To study this effect, the extractant concentration in the ELMs was varied in the range of 2–6% in the membrane phase. The results obtained were shown in Fig. 7. It can be seen that an increase in extractant concentration from 2% to 6% leads to an increase in extraction efficiency. But after sixth minute, with increasing of extractant concentration from 4% to 6% does not show significant change in the extraction efficiency of chromium (VI). It is due to the access of free extractant in membrane phase. Under the present extractant concentration, the free extractant is considered to be enough for forward extraction. Further increase in the extractant concentration leads to the decrease in the stripping reaction rate. This is because the chromium (VI) remains in the complex form (in the membrane phase) without getting stripped which in its turn affected the final recovery by the emulsion liquid membrane process. Similar results were obtained by Othman et al. [17]. Therefore, extractant concentration of 4% was considered to be sufficed for Cr (VI) extraction and was accepted as the best extractant concentration.
Parameter
Value
Surfactant (ECA 4360J) Extractant (TOPO) Diluent (kerosene) Type and concentration of the stripping solution Cr (IV) concentration in the feed solution Acid type and concentration of the feed solution Mixing speed Phase ratio Treatment ratio
2% 4% 92% 18 mL 0.5 M (NH4 )2 CO3 100–500 mg/L 0.5 M HCl 325 rpm 3/5 250/48
3.9. Effect of phase ratio The effect of the phase ratio (the stripping phase/membrance phase, Vs/Vm) on the extraction rate, by maintaining membrane volume constant, is depicted in Fig. 9. As seen in Fig. 9, emulsions formed in the ratios of 4/5 and 5/5 were not stable during 10 min; therefore the extraction efficiencies obtained with the ratios of 4/5 and 5/5 were lower. For the volume ratios of 2/5 and 3/5, the extraction rate increased with increasing ratio of the stripping phase/membrance phase. Because, walls of membrane globules formed with the volume ratio of 3/5 are thinner than that of 2/5.
3.8. Effect of surfactant concentration Influence of surfactant concentration in the membrane phase of the emulsion on the extraction rates was investigated at five ECA 4360J concentration levels from 1% to 6%. Emulsion formed with 1% ECA 4360J was not stable during 10 min. Except for 1% ECA 4360J, decreasing the surfactant concentration from 6% to 2% resulted in only a slightly increase in the extraction efficiency of chromium (VI) as shown in Fig. 8. As ECA 4360J concentration increases, the decrease in the rates of extraction could be attributed to a number of possible factors caused by high interfacial occupancy of the surfactant that includes decrease in rate of Cr (VI) complexation at the membrane phase–feed phase interface, increase in interfacial viscosity and decrease in movement of inner droplets within the emulsion globule and so on [18]. With 1 wt% ECA 4360J, although the extraction rate was higher than in the other cases in the first 2 min, the emulsion was less stable under the experimental conditions. Thus, 2% ECA 4360J was selected as the best surfactant concentration.
Fig. 10. Effect of chromium (VI) concentration on the extraction rate of chromium (VI) at optimum condition.
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Table 2 Experimental results in the optimum conditions. Initial concentration in the feed solution
500 mg/L Cr (VI) 1000 mg/L Co 1000 mg/L Ni 1000 mg/L Cd 1000 mg/L Zn 1000 mg/L Cu
Separation factors, ˇij
Extraction (%) 2 min
4 min
6 min
10 min
2 min
4 min
6 min
10 min
84.0 0.5 0.3 1.0 1.5 0.5
97.0 0.8 0.5 2.0 3.0 0.9
99.0 1.1 0.7 5.0 7.0 1.5
99.0 1.5 1.0 12.0 17.1 1.8
– 169 280 84 56 168
– 121 194 48 32 107
– 90 141 20 14 66
– 66 99 8 6 55
Consequently, the best extraction efficiency was obtained with the volume ratio of 3/5. Therefore, the volume ratio of 3/5 was selected as the best volume ratio.
percentages of extraction of metal ions during 10 min were shown in Table 2. 3.12. Membrane selectivity
3.10. Effect of Cr (VI) concentration on the extraction rate of chromium (VI) at the optimum conditions The effect of initial Cr (VI) concentration on the extraction efficiency of chromium (VI) at the optimum conditions (Table 1) was shown in Fig. 10. The chromium (VI) concentration in the multicomponent acidic solution was varied from 100 to 500 mg/L. The results showed that it was possible to extract 99% of chromium (VI) after contact time of 10 min. As can be seen from Fig. 10, the concentration of chromium (VI) in the multicomponent acidic solutions containing 100, 300, and 500 mg/L Cr (VI) at the optimum conditions was reduced to 1.0 mg/L within 10 min. On the other hand, concentration of chromium (VI) in the stripping solutions increased from zero to 1368, 4136, and 6862 mg/L within 10 min, respectively.
The separation factors ˇij of chromium (VI) with respect to the other ions that exist in the solutions are given in Table 2. The separation factor ˇij is given as follows: ˇij =
(Ci /Cj )strip (Ci /Cj )feed,o
(4)
where Ci and Cj are the concentrations of i and j components in the stripping and initial feed solutions. At the end of one experiment, in 10 min, liquid membrane selectivity of chromium (VI) with respect to cobalt, nickel and copper ions are high. The separation factors for chromium (VI) are shown in Table 2. As seen in Table 2, the separation factors in tenth minute compared reasonably well, except for zinc and cadmium. 4. Conclusions
3.11. Extraction of chromium (VI) and other ions at optimum conditions The effect of optimum conditions (Table 1) on the extraction efficiencies of chromium (VI) and other ions from the multicomponent acidic solution was shown in Fig. 11. From Fig. 11, it was observed that 99% extraction of chromium (VI) was achieved within 10 min, and the emulsion stability was also maintained during this period. Again, as seen from Fig. 11, the concentrations of copper, cobalt, and nickel ions during 10 min and of zinc and cadmium ions in the first 4 min almost remain fairly steady. But after the fourth minute, due to the decreasing of chromium (VI) concentration in the feed solution, cadmium and zinc were extracted into the stripping solution at the highest ratio, as compared to the other metal ions. The
An ELM process using TOPO to extract chromium (VI) from the multicomponent acid solution has been investigated. From this study the following conclusions can be drawn: 1. The optimum conditions were determined experimentally as stated above. 2. At the optimum conditions, at fourth minute, chromium (VI) was extracted with an extraction efficiency of about 97%. The liquid membrane selectivity was higher within the first 4 min. But after the fourth minute, due to the decreasing of chromium (VI) concentration in the feed solution, cadmium and zinc were extracted into the stripping solution at the highest ratio, as compared to the other metal ions. 3. The experimental results obtained showed the validity of the ELM method. 4. Cr (VI) concentration could be increased about 13 times in one stage, and using more stages the concentration of Cr (VI) could be further improved. 5. The reduced of solvent amount required for selective separation and concentration of toxic chromium metal, account for the promising performance of this technology in practical applications. Acknowledgements The author wish to express his sincere gratitude to the State Planning Organization of Turkiye (DPT), that supported this work, and Mehmet Yilmaz, coordinator of BAPK in Sakarya University. References
Fig. 11. Extraction of chromium (VI) and other ions at optimum condition.
[1] A. Zouhri, B. Ernst, M. Burgard, Bulk liquid membrane for the recovery of chromium(VI) from a hydrochloric acid medium using dicyclohexano-18crown-6 as extractant-carrier, Sep. Sci. Technol. 34 (1999) 1891–1905.
R. Ali Kumbasar / Journal of Hazardous Materials 167 (2009) 1141–1147 [2] T.-C. Huang, C.-C. Huang, D.-H. Chen, Thermodynamic equilibria of the extraction of chromium(vi) with tri-n-octylphosphine oxide from aqueous solutions, Solv. Extr. Ion Exch. 15 (1997) 837–862. [3] C. Basualto, M. Poblete, J. Marchese, A. Ochoa, A. Acosta, J. Sapaga, F. Valenzuela, Extraction of cadmium from aqueous solutions by emulsion liquid membranes using a stirred transfer cell contactor, J. Braz. Chem. Soc. 17 (2006) 1347–1354. [4] P.R. Danesi, Separation of metal species by supported liquid membranes, Sep. Sci. Technol. 19 (1984) 857–909. [5] P.R. Danesi, C. Clanetti, Permeation of metal ions through a series of two complementary supported liquid membranes, J. Membr. Sci. 20 (1984) 201– 213. [6] N.N. Li, Separating hydrocarbons with liquid membranes, U.S. Patent 3,410,794 (1968). [7] N.N. Li, R.P. Chan, A.L. Shrier, Liquid membrane process fort the separation of aqueous mixtures, U.S. Patent 3,779,907 (1973). [8] N. Alizadeh, S. Salimi, A. Jabbari, Transport study of palladium through a bulk liquid membrane using hexadecylpyridinium as carrier, Sep. Purif. Technol. 28 (2002) 173–180. [9] P. Kulkarni, Recovery of uranium(VI) from acidic wastes using tri-noctylphosphine oxide and sodium carbonate based liquid membranes, Chem. Eng. J. 92 (2003) 209–214. [10] P. Pal, S. Datta, P. Bhattacharya, Multi-enzyme immobilization in eco-friendly emulsion liquid membrane reactor—a new approach to membrane formulation, Sep. Purif. Technol. 27 (2002) 145–154.
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[11] J.B. Wright, D.N. Nilsen, G. Hundley, G.J. Galvan, Field test of liquid emulsion membrane technique for copper recovery from mine solutions, Miner. Eng. 8 (1995) 549–556. [12] T.-C. Huang, C.-C. Huang, D.-H. Chen, Extraction equilibria of chromium(vi) from sulfuric acid solutions with tri-n-octylphosphine oxide, J. Chem. Technol. Biotechnol. 73 (1998) 43–53. [13] A. Bhowal, S. Datta, Studies on transport mechanism of Cr(VI) extraction from an acidic solutions using liquid surfactant membranes, J. Membr. Sci. 188 (2001) 1–8. [14] C.F. Baes Jr., R.E. Mesmer, The Hydrolysis of Cations, Wiley-Inter-science, New York, 1976. [15] J. Strzelbicki, W.A. Charewicz, A. Mackiewicz, Permeation of chromium(VI) and rhenium(VII) oxyanions through liquid organic membranes facilitated by quaternary ammonium chlorides, Sep. Sci. Technol. 19 (1984) 321–336. [16] T. Hirato, I. Kishigami, Y. Awakura, H. Majima, Concentration of uranyl sulfate solution by an emulsion-type liquid membrane process, Hydrometallurgy 26 (1991) 19–33. [17] N. Othman, H. Mat, M. Goto, Separation of silver from photographic wastes by emulsion liquid membrane system, J. Membr. Sci. 282 (2006) 171–177. [18] L. Yang, Y. Zhang, Z. Guo, X. Gao, H. Takeuchi, Uranium(VI) extraction by liquid surfactant membrane with N-alkylcaprolactams as a carrier, Sep. Purif. Technol. 47 (2005) 88–94.