Adsorption Equilibrium of Zinc from Aqueous Sulfate Solution by

Adsorption equilibrium of zinc ions from aqueous sulfate solution on Amberlite XAD-2 resins impregnated with extractant Cyanex 272 as adsorbent has be...
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Ind. Eng. Chem. Res. 2005, 44, 4771-4777

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Adsorption Equilibrium of Zinc from Aqueous Sulfate Solution by Solvent-Impregnated Resins Containing Cyanex 272 Ching-Yeh Shiau,*,† Cheng-Long Lin,‡ and Hung-Szu Chang† Department of Chemical Engineering, National Taiwan University of Science & Technology, Taipei, Taiwan, R.O.C., and Department of Chemical Engineering, Northern Taiwan Institute of Science & Technology, Taipei, Taiwan, R.O.C.

Adsorption equilibrium of zinc ions from aqueous sulfate solution on Amberlite XAD-2 resins impregnated with extractant Cyanex 272 as adsorbent has been studied. The effect of parameters such as modifier addition, solution pH, ionic strength, and temperature on the sorption equilibrium was examined by batch experiments. The activity coefficient of various species in the aqueous solution was evaluated by employing Bromley and Pitzer equations for the strong electrolyte solutions. The adsorption was also conducted in a column operation. The loaded Zn in the column can be completely and rapidly recovered by stripping with 1.0 M HNO3. Introduction Because of stringent regulation of metal ions in the discharge solution, selective separation and recovery of metal ions from aqueous solutions have become steps of great importance for the industries. Solvent extraction and ion exchange are widely used in metal separation from a dilute aqueous solution. The solvent extraction process requires great mixing to provide large contact surface for extraction and settling for separation. The main drawback of this process is attributed to the loss of extractant into the aqueous solution. In comparison to solvent extraction, ion exchange is much simpler. However, its low selectivity to metal ions, low absorption rate, and high cost of the resin are its main problem.1,2 To bridge the gap between solvent extraction and ion exchange, the idea of resin impregnation with extractant was developed. Because of high surface area-tovolume ratio, this solvent-impregnated resin (SIR) is efficient and selective in removing metal ions from aqueoussolution.3,4 Amongmanysubstances,macroporous resins have been considered as one of the most useful adsorbents for organic extractants since they have good physical strength and high surface-to-volume ratio. Furthermore, the impregnated extractant would exhibit strong affinity to the polymeric matrix and could behave as in the liquid state.5-17 Bis(2,4,4-trimethylpentyl)phosphinic acid, Cyanex 272, developed by American Cyanide Company is an acidic organophosphorus extractant and can effectively extract the first-row transition metals such as iron, zinc, copper, cobalt, cadmium, and vanadium.17 Either solvent extraction or SIR process has been extensively reported by using Cyanex 272 as an extractant.13-17 Several batch equilibrium studies have been done for the adsorption of metal ions on the impregnated resins related to the determination of the resin capacity, extractant percentages as a function of pH, and the elution conditions. Only a few fundamental studies5,7,15 * To whom correspondence should be addressed. Fax: 8862-2737-6644. E-mail: [email protected]. † National Taiwan University of Science & Technology. ‡ Kun-Wu Institute of Technology.

have been done for the adsorption of metal ions with impregnated resin tending to explain the adsorption process in terms of chemical reactions and equilibrium constants and to use the activity concept for the electrolyte aqueous phase. In this paper, the sorption equilibrium of zinc from aqueous sulfate solution with Cyanex 272-SIR was studied in either batch or continuous operation. The effects of metal concentration, ionic strength, pH of the aqueous solution, the extractant concentration in the resin phase, and the temperature were considered. The thermodynamic data for the system were calculated by considering the activity coefficient based on Bromley and Pitzer equations of electrolyte solutions and compared with those obtained by the conventional methods. Copper adsorption with Cyanex 272-SIR was also included for comparison. Experimental Procedures Reagents. The commercial extractant Cyanex 272 was kindly provided by Cytec Company (West Paterson, NJ) and used as supplied. The hydrophobic macroporous resin Amberlite XAD-2 (Rohm & Haas Co., Philadelphia, PA) has a specific area of 330-350 m/g and a particle size of 0.3-0.9 mm. Before impregnation, the XAD-2 resin was first washed with acetone followed by n-hexane to remove any contaminants and dried at 50 °C in a vacuum for 2 h. In the aqueous phase, the total sulfate content was kept constant at 0.5 M and the initial concentration of metal ion was 1.58 × 10-3 mol/dm3, unless otherwise specified. The initial pH value of the solution varied from 3.0 to 6.0. In the SIR phase, the initial concentration of monomeric Cyanex 272 was varied from 0.2 to 1.0 mol/kg of SIR. Preparation of the SIR. The Cyanex 272-impregnated resins were prepared using the method described by Juang and Su.7 First, the impregnating solution was prepared by dissolving Cyanex 272 (0.1-0.8 g) into a precalculated amount of n-hexane (2 cm3). The resulting n-hexane solution was contacted with fresh resin (1-5 g) until all the organic solution was absorbed by the resin. Generally, this step was accomplished within 12 h in a drying oven at 60 °C. The resin was finally dried at 50 °C in a vacuum for 2 h to completely remove the

10.1021/ie049252p CCC: $30.25 © 2005 American Chemical Society Published on Web 05/17/2005

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solvent and was ready for application. During the impregnation process, 2-butoxyethanol was added into organic solution as modifier for the SIR. Batch Operation. In the batch operation, the SIR (0.4 g) and aqueous zinc or copper solution (40 mL) were placed in a 125-mL glass-stoppered flask and shaken at 110 rpm for at least 24 h using a thermostated shaker. Preliminary experiments had shown that the adsorption was complete after 12 h. After standing for 1 h, the aqueous phase was separated from the SIR and its equilibrium pH was then measured with a pH meter. The concentration of metals in the aqueous phase was determined with an atomic absorption spectrometer (model Varian Spectra AA-20) at an appropriate wavelength. The contents of both metal-adsorbed and unreacted Cyanex 272 in SIR were calculated from a mass balance. The ionic strength was adjusted with sulfuric acid. Continuous Operation. For the continuous operation, 10 g of SIR was packed into a glass tube with an internal diameter of 0.85 cm. The column was prewetted with deionized water. The sulfate solution containing Zn ions was fed from the top of the column by a peristaltic pump at a constant flow rate. The eluted solution was collected at appropriate time intervals, and the metal contents were analyzed by the method described above. Desorption operation of the column was conducted by feeding nitric acid into the column at a flow rate of 1 mL/min. The eluent was analyzed for the metal content.

When eqs 2 and 4 are combined, this gives

log(D[H+]2) ) log RK +

D ) Qe/Ce

Zn

+

+ [(n + 2)/2](HR)2 T ZnR2(HR)n + 2H

(1)

In this study it is assumed that the mechanism of zinc sorption on the SIR with Cyanex 272 is the same as that of the solvent extraction, provided that the extractant is not chemically bonded to the polymeric matrix.5,13 Therefore, the equilibrium constant K, can be expressed as

K)

[ZnR2(HR)n][H+]2 [Zn2+][(HR)2](n+2)/2

(2)

The overbar denotes the species in the SIR phase. In the aqueous sulfate solution, the following equilibrium is held:

Zn2+ + SO42-

β

ZnSO4

(3)

Assuming R is the free zinc fraction in the aqueous phase, that is, R ) [Zn2+]/[Zn]total in soluton, then the R value is given by

R ) 1/{1 + β[SO42-]}

(4)

(6)

If activity concept for the aqueous sulfate solution is adopted, eq 5 becomes

(

)

D[H+]2(γH+)2 (n + 2) log[(HR)2] (7) ) log RK + log γZn2+ 2 It should be noted that the activity coefficients of various species in the SIR phase are assumed to be constant, since they are difficult to experimentally measure or theoretically estimate.19 The value of (γH+)2/γZn2+ can be calculated by the following three methods. (1) Concentration method. This method considers γH+ and γZn2+ as one. This treatment is not theoretically correct but is frequently adopted by most investigators. The value of K obtained is a conditional constant and will change with the aqueous composition. (2) Bromley method. The values of γH+ and γZn2+ are estimated by Bromley equations.20 The equation for cation M in the mixed electrolyte solution is expressed by

[

Theoretical

2+

(5)

where D is defined as

log γM ) For the batch operation, a great number of investigations have studied solvent extraction of divalent metal ions from sulfate solutions with Cyanex 272. It was reported that Cyanex 272 could extract zinc ions in the aqueous phase according to the following relations:

(n + 2) log[(HR)2] 2

AγzM2I1/2

(1 + I1/2)

]∑

BMAZMA2mA

(8)

(3) Pitzer method. The values of γH+ and γZn2+ are estimated by Pitzer equations.21-24 Here, two mixing coefficients of two ions of the same sign and that of three ions including an ion of the opposite sign are omitted in our calculation because of the lack of literature data.

ln γM ) zM2F +

∑mA(2βMA + zCMA) + zM∑∑mMmACMA

(9)

For both Bromley and Pitzer methods, the estimation of their parameters used to calculate activity coefficient of various species are given in the appendix. Results and Discussion Preparation of SIR. (1) Extractant Content on the Resin. Figure 1 shows the effect of the amount of extractant in impregnating solution on the extractant content in SIR (either in mol/kg of resin or in mol/kg of SIR). It can be seen that the content of Cyanex 272 increases linearly with increasing solution concentration. The amount of extractant transferred from organic solution to the resin phase was found to be near 100% for all the impregnations under the experimental ranges studied. Although the content of extractant in the SIR can be as high as 1.0 mol/kg of SIR, the resulting SIR will become adhesive even after evaporation of the diluent when the content exceeds 0.9 mol/kg of SIR for Cyanex 272. Therefore, the adsorbent with content less than 0.8 mol/kg of SIR was used. (2) Effect of Modifier Addition on the Adsorption. During the impregnation process, 2-butoxyethanol was added into organic solution as modifier for the SIR. The purpose of this addition is to improve SIR hydro-

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Figure 1. Effect of Cyanex 272 concentration in impregnating solution on content of Cyanex 272 on a fresh resin and SIR basis. Figure 3. The equilibrium data obtained at different zinc concentration at 25 °C. pH0 ) 5, [HR]0 ) 0.6 mol/kg-SIR, and [SO42-] ) 0.5 M.

Figure 2. Effect of modifier content on distribution ratio of zinc at 25 °C. pH0 ) 5, [Zn]0 ) 0.765 × 10-4 mol/dm3, [HR]0 ) 0.6 mol/ kg-SIR, and [SO42-] ) 0.5 M.

philic character, an important factor for the adsorption of metal ions from aqueous solution. The effect of modifier content in the resin on the distribution ratio of zinc is illustrated in Figure 2. The figure shows that the distribution ratio was proportional to the modifier content in the resin to an amount about 0.3 mL/g of SIR for both metal ions. The distribution ratio no longer increased with the modifier content beyond this amount. This indicates that proper addition of modifier into the resin can significantly increase the SIR adsorption capability. Consequently, all SIRs used in this work contain modifier with an amount of 0.3 mL/g of SIR. Adsorption Equilibrium Study. Figure 3 shows the equilibrium data obtained at different zinc concentration. The linearized plot of Ce/Qe versus Ce of this figure obeys Langmuir adsorption isotherm for the SIR, indicating that the adsorption of zinc is monolayer. For the case of the impregnation ratio of 0.6 mol Cyanex 272/ kg of SIR, the maximum uptake of zinc was about 0.09 mol/g of SIR. Effect of pH on the Adsorption Equilibrium. Figure 4 shows the influence of final pH on the removal of zinc with Cyanex 272-SIR. Adsorption of copper is also included for comparison. The initial pH varied from 1.5 to 6.5. This figure indicates that the adsorption is

Figure 4. Effect of pH on removal of zinc and copper at 25 °C. [Zn]0 ) [Cu]0 ) 0.765 × 10-4 mol/dm3, [HR]0 ) 0.6 mol/kg-SIR, and [SO42-] ) 0.5 M.

quite limited when the final pH is below 2.0 for zinc and 4.0 for copper. Beyond that, the adsorption increases fast, especially for zinc. Apparently, the zinc adsorption is much better than the copper adsorption under the conditions used in this study. Thus, the present Cyanex 272-SIR has a viability of continuous separation of zinc and copper from their dilute sulfate solution. This will be demonstrated in column operation in the following section. Effect of Aqueous Ionic Strength on the Adsorption Equilibrium. Because of the strong electrolyte nature of the sulfate solution, the activity coefficients (γH+ and γZn2+) may deviate significantly from one. For instance, the activity coefficients calculated by the Bromley method are from 0.75 to 0.65 and from 0.29 to 0.15 for γH+ and γZn2+, respectively, when the sulfate content varies from 0.1 to 0.7 M. Hence, eq 10 must be used for the adsorption equilibrium calculation. Figure 5 shows the effect of aqueous ionic strength (total sulfate content) on the sorption equilibrium of zinc. Apparently, the total content of sulfate ions in the solution significantly affects the zinc adsorption onto SIR. The stronger

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Figure 6. Effect of Cyanex 272 content on the distribution ratio of zinc at 25 °C. [Zn]0 ) 0.765 × 10-4 mol/dm3, [SO42-] ) 0.5 M, and pH0 ) 1.0-7.0. Figure 5. Effect of aqueous ionic strength on the distribution ratio of zinc at 25 °C. pH0 ) 5, [Zn]0 ) 0.765 × 10-3 mol/dm3, and [HR]0 ) 0.6 mol/kg-SIR. Table 1. Logarithm Values of Equilibrium Constant for Zinc Adsorption with Cyanex 272-SIR Calculated by Various Methods at 25 °C [SO42-] (mol/dm3)

stoichiometric

Bromley

Pitzer

0.10 0.30 0.50 0.70

-1.72 -1.81 -1.92 -2.03

-1.52 -1.49 -1.50 -1.54

-1.49 -1.53 -1.57 -1.63

ionic strength in the solution, the lower zinc adsorption will be. It should be noted that the activity coefficients used in Figure 5 were calculated by the Bromley method. The equilibrium constant K for such strong electrolyte solution can be rewritten as

K)

[ZnR2(HR)n][H+]2(γH+)2 [Zn2+](γZn2+)[(HR)2](n+2)/2

(10)

Table 1 lists the K values calculated by various methods described in the theoretical section. As can be seen from Table 1, unique thermodynamic equilibrium constants of log K ) -1.51 could be obtained at 25 °C over the aqueous ionic strength ranges studied if the activity correction by Bromley method was made. Apparently, the Bromley method is considered to be more suitable for the calculation of activity coefficients of the aqueous sulfate solution used in this study. On the other hand, the Pitzer method and the concentration method show a monotonic increase and a relatively high deviation in log K for different aqueous ionic strengths. Hence, the Bromley method will be adopted for all activity coefficient calculations. Effect of Cyanex 272 Content on the Adsorption Equilibrium. Figure 6 is a plot of log(D[H+]2(γH+)2/ γZn2+) versus log[(HR)2]. The figure shows that all data points lie on straight lines with a slope of 2.09 as expected from eq 7 except that the Cyanex 272 content is less than 0.7 mol/kg of SIR. These exceptions are mainly due to the extractant loss from SIR.7 The value of n calculated from the slope equals to 2.18 which is close to 2 indicating that ZnR2(HR)2 is the predominant complex species in the resin phase. It is worthy to

Figure 7. Effect of operating temperature on the distribution ratio of zinc. pH0 ) 5, [Zn]0 ) 0.765 × 10-4 mol/dm3, [HR]0 ) 0.6 mol/kg-SIR, and [SO42-] ) 0.5 M.

note that according to eqs 3 and 4 the fraction of free dimer [(HR)2] present in the SIR phase at equilibrium is only about 35 to 60% of the total free extractant that exists in the SIR phase. Effect of Temperature on the Adsorption Equilibrium. Figure 7 shows the plots of the distribution ratio of zinc with 0.5 M H2SO4 over the temperature range 25-55 °C. It is shown that the distribution ratio increases with temperature, indicating that the adsorption of zinc was favored at higher temperature. The heat of adsorption (∆H) could be calculated from the temperature dependence of adsorption equilibrium constant, K, according to the van’t Hoff relation

d(log K)/d(l/T) ) -∆H/(2.303R)

(11)

A linear plot of log K against 1/T with a slope of ∆H/R is shown in Figure 8. In Figure 8, the apparent free energy, ∆G, is also plotted against T according to the following relations:

∆G ) -2.303RT log K

(12)

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Figure 10. Elution curves of zinc from the adsorption column loaded with zinc. Flow rate ) 1.0 dm3/min. Figure 8. van’t Hoff relations for adsorption reaction of zinc with Cyanex 272-SIR and plot of ∆G against T.

Figure 11. Breakthrough curve for a mixed solution of zinc and copper in column operation at 25 °C. pH0 ) 5, [Zn]0 ) [Cu]0 ) 0.765 × 10-4 mol/dm3, [HR]0 ) 0.6 mol/kg-SIR, and [SO42-] ) 0.5 M. Solid symbol, 10.0 cm3/min; open symbol, 1.0 cm3/min.

Figure 9. Breakthrough curves for a solution of zinc in column operation at 25 °C. pH0 ) 5, [Zn]0 ) 0.765 × 10-4 mol/dm3, [HR]0 ) 0.6 mol/kg-SIR, and [SO42-] ) 0.5 M.

The entropy change is calculated according to the following equation:

∆S ) (∆H - ∆G)/T

(13)

The value of ∆H determined from Figure 8 is 53.8 kJ/ mol. In general, the enthalpy change due to chemical adsorption is in the range of 40-120 kJ/mol. Hence, the adsorption of zinc on SIR is indeed due to chemical adsorption in the studied temperature ranges. The positive value of ∆H indicates the process is endothermic. The positive values of ∆G as shown in Figure 8 indicate that the equilibrium adsorption is a slow, nonspontaneous process. The mean value of ∆S calculated from eq 13 is about 136.9 J/mol‚K. Column Operation. The column adsorption of Zn with Cyanex 272-impregnated XAD-2 was conducted using 50 ppm Zn(II) prepared in 0.5 M H2SO4 in a column with ID of 0.85 cm. Ten grams of the adsorbent was packed in the column. Figure 9 shows the breakthrough curves for different flow rates with cyclic operation. It is found that the metal concentration in

the effluent steadily increases and finally equals the feed concentration. As the flow rate increases, the breakthrough curve becomes steeper. For a higher flow rate (10.0 mL/min), no clear breakpoint appears, while for a lower flow rate (1.0 mL/min) a clear S-shape breakthrough curve with elapsed time was observed and the breakpoint is at about 800 mL. For the cyclic operation, the breakthrough curve for the second run is in good agreement with that for the first run. This indicates that the loss of Cyanex 272 from SIR is small enough to be ignored. Figure 10 shows the desorption curve of the zinc from the loaded column using different concentrations of HNO3 at a flow rate of 1 mL/min. A sharp elution curve with a short tail was obtained for each concentration case. The total amount of zinc eluted from the bed was very close to the value retained in the column. Almost all presorbed zinc loaded was recovered. Figure 11 illustrates the separation of zinc and copper from mixed metal ion solution through the column for the flow rates of 1.0 and 10.0 cm3/min. Copper ion in the feed was quickly discharged from the column, while zinc ion was eluted more slowly for both flow rate cases. Apparently, the separation of zinc from copper in dilute sulfate solution with proper initial pH can be achieved in the column packed with Cyanex 272-SIR. This figure

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also indicates that a lower flow rate might get more effective separation.

where

f(x) ) 2[1 - (1 + x) exp(-x)]/x2

[ (

Conclusion The sorption equilibrium of zinc ions from aqueous sulfate solution with Cyanex 272-impregnated resins was thermodynamically studied in the temperature range of 25-55 °C. The following results were obtained. 1. The impregnation of Cyanex on Amberlyte XAD2 was achieved to a content below 0.8 mol/kg of SIR. 2. The optimum concentration of modifier for the SIR is 0.3 mL/g of SIR. 3. The Bromley equation is suitable for activity coefficient calculation of strong electrolyte sulfate solution. The equilibrium constant thus calculated for Zn adsorption from strong electrolyte sulfate solution onto SIR was found to be log K ) -1.51. 4. The zinc complexes formed in the SIR phase include ZnR2(HR)2 and ZnR3(HR)2, and the predominant one is ZnR2(HR)2. 5. The distribution ratio was found to be affected by the operating temperature significantly. 6. The changes in enthalpy and in entropy for the sorption reactions of Zn with Cyanex 272-SIR are found to be 53.8 kJ/mol and 136.9 J/(mol‚K) when the activity correction by the Bromley method is employed. 7. In the column operation, zinc can be separated from copper in the mixed dilute sulfate solution and the loaded Zn in the column can be completely and rapidly recovered by stripping with 1.0 M HNO3. Appendix For the Bromley method, eq 8, BMX, ZMX, and I are given by

BMA )

[

]

(0.06 + 0.6BMA(0))|zMzA| (1 + 1.5I/|zMzA|)

2

ZMA ) (|zM| + |zA|)/2 I ) (1/2)

+ BMA(0) (A1) (A2)

∑(mizi2)

(A3)

and Aγ ) 0.511 (kg/mol)1/2 at 25 °C. In eqs A1-A3, A denotes anion, and sums over A cover all anions. BMA(0) is a constant characteristic of the single electrolyte MA and is taken from Bromley.20 For the Pitzer method, eq 9, F and z are given by

F ) -Aφ

[

]

I1/2 2 + ln(1 + bI1/2) + b (1 + bI1/2) mCmAβ′MA (A4)

()

∑∑

∑mi|zi|

z)

(A5)

and Aφ ) 0.391 (kg/mol)1/2 at 25 °C, and b ) 1.2. Throughout eqs 8, A4, and A5, M denotes cation. Sums over M and A cover all cations and anions, respectively. For 1-1, 1-2, and 2-1 electrolytes, βMX and β′MX are given by (0)

βMX ) βMX

+ βMX

(1)

f(x)

β′MX ) βMX(1) f′(x)/I

(A6) (A7)

f′(x) ) -2 1 - 1 + x +

)

2

]

x exp(-x) /x2 2

x ) RI1/2 (R ) 2.0.)

(A8) (A9) (A10)

For 2-2 electrolytes

βMX ) βMX(0) + βMX(1) f(p) + βMX(2) f(q)

(A11)

β′MX ) βMX(1) f′(p)/I + βMX(2) f′(q)/I

(A12)

p ) R1I1/2 (R1 ) 1.4)

(A13)

q ) R2I1/2 (R2 ) 12)

(A14)

where

and βMX(0), βMX(1), βMX(2), and CMA are constant characteristics of the single electrolyte MA, and their values are taken from Pitzer.24 In the calculation by Bromley and the simplified Pitzer methods, the first dissociation reaction of H2SO4 and Na2SO4 is assumed to be complete in the aqueous (Na, H, Zn)SO4 solution. Thus, this aqueous system can be described by the following set equations:

log(β10/β1) ) log[1/(γZn2+γSO42-)]

(A15)

log(β30/β3) ) log[γNaSO4-/(γNa+γSO42-)]

(A16)

where β10 and β30 are the values at zero ionic strength and are 126 and 11.5 at 25 °C, respectively.25 Since our system is a dilute solution, the molalities for all species are assumed to be equal to molarities. However, the molality of each species for the calculation of both methods must be known beforehand. In the aqueous (Na, H, Zn)SO4 solution, the first dissociation reaction of H2SO4 and Na2SO4 is assumed to be complete. Thus, this aqueous system can be described by the following set equations: (a) mass balances

m(Zn2+)0 ) mZn2+ + mZnSO4

(A17)

2m(Na+)0 ) mNa+ + mNaSO4-

(A18)

m(SO42-)0 ) mSO42- + mHSO4- + mNaSO4- + mZnSO4 (A19) (b) formation equilibria

β1 ) mZnSO4/(mZn2+γZn2+mSO42-γSO42-)

(A20)

β2 ) mHSO4-γHSO4-/(mH+γH+mSO42-γSO42-) (A21) β3 ) mNaSO4-γNaSO4-/(mNa+γNa+mSO42-γSO42-) (A22) where β1, β2, and β3 are the stability constants of ZnSO4, HSO4-, and NaSO4-, respectively. The thermodynamic value of β2 is 95.23 at 25 °C.23 The values of β1 and β3 at any ionic strength could be corrected by the following expressions:

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log(β10/β1) ) log[1/(γZn2+γSO42-)]

(A23)

log(β30/β3) ) log[γNaSO4-/(γNa+γSO42-)]

(A24)

where β10 and β30 are the values at zero ionic strength, and are 126 and 11.5 at 25 °C, respectively.24 The set of eqs A17-A24 with appropriate correlations for activity coefficient can be solved by a simple iteration procedure. Nomenclature Ce ) total zinc concentration in the aqueous solution, mol/ dm3 D ) distribution ratio of zinc, dm3/kg of SIR ∆G ) apparent free energy, kJ/mol HR ) monomeric form of Cyanex 272 (HR)2 ) dimeric form of Cyanex 272 ∆H ) enthalpy change for sorption reaction, kJ/mol Qe ) total zinc concentration in the SIR phase, mol/kg of SIR ∆S ) entropy, kJ/mol‚K K ) equilibrium constant defined in eq 2, (kg-SIR/mol)n/2 (mol/dm3) K′ ) dimerization constant of Cyanex 272, (dm3/mol) T ) temperature, °C [ ] ) molar concentration of species in the brackets, mol/ dm3 Greek Letters β ) equilibrium constant defined in eq 3, dm3/mol γ ) activity coefficient Subscripts org ) organic phase 0 ) initial e ) equilibrium state Superscript --

) SIR phase

Literature Cited (1) Flett, D. S. Resin impregnates: The current position. Chem. Ind. 1977, Aug 6, 641-646. (2) Tavlaride, L. L.; Bae, J. H.; Lee, C. K. Solvent extraction, membranes, and ion exchange in hydrometallurgical dilute metals separation. Sep. Sci. Technol. 1987, 22, 581-617. (3) Inoue, K.; Baba, Y.; Sakamoto, Y. Adsorption of Ni(II) and Co(II) from aqueous solutions on Levextrel resin containing acidic organophosphinic extractant and phosphorus-based chelating resins: comparative study on the selectivity of the resins. Sep. Sci. Technol. 1987, 22, 1349-1357. (4) Warshawsky, A. Extraction with solvent-impregnated resins. In Ion Exchange and Solvent Extraction; Marinsky, J. A., Marcus, Y., Eds.; Marcel-Dekker: New York, 1981; Vol. 8, Chapter 3, pp 229-310. (5) Akita, S.; Takeuchi, H. Sorption and separation of metals from aqueous solution by a macromolecular resin containing trin-octylamine. J. Chem. Eng. Jpn. 1990, 23, 439-443. (6) Shakir, K.; Aziz, N. L.; Beheir, Sh. G. Extraction of certain actinide and tanthanide elements from different acidic media by polyurethane foams loaded with di(2-ethylhexyl)phosphoric acid (HDEHP). I. Extraction of cerium(III) from acid perchlorate solutions of constant ionic strength by foams loaded with HDEHP in nitrobenzene. J. Radioanal. Nucl. Chem. 1991, 147, 297-308.

(7) Juang, R. S.; Su, J. Y. Sorption of copper and zinc from aqueous sulfate solutions with bis(2-ethylhexyl)phosphoric acidimpregnated macroporous resin. Ind. Eng. Chem. Res. 1992, 31, 2774-2779. (8) Korkisch, J.; Steffan, I. Separation of uranium on polyurethane foam impregnated with trioctylphosphine oxide. Solvent Extr. Ion Exch. 1993, 1, 607-617. (9) Cortina, J. L.; Miralles, N.; Sastre, A. M.; Aguilar, M. Solidliquid extraction studies of Zn(II), Cu(II) and Cd(II) from chloride media with impregnated resins containing mixtures of organophosphorus compounds immobilized on to Amberlite XAD2. Hydrometallurgy 1995, 37, 301-322. (10) Merdivan, M.; Zahir Du¨z, M. Sorption behaviour of uranium(VI) with N,N-dibutyl-N′-benzoylthiourea impregnated in Amberlite XAD-16. Talanta 2001, 55, 639-645. (11) Kabay, N.; Arda, M.; Saha, B.; Streat, M. Removal of Cr(VI) by solvent impregnated resin (SIR) containing aliquat 336. React. Funct. Polym.ers 2003, 54, 103-115. (12) Kabay, N.; Gizli, N.; Demircioglu, M.; Yuksel, M.; Saglam, M.; Arda, M.; Yuksel, M.; Saha, B.; Streat, M. Removal of Cadmium from phosphoric acid solvent by sorption kinetics and equilibrium studies. Chem. Eng. Commun. 2003, 190, 936-947. (13) Yoshizuka, K.; Sakomoto, Y.; Baba, Y.; Inoue, K. Distribution equilibria in the adsorption of cobalt(II) and nickel(II) on Levextrel resin containing Cyanex 272. Hydrometallurgy 1990, 23, 309-318. (14) Villaescusa, I.; Salvado, V.; De Pablo, J.; Valiente, M.; Aguilar, M. Liquid-solid extraction of gold(III) from aqueous chloride solutions by macroporous resins impregnated with triisobutyl phosphine sulfide (Cyanex 471). React. Polym. 1992, 17, 69-73. (15) Cortina, J. L.; Miralles, N.; Sastre, A. M.; Aguilar, M.; Profumo, A.; Pesavento, M. Solvent-impregnated resins containing di-(2,4,4-trimethylpentyl)phosphinic acid. II. Study of the distribution equilibria of Zn(II), Cu(II) and Cd(II). React. Polym. 1993, 21, 103-116. (16) Kabay, N.; Demircioglu, M.; Ekinci, H.; Yuksel, M.; Saglam, M.; Streat, M. Extraction of Cd(II) and Cu(II) from phosphoric acid solutions by solvent-impregnated resins (SIR) containing Cyanex 302. React. Funct. Polym. 1998, 38, 219-226. (17) Gonzalez, M. P.; Saucedo, I.; Navarro, R.; Avila, M.; Guibal, E. Selective separation of Fe(III), Cd(II), and NI(II) from dilute solutions using solvent-impregnated resins. Ind. Eng. Chem. Res. 2001, 40, 6004-6013. (18) Rickelton, W. A. Phosphine and Its Derivatives. KirkOthmer Encyclopedia of Chemical Technology, 4th ed.; John Wiley & Sons: New York, 1996; Vol. 18, pp 657-668. (19) Myers, A.; Byington, S. Thermodynamics of ion exchanger. Prediction of multicomponent equilibria from binary data. In Ion Exchange: Science and Technology; Rodrigues, A. E., Ed.; Martinus Nijhoff: Dordrecht,The Netherlands, 1986; pp 119-145. (20) Bromley, L A. Thermodynamic properties of strong electrolytes in aqueous solutions. AIChE J. 1973, 19, 313-320. (21) Pitzer, K. S.; Mayorga, G. Thermodynamics of electrolytes. II. Activity and osmotic coefficients for strong electrolytes with one or both ions univalent. J. Phys. Chem. 1973, 77, 2300-2308. (22) Pitzer, K. S.; Mayorga, G. Thermodynamics of electrolytes. III. Activity and osmotic coefficients for 2-2 electrolytes. J. Solution Chem. 1974, 3, 539-546. (23) Pitzer, K. S.; Mayorga, G. Thermodynamics of electrolytes. IV. Activity and osmotic coefficients for mixed electrolytes. J. Am. Chem. Soc. 1974, 96, 5701-5707. (24) Pitzer, K. S.; Roy, R. N.; Silvester, L. F. Thermodynamics of electrolytes. 7. Sulfuric acid. J. Am. Chem. Soc. 1977, 99, 49304936. (25) Morel, F. M. M. Principles of Aquatic Chemistry; WileyInterscience: New York, 1983; pp 242-249.

Received for review August 17, 2004 Revised manuscript received March 11, 2005 Accepted April 18, 2005 IE049252P