Extraction Mechanism for Copper(II) with 2-Hydroxy-4-n

In general, hydroxyoximes extract not only copper(II) but also nickel(II) and ... with LIX 65N, an aromatic β-hydroxyoxime developed for copper hydro...
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Ind. Eng. Chem. Res. 2002, 41, 5835-5841

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Extraction Mechanism for Copper(II) with 2-Hydroxy-4-n-octyloxybenzophenone Oxime Yoshinari Baba* Department of Applied Chemistry, Miyazaki University

Minako Iwakuma Department of Chemical Science and Engineering, Miyakonojo National College of Technology

Hideto Nagami Department of Chemical Science and Engineering, Osaka University

2-Hydroxy-4-n-octyloxybenzophenone oxime (HOBO) was recently synthesized to develop a selective extractant for copper(II). HOBO exhibited a high selectivity for only copper(II) over other base metals such as nickel(II) and cobalt(II) which are typically extracted with LIX series hydroxyoxime reagents in the high pH region from 1 M aqueous ammonium nitrate solution. This is due to the introduction of an alkoxyl group to the phenyl group of hydroxyoximes, which causes a lowering of the dissociation constant of phenol. Copper(II) was extracted as a 1:2 complex with HOBO ()HR) according to the following reaction: Cu2+ + 2HR S CuR2 + 2H +; Kex. The extraction equilibrium constant, Kex ) 1.1 × 10-1, was obtained at 303 K. The extraction rate of copper(II) was measured using a Lewis-type transfer cell at 303 K. The extraction reaction of copper(II) with HOBO is interpreted as an interfacial reaction where the elementary reaction step between the intermediate complex adsorbed at the interface and free extractant in the aqueous phase is rate-determining. The reason this step is rate-determining was inferred. Introduction The extraction of metal ions with chelating reagents has been used for hydrometallurgy processes and for the treatment of wastewater. Hydroxyoxime reagents (LIX series)1 have been utilized to separate copper(II) from the leaching solution of copper ore. In general, hydroxyoximes extract not only copper(II) but also nickel(II) and cobalt(II) in the high pH region. An extraction reagent having a higher selectivity for copper(II) even at the high pH region is required in the case of ammonia leach solutions.2 Therefore, we planned the introduction of an alkoxyl group having an electron donor property to the phenol group in hydroxyoximes. This extractant can be expected to selectively extract copper even in the high pH region because the introduction of the alkoxyl group causes a lowering of the pKa of the extractant. Since the pioneering work3 on the extraction kinetics of copper with LIX 65N, an aromatic β-hydroxyoxime developed for copper hydrometallurgy, the extraction rate mechanism of copper with hydroxyoximes has been a subject attracting the interest of many researchers in the field. Many researchers4 proposed the same rate expression, which is first order with respect to metal ion and monomeric species of the extraction reagent and inverse first order with respect to hydrogen ion. This is for the forward extraction rate of copper with anti-2hydroxy-5-nonylbenzophenone oxime (the active species of LIX 65N) and anti-2-hydroxy-5-octylacetophenone oxime, respectively. Their rate expressions are based on the interfacial reaction scheme where the elementary reaction step between the intermediate complex, CuR+, and the monomeric species of the hydroxyoxime at the

interface or in the organic phase is the rate-determining step. However, this reaction scheme is in conflict with Eigen’s mechanism5 of complex formation in the aqueous phase, in which the ligand substitution step (i.e., reagent molecule or anion replacing water molecules hydrated to the metal cation) is rate-determining. This can indeed give satisfactory and reasonable explanations for the rate of complex formation in the aqueous phase, with the extraction reagents commonly used in analytical chemistry which have rather high aqueous solubility and low interfacial activity. On the contrary, it cannot interpret the rate law observed in solvent extractions with commercial extracting reagents which have high interfacial activity and very low aqueous solubility. Hence, it is important to elucidate why the extraction rate with commercial hydroxyoxime extractants cannot be explained by Eigen’s mechanism or why the elementary reaction step to form the final complex, instead of the intermediate complex, is rate-determining in the interfacial reactions. We have proposed in this study that the attack of the extractant from the aqueous phase to the first order complexes adsorbed at the interface is the rate-determining step, because the attack from the aqueous phase to the first order complexes is natural judging from the viewpoint of the entropy, and also, the lower apparent extraction rate should be observed because the extractant concentration in the aqueous phase is very low. To clarify this problem, 2-hydroxy-4-n-octyloxybenzophenone oxime was synthesized to examine the selectivity and the extraction equilibrium for metal ions. In addition, the extraction mechanism of copper was elucidated by measuring the extraction rate.

10.1021/ie0106736 CCC: $22.00 © 2002 American Chemical Society Published on Web 10/03/2002

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Experimental Section (i) Reagents. 2-Hydroxy-4-octyloxybenzophenone oxime (HOBO) was synthesized from 2-hydroxy-4-noctyloxybenzophenone and hydroxylamine hydrochloride by a conventional method. The reaction mixture was evaporated, and the residue was dissolved in toluene and then was washed with 2 M hydrochloric acid. The crude hydroxyoxime dissolved in the ethanol was deposited as copper complexes by adding 0.1 M aqueous copper sulfate solution to separate the inactive syn-form. After the complex was filtered, the copper ion was stripped by 4 M sulfuric acid to obtain only anti-form oxime. Finally, the product was recrystallized by hexane. The final product was a light yellow powder. The identification of this product was carried out using IR and NMR spectra. The purity of HOBO was 98%. (ii) Distribution Equilibria of Metal Ions. The aqueous phase was prepared by dissolving metal nitrate into 1 M aqueous ammonium nitrate solution. The pH was adjusted by adding a small amount of nitric acid and ammonia. The organic phase was prepared by diluting with toluene gravimetrically. Selectivity and distribution equilibrium for metal ions were measured batchwise at 303 K for 24 h. The initial concentration of each metal was about 1 × 10-3 M. (iii) Aqueous Solubility of HOBO. The solubility of the extractant in the aqueous phase was indirectly determined by measuring the copper(II) concentration. This was based upon the complete complex formation of copper(II) with the extractant distributed to the aqueous phase under the appropriate condition. Toluene solutions of each extractant of known concentration and 1 M aqueous ammonium nitrate solution adjusted to each pH were shaken at 303 K for 24 h. An aqueous copper(II) solution of 5 mM was added to the aqueous phase, and then, toluene was added to make the complex distribute to the toluene phase containing the distributed HOBO. It was again shaken at 303 K for 24 h. The organic phase was finally shaken with 2 M sulfuric acid to strip copper(II) ion. The solubility of extractant in the aqueous phase was determined by measuring the copper(II) ion concentration taking into account the reaction mole ratio of the extractant and the copper and the volume ratio of both phases. (iv) Interfacial Tension. Interfacial tension between the extractant in toluene and the 1 M aqueous ammonium nitrate solution was measured at 303 K by the pendant-drop method to examine the interfacial adsorption equilibria of the extractant.6 (v) Extraction Rate. The extraction rate was measured using a stirred transfer cell.7 The aqueous and organic phases were stirred independently by twoblade stirrers in opposite directions with equal rotating speeds of 120 rpm, except for the measurement of the effect of stirring speed on the extraction rate. After introducing each phase into the cell, a small sample was taken at intervals from the organic phase, from which copper was stripped out with 2 M sulfuric acid to determine the copper concentration by atomic absorption analysis. Results and Discussion (i) Selectivity of Metal Ion with HOBO. Figure 1 shows the effect of pH on the percent extraction of metal ions with HOBO. HOBO exhibits a high selec-

Figure 1. Effect of pH on the extraction percent of metal ions with HOBO. [HR] ) 0.01 mol/dm3; CCuw ) 0.001 mol/dm3.

tivity for only copper(II) over the higher pH region compared with that of commercial hydroxyoxime reagents (LIX series) which also extract nickel and cobalt. This is attributable to the introduction of an alkoxyl group at the 4-position to the phenol group of hydroxyoximes. This high selectivity for copper in the high pH region suggests that HOBO can be utilized in the selective separation of copper from nickel and cobalt in ammonia leach liquors. (ii) Aqueous Solubility of HOBO. Because the organic compound having carboxyl groups or hydroxyl groups tends to form a dimeric species, the distribution of HOBO between the aqueous and organic phases can be described as follows: (1) dimerization of HOBO in the organic phase

2HR S (HR)2; Km

(1)

(2) physical partition of the monomer of HOBO into the aqueous phase

HR S HR; KD

(2)

(3) dissociation of the monomer of HOBO in the aqueous phase

HR S H+ + R-; Ka

(3)

where the overbar denotes the extractant in the organic phase. Total extractant concentrations in the aqueous phase, Caq, and organic phase, Corg, can be expressed by eqs 4 and 5, respectively, by considering eqs 1-3

Caq ) [HR] + [R-] ) KD[HR](1 + Ka/[H+ ])

(4)

Corg ) [HR] + 2[(HR)2] ) [HR] + 2Km[HR]2 (5) Figure 2 shows the relationship between the total extractant concentration, Caq, in the aqueous phase and pH for the various extractant concentrations in the organic phase, Corg. As seen from Figure 2, Caq depends only on Corg regardless of pH in the lower pH region. This suggests that the dissociation of the oxime in the aqueous phase can be ignored. On the other hand, we should note that Caq depends not only on Corg but also on the pH in the higher pH region where the dissocia-

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Figure 2. Effect of pH on the HOBO concentration in the aqueous phase. The solid lines are theoretical lines.

Table 1. The values of Ka, Km, and KD reported in the literature for LIX 65N and SME 529 are also listed in Table 1 for comparison. Although KD of HOBO is almost the same order as those reported for LIX 65N and SME 529, Km is greater than the values for LIX 65N in aromatic diluents and significantly less than LIX 65N and SME 529 values in aliphatic diluents. The Ka value of HOBO is two orders smaller than those of LIX 65N and SME 529. This is considered to be caused by an introduction of alkoxyl group at the 4-position of phenol. The solid lines in Figure 2 show the results calculated from eq 4 using the values evaluated by the method mentioned previously. The theoretical lines are in good agreement with the experimental results. (iii) Interfacial Tension. In Figure 4, the interfacial pressure, π, was plotted against the concentration of the extractant in the organic phase at each pH. The plots indicate a linear relationship in the high concentration region of extractant. This means that the interface is saturated with the extractant in the range of the linear relationship. The interfacial pressure in the pH region below 8 is independent of pH, indicating that the extractant species adsorbed at the interface is only HR in the pH region below 8; that is, R- is not adsorbed at the interface. Thus, the adsorption equilibrium of the extractant is considered as follows:

HR S HRad; Kad

(8)

where “ad” denotes the extractant species at the interface. Equation 9 was derived from the Langmuir equation and Gibb’s adsorption isotherm to relate the adsorption pressure with the concentration of extractant in the organic phase:4

π ) RT/SHR ln(1 + Kad[HR]) Figure 3. Relationship between the distribution ratio of HOBO and total HOBO concentration in the aqueous phase in the pH region of 4-6.

tion of the oxime in the aqueous phase is predominant. Thus, Caq can be approximated in the lower pH region as follows:

Caq ≈ [HR] ) KD[HR]

(6)

Equations 4-6 can be combined to give the following distribution ratio of the oxime:

D ) Corg/Caq ) 1/KD + 2(Km/KD2)Caq

(7)

Figure 3 shows a plot based on eq 7 for the experimental results in the lower pH region in Figure 2, where the ordinate, Caq, denotes the average value of Caq in this region. The plotted points in Figure 3 appear to lie on a straight line as expected from eq 7. From the intercept and slope of this straight line, the values of KD and Km were evaluated according to eq 7 (as shown in Table 1.) The value of Ka was evaluated by a nonlinear leastsquares method to give the minimum standard deviation between the experimental results in the higher pH region and the values calculated from eqs 4 and 5 for various presumed values of Ka using the values of Km and KD previously evaluated. The results are shown in

(9)

where SHR denotes the interfacial area occupied by a unit mole of the extractant. The values of Kad and SHR were evaluated by a nonlinear least-squares method as 4.2 × 10-6 m and 4.4 × 105 m2 mol-1, respectively. The theoretical lines based on eq 9 using these values were shown in Figure 4. The curves are in good agreement with the experimental points. (iv) Extraction Rate of Copper(II). The initial extraction rate, N, was calculated using the volume of the organic phase and contact area from the slope of the linear relation between the copper(II) concentration extracted in the organic phase and contact time. As mentioned earlier, HOBO exists not only as a monomeric species but also as a dimeric species in nonpolar diluents.7 Of these, only the monomeric species is interfacially active7 and takes part in the complex formation at the interface. Consequently, the initial extraction rate did not correlate with the total concentration but with the monomeric HOBO concentration as shown in Figure 5. The plotted points lie on a straight line of slope 1 in the range of low HOBO concentration and then asymptotically approach a constant value. Figure 6 shows the effect of copper concentration in the aqueous phase on the initial extraction rate. The points appear to lie on a straight line of slope 1. Figure 7 shows the effect of hydrogen ion concentration on the initial extraction rate. The points lie on a straight line with a slope of -1 at low pH while they

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Table 1. Various Equilibrium Constants in the Extraction of Copper with LIX 65N and SME 529 author

65Na

Kojima et al. Komasawa et al.

LIX LIX 65Nb

Akiba and Freiser

LIX 65Na

Inoue et al. this work a

c

extractant

SME 529b HOBOb

aqueous phase

diluent

Kex

Km [M-1]

Ka [M-1]

KD 10-4

10-9

literature

Na2SO4 pure water 1 M Na2SO4 pure water 1 M Na2SO4 1 M Na2SO4 0.1 M NaClO4

dispersol n-heptane n-heptane toluene toluene benzene n-hexane

2.27 56 4.9 0.95 0.063 0.044 20

11 120 120 3 3 2 126

1.1 × 1.1 × 10-4 1.3 × 10-4 1.4 × 10-5

1.1 × 3.0 × 10-9 3.0 × 10-9

12 9

3.5 × 10-4

2.0 × 10-9

11

22 7.2 0.55 0.83 1.7 0.63 19 0.11

126 32

1 M NH4NO3 1 M NH4NO3

n-heptane CCl4 CH2Cl2 CHCl3 C6H5Cl toluene MSB210c toluene

6.3 × 10-4 1.6 × 10-4 9.8 × 10-5 2.5 × 10-5 7.9 × 10-5 6.3 × 10-5 2.2 × 10-5 1.0 × 10-4

5.3 × 10-10 1.1 × 10-11

7

31 6.4

Unpurified reagent. b Purified reagent as

20% aromatic hydrocarbons.

constant value with increasing [HR]CCuw /[H+]. This result appears to be attributable to the diffusional contribution of HOBO or copper in the high range of [HR]CCuw/[H+]. The apparent extraction rate constant, k, was determined as 2.0 × 10-8 m s-1 from the intercept of a straight line of slope 1 in Figure 8. (v) Extraction Mechanism. The extraction equilibrium of copper with HOBO expressed by eq 11 is similar to that with hydroxyoximes as follows:12

Cu2+ + 2HR S CuR2 + 2H+; Kex

(11)

where the extraction equilibrium constant, Kex, has been determined in the present study as Kex ) 1.1 × 10-1 [-]. The various extraction mechanisms of copper with hydroxyoximes have been proposed until now.2,3,7,10,13-16 In this study, we propose the interfacial extraction mechanism of copper with HOBO as follows: Figure 4. Effect of the extraction concentration in the organic phase on the interfacial pressure. The solid lines are calculated from eq 9.

HR S HR; KD

(12)

also asymptotically approach a constant value as the hydrogen ion concentration decreases. From these experimental results, the initial extraction rate was expressed by eq 10 in the high concentration region of hydrogen ion.

HR S HRad; Kad

(13)

Cu2+ + HRad S CuRad+ + H+; K1

(14)

CuRad+ + HR 98 CuR2ad + H+

(15)

N0 ) k[HR]CCuw/[H+]

CuR2ad S CuR2

(16)

(10)

This is in good agreement with results observed in the extraction of copper with anti-2-hydroxy-5-nonylbenzophenone oxime8,9 and anti-2-hydroxy-5-nonylacetophenone oxime10 and in the extraction of nickel with LIX 65N.11 All the data are summarized as a plot of log N against log[HR]CCuw/[H+] in Figure 8. The plotted points appear to cluster on a single straight line of slope 1 as expected from eq 10 in the region where [HR]CCuw /[H+] is low, and they asymptotically approach a

k2

The intermediate complex, CuR+, is considered to be strongly orientated with the partially hydrated copper ion pointing toward the aqueous phase. Hence, the second extractant is probably not the monomeric HOBO molecules in the organic phase or at the interface but those in the aqueous phase that attack the intermediate complex at the interface to form the final chelate by judging from the steric viewpoint. Furthermore, the reaction rate of this elementary reaction step is considered to be very slow owing to the low partition coefficient of monomeric HOBO to the aqueous phase. On the other

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Figure 5. Effect of the extractant concentration in the organic phase on the extraction rate of Cu(II) with HOBO. pH ) 4.20; CCuw ) 0.001 mol/dm3.

Figure 7. Effect of hydrogen ion concentration on the extraction rate of Cu(II) with HOBO. pH ) 4.20, CCuw ) 0.001mol/dm3.

Figure 8. Relationship between extraction rate and [HR] CCuw/ [H+]. Figure 6. Effect of copper concentration on the extraction rate of Cu(II) with HOBO. pH ) 4.20; [HR] ) 0.01 mol/dm3.

hand, the reaction rate of the preceding step described by eq 14 is considered to be rapid because one of the reacting species, HOBO, exists in high concentration in the adsorbed layer at the interface. Here, the elementary reaction step expressed by eq 15 is the rate-determining, thus the forward reaction rate is expressed as

N ) k2KDθCuR+ [HR]

(17)

For the description of θCuR+ as a function of the concentration of the reaction species, three kinds of species should be taken into consideration as adsorbed species: monomeric HOBO, the intermediate complex, and the final complex. Of these, adsorption of the final complex may be ignored at the initial stage of extraction, and the intermediate complex is considered to be the most interfacially active because it contains both the hydrophobic part of the extractant molecule and several water molecules hydrated to copper ion. From the equilibrium relation of the elementary steps described by eqs 13 and 14, it is expressed as

θCuR+ )

K1KadCCuw[HR]/[H+] 1 + Kad[HR] + KadK1CCuw[HR]/[H+]

≈

K1CCuw/[H+] 1 + K1CCuw/[H+]

(18)

Equations 17 and 18 are combined to give eq 19:

[HR]CCuw/[H+] N0 ) k2K1KD 1 + K1CCuw/[H+]

(19)

The preceding equation can be approximated by eq 20 in the high pH region, where the interface is almost completely saturated with the intermediate complex and by eq 21 in the low pH region where it is almost completely saturated with the unreacted monomeric HOBO.

K1CCuw/[H+] . 1 N ) k2KD[HR]

(20)

[HR]CCuw K1CCuw/[H+] , 1 N ) k2K1KD [H+]

(21)

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Figure 9. Relationship between extraction rate and [HR] CCuw/ [H+].

Figure 11. Effect of Cu(II) ion concentration on the extraction rate at pH 7.0.

where subscripts b and i denote the species in the bulk phase and at the interface, respectively. kCu2+ is a mass transfer coefficient in the aqueous phase. In Figure 11, the initial extraction rate in this region was plotted against the copper concentration according to eq 22. The points in Figure 11 lie on a straight line with a slope of 1 as expected from eq 22. From the intercept of this straight line with the ordinate, the apparent mass transfer coefficient of copper, kCu2+, was determined as 3.2 × 10-4 [cm s-1]. It is considered that the value is proper as a mass transfer coefficient.17 As a result of the extraction rate, the extraction process may be described by two-step consecutive reactions of the diffusion of copper from the bulk phase to the interface and the complex formation at the interface. Consequently, the extraction rate of copper may be expressed as follows: Figure 10. Relationship between extraction rate and [HR] CCuw/ [H+].

In the low pH region, where K1CCuw /[H+] , 1, it is apparent that these can qualitatively explain the experimental results shown in Figure 8. The product of the forward reaction rate constant of the step of eq 15, k2, and the equilibrium constant of the step represented by eq 14, K1, was evaluated from the intercept of a straight line with a slope of 1 as follows: k2K1 ) 1.5 × 10-4 m s-1. On the other hand, the extraction rate seems to depend on only the extractant concentration in the high pH region, where K1CCuw/[H+] . 1 as expected by eq 20. To elucidate it, therefore, the effects of the extractant concentration and copper on the extraction rate were examined in this region. These results are shown in Figures 9 and 10, respectively. As seen from these figures, it was found that the extraction rate is not dependent on the extractant concentration but on the copper concentration. This result appears to be attributable to the diffusional contribution of copper ion in the aqueous phase resulting from enhancement of the complex formation rate at the interface in this region. Thus, the initial extraction rate could be expressed by eq 22 on the basis of the film theory

NCu2+ ) kCu2+(CCuwb - CCuwi) = kCu2+CCuwb (22)

N)

k2K1KD[HR]b CCuw/[H+]b 1+

(23)

k2K1KD[HR]b kCu2+ [H+]b

The solid lines in Figures 5-7 are the theoretical lines calculated on the basis of eq 23 using the values of KD, k2K1, and kCu2+ obtained previously. These lines are in good agreement with the experimental results. Conclusions 2-Hydroxy-4-n-octyloxy-benzophenoneoxime (HOBO) was found to be highly selective to copper(II) over base metals such as nickel(II) and cobalt(II) even from an ammoniacal solution. The decrease of the acid dissociation constant of HOBO due to the introduction of an electron donating group such as an alkoxyl group to the phenol group improves the metal selectivity compared with those of extractants of analogous oxime series such as LIX 860. The extraction rate of copper with HOBO in toluene from 1 M aqueous ammonium nitrate solution was measured using a stirred transfer cell at 303 K to elucidate the extraction mechanism. The initial extraction rate was found to be expressed by eq 23 as a function of the concentration of copper ion, monomeric species of the reagent, and hydrogen ion. We concluded that the elementary reaction between the intermediate

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complex adsorbed at the interface and the monomeric species of the extraction reagent in the aqueous phase to form the final chelate is rate-determining. Nomenclature Corg ) total extractant concentration in the aqueous phase [mol dm-3] Caq ) total extractant concentration in the organic phase [mol dm-3] CCuw ) total concentration of metal in the aqueous phase [mol dm-3] Km ) dimerization constant [dm3 mol-1] KD ) dissolution constant [-] Ka ) dissociation constant [mol dm-3] π ) interfacial pressure [N m-1] Kad ) interfacial adsorption constant [m] S ) interfacial area occupied by a unit mole of the extractant [m2 mol-1] N ) extraction rate [mol cm-2 s-1] k ) extraction rate constant [m s-1] Kex ) distribution equilibrium constant [-] θCuR+ ) function of the concentration of the extraction species [-] [ ] ) concentration of species [mol dm-3]

Literature Cited (1) Pnavarro, J. S.; Aliguacil, F. J. Iron(III) Extraction by LIX860 and Its Influence on Copper(II) Extraction from Sulphuric Solution. Hydrometallurgy 1996, 42, 13. (2) Ek, C. S. Copper-nickel separation from ammoniacal solutions using hydroxyoxims reagents. Proc. Int. Solvent Extr. Conf., Denver 1983, 1, 224. (3) Flett, D. S.; Okuhara, D. N.; Spink, D. R. Solvent Extraction of Copper by Hydroxyoximes. J. Inorg. Nucl. Chem. 1973, 35, 2471. (4) (a) Danesi, P. R.; Vandegrift, G. F.; Horwitz, E. P. Simulation of Interfacial Two-Step Consecutive Reactions by Diffusion in the Mass-Transfer Kinetics of Liquid-Liquid Extraction of Metal Cations. J. Phys. Chem. 1980, 84, 3582. (b) Baba, Y.; Inoue, K. The kinetics of Solvent Extraction of Palladium(II) from Acidic Chloride Media with Sulfur-Containing Extractants. Ind. Eng. Chem. Res. 1988, 27, 1613. (c) Komazawa, I.; Otake, T. Extraction

Kinetics of Copper with Hydroxyoxime Extractant. J. Chem. Eng. Jpn. 1980, 13, 204-208. (5) Eigen, M.; Tamm, K. Schallabsorption in Elektrolytlosungen als Folge chemischer Relaxation. Z. Elektrochem. 1962, 66, 107. (6) Yoshizuka, K.; Sakamoto, Y.; Baba, Y.; Inoue, K. Solvent Extraction of Holmium and Yttrium with Bis(2-ethylhexyl)phosphoric Acid. Ind. Eng. Chem. Res. 1992, 31, 1372. (7) Inoue, K.; Tomita, S.; Maruuchi, T. Extraction Kinetics of Nickel with a Hydroxyoxime Extractant. J. Chem. Eng. Jpn. 1985, 18, 445. (8) Komasawa, I.; Otake, T.; Yamashita, T. Mechanism and Kinetics of Copper Permeation through a Supported Liquid Membrane Containing a Hydroxyoxime as a Mobil Carrier. Ind. Eng. Chem. Fundam. 1983, 22, 127. (9) Komasawa, I.; Otake, T. The Effect of Diluent in the Liquid-Liquid Extraction of Copper and Nickel Using 2-Hydroxy5-Nonylbenzophenone Oxime. J. Chem. Eng. Jpn. 1983, 16, 377. (10) Miyake, Y.; Takenoshita, Y.; Teramoto, M. Extraction of Copper with SME529. J. Chem. Eng. Jpn. 1983, 16, 203. (11) Akiaba, K.; Freiser, H. The Role of the Solvent in Equilibrium and Kinetics Aspects of Metal Chelate Extractions. Anal. Chim. Acta 1982, 136, 329. (12) Kojima, T.; Miyauchi, T. Extraction Equilibrium Copper by LIX63. Kagaku Kogaku Ronbunshu 1981, 7, 200. (13) Kojima, T.; Miyauchi, T.; Toshinori. Extraction Kinetics of Copper-LIX65N System. 1. Forward Extraction Rate. Ind. Eng. Chem. Fundam. 1981, 20, 14. (14) Kojima, T.; Miyauchi, T.; Toshinori. Extraction Kinetics of Copper-LIX65N System. 2. Stripping Rate of Copper. Ind. Eng. Chem. Fandam. 1981, 20, 20. (15) Harada, M.; Miyake, Y. Formulation of Metal Extraction Rates in Solvent Extraction with Chelating Agents. J. Chem. Eng. Jpn. 1986, 19, 196. (16) Frant, K.; Andreas, G.; Nitshch, W. Europium Extraction into D2EHPA: Kinetics of Mass Transfer in a Stirred Cell. Solvent Extr. Ion Exch. 1999, 17, 475 (17) Miyake, Y.; Imanishi, Y.; Katayama, Y.; Hamatani, T.; Teramoto, M. Effect of Alkyl Chain Length of o-Hydroxyoxime on the Extraction of Copper. J. Chem. Eng. Jpn. 1986, 19, 117.

Received for review August 9, 2001 Revised manuscript received August 27, 2002 Accepted August 30, 2002 IE0106736