2774
Ind. Eng. Chem. Res. 1992, 31, 2774-2779
Sorption of Copper and Zinc from Aqueous Sulfate Solutions with Bis(2-ethylhexy1)phosphoric Acid-Impregnated Macroporous Resin Ruey-Shin J u a n g * and J e n n - Y i h S u Department of Chemical Engineering, Yuan-Ze Institute of Technology, Nei-Li, Taoyuan, 32026, Taiwan, R.O.C.
Equilibrium studies were thermodynamically made for the sorption of divalent copper and zinc ions from aqueous sulfate solutions with bis(2-ethylhexy1)phosphoric acid-impregnated hydrophobic macroporous resins, by employing either Bromley or the simplified Pitzer equations to estimate the stoichiometric activity coefficient of various species in the aqueous phase. The mechanisms of copper and zinc sorption were found to be the same as those of the solvent extraction. The operating lifetime of the impregnated resin and the influence of preparation method on the impregnation capacity, as well as the effects of aqueous ionic strength and temperature on the sorption equilibrium, were also examined. Introduction Solvent extraction has been widely applied to concentrate and separate the metallic species in hydrometallurgical and wastewater treatment processes. It, of course, requires violent mixing of the phases to provide sufficient contact area for a satisfactory rate of extraction followed by gravity settling of the mixed phases. Therefore, there is an innate attractiveness in creating a solid phase well dispersed (for example, in small bead form) which possesses some properties identical to those of liquid organic phase in solvent extraction, such as with high selectivity by chelating extractanta but without the need of mixing and settling apparatus and the problem of reagent loss through entrainment (Flett, 1977; Tavlaride et al., 1987). I t was recognized that chelating ion exchange resins could fulfll these requirements; however, there are bound to be some difficulties in the preparation and cost (Yoshizuka et al., 1990). Thus,the idea of adsorbing or absorbing of an organic extractant into a solid polymeric matrix, although it is not new, has attracted growing attention in recent years, due to the spectacular developments of highly-selective chelating extractants, macroporous polymeric matrix, and techniques for impregnation (Warshawsky and Patchornik, 1976; Flett, 1977; Warshawsky, 1981; Guan and Wu, 1990). At present, many substances, such as silica, celite, cellulose powder, activated charcoal, polyurethane foam, and hydrophobic macroporous resins, have been suggested as adsorbents for organic chelating extractanta (Warshawsky and Patchornik, 1976; Flett, 1977; Warshawsky, 1981; Korkisch and Steffan, 1983; Guan and Wu, 1990; Shakir et al., 1991), but macroporous resins seem to be more advantageous since they have the necessary physical strength and high surface area/volume ratio (Flett, 1977). In addition, the impregnated extractant would exhibit strong affinity to the polymeric matrix and could behave as in the liquid state (Warshawsky, 1981; Akita and Takeuchi, 1990). Bis(2-ethylhexy1)phosphoric acid (abbreviated as D2EHPA or simply HR) is -an acidic organophosphorus extractant and widely used in the hydrometallurgical processes for the separation and purification of a number of metals. It can effectively extract the first-row transition metals such as vanadium, copper, cobalt, nickel, and zinc, as well as uranium and other rare earth metals in the familiar nuclear processing, in a wide range of operation conditions (Flett et al., 1983).
* To whom correspondence should be addressed. 0888-5885/92/2631~2774$03.00/0
Few fundamental studies have been carried out for the sorptions of divalent metal ions with the so-called DSEHPA extractant-impregnated resin (DPEHPA-EIR) (Flett, 1977; Tavlaride et al., 1987). In this paper, the sorption equilibria of copper and zinc ions from aqueous sulfate solutions with D2EHPA-EIR were studied by changing the variables such as the metal concentration, ionic strength and pH in the aqueous phase, the extractant concentration in the resin phase, and the temperature. Furthermore, the operating lifetime of D2EHPA-EIR and the influence of the preparation method for EIR on the impregnation capacity were also examined. Experimental Section Reagents a n d Solutions. D2EHPA was the product of Merck Co., with a purity of approximately 98.5% determined by potentiometric titration of an 80 vol % ethanol solution of the acid with 0.1 mol/dm3 NaOH in ethanol. It was used as received. The diluent n-hexane and other inorganic chemicals were supplied by RDH AG, as analytical reagent grade. Amberlite XAD-2, supplied by Rohm & Haas Co., USA, is a macroporous resin made of styrene-divinylbenzene copolymer with highly aromatic structure. It has been widely used as a sorbent to extract metal ions while impregnated with chelating extractanta (Mataunaga and Suzuki, 1986; Tavlaride et al., 1987; Akita and Takeuchi, 1990) and to sample and analyze the organic pollutants in water (Junk, 1987). It, on a dry basis, has a specific surface area of 330-350 m2/g, a porosity of 0.42, an average pore diameter of 9 nm, and a particle size of 0.3-0.9 mm (20-50 mesh) (Junk, 1987). This resin was washed by acetone and n-hexane and dried at 50 "C in a vacuum for 2 h before impregnation. The aqueous composition was 0.5 mol/dm3 (Na,H,M)SO4, which means that the total sulfate content was kept constant, unless otherwise specified. In the aqueous phase, the initial concentration of copper or zinc ranged from 1.25 x to 1.22 X mol/dm3, but usually fixed at about 3.15 X low3mol/dm3. The initial pH values varied from 2.95 to 5.49 for copper solution and from 2.15 to 3.51 for zinc solution. In the EIR phase, the initial concentration of monomeric D2EHPA was from 0.517 to 1.277 mol/kg of EIR, but usually fixed at 1.034 mol/kg of EIR. Experimental Procedures. 1. Preparation of the EIR. Amberlite XAD-2 resins were impregnated by the following three different dry or wet procedurea (Flett, 1977; Warshawsky, 1981; Guan and Wu; 1991). A dry method was first performed by diluting D2EHPA with fresh n0 1992 American Chemical Society
Ind. Eng. Chem. Res., Vol. 31, No. 12, 1992 2778 0.0
Eb,
Amount of DPEHPA ( E ) 0.2 0.4 0.6 0.8
1.0
1.2
Y
e
8 ! u
0.8
4
2
0.4
3 N CI
0.0
0
5
10
15
Amount of DPEHPA ( E ) Figure 1. Effect of amount of DSEHPA in impregnating solution (n-hexane) on content of D2EHPA in EIR by various methods. Method: dry-EIR I (A),dry-EIR I1 (O),and wet-EIR (0).
hexane to a required concentration (0.149 mol/dm3). The resulting organic solution (40 cm3) was mixed with fresh resin (1.0 g) for 1h. The resin was then evaporated at 50 "C in a vacuum fo; 2 h. This resin treated thus contains DBEHPA, and it is called the dry D2EHPA-impregnated resin (dry-EIR I). Additionally, the dry method could also be made by dissolving D2EHPA (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. This resin was finally evaporated to completely remove the solvent a t 50 OC in a vacuum for 2 h (dry-EIR 11). The wet method was carried out following the same procedures of dry-EIR I1 except for the final drying process. Here, the resin beads were then immersed in an mol/dm3). aqueous copper sulfate solution (6.30 X After completion of the formation of copper-D2EHPA complex (about 12 h), the EIR was washed with water, the copper was eluted by about 2.0 mol/dm3 "OB, and the resin was rewashed with water. Wet-EIR was thus ready for application. The D2EHPA content in these three types of EIR was determined by potentiometric titration of the amount of D2EHPA eluted with n-hexane from the EIR with 0.1 mol/dm3 NaOH in ethanol. 2. Sorption Equilibrium. In the sorption equilibrium experiments the EIR (1.0 g) and aqueous copper or zinc solution (40 cm3)were placed in a 250-cm3 glass-stoppered flask and shaken a t 150 rpm for at least 24 h using a thermostated shaker (Firstek Model B603, Taiwan). Preliminary experiments had shown that the sorptions studied were complete after 12 h. After standing for 1h, the aqueous phase was separated from the EIR and its equilibrium pH value was then measured with a pH meter (Radiometer Model PHM82). The concentration of metal in the aqueous phase was determined directly with a Perkin-Elmer atomic absorption spectrophotometer (Model 5100 PC) at an appropriate wavelength. Both the contents of metal sorbed and unreacted D2EHPA in EIR were calculated from a mass balance.
Results and Discussion Sorption Equilibrium. Figure 1 shows the effect of the content of D2EHPA in impregnating solution on the
DBEHPA content in EIR prepared by various methods. The content increases with increasing solution concentration. The amounts of D2EHPA transferred from organic solution to the resin phase were found to be less than 3.7% and 88% for wet-EIR and dry-EIR I, respectively, and almost 100% for dry-EIR I1 under the experimental ranges studied. The incomplete impregnation of D2EHPA for the former two methods is probably due to the equilibrium restrictions or the washing loss (see Experimental Procedures). Consequently, the easy-to-use impregnating method of dry-EIR I1 was adopted for the latter applications. It should be noted that the resulting EIR became adhesive even after evaporation of the diluent when the content exceeded about 1.277 mol/kg of EIR, which is equivalent to 41.2 wt % D2EHPA of EIR. This result is the same as that of the literature value (Flett, 1977). The D2EHPA content contained by the titration was in good agreement with the values calculated from the change in the weight of resin before and after the impregnations. Solvent extraction of trace divalent metals from sulfate solutions with acidic organophosphorus extractants has been studied extensively. It was reported the extractions of trace copper and zinc with D2EHPA can be generally represented by the following relation (Ajawin et al., 1983; Sastre and Muhammed, 1984; Huang and Juang, 1986; Juang and Chang, 1991): M2++ [(n+ 2)/2l((HR)~)org+ (M&(HR)n)org
+ 2H+ (1)
It is assumed that the mechanisms of copper and zinc sorptions on the D2EHPA-impregnated resin are the same as that of the solvent extraction, provided that the extractant is not chemically bonded to the polymeric matrix (Akita and Takeuchi, 1990; Yoshizuka et al., 1990). Therefore, the equilibrium constant Kexand distribution ratio D can be expressed as eqs 2 and 3 from eq 1: Kex
= {[MRz(HR)nI[H+12)/{[M2+l [ 0 , 1 ( n + 2 ) / 2 1(2)
D = [MR2(HR),]/[M2+] = Kex[o,](n+2)/2[H+]-2
(3)
where the overbar indicates the species in the EIR phase. The values of n obtained for solvent extractions of copper and zinc from aqueous sulfate solutions with D2EHPA were reported to be 2.0 and 1.2, respectively (Juang and Chang, 1991). To make sure of the above relationships, the effect of dimeric D2EHPA concentration on the sorption equilibria of metals were further examined. Equation 3 can be rewritten as l0g(D[H+l2)= log K e x
+ [(n+ 2)/21
log[(HR)zl (4)
In the determination of equilibrium constant, the content of free DBEHPA, [(HR)2], is calculated by the following mass balance:
[HRIo = [ m l + 2[(HR),I + (n + 2)[MRz(HR)n] and
(5)
--
2HR + 0
2
,
K2 = [ (HR),] / [HR]
(6)
where [ m ] , indicates the initial content of monomeric D2EHPA in EIR and K2 is the dimerization constant of D2EHPA and is taken to be 2.63 X lo4 dm3/mol in kerosene at 25 OC (Huang and Juang, 1986). The results obtained for the sorptions of copper and zinc are plotted according to eq 4 in Figures 2 and 3, respectively. It was found that all data points lie on straight lines
2776 Ind. Eng. Chem. Res., Vol. 31, No. 12, 1992
t
/
i
h
d
w
0 . . I
X Y
/
0
10
-+ 10
Q" ,
,
,
, , , ,
-'
,j 3
1
12
9
15
[ Y " ] o ~10' (rnol/drn')
[(HR)II (mol/kg-EIR) Figure 2. Effect of dimeric D2EHPA concentration in EIR on mol/dm3, distribution ratio of copper at 25 "C. [Cu2+],= 3.15 X p& = 2.95-5.49.
6
Figure 4. Effect of initial metal concentration in the aqueous phase = 1.034 mol/kg of EIR, pHo = 2.15. on sorption at 25 "C.
[mIo
Table I. Logarithm Values of Equilibrium Constants and Standard Deviation for Copper Sorption with D2EHPA-EIR Obtained by Various Methods at 25 OC
[so,2-lo (mol/dm3) 0.10 0.30 0.50 0.70
stoichiometric' -3.56 -3.90 -4.01 -4.27
f 0.06 f 0.05 f 0.07
f 0.08
overall
'Units:
Bromley -2.87 -2.89 -2.95 -2.92
0.04 f 0.03 f 0.04 f 0.05
f
Pitzer -2.61 -2.70 -2.83 -2.79
f 0.10 f 0.06 f 0.08 f 0.09
-2.91 f 0.04
kg of EIR/dm3.
Table 11. Logarithm Values of Equilibrium Constants and Standard Deviation for Zinc Sorption with D2EHPA-EIR Obtained by Various Methods at 25 OC
[so4z-lo (mol/dm3)
[(HR)II (mol/kg-EIR) Figure 3. Effect of dimeric D2EHPA concentration in EIR on mol/dm3, distribution ratio of zinc at 25 "C. [Zn2+Io= 3.15 X p& = 2.15-3.51.
0.10 0.30 0.50 0.70
overall
stoichiometric' -1.21 -1.63 -1.77 -1.91
f 0.07 f 0.08 f 0.09 f 0.07
Bromley -1.14 -1.09 -1.19 -1.25
f 0.04 f
0.06
f 0.05 f 0.05
Pitzer 4 . 8 3 f 0.09 4 . 9 2 f 0.10 -1.06 f 0.09 -1.11 f 0.10
-1.17 f 0.06
aUnits: (kg of EIR/mol)0~6(mol/dm3). with a slope of [(n+ 2)/2] as expected from eq 4, except that the D2EHPA content is less than about 0.75 mol/kg Thermodynamic Studies of Sorption Reaction. The of EIR for copper or 0.70 mol/kg of EIR for zinc. These use of the activity concept for the aqueous phase and of exceptions will be discussed in the following section. the concentration concept for the organic phase has been The values of K,, thus calculated from the intercept in introduced in order to adapt the model to different these plots were 9.77 X lod kg of EIR/dm3 and 1.70 X aqueous molalities and compositions in solvent extraction [(kg of EIR/mol)o~6(mol/dm3)] for copper and zinc, re(Tanaka, 1990; Juang and Jiang, 1992; Juang and Su, spectively, at 25 OC. These values are surprisingly found 1992). Similarly,the activity coefficients of various species to be very close to those obtained from solvent extraction of 1.20 X lo4 (dimensionless) and 1.26 X (m~l/dm~)O.~ in the EIR phase are assumed to be kept constant, since they are difficult to experimentally measure or theoretiat 25 "C under similar experimental conditions (Juang and cally estimate (Myers and Byington, 1986)and the aqueous Chang, 1991). As also stated by Akita and Takeuchi molalities and compositions do not significantly change in (1990),however, the loading capacity of metals to the imthis study. Thus, eq 2 can be written as pregnated D2EHPA is found to be less than that to the solvent extraction. Ket = ( [ ~ " ) ~ I ( ~ H + ) ~ ~ / I ( ~ M ~ + ) [ ( H R ) Z(7) I'"+~"~) The effect of the initial concentration of metals in the aqueous phase on the sorption was shown in Figure 4. It where K,, is the thermodynamic equilibrium constant. is evident that the sorption isotherms for copper and zinc The value of ((aH+)2/(aM1+)} is calculated by employing the Bromley and the simplified Pitzer methods for strong are significantly different. The linear relationship for electrolyte solutions (Bromley, 1973; Pitzer, 1979). The copper is due to the lower sorption loading of D2EHPAEIR, which results from the equilibrium restriction at this estimation equations and their parameters used to calcuaqueous pH. It should be noted that the distribution ratio late the stoichiometric activity coefficient of various speciea in the aqueous sulfate solutions are given elsewhere (Juang of metal sorption with fresh resin was found to be negligibly small under the experimental conditions studied (less and Su, 1992). The possible aqueous complexation reacthan 2.5 X loT3dm3/kg of EIR). and sulfate ions were tions of cations (H+, Na+, and M2+)
*
Ind. Eng. Chem. Res., Vol. 31, No. 12, 1992 2777
a
c
0
0 I
I
I
0.7
1.1
1.5
0.0
0.4
[=IO
[E],(mol/kg-ELR) Figure 5. Effect of amount of D2EHPA (in 2 cm3 of n-hexane) impregnated into 1.0 g of fresh resin on percentage of D2EHPA loss 0). from EIR at 25 OC. Shaker speed 220 ( 0 ) and 150 rpm (0,
1.2
0.8
1.6
(mol/kg-EIR)
Figure 7. Distribution ratio of copper in cyclic batch sorption at 25 OC. [ C U ~ +=] ~3.15 X mol/dm3, pHo = 4.04. First run ( O ) , second run (o),and third run ( 0 ) . 1
I
I
T - r
i
2o
c
\
I
0.620 I
10
Weight of fresh resin (g) Figure 6. Effect of amount of fresh resin used for impregnation on distribution ratio of metale at a f i e d total amount of D2EHPA of 0.5 g in EIR at 25 OC. [ C U ~ +=]3.15 ~ X mol/dm3, p& = 3.12 mol/dm3, p& = 2.05 (0). (0); [ZnZ+lo= 3.15 X
also considered. The calculated results were compiled in Tables I and I1 for comparison. Extractant Loss and Operating Lifetime of the D2EHPA-EIR. In order to investigate the reason why the experimental distribution ratio is remarkably lower than that predicted by eq 4 when the DBEHPA content in EIR is less than about 0.75 mol/kg of EIR, the extractant loss and operating lifetime of the DSEHPA-EIR are examined. Figure 5 shows the effect of the amount of DSEHPA impregnated into 1.0 g of fresh resin on the DBEHPA loss from EIR at different shaker speeds for 24 h. It was found that there is a serious loss of D2EHPA from EIR when the initial amount of D2EHPA impregnated increases at a shaker speed of 220 rpm. However, at 150 rpm, the DSEHPA loss is less than 3% when the amount of D2EHPA is more than 0.3 g, which is equivalent to 0.72 mol/kg of EIR. A more intensive contact between the EIR and aqueous solution at 220 rpm might explain such behavior. Accordingly, a shaker speed of 150 rpm was seleded in this study. Figure 6 shows the effect of the amount of fresh resin used for impregnation on the distribution ratio of metals at a fiied total amount of D2EHPA of 0.5 g in EIR. It was
-'
1
[(HR),] (mol/kg-EIR) Figure 8. Effect of aqueoua ionic strength on distribution ratio of zinc at 25 "C. [Zn2+Io= 3.15 X mol/dm3, p& = 1.60-2.26, = 0.1 ( O ) , 0.3 (A), 0.5 ( O ) , and 0.7 mol/dm3 ( 0 ) .
found that the distribution ratios, especially for zinc, sharply drop when more than about 1.5 g is used, which is equivalent to 0.775 mol/kg of EIR. These results may be applied to describe the abnormal behavior of Figures 3 and 4. Figure 7 shows the behavior of a cyclic batch operation of DBEHPA-EIR for copper sorption. It was evident that the loss of D2EHPA from EIR is s m a l l enough to be neglected as long as the D2EHPA content in EIR is more than 0.75 mol/kg of EIR. Effect of Aqueous Ionic Strength on the Sorption Equilibrium. The effect of aqueous ionic strength or the total sulfate content on the sorption equilibrium of zinc is shown in Figure 8. It was obvious that the sorption mechanism by eq 2 is still applicable. The equilibrium constants, as listed in Tables I and 11,were found to decrease with increasing aqueous ionic strength, which agrees with those observed in solvent extraction (Ajawin et al., 1983). However, unique thermodynamic equilibrium constante of log Ket = -2.91 and -1.17 could be obtained for copper and zinc sorptions, respectively, at 25 OC over the aqueous ionic strength ranges studied, if the activity correction by Bromley method was made. This implies the assumption that the activity coefficients of various species in the EIR
2778 Ind. Eng. Chem. Res., Vol. 31, No. 12, 1992
study are the typical ones for solvent extraction of divalent metals with D2EHPA (Rublev, 1984),but are significantly larger than those found in the sorption of nonelectrolyte or metal ion exchange process by ion exchanger (Helfferich, 1962).
r"I
10
v
b!
10 . I
3.3
2.9
T-'xlOS
3.6
(P')
Figure 9. van't Hoff relations for sorption reaction of metals with D2EHPA-EIR. Method: stoichiometric(0, 0 ) and Bromley (A, A). Table 111. Changes in Enthalpy and in Entropy for Sorption Reactions of Copper and Zinc from Sulfate Solutions with D2EHPA-EIR at 15-65 OC cu Zn
AH
As
AH
As
method (kJ/mol) (J/ (mo1.K)) (kJ/mol) (J/ (mo1.K)) 13.05 9.71 i 0.75 24.25 f 2.11 stoichiometric 30.01 26.60 2.52 54.96 3.80 14.86 33.02 Bromley
*
phase are kept constant is reasonable. The Pitzer method, however, shows relatively high deviations in log Ket for different aqueous ionic strengths, which may be due to the improper simplification in estimation equations employed for this partially-dissociated aqueous sulfate system (Juang and Su, 1992). Effect of Temperature on t h e Sorption Equilibrium, The distribution ratio of metals was found to be increased with an increase in temperature. In order to obtain the 'true" thermodynamic data for the sorption reaction, the Bromley method was again employed to estimate the equilibrium constants at different temperatures (Juang and Jiang, 1992). The free energy change, AG, of the sorption reaction at any temperature is defined as AG = -2.303RT log K,t (8) where R denotes the universal gas constant and T denotes the absolute temperature. The enthalpy change, AH, is usually given by the van't Hoff relation: d(l0g KeJ/d( 1/ 5") = -AI?/ (2.303R)
(9)
The entropy change, AS, is thus calculated from eq 1 0 A S = (AH - A G ) / T (10) Figure 9 shows van't Hoff relation for the sorption reaction of metals with D2EHPA-EIR. The changes in enthalpy and in entropy a t the temperature range of 15-55 "C are listed in Table 111. It is evident that AH values obtained by the stoichiometric (namely, based on Kex)and Bromley methods are not apparently different, but significant differences in AS are observed due to the effect of activity corrections. This results from as apparent difference in Ket and hence AG, as indicated by eq 8, found by these two methods. Obviously, an accurate determination of the equilibrium constant plays an important role in calculating the thermodynamic data of a sorption reaction. Actually, the AH and AS values obtained in this
Conclusions The sorption equilibria of divalent copper and zinc ions from aqueous sulfate solutions with D2EHPA-impregnated resins were thermodynamically studied at the temperature range of 15-55 "C. The following results were obtained. 1. The impregnation of D2EHPA on Amberlite XAD-2 could be achieved by dry method I1 to almost loo%, and to a content below 1.277 mol/kg of EIR. 2. The mechanism of copper and zinc sorptions are the same as those of the solvent extraction, and the equilibrium constants are found to be 9.77 X la6 (kg of EIR/dm3) and 1.70 X [(kg of EI€€/rn~l)~~~(mol/dm~)] for copper and zinc, respectively, at 25 "C. 3. The distribution ratio, hence the equilibrium constant, decreases with an increase in the aqueous ionic strength, which also agrees with the results obtained from solvent extraction. 4. The changes in enthalpy and in entropy for the sorption reactions of copper and zinc with D2EHPA-EIR are found to be 33.02 kJ/mol and 54.96 J/(mol*K), and 14.86 kJ/mol and 26.60 J/(mol.K), when the activity correction by the Bromley method is employed. Both the sorption reactions are thus favored by entropy change and unfavored by enthalpy change. Acknowledgment
This work was supported by the ROC National Science Council under Grant No. NSC81-0402-E155-510,which is greatly appreciated. Nomenclature
D = distribution ratio of metal by EIR, dm3/kg of EIR EIR = extractant- (solvent-) impregnated resin AG = free energy change for sorption reaction, kJ/mol AH = enthalpy change for sorption reaction, kJ/mol HR = monomeric form of D2EHPA (HR), = dimeric form of D2EHPA K,, = equilibrium constant defined in eq 2, (kg of EIR/ mol)n/z (mol/dm3) K,,= thermodynamic equilibrium constant defined in eq 7 K2= dimerization constant of DSEHPA, dm3/mol M = metal ion n = number of monomeric D2EHPA solvated in the metal complex A S = entropy change for sorption reaction, J/(mol.K) T = absolute temperature, K [ ] = molar concentration of species in the brackets, mol/dm3 Subscripts
org = organic phase 0 = initial Superscript
- = EIR phase RedBtry NO. DSEHPA, 298-07-7; XAD-2, 9060-05-3; CU, 7440-50-8;Zn, 7440-66-6.
Literature Cited Ajawin, L. A.; Perez de Ortiz, E. S.; Sawistowski, H. Extraction of Zinc by Di(2-ethylhexy1)phosphoric Acid. Chem. Eng. Res. Des. 1983, 61 (l), 62-66. Akita, S.; Takeuchi, H. Sorption and Separation of Metals from Aqueous Solution by a Macromolecular Resin Containing Tri-n-
Ind. Eng. Chem. Res. 1992,31, 2779-2783 octylamine. J . Chem. Eng. Jpn. 1990,23 (4),439-443. Bromley, L. A. Thermodynamic Properties of Strong Electrolytes in Aqueous Solutions. AZChE J . 1973,19(21,313-320. Flett, D. S.Resin Impregnates: the Current Position. Chem. Znd. 1977,Aug 6,641-646. Flett, D. S.; Melling, J.; Cox, M. Commercial Solvent Systems for Inorganic Processes. In Handbook of Solvent Extraction; Lo, T. C., Baird, M. H. I., Hanson, C., Eds.; Wiley: New York, 1983;pp 629-647. Guan, Y.; Wu, X. Y. The Theory and Application of Solvent-Impregnated Resins. Zon Exch. Adsorpt. 1990, 6 (l),60-67 (in Chinese). Helfferich, F. Zon Exchange; McGraw-Hill: New York, 1962;Chapter 5, pp 125-169. Huang, T. C.; Juang, R. S. Extraction Equilibrium of Zinc from Sulfate Media with Bia(2-ethylhexy1)phosphoric Acid. Znd. Eng. Chem. Fundam. 1986,25 (4),752-757. Juang, R. S.;Chang, Y. T. Extraction of Zinc from Sulfate Solutions with Bis(2-ethylhexy1)phosphoricAcid in the Presence of Tri-noctylphosphine Oxide. Znd. Eng. Chem. Res. 1991, 30 (ll), 2444-2449. Juang, R. S.; Jiang, J. D. Calculation of the Thermodynamic Data for Zinc Extraction from Chloride Solutions with Di-n-pentyl Pentanephosphonate. Znd. Eng. Chem. Res. 1992, 31 (4), 1222-1227. Juang, R. S.; Su, J. Y. Thermodynamic Studies of Weak Aqueous Sulfate Solutions in Solvent Extraction Systems. J . Chem. Technol. Biotechnol. 1992,53 (3),237-242. Junk, G. A. Synthetic Polymers for Accumulating Organic Compounds from Water. In Organic Pollutant in Water; Suffet, I. H., Malaiyandi, M., Eds.; Advances in Chemistry Series 214;American Chemical Society: Washington, DC, 1987;Chapter 10,pp 201-246. Korkiach, J.; Steffan, I. Separation of Uranium on Polyurethane Foam Impregnated with Trioctylphosphine Oxide. Solvent Extr. Zon Exch. 1983,l (3),607417. Mataunaga, H.; Suzuki, T. Selective Separation and Concentration of Gold(III), Platinum(1V) and Palladium(I1) by Macroreticular Hydrophobic Resin Loaded with Tri-n-octylamine. Nippon Kagaku Kaishi 1986,859-865.
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Separation of Zinc and Copper from Aqueous Sulfate Solutions Using Bis(2-ethylhexy1)phosphoric Acid-Impregnated Macroporous Resin Ruey-Shin Juang* and Jenn-Yih Su Department of Chemical Engineering, Yuan-Ze Institute of Technology, Nei-Li, Taoyuan, 32026, Taiwan, R.O.C.
The separation of zinc and copper from aqueous sulfate solutions using bis(2-ethylhexy1)phosphoric acid-impregnated hydrophobic macroporous resin has been examined in either batch or continuous operation. This resin could be successfully impregnated by the modified dry method. It was found that the impregnated resin gives high selective separation of zinc to copper, and they can be satisfactorily separated from 0.5 mol/dm3 (Na,H)S04 aqueous solution.
Introduction Solvent extraction has been widely applied to concentrate and separate the metallic species from the aqueous stream in the hydrometallurgical processes. It requires violent mixing of the phases to provide sufficient contact area for a satisfadory rate of extraction followed by gravity settling of the mixed phases (Andersson and Reinhardt, 1983; Ritcey and Ashbrook, 1984). Also, metallic species separation by the solvent extraction process is generally considered to be economical in the range of aqueous metal concentration from about 0.01 to 1.0 mol/dm3 (Akita and
* T o whom correspondence should be addressed.
Takeuchi, 1990). Thus, there is an innate attractiveness in creating a solid phase well dispersed which possesses some properties identical to those of liquid organic phase in solvent extraction for the treatment of very dilute solutions (Flett, 1977; Warshawsky, 1981; Tavlaride et d., 1987). It was recognized that the chelating ion exchange resins could fulfill these requirements. They have various advantages over solvent extraction: high loading capacities of metal ions, ease of liquid/solid phase separation associated with a lack of serious problems such as crud formation and solvent losses into the aaueous Dhase, ease of handling, and simplicity of equipment by operating with packed columns. They, however, also have various draw-
0888-588519212631-2779$03.00/0 0 1992 American Chemical Society
