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Equilibria of solvent extraction of copper(II) with 5-dodecylsalicylaldoxime
HydrometaUurgy, 23 (1990) 247-261 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
247
Equilibria of Solvent Extraction of Copper(II) with 5-Dodecylsalicylaldoxime KAZUHARU YOSHIZUKA, HIROSHI ARITA, YOSHINARI BABA and KATSUTOSHI INOUE
Department of Applied Chemistry, Saga University, Honjo-machi, Saga 840 (Japan) (Received June 16, 1988; revised and accepted March 10, 1989)
ABSTRACT Yoshizuka, K., Arita, H., Baba, Y and Inoue, K., 1990. Equilibria of solvent extraction of copper (II) with 5-dodecylsalicylaldoxime. HydrometaUurgy, 23:247-261. The equilibrium studies on the solvent extraction of copper (II) with 5-dodecylsalicylaldoxime, the active component of LIX 860, were carried out at 303 K to clarify the effects of the organic diluent and the aqueous media, together with measurements of the apparent molecular weight and aqueous solubility of the extractant. It was found that the title extractant exists as a monomeric species in the organic diluents, i.e., hexane, cyclohexane and toluene and is sparingly soluble in the aqueous solutions as well as other commercial hydroxyoximes. Copper (II) was extracted as a chelate of the type CuR2 in the organic solution and the extraction equilibrium constant in hexane is about five times and twice greater than those in toluene and cyclohexane respectively, and further, the extraction equilibrium constant with 5-dodecylsalicylaldoxime was several times greater than those with other commercial hydroxyoximes. The effect of 1-tridecanol as a modifier on the extraction equilibrium was quantitatively clarified by taking account of the formation of the hydrogen bond between the extractant and 1-tridecanol.
INTRODUCTION
Aromatic fl-hydroxyoximes as extracting reagents of copper (II) are divided into two classes: ketoximes and salicylaldoximes as shown in Fig. 1. The former are further divided into two subclasses, i.e., benzophenone oximes such as LIX 65N and ABF 2, a Soviet commercial hydroxyoxime, and alkanophenone oximes such as SME 529 (now available as Henkel's LIX 84 ) and OMG, another Soviet commercial hydroxyoxime. Compared with ketoximes, the salicylaldoximes are much stronger copper extractants with considerable advantages of rapid copper transfer kinetics, excellent copper over iron selectivity and rapid phase separation. These are the reasons of remarkable market penetration achieved by the Acorga reagents since 1979 [1 ]. Salicylaldoximes are, however, so strong as copper extractants
0304-386X/90/$03.50
© 1990 Elsevier Science Publishers B.V.
248
K. YOSHIZUKAET AL.
Aromotic [3-hydroxyoxime SaLicylaidoxime (o} , . . rI3enzophenone oxime (b} ~e~°xlme/A [ k (1nophenone oxime (c) OH--I~.o H
O•H .. ~ ' ~
(c)
"OH
R: C9H~9
P -50
R = Q~H2s
LIX 860
R =C9H19
LIX 65N
R=t-C,H,7
AI3F2
LIX 64N= L[X65N*L[X 63 (-lvol°/o)
C9H19 X= CH3
" LIX 84 (SME 529)
X: C,H2n.l(n=4_S)
" OMG
c-x OH..N.oH
Fig. 1. Chemical structure of commercial hydroxyoxime reagents.
that they are often used in combination with an equilibrium modifier so that they can be stripped with a typical tankhouse electrolyte. Acorga P-5100 and 5300 reagents are the combination of P-50 reagent, 5nonylsalicylaldoxime, and p-nonylphenol with the ratios of 1:1 and 1:3 respectively while PT-5050 reagent is a version of P-5300 reagent, in which the p-nonylphenol is replaced with tridecanol to avoid some troubles of accelerating reagent degradation and deleterious effects of certain materials of construction by p-nonylphenol [2 ]. To compete with the Acorga reagents, Henkel Corp. offered a series of new reagents, the active component of which is 5-dodecylsalicylaldoximeas follows
[21: LIX 860: 5-dodecylsalicylaldoximewith kerosene make-up LIX 864: a mixture of LIX 64N with LIX 860 LIX 865: a mixture of LIX 65N with LIX 860 LIX 984: a mixture of LIX 84 with LIX 860 LIX 622: a mixture of LIX 860 with tridecanol in LIX 864, 865 and 984. It has been suggested that the ketoxime acts in the same way as a modifier for the salicylaldoxime on the strip side of the solvent extraction circuit [ 1 ]. There appears to be only a small number of works on the solvent extraction of metal ions with 5-alkylsalicylaldoximes though numerous works have been done on that with benzophenone-type ketoximes, especially with E-2-hydroxy5-nonylbenzophenone oxime, the active species of LIX 65N and 64N. Stepniak-Biniakiewicz and Szymanowski conducted a series of fundamental investigations on the equilibrium aspects of extraction of copper (II) and nickel (II)
EXTRACTION OF COPPER WITH 5-DODECYLSALICYLALDOXIME
249
with some pure 5-alkylsalicylaldoximes including 5-tert-butylaldoxime and elucidated the composition of the extracted species and the diluent effects [36]. In the present paper, we conducted a fundamental investigation on the equilibrium aspects of the solvent extraction of copper(II) with 5-dodecylsalicylaldoxime, the active species of Henkel's "second generation" hydroxyoximes mentioned earlier and elucidated the stoichiometric relation of the extraction reaction and the effects of the chemistry of the aqueous media, the organic diluents and 1-tridecanol as an equilibrium modifier as well as the aqueous distribution of the extractant. EXPERIMENTAL
Reagents 5-dodecylsalicylaldoxime, abbreviated to CleSAO and denoted by HR hereafter, was kindly supplied from Henkel Corp. and used as received without further purification. The molecular weight of monomeric species of C12SAO is 305.5. The purity of the reagent was found to be above 90% by measurement of the ultimate loading of copper (II) to the reagent. Commercial reagent grade of 1-tridecanol (Tokyo Kasei Co. Ltd. ), denoted by L hereafter, was used also as received without further purification. Commercial reagent grade of toluene, hexane and cyclohexane were used as organic diluents also without further purification. Other inorganic reagents, copper(II) nitrate, nitric acid, ammonium nitrate, hydrochloric acid and sulfuric acid were all commercial reagent grade. Working solution of the organic phase was prepared by dissolving C12SAO and/or 1-tridecanol in each organic diluent to required concentrations on a gravimetric basis. The concentration of the active component was determined by the ultimate loading of copper (II) to the organic phase. Aqueous copper solutions were prepared by dissolving copper(II) nitrate into the following aqueous media: (1) aqueous mixture of 1.0 kmol m -3 ammonium nitrate and nitric acid in which ionic strength was maintained constant at 1.0 kmol m -:~ and pH was varied by changing the volume ratio of the two solutions, (2) hydrochloric acid and (3) sulfuric acid with varying concentrations.
Apparent molecular weight of CI2SAO Apparent molecular weight of C12SAO in each organic solvent was measured using a Corona model 117 vapor-phase osmometer, with benzil as a standard material.
250
K. YOSHIZUKA ET AL.
Aqueous distribution of CI2SAO The aqueous distribution of C12SAO was measured at 303 K, according to the same methods of Komasawa et al. [8] and Ashbrook [9]. Solution of C12SAO in each diluent and 1.0 kmol m -3 aqueous ammonium nitrate solution were shaken with appropriate volume ratios ( 1 : 5 0 - 1 : 2 0 ) for 12 h. After the two phases had been allowed to be settled for more than 2 h, they were separated. A weighed aqueous phase was transferred to a separatory funnel, to which a small volume of copper (II) nitrate solution (30 mol m - 3, p H = 6 ) was added, and shaken gently for 10 min. C~2SAO dissolved in the aqueous phase was thus completely converted to be copper(II) chelate. A small amount of hexane (usually 10 cm 3) was added and shaken vigorously for 2 h to transfer the copper chelate into hexane. The concentration of the copper (II) chelate in the organic phase was measured at 355 nm using a Shimadzu model UV-160 spectrophotometer. The p H of the aqueous phase was measured using a TOA model H M 20E p H meter.
Equilibrium distribution of copper(II) Equal volumes of aqueous and organic phases were shaken in a flask immersed in a thermostatted water-bath maintained at 303 K to attain equilibrium. After 8 h, the two phases were separated. A known volume of the organic phase was stripped with 3.0 kmol m -3 hydrochloric acid and diluted to an appropriate ratio. Copper concentration in the resulting aqueous were determined by E D T A titration; the concentration of hydrogen ion in the aqueous phase after equilibration was determined by titration with sodium hydroxide solution using phenolphthalein as an indicator to calculate the activity of hydrogen ion referring to the activity coefficient in literature [ 10 ].
Spectroscopic studies of CI2SAO and 1-tridecanol Infrared spectra between 4000 and 2000 cm - ~ were recorded for CC14solutions of CI2SAO a n d / o r l-tridecanol under investigation using a JASCO model A-100 spectrometer, with 0.05 mm calcium fluoride cells. iH-n.m.r, spectra for C12SAO and l-tridecanol dissolved in CDC13 were registered with a J E O L model J N M - G X 2 7 0 T - N M R spectrometer. RESULTS AND DISCUSSION
Apparent molecular weight of Ci2SAO Since it is known that commercial hydroxyoximes such as L I X 65N and S M E 529 partly exist as dimeric species in nonpolar organic diluents
EXTRACTIONOF COPPER WITH 5-DODECYLSALICYLALDOXIME
251
[5,8,12,13 ], it is necessary to examine the aggregation of C,2SAO in the various diluents to clarify the extraction mechanism. From the measurement of the apparent molecular weights, Mw, in the organic diluents by means of vapor-phase osmometry, the apparent molecular weights were evaluated as follows: M w = 302 in toluene, 296 in cyclohexane and 303 in hexane. Since all of the apparent molecular weights of C,2SAO in each diluent are in good agreement with the calculated molecular weight of monometric C12SAO, it can be concluded that C,2SAO exists as a monomeric species in the above-mentioned organic diluents, contrary to the other hydroxyoximes.
Aqueous distribution of C~2SAO A hydroxyoxime extractant in the organic phase is partitioned to the aqueous phase accompanied by acid dissociation at high pH, as follows: HR.
"HR
;Kd
HR.
"R-+H +
(1) ;Ka
(2)
where Kd and Ka denote the partition coefficient and the acid dissociation constant of the extractant, respectively and the bar superscript denotes the organic phase. Since the aggregation of C12SAO in the organic phases can be ignored as mentioned above, the concentration of the monomeric species of ClzSAO in the organic phase, [HR], is nearly equal to its total or analytical concentration, CHR. From the above equilibrium relations, the analytical concentration of C12SAO in the aqueous phase, CuR, is described as follows: CHR =Ka X (l +Ka/aH) x C ~
(3)
where aH is the activity of hydrogen ion. Figure 2 shows the effect of pH on the distribution of C12SAO between toluene and 1.0 kmol m-3 aqueous ammonium nitrate solutions for various initial concentration of C12SAO in the organic phase, CHRO- It is evident that CHR is independent of pH, which suggests that the acid dissociation of C12SAO in the aqueous phase is negligibly small over the whole pH under the present experimental conditions. From this result, Eq. 3 can be simplified and the logarithm of CHR is approximately expressed as follows: l o g CHR
=log Ch~ +log Kd
The subsequent measurements were carried out at a constant pH of 4.7.
(4)
'.2)52
K. YOSHIZUKA ET AL.
Organic diluent Key F r r Hexane O -I .5 Cyc[ohexane z~ k £ Toluene 1" [Z] ] / / ~~O j / ~ A •----1
C~[molm -3] Key Organicdiluent : Toluene 202 O Aqueousmedia: HNO3-NH~N01 106 A 31 [] '
]
'
I
'
I
'
I
--O--O E
o/
-~ -20 E
10-2
[]
--D.
[]
-2.5
[113-
"
nn_/"/
Aqueousmedia i
I
"2
z~
~10-~
3.0
/
O--O--O--
-~,-z~z~-
2.0
o/
T'-
,
I
,
40 pH
I
50
,
z[~D/~ [Z]
NH,N03 (1.0kmolm q, pH=Z,.7]
I
5.0
1.5
20 [og[C@/(moI.m-3)]
2.5
Fig. 2. E f f e c t o f p H on a q u e o u s d i s t r i b u t i o n of C,2SAO [ O r g a n i c d i l u e n t : t o l u e n e , a q u e o u s m e d i a : 1.0 k m o l m -:~ ( H , N H 4 ) N 0 3 ] .
Fig. 3. Distribution of C12SAObetween aqueous nitrate media and each organic diluent (aqueous media: 1.0 kmol m -3 NH4N03, pH=4.7). TABLE1 Partition coefficients of hydroxyoxime e x t r a c t a n t Extractant
Organic diluent
Aqueous media
E-HNBPO' E-HNBPO 1 E-HNBPO 1 E-HNBPO 1 P 502 E-HNAPO 3 E - H N A P O '~ C,2SAO CL2SAO C12SAO
n-Heptane Toluene Chloroform Dispersol4 n-Heptane Dispersol4 MSB 2105 Hexane Cyclohexane Toluene
1.0 1.0 0.1 0.2 10.0 0.1 1.0 1.0 1.0 1.0
kmol kmol kmol kmol kmol kmol kmol kmol kmol kmol
m -3 m -3 m -3 m -3 m -3 m -3 m -3 m -3 m -3 m -a
Na2S04 Na2S04 NaCI04 Na2S04 H2S04 Na2S04 NH4N04 NH4N04 NH4N04 NH4N04
Ka [ - ]
Reference
1.1 × 10 -4 1.4 × 10 -5 2.5 × 10 -5 1.1 × 10 -4 9.3× 10 -5 1.4× 10 -4 2.2 × 10 -4 (3.0 _+0.1 ) × 10 -4 ( 1.4 _+0.2 ) × 10 4 (5.8 +_0.4) × 10 5
8 8 11 12 13 14 15 Thi s work Thi s work Thi s work
'E-2-hydroxy-5-nonylbenzophenone oxime isolated from LIX 65 N. ~5- nonylsalicylaldoxime. 3E-2-hydroxy-5-nonylacetophenone oxime isolated from S M E 529. 4Commercial kerosene-type diluent of Shell Chemical Co. of Japan, Ltd. 5Commercial naphthene-type diluent of Shell Chemical Co. of the Netherland, Ltd.
Figure 3 shows the effect of the reagent c o n c e n t r a t i o n on the distribution of C ~2SAO between 1.0 kmol m -'~ aqueous a m m o n i u m nitrate solution and each organic diluent, i.e., toluene, cyclohexane and hexane based on Eq. 4. T h e plots appear to lie on straight lines with the slope of 1 as expected, for all organic
EXTRACTIONOF COPPERWITH 5-DODECYLSALICYLALDOXIME
253
diluents. The partition coefficient, Kd, was evaluated from the intercept of these straight lines with the ordinate in Fig. 3 for each diluent as listed in Table 1, together with the values with other hydroxyoximes for comparison [8,1115 ]. From Table 1, it is evident that C12SAO is sparingly soluble in the aqueous phase as well as other hydroxyoximes and that Kd increase in the other, toluene < cyclohexane < hexane. This is in accordance with the order of the dielectric constants of these diluents, i.e., toluene < cyclohexane < hexane, which suggests that the partition of C12SAO, an amphiphile compound, to the aqueous phase is affected by the polarity of the organic diluent.
Extraction equilibria of copper(II) Effect of organic diluent on the extraction equilibria The diluent effect on the extraction equilibrium of copper (II) with C12SAO was investigated using aqueous mixtures of ammonium nitrate and nitric acid as the aqueous phase. In the nitrate media, copper(II) ion gives rise to an ion-pair complex with a nitrate anion. Cu ~+ + NO.~_,
"CuNO,+
;~1
(5)
However, the stability constant of this complex, fll is so small (6.3 X 10 -5 m3/ mol [16] ) that its formation can be negligible under the present experimental conditions. It has been reported in a number of papers that copper (II) is extracted with hydroxyoximes as a square planner chelate of the type CuR2, in the organic phase [8,11-15,19 ]. On the other hand, Szymanowski et al. suggested the possibility of the solvation of the chelate, CUR2, by the reagent molecules to form the adducts of the type, CuR2"HR or CuR2-2HR [6]. Consequently, the extraction equilibrium of copper (II) ion with C l eSAO can be generally expressed by the following equation. Cu 2+ + ( 2 + x ) H R ,
"CuR2 "xHR+ 2H +
;Kex
(6)
The extraction equilibrium constant, Kex, is written by: Kox -
[CUR2 "xHR]aH~ [Cu 2+] [HR] 2+x
(7)
The following equation can be obtained, by combining Eq. 7 and the distribution ratio of copper (II), D, defined by Eq. 9. log D'aH2 = (2+x)log [HR] +log K~x
(8)
D - [CUR2-xHR] _ [CUR2-xHR]
(9)
Ccu
[ C u ~+ ]
954
K. YOSHIZUKA ET AL. -7-
I
T
Aqueous mediQ HN03-NH,NO]
5.5
T
1
/~/ /~ /
:/.," o/o
•50
o/?
r~
o 45
4.0 1.0
1.5
2.0
log[C~/(molm-3)] Fig. 4. D i s t r i b u t i o n of copper (II) in e x t r a c t i o n f r o m a q u e o u s n i t r a t e m e d i a w i t h C12SAO in various organic d i l u e n t s [ A q u e o u s media: 1.0 k m o l m -3 ( H , N H 4 ) N 0 3 ] . TABLE2 Equilibrium constants of copper (II) extraction with hydroxyoxime extractants Extractant
Organic diluent
Aqueous media
Kex [ - ]
Reference
E-HNBPO E-HNBPO E-HNBPO E-HNBPO E-HNAPO E-HNAPO CL2SAO C~2SAO C,2SAO C~zSAO C~2SA0
n-Heptane Toluene Dispersol Toluene Dispersol MSB 210 Hexane Cyclohexane Toluene Toluene Toluene
1.0 kmol m -3 NauSO 4 1.0 kmol m -3 Na2S04 0.2 kmol m -3 Na2S04 1.0 kmol m -~ NaeS04 0.2 kmol m -~ Na~SO4 1.0 kmol m -3 NH4N03 1.0 kmol m -~ NH4NO3 1.0 kmol m -3 NH4N03 1.0 kmol m -3 NH4N03 H 2 S Q (var. conc. ) HC1 (var. conc.)
1.55 × 102 3.60 2.50 7.2 × 10-2 1.1 +-0.3 1.9× 101 (9.32 +- 0.45) × 101 (5.37 +_0.30) × 101 ( 1.26 _+0.07 ) × 10' (1.21 _+0.07) × 10' (1.46+_0.08)×101
8 8 12 19 14 15 This This This This This
work work work work work
where Ccu and [Cu 2+ ] are the concentrations of the total copper (II) and the free aqua-copper (II) ion, respectively and these are equal under the present experimental conditions as mentioned earlier. Furthermore, since [HR] is equal to C ~ , Eq. 8 is reduced as follows: log D.
all2 = ( 2
+ x) log Ch~ + log Kex
(10)
Figure 4 shows the plot of the experimental data for each diluent according to Eq. 10. Straight lines with the slope of 2 were obtained for all diluents. This
EXTRACTION OF COPPERWITH 5-DODECYLSALICYLALDOXIME
255
fact indicates that x = 0, that is, copper (II) is extracted as a chelate of the type, CUR2, in the organic phase. The equilibrium constants of the extraction reaction described by Eq. 6, Kex, were evaluated for each diluent from the intersections of the straight lines with the ordinate in Fig. 4 as listed in Table 2. It can be seen from Table 2 that K~x markedly increase in the order, toluene < cyclohexane < hexane, which is in agreement with the expected increase in the aqueous solubility of C12SAO mentioned earlier. However, the increase is not se great as that observed in the extraction with E - H N B P O by Komasawa et al. [8] who reported that the value of Kex obtained in the extraction using heptane as a diluent is about forty times greater t h a n that using toluene.
Ef[ect of aqueous media on extraction equilibrium The effect of aqueous media on the extraction equilibrium of copper (II) with C12SAO dissolved in toluene was examined using three kinds of the aqueous media, i.e., sulfuric acid and hydrochloric acid in addition to the aqueous mixture of a m m o n i u m nitrate and nitric acid. Cupric sulfate and chloride are not completely dissociated in the aqueous phase, but give rise to ion-pair complexes, depending on the activity of sulfuric acid or hydrochloric acid. The concentration of free aqua-copper(II) ion, [Cu 2÷ ] is expressed using the correlation factor, a, as follows: [Cu 2+ ] =Ccu/a
(11)
The correlation factor, a, is nearly equal to 1 for nitrate media as mentioned earlier and expressed for the other two aqueous media as follows: for sulfate media [17],
~ C u S O 4 ; ~1 = 1 . 9 1 × 1 0
Cu2+ --~SO2-
-1 [m a mo1-1 ]
(12)
( 13 )
= 1 +ill as04 for chloride media [ 18 ], Cu2+ +C1 - .
"CuCI+; fll = 1.55× 10 -5 [ma mo1-1]
Cu2++2C1 - . OL: 1 + ~1 acl
,CuC12;f12=1.00×10-8 [m6mol 2] +
fl2a~l
(14) (15) (16)
Taking account of the complexation of copper (II) ion in the aqueous media, the distribution ratio of copper (II) is rewritten using ~ as follows: D. a -
[ uR2]-a Cc,
=Kex (CH~/aH)2
l o g D ' a = 2 log (CHR/aH) +logKex
( 17 ) (18)
25~
K.YOSHIZUKAETAL.
2.O Aqueous media Key I-HNO3-NH~N03 o l 1 H2SO~(varconc.) A I
I
S
/
HC[ (v?rconc) 1 [] I-
Organic diluent :Toluene 1.0
g
~o O
-1.0
~1~ ~ S
? -2.C -2.0
I
I I -I .0 logC~/OH
Fig. 5. Distribution of copper (II) in extraction from various aqueous media with C,2SAOin toluene. Figure 5 shows the plot of log D ' a against log ( C ~ / a n ) for each aqueous media according to Eq. 18. The plots are lying on a single straight line with the slope of 2 regardless of the aqueous media, which suggests that the values of Kex are nearly the same for each aqueous medium. The extraction equilibrium constants evaluated in the present study for various diluents and aqueous media are summarized in Table 2, together with the literature values observed with other commercial hydroxyoximes for comparison [8,12,14,15,19]. Compared with E-HNBPO and E-HNAPO, the active component of LIX 65 N and SME 529, respectively, the values with C,2SAO are several times greater than those with E-HNBPO and E-HNAPO. This suggests that LIX 860 is much more powerful extractant for copper (II) than LIX 65N and SME 529 as mentioned in the literature [ 1 ].
Effect of addition of 1-tridecanol on extraction equilibrium Figure 6 shows the effect of the initial concentration of 1-tridecanol added, CLO, on the relation between the distribution ratio of copper (II) and pH in the extraction with CleSAO in hexane and toluene from 1.0 kmol m -~ aqueous nitrate media under the initial concentration of C,2SAO, Chno = 37.6 mol m - 3 Figure 7 shows the relationship between the ratio of the distribution ratio of copper(II) with the organic phase containing 1-tridecanol, D', to that containing the extractant alone, D, and the concentration of 1-tridecanol in the
EXTRACTIONOF COPPERWITH 5-DODECYLSALICYLALDOXIME
/ /O
/ O O
257
Aqueous media HNO3-NH~NO3 C~:37.6 mol.m 3
1.0 = O ' --- / ~ .
'
'
' -J Organic diluent Key ~ Hexane O
[]
/
l
I
I
I
I
i
]
-1.0 10-1
~
=
t
-2.0
/
,"./to
•l
t
i
i
I
- / u # " • / I C~o
-3.0
O
D
/"
'".~
~" • "
,
,
-to /
/"
~ ,
I
I '
I | 0.5
o
[]
156
e
-
936
• 1.0
•
pH
\o
10 2
/[mol.m-3]Hexane Toluene
4
/ w
I
Key
Aqueousme6ia ~ O HNO~-NH~N03(pH=05} C~=37.6 mol.m -3
10-
I
0
i
i
i
i
I
I
I
]
i
5 10 10-~C[~ [mol.m -3]
Fig. 6. Effect of addition of 1-tridecanol on distribution of copper(II) [organic diluent: hexane and toluene, aqueous media: 1.0 kmol m -3 (H,NH4)N03]. Fig. 7. Relationship between ratio, D'/D, and concentration of 1-tridecanol in organic phase [organic diluent: hexane and toluene, aqueous media: 1.0 kmol m -3 ( H , N H 4 ) N Q ] .
organic phase. From these figures, it is evident that the distribution ratio of copper (II) remarkably decreases with increasing CLO, and that the decrease is greater in hexane than in toluene. The infrared spectra of C12SAO alone and the mixture of C12SAO and 1tridecanol in CC14 are shown in Fig. 8. In the case of C,2SAO alone, the weak absorption bands at 3560 c m - 1 and 3400 c m - 1 are assigned to the free oximic OH and the phenolic OH associated with oxime group through the intramolecular hydrogen bond, respectively. By the addition of 1-tridecanol, the intensity of the absorption bands at 3560 c m - 1 and 3400 c m - 1 decrease, while the weak absorption band at 3610 c m - 1 due to the free OH of 1-tridecanol and the strong adsorption band at 3300 c m - 1 due to the associated OH increases with increasing 1-tridecanol concentration, owing to the increase of intermolecular hydrogen bond between C12SAO and 1-tridecanol. The 1H-n.m.r. spectra of C12SAO alone and the mixture of C12SAO and 1tridecanol are shown in Fig. 9. At low concentration of 1-tridecanol (spectra 2, 3), the signal of oximic OH (signal a) shifts toward the lower magnetic field with increasing 1-tridecanol concentration due to the increase of intermolecular hydrogen bond between C12SAO and 1-tridecanol. While in the high concentration region of 1-tridecanol (spectra 4, 5 ), the signal of phenolic OH ( signal b) shifts toward the lower magnetic field with increasing 1-tridecanol
258
K. YOSHIZUKAET AL. I
I
I
I
Cl) 0.1 kmol.rrr3 C12SAO
~'~ g
/,v~ ~kmol-m-3 C12SA0
I
~ ~J"31
I
4000
J/
(3)oi kmol-~-3C~2SA0
"" \
~1 I [
(4) o] kmoim-3 G2SA0
3500
3000 2500 [cm-q
2000
Fig. 8. Infrared spectra of C12SAO alone a n d mixture of C12SAO and 1-tridecanol (in CC14 at 300 K, 0.05 m m calcium fluoride cell).
(5) 0.1 kmolm-3 Q2SAO*2 5kmoL m-31-Trideconol
[b)
Co)
[4) 0.1 kmol m-3 C12SA0.I 0 kmol.rn-3 l-Trideconol (b)
(a]
(3) 0.1 kmol.m-] C12SA0÷0.Ikmo{ m-31-Trideconol [b) (2) 0.1kmol m-3C12SAO
I ....
[b)
ILlj! l,il~ Ca) t
jk ...Ca)
:1)0.01 kmoL m-3 C12SAO
_ .I~LIJ,h,
(b)
12
1'1
i'o
6 5 [ppm]
Fig. 9. ~H-n.m.r. spectra of C~2SAO alone and mixture of C~2SAO and l-tridecanol (in CDCL:~ at 300 K, 270 MHz T M S as an internal standard).
concentration. It is considered that two molecules of 1-tridecanol consecutively form the hydrogen bonds with two hydroxyl groups of C12SAO, which decreases the activity of C12SAO, as shown in Fig. 10.
EXTRACTION OF COPPER WITH 5-DODECYLSALICYLALDOXIME
R'-0%
~,H OH---N,,oH
259
2'-o~_
c,H OH---N
"OH ,o~
c,H OH, N\
R"
,'OILIOH R" ,0~ R"
R = C,2H2s, R'=C13H27 Fig, 10. Formation scheme of intermolecular complex between C]2SAO and 1-tridecanol.
Consequently, the consecutive formations of the hydrogen bonds between C12SAO and 1-tridecanols can be described by: HR +L. HR-L + L .
" HR.L " HR-2L
;Kf, ;K~2
(19) (20)
Here, HR" L and HR" 2L represent the intermolecular complexes by the formation of hydrogen bonds. Assuming that the formation constant, Kfl is much greater than K,.2, for simplicity, the concentration of active C12SAO, [HR], CHR and C~o are expressed as follows:
[HR] = CH~/(l+Kr, [L] )
(21)
CHR= [HR] + [HR'L]
(22)
CL6= ILl + [HR'L]
(23)
where [L] denotesthe concentrationof free l-tridecanol at equilibrium and can be expressedby the followingequation from Eqs. (21)-(23). [ L ] = ( CLO -- C . R -- 1/Kr~ ) + x ~ L 0 2 -- C~n - 1/Kf, )2 + 4CL~/Kf,
(24)
The ratio, D ' / D , is expressed as follows: log D ' / D = - 2 log (1 +Kfl [L] )
(25)
By means of the curve fitting method on the basis of Eq. 25, the equilibrium constants for the formation of the intermolecular complex, Kn, were evaluated as (1.85 + 0.33 ) × 10-z m3/mol for hexane and (4.66 +_1.04 ) × 10-3 m3/mol for toluene. The solid curves in Figs. 6 and 7 were calculated from Eqs. (24) and (25) using the evaluated values of Kn. From the comparison of these two values, it is seen the extent of the formation of the intermolecular complex in
260
K. YOSHIZUKA ET AL.
hexane is four times greater than that in toluene. This suggests that toluene keeps the activity of C12SAO, due to the formation of hydrogen bonds between the two hydroxyl groups of C12SAO and conjugated double bonds of toluene [ 20 ], excluding the hydrogen bond with 1-tridecanol. CONCLUSION
The equilibrium studies were conducted at 303 K to clarify the effects of the organic diluent, the aqueous media and the addition of 1-tridecanol as the equilibrium modifier on the extraction equilibria of copper (II) with 5-dodecylsalicylaldoxime, the active component of LIX 860, together with measurements of apparent molecular weight and aqueous solubility of the extractant, and infrared and 1H-n.m.r. spectra of the extractant and 1-tridecanol. The following results were obtained. (1) The extractant exists as a monomeric species in the organic diluents, i.e., hexane, cyclohexane and toluene. (2) The extractant is sparingly soluble in the aqueous phase as well as other commercial hydroxyoximes. (3) Copper (II) is extracted as a chelate of the type CuR2 into the organic phase and the extraction equilibrium constant increases in the order, toluene < cyclohexane < hexane. (4) As to the effect of the aqueous media, the equilibrium distribution of copper (II) can be quantitatively expressed in terms of the nearly same values of the equilibrium constant whether for the extraction from aqueous nitrate media or for those from hydrochloric acid and sulfuric acid by properly correcting the effects of the complexing anions, i.e., chloride and sulfate ions in the aqueous phase. (5) The extraction of copper(II) remarkably decreased by the addition of 1-tridecanol, due to the formation of the hydrogen bond between the extractant and 1-tridecanol in the organic phase and the extent of the formation of the hydrogen bond in hexane was greater than that in toluene. ACKNOWLEDGEMENTS
The authors gratefully acknowledge the kind supply of 5-dodecylsalicylaldoxime from Henkel Corporation, Minneapolis U.S.A., and also grateful to Profs. T. Matsuda and F. Wada of Kyushu University for their helpful suggestions and discussions on the infrared and 1H-n.m.r. spectra of the reagents.
EXTRACTION OF COPPER WITH 5-DODECYLSALICYLALDOXIME
261
REFERENCES 1 Dalton, R.F. and Seward, G.W., 1984. In: M.J. Jones and R. Oblatt (Editors), Reagent in the Mineral Industry, Inst. Min. Metall., London, pp. 107-116. 2 Kordosky, G.A., Olafson, S.M., Lewis, R.G., Definer, V.L. and House, J.E., 1987. Sep. Sci. Technol., 22: 215-232. 3 Stepniak-Biniakiewicz, D. and Szymanowski, J., 1979. J. Chem. Tech. Biotechnol., 29: 686693. 4 Stepniak-Biniakiewicz, D. and Szymanowski, J., 1981. J. Chem. Tech. Biotechnol., 31: 470474. 5 Stepniak-Biniakiewicz, D. and Szymanowski, J., 1981. J. Hydrometallurgy, 7: 299-313. 6 Szymanowski, J., Sobczynska, A., Stepniak-Biniakiewicz, D. and Borowiak-Resterna, A., 1983. J. Prak. Chem., 325: 985-994. 7 Nakashio, F., Kondo, K., Murakami, A. and Akiyoshi, Y., 1982. J. Chem. Eng. Jpn., 15: 274279. 8 Komasawa, I., Otake, T. and Yamada, A., 1980. J. Chem. Eng. Jpn., 13:130 136. 9 Ashbrook, A.W., 1972. Anal. Chim. Acta, 58: 115-118. 10 Marcus, Y. and Kertes, A.S., 1969. Solvent Extraction and Ion Exchange of Metal Complexes. Wiley, New York, N.Y., pp. 922-923. 11 Carter, S.P. and Freiser, H., 1980. Anal. Chem., 52: 511-514. 12 Kojima, T., Tomita, J. and Miyauchi, T., 1979. Kagaku Kogaku Ronbunshu, 5: 476-481. 13 Whewell, R.J., Hughes, M.A. and Hanson, C., 1979. Proc. Int. Solvent Extr. Conf. (ISEC 77), CIM Spec. Vol., 185-192. 14 Miyake, Y., Takenoshita, Y. and Teramoto, M., 1983. J. Chem. Eng. Jpn., 16: 203-209. 15 Inoue, K. and Tsunomachi, H., 1984. Hydrometallurgy, 13: 73-87. 16 Davis, A.R. and Chong, C., 1972. Inorg. Chem., 11:1891 1895. 17 Hemmes, P. and Petrucci, S., 1970. J. Phys. Chem., 74: 467-468. 18 Aguilar, M., Valiente, M., Massana, A., Coello, J., Aparicio, J.L., Ferngndez, L.A. and Muhammed, M., 1986. Proc. Int. Solvent Extr. Conf. (ISEC '86) 2, pp. 239-246. 19 Flett, D.S., Okuhara, D.N. and Spink, D.R., 1973. J. Inorg. Nucl. Chem., 25:2471 2476. 20 Komasawa, I. and Otake, T., 1983. J. Chem. Eng. Jpn., 16: 377-383.
247
Equilibria of Solvent Extraction of Copper(II) with 5-Dodecylsalicylaldoxime KAZUHARU YOSHIZUKA, HIROSHI ARITA, YOSHINARI BABA and KATSUTOSHI INOUE
Department of Applied Chemistry, Saga University, Honjo-machi, Saga 840 (Japan) (Received June 16, 1988; revised and accepted March 10, 1989)
ABSTRACT Yoshizuka, K., Arita, H., Baba, Y and Inoue, K., 1990. Equilibria of solvent extraction of copper (II) with 5-dodecylsalicylaldoxime. HydrometaUurgy, 23:247-261. The equilibrium studies on the solvent extraction of copper (II) with 5-dodecylsalicylaldoxime, the active component of LIX 860, were carried out at 303 K to clarify the effects of the organic diluent and the aqueous media, together with measurements of the apparent molecular weight and aqueous solubility of the extractant. It was found that the title extractant exists as a monomeric species in the organic diluents, i.e., hexane, cyclohexane and toluene and is sparingly soluble in the aqueous solutions as well as other commercial hydroxyoximes. Copper (II) was extracted as a chelate of the type CuR2 in the organic solution and the extraction equilibrium constant in hexane is about five times and twice greater than those in toluene and cyclohexane respectively, and further, the extraction equilibrium constant with 5-dodecylsalicylaldoxime was several times greater than those with other commercial hydroxyoximes. The effect of 1-tridecanol as a modifier on the extraction equilibrium was quantitatively clarified by taking account of the formation of the hydrogen bond between the extractant and 1-tridecanol.
INTRODUCTION
Aromatic fl-hydroxyoximes as extracting reagents of copper (II) are divided into two classes: ketoximes and salicylaldoximes as shown in Fig. 1. The former are further divided into two subclasses, i.e., benzophenone oximes such as LIX 65N and ABF 2, a Soviet commercial hydroxyoxime, and alkanophenone oximes such as SME 529 (now available as Henkel's LIX 84 ) and OMG, another Soviet commercial hydroxyoxime. Compared with ketoximes, the salicylaldoximes are much stronger copper extractants with considerable advantages of rapid copper transfer kinetics, excellent copper over iron selectivity and rapid phase separation. These are the reasons of remarkable market penetration achieved by the Acorga reagents since 1979 [1 ]. Salicylaldoximes are, however, so strong as copper extractants
0304-386X/90/$03.50
© 1990 Elsevier Science Publishers B.V.
248
K. YOSHIZUKAET AL.
Aromotic [3-hydroxyoxime SaLicylaidoxime (o} , . . rI3enzophenone oxime (b} ~e~°xlme/A [ k (1nophenone oxime (c) OH--I~.o H
O•H .. ~ ' ~
(c)
"OH
R: C9H~9
P -50
R = Q~H2s
LIX 860
R =C9H19
LIX 65N
R=t-C,H,7
AI3F2
LIX 64N= L[X65N*L[X 63 (-lvol°/o)
C9H19 X= CH3
" LIX 84 (SME 529)
X: C,H2n.l(n=4_S)
" OMG
c-x OH..N.oH
Fig. 1. Chemical structure of commercial hydroxyoxime reagents.
that they are often used in combination with an equilibrium modifier so that they can be stripped with a typical tankhouse electrolyte. Acorga P-5100 and 5300 reagents are the combination of P-50 reagent, 5nonylsalicylaldoxime, and p-nonylphenol with the ratios of 1:1 and 1:3 respectively while PT-5050 reagent is a version of P-5300 reagent, in which the p-nonylphenol is replaced with tridecanol to avoid some troubles of accelerating reagent degradation and deleterious effects of certain materials of construction by p-nonylphenol [2 ]. To compete with the Acorga reagents, Henkel Corp. offered a series of new reagents, the active component of which is 5-dodecylsalicylaldoximeas follows
[21: LIX 860: 5-dodecylsalicylaldoximewith kerosene make-up LIX 864: a mixture of LIX 64N with LIX 860 LIX 865: a mixture of LIX 65N with LIX 860 LIX 984: a mixture of LIX 84 with LIX 860 LIX 622: a mixture of LIX 860 with tridecanol in LIX 864, 865 and 984. It has been suggested that the ketoxime acts in the same way as a modifier for the salicylaldoxime on the strip side of the solvent extraction circuit [ 1 ]. There appears to be only a small number of works on the solvent extraction of metal ions with 5-alkylsalicylaldoximes though numerous works have been done on that with benzophenone-type ketoximes, especially with E-2-hydroxy5-nonylbenzophenone oxime, the active species of LIX 65N and 64N. Stepniak-Biniakiewicz and Szymanowski conducted a series of fundamental investigations on the equilibrium aspects of extraction of copper (II) and nickel (II)
EXTRACTION OF COPPER WITH 5-DODECYLSALICYLALDOXIME
249
with some pure 5-alkylsalicylaldoximes including 5-tert-butylaldoxime and elucidated the composition of the extracted species and the diluent effects [36]. In the present paper, we conducted a fundamental investigation on the equilibrium aspects of the solvent extraction of copper(II) with 5-dodecylsalicylaldoxime, the active species of Henkel's "second generation" hydroxyoximes mentioned earlier and elucidated the stoichiometric relation of the extraction reaction and the effects of the chemistry of the aqueous media, the organic diluents and 1-tridecanol as an equilibrium modifier as well as the aqueous distribution of the extractant. EXPERIMENTAL
Reagents 5-dodecylsalicylaldoxime, abbreviated to CleSAO and denoted by HR hereafter, was kindly supplied from Henkel Corp. and used as received without further purification. The molecular weight of monomeric species of C12SAO is 305.5. The purity of the reagent was found to be above 90% by measurement of the ultimate loading of copper (II) to the reagent. Commercial reagent grade of 1-tridecanol (Tokyo Kasei Co. Ltd. ), denoted by L hereafter, was used also as received without further purification. Commercial reagent grade of toluene, hexane and cyclohexane were used as organic diluents also without further purification. Other inorganic reagents, copper(II) nitrate, nitric acid, ammonium nitrate, hydrochloric acid and sulfuric acid were all commercial reagent grade. Working solution of the organic phase was prepared by dissolving C12SAO and/or 1-tridecanol in each organic diluent to required concentrations on a gravimetric basis. The concentration of the active component was determined by the ultimate loading of copper (II) to the organic phase. Aqueous copper solutions were prepared by dissolving copper(II) nitrate into the following aqueous media: (1) aqueous mixture of 1.0 kmol m -3 ammonium nitrate and nitric acid in which ionic strength was maintained constant at 1.0 kmol m -:~ and pH was varied by changing the volume ratio of the two solutions, (2) hydrochloric acid and (3) sulfuric acid with varying concentrations.
Apparent molecular weight of CI2SAO Apparent molecular weight of C12SAO in each organic solvent was measured using a Corona model 117 vapor-phase osmometer, with benzil as a standard material.
250
K. YOSHIZUKA ET AL.
Aqueous distribution of CI2SAO The aqueous distribution of C12SAO was measured at 303 K, according to the same methods of Komasawa et al. [8] and Ashbrook [9]. Solution of C12SAO in each diluent and 1.0 kmol m -3 aqueous ammonium nitrate solution were shaken with appropriate volume ratios ( 1 : 5 0 - 1 : 2 0 ) for 12 h. After the two phases had been allowed to be settled for more than 2 h, they were separated. A weighed aqueous phase was transferred to a separatory funnel, to which a small volume of copper (II) nitrate solution (30 mol m - 3, p H = 6 ) was added, and shaken gently for 10 min. C~2SAO dissolved in the aqueous phase was thus completely converted to be copper(II) chelate. A small amount of hexane (usually 10 cm 3) was added and shaken vigorously for 2 h to transfer the copper chelate into hexane. The concentration of the copper (II) chelate in the organic phase was measured at 355 nm using a Shimadzu model UV-160 spectrophotometer. The p H of the aqueous phase was measured using a TOA model H M 20E p H meter.
Equilibrium distribution of copper(II) Equal volumes of aqueous and organic phases were shaken in a flask immersed in a thermostatted water-bath maintained at 303 K to attain equilibrium. After 8 h, the two phases were separated. A known volume of the organic phase was stripped with 3.0 kmol m -3 hydrochloric acid and diluted to an appropriate ratio. Copper concentration in the resulting aqueous were determined by E D T A titration; the concentration of hydrogen ion in the aqueous phase after equilibration was determined by titration with sodium hydroxide solution using phenolphthalein as an indicator to calculate the activity of hydrogen ion referring to the activity coefficient in literature [ 10 ].
Spectroscopic studies of CI2SAO and 1-tridecanol Infrared spectra between 4000 and 2000 cm - ~ were recorded for CC14solutions of CI2SAO a n d / o r l-tridecanol under investigation using a JASCO model A-100 spectrometer, with 0.05 mm calcium fluoride cells. iH-n.m.r, spectra for C12SAO and l-tridecanol dissolved in CDC13 were registered with a J E O L model J N M - G X 2 7 0 T - N M R spectrometer. RESULTS AND DISCUSSION
Apparent molecular weight of Ci2SAO Since it is known that commercial hydroxyoximes such as L I X 65N and S M E 529 partly exist as dimeric species in nonpolar organic diluents
EXTRACTIONOF COPPER WITH 5-DODECYLSALICYLALDOXIME
251
[5,8,12,13 ], it is necessary to examine the aggregation of C,2SAO in the various diluents to clarify the extraction mechanism. From the measurement of the apparent molecular weights, Mw, in the organic diluents by means of vapor-phase osmometry, the apparent molecular weights were evaluated as follows: M w = 302 in toluene, 296 in cyclohexane and 303 in hexane. Since all of the apparent molecular weights of C,2SAO in each diluent are in good agreement with the calculated molecular weight of monometric C12SAO, it can be concluded that C,2SAO exists as a monomeric species in the above-mentioned organic diluents, contrary to the other hydroxyoximes.
Aqueous distribution of C~2SAO A hydroxyoxime extractant in the organic phase is partitioned to the aqueous phase accompanied by acid dissociation at high pH, as follows: HR.
"HR
;Kd
HR.
"R-+H +
(1) ;Ka
(2)
where Kd and Ka denote the partition coefficient and the acid dissociation constant of the extractant, respectively and the bar superscript denotes the organic phase. Since the aggregation of C12SAO in the organic phases can be ignored as mentioned above, the concentration of the monomeric species of ClzSAO in the organic phase, [HR], is nearly equal to its total or analytical concentration, CHR. From the above equilibrium relations, the analytical concentration of C12SAO in the aqueous phase, CuR, is described as follows: CHR =Ka X (l +Ka/aH) x C ~
(3)
where aH is the activity of hydrogen ion. Figure 2 shows the effect of pH on the distribution of C12SAO between toluene and 1.0 kmol m-3 aqueous ammonium nitrate solutions for various initial concentration of C12SAO in the organic phase, CHRO- It is evident that CHR is independent of pH, which suggests that the acid dissociation of C12SAO in the aqueous phase is negligibly small over the whole pH under the present experimental conditions. From this result, Eq. 3 can be simplified and the logarithm of CHR is approximately expressed as follows: l o g CHR
=log Ch~ +log Kd
The subsequent measurements were carried out at a constant pH of 4.7.
(4)
'.2)52
K. YOSHIZUKA ET AL.
Organic diluent Key F r r Hexane O -I .5 Cyc[ohexane z~ k £ Toluene 1" [Z] ] / / ~~O j / ~ A •----1
C~[molm -3] Key Organicdiluent : Toluene 202 O Aqueousmedia: HNO3-NH~N01 106 A 31 [] '
]
'
I
'
I
'
I
--O--O E
o/
-~ -20 E
10-2
[]
--D.
[]
-2.5
[113-
"
nn_/"/
Aqueousmedia i
I
"2
z~
~10-~
3.0
/
O--O--O--
-~,-z~z~-
2.0
o/
T'-
,
I
,
40 pH
I
50
,
z[~D/~ [Z]
NH,N03 (1.0kmolm q, pH=Z,.7]
I
5.0
1.5
20 [og[C@/(moI.m-3)]
2.5
Fig. 2. E f f e c t o f p H on a q u e o u s d i s t r i b u t i o n of C,2SAO [ O r g a n i c d i l u e n t : t o l u e n e , a q u e o u s m e d i a : 1.0 k m o l m -:~ ( H , N H 4 ) N 0 3 ] .
Fig. 3. Distribution of C12SAObetween aqueous nitrate media and each organic diluent (aqueous media: 1.0 kmol m -3 NH4N03, pH=4.7). TABLE1 Partition coefficients of hydroxyoxime e x t r a c t a n t Extractant
Organic diluent
Aqueous media
E-HNBPO' E-HNBPO 1 E-HNBPO 1 E-HNBPO 1 P 502 E-HNAPO 3 E - H N A P O '~ C,2SAO CL2SAO C12SAO
n-Heptane Toluene Chloroform Dispersol4 n-Heptane Dispersol4 MSB 2105 Hexane Cyclohexane Toluene
1.0 1.0 0.1 0.2 10.0 0.1 1.0 1.0 1.0 1.0
kmol kmol kmol kmol kmol kmol kmol kmol kmol kmol
m -3 m -3 m -3 m -3 m -3 m -3 m -3 m -3 m -3 m -a
Na2S04 Na2S04 NaCI04 Na2S04 H2S04 Na2S04 NH4N04 NH4N04 NH4N04 NH4N04
Ka [ - ]
Reference
1.1 × 10 -4 1.4 × 10 -5 2.5 × 10 -5 1.1 × 10 -4 9.3× 10 -5 1.4× 10 -4 2.2 × 10 -4 (3.0 _+0.1 ) × 10 -4 ( 1.4 _+0.2 ) × 10 4 (5.8 +_0.4) × 10 5
8 8 11 12 13 14 15 Thi s work Thi s work Thi s work
'E-2-hydroxy-5-nonylbenzophenone oxime isolated from LIX 65 N. ~5- nonylsalicylaldoxime. 3E-2-hydroxy-5-nonylacetophenone oxime isolated from S M E 529. 4Commercial kerosene-type diluent of Shell Chemical Co. of Japan, Ltd. 5Commercial naphthene-type diluent of Shell Chemical Co. of the Netherland, Ltd.
Figure 3 shows the effect of the reagent c o n c e n t r a t i o n on the distribution of C ~2SAO between 1.0 kmol m -'~ aqueous a m m o n i u m nitrate solution and each organic diluent, i.e., toluene, cyclohexane and hexane based on Eq. 4. T h e plots appear to lie on straight lines with the slope of 1 as expected, for all organic
EXTRACTIONOF COPPERWITH 5-DODECYLSALICYLALDOXIME
253
diluents. The partition coefficient, Kd, was evaluated from the intercept of these straight lines with the ordinate in Fig. 3 for each diluent as listed in Table 1, together with the values with other hydroxyoximes for comparison [8,1115 ]. From Table 1, it is evident that C12SAO is sparingly soluble in the aqueous phase as well as other hydroxyoximes and that Kd increase in the other, toluene < cyclohexane < hexane. This is in accordance with the order of the dielectric constants of these diluents, i.e., toluene < cyclohexane < hexane, which suggests that the partition of C12SAO, an amphiphile compound, to the aqueous phase is affected by the polarity of the organic diluent.
Extraction equilibria of copper(II) Effect of organic diluent on the extraction equilibria The diluent effect on the extraction equilibrium of copper (II) with C12SAO was investigated using aqueous mixtures of ammonium nitrate and nitric acid as the aqueous phase. In the nitrate media, copper(II) ion gives rise to an ion-pair complex with a nitrate anion. Cu ~+ + NO.~_,
"CuNO,+
;~1
(5)
However, the stability constant of this complex, fll is so small (6.3 X 10 -5 m3/ mol [16] ) that its formation can be negligible under the present experimental conditions. It has been reported in a number of papers that copper (II) is extracted with hydroxyoximes as a square planner chelate of the type CuR2, in the organic phase [8,11-15,19 ]. On the other hand, Szymanowski et al. suggested the possibility of the solvation of the chelate, CUR2, by the reagent molecules to form the adducts of the type, CuR2"HR or CuR2-2HR [6]. Consequently, the extraction equilibrium of copper (II) ion with C l eSAO can be generally expressed by the following equation. Cu 2+ + ( 2 + x ) H R ,
"CuR2 "xHR+ 2H +
;Kex
(6)
The extraction equilibrium constant, Kex, is written by: Kox -
[CUR2 "xHR]aH~ [Cu 2+] [HR] 2+x
(7)
The following equation can be obtained, by combining Eq. 7 and the distribution ratio of copper (II), D, defined by Eq. 9. log D'aH2 = (2+x)log [HR] +log K~x
(8)
D - [CUR2-xHR] _ [CUR2-xHR]
(9)
Ccu
[ C u ~+ ]
954
K. YOSHIZUKA ET AL. -7-
I
T
Aqueous mediQ HN03-NH,NO]
5.5
T
1
/~/ /~ /
:/.," o/o
•50
o/?
r~
o 45
4.0 1.0
1.5
2.0
log[C~/(molm-3)] Fig. 4. D i s t r i b u t i o n of copper (II) in e x t r a c t i o n f r o m a q u e o u s n i t r a t e m e d i a w i t h C12SAO in various organic d i l u e n t s [ A q u e o u s media: 1.0 k m o l m -3 ( H , N H 4 ) N 0 3 ] . TABLE2 Equilibrium constants of copper (II) extraction with hydroxyoxime extractants Extractant
Organic diluent
Aqueous media
Kex [ - ]
Reference
E-HNBPO E-HNBPO E-HNBPO E-HNBPO E-HNAPO E-HNAPO CL2SAO C~2SAO C,2SAO C~zSAO C~2SA0
n-Heptane Toluene Dispersol Toluene Dispersol MSB 210 Hexane Cyclohexane Toluene Toluene Toluene
1.0 kmol m -3 NauSO 4 1.0 kmol m -3 Na2S04 0.2 kmol m -3 Na2S04 1.0 kmol m -~ NaeS04 0.2 kmol m -~ Na~SO4 1.0 kmol m -3 NH4N03 1.0 kmol m -~ NH4NO3 1.0 kmol m -3 NH4N03 1.0 kmol m -3 NH4N03 H 2 S Q (var. conc. ) HC1 (var. conc.)
1.55 × 102 3.60 2.50 7.2 × 10-2 1.1 +-0.3 1.9× 101 (9.32 +- 0.45) × 101 (5.37 +_0.30) × 101 ( 1.26 _+0.07 ) × 10' (1.21 _+0.07) × 10' (1.46+_0.08)×101
8 8 12 19 14 15 This This This This This
work work work work work
where Ccu and [Cu 2+ ] are the concentrations of the total copper (II) and the free aqua-copper (II) ion, respectively and these are equal under the present experimental conditions as mentioned earlier. Furthermore, since [HR] is equal to C ~ , Eq. 8 is reduced as follows: log D.
all2 = ( 2
+ x) log Ch~ + log Kex
(10)
Figure 4 shows the plot of the experimental data for each diluent according to Eq. 10. Straight lines with the slope of 2 were obtained for all diluents. This
EXTRACTION OF COPPERWITH 5-DODECYLSALICYLALDOXIME
255
fact indicates that x = 0, that is, copper (II) is extracted as a chelate of the type, CUR2, in the organic phase. The equilibrium constants of the extraction reaction described by Eq. 6, Kex, were evaluated for each diluent from the intersections of the straight lines with the ordinate in Fig. 4 as listed in Table 2. It can be seen from Table 2 that K~x markedly increase in the order, toluene < cyclohexane < hexane, which is in agreement with the expected increase in the aqueous solubility of C12SAO mentioned earlier. However, the increase is not se great as that observed in the extraction with E - H N B P O by Komasawa et al. [8] who reported that the value of Kex obtained in the extraction using heptane as a diluent is about forty times greater t h a n that using toluene.
Ef[ect of aqueous media on extraction equilibrium The effect of aqueous media on the extraction equilibrium of copper (II) with C12SAO dissolved in toluene was examined using three kinds of the aqueous media, i.e., sulfuric acid and hydrochloric acid in addition to the aqueous mixture of a m m o n i u m nitrate and nitric acid. Cupric sulfate and chloride are not completely dissociated in the aqueous phase, but give rise to ion-pair complexes, depending on the activity of sulfuric acid or hydrochloric acid. The concentration of free aqua-copper(II) ion, [Cu 2÷ ] is expressed using the correlation factor, a, as follows: [Cu 2+ ] =Ccu/a
(11)
The correlation factor, a, is nearly equal to 1 for nitrate media as mentioned earlier and expressed for the other two aqueous media as follows: for sulfate media [17],
~ C u S O 4 ; ~1 = 1 . 9 1 × 1 0
Cu2+ --~SO2-
-1 [m a mo1-1 ]
(12)
( 13 )
= 1 +ill as04 for chloride media [ 18 ], Cu2+ +C1 - .
"CuCI+; fll = 1.55× 10 -5 [ma mo1-1]
Cu2++2C1 - . OL: 1 + ~1 acl
,CuC12;f12=1.00×10-8 [m6mol 2] +
fl2a~l
(14) (15) (16)
Taking account of the complexation of copper (II) ion in the aqueous media, the distribution ratio of copper (II) is rewritten using ~ as follows: D. a -
[ uR2]-a Cc,
=Kex (CH~/aH)2
l o g D ' a = 2 log (CHR/aH) +logKex
( 17 ) (18)
25~
K.YOSHIZUKAETAL.
2.O Aqueous media Key I-HNO3-NH~N03 o l 1 H2SO~(varconc.) A I
I
S
/
HC[ (v?rconc) 1 [] I-
Organic diluent :Toluene 1.0
g
~o O
-1.0
~1~ ~ S
? -2.C -2.0
I
I I -I .0 logC~/OH
Fig. 5. Distribution of copper (II) in extraction from various aqueous media with C,2SAOin toluene. Figure 5 shows the plot of log D ' a against log ( C ~ / a n ) for each aqueous media according to Eq. 18. The plots are lying on a single straight line with the slope of 2 regardless of the aqueous media, which suggests that the values of Kex are nearly the same for each aqueous medium. The extraction equilibrium constants evaluated in the present study for various diluents and aqueous media are summarized in Table 2, together with the literature values observed with other commercial hydroxyoximes for comparison [8,12,14,15,19]. Compared with E-HNBPO and E-HNAPO, the active component of LIX 65 N and SME 529, respectively, the values with C,2SAO are several times greater than those with E-HNBPO and E-HNAPO. This suggests that LIX 860 is much more powerful extractant for copper (II) than LIX 65N and SME 529 as mentioned in the literature [ 1 ].
Effect of addition of 1-tridecanol on extraction equilibrium Figure 6 shows the effect of the initial concentration of 1-tridecanol added, CLO, on the relation between the distribution ratio of copper (II) and pH in the extraction with CleSAO in hexane and toluene from 1.0 kmol m -~ aqueous nitrate media under the initial concentration of C,2SAO, Chno = 37.6 mol m - 3 Figure 7 shows the relationship between the ratio of the distribution ratio of copper(II) with the organic phase containing 1-tridecanol, D', to that containing the extractant alone, D, and the concentration of 1-tridecanol in the
EXTRACTIONOF COPPERWITH 5-DODECYLSALICYLALDOXIME
/ /O
/ O O
257
Aqueous media HNO3-NH~NO3 C~:37.6 mol.m 3
1.0 = O ' --- / ~ .
'
'
' -J Organic diluent Key ~ Hexane O
[]
/
l
I
I
I
I
i
]
-1.0 10-1
~
=
t
-2.0
/
,"./to
•l
t
i
i
I
- / u # " • / I C~o
-3.0
O
D
/"
'".~
~" • "
,
,
-to /
/"
~ ,
I
I '
I | 0.5
o
[]
156
e
-
936
• 1.0
•
pH
\o
10 2
/[mol.m-3]Hexane Toluene
4
/ w
I
Key
Aqueousme6ia ~ O HNO~-NH~N03(pH=05} C~=37.6 mol.m -3
10-
I
0
i
i
i
i
I
I
I
]
i
5 10 10-~C[~ [mol.m -3]
Fig. 6. Effect of addition of 1-tridecanol on distribution of copper(II) [organic diluent: hexane and toluene, aqueous media: 1.0 kmol m -3 (H,NH4)N03]. Fig. 7. Relationship between ratio, D'/D, and concentration of 1-tridecanol in organic phase [organic diluent: hexane and toluene, aqueous media: 1.0 kmol m -3 ( H , N H 4 ) N Q ] .
organic phase. From these figures, it is evident that the distribution ratio of copper (II) remarkably decreases with increasing CLO, and that the decrease is greater in hexane than in toluene. The infrared spectra of C12SAO alone and the mixture of C12SAO and 1tridecanol in CC14 are shown in Fig. 8. In the case of C,2SAO alone, the weak absorption bands at 3560 c m - 1 and 3400 c m - 1 are assigned to the free oximic OH and the phenolic OH associated with oxime group through the intramolecular hydrogen bond, respectively. By the addition of 1-tridecanol, the intensity of the absorption bands at 3560 c m - 1 and 3400 c m - 1 decrease, while the weak absorption band at 3610 c m - 1 due to the free OH of 1-tridecanol and the strong adsorption band at 3300 c m - 1 due to the associated OH increases with increasing 1-tridecanol concentration, owing to the increase of intermolecular hydrogen bond between C12SAO and 1-tridecanol. The 1H-n.m.r. spectra of C12SAO alone and the mixture of C12SAO and 1tridecanol are shown in Fig. 9. At low concentration of 1-tridecanol (spectra 2, 3), the signal of oximic OH (signal a) shifts toward the lower magnetic field with increasing 1-tridecanol concentration due to the increase of intermolecular hydrogen bond between C12SAO and 1-tridecanol. While in the high concentration region of 1-tridecanol (spectra 4, 5 ), the signal of phenolic OH ( signal b) shifts toward the lower magnetic field with increasing 1-tridecanol
258
K. YOSHIZUKAET AL. I
I
I
I
Cl) 0.1 kmol.rrr3 C12SAO
~'~ g
/,v~ ~kmol-m-3 C12SA0
I
~ ~J"31
I
4000
J/
(3)oi kmol-~-3C~2SA0
"" \
~1 I [
(4) o] kmoim-3 G2SA0
3500
3000 2500 [cm-q
2000
Fig. 8. Infrared spectra of C12SAO alone a n d mixture of C12SAO and 1-tridecanol (in CC14 at 300 K, 0.05 m m calcium fluoride cell).
(5) 0.1 kmolm-3 Q2SAO*2 5kmoL m-31-Trideconol
[b)
Co)
[4) 0.1 kmol m-3 C12SA0.I 0 kmol.rn-3 l-Trideconol (b)
(a]
(3) 0.1 kmol.m-] C12SA0÷0.Ikmo{ m-31-Trideconol [b) (2) 0.1kmol m-3C12SAO
I ....
[b)
ILlj! l,il~ Ca) t
jk ...Ca)
:1)0.01 kmoL m-3 C12SAO
_ .I~LIJ,h,
(b)
12
1'1
i'o
6 5 [ppm]
Fig. 9. ~H-n.m.r. spectra of C~2SAO alone and mixture of C~2SAO and l-tridecanol (in CDCL:~ at 300 K, 270 MHz T M S as an internal standard).
concentration. It is considered that two molecules of 1-tridecanol consecutively form the hydrogen bonds with two hydroxyl groups of C12SAO, which decreases the activity of C12SAO, as shown in Fig. 10.
EXTRACTION OF COPPER WITH 5-DODECYLSALICYLALDOXIME
R'-0%
~,H OH---N,,oH
259
2'-o~_
c,H OH---N
"OH ,o~
c,H OH, N\
R"
,'OILIOH R" ,0~ R"
R = C,2H2s, R'=C13H27 Fig, 10. Formation scheme of intermolecular complex between C]2SAO and 1-tridecanol.
Consequently, the consecutive formations of the hydrogen bonds between C12SAO and 1-tridecanols can be described by: HR +L. HR-L + L .
" HR.L " HR-2L
;Kf, ;K~2
(19) (20)
Here, HR" L and HR" 2L represent the intermolecular complexes by the formation of hydrogen bonds. Assuming that the formation constant, Kfl is much greater than K,.2, for simplicity, the concentration of active C12SAO, [HR], CHR and C~o are expressed as follows:
[HR] = CH~/(l+Kr, [L] )
(21)
CHR= [HR] + [HR'L]
(22)
CL6= ILl + [HR'L]
(23)
where [L] denotesthe concentrationof free l-tridecanol at equilibrium and can be expressedby the followingequation from Eqs. (21)-(23). [ L ] = ( CLO -- C . R -- 1/Kr~ ) + x ~ L 0 2 -- C~n - 1/Kf, )2 + 4CL~/Kf,
(24)
The ratio, D ' / D , is expressed as follows: log D ' / D = - 2 log (1 +Kfl [L] )
(25)
By means of the curve fitting method on the basis of Eq. 25, the equilibrium constants for the formation of the intermolecular complex, Kn, were evaluated as (1.85 + 0.33 ) × 10-z m3/mol for hexane and (4.66 +_1.04 ) × 10-3 m3/mol for toluene. The solid curves in Figs. 6 and 7 were calculated from Eqs. (24) and (25) using the evaluated values of Kn. From the comparison of these two values, it is seen the extent of the formation of the intermolecular complex in
260
K. YOSHIZUKA ET AL.
hexane is four times greater than that in toluene. This suggests that toluene keeps the activity of C12SAO, due to the formation of hydrogen bonds between the two hydroxyl groups of C12SAO and conjugated double bonds of toluene [ 20 ], excluding the hydrogen bond with 1-tridecanol. CONCLUSION
The equilibrium studies were conducted at 303 K to clarify the effects of the organic diluent, the aqueous media and the addition of 1-tridecanol as the equilibrium modifier on the extraction equilibria of copper (II) with 5-dodecylsalicylaldoxime, the active component of LIX 860, together with measurements of apparent molecular weight and aqueous solubility of the extractant, and infrared and 1H-n.m.r. spectra of the extractant and 1-tridecanol. The following results were obtained. (1) The extractant exists as a monomeric species in the organic diluents, i.e., hexane, cyclohexane and toluene. (2) The extractant is sparingly soluble in the aqueous phase as well as other commercial hydroxyoximes. (3) Copper (II) is extracted as a chelate of the type CuR2 into the organic phase and the extraction equilibrium constant increases in the order, toluene < cyclohexane < hexane. (4) As to the effect of the aqueous media, the equilibrium distribution of copper (II) can be quantitatively expressed in terms of the nearly same values of the equilibrium constant whether for the extraction from aqueous nitrate media or for those from hydrochloric acid and sulfuric acid by properly correcting the effects of the complexing anions, i.e., chloride and sulfate ions in the aqueous phase. (5) The extraction of copper(II) remarkably decreased by the addition of 1-tridecanol, due to the formation of the hydrogen bond between the extractant and 1-tridecanol in the organic phase and the extent of the formation of the hydrogen bond in hexane was greater than that in toluene. ACKNOWLEDGEMENTS
The authors gratefully acknowledge the kind supply of 5-dodecylsalicylaldoxime from Henkel Corporation, Minneapolis U.S.A., and also grateful to Profs. T. Matsuda and F. Wada of Kyushu University for their helpful suggestions and discussions on the infrared and 1H-n.m.r. spectra of the reagents.
EXTRACTION OF COPPER WITH 5-DODECYLSALICYLALDOXIME
261
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