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Interactions between components of the extractants LIX 622 and LIX 622N in toluene
Fluid Phase Equilibria 258 (2007) 186–190
Interactions between components of the extractants LIX 622 and LIX 622N in toluene M.S. R´ua, A. Almela, M.P. Elizalde ∗ Dpto. Qu´ımica Anal´ıtica, Univ. Pa´ıs Vasco, Apdo. 644, 48080 Bilbao, Spain Received 31 January 2007; received in revised form 18 June 2007; accepted 19 June 2007 Available online 23 June 2007
Abstract Interaction reactions between 5-dodecylsalicylaldoxime and 5-nonylsalicylaldoxime, the active components of LIX 622 and LIX 622N, respectively, and 1-tridecanol and isotridecanol-N in toluene at 301 K have been studied by vapour pressure osmometry. The osmometric results have been numerically treated and interpreted in terms of the formation of 1:1 species for which the formation constants have been evaluated. Finally, the osmometric behaviour of commercial reagents containing the salicylaldoxime derivatives and isotridecanol-N has been also studied and interpreted on the basis of the model of interactions of their components previously derived. © 2007 Elsevier B.V. All rights reserved. Keywords: Aggregation; LIX 622; LIX 622N; Tridecanol; Vapour pressure osmometry
1. Introduction It is believed that future developments in solvent extraction will involve new and improved synergistic mixtures of old reagents and modifiers rather than manufacturing new extractants. Modifiers (usually long-chain alcohols and phenol derivatives) are used in extraction processes to increase the solubility of the extractants, to avoid third phase formation and to modify the extraction properties. The last application is particularly interesting in extractant reagents based on some hydroxyoximes used for copper recovery. The association phenomena in organic phases of liquid extraction processes (extractant association, modifier association, and extractant-modifier co-association) influence the metal transfer. The optimum metal transfer from the feed to the loaded solution is obtained when an appropriate combination of equilibrium constants of extraction, association and co-association is found [1,2]. Co-association of hydroxyoximes and modifiers having hydroxyl groups has been reviewed recently [3] indicating that
∗
Corresponding author. Fax: +34 94 601 35 00. E-mail address: [email protected] (M.P. Elizalde).
0378-3812/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.fluid.2007.06.013
theoretically up to five molecules of alcohols can be bound into hydroxyoxime associates. However, species containing only one or two modifier molecules have been reported [4,5]. On the other hand, the steric hindrance must be considered when branched alcohol molecules are involved. In a previous work, the aggregation equilibria of components of the extractants LIX 622 and LIX 622N in toluene by vapour pressure osmometry (VPO) have been reported [6]. Their active components, 5-dodecylsalicylaldoxime and 5nonylsalicylaldoxime, dimerize partially in toluene, the values of the dimerization constants being log β2(DSA) = −0.70 and log β2(NSA) = 0.05 [6]. In addition, these extractants contain isotridecanol-N as modifier whose behaviour in toluene has also been studied and interpreted through the formation of dimeric species with log β2(I) = 0.037 [6]. However, in order to get a complete understanding of the biphasic system it is necessary to clarify the interactions between the hydroxyoximes and the alcohols used as modifiers. Several authors have observed a decrease in the distribution coefficient of copper(II) with salicylaldoxime derivatives when increasing the alcohol concentration [7,8], indicating that other than a non-specific solvent modification was occurring. Majdan et al. [7] proposed the formation of 1:1 and 1:2 associates of 5-dodecylsalicylaldoxime and 5-nonylsalicylaldoxime with n-tridecylalcohol in n-heptane through IR measure-
M.S. R´ua et al. / Fluid Phase Equilibria 258 (2007) 186–190
ments. On the other hand, Yoshizuka et al. [8] reported the equilibrium constant values of the formation of an 1:1 adduct between 5-dodecylsalicylaldoxime and 1-tridecanol in n-hexane and toluene, the complex being much more stable in n-hexane. The results reported in those works reveal some discrepancies, probably due to differences in the experimental conditions and techniques used. Moreover, there is no available information about interactions of the hydroxyoximes with isotridecanol-N. For this reason, it seems interesting to get more information on the interactions between salicylaldoxime derivatives and modifiers. For this purpose, the study of the interactions 5-dodecylsalicylaldoxime/1-tridecanol, 5-nonylsalicylaldoxime/1-tridecanol and 5-nonylsalicylaldoxime/isotridecanol-N in toluene by VPO has been carried out. 1-tridecanol has been included because this alcohol is said to be used as modifier in commercial extractants. So, the present work will complete the knowledge of the equilibria taking place in toluene solutions of the extractants LIX 622 and LIX 622N.
187
3. Results and discussion 3.1. 5-Dodecylsalicylaldoxime/1-tridecanol interactions The experimental osmometric results (Rexp ) for mixed solutions of 5-dodecylsalicylaldoxime (DSA) and 1-tridecanol (T) are shown in Fig. 1, and are compared with the theoretical values calculated assuming the absence of interaction between both solutes, according to the following expression: 2 R = k1 Stotal + k2 Stotal
(1)
where k1 and k2 are the calibration constants obtained with benzil solutions (k1 = 8511 ± 92 and k2 = −5731 ± 435) and S is the sum of all solute concentrations: Stotal = SDSA + S1−tridecanol + SShellsol
(2)
where the diluent Shellsol-D 70, previously checked to behave as the standard, has also been included. Using the dimerization constants of DSA and 1-tridecanol in toluene the individual values of S have been calculated as SDSA = [DSA] + [(DSA)2 ] = [DSA] + β2 [DSA]2
(3)
2. Experimental
S1-tridecanol = [T] + [(T)2 ] = [T] + β2 [T]2
(4)
2.1. Reagents and solutions
whereas SShellsol = CShellsol (total concentration) due to the monomeric behaviour of this diluent. As it can be appreciated in Fig. 1, there are clear differences between the theoretical behaviour, if we do not consider any interactions between compounds, and the experimental one, that can be attributed to interactions of 5-dodecylsalicylaldoxime and 1-tridecanol. In order to elucidate the mixed species formed in toluene, a numerical data treatment using the CPMIN (Colligative Properties Minimal) program [11] was carried out. The dimerization constant values of 5-dodecylsalicylaldoxime (log β2 = −0.70 ± 0.11) and 1-tridecanol (log β2 = 0.20 ± 0.03) previously reported [6] were included in the input of the program.
LIX 860-IC (90% (w/w) 5-dodecylsalicylaldoxime and 10% Shellsol D-70) and LIX 860N-IC (90% (w/w) 5nonylsalicylaldoxime and 10% Shellsol D-70) were kindly supplied by Cognis Ireland (Little Island Co., Cork, Ireland). Shellsol D-70 (Shell Spain Group) was a diluent consisted predominantly of a mixture of paraffins and naphthenics. The modifiers 1-tridecanol (Fluka p.a.) and isotridecanol-N (Basf) were used. The commercial extractants LIX 622 and LIX 622N were also donated by Cognis. Toluene (Fluka p.a.) was used as organic solvent. Mixed solutions of LIX 860-IC or LIX 860N-IC and the modifiers in toluene were prepared by weighing. In all cases series of solutions containing 0.1 and 0.2 mol kg−1 of each salicylaldoxime derivative, and modifier concentration up to 0.30 mol kg−1 were prepared. It was assumed that at these concentrations the activity coefficients in the organic phase remain constant [9]. Benzil (Merck p.a.) solutions in toluene were used as standard because it is known the monomeric behaviour of this reagent in toluene [10]. 2.2. Experimental procedure The osmometric measurements were carried out using a vapour pressure osmometer (Knauer) with an universal probe. The drop size was kept as constant as possible and equal on both thermistors. The mean value of at least three R measurements was taken for each solution being the standard deviation of R measurements 2–5%. The study was carried out at 301 K.
Fig. 1. Osmometric results of mixtures 5-dodecylsalicylaldoxime (DSA) and 1-tridecanol in toluene as a function of the modifier concentration. Dotted lines represent the theoretical behaviour in absence of interactions. Continuous lines have been drawn according to the proposed interaction model.
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Table 1 Results of the numerical calculations for the interactions between 5-dodecylsalicylaldoxime (DSA) and 5-nonylsalicylaldoxime (NSA) and the alcohol solutions at 301 K Model of species hydroxyoxime: alcohol
DSA/1-tridecanol
NSA/1-tridecanol
NSA/isotridecanol-N
U
σ(R)
U
σ(R)
U
σ(R)
1:1 1:2 1:3 2:1 3:1 2:2 3:3 1:1, 1:2 1:1, 1:3
0.0154 0.0671 0.1304 0.0656 0.1224 0.0698 0.1246 0.0258 0.0154b
0.0374 0.0781 0.1089 0.0773 0.1055 0.0797 0.1064 0.0379 0.0374
0.0284 0.0454 0.0672 0.0568 0.0829 0.0652 0.0999 0.0284a 0.0283b
0.0532 0.0673 0.0819 0.0753 0.0910 0.0808 0.0999 0.0532 0.0532
0.0014 0.0073 0.0135
0.0164 0.0382 0.0520
0.0067 0.0122 0.0014a 0.0014b
0.0365 0.0494 0.0169 0.0177
Proposed models are bolded. a 1:2 rejected. b 1:3 rejected.
The computer calculates both U (error square sum) and σ(R) (mean standard deviation) for each set of species and constants, being the best fit that which gives minimum values for both magnitudes. Table 1 summarizes the results of the numerical data treatment, the best fit corresponding to the formation of 1:1 species. The formation constant value of (DSA)T species is collected in Table 2. 3.2. Interactions of 5-nonylsalicylaldoxime and 1-tridecanol or isotridecanol-N A similar procedure was followed for the mixtures 5-nonylsalicylaldoxime/1-tridecanol and 5-nonylsalicylaldoxime/isotridecanol-N in toluene. The results, shown in Fig. 2, indicate that 5-nonylsalicylaldoxime interacts with both alcohols. The results of the numerical treatment of the data are included in Table 1. The minimum values of U and σ(R) are obtained again in both systems for the 1:1 species model. The corresponding values of the formation constants are included in Table 2. It can be seen that the degree of interaction of 1-tridecanol with 5-nonylsalicylaldoxime is lower than with 5dodecylsalicylaldoxime. The results obtained in the present work differ from those reported by Majdan et al. [7] who proposed 1:1 and 1:2 species of 5-nonylsalicylaldoxime and 5-dodecylsalicylaldoxime with 1-tridecanol in n-heptane. However, there are differences in the organic solvent, reagent concentrations and temperature Table 2 Values of the interaction constants obtained in the numerical treatments (molal scale) Oxime
Modifier
Interaction constant
5-Dodecylsalicylaldoxime 5-Nonylsalicylaldoxime 5-Nonylsalicylaldoxime 5-Dodecylsalicylaldoxime
1-Tridecanol 1-Tridecanol Isotridecanol-N Isotridecanol-N
log β11 = 1.06 ± 0.05 log β11 = 0.78 ± 0.08 log β11 = 0.65 ± 0.04 log β11 = 0.85 ± 0.04a
a
Value estimated from the fit of osmometric data for LIX 622 (Fig. 4).
used in their IR experiments with regard to the ones used in this work. It is known that aggregation decreases with temperature and that it is lower in aromatic than in aliphatic solvents. The 1:1 species proposed in the present work agrees with that reported by Yoshizuka et al. for interactions between 5dodecylsalicylaldoxime and 1-tridecanol in toluene [8] although their constant value, log β11 = −2.33, is significatively lower than that obtained in the present work. Taking into account the equilibrium constant values obtained in this work, distribution diagrams of DSA and NSA as a function of the modifier concentration for the systems studied have been drawn using the SED program [12]. The corresponding diagrams of 5-dodecylsalicylaldoxime/1tridecanol, 5-nonylsalicylaldoxime/1-tridecanol and 5-nonylsalicylaldoxime/isotridecanol-N in toluene are shown in Fig. 3. It can be appreciated that the distribution of DSA and NSA species varies significantly with the modifier percentage. The adduct (DSA)T is the most important species at CT > 0.16 mol kg−1 , whereas in the case of NSA the adduct contribution is smaller than that of the monomer for both modifiers in concentrations up to 0.30 mol kg−1 . In all the cases the free extractant concentration, responsible for metal extraction, decreases when increasing the modifier concentration, the decrease being more important in the case of 5-dodecylsalicylaldoxime. In fact, an increase in 1-tridecanol concentration produces a significant decrease in the free DSA concentration, whereas the free NSA concentration decrease is less important in the same conditions, and even is lower when isotridecanol-N is used as modifier. 3.3. Application to industrial LIX 622 and LIX 622N samples In order to check the validity of the above results on the individual components in the industrial extractants, the osmometric behaviour of LIX 622 and LIX 622N in toluene solutions at 301 K was also studied both through experimental measurements and theoretically using the aggregation and interaction
M.S. R´ua et al. / Fluid Phase Equilibria 258 (2007) 186–190
189
Fig. 2. Osmometric results of mixtures of 5-nonylsalicylaldoxime (NSA) and (a) 1-tridecanol and (b) isotridecanol-N in toluene as a function of the modifier concentration. Dotted lines represent the theoretical behaviour without interactions. Continuous lines have been drawn according to the proposed interaction model.
constants known for the components. The experimental results are illustrated in Fig. 4. Taking into account the percentage of the components in LIX 622N: 55.3% (w/w) 5-nonylsalicylaldoxime and 18.2% (w/w) isotridecanol-N [13,14], and considering the dimerization values of each component in toluene [6], as well as the interaction between them obtained in the present work (log β11 = 0.65), the theoretical osmometric behaviour of this industrial extractant has been simulated. For this purpose the CPMIN program has been used and the results are also included in Fig. 4 (continuous line). A good agreement between experimental and theoretical predictions can be appreciated. In the case of LIX 622 (67.7% (w/w) 5-dodecylsalicylaldoxime and 15.9 % (w/w) isotridecanol-N [13,14]), there is no data available for the interaction between 5-dodecyl-
salicylaldoxime and isotridecanol-N in toluene. However, the good agreement between the experimental data for LIX 622N and the theoretical behaviour predicted with the proposed model lead us to use the experimental osmometric data obtained for LIX 622 to indirectly obtain the interaction constant of 5-nonylsalicylaldoxime with isotridecanol-N. The dimerization constants of 5-dodecylsalicylaldoxime and isotridecanol-N [6] were included in the input, whereas the interaction constant was treated as a fitting parameter. In this way the value log β11 = 0.85 ± 0.04 was obtained (included also in Table 2). The good agreement between the experimental data and the theoretical behaviour for both commercial extractants (Fig. 4) allows us to conclude that the aggregation and interaction models proposed using the individual components can explain the osmometric behaviour of the commercial extractants in
Fig. 3. Distribution diagrams of: (a) 5-dodecylsalicylaldoxime (DSA) as a function of 1-tridecanol concentration and (b) 5-nonylsalicylaldoxime (NSA) as a function of 1-tridecanol (dotted lines) and isotridecanol-N (continuous lines) concentration.
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mer, as it was expected due to steric hindrance. These results differ apparently from those of Majdan et al. [7] but they used a high modifier/extractant ratio in their experiments and proposed the formation of 1:2 adduct for DSA and NSA. Finally, taking into account the values of the aggregation constants of the components in the commercial extractants as well as the interaction constant values obtained in this work, the osmometric behaviour of the extractants has been simulated, and the theoretical predictions are in good agreement with the experimental behaviour. References
Fig. 4. Osmometric results of LIX 622 and LIX 622N solutions in toluene. Continuous lines represent the proposed interaction models.
toluene, giving consistency to the interaction model proposed for 5-dodecylsalicylaldoxime and 5-nonylsalicylaldoxime with isotridecanol-N in toluene. 4. Conclusions It has been proved that there are interactions between the components of the commercial extractants LIX 622 and LIX 622N in toluene solutions. Salicylaldoxime derivatives form adducts of 1:1 stoichiometry with 1-tridecanol and isotridecanol-N. The interaction is greater for the dodecyl derivative than for the nonyl one, probably due to the fact that DSA has a dimerization constant lower than NSA [6] and consequently a higher value of the free monomer concentration of DSA, being easier the formation of the adduct with the alcohol. On the other hand, interactions with the linear alcohol are stronger than that with the branched iso-
[1] M. Tanaka, K. Koyama, J. Shibata, Ind. Eng. Chem. Res. 37 (1998) 1943–1949. [2] M.B. Bogacki, Ind. Eng. Chem. Res. 38 (1999) 1611–1617. [3] A.M. Sastre, J. Szymanowski, Solvent Extr. Ion Exch. 22 (5) (2004) 737–759. [4] M.B. Bogacki, M. Lozynski, J. Szymanowski, Solvent Extr. Res. Dev. Jpn. 1 (1994) 108–122. [5] M.B. Bogacki, Solvent Extr. Ion Exch. 15 (1997) 731–755. [6] M.S. Rua, A. Almela, M.P. Elizalde, Fluid Phase Equilib. 244 (2006) 111–116. [7] M. Majdan, R.P. Sperline, W. Gu, W. Yu, H. Freiser, Solvent Extr. Ion Exch. 7 (6) (1989) 987–1005. [8] Y. Yoshizuka, H. Arita, Y. Baba, K. Inoue, Hydrometallurgy 23 (1990) 247–261. [9] E. H¨ogfeldt, in: Y. Markus, A.S. Kertes (Eds.), Solvent Extraction Research, Wiley–Interscience, New York, 1969, p. 157. [10] J. Paatero, Inst. Ind. Chem., Abo Akad., Abo, Finland. Acta Academiae Aboensis, Series B: Mathematica et Physica, 34 (10) (1974). [11] J. Havel, N. Miralles, A.M. Sastre, M. Aguilar, Comput. Chem. 16 (4) (1992) 319–323. [12] I. Puigdomenech, INPUT, SED and PREDOM: Computer Programs Drawing Equilibrium Diagrams, TRITA-OOK-3010, Dept. Inorg. Chem., The Royal Inst. Technol. (KTH), Stockholm, 1983. [13] A. Ocio, M. Elizalde, J.A. Prieto, J. Chromatogr. A 1032 (2004) 129–133. [14] A. Ocio, B. Menoyo, M. Elizalde, Euroanalysis XIII, Salamanca, Spain, 2004, PS2-231.
Interactions between components of the extractants LIX 622 and LIX 622N in toluene M.S. R´ua, A. Almela, M.P. Elizalde ∗ Dpto. Qu´ımica Anal´ıtica, Univ. Pa´ıs Vasco, Apdo. 644, 48080 Bilbao, Spain Received 31 January 2007; received in revised form 18 June 2007; accepted 19 June 2007 Available online 23 June 2007
Abstract Interaction reactions between 5-dodecylsalicylaldoxime and 5-nonylsalicylaldoxime, the active components of LIX 622 and LIX 622N, respectively, and 1-tridecanol and isotridecanol-N in toluene at 301 K have been studied by vapour pressure osmometry. The osmometric results have been numerically treated and interpreted in terms of the formation of 1:1 species for which the formation constants have been evaluated. Finally, the osmometric behaviour of commercial reagents containing the salicylaldoxime derivatives and isotridecanol-N has been also studied and interpreted on the basis of the model of interactions of their components previously derived. © 2007 Elsevier B.V. All rights reserved. Keywords: Aggregation; LIX 622; LIX 622N; Tridecanol; Vapour pressure osmometry
1. Introduction It is believed that future developments in solvent extraction will involve new and improved synergistic mixtures of old reagents and modifiers rather than manufacturing new extractants. Modifiers (usually long-chain alcohols and phenol derivatives) are used in extraction processes to increase the solubility of the extractants, to avoid third phase formation and to modify the extraction properties. The last application is particularly interesting in extractant reagents based on some hydroxyoximes used for copper recovery. The association phenomena in organic phases of liquid extraction processes (extractant association, modifier association, and extractant-modifier co-association) influence the metal transfer. The optimum metal transfer from the feed to the loaded solution is obtained when an appropriate combination of equilibrium constants of extraction, association and co-association is found [1,2]. Co-association of hydroxyoximes and modifiers having hydroxyl groups has been reviewed recently [3] indicating that
∗
Corresponding author. Fax: +34 94 601 35 00. E-mail address: [email protected] (M.P. Elizalde).
0378-3812/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.fluid.2007.06.013
theoretically up to five molecules of alcohols can be bound into hydroxyoxime associates. However, species containing only one or two modifier molecules have been reported [4,5]. On the other hand, the steric hindrance must be considered when branched alcohol molecules are involved. In a previous work, the aggregation equilibria of components of the extractants LIX 622 and LIX 622N in toluene by vapour pressure osmometry (VPO) have been reported [6]. Their active components, 5-dodecylsalicylaldoxime and 5nonylsalicylaldoxime, dimerize partially in toluene, the values of the dimerization constants being log β2(DSA) = −0.70 and log β2(NSA) = 0.05 [6]. In addition, these extractants contain isotridecanol-N as modifier whose behaviour in toluene has also been studied and interpreted through the formation of dimeric species with log β2(I) = 0.037 [6]. However, in order to get a complete understanding of the biphasic system it is necessary to clarify the interactions between the hydroxyoximes and the alcohols used as modifiers. Several authors have observed a decrease in the distribution coefficient of copper(II) with salicylaldoxime derivatives when increasing the alcohol concentration [7,8], indicating that other than a non-specific solvent modification was occurring. Majdan et al. [7] proposed the formation of 1:1 and 1:2 associates of 5-dodecylsalicylaldoxime and 5-nonylsalicylaldoxime with n-tridecylalcohol in n-heptane through IR measure-
M.S. R´ua et al. / Fluid Phase Equilibria 258 (2007) 186–190
ments. On the other hand, Yoshizuka et al. [8] reported the equilibrium constant values of the formation of an 1:1 adduct between 5-dodecylsalicylaldoxime and 1-tridecanol in n-hexane and toluene, the complex being much more stable in n-hexane. The results reported in those works reveal some discrepancies, probably due to differences in the experimental conditions and techniques used. Moreover, there is no available information about interactions of the hydroxyoximes with isotridecanol-N. For this reason, it seems interesting to get more information on the interactions between salicylaldoxime derivatives and modifiers. For this purpose, the study of the interactions 5-dodecylsalicylaldoxime/1-tridecanol, 5-nonylsalicylaldoxime/1-tridecanol and 5-nonylsalicylaldoxime/isotridecanol-N in toluene by VPO has been carried out. 1-tridecanol has been included because this alcohol is said to be used as modifier in commercial extractants. So, the present work will complete the knowledge of the equilibria taking place in toluene solutions of the extractants LIX 622 and LIX 622N.
187
3. Results and discussion 3.1. 5-Dodecylsalicylaldoxime/1-tridecanol interactions The experimental osmometric results (Rexp ) for mixed solutions of 5-dodecylsalicylaldoxime (DSA) and 1-tridecanol (T) are shown in Fig. 1, and are compared with the theoretical values calculated assuming the absence of interaction between both solutes, according to the following expression: 2 R = k1 Stotal + k2 Stotal
(1)
where k1 and k2 are the calibration constants obtained with benzil solutions (k1 = 8511 ± 92 and k2 = −5731 ± 435) and S is the sum of all solute concentrations: Stotal = SDSA + S1−tridecanol + SShellsol
(2)
where the diluent Shellsol-D 70, previously checked to behave as the standard, has also been included. Using the dimerization constants of DSA and 1-tridecanol in toluene the individual values of S have been calculated as SDSA = [DSA] + [(DSA)2 ] = [DSA] + β2 [DSA]2
(3)
2. Experimental
S1-tridecanol = [T] + [(T)2 ] = [T] + β2 [T]2
(4)
2.1. Reagents and solutions
whereas SShellsol = CShellsol (total concentration) due to the monomeric behaviour of this diluent. As it can be appreciated in Fig. 1, there are clear differences between the theoretical behaviour, if we do not consider any interactions between compounds, and the experimental one, that can be attributed to interactions of 5-dodecylsalicylaldoxime and 1-tridecanol. In order to elucidate the mixed species formed in toluene, a numerical data treatment using the CPMIN (Colligative Properties Minimal) program [11] was carried out. The dimerization constant values of 5-dodecylsalicylaldoxime (log β2 = −0.70 ± 0.11) and 1-tridecanol (log β2 = 0.20 ± 0.03) previously reported [6] were included in the input of the program.
LIX 860-IC (90% (w/w) 5-dodecylsalicylaldoxime and 10% Shellsol D-70) and LIX 860N-IC (90% (w/w) 5nonylsalicylaldoxime and 10% Shellsol D-70) were kindly supplied by Cognis Ireland (Little Island Co., Cork, Ireland). Shellsol D-70 (Shell Spain Group) was a diluent consisted predominantly of a mixture of paraffins and naphthenics. The modifiers 1-tridecanol (Fluka p.a.) and isotridecanol-N (Basf) were used. The commercial extractants LIX 622 and LIX 622N were also donated by Cognis. Toluene (Fluka p.a.) was used as organic solvent. Mixed solutions of LIX 860-IC or LIX 860N-IC and the modifiers in toluene were prepared by weighing. In all cases series of solutions containing 0.1 and 0.2 mol kg−1 of each salicylaldoxime derivative, and modifier concentration up to 0.30 mol kg−1 were prepared. It was assumed that at these concentrations the activity coefficients in the organic phase remain constant [9]. Benzil (Merck p.a.) solutions in toluene were used as standard because it is known the monomeric behaviour of this reagent in toluene [10]. 2.2. Experimental procedure The osmometric measurements were carried out using a vapour pressure osmometer (Knauer) with an universal probe. The drop size was kept as constant as possible and equal on both thermistors. The mean value of at least three R measurements was taken for each solution being the standard deviation of R measurements 2–5%. The study was carried out at 301 K.
Fig. 1. Osmometric results of mixtures 5-dodecylsalicylaldoxime (DSA) and 1-tridecanol in toluene as a function of the modifier concentration. Dotted lines represent the theoretical behaviour in absence of interactions. Continuous lines have been drawn according to the proposed interaction model.
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Table 1 Results of the numerical calculations for the interactions between 5-dodecylsalicylaldoxime (DSA) and 5-nonylsalicylaldoxime (NSA) and the alcohol solutions at 301 K Model of species hydroxyoxime: alcohol
DSA/1-tridecanol
NSA/1-tridecanol
NSA/isotridecanol-N
U
σ(R)
U
σ(R)
U
σ(R)
1:1 1:2 1:3 2:1 3:1 2:2 3:3 1:1, 1:2 1:1, 1:3
0.0154 0.0671 0.1304 0.0656 0.1224 0.0698 0.1246 0.0258 0.0154b
0.0374 0.0781 0.1089 0.0773 0.1055 0.0797 0.1064 0.0379 0.0374
0.0284 0.0454 0.0672 0.0568 0.0829 0.0652 0.0999 0.0284a 0.0283b
0.0532 0.0673 0.0819 0.0753 0.0910 0.0808 0.0999 0.0532 0.0532
0.0014 0.0073 0.0135
0.0164 0.0382 0.0520
0.0067 0.0122 0.0014a 0.0014b
0.0365 0.0494 0.0169 0.0177
Proposed models are bolded. a 1:2 rejected. b 1:3 rejected.
The computer calculates both U (error square sum) and σ(R) (mean standard deviation) for each set of species and constants, being the best fit that which gives minimum values for both magnitudes. Table 1 summarizes the results of the numerical data treatment, the best fit corresponding to the formation of 1:1 species. The formation constant value of (DSA)T species is collected in Table 2. 3.2. Interactions of 5-nonylsalicylaldoxime and 1-tridecanol or isotridecanol-N A similar procedure was followed for the mixtures 5-nonylsalicylaldoxime/1-tridecanol and 5-nonylsalicylaldoxime/isotridecanol-N in toluene. The results, shown in Fig. 2, indicate that 5-nonylsalicylaldoxime interacts with both alcohols. The results of the numerical treatment of the data are included in Table 1. The minimum values of U and σ(R) are obtained again in both systems for the 1:1 species model. The corresponding values of the formation constants are included in Table 2. It can be seen that the degree of interaction of 1-tridecanol with 5-nonylsalicylaldoxime is lower than with 5dodecylsalicylaldoxime. The results obtained in the present work differ from those reported by Majdan et al. [7] who proposed 1:1 and 1:2 species of 5-nonylsalicylaldoxime and 5-dodecylsalicylaldoxime with 1-tridecanol in n-heptane. However, there are differences in the organic solvent, reagent concentrations and temperature Table 2 Values of the interaction constants obtained in the numerical treatments (molal scale) Oxime
Modifier
Interaction constant
5-Dodecylsalicylaldoxime 5-Nonylsalicylaldoxime 5-Nonylsalicylaldoxime 5-Dodecylsalicylaldoxime
1-Tridecanol 1-Tridecanol Isotridecanol-N Isotridecanol-N
log β11 = 1.06 ± 0.05 log β11 = 0.78 ± 0.08 log β11 = 0.65 ± 0.04 log β11 = 0.85 ± 0.04a
a
Value estimated from the fit of osmometric data for LIX 622 (Fig. 4).
used in their IR experiments with regard to the ones used in this work. It is known that aggregation decreases with temperature and that it is lower in aromatic than in aliphatic solvents. The 1:1 species proposed in the present work agrees with that reported by Yoshizuka et al. for interactions between 5dodecylsalicylaldoxime and 1-tridecanol in toluene [8] although their constant value, log β11 = −2.33, is significatively lower than that obtained in the present work. Taking into account the equilibrium constant values obtained in this work, distribution diagrams of DSA and NSA as a function of the modifier concentration for the systems studied have been drawn using the SED program [12]. The corresponding diagrams of 5-dodecylsalicylaldoxime/1tridecanol, 5-nonylsalicylaldoxime/1-tridecanol and 5-nonylsalicylaldoxime/isotridecanol-N in toluene are shown in Fig. 3. It can be appreciated that the distribution of DSA and NSA species varies significantly with the modifier percentage. The adduct (DSA)T is the most important species at CT > 0.16 mol kg−1 , whereas in the case of NSA the adduct contribution is smaller than that of the monomer for both modifiers in concentrations up to 0.30 mol kg−1 . In all the cases the free extractant concentration, responsible for metal extraction, decreases when increasing the modifier concentration, the decrease being more important in the case of 5-dodecylsalicylaldoxime. In fact, an increase in 1-tridecanol concentration produces a significant decrease in the free DSA concentration, whereas the free NSA concentration decrease is less important in the same conditions, and even is lower when isotridecanol-N is used as modifier. 3.3. Application to industrial LIX 622 and LIX 622N samples In order to check the validity of the above results on the individual components in the industrial extractants, the osmometric behaviour of LIX 622 and LIX 622N in toluene solutions at 301 K was also studied both through experimental measurements and theoretically using the aggregation and interaction
M.S. R´ua et al. / Fluid Phase Equilibria 258 (2007) 186–190
189
Fig. 2. Osmometric results of mixtures of 5-nonylsalicylaldoxime (NSA) and (a) 1-tridecanol and (b) isotridecanol-N in toluene as a function of the modifier concentration. Dotted lines represent the theoretical behaviour without interactions. Continuous lines have been drawn according to the proposed interaction model.
constants known for the components. The experimental results are illustrated in Fig. 4. Taking into account the percentage of the components in LIX 622N: 55.3% (w/w) 5-nonylsalicylaldoxime and 18.2% (w/w) isotridecanol-N [13,14], and considering the dimerization values of each component in toluene [6], as well as the interaction between them obtained in the present work (log β11 = 0.65), the theoretical osmometric behaviour of this industrial extractant has been simulated. For this purpose the CPMIN program has been used and the results are also included in Fig. 4 (continuous line). A good agreement between experimental and theoretical predictions can be appreciated. In the case of LIX 622 (67.7% (w/w) 5-dodecylsalicylaldoxime and 15.9 % (w/w) isotridecanol-N [13,14]), there is no data available for the interaction between 5-dodecyl-
salicylaldoxime and isotridecanol-N in toluene. However, the good agreement between the experimental data for LIX 622N and the theoretical behaviour predicted with the proposed model lead us to use the experimental osmometric data obtained for LIX 622 to indirectly obtain the interaction constant of 5-nonylsalicylaldoxime with isotridecanol-N. The dimerization constants of 5-dodecylsalicylaldoxime and isotridecanol-N [6] were included in the input, whereas the interaction constant was treated as a fitting parameter. In this way the value log β11 = 0.85 ± 0.04 was obtained (included also in Table 2). The good agreement between the experimental data and the theoretical behaviour for both commercial extractants (Fig. 4) allows us to conclude that the aggregation and interaction models proposed using the individual components can explain the osmometric behaviour of the commercial extractants in
Fig. 3. Distribution diagrams of: (a) 5-dodecylsalicylaldoxime (DSA) as a function of 1-tridecanol concentration and (b) 5-nonylsalicylaldoxime (NSA) as a function of 1-tridecanol (dotted lines) and isotridecanol-N (continuous lines) concentration.
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mer, as it was expected due to steric hindrance. These results differ apparently from those of Majdan et al. [7] but they used a high modifier/extractant ratio in their experiments and proposed the formation of 1:2 adduct for DSA and NSA. Finally, taking into account the values of the aggregation constants of the components in the commercial extractants as well as the interaction constant values obtained in this work, the osmometric behaviour of the extractants has been simulated, and the theoretical predictions are in good agreement with the experimental behaviour. References
Fig. 4. Osmometric results of LIX 622 and LIX 622N solutions in toluene. Continuous lines represent the proposed interaction models.
toluene, giving consistency to the interaction model proposed for 5-dodecylsalicylaldoxime and 5-nonylsalicylaldoxime with isotridecanol-N in toluene. 4. Conclusions It has been proved that there are interactions between the components of the commercial extractants LIX 622 and LIX 622N in toluene solutions. Salicylaldoxime derivatives form adducts of 1:1 stoichiometry with 1-tridecanol and isotridecanol-N. The interaction is greater for the dodecyl derivative than for the nonyl one, probably due to the fact that DSA has a dimerization constant lower than NSA [6] and consequently a higher value of the free monomer concentration of DSA, being easier the formation of the adduct with the alcohol. On the other hand, interactions with the linear alcohol are stronger than that with the branched iso-
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