ANALYTICAL SCIENCES JUNE 2011, VOL The Japan Society for Analytical Chemistry

Size: px

Start display at page:

Download "ANALYTICAL SCIENCES JUNE 2011, VOL The Japan Society for Analytical Chemistry"

Leslie Maxwell
5 years ago
Views:

1 ANALYTICAL SCIENCES JUNE 2011, VOL The Japan Society for Analytical Chemistry Solid-Phase Extraction of Cobalt(II) from Lithium Chloride Solutions Using a Poly(vinyl chloride)-based Polymer Inclusion Membrane with Aliquat 336 as the Carrier Notes Shigehiro KAGAYA,*, ** Robert W. CATTRALL,** and Spas D. KOLEV** * Graduate School of Science and Engineering for Research, University of Toyama, 3190 Gofuku, Toyama , Japan ** School of Chemistry, The University of Melbourne, Victoria 3010, Australia The extraction of cobalt(ii) from solutions containing various concentrations of lithium chloride, hydrochloric acid, and mixtures of lithium chloride plus hydrochloric acid is reported using a poly(vinyl chloride) (PVC)-based polymer inclusion membrane (PIM) containing 40% (w/w) Aliquat 336 as a carrier. The extraction from lithium chloride solutions and mixtures with hydrochloric acid is shown to be more effective than extraction from hydrochloric acid solutions alone. The solution concentrations giving the highest amounts of extraction are 7 mol L 1 for lithium chloride and 8 mol L 1 lithium chloride plus 1 mol L 1 hydrochloric acid for mixed solutions. Cobalt(II) is easily stripped from the membrane using deionized water. The cobalt(ii) species extracted into the membrane are CoCl 4 2 for lithium chloride solutions and HCoCl 4 for mixed solutions; these form ion-pairs with Aliquat 336. It is also shown that both lithium chloride and hydrochloric acid are extracted by the PIM and suppress the extraction of cobalt(ii) by forming ion-pairs in the membrane (i.e. R 3MeN + HCl 2 for hydrochloric acid and R 3MeN + LiCl 2 for lithium chloride). (Received February 2, 2011; Accepted April 12, 2011; Published June 10, 2011) Introduction The liquidliquid extraction of cobalt(ii) from solutions containing a high concentration of chloride using quaternary ammonium compounds 113 including Aliquat has been widely studied by many researchers. The extraction mechanism has been shown to involve chlorocobaltate(ii) complexes, such 2 as the tetrachlorocobaltate ion, CoCl 4, 1,3,4,6,913 or the hydrogen tetrachlorocobaltate ion, HCoCl 4, 5 which are extracted into the organic phase by an ion-exchange mechanism. These solvent extraction techniques are effective for separating cobalt(ii); however, toxic organic diluents, such as chloroform 3-5,12 and benzene, 3,6,7,10,12 are used in the extraction. To overcome the problem of using large amounts of toxic diluents, solid-phase extraction techniques have been developed. 14 Polymer inclusion membranes (PIMs) are useful tools for the solid-phase extraction of various chemical species, including metal ions. 15 PIMs are thin, flexible, and stable films that are easily prepared by casting an organic solution containing a base polymer, such as cellulose triacetate or poly(vinyl chloride) (PVC), a plasticizer and an extractant. In solid-phase extraction using PIMs, metal ions are generally extracted by mechanisms similar to those in conventional liquidliquid extraction. These mechanisms are often based on the formation of complexes and ion-pairs with the extractant without the need for large amounts of toxic organic solvents. 15 Solid-phase extraction using PIMs has been proposed for separating various To whom correspondence should be addressed. kagaya@eng.u-toyama.ac.jp; s.kolev@unimelb.edu.au metal ions, such as chromium(vi), 16,17 copper(ii), 1820 cadmium(ii), 1820 palladium(ii) 21 and gold(iii) A PVC-based PIM with Aliquat 336 as the carrier has been found to effectively extract cobalt(ii) from 7 mol L 1 hydrochloric acid solutions 25 by the same mechanism as in liquidliquid extraction. 5 However, the use of hydrochloric acid at high concentrations is not desirable because of its corrosiveness. Therefore, it would be more useful if the extraction of cobalt(ii) using the PIM could be conducted under weakly acidic or neutral conditions. It has been reported that cobalt(ii) can be extracted in a liquidliquid extraction system from solutions containing high concentrations of lithium chloride using Aliquat ,4 Such an approach is expected to assist in the selective and sensitive determination of cobalt(ii) in samples containing nickel(ii), which often interferes with analytical measurements. Thus, this paper reports on a fundamental investigation of using lithium chloride solutions for the solid-phase extraction of cobalt(ii) into PVC-based PIMs containing Aliquat 336 as a carrier. These results are compared with those obtained for the extraction of cobalt(ii) from hydrochloric acid and calcium chloride solutions. The possibilities of using this solid-phase extraction approach for the selective separation of cobalt(ii) from nickel(ii) is also discussed. Experimental Reagents and chemicals Deionized water (18 MΩ cm, Millipore, Synergy 185, France) was used for all experiments. Aliquat 336 (Aldrich, USA), a high molecular mass PVC (Selectophore, Fluka, USA), and

2 654 ANALYTICAL SCIENCES JUNE 2011, VOL. 27 tetrahydrofuran (THF; BDH, UK) were used for the preparation of PIMs. Standard solutions of cobalt(ii) and nickel(ii) were prepared by dissolving cobalt(ii) chloride hexahydrate and nickel(ii) chloride hexahydrate (Aldrich, USA) in deionized water. Lithium chloride was purchased from Aldrich (USA). Hydrochloric acid (BDH, UK) and calcium chloride dihydrate (Ajax Finechem, Australia) were used to prepare solutions for extraction experiments. Procedures PIMs were prepared according to Blitz-Raith et al. 25 Aliquat 336 (320 mg) was dissolved in THF (10 ml) in a beaker, and then PVC (480 mg) was dissolved in the solution. The solution was poured into a glass ring (inner diameter of 75 mm) on a flat glass plate. The THF was allowed to evaporate in air at room temperature for more than 12 h. The PIM, which was colorless and flexible, was peeled from the glass plate and cut into four segments of approximately equal size. Each segment was weighed before use. The extraction of cobalt(ii) was conducted in beakers containing 75 ml of aqueous solutions containing 25 mg L 1 of cobalt(ii) and various concentrations of lithium chloride, calcium chloride and hydrochloric acid. Two segments of the PIM ( g; ± g (mean ± standard deviation, n = 25)) were immersed in the solution, which was stirred vigorously with a magnetic stirring bar to facilitate the extraction of cobalt(ii). Aliquots of the solution (0.5 ml) were taken at various time intervals during extraction, and replaced with an equal volume of the initial solution. The additional amount of cobalt(ii) introduced as a result of sampling was taken into account in all subsequent calculations. The cobalt(ii) concentration in the samples was determined using flame atomic absorption spectrometry (FAAS; Z-2000 polarized Zeeman atomic absorption spectrophotometer, Hitachi, Japan). In studies concerning the separation of cobalt(ii) from nickel(ii), 75 ml solutions containing 25 mg L 1 of both cobalt(ii) and nickel(ii) and 7 mol L 1 of lithium chloride, or 8 mol L 1 of lithium chloride and 1 mol L 1 of hydrochloric acid, were used. In PIM studies on the back extraction of cobalt(ii), PIMs containing extracted cobalt(ii) were immersed in 75 ml of deionized water, 25 and the solutions were stirred vigorously. The cobalt(ii) concentration in the aqueous phase was monitored by FAAS. Results and Discussion Extraction of cobalt(ii) from solutions containing lithium chloride, calcium chloride, and hydrochloric acid Initially, the amount of cobalt(ii) extracted from solutions containing 5 10 mol L 1 lithium chloride or mol L 1 calcium chloride and 7 mol L 1 hydrochloric acid solution was examined. When the solutions containing lithium chloride and hydrochloric acid were used, the concentration of cobalt(ii) decreased gradually with increasing the stirring time. The PIM concentrations of cobalt(ii) after 3 h of extraction and expressed as mg of cobalt(ii) per 1 g of the PIM are summarized in Fig. 1(a). It can be seen that the amount of cobalt(ii) extracted increased with increasing concentration of lithium chloride in the range of 5 to 7 mol L 1. However, the amount extracted decreased steadily for concentrations of lithium chloride greater than 7 mol L 1. Also, the amount of cobalt(ii) extracted from the lithium chloride solutions was significantly higher than that from 7 mol L 1 hydrochloric acid. When calcium chloride solutions were used, although the amount extracted increased Fig. 1 PIM concentration of cobalt(ii) obtained after 3 h of extraction from solutions containing lithium chloride, calcium chloride and hydrochloric acid. slightly with increasing concentration of calcium chloride, the amount was much smaller than that when lithium chloride solutions were used, even when the solution contained 5 mol L 1 calcium chloride corresponding to 10 mol L 1 chloride. The extraction of cobalt(ii) from solutions containing mixtures of both lithium chloride or calcium chloride, on one hand, and hydrochloric acid, on the other, was then examined; the results are shown in Fig. 1(b). These results show that, for extraction from solutions containing various concentrations of lithium chloride and 1 mol L 1 hydrochloric acid, the extracted amount of cobalt(ii) increased with increasing concentration of lithium chloride, and reached a maximum value at 8 mol L 1 lithium chloride. One interesting feature shown in Fig. 1(b) is that, when the total concentration of chloride in the solution containing lithium chloride and hydrochloric acid was maintained at 7 mol L 1, the amount of cobalt(ii) extracted decreased with increasing concentration of hydrochloric acid. This suggests that the lithium ion is essential for achieving the maximum extraction. The extraction from solutions containing both calcium chloride and hydrochloric acid was also investigated; however, the amounts of cobalt(ii) extracted were extremely low, as shown in Fig. 1(b). The PVC-based PIM with Aliquat 336 can selectively extract cobalt(ii) from 7 mol L 1 hydrochloric acid solutions containing both cobalt(ii) and nickel(ii). 25 Therefore, the extraction of cobalt(ii) and nickel(ii) was attempted using a solution containing 7 mol L 1 lithium chloride or 8 mol L 1 lithium chloride and 1 mol L 1 hydrochloric acid. As a result,

3 ANALYTICAL SCIENCES JUNE 2011, VOL Fig. 3 Speciation diagram for the chloro-complexes of cobalt(ii) in highly acidic aqueous solutions. 27 A, H 2CoCl 4; B, HCoCl 4 ; C, CoCl 4 2. Fig. 2 Speciation diagrams for the chloro-complexes of cobalt(ii) in aqueous solutions with different concentrations of (a) hydrochloric acid, (b) lithium chloride, and (c) calcium chloride. 26 A, Co 2+ ; B, CoCl + ; C, CoCl 2; D, CoCl 3 ; E, CoCl 4 2. the selective extraction of cobalt(ii) was achieved. The extraction percentages of cobalt(ii) after extraction for 3 h were 27.0 ± 4.3% (mean ± standard deviation, n = 3) for a solution containing 7 mol L 1 lithium chloride and 32.8 ± 1.4% for a solution containing 8 mol L 1 lithium chloride and 1 mol L 1 hydrochloric acid. In both cases, nickel(ii) was not extracted at all. The cobalt(ii) extracted into the PIMs outlined above could be quantitatively back-extracted using deionized water. 25 Proposed mechanism for the extraction of cobalt(ii) from lithium chloride solutions The following discussion proposes a mechanism for the extraction of cobalt(ii) based on the experimental results described above. As mentioned in the introduction, it has been reported that, in the liquidliquid extraction of cobalt(ii) from lithium chloride or hydrochloric acid solutions with Aliquat 336, cobalt(ii) is extracted into the organic phase by an anion-exchange 2 1,3,4,6,9-13 mechanism involving the species CoCl 4 or HCoCl 4. 5 In the solid phase extraction of cobalt(ii) from hydrochloric acid solutions into a PVC-based PIM incorporating Aliquat 336 as a carrier, the proposed extraction mechanism is based on the formation of an ion-pair between HCoCl 4 and the Aliquat 336 cation. 25 Thus, it can be expected that these species are also involved in the extraction processes outlined in the present study. Figure 2 shows a speciation diagram of the various chloro-complexes of cobalt(ii) in solutions containing various concentrations of hydrochloric acid, lithium chloride or calcium chloride. The associated calculations took into account solution activity effects following a procedure proposed by Bjerrum et al. 26 It can be seen that for solutions containing 7 mol L 1 2 chloride, the fraction of CoCl 4 decreases in the order HCl > LiCl >> CaCl 2. A speciation diagram for the protonated chlorocobaltate(ii) species HCoCl 4 and H 2CoCl 4 in highly acidic solutions is shown in Fig. 3. This diagram was constructed using the acid dissociation constants K a1 = and K a2 = , determined by Belousov and Ivanov. 27 It can be seen that the dominant species in all of the solutions used in our experimental 2 studies is CoCl 4. However, the fraction of HCoCl 4 increases 2 with increasing acid concentration. Thus, if CoCl 4 and HCoCl 4 are the extracted species, then the extraction efficiency is expected to increase with increasing concentrations of lithium chloride and hydrochloric acid. However, the results given in Fig. 1 do not agree with these expectations, since the amount of cobalt(ii) extracted decreased with increasing the concentration of the chloride anion and/or hydrochloric acid (Fig. 1). In order to further elucidate this unexpected phenomenon, membranes were immersed for 120 h in solutions containing various concentrations of hydrochloric acid or lithium chloride without cobalt(ii), rinsed in deionized water for 10 s, and then immersed in 50 ml of deionized water and stirred vigorously for 24 h. The concentrations of H + and Li + ions were measured using a ph meter and FAAS, respectively. As shown in Fig. 4, H + and Li + were detected in the back-extraction solutions, thus indicating that hydrochloric acid and lithium chloride were also extracted by the PIM. The extracted amounts increased with increasing concentration of hydrochloric acid or lithium chloride, and the amount of hydrochloric acid was larger than that of lithium chloride for each initial concentration. In the liquidliquid extraction of cobalt(ii) from hydrochloric acid

4 656 ANALYTICAL SCIENCES JUNE 2011, VOL. 27 Fig. 4 Concentrations of (A) H + or (B) Li + back-extracted from PIMs exposed prior to the back-extraction process to various concentrations of hydrochloric acid or lithium chloride. solutions with long-chain alkyl amines as extractants, including Aliquat 336 (R 3MeN + Cl ), the extraction percentages decreased with increasing the concentration of hydrochloric acid. 1,28 This is most probably due to the extraction of hydrochloric acid (Eq. (1)), which competes with the extraction of cobalt(ii): 1 R 3MeN + Cl org + H + + Cl R 3MeN + HCl 2 org (1) It has also been reported that lithium chloride can be extracted from its aqueous solutions into benzene solutions of Aliquat Thus, it can be expected that the extraction of hydrochloric acid and/or lithium chloride would suppress the extraction of cobalt(ii). Since the amount of hydrochloric acid extracted was larger than that of lithium chloride, as shown in Fig. 4, the suppression caused by hydrochloric acid would be significantly greater compared to that by lithium chloride. Also, suppression of the cobalt(ii) extraction would increase with increasing the concentration of lithium chloride above 7 mol L 1, as can be seen in Fig. 1(a). The results presented in this paper support the assumption that 2 CoCl 4 and HCoCl 4 are involved in the extraction of cobalt(ii). In lithium chloride solutions the dominant cobalt(ii) species 2 extracted is CoCl 4, while in the presence of hydrochloric acid HCoCl 4 can also be extracted; in some cases it could be the predominant cobalt(ii) species extracted. For example, a solution containing 8 mol L 1 lithium chloride and 1 mol L 1 hydrochloric acid gave the highest cobalt(ii) extraction among all solutions studied (Fig. 1(b)); it is suggested that this is due to the ease of formation and/or diffusion of R 3MeN + HCoCl 4 compared to the bulkier (R 3MeN + ) 2 CoCl 2 4. Conclusions On the basis of the obtained results, it can be concluded that the use of lithium chloride solutions is preferable to the use of hydrochloric acid solutions for the solid phase extraction of cobalt(ii) using a PVC-based PIM containing Aliquat 336 as a carrier, since higher extraction is obtained. In addition, lithium chloride solutions are less corrosive than those of hydrochloric acid. The concentration of a solution containing only lithium chloride, which gives the highest extraction, is 7 mol L 1 ; however, an even higher extraction is obtained using 8 mol L 1 lithium chloride and 1 mol L 1 hydrochloric acid. Cobalt(II) is easily stripped from the membrane using deionized water. The solid-phase extraction of cobalt(ii) into PVC-based PIMs containing Aliquat 336 from its lithium chloride solutions is an attractive alternative for separating this metal ion from nickel(ii), compared to using 7 mol L 1 hydrochloric acid solutions. 25 The research outlined above suggests that the predominant cobalt(ii) species extracted into the membrane are CoCl 4 2 for extraction from lithium chloride solutions and HCoCl 4 for extraction from solutions containing both lithium chloride and hydrochloric acid. In addition, it has been shown that both lithium chloride and hydrochloric acid are extracted by the PIM studied, and it is suggested that these form ion-pairs with the Aliquat 336 cation, i.e., R 3MeN + HCl 2 for hydrochloric acid and possibly R 3MeN + LiCl 2 for lithium chloride. The extraction of these species suppresses to a minimal extent the extraction of cobalt(ii). Acknowledgements One of the authors (S. K.) is grateful for the award of the Excellent Young Researchers Overseas Visit Program (No ) from the Japan Society for the Promotion of Science. References 1. M. L. Good, S. E. Bryan, F. F. Holland, Jr., and G. J. Maus, J. Inorg. Nucl. Chem., 1963, 25, F. G. Seeley and D. J. Crouse, J. Chem. Eng. Data, 1966, 11, T. Sato, T. Nakamura, and T. Fujimatsu, Bull. Chem. Soc. Jpn., 1981, 54, R. Paimin and R. W. Cattrall, Aust. J. Chem., 1982, 35, R. Paimin and R. W. Cattrall, Aust. J. Chem., 1983, 36, T. Sato, T. Shimomura, S. Murakami, T. Maeda, and T. Nakamura, Hydrometallurgy, 1984, 12, B. K. Tait and D. P. Shillington, Solvent Extr. Ion Exch., 1992, 10, I. M. Ivanov, L. M. Gindin, and Z. A. Nal kina, Izv. Sib. Otd. Akad. Nauk SSSR, Ser. Khim. Nauk, 1969, J. G. H. du Preez, E. S. Herselman, H. E. Rohwer, and B. J. A. M. Van Brecht, S. Afr. J. Chem., 1985, 38, I. Komasawa, Y. Maekawa, and T. Otake, J. Chem. Eng. Jpn., 1987, 20, I. Komasawa and T. Otake, J. Chem. Eng. Jpn., 1987, 20, T. Hirai and I. Komasawa, J. Chem. Eng. Jpn., 1991, 24, J. G. H. du Preez, D. P. Shillington, E. Herselman, H. E. Rohwer, B. J. A. M. van Brecht, and H. Wile, Solvent Extr. Ion Exch., 1995, 13, V. Camel, Spectrochim. Acta, Part B, 2003, 58, L. D. Nghiem, P. Mornane, I. D. Potter, J. M. Perera, R. W. Cattrall, and S. D. Kolev, J. Membr. Sci., 2006, 281, C. Fontas, I. Queralt, and M. Hidalgo, Spectrochim. Acta, Part B, 2006, 61, O. Kebiche-Senhadji, S. Tingry, P. Seta, and M. Benamor, Desalination, 2010, 258, L. Wang, R. Paimin, R. W. Cattrall, W. Shen, and S. D. Kolev, J. Membr. Sci., 2000, 176, A. Upitis, J. Peterson, C. Lukey, and L. D. Nghiem, Desalin. Water Treat., 2009, 6, J. Peterson and L. D. Nghiem, Int. J. Environ. Technol.

5 ANALYTICAL SCIENCES JUNE 2011, VOL Manage., 2010, 12, S. D. Kolev, Y. Sakai, R. W. Cattrall, R. Paimin, and I. D. Potter, Anal. Chim. Acta, 2000, 413, S. D. Kolev, G. Argiropoulos, R. W. Cattrall, I. C. Hamilton, and R. Paimin, J. Membr. Sci., 1997, 137, G. Argiropoulos, R. W. Cattrall, I. C. Hamilton, S. D. Kolev, and R. Paimin, J. Membr. Sci., 1998, 138, Y. Y. N. Bonggotgetsakul, M. Ashokkumar, R. W. Cattrall, and S. D. Kolev, J. Membr. Sci., 2010, 365, A. H. Blitz-Raith, R. Paimin, R. W. Cattrall, and S. D. Kolev, Talanta, 2007, 71, J. Bjerrum, A. S. Halonin, and L. H. Skibsted, Acta Chem. Scand. A, 1975, 29, E. A. Belousov and V. M. Ivanov, Russ. J. Phys. Chem., 1977, 51, M. L. Good and S. E. Bryan, J. Inorg. Nucl. Chem., 1961, 20, G. Scibona, P. R. Danesi, F. Orlandini, and C. D. Coryell, J. Phys. Chem., 1966, 70, 141.

HYDROMETALLURGICAL RECOVERY OF COBALT(II) FROM ACIDIC CHLORIDE SOLUTIONS BY TRANSPORT THROUGH POLYMER INCLUSION MEMBRANES

HYDROMETALLURGICAL RECOVERY OF COBALT(II) FROM ACIDIC CHLORIDE SOLUTIONS BY TRANSPORT THROUGH POLYMER INCLUSION MEMBRANES Physicochem. Probl. Miner. Process. 49(2), 2013, 641 649 www.minproc.pwr.wroc.pl/journal/ Physicochemical Problems of Mineral Processing ISSN 1643-1049 (print) ISSN 2084-4735 (online) Received March 14,