Micellar-extraction concentration of cobalt and nickel in ... - Springer Link

ISSN 1063455X, Journal of Water Chemistry and Technology, 2007, Vol. 29, No. 2, pp. 96–101. © Allerton Press, Inc., 2007. Original Russian Text © S. A. Kulichenko, V. A. Doroshshuk, S. A. Lelyushok, and N. A. Gonta, 2007, published in Khimiya i Tekhnologiya Vody, 2007, Vol. 29, No. 2, pp. 171– 181.

ANALYTICAL CHEMISTRY OF WATER

MicellarExtraction Concentration of Cobalt and Nickel in the Form of Aminocarboxylate Complexes S. A. Kulichenko, V. A. Doroshchuk, S. A. Lelyushok, and N. A. Gonta Shevchenko National University, Kiev Received July 4, 2006

Abstract—The paper has investigated extraction of carboxylate, amine, and aminocarboxylate complexes of cobalt and nickel into a phase of a nonionic surfaceactive substance at the cloud temperature. The technique of atomicabsorption determination of these metals in natural and waste waters has been developed with preliminary micellarextraction concentration. DOI: 10.3103/S1063455X07020051

Cobalt and nickel belong to microelements with a low content in the environmental objects [1]. When determining small amounts of these metals in natural and waste waters using the atomicabsorption and other methods it is necessary to do preliminary concentration by means of extraction with organic solvents or sorp tion on chemically modified silicas [2, 3]. A comparatively low degree of concentrating metals and toxicity of organic solvents used should be referred to as shortcomings of classical extraction [3]. An alternative for such an extraction is micellar extraction from aqueous solutions by phases of nonionogenic SAS (NSAS), which are formed at cloud temperature [4, 5]. In doing so, in a number of cases metrological characteristics of hybrid techniques improve [6, 8]. Aliphatic monocarboxylic acids and their blends with amines have been proposed for extraction and micel larextraction removal of many metals [9, 10]. The objective of the present paper is to study regularities of micellar extraction of cobalt and nickel with aliphatic carboxylic, amines, and their blends, and development of conditions for the atomicabsorption determination of metals with preliminary micellarextraction con centration. Polyoxyethylated alkylphenol OP7 (Plant of Thin Organic Synthesis, Ivano–Frankivsk [1]) was used as NSAS. The preparation weighted quantity was dissolved in distilled water. Monobasic carboxylic acids of a fatty series of the general formula CnH2n+1 were qualified as “pure for analysis” for a liquid and “pure” for solid acids. The latter were additionally purified by recrystallization from water–ethanole blends. We also used aliphatic amines of the general formula CnH2n+1NH2 (Merck). Weighted quantities of acids and amines were dissolved in OP7 aqueous solutions. The pH value was measured by means of a pH meter pH340 with a glass electrode ESL4307. Distribution of cobalt and nickel was monitored by means of an atomicabsorption spectrophotometer Saturn; combustible mixture: propan–butan–air. EXPERIMENTAL Aqueous solutions containing NSAS and other components of the reaction (10 cm3) were placed in cali bration measuring cylinders, which were fixed on a upright and immersed in a glass water bath. When achiev ing the cloud temperature, whereby one can see characteristic opalescence, the solutions were held until com plete phase separation into layers. The NSAS micellar phase was collected on the bottom of the cylinders. The aqueous phase was separated by decantation after phase separation and cooling of the solutions to room tem perature. The volume of the OP7 micellar phase being formed depended on the content of the preparation in the initial solution. As the NSAS concentration increases from 0.5 to 5% the volume of the micellar phase grew from 0.1 to 1.8 cm3 [13]. We determined the contents of metals in the micellar phase and based on the data obtained we calculated the degree of removal (R) and distribution coefficient (D) of cobalt and nickel. 96

MICELLAREXTRACTION CONCENTRATION

97

RESULTS AND DISCUSSION Quantitative parameters for extraction of intracomplex compounds (ICC) depend on hydrophobicity of the ligand and the complex formed. According to basic ideas (including the multifactor and the most adequate Coltgoff–Sendel model) the degree of removing ICC to the organic solvent increases as the constant of ligand distribution decreases, i.e. as its hydrophobicity decreases [14]. In the case of micellar extraction of ICC one can observe an opposite impact of the hydrophobicity of the complexing agent on the removal of the metal complex [15, 16]. According to our viewpoint it is hydrophobicity of the ligand in combination with its struc ture that is a main criterion for the choice of a reagent when creating optimal micellarextraction systems. MICELLAR EXTRACTION OF CARBOXYLIC COMPLEXES OF COBALT AND NICKEL We investigated the impact of the nature of carboxylic acid on the degree of removing cobalt and nickel to the OP7 micellar phase. It was found out that as the length of the hydrocarbon radical of carboxylic acid increases the degree of removing metals increases (Table 1). Table 1. Impact of the length of the hydrocarbon radical of carboxylic acids on the degree of removing (R) cobalt and nickel to the OP7 micellar phase (CAm = 0.01 mol/dm3, CCo = 3.0 mg/dm3, CNi = 1.3 mg/dm3, COP7 = 2%, pH 6) Acid Acetic Butyric Valeric Caproic Enanthic Caprylic Capric Undecanoic* Tridecanoic

n 1 3 4 5 6 7 9 10 12

RCo ,% 7.5 11 18 25 30 38 48 – –

RNi , % 4.3 15 17 23 34 36 51 – –

* In the presence of undecanoic and tridecanoic acids under the given conditions the micellar phase does not form.

By their extraction efficiency the studied carboxylic acids may be divided into two groups. The first group consists of moderately hydrophobic acids with n ≤ 9. The degree of removing metals to the micellar phase by acids of this group increases effectively linearly as the number of hydrogen atoms in the hydrocarbon radical increases. The second groups included carboxylic acids with n > 9, which are characterized with the highest values of distribution coefficients in the water–NSAS phase system. However, under optimal conditions for extraction of cobalt and nickel (6 ≤ pH < 9) these acids are in the NSAS micellar solution in the anionic form [17]. Solubilization of their longchain anions hydrophilizes the micellarextraction system and prevents the formation of the micellar phase. Dependence of the degree of removal of nickel and cobalt by caprylic acid is characterized by the plateau sections within the pH interval respectively 5.8–7.5 and 6.0–8.2 (Fig. 1). Compared with extraction of chlo roform the pH values of a half of micellar extraction of metals by caprylic acid are shifted by 0.5–1.0 unit to R, % 40 2

30 20

1

10 0

2 4 6 8 10 pH Fig. 1. Relationship between the degree of removing nickel (1) and cobalt (2) in the presence of caprylic acid and the pH value. CHA = 0.01 mol/dm3, CNi = 4.3 mg/dm3, CCo = 10 mg/dm3, COP7 = 2%.

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the region of large values, which may be explained by the weakening of protonodonor properties of caprylic acids in NSAS micellar media [18]. The ratio metal:acid (1:1) in carboxylate complexes removed was found by the method of shifting the equi librium (Fig. 2b). This means that metals under study may be extracted to the micellar phase in the cationic form (MA)+. R, %

lg D

40

1.2

30 0.8

20

0.4 10

0.0

0

2.5 2.0 3 Lg CAm, mol/dm (a) (b) Fig. 2. Relationship between the removal degree (a), the cobalt distribution coefficient (b) and the concentration of caprylic acid. CCo = 10 mg/dm3, COP7 = 2%; pH 6. 3.0

2.5

2.0

1.5

3.0

The ability of removing hydrophobic and hydrophilic particles including charged ones is a specific feature of the phases that are formed when heating NSAS solutions [15, 16]. However, when extracting with chloro form, carboxylate electroneutral complexes solvated with acid molecules of the composition MA2·mHA are removed [19]. MICELLAR EXTRACTION OF AMINE COMPLEXES OF COBALT AND NICKEL Introduction of amines into the system is a known method of raising the degree of extracting complexes of metals. In this case highly hydrophobic aminocarboxylate complexes are extracted to an organic phase [19]. Therefore, we also investigated the micellar extraction of amine complexes of cobalt and nickel. The relationship between the degree of extracting metals and the pH in the presence of hydrophobic octy lamine is characterized by the presence of a plateau (RNi ≈ 60, RCo ≈ 40%) within the pH interval 4–10 (Fig. 3). Low efficiency of metal extraction at low pH values is explained by protonation of octylamine, while at pH > 10—by hydrolysis of metals when heating solutions and destruction of NSAS in a strong alkaline medium. It should be noted that nickel in the presence of octylamine is extracted to the micellar phase better than cobalt. In this case substantial extraction of metals is retained also in a weakly acid medium, which is an evidence of a sufficiently high resistance of amine complexes formed. In the investigated system the relationships RM = f(CAm) have a form of saturation curves terminating in a plateau (RNi ≈ 60, RCo ≈ 40%) at a ~20fold molar excess of octylamine with respect to a metal. However, we failed to find the composition of amine complexes, which are extracted to the NSAS phase by the methods of the equilibrium shift. It was found that the increase of a number of carbon atoms in a hydrocarbon radical of amines increases the efficiency of micellar extraction of metals (Fig. 4). Thus, in the presence of amilamine—the most hydro philic in the series of amines under study—the coefficients of distribution of nickel and cobalt constitute JOURNAL OF WATER CHEMISTRY AND TECHNOLOGY

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99

R, % 1

60

D 50

1

2 40

40

30 20

2

20 10

0

6 8 10 12 n 8 12 pH Fig. 3. Fig. 4. Fig. 3. Relationship between the degree of removing nickel (1) and cobalt (2) in the presence of octylamine and the pH value. CAm = 0.01 mol/dm3, CNi = 4.3 mg/dm3, CCo = 10 mg/dm3, COP7 = 2%. Fig. 4. Impact of a hydrocarbon radical of aliphatic amine on the coefficients of distribution of nickel (1) and cobalt (2). CAm = 0.01 mol/dm3, CNi = 4.3 mg/dm3, CCo = 10 mg/dm3, COP7 = 2%; pH 8. 0

4

respectively 13 and 8, while using hydrophobic dodecylamine—44 and 22. A similar regularity is also charac teristic of classic extraction systems [20]. In this case in the water–organic solvent system the relationship DM = f(n) within a wide interval n is close to linear. For the investigated micellarextraction system a detailed analysis of the relationship DM = f(n) makes it possible to isolate three linear sections with different slope angles. Hydrophilic aliphatic amines with n < 7 extract nickel and cobalt to the OP7 micellar phase weakly, which is explained by low coefficients of distribution of amines themselves in the water–NSAS phase system [21]. The degree of metal extraction to the micellar phase by amines from 7 ≤ n ≤ 9 as their hydrophobicity increases goes up virtually linearly. It is conspicuous that a contribution of a methylene fragment of a hydro carbon radical of amines of this group to the coefficient of distribution of metals is greatest. The variation of hydrophobicity of longchain amines from n > 9 virtually does not affect the degree of removing nickel and cobalt. It should be noted that the use of individual carboxylic acids and amines does not ensure complete extrac tion of metals to the NSAS phase. MICELLAR EXTRACTION OF AMINE CARBOXYLATE COMPLEXES OF COBALT AND NICKEL More acceptable results were obtained when investigating a mixture of longchain carboxylic acids and amines. Thus, within the pH interval 7–11 cobalt and nickel, for all intents and purposes, completely go to the NSAS micellar phase in the presence of capric acid and octylamine (Fig. 5). The same combination of ligands was successfully used for micellarextraction removal of other metals [10, 22]. R, % 100

80

60

1 2

40

20

4

6

8

10

12

pH

Fig. 5. Relationship between the degree of removing nickel (1) and cobalt (2) in the presence of octylamine and capric acid and the pH value. CAm = 0.01 mol/dm3, CHA = 0.01 mol/dm3, CNi = 4.3 mg/dm3, CCo = 10 mg/dm3, COP7 = 2%.


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A large significance of pH1/2 during micellar extraction of nickel and cobalt by a mixture of capric acid and octylamine compared with extraction by individual reagents is attributable to the formation in the amine sys tem of a salt possessing a lower complexing capacity. Paper [19] described also the increase of the efficiency of usual extraction by the solvents of carboxylates of metals when introducing amines, which is explained by the formation of different ligand complexes containing amine molecules in the internal coordination sphere of the central ion. The metal:capric acid ratio in the compounds being extracted was defined as slope tangent of the relationship logD = f(logCHA) at the constant amine concentration. Taking into account the obtained results, the micellar extraction of cobalt and nickel may be represented by the equation M2+(W) + 2HA·Am(M) = MeAm2A2A2(M) + 2H+(W). By passing we will note that in the investigated system octylamine acts not only as a complexing agent, but is also conducive to the micellar phase of a hydrophobic additive. Solubilization of the hydrophobic amine hardly soluble in water weakens the hydration of NSAS micelles and the hydrophilichydrophobic balance in the system disturbed by an anion of acid is not restored. This manifests itself in the reduction of the initial parameters of phase formation in the OP7 solutions in a weakly alkaline medium in the presence of long chain acids. Based on the data obtained we have proposed conditions for atomicabsorption determination of nickel and cobalt in waters with preliminary micellarextraction concentration to the NSAS phase. METHODS OF DETERMINING NICKEL AND COBALT A prepared sample of water (100 cm3) was introduced to a beaker of 50 cm3 and 1.0 g of the OP7 prepa ration was dissolved in this water. The resultant solution was topped up with 0.090 g of capric acid and 0.130 g of octylamine and stirred it to complete dissolution of the reagents. The pH value equal to 9 was set by means of potassium hydroxide. The resultant solution was heated on a water bath till cloud temperature (75°C) and held at this temperature within 20 min until complete separation of the phases into layers. After cooling the aqueous phase was separated by decantation, while the isolated micellar phase (3 cm3) was diluted with dis tilled water (2 cm3) and conducted the atomicabsorption determination of nickel and cobalt. The contents of ions of metals in the sample were found by the graduation graph for whose construction 6 measuring flasks of 25 cm3 each were used to receive 0.7 to 3.0 cm3 of standard solutions of cobalt and nickel with concentra tion 1 × 104 mol/dm3 and were topped to the mark with a 20% solution of OP7, which corresponds to the NSAS concentration in the extract after dilution. This technique was tested when doing the analysis of model solutions containing cobalt, nickel, and typical macro and microcomponents of natural waters and when determining the content of nickel in wastewaters after their dilution before the discharge. For elimination of the interfering action of the matrix (organic com plexants) a sample of water acidified to pH 1–2 was subjected to the ultrasound treatment within 5 min [6]. The data of Tables 2 and 3 indicate satisfactory correctness and reproducibility of the obtained results of the analysis. Table 2. Results of determination of nickel and cobalt in model solutions in wastewaters (P = 0.95; n = 4) Metal

Introduced

Found

Sr

μg/dm3

Nickel

250

242 ± 16

0.04

Cobalt

200

194 ± 14

0.05

*The solutions contained, mg/dm3: Ca—100, Mg—40, Fe(III)—0.2, Cu—0.001, HCO3—200, Cl—50, SO42—50.

The preliminary experiments have shown that the lower boundary of metal determination may go down additionally when using for concentration of more diluted solutions of NSAS and raising the temperature of atomization. JOURNAL OF WATER CHEMISTRY AND TECHNOLOGY

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Table 3. Results of determination of the content of nickel in wastewaters (P = 0.95; n = 4) Water Wastewaters at nickel plating section Ditto of the galvanic shop

Found according to the developed tech nique 53 ± 4

Sr

Found according to [2], μg/dm3

Sr

0.04

49 ± 6

0.05

74 ± 5

0.05

77 ± 6

0.06

Thus, the paper has investigated the micellar extraction of cobalt and nickel in the form of carboxylate and amine complexes to OP7 NSAS phase at cloud temperature. It has been shown that complete extraction of metals to the indicated phase is achieved when using mixtures of longchain carboxylic acids and amines due to the formation of stable and highly hydrophobic aminocarboxylates. We have developed the technique of the atomicabsorption determination of nickel and cobalt in waters with the preliminary micellarextraction con centration. REFERENCES 1. Kuz’min, N.M. and Zolotov, Yu.A., Kontsentrirovaniye sledov elementov (Concentration of Element Traces), Mos cow: Nauka, 1988. 2. Lur’e, Yu.Yu., Analiticheskaya khimiya promyshlenykh stochnykh vod (Analytical Chemistry of Industrial Wastewa ters), Moscow: Khimiya, 1984. 3. Moskvin, L.N. and Tsarytsyna, L.G., Metody razdeleniya i kontsentririvaniya v analiticheskoy khimii (Methods of Sep aration and Concentration in Analytical Chemistry), Leningrad: Khimiya, 1991. 4. Shtykov, S.N., Zhurn. Anal. Khimii, 200, vol. 55, no. 7, p. 679. 5. Quina, F.H. and Hinze, W.L., Ind. Eng. Chem. Res., 1999, vol. 38, no. 11, pp. 4150–4168. 6. Kulichenko, S.A., Doroshchuk, V.O., and Lelyushok, S.O., Talanta, 2003, vol. 59, no. 4, pp. 767–773. 7. Song, G.Q., Lu, C., Hayakawa, K., and Lin, J.M., Anal. Bioanal. Chem., 2006, vol. 384, no. 4, pp. 1007–1012. 8. Doroshchuk, V.O., Lelyushok, S.O., Ishchenko, S.O., and Kulichenko, S.A. Talanta, 2004, vol. 64, no. 4, pp. 853– 856. 9. Charykov, A.K., and Osipov, N.N., Karbonovyye kisloty i karboksilatnye kompleksy v khimicheskom analize (Carbox ylic Acids and Carboxylate Complexes in Chemical Analyis), Leningrad: Khimiya, 1991. 10. Doroshchuk, V.A. and Kulichenko, S.A., Zhurn Analit. Khimii., 2005, vol. 60, no. 5, pp. 458–462. 11. Klimenko, N., Winther–Nielsen, M., Smolin, S., et al., Water Res., 2002, vol. 36, p. 5132. 12. Korestelev, P.P., Prigotovleniye rastvorov dla khimikoanaliticheskikh rabot (Preparing Solutions for ChemicalAna lytical Experiments), Moscow: Izdatelstvo AN SSSR, 1964. 13. Kulichenko, S.A. and Doroshchuk, V.O., Visn. Kyiv. Universytetu, series Chemistry, 2002, issue 38, pp. 20–24. 14. Zolotov, Yu.A., Osnovy analiticheskoy khimii (Principles of Analytical Chemistry), Moscow: Vyssh. Shkola, 2002. 15. Doroshchuk, V.O., Kulichenko, S.A., and Lelyushok, S.O., J. Colloid Interface Sci., 2005, vol. 291, no. 1, pp. 251– 255. 16. Doroshchuk, V.A., Cand. of Sc. (Chem.) Dissertation, Kiev, 2003. 17. Kulichenko, S.A. and Doroshchuk, V.A., Zhurn. Obshchey Khimii, 2003, vol. 73, no. 6, pp. 909–913. 18. Kulichenko, S.A., Visn. Kyiv. Universytetu, series Chemistry, 2000, issue 36, pp. 37–40. 19. Sukhan, V.V., Doctorate (Chem.) Dissertation, Kiev, 1980, p. 40. 20. Schmidt, V.S. Ekstraktsiya aminami (Extraction with Amines), Moscow: Atomizdat, 1970. 21. Lelyushok, S.O., Doroshchuk, and Kulichenko, S.A., Int. Conf. “Analytical Chemistry and Chemical Analysis”, Book of Abstracts, (Kiev, Sept. 12–18, 2005), Kiev, 2005, p. 276. 22. Kulichenko, S.A. and Doroshchuk, V.A., Zhurn Analit. Khimii, 2003, vol. 58, no. 6, pp. 586–589.


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