Problems of Phase Formation in the Polyethylene ... - Springer Link

Radiochemistry, Vol. 43, No. 6, 2001, pp. 5583561. Translated from Radiokhimiya, Vol. 43, No. 6, 2001, pp. 490 3493. Original Russian Text Copyright C 2001 by Rozen, Safiulina, Shkinev.

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Problems of Phase Formation in the Polyethylene Glycol3Inorganic Salt3Water Systems at Metal Extraction: I. Selected Anions Inducing Phase Separation

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A. M. Rozen* , A. M. Safiulina**, and V. M. Shkinev*** * Bochvar Russian Research Insitute of Inorganic Materials, State Scientific Center of the Russian Federation, Moscow, Russia ** Mendeleev Russian University of Chemical Engineering, Moscow, Russia *** Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Moscow, Russia

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Received November 16, 2000

Abstract Anions PO343, CO233, HPO243, SO243, and SCN3 inducing establishment of the two-phase equilibrium in water3polyethylene glycol3inorganic salt systems are characterized by weak interaction with water (negative hydration, DG > 0) and positive but weak deviation from Raoult’s law in water3salt (gH O > 1.0) binary 2 subsystems.

Recently there has been an interest in extraction systems based on water-soluble polymers. They consist of two aqueous phases, one of which contains mainly a soluble polymer (e.g., polyethylene glycol, PEG) and the second, a phase-forming salt (or another polymer, e.g., dextran).

only when the concentrations of the polymer and salt exceed a definite critical value, while the other mixtures with their lower concentrations form homogeneous solutions. The solid line separating the twophase region (point A) from the single-phase region (point B) is termed binodal.

Advantages of such systems are their nontoxicity and fire safety. In addition, production of PEG is environmentally clean and inexpensive.

The composition of the two-phase system suitable for practical separations should be fairly far from the critical point to provide the system stability.

For the first time, the systems with water-soluble polymers were advanced and used in biotechnology for separation of proteins, cells, and viruses. The systems with two polymers and polymer3inorganic salt systems were studied. Systems with water-soluble polymers are used for separation of biologically active substances on an industial scale. Works of biochemical orientation are summarized in Albertsson’s monograph [1].

As noted above, such systems can be used for metal separation. Binodals for ten systems are presented [5]. It was shown that not all but only selected anions exhibit salting-out effect (in the order of decreasing salting-out power): CO233, HPO243, SO243, F3, ClO34, and SCN3. The minimal concentrations of the salting-out agents providing phase separation, which quantitatively characterize the salting-out effect, are listed in Table 2 (data of [5]).

It was shown (Table 1, see review [2]) that many metals (including actinides) can be recovered with polymer3inorganic salt systems. To compensate for complexation of metals with anions of the phase-forming salt, efficient organic reagents should be used [2, 4].

Explanations of phase formation in aqueous solutions presented in the literature cannot be deemed satisfactory. For instance, Albertsson [1] believes that

The problems of phase formation, particularly for systems with two aqueous phases, are studied insufficiently. The phase diagram is the quantitative characteristic of phase formation; an example concerning the mixture of aqueous solutions of polymer (P) and salt (Q) is shown in Fig. 1 [1]. Phase separation can occur

ÄÄÄÄÄÄÄÄÄÄÄÄ K Deceased.

Fig. 1. Typical phase diagram. 1066-3622/01/4306-0558$25.00 C 2001 MAIK [Nauka/Interperiodica]

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Table 1. Distribution coefficients of various metals in extraction with PEG in the presence of organic reagents and potassium phosphorotungstate (PP) [2]

ÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄ ³ Na2CO3 ³ (NH4)2SO4 ³ (NH4)2HPO4 ³ K2CO3 Element ÃÄÄÄÄÄÂÄÄÄÄÄÂÄÄÄÄÄÂÄÄÄÄÄÄÂÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄ ³ N/r ³ XO ³ MTB ³ OPIDA ³ AC ³ AC ³ N/r ³ Arsenazo III ³ PP ³ PP ÄÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄ 2523254Es ³0.004 ³144 ³ 0.6 ³ 7.7 ³ 88.7 ³ 79.7 ³ 3 ³ 3 ³ 3 ³ 3 249Cf ³0.03 ³ 69.6 ³ 1.1 ³ 13.2 ³ 36.8 ³ 108.9 ³ 0.1 ³ 51.4 ³ 3 ³ 3 249Bk ³0.02 ³ 48.2 ³ 1.4 ³ 25.7 ³ 42.5 ³ 96.1 ³ 3 ³ 101 ³ 3 ³ 3 243Cm ³0.07 ³ 47.4 ³ 1.0 ³ 4.5 ³ 67.6 ³ 128.0 ³ 0.2 ³ 39.8 ³ 120 ³ 3 241Am ³0.007 ³ 32.7 ³ 2.5 ³ 4.8 ³105.8 ³ 138.1 ³ 0.2 ³ 45.1 ³ 137 ³ 6.8 ³0.12* ³ ³ ³ ³ ³ ³ 0.01* ³ ³ ³ 239Pu ³0.005 ³ 0.05 ³ 0.05 ³ 0.03 ³ 13.4 ³ 77.4 ³ 0.6 ³ 89.6 ³ 4.5 ³ 0.3 ³0.02* ³ ³ ³ ³ ³ ³ 0.02* ³ ³ ³ 237Np ³ 3 ³ 0.1 ³ 0.02 ³ 0.1 ³ 0.14 ³ 2.0 ³ 0.02 ³ 1.0 ³ 0.05 ³ 0.02 ³ ³ ³ ³ ³ ³ ³ 0.08* ³ ³ ³ 233U ³0.006* ³ 0.02 ³ 0.03 ³ 0.02 ³ 0.05 ³ 0.5 ³ 0.2 ³ 23.8 ³ 0.3 ³ 0.44 233Pa ³ 3 ³ 0.08 ³ 0.13 ³ 0.03 ³ 0.22 ³ 2.2 ³ 0.5 ³ 3 ³ 0.3 ³ 1.1 1523154Eu ³0.002 ³ 16.9 ³ 1.01 ³ 3.7 ³ 31.8 ³ 95.7 ³ 0.3 ³ 44.6 ³ 12.6 ³ 3 144Ce ³ 3 ³ 16.9 ³ 0.07 ³ 0.3 ³ 30.2 ³ 80.4 ³ 0.3 ³ 3 ³ 63.7 ³ 9.5 ÄÄÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄ

Note: Organic reagents used [2, 4]: N,N `-di(carboxymethyl)aminomethyl derivative of anthraquinone, alizarin complexone (AC); di(carboxymethylaminomethyl)-o-cresolsulfophthalein, xylene orange (XO); thymolsulfophthalexon, methylthymol blue (MTB); oxyphenyliminodiacetic acid (OPIDA); arsenazo III. (N/r) Extraction without reagent. * Data of [3].

phase separation is due to formation of coacervates. In [5], to explain separation of the solution in two and more phases, the O. Samoilov’s kinetic concept was used, although here we obviously deal with a thermodynamic phenomenon. Sergievskii et al. [6] attempted to describe the thermodynamic properties of the PEG3salt3water system assuming substantial hydration of PEG. High hydration numbers from 100 to 1000 (for the PEG3 water system) were determined. However, the authors did not take into account the athermal entropy which is usually considered in the theory of polymer solutions. This effect appears when mixing substances with molecules of different size, and in this case it is fairly high because the above difference is large (water and PEG): the ratio of molar volumes of PEG 2000 and water molecules is 110. We will consider this problem in detail in the second communication. The goal of this communication is to demonstrate the specificity of the selected phase-forming salts. By a series of examples, we found that the second phase is formed in systems containing salts that weakly interact with water [7]. In this work, we try to determine to what extent this conclusion is general. The majority of salts are unsuitable for obtaining two-phase systems. These salts are characterized by the positive hydration: DGhydr < 0 (Table 3), i.e., their RADIOCHEMISTRY

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hydration is thermodynamically favorable. This means that these salts interact with water comparatively strongly: the electrostatic ion3dipole interaction can be supplemented by the chemical (donor3acceptor) interaction for small cations. The substantial decrease in the water activity at increasing salt concentration (Fig. 2) and increase in the salt activity coefficient in the region of high salt concentrations, caused by hydration, also indicate strong interaction of such salts Table 2. Minimal concentrations of anions for formation of the second phase [5]

ÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÒÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄ Anion ³ Cmin, mol kg31 º Anion ³ Cmin, mol kg31 ÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄ×ÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄ 0.69 º F3 ³ 3.36 CO233 ³ 0.72 º ClO34 ³ 5.72 HPO243 ³ ³ 1.03 º SCN3 ³ 9.06 SO243 ÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÐÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄ Table 3. Hydration energy of salts [7]

ÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÒÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄ º ³ D Ghydr, ³ D Ghydr, Salt ³ kcal mol31 º Salt ³ kcal mol31 ÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄ×ÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄ 36 º NaNO3 ³ 31.5 LiNO3 ³ LiCl ³ 39.6 º NaCl ³ 32.1 LiBr ³ 313.1 º NaBr ³ 34.1 311.7 º NaClO4 ³ 33.7 LiClO4 ³ ÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÐÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄ

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panied by cooling) [7]. In this case, the dependence of the salt activity coefficient on the salt concentration has no ascending branch caused by hydration (Fig. 3), and the water activity coefficient in the saturated solution only slightly differs from unity. The fact of the phase separation in such systems itself indicates the substantial positive nonideality of solutions. In this work, we calculated DGhydr for SO243, CO233, HPO243, H2PO34, and PO343 (anions producing the two-phase systems with PEG). These data are lacking from [7]. The following equation was used for calculation [9]: Fig. 2. Water activity coefficient as a function of salt concentration.

DGhydr = 3RT ln as,

where as is the activity of the electrolyte and as = cns gn ahH O, where h is the number of water molecules 2 in the crystal hydrate. The results are listed in Table 4. As seen, the above anions are, indeed, characterized by the negative hydration (DGhydr > 0). This confirms weak interaction of the phase-forming salt with water.

Fig. 3. Salt activity coefficient as a function of salt concentration.

with water [8]. Salts generating two-phase systems belong to electrolytes with weak (negative) hydration (DGhydr > 0, see Table 4). The enthalpy of solution of such salts is positive (the salt dissolution is accomTable 4. Hydration energies of salts calculated by Eq. (1). Phase-forming salts are placed in the left column

ÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÒÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄ ³ D Ghydr , º ³ D Ghydr , Salt ³ kcal mol31 º Salt ³ kcal mol31 ÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄ×ÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄ Na3PO4 ³ 7.85 ºCu(NO3)2 ³ 33.09 Na2HPO4 ³ 4.04 ºZn(NO3)2 ³ 33.7 NaH2PO4 ³ 30.74 ºNH4NO3 ³ 31.46 Na2SO4 ³ 3.22 ºNaF ³ 0.67 NaHSO4 ³ 2.06 ºKF ³ 33.46 (NH4)2SO4 ³ 1.27 ºLiBr ³ 37.24 Na2CO3 ³ 1.96 ºLiI ³ 36.27 K2SO4 ³ 4.22 ºCsF ³ 38.65 KHSO4 ³ 1.99 ºCa(NO3)2 ³ 31.82 KH2PO4 ³ 0.76 ºLi2SO4 ³ 0.11 K2CO3 ³ 34.2 º ³ ÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÐÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄ

We have no characteristics of ternary solutions water3salt3polyethylene glycol; however, we can estimate the sign of nonideality of the salt3water binary solutions via the water activity using reference data on osmotic coefficients j. In addition Mikulin’s monograph [10] contains tables of salt concentrations at fixed values of water activities. Using the equations ln aH O = 3 0.018n m j, aH O = NH O gH O, 2 2 2 2 and NH O = 55.4/(55.4 + mn), we determined the 2 water activity coefficients. The results are shown in Fig. 2. As seen, for phase-forming salts, water activity coefficients exceed unity and increase with increasing salt concentration. In the other words, positive (although small) deviations from Raoult’s law are observed. The other salts, which exhibit no phaseforming properties (e.g., LiCl, NaCl), are characterized by the negative deviations from Raoult’s law, indicating substantial interaction between the salt and water. Thus, we proved that the phase-forming properties of salts are, as a rule, caused by the negative hydration, i.e., by stronger interaction of cations with anions as compared to their interaction with water. Table 5 shows that, as the metal ion is substituted by hydrogen ion, the salt interaction with water increases. Finally (as seen by an example of sodium dihydrophosphate), the salt loses the phase-forming power (partially, this may be due to the low salt solubility; with increasing temperature the solubility increases and the phase-forming power arises). In the K, Na, Li sulfate series, as the cation radius decreases, interRADIOCHEMISTRY

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Table 5. Characteristics of salts

ÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ Salt ³ DGhydr, kcal mol31 ³ Cation radius, nm [11] ³ Solubility, mol kg31 ³ Phase-forming power ÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ ³ 7.85 ³ 0.098 ³ 0.86 ³ + Na3PO4 ³ 4.04 ³ 0.098 ³ 0.85 ³ + Na2HPO4 ³ 30.74 ³ 0.098 ³ 7.90 ³ 3 NaH2PO4 ³ ³ ³ ³ ³ 4.22 ³ 0.133 ³ 0.69 ³ + K2SO4 ³ 1.99 ³ 0.133 ³ 4.17 ³ + KHSO4 ³ ³³ ³ 3.22 ³³ 0.098 ³³ 1.96 + Na2SO4 ³ 2.06 ³ 0.098 ³ 2.38 ³ + NaHSO4 ³ ³ ³ ³ ³ 0.11 ³ 0.068 ³ 3.19 ³ 3 Li2SO4 ÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ action with water is enhanced; for the Li salt the phase-forming power is completely lost (Table 5). Similar to phosphates, for sulfates substitution of the metal ion by proton enhances to certain extent the interaction with water; however, the phase-forming power is not lost. The positive deviation from Raoult’s law increases when PEG is incorporated into the system, and at the sufficient PEG concentration the system is separated in two phases. REFERENCES 1. Albertsson, P.A., Partition of Cell Particles and Macromolecules. Distribution and Fractionation of Cells, Mitochondria, Chloroplasts, Viruses, Proteins, Nucleic Acids, and Antigen3Antibody Complexes in Aqueous Polymer Two-Phase Systems, New York: Wiley3Interscience, 1971, 2nd ed. 2. Molochnikova, N.P., Shkinev, V.M., and Myasoedov, B.F., Radiokhimiya, 1995, vol. 37, no. 5, pp. 3853397. 3. Rogers, R.D., Bond, A.H., and Bauer, C.B., Sep. Sci.

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Technol., 1993, vol. 28, no. 133, pp. 1393153. 4. Nifant’eva T.I., Shkinev, V.M., Spivakov, B.Ya., and Zolotov, Yu.A., Dokl. Akad. Nauk SSSR, 1989, vol. 308, no. 4, pp. 8793881. 5. Nifant’eva T.I., Matoushova, V., Adamtsova, Z., and Shkinev, V.M., Vysokomol. Soedin., Ser. A, 1989, vol. 31, no. 10, pp. 213132135. 6. Sergievskii, V.V., Dzhakupova, Zh.E., Shkinev, V.M., and Spivakov, B.Ya., Zh. Obshch. Khim., 1994, vol. 64, no. 1, pp. 23326. 7. Rozen, A.M., Nikolotova, Z.I., and Kartasheva, N.A., Radiokhimiya, 1993, vol. 35, no. 6, pp. 493 62. 8. Robinson, R.A. and Stokes, R.H., Electrolyte Solutions, London: Butterworths, 1955. 9. Rozen, A.M., Zh. Fiz. Khim., 1995, vol. 69, no. 2, pp. 2353241. 10. Mikulin, G.I., Voprosy fizicheskoi khimii rastvorov elektrolitov (Problems of Physical Chemistry of Electrolyte Solutions), Leningrad: Khimiya, 1968. 11. Rabinovich, V.A. and Khavin, V.Ya., Kratkii khimicheskii spravochnik (Concise Handbook of Chemistry), Leningrad, Khimiya, 1991, p. 24.