ISSN 0040-5795, Theoretical Foundations of Chemical Engineering, 2008, Vol. 42, No. 5, pp. 740–743. © Pleiades Publishing, Ltd., 2008. Original Russian Text © N.S. Smirnov, I.D. Troshkina, A.B. Maiboroda, A.M. Chekmarev, 2007, published in Khimicheskaya Tekhnologiya, 2007, Vol. 8, No. 10, pp. 468–471.
CHEMISTRY AND TECHNOLOGY OF RARE, DISPERSED, AND RADIOACTIVE ELEMENTS
Ultrafiltration Concentration of Diluted Rhenium Solutions N. S. Smirnov, I. D. Troshkina, A. B. Maiboroda, and A. M. Chekmarev Mendeleev University of Chemical Technology, Miusskaya pl. 9, Moscow, 125190 Russia Received April 2, 2007
Abstract—The ultrafiltration concentration of rhenium is investigated with the use of the Praestol flocculants of the cation type using a setup with separating membranes in the form of polysulfone-based hollow fibers. The dependence of selectivity of the membrane on the impurity concentration in the solution is studied. The possibility of eluting rhenium from the obtained concentrates is shown. When extracting rhenium from mineralized solutions that model the composition of natural chloride–sulfate waters, the selectivity of the membrane reaches 88% for three cycles of the complex-forming ultrafiltration. DOI: 10.1134/S0040579508050461
In recent years, applications of rhenium have substantially increased in the production of high-quality alloys for aerospace industry and catalysts [1]. The world production of rhenium is approximately 40 t of primary and 10 t of secondary metal per year. Since the developed raw material sources of rhenium of industrial value are absent in Russia, the use of nontraditional sources with low rhenium contents to accompany its obtainment becomes topical. These sources can be natural mineralized and mine waters, as well as recycle and discharge solutions [2]. An increase in the production of rhenium with the assimilation of such natural resources can be achieved due to the development of new hydrometallurgical methods of isolation, for example, membrane methods.
The selection of polyelectrolytes was conditioned by the state of rhenium in diluted solutions, where it is – situated in the form of the perrenate ion (Re O 4 ). In addition, large-scale industrial production of these polyelectrolytes is developed, which guarantees their high quality.
Among the baromembrane methods, the combined method of complex formation and ultrafiltration (CFUF) is characterized by increased selectivity [3–7]. This method involves the formation of macromolecular compounds with metal due to preliminary introduction of water-soluble polymer into the solution and concentration of obtained complexes during their passage through the ultrafiltration setup. The complex of polymer with metal remains in the concentrate (retant), while the low-molecular compounds pass through the ultrafiltration membrane forming the filtrate (permeate). Large advantages of the CFUF method are large productivity at insignificant power consumption caused by the use of low working pressures (0.02–0.2 MPa), continuity of the process, and its simple automation.
The experiments were performed using a laboratory setup, the main part of which is a tubular ultrafiltration apparatus with separating membranes made in the form of hollow polysulfone fibers, the rated cut molecular weight of dissolved substances is 20000 amu (Fig. 2).
The structures of elementary units of cation polyelectrolytes Praestol are depicted in Fig. 1. In order to wash out the low-molecular components, the solution of polyelectrolyte was preliminary subjected to ultrafiltration under the continuous introduction of distilled water. The filtrate volume equals four volumes of the solution circulating in the setup.
The membrane material is characterized by a high strength, stability to the effect of oxidants and microorganisms, and operational stability in both acidic and
As complexing agents, we used polyelectrolytes (PE) Praestol (Degussa, Germany) containing the groups of quaternary ammonium bases. Polyelectrolyte with a molecular weight of 6–20 million amu is a transparent, colorless, solid substance. 740
CH2
CH
CH2
C O
CH R
Cl–
CH3 N+ CH3
NH2 A
CH3
B n
Fig. 1. Structural unit of polyelectrolytes Praestol 658 and Praestol 859.
ULTRAFILTRATION CONCENTRATION OF DILUTED RHENIUM SOLUTIONS 2
starting solution + PE
3
4 3 1
concentrate
permeate
Degree of selectivity, % 100 90 80 70 60 50 40 30 20 10 0
Fig. 2. Ultrafiltration setup: (1) membrane module, (2) peristaltic pump, (3) manometers, and (4) valve.
alkali media. The main characteristics of the laboratory ultrafiltration setup are given below: Filtration surface, m2
0.02;
Membrane material Sizes of the ultrafilter, mm: diameter length filtration rate, ml/min* rated cut molecular weight, amu
Polysulfone 25 250 20 20000
* By water at a transmembrane pressure of 0.1 MPa.
Ultrafiltration of solutions after the addition of the polyelectrolyte was performed in the circulation mode. At the input into the membrane unit, an excess pressure of 0.02 MPa was maintained. The degree of rhenium retention by the membrane (degree of selectivity) (ϕ, %) was determined from the relation C ϕ = ⎛ ------i ⎞ × 100 %, ⎝ C p⎠
0.02
741
Praestol 859 Praestol 658
0.04
0.06
0.08
0.10 CPE, %
Fig. 3. Dependence of the selectivity of the membrane by rhenium on the concentration of polyelectrolytes Praestol 859 and Praestol 658 in the solution.
the solutions and the increase in their viscosity. The degree of concentration is proportional to the selectivity of extraction and the coefficient of decreasing the volume. At a selectivity tending to 100%, the degree of concentration will be equal to the coefficient of decreasing the volume, the value of which is limited by the initial concentration of polyelectrolyte in the solution. We studied the dependence of selectivity of the membrane by rhenium on the volume of electrolyte passed though a 0.1% solution of Praestol 859 (Fig. 4). The rhenium concentration in the passed solution CRe was 25 mg/dm3. It is evident from Fig. 4 that the selectivity of the membrane (>90%) is retained during the passage of Selectivity, % 100 95 90 85
where Ci and Cp are the rhenium concentrations in the initial solution and in the permeate, mg/dm3, respectively. The data on the effect of the concentration of polyelectrolytes Praestol 859 and Praestol 658 in the solution on the selectivity of the membrane are presented in Fig. 3. It is evident from the plot that the selectivity of the membrane with the use of Praestol 859 reaches 90% at the polyelectrolyte concentration of 0.017%, and with the use of Praestol 658—starting from 0.1%. A further increase in the coagulant concentration is inexpedient due to the increasing degree of structure in
80 75 70 65 60
0
100
200
300
400
500 V, cm3
Fig. 4. Dependence of the selectivity of the polysulfone membrane by rhenium on the volume of the passed solution.
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was introduced into a concentrate solution containing 0.1 wt % of polyelectrolyte until the required concentration was reached. The obtained rhenium-containing solution was subjected to ultrafiltration, after which the rhenium concentration in the permeate (filtrate) was determined. The solution of polyelectrolyte containing no rhenium was washed of nitrate ions and directed to the beginning of the cycle.
Cp/Ci 1.0 0.9 0.8 Preastol 859 Preastol 658
0.7
The degree of elution was calculated by the formula C ϕ E = ------p , Cc
0.6 0.5 0
0.02
0.04
0.06
0.08 0.10 CNaNCO3, mol/dm3
Fig. 5. Effect of the concentration of sodium nitrate on the degree of elution of rhenium from polyelectrolytes during ultrafiltration.
450–475 ml of the rhenium solution. The rhenium concentration in the polyelectrolyte solution on finishing the experiment calculated by the balance relations at the known rhenium content in the starting solution and in permeate was 500 mg/dm3. Therefore, under the selected experimental conditions, the application of Praestol 859 at a content of 0.1 % allows one to concentrate rhenium by the CFUF method by a factor of 20. To effectively force the perrenate ions out of the polyelectrolyte, we used solutions of sodium nitrate with various concentrations [8]. Sodium nitrate in the form of a solution with a concentration of 3 mol/dm3 Degree of selectivity, % 80 70 60
NaCl Na2SO4
50 40
The dependence of the degree of elution of rhenium on the sodium nitrate concentration is presented in Fig. 5. The data obtained indicate that the optimum NaNO3 concentration for elution of perrenate ions from Praestol 658 is 0.05 mol/dm3, and from Praestol 859—0.1 mol/dm3. In this case, on one hand, a high degree of regeneration (98%) is reached, which allows one to obtain a permeate enriched by rhenium. On the other hand, at such a relatively low concentration of nitrate ions in the solution, processing the obtained permeate by hydrometallurgical methods, e.g., by liquid extraction, is facilitated. When carrying out three cycles of the ultrafiltration extraction of rhenium, its elution, and the regeneration of polyelectrolyte under the conditions selected in this work, the selectivity of the polysulfone membrane using Praestol 859 as the polymer that bonds rhenium remains almsot invariable. The rhenium content in natural waters depends on the degree of their mineralization. The highest rhenium concentrations are observed in chloride–sodium waters, while the lowest ones are observed in sulfate– calcium waters [9]. The near-surface waters at a depth of 10–12 m are more enriched by rhenium than the deep waters. Sulfate and chloride ions, which are present in natural waters, are the main impurities that affect the formation of the complex of polyelectrolyte with the perrenate ion.
30 20 10 0
where Cp is the rhenium concentration in the permeate obtained after introduction of NaNO3 into the solution, and Cc is the rhenium concentration in the permeate corrected to the volume of the introduced NaNO3 solution.
0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 Salt concentration, mol/dm3
Fig. 6. Effect of the concentration of Na2SO4 and NaCl in the solution on the degree of selectivity of the membrane by rhenium.
Figure 6 represents the data on the investigation of the separate effect of Na2SO4 and NaCl on the selectivity of the membrane by rhenium. The effective concentration of Re proceeds at concentrations of Na2SO4 lower than 0.005 and NaCl lower than 0.004 mol/dm3.
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ULTRAFILTRATION CONCENTRATION OF DILUTED RHENIUM SOLUTIONS
We studied the possibility of selectively extracting rhenium from the solution modeling the natural waters of the following composition: ReO4
Na+
Cl–
SO 4
C, mol/dm3 × 102
0.01
56.6
11.4
22.6
The experiments were carried out by the following procedure. Polyelectrolyte was added into the model solution to a concentration of 0.1% and the model solution was passed through the ultrafiltration installation. The rhenium content in the obtained permeate was determined. After introducing the new portion of polyelectrolyte, the permeate was directed to the following cycle of the ultrafiltration extraction of rhenium. It was established that the total selectivity by rhenium from the solutions modeling the natural waters reaches 88% for three cycles of the CFUF process. The results of a multistage extraction of rhenium from the solution modeling the natural waters are presented below:
1 2 3
1.0 mol/dm3. It is established that, for three cycles of complex-forming ultrafiltration of rhenium from an aqueous solution imitating the mineralized natural waters, the degree of extraction of rhenium is 88%.
–
Ion
Cycle number
743
Selectivity, %: 36 61 88
CONCLUSIONS The possibility of the ultrafiltration concentration of rhenium from the aqueous solution of ammonium perrenate by cation polyelectrolytes Praestol using a setup with that involves membranes in the form of polysulfone-based hollow fibers is shown. The concentrations of the Praestol 859 and Praestol 658 polyelectrolytes are determined at which the degree of membrane concentration for rhenium is 20–100. Elution of rhenium from the polyelectrolyte solution proceeds with the use of the sodium nitrate solutions with concentrations 0.5–
REFERENCES 1. Problems of the World Market of Rhenium, Bull. Inostr. Kommerch. Inform., 2006, no. 120 (9066), p. 15. 2. Palant, A.A., Troshkina, I.D., and Chekmarev, A.M., Metallurgiya reniya (Metallurgy of Rhenium), Moscow: Nauka, 2007. 3. Tokareva, G.I., Tokarev, N.I., Dytnerskii, Yu.I., Volchek, K.A. et al., Laboratornye i tekhnologicheskie issledovaniya i obogashchenie mineral’nogo syr’ya: Obzor (Laboratory and Technological Investigations and Enrichment of Mineral Raw Materials: Review), Moscow: VIEMS, 1988, p. 60. 4. Shkinev, V.M., Vorobieva, G.A., Spivakov, B.Ya. et al., Enrichment of Arsenic and Its Separation from Other Elements by Liquid-Phase Polymer-Based Retention, Sep. Sci. Technol., 1987, vol. 22, no. 10, pp. 2165–2173. 5. Geckeler, K.E., Bayer, E., Spivakov, V.Y. et al., LiquidPhase Polymer-Based Retention, a New Method for Separation and Preconcentration of Elements, Anal. Chim. Acta, 1986, vol. 189, pp. 285–292. 6. Volchek, K.A., Dytnerskii, Yu.I., Al’-Naif, N. et al., Ul’trafil’tratshionnoe kontsentririvanie skandiya is mnogokomponentnykh rastvorov (Ultrafiltration Concentration of Scandium from Multicomponent Solutions), Khim. Tekhnol. Vody, 1991, vol. 13, no. 3, pp. 255–259. 7. Topchiev, D.A. and Malkanduev, Yu.A., Kationnye polielektrolity: poluchenie, svoistva i primenenie (Cation Polyelectrolytes: Obtainment, Properties, and Application), Moscow: Akademkniga, 2004. 8. Troshkina, I.D., Petrov, D.G., Maiboroda, A.B., and Chekmarev, A.M., Ultrafiltration Extraction of Rhenium from Recycle Waters of Copper Production, Tsvetn. Met., 2001, no. 4, pp. 71–73. 9. Ivanov, V.V., Ekologicheskaya geologiya elementov: Spravochnik: Kn. 5 (Environmental Geology of Elements: Handbook: vol. 5), Burenkov, E.K., Ed., Moscow: Ekologiya, 1997.
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