removal of copper(ii) ions using micellar-enhanced ultrafiltration

XXIII ARS SEPARATORIA – Toruń, Poland 2008

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REMOVAL OF COPPER(II) IONS USING MICELLAR-ENHANCED ULTRAFILTRATION Katarzyna STASZAK and Krystyna PROCHASKA Institute of Chemical Engineering and Technology, Poznań University of Technology, pl. M. Skłodowskiej-Curie 2, 60-965 Poznań, Poland e-mail: [email protected]

Abstract Removal of copper(II) ions from micellar solutions was studied in the crossflow SEPA CF Osmonics module. In the case of high concentration of copper(II) ions (0.1 M) the efficiency of ultrafiltration is not satisfactory. That’s why the next step of this work is using the hydrophobic reagents to complexation the metal ions in order to improve the ultrafiltration process.

1. INTRODUCTION The traditional techniques for the removal of metal ions from aqueous effluents like process of ion exchange, activated carbon adsorption and electrolytic removal are rather expensive but still used [1]. The use of techniques for the elimination of metal from liquid effluents based on separation by means of membranes is becoming increasingly more frequent. Reverse osmosis (or at least nanofiltration) can be used due to the size of the ions in aqueous solutions. But the usual permeate fluxes of RO membranes are limited and require high transmembrane pressure, which makes the process expensive [2]. In recent years Micellar-Enhanced Ultrafiltration (MEUF) has also been used. This technique combines the high resistance of reverse osmosis with the high relative flow of ultrafiltration. The MEUF technique has been used in the elimination of microcontaminants in three ways: i) the use of an anionic surfactant allows micelles to formed where the organic part is facing the centre and the negatively charged hydrophilic part is facing out. The metals or cationic contaminants bind on this negatively charged surface; ii) the use of a cationic surfactant allows the formation of micelles, where the organic part is facing the centre and the positively charged hydrophilic part is facing out. The oxianions or anionic contaminants bind on the surface; iii) the water-repelling contaminants solubilize inside the micelles.

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Many researchers have studied the application of MEUF for the separation of various ionic pollutants, but mainly in the much diluted systems (below 0.01M) [1, 3-5]. In the present work the retention of copper(II) ions with anionic surfactant – sodium dodecyl sulfate (SDS) were studied. The aim of this work is testing the usefulness of MEUF technique in the case of feed solution of high concentration of copper(II) ions (0.1M). 2. EXPERIMENTAL 2.1. REAGENTS

The following regents were used: Sodium Dodecyl Sulfate (>99% pure, Sigma Aldrich) and copper sulfate (CuSO4⋅5H2O, pure). For the spectrometric measurements the ammonia and sulfate acid were used. 2.2. INSTRUMENTATION AND PROCEDURE

The ultrafiltration experiments were carried out in the SEPA CF Membrane Cell produced by OSMONICS, USA. The flat sheet polymeric membrane made of polyvinylidene fluoride. The effective surface area of the membrane was 0.0155 m2. The fluid was forced through the membrane at a pressure of 0.2 MPa. The inlet reservoir was initially filled with a 1000 ml feed solution and the process was stopped when 500 ml was taken as a permeate. The CMC of surfactant and the concentration of surfactant in permeate was determined by the conductometric method [6]. The metal concentration in permeate was determined by UV spectroscopy using a Specol 1200, Analytic Jena, Germany by the complexation of copper ions by the ammonium solution [7]. The retention of metal was calculated from the equation: R = 1− c P / c N where cP – concentration of metal ion in permeate, cN – initial concentration of metal in feed solution. 3. RESULTS AND DISCUSSION 3.1. DETERMINATION OF SURFACTANT

During the ultrafiltration process the monomers of surfactant could be transported through the membrane. To check these phenomena the filtration of 5CMC SDS solution has been performed.

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CMC of SDS

1 0.9

90

0.8

80

0.7

70

0.6

87

60

0.5

50 R [%]

0.4

40

0.3 30

0.2

20

0.1

12

13

14

10

0 0

50

100 time, t [min]

150

200

0 0.1M CuSO4

0.1M CuSO4 + 5CMC SDS



Fig.1. Concentration of SDS in permeate Fig.2. Average retention, R, of copper(II) (CMC of SDS) as a function of time ions during the ultrafiltration process

Significant changes of surfactant concentration were observed during first 30 min of the separation process (Fig. 1). However, during the whole time of experiment (3 hours) the concentration of SDS was bellow its CMC. 3.2. METAL RETENTION

Four solutions of different Cu(II) concentration were filtrated. Three of them contained the total concentration of copper(II) ion equal to 0.1M and different concentration of anionic surfactant (0, 5 and 10 CMC) and in one solution with 0.01M CuSO4 and 5 CMS of SDS. Fig.2 presents the variation of average retention in the case of UF of solutions of different composition. In dilute stream of copper ions the retention of metal is near 90%. However, in the case of high concentration of copper(II) ions the efficiency of ultrafiltration is not satisfactory. The retention is at the level of 12-14%. In order to enhance selectivity and efficiency of MEUF the ligand-modifed micellar enhanced ultrafiltration (LM-MEUF) should be used. This method involves additionally an amphiphilic ligand and a surfactant to the feed solution under conditions where most of the surfactant is present as micelles. The ligand reveals a high degree of solubilization in the micelles and a tendency to selectively complex the target metal ion [3]. Thus the next step of this work is investigation of MEUF with commercially available hydrophobic chelating extractant LIX 54 added to the separation systems. 4. CONCLUSIONS The cross-flow micellar ultrafiltration experiments showed the usefulness of this method only for feeds of low concentration of copper(II) ions. In high concentration (0.1M) the retention is very small. However, the addition of anionic surfactant caused increase in retention of metal ions, but

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the differences are over-slight. That’s way the next step of this work is using the hydrophobic reagents to complexation the metal ions in the order to improve the ultrafiltration process. Acknowledgements The work was supported by 32-270/BW/2008. REFERENCES [1] L. Gzara, M. Dhahbi, Desalination, 2001, 137, 241. [2] C. Guohua, J. Memb. Sci., 1997, 127, 93. [3] B.R Fillipi., J. F Scamehorn., S. D Christian., R.W Tayloret., J. Membr. Sci., 1998, 145, 27. [4] M. Aoudia, N. Allal., A. Djennet, L. Toumib, J. Memb. Sci., 2003, 217, 181. [5] K. Back, H. Leeb, J-W Yang, Desalination, 2003, 158, 157. [6] J. Garcia-Anton, J. L. Guinon, Colloid Surface, 1991, 61, 137. [7] A. Cygański, Metody spektroskopowe w chemii analitycznej, WNT, Warszawa, 1993.