Solvent Extraction and Ion Exchange CHELATION

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Solvent Extraction and Ion Exchange

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CHELATION PROPERTIES OF POLY(8-HYDROXYQUINOLINE 5,7DIYLMETHYLENE) TOWARDS SOME TRIVALENT LANTHANIDE METAL IONS K.A.K. Ebraheem a; M.S. Mubarak a; Z.J. Yassien a; F. Khallli a a Department of Chemistry, Faculty of Science, University of Jordan, Amman, Jordan

To cite this Article Ebraheem, K.A.K., Mubarak, M.S., Yassien, Z.J. and Khallli, F.(1998) 'CHELATION PROPERTIES OF

POLY(8-HYDROXYQUINOLINE 5,7-DIYLMETHYLENE) TOWARDS SOME TRIVALENT LANTHANIDE METAL IONS', Solvent Extraction and Ion Exchange, 16: 2, 637 — 649 To link to this Article: DOI: 10.1080/07366299808934544 URL: http://dx.doi.org/10.1080/07366299808934544

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SOLVENT EXTRACTION AND ION EXCHANGE, 16(2),637-649 (1998)

CHELATION PROPERTIES OF POlY(8-HYDROXYQUINOLINE 5,7-DIYlMETHYlENE) TOWARDS SOME TRIVALENT LANTHANIDE

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METAL IONS

K.A.K. EBRAHEEM', M.S. MUBARAK, Z.J. YASSIEN and

F. KHALILf

Department of Chemistry, Faculty of Science, University of Jordan, Amman-11942, Jordan

ABSTRACT

The sorption and desorption properties of the chelate-forming phenolformaldehyde resin,

poly(8-hydroxyquinoline 5,7-diylmethylene) towards various

trivalent lanthanide ions such as La+3 , Ce+3 , Nd+3 , Sm+3 , and Gd+3 were studied by a static batch equilibration technique as a function of pH and contact time. The resin selectivity and binding capacity towards various lanthanide metal ions are discussed.

'J

Author to whom all correspondence should be addressed.

637 Copyright C 1998 by Marcel Dekker, Inc.

638

EBRAHEEM ET AL.

INTRODUCTION

The chelation properties of chelate-forming polymers have been the subject of considerable current interest [1-4]. Interest in these materials stems from their high selectivity towards heavy metal ions and their potential applications for the separation and monitoring of heavy metal ions in environmental waters [5-8].


Chelate-forming polymers are produced by incorporating active chelating groups into a polymeric matrix [2,9,10]. Such chelating groups may be covalently bound to a polymer matrix as pendent groups or incorporated into the repeating units of the polymer backbone

by polymerization of a suitable monomer

containing the required chelating group. 8-Hydroxyquinoline (mane) and related derivatives represent attractive chelating agents

for a variety of metal ions. For example, the Kelex-I 00 chelants

patented by Ashland Chemicals (Columbus, Ohio, USA) as specific extractants for copper are 7-alkenyl substituted derivatives of 8-hydroxyquinoline [II]. The incorporation of 8-hydroxyquinoline in chelating polymers has been achieved via several reaction routes. Von Lillin [12], Pennington and Williams [13] and . Vernon and Eccles [14] have incorporated 8-hydroxy-quinoline in resorcinolformaldehyde polymers. Moreover, several studies have been reported on the condensation of 8-hydroxyquinoline with formaldehyde [15,16], furfural [17] and with 1,2-dichloroethylene by a Friedel-Craft type reaction [18]. Although, the chelation properties of these

oxine-containing chelate-

forming polymers towards some transition and alkaline earth metal ions have been studied in detail [14-16, 19], no work has been reported on the interaction of these polymers with the lanthanide metal ions. The present paper focuses on the chelation properties of poly(8-hydroxyquinoline 5,7-diylmethylene) towards some trivalent lanthanide ions such as La+ 3 , Ce+ 3

,

Nd+ 3

,

Sm+3

,

and Gd+3 . The rate of metal ion uptake and the pH-binding

capacity profiles were investigated with the view to determine the efficiency and selectivity of the chelate-forming resin.

639

POL Y(8-HYDROXYQUINOLINE 5,7-DIYLMETHYLENE)

EXPERIMENTAL

Materials: Unless otherwise indicated, all materials were of analytical grade and were used without further purification. 8-Hydroxyquinoline was obtained from Riedel de-Haan (Germany); formaldehyde solution (37% - 41%) was purchased from BDH Chemicals Ltd. (England); the lanthanide salts, LaCI,. 7H2 0 , CeCI, .6H2 0 , Downloaded By: [University of Jordan] At: 07:15 23 February 2010

NdCl, .6H2 0 and SmCI, .6H20 were obtained from Fluka Co. (Switzerland) and

the salt GdCI, . 6H 20 was obtained from Koch-Light Laboratories Ltd. (England).

Prepgmtion of Poly(8-hydroxvquinoline 5 7-diYlmethYlene) :

The polymer was prepared and characterized as described elsewhere [16]. The polymer was purified by reprecipitation from N,N-dimethylformamide (DMF) solution by excess methanol. Finally, the pure polymer was dried at 90 ·C for 24 hours in vacuum, crushed and sieved (35-60 mesh). Satisfactory elemental analyses were obtained. Polymer

(Found)

Ca1cd. for [C IOH7NO].

%C 72.28

%H

5.08

%N 8.65

%C 76.42

%H

4.49

%N 8.91

The polymer is non-porous and not crosslinked. It dissolves in DMF and to a lesser extent in dimethylsulphoxide (DMSO) but is insoluble in other common organic solvents. The polymer is insoluble in water but readily soluble in acids.

Measurements: Infrared spectra of polymers of all solid samples were recorded as KBr discs using a Nicolet Impact 400 FT-IR spectrophotometer from 4000 to 400cm· 1 Scanning electron microscope (SEM) photographs were recorded with a DSM 950 electron microscope which allowed a wide range of magnification up to

640

EBRAHEEM ET AL.

x1000.

Complexometric titrations were carried out with a Metrohm 655 Dosimat

titrator.

Sorption ofMetal Ions on the Polvmer : The metal chelation characteristics of each metal ion were studied by the batch equilibrium technique. Duplicate experiments involving 0.50g of 35- 60 mesh size resin samples were equilibrated with 75 mL of sodium acetate-acetic Downloaded By: [University of Jordan] At: 07:15 23 February 2010

acid buffer solution for 3 hrs. Then 25 mL of metal ion solution containing a total of 50 mg metal ion was added. After being stirred for a definite period of time at 25°C, the mixture was filtered and the amount of metal ion remaining in the filterate was determined by complexometric titration using a standard EDTA solution and xylenol orange solution as an indicator. The rate of metal ion uptake was examined under similar experimental conditions where the contact time was varied from 1 hr to 24 hrs at 25°C and pH 7. Similar experiments were also carried out in buffer solutions of pH values 5 to 8 for a fixed contact time of 6 hrs. Desorption ofmetal ions on the polymer: A 0.50g experiment, hrs,

sample of the resin, chelated with metal ions from a sorption

was suspended in 40 mL of 3M He!. The mixture was stirred for 6

neutralized with 3 M NaOH solution, filtered and washed with deionized

distilled water. The amount of metal ion desorbed in the filtrate was determined by complexometric titration using a standard EDTA solution.

RESULTS AND DISCUSSION

Characterization Il.(the Polymer and its Polymeric Chelates :

Poly(8-hydroxyquinoline 5,7-diylmethylene) was prepared as described elsewhere [16] with a number average molar mass M; of ca. 5700 glmol. The FT-

POLY(8-HYDROXYQUINOLINE 5,7-DIYLMETHYLENE)

641

IR spectra of the polymer and its polymeric chelates resemble that of the monomer and are consistent with the structure assigned to the polymer. Hence, only some important assignments are discussed here. The broad band at 3353cm'\ has been assigned to the hydroxy group of 8-hydroxyquinoline intramolecularly hydrogen bonded to the nitrogen [16,18]. This band is also observed in the spectra of the polymeric chelates, since only a fraction of the ligand moieties on the


polymer are involved in chelate formation. The bands in the region 3060-2950 cm-\ have been assigned to the aromatic C-H stretching, while the bands at 29302850cm'\

have been attributed

to the C-H stretching of the methylene bridges

connecting the aromatic rings[I6]. The band due to the VC=N at 1580 cm'\ is shifted by ca. 4 cm'! to higher frequency in the spectra of the polymeric chelates. Charles and co-workers[20] have attributed the band observed at II OOcm'1 in the IR spectra of metal complexes of 8-hydroxy-quinoline and some of its methylsubstituted derivatives to the C-O-M stretching. They have found the frequency of this band to correlate with the atomic number of the metal. Similar trend was reported [21] for the coordination polymers of bis(8-hydroxyquinoline)-methane. In the present series of lanthanide polymeric chelates, this band is observed at relatively higher frequencies

(1120-1135 cm'l ) in agreement with the

aforementioned trend. Scanning electron microscope photographs were employed to show the surface morphology of the resin, and the changes that result from the interaction of the resin with metal ions. Plate (I) shows the lamellar structure of the purified and dried resin. No significant changes have been observed in the surface morphology of the resin after equilibration with the buffer solution used in the sorption experiments. Upon complexation with metal ions, the surface morphology undergoes considerable changes as exemplified in plates (2) and (3) for the polymer chelates of Ce (III) and Gd (III),

respectively. Such changes are indicative of chelate

formation on surface binding sites.




645

POLY(8-HYDROXYQUINOLINE 5.7-DIYLMETHYLENE) Table 1.

The rate of metal ion uptake by poly(8-hydroxyquinoline 5,7-diylmethylene).

I hour

Milligrammes of metal ions taken up by the polymer') 24 hours 2 hours 3 hours 4 hours 6 hours 8 hours

La3+

7.22

8.53

9.60

10.07

10.62

11.97

12.92(69.7)

Ce 3+

10.08

10.86

11.53

12.75

12.93

14.04

15.95(93.7)

Nd 3+

10.74

11.48

12.23

13.87

14.51

15.59

16.06(94.6)

8m 3+

11.03

11.24

12.19

12.74

15.16

16.00

17.78(110.4)

Gd 3+

12.39

12.52

13.79

14.06

14.93

16.28

16.71(100.4)


Ln 3+

b)

Volume of solution = 100mL. Initial metal ion content in solution = 50 mg. Mass of polymer sample used = 0.50 g. b) Values between brackets are for distribution coefficients K1 , defined as K1 = [M]resiJ[M]solution where [M]resin is the amount (in mg) of metal ions taken up by Ig of resin and [M]solution is the amount (in mg) of metal ions remaining in 1 mL of solution.

a)

18

...= ..

16

C.

12

.S

..

10

-'l

8

.;;

on Q

e

.:!

14 -6

1---6- La(lll) -0-- Ce(1II)

Co

=

=

.S!

s. ::0

6

-.-Nd(lll)

4

--e- 8m(III) -+-Gd(III)

2 0 0

5

10

15

20

25

Contact time ( hrs) Figure 1. The rate of metal ion uptake by the polymer.

EBRAHEEM ET AL.

646 Table 2.

The pH-dependence of metal ion uptake by poly(8-hydroxyquinoline 5,7diylmethylene). Milligrammes of metal ions taken up by the polymer" pH=5

pH = 5.5

pH=6

pH= 6.5

pH=7

pH = 7.5

pH=8

~

1.97

3.49

4.46

8.58.

10.96

11.45

11.57

Ce 3+

4.08

5.63

6.41

10.75

12.19

13.64

13.91

Nd3+

5.58

7.14

10.10

13.10

15.25

15.44

15.59

Sm3+

8.57

9.09

10.62

14.91

14.95

15.52

15.89

Gd3+

9.09

9.50

11.48

15.15

15.38

15.68

16.00


Metal ion

oj

Volume of solution = 100mL. Initial metal ion content in solution = 50 mg. Mass of polymer sample used = 0.50 g.

..

.;;

.. ~

.

= I I'l

=

18 16 14 12

El .S

10

~

8

-.......... •S!

6

'3

4

:;;

2

Qj

....... La(llI) __ Ce(llI) -6-Nd(llI) -e-Sm(llI) __ Gd(llI)

0

4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 pH Figure 2. The pH-binding capacity profiles for metal ion uptake by the polymer

647


Table 3.


Desorption of lanthanide polymeric chelates by 3M HCl. Temperature = 25°C. Shaking time = 6 hours.

La(llI)

Ce(llI)

Nd(IlI) Sm(IlI) Gd (III)

Metal ion sorbed on the polymer (in mg)

14.03

16.41

17.74

16.48

16.92

Metal ion desorbed (mg)

7.79

7.10

4.75

3.26

1.86

% Recovery

55.52

43.26

26.77

19.78

11.00

for 6 hrs

with

3M HCI

as an eluent. The results shown in Table 3 indicate a

strong binding of these ions with the polymer with percent desorption ranging from

11.0% for Gd 3+ to 55.5% for La3+. This is also consistent with the relative

stability of these chelates and correlate with the relative sizes of the metal ions. In conclusion, the observed variations in the rates of metal ion uptake and the binding affinity of the present resin towards various lanthanoids are determined by the stability constants of the metal chelates and the relative sizes of the hydrated metal ions which control the penetration of metal ions into the less exposed binding sites on the surface. ACKNOWLEDGEMENTS

The authors gratefully acknowledge the financial support provided by the Deanship of Scientific Research, and the assistance of the Department of Geology for the use of their Scanning Electron Microscope.

648

EBRAHEEM ET AL. REFERENCES

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Received by Editor April 2, 1997