International Journal of Inorganic ChemistryVolume 2012 (2012), Article ID 515196, 6 pagesdoi:10.1155/2012/515196

Research Article

Reversed-Phase Column Extractive Separation of Gd(III) with Poly[dibenzo-18-crown-6]

K. R. Mahanwar,¹ S. R. Sabale,1,2 R. B. Kadam,¹ and B. S. Mohite¹

¹Analytical and Environmental Research Lab, Department of Chemistry, Shivaji University, Kolhapur 416 004, India²Department of Chemistry, Jaysingpur College, Jaysingpur 416101, India

Received 12 November 2011; Accepted 6 February 2012

Academic Editor: Karl Kirchner

Copyright © 2012 K. R. Mahanwar et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

A poly[dibenzo-18-crown-6] exhibits good chemical stability, reusability, and faster rate equilibrium for the separation of Gd(III). Both uptake and stripping of metal ions were rapid, indicating a better accessibility of the complexing sites. The proposed method has been applied for chromatographic separation of Gd(III) by using picric acid as medium and poly[dibenzo-18-crown-6] as stationary phase. The influences of picric acid concentration, different eluting agents, and so forth, were discussed and the optimum conditions were established. The breakthrough capacity of poly[dibenzo-18-crown-6] for Gd(III) was  mmolg⁻¹ of crown polymer. The proposed method has been applied to sequential chromatographic separation of their binary and multicomponent mixtures. Gd(III) has been determined from real samples with good analytical reliability.

1. Introduction

In recent years the separation chemistry of rare earth elements (REEs) continues to receive a growing interest. The major reasons for this stems from the importance of rare earths not only in industrial application but also in energy generation activities and environmental mitigation. Gadolinium is useful in nuclear techniques, in fuel element fabrication and in ceramic industries and as control rod and as refractory material [1, 2]. In view of all the above applications the separation and purification of Gd(III) are important.

The main focus of the extensive research on chelating resins is the preparation of functionalized polymer that can provide more flexible working conditions together with good stability, selectivity, high concentrating ability, high capacity of metal ions, and simpler operation [3–6].

Crown ethers are effective extractants due to their ability to form stable complexes with metal ions. In recent years extraction chromatography has emerged as a versatile and effective method for analytical and preparative scale metal ion separation [7–9]. Also crown ethers are used as sorbents in chromatographic techniques [10–17] like TLC, extraction chromatography-liquid chromatography on columns, and gas chromatography for actinides and lanthanides.

By using poly[dibenzo-18-crown-6] we have reported the sorption behavior and separation study of alkali and alkaline earth metal in various mediums like ascorbic acid, sodium nitrate, hydrochloric acid, and L-arginine [18–23].

To our knowledge no successful attempts were reported in the literature for the separation of Gd(III) using poly[dibenzo-18-crown-6] in picric acid media and column chromatography. The present paper describes a simple and sensitive method for the determination of Gd(III) using poly[dibenzo-18-crown-6] as stationary phase in picric acid media. In our study we use picric acid as medium because picrate is bulkier anion with higher hydrophobicity. The proposed method has been successfully applied for the separation and determination of Gd(III) from real materials.

2. Experimental

2.1. Apparatus and Reagents

All absorbance measurements were carried out using a digital visible spectrophotometer (215 D, Thermo Electron LLS, India), a digital pH meter (Model LI-120. Elico, India) equipped with glass and a calomel electrode for pH determination, and a digital flame photometer (PI, Model no. 041, India).

A stock solution of Gd(III) was prepared by dissolving 1.091 g of gadolinium nitrate (AnalR grade, BDH, Poole, UK) in 100 mL of distilled deionised water and standardized gravimetrically [24]. A solution containing 100 μgmL⁻¹ of Gd(III) was prepared by appropriate dilution of the standard stock solution. Picric acid solution (5 × 10⁻² moleL⁻¹) was prepared by dissolving 2.846 g of picric acid in distilled deionised water and diluted to 250 mL. All aqueous solutions were prepared with double distilled deionised water.

Poly[dibenzo-18-crown-6] from Merck Darmstadt, Germany was used after screening to 100–200 mesh. A total of 0.5 g of polymer was slurred with distilled deionised water and poured into a Pyrex glass chromatographic column (20 × 0.8 cm i.d.). The column was used after preconditioning with picric acid solution. All chemicals used are of analytical grade.

2.2. General Procedure

100 μg of Gd(III) was mixed with picric acid solution in concentration range of 1 × 10⁻² to 1 × 10⁻⁷ moleL⁻¹ in a total volume of 10 mL. Then, the solution was passed through poly[dibenzo-18-crown-6] column preconditioned with the same concentration of picric acid as that of the sample solution at flow rate of 0.5 mLmin⁻¹. Afterwards the column was washed with the same concentration of picric acid, and the sorbed Gd(III) was then eluted with different eluting agents at the flow rate of 0.5 mLmin⁻¹. 5.0 mL fractions were collected and analyzed spectrophotometrically with Arsenazo(III) [25, 26] at 650 nm. The concentration of Gd(III) was calculated from a calibration graph.

3. Results and Discussion

3.1. Sorption of Gadolinium(III) on Poly[dibenzo-18-crown-6] as a Function of Picric Acid Concentration

Sorption studies of Gd(III) were carried out from picric acid medium using 100 μgmL⁻¹ of Gd(III). The concentration of picric acid was varied from 1 × 10⁻² to 1 × 10⁻⁷ moleL⁻¹. It was found that there is quantitative sorption of Gd(III) from 1 × 10⁻² to 1 × 10⁻⁴ moleL⁻¹ picric acid as shown in Table 1. Sorbed Gd(III) was eluted with 4.0 M HCl. With further decrease in the concentration of picric acid the sorption of gadolinium also decreases. The subsequent sorption studies of Gd(III) were carried out with 1 × 10⁻³ moleL⁻¹ picric acid.

Table 1: Sorption of gadolinium(III) as a function of picric acid concentration (Gd(III): 100 μgmL⁻¹, eluent: 4.0 M HCl).

Picric acid concentration(Mole L⁻¹)
Sorption of gadolinium(III)(%)

1 10⁻²
100

1× 10⁻³
100

1 × 10⁻⁴
100

110⁻⁵
97.4

1 10⁻⁶
95.4

1 × 10⁻⁷
90.2

3.2. Elution Studies of Gadolinium(III) with Various Eluting Agents

Gd(III) was eluted out from the column with different strengths of acids such as HCl, H₂SO₄, HClO₄, CH₃COOH, and HBr. The concentrations of the eluting agents were varied from 0.1 to 8.0 M. Gadolinium(III) was eluted quantitatively with 2.0–8.0 M HCl, 0.1–0.5 M H₂SO₄, 1.0–8.0 M HClO₄, 7.0-8.0 M CH₃COOH, and 0.1–5.0 M HBr. Further, the elution study of Gd(III) in this work was carried out with 0.1 M HBr. The elution profile of Gd(III) with different eluting agents is shown in Figure 1.

Figure 1: Elution study of Gd(III) with various eluents. Eluents used such as HCl, H₂SO₄, HClO₄, HBr, CH₃COOH out of this 2.0–8.0 M HCl, 0.1–0.5 M H₂SO₄, 1.0–8.0 M HClO₄, 0.1–5.0 M HBr and 7.0-8.0 M CH₃COOH were efficient eluting agent for Gd(III).

3.3. Breakthrough Capacity of Poly[dibenzo-18-crown-6]

The breakthrough capacity of Gd(III) was carried out on 1.0 g of poly[dibenzo-18-crown-6] with 1 × 10⁻³  moleL⁻¹ picric acid. The volume of Gd(III) sample solution employed was 10.0 mL. The concentration of Gd(III) was varied from 100 to 1100 μg of Gd(III) 10 mL⁻¹ of solution. After sorption, the elution of Gd(III) was carried out with 0.1 M HBr at a flow rate of 0.5 mL min⁻¹. Sorption of Gd(III) was quantitative up to 900 μg10 mL⁻¹. The extent of sorption of Gd(III) is decreased with the increase in the concentration of Gd(III) as shown in Figure 2. The breakthrough capacity of poly[dibenzo-18-crown-6] for Gd(III) was found to be 0.57 mmolg⁻¹ of crown polymer.

Figure 2: Effect of varying concentrations of Gd(III). The concentration of Gd(III) was varied from 100 to 1100 μg of Gd(III) 10 mL⁻¹ of solution. Sorption of Gd(III) was quantitative up to 900 μg10mL⁻¹.

3.4. Diverse Ion Effect

To assess the usefulness of this method, the effects of foreign ions, which are likely to interfere with the proposed method for determination of Gd(III) were studied. An aliquot of solution containing 100 μg of Gd(III) was mixed with foreign ions and picric acid was added so that its concentration was 1 × 10⁻³ moleL⁻¹ in total volume of 10 mL. The tolerance limit was set not to cause more than ±2% deviation in the recovery of Gd(III). The column was equilibrated with 1 × 10⁻³ moleL⁻¹ picric acid, and binary mixture solution was passed through a poly [dibenzo-18-crown-6] column at flow rate of 0.5 mLmin⁻¹. Subsequently, the column was washed with 15 mL of 1 × 10⁻³ moleL⁻¹ picric acid to remove unsorbed metal ions. Various foreign ions were not sorbed and hence passed through the column. The effluent was collected and analyzed for foreign ion content. It was found that most of alkali metals show high tolerance limits. The alkaline earth metals were sorbed quantitatively. Most of the p-block and d-block elements showed low tolerance limit. Amongst the inner transition elements U (VI) was sorbed along with Gd(III) and its separation is carried out in our subsequent study employing multicomponent mixtures. The anions of inorganic and organic acids have shown high tolerance limit except . The tolerance limit of various foreign ions is shown in Table 2.

Table 2: Diverse ion effect (Gd(III): 100 μgmL⁻¹, sorption: 1 × 10⁻³ M picric acid, eluent: 0.5 M HCl).

Ion
Added as
Tol. limit (mg)
Ion
Added as
Tol. limit (mg)

Li+
LiCl
4
Al3+
Al₂(SO₄)₃·16H₂O
0.5

Na+
NaCl
4
Zr4+
Zr(NO₃)₄·4H₂O
1

K+
KCl
2
La³⁺
La(NO₃)₃
0.8

Rb+
RbCl
5
Ce³⁺
CeCl₂·6H₂O
0.2

Cs+
CsCl
4
V4+
VOSO₄·4H₂O
0.4

NH₄Cl
4
Th4+
Th(NO₃)4
0.2

Be2+
BeSO₄·4H₂O
0.1
Mo6+
(NH₄)₆Mo₇O₂₄4H₂O
0.9

Ca2+
CaCl2
0.4
W6+
Na₂WO₄·4H₂O
0.8

Sr2+
Sr(NO₃)2
0.5
U6+
UO₂(NO₃)₂·6H₂O
0.5

Ba2+
Ba(NO₃)2
0.3
Cl−
HCl
3

Co2+
CoCl₂·6H₂O
8
Br⁻
HBr
4

Ni2+
NiCl₂·6H₂O
0.8
SCN−
NaSCN
1

Mn2+
MnCl₂·4H₂O
2

HClO4
5

Zn2+
ZnCl2
0.5
CH₃COO−
CH₃COOH
5

Cd2+
(CH₃COO)₂Cd·H₂O
3

H₂SO4
0.8

Pb2+
Pb(NO₃)2
1
Tartrate
Tartaric acid
4

Cr3+
Cr(NO₃)₃·9H₂O
0.5
EDTA
EDTA
4

Fe3+
FeCl₃·6H₂O
0.1
Ascorbate
Ascorbic acid
4

Cu²⁺
CuCl₂
0.8
Citrate
Citric acid
4

3.5. Separation of Gadolinium(III) from Multicomponent Mixtures

A mixture of Li(I)/Fe(III)/Mo(VI)/Sr(II)/Ca(II), U(VI), Gd(III), and Ba(II) was resolved by following the proposed procedure of Gd(III). The mixture was passed through the poly[dibenzo-18-crown-6] column under optimum condition of Gd(III), where Li(I)/Fe(III)/Mo(VI)/Ca(II)/Sr(II) was not sorbed and passed through column which was then determined by standard procedure [24, 26]. U(VI) and Ba(II) were quantitatively sorbed on column along with Gd(III). The separation of Gd(III) from U(VI) can be achieved by the use of 0.2 M LiOH as a eluting agent; at this condition Gd(III) and Ba(II) was not eluted and remained on column. Gd(III) was eluted with 2.0 M perchloric acid, and the remaining Ba(II) on column was eluted with 4.0 M hydrochloric acid and determined by standard methods [24, 26]. The results are shown in Table 3 and chromatograms of all metal ions in Figure 3.

Table 3: Separation of gadolinium(III) from associated elements (multicomponent mixture).

Sr. no.
Mixture
Taken (μg)
Recovery* (%)
S.D.
Eluent

1
Fe(II)
100
98.16

NSPC**

U(VI)
100
98.78

0.2 M LiOH

Gd(III)
100
98.83

2.0 M HClO₄

Ba(II)
100
97.94

4.0 M HCl

2
Ca(II)
100
100

NSPC**

U(VI)
100
97.76

0.2 M LiOH

Gd(III)
100
100

2.0 M HClO₄

Ba(II)
100
98

4.0 M HCl

3
Li (I)
100
99

NSPC**

U(VI)
100
99

0.2 M LiOH

Gd(III)
100
98.6

2.0 M HClO₄

Ba (II)
100
98.10

4.0 M HCl

4
Mg(II)
100
98.4

NSPC**

U(VI)
100
98

0.2 M LiOH

Gd(III)
100
100

2.0 M HClO₄

Ba(II)
100
97.5

4.0 M HCl

5
Mo(II)
100
99.1

NSPC**

U(VI)
100
98.6

0.2 M LiOH

Gd(III)
100
99.2

2.0 M HClO₄

Ba(II)
100
97.3

4.0 M HCl

6
Sr(II)
100
98.9

NSPC**

U(VI)
100
98

0.2 M LiOH

Gd(III)
100
99

2.0 M HClO₄

Ba(II)
100
97.92

4.0 M HCl

*Average of triplicate analysis.

**No sorption passing through the column.

(a) Separation of Fe(III), U(VI), Gd(III), Ba(II)

(b) Separation of Ca(II), U(VI), Gd(III), Ba(II)

(c) Separation Li(I), U(VI), Gd(III), Ba(II)

(d) Separation of Mg(II), U(VI), Gd(III), Ba(II)

(e) Separation of Mo(VI), U(VI), Gd(III), Ba(II)

(f) Separation of Mo(VI), U(VI), Gd(III), Ba(II)

Figure 3: Chromatogram of Multicomponent Mixtures. Separation different metal ions such as U(VI), Ba(II), Mo(VI), Ca(II), Sr(II), Mg(II) from Gd(III).

3.6. Reproducibility of the Method

Reproducibility of the method was checked by thirty replicate analyses of a standard Gd(III) solution. The results indicate the method to be fairly reproducible. The poly[dibenzo-18-crown-6] could be recycled many times without affecting its sorption capacity. The reusability of poly[dibenzo-18-crown-6] with standard deviations is shown in Table 4.

Table 4: Reproducibility of the method.

Sr. no.
Gd(III) 100 μg
Recovery %
S.D

1
100
99.9
0.010

2
100
99.9
0.069

3
100
98.9
0.005

4
100
99.2
0.032

5
100
99
0.014

6
100
99.3
0.010

7
100
98.9
0.032

8
100
99.6
0.062

9
100
99
0.015

10
100
99.8
0.033

11
100
99.8
0.047

12
100
99.8
0.023

13
100
99.6
0.010

14
100
99
0.015

15
100
99.8
0.037

16
100
99.85
0.031

17
100
99.92
0.060

18
100
99.8
0.034

19
100
98.75
0.010

20
100
98.99
0.016

21
100
99.96
0.011

22
100
99.93
0.040

23
100
98.8
0.015

24
100
98.88
0.010

25
100
99.9
0.010

26
100
98.75
0.053

27
100
98.89
0.016

28
100
99
0.005

29
100
99.36
0.008

30
100
99.63
0.011

3.7. Determination of Gadolinium(III) from Real Samples

The composite material sample (GdSrO₂) after acid treatment is subjected to the proposed method for the determination of Gd(III). The percentage of Gd(III) found after triplicate analysis is 9.89 (±0.11) as against the reported value of 10.0%.

4. Conclusion

The proposed method affords an attractive feature as compared to the solvent extraction technique, that is, it is free from any organic diluents, leading to potential green chemistry applications. It permits the separation of Gd(III) from nuclear fission products such as Ba(II), U(VI) and Sr(II) is the significant achievement of our work. The poly[dibenzo-18-crown-6] could be recycled many times without affecting its sorption capacity, that is, it has higher stability as a stationary phase. Low reagent and acid concentrations are required for quantitative recovery of Gd(III). Precision in terms of the standard deviation of the present method is very retainable for the determination of Gd(III). It is applicable for the analysis of Gd(III) in real sample.

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