AS EXTRACTANTS FOR f-ELEMENTS

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May 10, 2007 - uranium(VI) and trivalent lanthanoids when extracted from 0.2 molldm3 nitric acid solutions using 4-acylbis(1-phenyl-3-methyl- 5-pyrazolones).
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4-ACYLBIS(1-PHENYL-3-METHYL-5-PYRAZOLONES) AS EXTRACTANTS FOR f-ELEMENTS a

b

M.L.P. Reddy , Sushanta K. Sahu & V. Chakravortty a

b

Regional Research Laboratory (CSIR) , Trivandrum, 695 019, India

b

Department of Chemistry , Utkal University , Bhubaneswar, 751 004, India Published online: 10 May 2007.

To cite this article: M.L.P. Reddy , Sushanta K. Sahu & V. Chakravortty (2000) 4-ACYLBIS(1-PHENYL-3-METHYL-5PYRAZOLONES) AS EXTRACTANTS FOR f-ELEMENTS, Solvent Extraction and Ion Exchange, 18:6, 1135-1153, DOI: 10.1080/07366290008934725 To link to this article: http://dx.doi.org/10.1080/07366290008934725

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SOLVENT EXTRACTION AND ION EXCHANGE, 18(6), 1135-1153 (2000)

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4-ACYLBIS(1-PHENYL-3·METHYL-5-PYRAZOLONES) AS EXTRACTANTS FOR f-ELEMENTS

M.L.P. Reddy· Regional Research Laboratory (CSIR) Trivandrum - 695019, India Sushanta K. Sahu, V. Chakravortty Department of Chemistry, Utkal University Bhubaneswar - 751 004, India

ABSTRACT The liquid-liquid extraction of early actinides such as thorium(IV) and uranium(VI) and trivalent lanthanoids such as neodymium(III), europium(lIl) and lutetium(lIl) from nitrate solutions was studied using 4sebacoylbis(1-phenyl-3-methyl-5-pyrazolone) (H2SP) and 4-dodecandioylbis(1-phenyl-3-methyl-5-pyrazolone) (H2DdP) in chloroform as extractants. The results demonstrate that these metal ions are extracted into chloroform as Th(SPh, Th(DdP)2, U02(HSP)2, U02(HDdP)2, Ln(SP)(HSP) and Ln(DdP)(HDdP) with H2SP or H2DdP. The equilibrium constants of the above species were deduced by non-linear regression analysis. The results clearly highlight that thorium(IV) can be selectively separated from uranium(VI) and trivalent lanthanoids when extracted from 0.2 molldm3 nitric acid solutions using 4-acylbis(1-phenyl-3-methyl- 5-pyrazolones). Thorium(IV), uranium(VI) and lutetium(lIl) complexes of H2SP were synthesised and characterised by IR and 'H NMR spectral data to further clarify the nature of the complexes.

• Corresponding author: +91-471-491712; E-mail: [email protected] 1135 Copyright 2000 by Marcel Dekker, Inc.

www.dekker.com

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REDDY, SAHU, AND CHAKRAVORITY

INTRODUCTION

4-Acylpyrazolones form an interesting class of l3-diketones capable of extracting metal ions from relatively strong acidic solutions due to their lower pKa values (2.56 - 4.01) as Compared to familiar l3-diketone 2thenoyltritluoroacstona (pI(" = 6.25) [1.:4). The nature of the substitueni in

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the 4-position of pyrazolons ring causes :?ignificant variations in the electronic, steric and solubility parameters of the ligand, thereby affecting complexation and extraction benaviour. A number of 4-acylbis(1-phenyl-3methyl- 5-pyrazo!Qne) derivatives

two

~hown

in Fig.1 were dl1lsigned in which

1-phenyl-3-m~~hyl-4-acyl-5-pyrazolone

subunits are linked by a

polymethylene chain of varying length and utilised for the extraction of some transition metals [5-7]. As the 4-acy1bil!( 1-phenyl-3-:methyl- 5pyrazolone) derivatives (H2L) have two ~-diketone donor sites on both ~ides

of polymethylene chains, they are expected to give rise to specific

complexations depending upon the polymethylene chain length. Recently, extraction of uranium(VI) and vanadium(V) with 4-adipolyl and 4-sebacoyl derivatives of 1-phenyl-3-methyl-5-pyrazolone from chloride solutions has been investigated by Uzoukwu et al [8).lt was reported that the addition of decanol to the organic phase resulted in enhancement in the extraction of vanadium(V) and diminution in the extraction of uranium(VI) at higher Hel coricentrations.

Fig. 1. n

=8 (H2SP), 10 (H2DdP)

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EXTRACTANTS FOR f-ELEMENTS

This paper reports on the selective extraction of thorium(IV) over uranium(VI) and trivalent lanthanoids using 4-sebacoylbis(1-phenyl- 3methyl-5-pyrazolone) (H2SP) or 4-dodecandioylbis(1-phenyl-3-methyl- 5pyrazolone) (H2DdP) and the stoichiometry of the complexes extracted

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into the organic phase.

EXPERIMENTAL

Chemicals 4-Sebacoylbis(1-phenyl-3-methyl-5-pyrazolone) dodecandioylbis(1-phenyl-3-methyl-5-pyrazolone)

(H2SP) (H2DdP)

and

4-

were

synthesised by the acylation of 1-phenyl-3-methyl-5-pyrazolone with corresponding acid dichlorides following Jensen's method [9]. The purity of the compounds was established by IR and lH NMR spectral data. Stock solutions of thorium(IV) and uranium(VI) were prepared by dissolving appropriate amounts of Th(N03)4.6H20 (Loba-Chemie, India) and U02(N03)2.6H20 (Loba-Chemie, India) in distilled water. The initial metal ion concentration was maintained at 1x1 0-4 molldm3 for thorium(IV) and 5x10-4 molldm3 for uranium(VI) for all extraction studies. Stock solutions of lanthanoids were prepared from their respective oxides by dissolving in concentrated nitric acid and diluting with distilled water to required volume. Initial lanthanoid ion concentration was maintained at 1x10-4 molldm3 for all extraction studies. Ionic strength was maintained at 1 mol/dm3 using NaN03. All organic phase solutions were prepared by dissolving weighed amounts of H2SP or H2DdP in chloroform and diluting to the required volume. Arsenazo III solution was prepared by dissolving 250 mg of the reagent in 250 cm3 of distilled water for determination of thorium(IV) or uranium(VI).

Arsenazo I solution was prepared by dissolving 25 mg of the reagent in 250 cm3 of distilled water for

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REDDY, SAHU, AND CHAKRAVORTIY

determination of trivalent lanthanoids. Ammonium acetate buffer (pH=7.5) was prepared by dissolving 19.25 gm in 250 cm3 of distilled water and adjusting the pH with HCI/NaOH. All other chemicals used were of analytical grade. Solvent extraction procedure

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Distribution ratios were determined by shaking equal volumes of aqueous and organic phases for 2 hours in a glass stoppered vial with the help of a mechanical shaker at 303±10 K.

Preliminary experiments

showed that the extraction equilibrium was attained within 60 min for trivalent lanthanoids and 90 min in the case of early actinides.

The

solutions were allowed to settle, centrifuged, separated and assayed spectrophotometrically using a Hitachi 200 double beam microprocessor based spectrophotometer.

Both thorium(IV) and uranium(VI) were

determined spectrophotometrically as their Arsenazo III complexes in 1 rnol/drrr' HCI solution at 660 and 656 nm respectively. The absorbances of the complexes were measured within 5 min of mixing. Lanthanoids were determined spectrophotometrically as their Arsenazo I complexes in ammonium acetate buffer of pH=7.5 at 575 nm. The metal concentrations in the aqueous phase were computed from the respective calibration graphs. The concentration of the metal ion in the organic phase was then obtained by a material balance.

These concentrations were used to

calculate the distribution ratio, D. All the computer programs were written in FORTRAN 77 and executed on a Pentium PC. Preparation of metal complexes 4-Sebacoylbis(1-phenyl-3-methyl-5"pyrazolone) (0.257 gm, 0.50 mmol) was dissolved in 30 cm3 of methanol by adding an aqueous ammonia solution (2 mol/dm3) and then the pH of this solution was adjusted to 5-6 with dilute HN03 solution. Methanol solution of thorium

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EXTRACTANTS FOR f-ELEMENTS

nitrate or uranyl nitrate or lutetium nitrate (0.25 mmol) was added to the H2SP methanol solution and a precipitate appeared immediately. The precipitate was filtered after being stirred for 4 hours and washed with dilute HN03 solution until no metal ion and NH4+ could be detected in the washings. Then the precipitate was washed with distilled water. Finally the products were dried at 3130K after being washed for 2 or 3 times with

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chloroform. The Nicolet Impact 4000 IR spectrometer using potassium bromide pellet was used to obtain IR spectral data and the Bruker 300 MHz NMR spectrometer was used to obtain the 1 H NMR spectra of complexes in COCb.. OMSO..Os mixture.

RESULTS AND DISCUSSION

The extraction equilibrium of a metal ion, Mn+, with a chelating extractant

4..acylbis(1..phenyl..3-methyl..5..pyrazolone),

H2L,

may

be

expressed as:

aMn+ .. + (b + c)H2L

Ku ~.

....M.L.(HL}c

..

=[M.L. (HL)c J[W](2.+C)

K

(1)

(2)

[M n+]" [H2L](. 0

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...J

=2.0

Slope

a

.Q.4

-1.0 -1.6 -3

-4

-2

-1

a

Log [H,OdP]

Fig. 6. Effect of H2DdP concentration on the extraction of thorium(IV) and uranium (VI): (a) Th~ = 1x10-4 mol/dm3 , HN0 3 = 0.2 mol/dm3 , (b) = 5x10-4 molldm 3 , HNOJ = 0.05 mol/dm3 .

uol+

0.3 Slope = 0

0.2

.

0

.§'

..

0.1

• • •

0 -0.1 -4.6

-4.2

-3.8

-3.4

-3.0

Log [Lu3+] Fig. 7. Effect of metal ion concentration on the extraction of lutetium(lIl) 3 with H2SP; H 2SP = 0.01 mol/dm in CHC!J; pH = 3.0

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REDDY, SAHU, AND CHAKRAVORTTY

1.5 , . . - - - - - - - - - - - - , Slope

~"'I"'I

o

-05

/

...J

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Lu(lIl)

/EU(III)

0.5

8'

=3.0

-1.5 -2.5 2.8

3.0

3.4

3.2

3.6

pH

Fig. 8. Effect of pH on the extraction of trivalent lanthanides with H2SP: H2SP 0.01 mol/dm 3 in CHCb, Ln3+ 1x10"" mol/dm3 .

=

=

1.6 Slope = 2.0

0.8 Nd(lII)

o

8'

.:

0

...J

-0.8 -1.6

-2.5

-2.0

-1.5

-1.0

Log [H 2SPJ

Fig. 9. Effect of H2SP concentration on the extraction of trivalent lanthanides: Ln3+ = 1x10"" molldm3 , pH = 3.0.

EXTRACTANTS FOR f-ELEMENTS

1145

1.0 Slope = 3.0 0.4 0

go

-D.2

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..J

-D.6 -1.4 2.6

3.0

3.2

3.4

3.6

pH

Fig. 10. Effect of pH on the extraction of trivalent lanthanides with H2DdP: H2DdP = 0.01 molldm3 in CHCb; Ln3+ = 1x10"" molldm3 .

1.0 Slope =2.0 Eu(lII) 0.2 0

go

..J

-D.6

-1.4 -2.5

-2.0

-1.5

-1.0

Log [H 2DdP)

Fig. 11. Effect of H2DdP concentration on the extraction of trivalent lanthanides: Ln3+ 1x10"" mol/dm3 ; pH 3.0.

=

=

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REDDY, SAHU, AND CHAKRAVORlTY

1, 0, 2; and 1, 1, 1 for the extraction of thorium(IV), uranium(VI) and trivalent lanthanoids, respectively. Substituting these values into Eq.1 yields Th 4 ' ., +2H 2L .,

(9) K"U

U0 2 2... + 2H2L ., .... U0 2 (HL), ., + 2W ..

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K

Ln3+ .. + 2H2L ., where Ln3+

=Nd3

+,

(10)

ln

Ln(L)(HL)., + 3W ..

(11)

Eu3+ and Lu3+.

The above extraction equilibria indicate that two moles of H2L interact with one mole of Th4+ through both the [3-diketone donor sites of H2L, releasing four moles of hydrogen ion. In the case of uranium(VI),

two moles of H2L interact with one mole of uol+ through one of the [3diketone donor sites of the ligand, releasing two moles of hydrogen ion. On the other hand, Ln3+ interact with two moles of H2L through both [3diketone donor sites of one mole of H2L and one [3-diketone donor site of the another mole of H2L, thereby releasing three moles of hydrogen ion in the process (Fig. 12). The formation of the above metal chelates was further confirmed by analysing the equilibrium data using Eq.(4) for thorium(IV), uranium(VI) and trivalent lanthanoids.

The equilibrium constants for the above

complexes were determined by non-linear regression analysis (as described in our earlier publication [13]) and are shown in Table 1. It is clear from Table1 that the log equilibrium constant (log Kex) value of thorium(IV), uranium(VI) and trivalent lanthanoids decrease from H2SP to H2DdP. This has been attributed to the increase in steric effect, caused by increase in polymethylene chain length (from n

=8 to n =10).

The results (Figs.2 and 6) clearly demonstrate that thorium(IV) can be selectively separated from uranium(Vl) at 0.2 mol/dm3 HN03 solution using 0.1 mol/dm3 H2SP in chloroform as an extractant (separation factor

=

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EXTRACTANTS FOR f-ELEMENTS

1147

Fig.12 . Extracted complexes of thorium(IV), uranium(VI) and trivalent lanthanoids with 4-acylbis( 1-phenyl-3-methyl-5-pyrazolone)

Table 1. Two phase equilibrium constants of f-elements with various 4-acylbis( 1-phenyl-3-methyl-5-pyrazolones) Metal ion

Log equilibrium constant H2DdP

Nd(lII)

-6.26±O.02

Eu(llI)

-5.48±O.03

-5.66±O.03

Lu(lIl)

-4.65±O.03

-5.09±O.03

Th(lV)

5.12±O.02

3.98±O.02

U(VI)

O.79±O.03

O.25±O.02

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REDDY, SAHU, AND CHAKRAVORTIY

Table 2. Elemental analyses of the complexes

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Complex

C% N% H% M% Found Calc. Found Calc. Found Calc. Found 57.54 8.91 8.84 5.10 4.88 18.45 18.40

Th(SP)2

Calc. 57.23

U02(SP)

46.04

46.06

7.16

7.18

4.09

4.44

30.43

30.35

LU2(SPh

57.23

57.42

8.90

9.23

5.09

5.35

18.54

18.50

=9.2x104 ) or 0.05 molldm3 H20dP in chloroform (separation factor = OTtJOU = 3.3x104 ) . Further, the extraction of trivalent lanthanoids from

OTtJOU

0.2 rnol/dm, HN03 solution was found to be negligible when 0.1 molldm 3 H2SP or 0.05 molldm3 H2DdP in chloroform were used. However, these trivalent lanthanoids were found to be extracted with H2SP or H2DdP from nitrate solution of pH

= 3.0. Thus,

it can be concluded from the above

study that thorium(lV) can be selectively separated from uranium(VI) and trivalent lanthanoids when extracted from 0.2molldm3 HN03 solution using 4-acylbis(1-phenyl-3-methyl- 5-pyrazolones). Elemental Analyses of the complexes Table 2 contains the elemental analyses of the complexes. C, H and N analyses were perfomed with a Perkin Elmer Series 2 Elemental Analyser 2400.

Metal ions in the complexes were determined by the

following method : a certain quantity of complex was decomposed by heating in a small amount of HN03 solution and excess acid was evaporated. This was diluted with distilled water and finally uranium and thorium were determined spectrophotometrically as their Arsenazo III complexes and lutetium was determined spectrophotometrically as its Arsenazo I complex. It is known from Table 2 that the composition of the complexes is Th(SP)2, U02(SP) and LU2(SPh.

EXTRACTANTS FOR f-ELEMENTS

1149

IR spectra The IR spectra of the extracted complexes showed that the stretching frequency of the C=O in H2SP has shifted from 1626 ern" to 1602 em" for thorium complex; 1626 ern" to 1608 ern" for uranyl complex and 1626 em" to 1619 em" for lutetium complex, which indicates that the carbonyl group is involved in the bonding. These data further confirm that

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there is a stronger interaction between 4-acylbis(1-phenyl-3-methyl-5pyrazolone) and thorium(lV) than that of uranium(VI) and lutetium(III), which is also evident from the equilibrium constant values of these felements with H2SP. The other strong absorption at 927 ern" in the uranyl complex may be assigned to v(O=U=O) of U022> [14]. The absorption peak at 419 em" in the lutetium complex may be assigned to Lu-O stretching frequency [15]. The presence of the broad absorption peak at 3414 ern" - 3426 em" [15] for all the metal complexes indicates the existence of water molecule in the complexes. 'H NMR spectra Table 3 contains the 1H NMR spectral data for H2SP and metal complexes of thorium(IV), uranium(VI) and lutetium(lIl) with H2SP in CDCb - DMSO-D6 mixture. The methyl proton of the free ligand H2SP was observed as a singlet at 2.47 ppm and the methylene proton signals were observed at 2.71-2.76 ppm as a triplet. 1.72-1.75 ppm as a multiplet and 1.40 ppm as a singlet.

The phenyl proton signal was observed as a

multiplet at 7.25-7.84 ppm. The hydroxyl proton of enolic form of the H2SP ligand was observed at 9.43 ppm. In the complexes, the lH NMR spectra contain greater shifts and changes in comparison with the 'H NMR of the H2SP ligand. In the 'H NMR spectra of Th-H2SP complex, the disappearance of the peak at 9.43 ppm due to enolic OH proton of H2SP indicates the ionisation of enolic OH group and involvement of oxygen hydroxyl group in chelation. It is evident

2.34 (5, 12H) 2.60 (5, 6H)

2.13 (5, 12H); ,2.38 (5, 6H)

7.02 - 7.92 (m, 20H 7.26 - 8.25 (m, 10H)

7.12 - 7.99 (m, 30H)

Th - H2SP

U -H2SP

Lu - H2SP

br = broad; s = singlet; m

H2SP

= multiplet

Enolic OH 9.43 (br, 5, 2H)

Methyl 2.47 (5, 6H)

Compound

Phenyl 7.25 - 7.85 (m, 10H)

Methylene 2.71 - 2.76 (t, 4H, CH 2) ; 1.72 - 1.75 (m, 4H, CH 2) ; 1.40 (s, 8H, CH 2) 2.38 - 2.77 (m, 8H); 1.22 - 1.62 (m, 24H) 3.23 (s, 4H, CH 2) ; 2.12 (s, 4H, CH 2) ; 1.63 (s, 8H, CH 2) 2.38 - 2.59 (m, 12H, CH 2) 1.34 - 1.67 (m, 36H, CH2)

Table 3. lH NMR spectral data for the ligand and complexes

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e

~

o


til

.~

g;

o '"

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EXTRACTANTS FOR f-ELEMENTS

from the extraction studies that two moles of H2SP interacted with one mole of

uol+

through one of the J3-diketone donor sites of the ligand,

releasing two moles of hydrogen ion. Thus in the 1 H NMR spectra of the solid complex a broad peak should be observed at 9.43 ppm due to two enolic OH protons. However, this peak was not observed in the 1H NMR spectra of U - H2SP complex. This may be due to the formation of

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U02(SP) complex in the solid state as reported elsewhere [16). The disappearance of the enolic OH peak in the 1H NMR spectra of Lu - H2SP complex may be due to the formation of a 2:3 lutetium to H2SP complex as reported by Li et al. [15] in the complexation of lanthanoids with bispyrazolones. In the lutetium complex the integrated intensity of methyl proton is in the ratio 2: 1; the ratio shows that the structure of the complexes have non-equivalent ligands with possibly a 2:3 lutetium to ligand ratio. The formation of the above complexes was further supported by elemental analysis data.

CONCLUSION The extraction equilibria of thorium(IV), uranium(Vl) and trivalent lanthanoids with

H2SP and H2DdP have

been investigated.

The

equilibrium constant values of these metal ions were found to decrease with an increase of the polymethylene chain length (n = 8 to n = 10). Very high

selectivities

have

been

observed

between

thorium(lV)

and

uranium(Vl) and trivalent lanthanoids when extracted from nitric acid solutions using 4-acylbis(1-phenyl-3-methyl-5-pyrazolones). Thus, these extraction systems may find potential applications in the separation of thorium(lV) from uranium(Vl) and rare earths.

ACKNOWLEDGEMENTS This work was supported by Council of Scientific and Industrial Research, New Delhi. The authors wish to thank Dr. G.D. Surender, Head,

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REDDY, SAHU, AND CHAKRAVORTIY

Mineral Processing Division and Dr. G.vijay Nair, Director, Regional Research Laboratory, Trivandrum, for their constant encouragement

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B.G. Oliver and AR. Davis, J. Inorg. NucI.Chem., 34, 2851 (1972).

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EXTRACTANTSFOR~ELEMENTS

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Received by Editor February 14, 2000