(VI) by Complexation with CYANE

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Apr 2, 2012 - 2Department of Chemistry, Yogi Vemana University, Kadapa, INDIA. 3Department of Chemistry, Rayalaseema University, Kurnool, INDIA.

Rao et al. Int. J. Res. Chem. Environ. Vol.2 Issue 2 April 2012(158-163)

International Journal of Research in Chemistry and Environment Vol. 2 Issue 2 April 2012(158-163) ISSN 2248-9649

Research Paper

Synergistic Extraction of Uranium (VI) by Complexation with CYANEX-272 and CYANEX-923, TPBD, TNBD, TOPO in Presence of Nitrate Reddy Jayarami M.1, Sudhavani T.J.2, 3, Reddy Sivagangi N.2, * Rao Krishna K.S.V.2, Reddy Krishna L.1 1

Department of Chemistry, Sri VenkateswaraUniversity, Kadapa, INDIA 2 Department of Chemistry, Yogi Vemana University, Kadapa, INDIA 3 Department of Chemistry, Rayalaseema University, Kurnool, INDIA

Available online at: www.ijrce.org (Received 03rd February 2012, Accepted 10th March 2012) Abstract- Synergistic extraction of uranium (VI) from nitrate medium by cyanex 272 (HA)2 along with cyanex 923, TPBD, TNBD, TOPO and their mixtures in xylene as extractants has been investigated. Analysis of the extraction data by graphical method by taking into account the complexation of the metal ion in the aqueous phase with organic ligands and all plausible complexes extracted into the organic phase is carried out. The metal ion is extracted into xylene as UO2(HA2)2. The results demonstrate that uranyl ion is extracted into xylene as UO2(HA2)2 with cyanex-272 alone and as UO2(HA2).NO3.S (where S = cyanex-923/TOPO )with cyanex-272 and cyanex-923/TOPO, and as UO2(HA2)2.S with cyanex-272 and TPBD/TNBD (where S = TPBD/TNBD). The synergistic systems enhance the extraction efficiency of uranium (VI) marginally. Keywords: Uranium, Cyanex-272, Solvent Extraction, Synergism. Introduction Liquid-liquid solvent extraction technology is used in numerous industrial processes such as petroleum and petrochemical processing, organic chemical and pharmaceutical production, food and fuel industries, effluent treatment, and hydrometallurgy [1].Although solvent extraction technology had its beginning more than 100 years ago, it owes a significant amount of its present prominence as a separation technique to its successful applications in the field of nuclear technology, when demands for simple separation processes for many elements, previously considered only laboratory curiosities, arose. The use of thorium, uranium, plutonium and other actinides in the nuclear energy programs have led to the rapid development of many solvent extraction processes that display selectivity, simplicity and speed. From 235U other important nuclides can be produced. A large number of synthetic isotopes of uranium have been prepared [2]. In nuclear reactors uranium has been used as a fuel material in its different forms. Uranium metal in research reactors is generally used as the fuel while in power reactors natural uranium and enriched uranium oxides are used as pure. The

separation of uranium (VI) and thorium (IV) has been carried out using organo-phosphorous extractants [3,4]. Better separation factors have been reported between uranium (VI) and thorium (IV) using tri-sec-butylphosphate in 1 mol/dm3 HNO3solutions [5]. A good review on the extraction of uranyl compounds with trioctylphosphine oxide (TOPO) has been published [6].Cyanex-272/xylene has been used by B. Rajeswari et.al in quantitative extraction of uranium & rare earths by ICP-AES method[7]. Uranium was quantitatively extracted by 1 × 10−3 M sodium salicylate with 5 × 10−4 M cyanex 272 in toluene[8]. Cyanex-272 isbis(2,4,4-trimethylpentyl)phosphinic acid. Since the active component of cyanex-272 extractant is a phosphinic acid, metals are extracted through a cation exchange mechanism [9-11].The extractant is totally miscible with common aromatic and aliphatic diluents, and is extremely stable to both heat and hydrolysis. The present research deals with the synergistic extraction of uranium (VI) from nitrate medium with mixtures of cyanex-272 Bis(2,4,4-trimethylpentyl)phosphinic acid and TOPO, cyanex 923, TPBD, TNBD and their mixtures in xylene. Distribution data were analysed graphically to determine the composition of the extracted complexes.

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were used to obtain the distribution ratio, D.

Material and Methods Cyanex-272, Cyanex 923 supplied by Cytec, Canada were used after purification[9]. Trioctylphosphine oxide (TOPO) was obtained from E. Merck (India) Limited. Xylene of analytical reagent quality was used as a diluent in the present work. All the other chemicals used were of analytical reagent grade. Stock solutions of uranium (VI) were prepared by dissolving appropriate amounts of UO2 (NO3)2.6H2O in distilled water. One milliliter of concentrated nitric acid was added to 100 ml of solution to suppress hydrolysis. The initial metal ion concentration was maintained at 1×104 M for uranium (VI) for all extraction studies. Preparation of metal complexes: The metal complexes were prepared by the following solvent extraction procedure: Uranyl nitrate dissolved in water was gradually added to a well stirred solution of Cyanex 272 and the synergistic ligands in xylene and then refluxed for 1 hour. The aqueous phase was changed with fresh metal ion solution after every 1 hour till the organic phase was completely loaded with metal ion. The organic phase was then separated. The Nicolet Nexus 670 FTIR spectrometer using KBr (Neat) was used to obtain the FTIR spectra of the loaded organic phase. The KBr (Neat) containing a film of metal ion solution was put under an FTIR lamp to evaporate xylene completely. For comparison, the IR spectrum of pure Cyanex272 was also taken.

Solvent extraction conditions: Solvent extraction studies were made on solutions of 0.1-1.0 mol/dm3 sodium nitrate at 30oC. The initial pH ofthe aqueous phase was generally maintained at 3 by adding nitric acid. The initial metal concentration was never exceeded 1X10-6 mol/dm3. Solutions of Cyanex 272(0-0005 mol/dm3) TPBD (0-0.5 mol/dm3), TNBD (0-0.4 mol/dm3), TRPO (0-0.6 mol/dm3) were used. The temperature was maintained at 30oC.

Results FTIR Spectrum of the extracted complex of Uranium (VI): The IR spectrum of the extracted complexes is shown in Table 1. The stretching frequency of the P=O in Cyanex272 has shifted from 1153 cm-1 to 1108 cm-1 in UO2(HA2)2. Complex and 1102, 1100, 1143 cm-1 in the synergistic extraction with TOPO,TRPO, TNBD, TPBD as synergistic ligands respectively. This indicates a stronger interaction between the phosphine oxide and uranium (VI) with cyanex 272 and even this is not affected in the presence of other synergistic ligands. The strong and sharp band at 926-924 cm-1 confirms the stretching of uranyl ion. Extraction of UO22+ with cyanex-272: The extraction of UO22+ from 1 mol/dm3NaNO3solutions by cyanex-272 in xylene was studied. The extraction equilibrium may be expressed as

(1) Solvent extraction procedure: Distribution ratios were determined by shaking equal volumes of aqueous and Where (HA)2 represents dimeric species of cyanex-272. It organic phase for 30 min in a glass Stoppard vial with the has been reported elsewhere that cyanex-272 exists as o help of a mechanical shaker at 303+1 K. The solutions dimer in diluents [12, 13]. were allowed to settle, centrifuged, separated and assayed spectrophotometrically using a Hitachi 220 double beam The equilibrium constant K2and the distribution microprocessor based spectrophotometer. Uranium (VI) ratio D2 can be written as was determined spectrophotometrically as its Arsenazo III (6.2) complexes in 1 M HCl solution at 660nm respectively. The absorbances of the complexes was measured within 5 min of mixing. The metal concentrations in the aqueous phase (3) 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 Table 1 Characteristic FTIR Spectral data of the extracted complexes of Uranium (VI) Cyanex-272

U + Cyanex272

U + TRPO + cyanex 272

2954 1169 3448 ---816 1706.44 1473.16

2952 1153 3484 919 810 1710 1460

2929-2862 1649 1465 819 924 1649 1465

U+ Cyanex272 + TNBD 2951 1198 3415 920 801 1696.37 1462

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U+ Cyanex272 + TPBD 2951 1154 3450 921 813 151.81 1466

U + Cyanex272 + TOPO

Probable assignment

2954 1138 --923 817 1691.40 1464

nC-H np=o nOH O=U=Ostret. p-cstret. npop nCH3

Rao et al. Int. J. Res. Chem. Environ. Vol.2 Issue 2 April 2012(158-163)

Effect of pH: The plot of logDvshydrogen ion concentration has a slope of -2 (Figure1) in conjunction with the slope of 2 observed with extractant concentration variation at constant pH value (Figure 2)

From equations 4.5 and 4.6, it follows

1.5

Log D

1

K12=D12[H+]2(aq)/[(HA) 2]2(org)[TRPO]y(org) (4.7)

y = 2.0825x + 5.6936

0.5

The effect of mixture of extractants on the extraction of U(VI) is studied by taking cyanex-272, NaNO3 concentrations as constant and varying the other extractant at once, and keeping the concentration of other extractant and NaNO3 as constant and cyanex 272 as varying one. The log - log plots for extraction of U(VI) from 1 mol/dm3 nitrate solutions by mixtures of cyanex272 -cyanex-923 (TRPO) [0.25-1.5 mol/dm3 Cyanex-272 at constant 0.00075 TRPO in xylene, 0.25-2.5 mol/dm3 Cyanex 923 at constant 0.00075 mol/dm3 in xylene] are given in figures 3 and 4.The log - log plots for extraction of U(VI) from 1 mol/dm3 nitrate solutions by mixtures of cyanex-272-TOPO [0.25-1.5 mol/dm3 Cyanex-272 at constant 0.00075 TOPO in xylene, 0.5-1.75 mol/dm3TOPO at constant 0.00075 mol/dm3cyanex-272 in xylene], are given in figure 4.5 and 4.6.

0 -0.5 -1 -3.1

-2.9

-2.7

-2.5

-2.3

-2.1

Log[H+]

Figure 1: Effect of concentration of H+ ion concentration 1.5

Log D

1.1

y = 2.0221x + 5.8177

0.7 0.3 -0.1 -0.5 -3.1

D12 = [UO2(HA2)2.y(TRPO)](org)/[UO22+](aq) K12=[UO2(HA2)2.y(TRPO)](org)[H+](aq)/[UO22]+(aq).[(HA)2]2(o y (4.6) rg).[TRPO] (org)

-2.9

-2.7

-2.5

Log [Cyanex 272]

Figure 2: Effect of concentration of cyanex-272 Effect of extractant concentration: The effect of cyanex272concentration (5X10-4mol/dm3 to 4X10-3mol/dm3) on the extraction of uranium (VI) has been investigated from 1 mol/dm3 NaNO3 solutions at pH 3. From Figure 4 it can be seen that the extraction of uranium (VI) increases with increase in cyanex272 concentration in the organic phase. From the slope of the plot it is inferred that two molecules of cyanex272are involved in the extracted complexes of uranium (VI). Extraction by mixtures: Synergitic extraction of UO22+from 1 mol/dm3 NaNO3 solutions at pH 3 with mixture of cyanex-272 and TRPO/TOPO, and with mixtures of cyanex-272 and cyanex-923 (TRPO) was studied. Considerablesynergytic enhancement in the extraction of UO22+ was observed.The extraction equilibrium of UO22+ with mixtures cyanex-272 and TRPO/TOPO may be represented as UO22+(aq)+2(HA)2(org)+yTRPO UO2(HA2)2.y(TRPO) (org)+2H+(aq)(4.4) Distribution ratio D12 is written as

=

The log - log plots for extraction of U(VI) from 1 mol/dm3 nitrate solutions by mixtures of cyanex-272TPBD [0.5-1.75 mol/dm3 Cyanex-272 at constant 0.00075 TPBD in xylene, 0.5-1.75 mol/dm3TPBD at constant 0.00075 mol/dm3cyanex-272 in xylene] are given in figures 7 and 8.The log - log plots for extraction of U(VI) from 1 mol/dm3 nitrate solutions by mixtures of cyanex-272TNBD [0.75-1.75 mol/dm3 Cyanex-272 at constant 0.00075 TNBD in xylene, 0.5-1.75 mol/dm3TNBD at constant 0.00075 mol/dm3cyanex-272 in xylene], are given in figures 9 and 10. Mixed species of the typeUO2(HA2).NO3.S (whereS = cyanex-923/TOPO )with cyanex-923/TOPO,UO2(HA2) 2.Swith cyanex-272 and TPBD/TNBD (whereS = TPBD/TNBD) may be responsible for the synergism. The slope of the plot, log D-logcyanex-272 concentration at constant S concentration [Figure 4, 7 and 9] is ~2 indicating that the number of cyanex-272 molecules participating in the complex formation is unaltered by the presence of the second extractant (TPBD/TNBD) concentration. On the other hand the log D - log (TPBD/TNBD) concentration plot at fixed second extractant (Cyanex-272) concentration has a slope value ~1 showing that it involves both substitution and addition reactions [Figures 8 and 10].The slope of the plot, log Dlog cyanex-272 concentration at constant S concentration [Figure 3 and 5] is ~1 indicating that the number of cyanex272 molecules participating in the complex formation are altered by the presence of the second extractant (TRPO/TOPO) concentration. On the other hand the log D - log (TRPO/TOPO) concentration plot at fixed second

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extractant (Cyanex-272) concentration has a slope value ~1 [Figures 4 and 6] showing that it involves a complex of the type UO2.HA2.NO3-.S.

y = 2.1005x + 5.7071 Log D

0

1.2 y = 1.0872x + 3.6948

0.8

Log D

-0.4 -0.8

0.4

-1.2 -3.2

-3

0 -0.4 -3.8

-3.3

-2.8

-2.6

Figure 7: Effect of cyanex-272 in presence of TPBD in xylene

-2.3

Log[Cyanex272]

0.1

Figure 3: Effect of cyanex-272in presence of cyanex-923 (TRPO) in xylene

y = 2.1005x + 5.7071 -0.1

Log D

1.2 0.8

Log D

-2.8

Log[Cyanex272]

y = 1.0114x + 3.4187

-0.3 -0.5 -0.7

0.4 -0.9 -3.2

0

-3

-2.8

-2.6

Log[272]

Figure8: Effect of TPBD in presence of cyanex-272 in xylene

-0.4 -4

-3.5

-3

-2.5

Log[Cyanex 923]

0 y = 1.0749x + 1.5233

Figure 4: Effect of cyanex-923 (TRPO) inpresence of cyanex-272 in xylene

Log D

-0.4

0.6

Log D

y = 1.0031x + 3.2257

-0.8

0.2

-1.2 -0.2

-2.4

-2.2

-2

-1.8

-1.6

Log [TNBD] -0.6 -3.7

-3.5

-3.3

-3.1

-2.9

-2.7

Figure 9: Effect of cyanex-272 in presence of TNBD in xylene

Log [Cyanex272]

0

Figure 5: Effect of cyanex-272 in presence of TOPO in xylene

y = 1.0749x + 1.5233

0.6 y = 1.0517x + 3.4378

0.4

Log D

Log D

-0.4

-0.8

0.2 0

-1.2

-0.2 -0.4 -3.7

-2.4 -3.5

-3.3

-3.1

-2.9

-2.2

-2

-1.8

-1.6

Log [TNBD]

-2.7

Log[TOPO]

Figure 6: Effect of TOPO in presence of cyanex-272 in xylene

Figure 10: Effect of TNBD in presence of cyanex-923 in xylene

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Table 2 Synergistic extraction of Uranium(VI) from nitrate solution at pH-3.0 by the mixture of Cyanex-272 and Cyanex-923 in Xylene S. No. 1 2 3 4 5

M Cyanex-272 2.50×10-4 1.50×10-3 1.00×10-3 1.00×10-3 1.00×10-3

M Cyanex-923 1.00×10-3 1.00×10-3 2.50×10-4 5.00×10-4 1.00×10-3

D1+D2 0.3479 0.9125 0.4046 0.517 0.6655

D SYN 0.588 1.5613 0.5944 0.9653 1.8357

Table 3 Synergistic extraction of Uranium (VI) from nitrate solution at pH-3.0 by the mixture of Cyanex-272 and TOPO in Xylene S. No. 1 2 3 4

M Cyanex272 7.50×10-4 1.00×10-3 1.25×10-3 7.50×10-4

M TOPO 7.50×10-4 7.50×10-4 7.50×10-4 1.25×10-3

D1+D2 0.4235 0.5063 0.6371 0.6364

D SYN 1.089 1.7007 2.308 1.7379

Table 4 Synergistic extraction of uranium (VI) from nitrate solution at buffer 4.76 by the mixture of cyanex-272 and TPBD in xylene S. No. 1 2 3 4

M Cyanex272 7.50×10-4 1.25×10-3 1.75×10-3 7.50×10-4

M TPBD 3.00×10-3 3.00×10-3 3.00×10-3 7.00×10-3

D1+D2 0.28211 0.49571 0.67451 0.28443

D SYN 0.4951 0.6748 0.9046 0.6883

Table 5 Synergistic extraction of Uranium (VI) from nitrate solution at buffer 4.76 by the mixture of Cyanex-272 and TNBD in Xylene S. No. 1 2 3 4

M Cyanex-272 1.00×10-3 1.00×10-3 1.00×10-3 1.00×10-3

M TNBD 1.00×10-3 1.50×10-3 2.00×10-3 2.50×10-3

Theory: Extractions [∑D] due to individual components at the corresponding concentrations, and may be mathematically denoted as Dsyn=DsI+DsII+∆D

(4.8)

Where ∆D gives the magnitude of the synergistic enhancement of extraction. The synergistic enhancement is more pronounced at higher concentrations of the extractant. The results are presented in Tables 2.to Table 5. The slope of the log D-log [extractant] concentration plot decreases progressively with increase in the concentration of the second extractant.

Conclusion The potentiality of cyanex-272 as extractant and

D1+D2 0.5782 1.033 1.7389 2.382

D SYN 2.0938 3.243 6.615 11.379

also as a synergistic agent has beenverifiedin the present investigation. The synergistic systems enhance the extraction efficiency of uranium (VI). The present results show that di-solvates such asUO2 (HA2).NO3.S (where S = cyanex-923/TOPO) with cyanex-923, TOPO, and as UO2(HA2)2.S with TPBD/TNBD (where S = TPBD/TNBD) were responsible for synergism. The synergistic effect increases with increase in the concentration of the extractant. Little synergism was observed with TPBD/TNBD. Nature of different metal species transferred into the organic phase has been clearly established.

Acknowledgement Authors gratefully thank the Board of Research in Nuclear Sciences (BRNS) for financial support for this work (Grant No.: 2010/37C/53BRNS/2538, Dated 23-02-

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