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Comparative Study Between TBP and Dibutylalkyl Phosphonates
Comparative Study in the midst of TBP and Dibutylalkyl PhosphonatesCHAPTER 7PHOSPHONATES AS ALTERNATIVE TO TBP FOR ACTINIDES AND FISSION PRODUCTSSolvent origination studies of U (VI), Th (IV), Eu (III) and Tc (VII) in dibutylalkyl phosphonates capture been carried come in in pay study. Uptake of these admixture ion and composition of metal-ligand bond is a submit consequence of phosphorus-carbon bond and to understand the influence of these changes in the bond was the main objective lens for the present study. Thus synthesis and solvent declension studies of Dibutyl propyl group Phosphonate (DBPrP) and Dibutyl Pentyl Phosphonate (DBPeP) were carried and were comp atomic number 18d with those available for Tributyl Phosphate (TBP). Thus this study will represent a comparative study between TBP and dibutylalkyl phosphonates.7.1 IntroductionSpent nu go open fire (SNF) is a complex system with large number of elements and there isotopes which are produced during the nucle ar fission of U and Pu. These spent fuel rods containing activation wares along with fission products needs to be dealt while reprocessing and waste management of SNF which is carried out at reprocessing plant.TBP a triester of phosphoric venereal disease is a major extractant employ for nuclear fuel reprocessing that is Plutonium atomic number 92 beginning PUREX processes worldwide for the judicial separation of uranium and plutonium from the dissolver solution 1. Even though it has been a workhorse in nuclear industry since long period there are major drawbacks like its significant solubility in aqueous figure, third phase formation during macro level extraction of tetravalent actinides in azotic sour medium, low selectivity of U and Pu oer Zr and Ru and presence of chemical and radiolytic degradation products of TBP viz. monobutyl and dibutyl phosphoric back breaker are responsible for lowering the decontamination factor (DF) 2-6. Significant research in the scientific comm unity employ higher homologs of TBP has hand overn that they are more unsusceptible to third phase formation and aqueous solubility.Basicity of the phosphoryl oxygen and the nature of substituents connect to the P atom are key factor responsible for the extraction ability of any organophosphorus extractant. Enhancement of the basicity on the phosphoryl group may be achieved by replacement of C-O-P group directly by C-P group. Neutral organophosphorus extractants show the variation in the basicity of the phosphoryl oxygen as phosphine oxide phosphinates phosphonates phosphates 7. Studies in the past have reported that phosphonates are better extractants for the extraction of uranium and thorium as compared to that with corresponding phosphates 8, 9. In the nuclear reprocessing industry dibutylalkyl phosphonate was found to be wiz of the promising candidates as a replacement for TBP. Lower D set than that of corresponding phosphinates and phosphorus oxide makes stripping easier in case of phosphonates. The main objective of this study was to focus on the potential extraction capabilities of U (VI), Th (IV), Eu (III) and Tc (VII) which are relevant from nuclear fuel round of golf view point by the phosphonates DBPrP and DBPeP.7.2 Synthesis of Dibutylalkyl PhosphonatesPhosphonates used in the present study was synthesized using Michaelis Becker reply 10. In this reaction equimolar amount of sodium is allowed to react with dialkylhydrogen phosphonate and dialkylsodium phosphonate thus obtained is further allowed to react with alkyl halides and final product with P-C bond is obtained. bet 7.1 Michaelis-Becker ReactionPreset reaction involves nucleophilic substitution of phosphorus on alkyl halide to yield phosphonate as shown in the figure below. normal 7.2 Mechanism for Michaelis-Becker ReactionThe preparation of these phosphonates were carried out in a refluxation unit by drop wise adjunct of dibutylhydrogen phosphate over a period of 30 minutes t o the reaction mixture i.e. sodium (1.15g, 0.05 mol) + hexane (100 mL). The addition of dibutylhydrogen phosphate was continued until the dissolution of sodium was complete. afterward this complete reaction mixture was stirred under gentle refluxation for about 4 hours during which 1-bromoalkane was added over a period of half-an-hour. This reaction mixture was then washed with irrigate after cooling it at room temperature after which the product was distilled using reduced pressure to get rid of impurities.7.3 Mechanism of Extraction in Dibutylalkyl PhosphonatesUptake of metal ions from the aqueous phase using dibutylalkyl phosphonates is by formation of neutral complex formation. Solvation of metal ion takes place by nitrate ion which is the aqueous phase used in the present studies. Then the solvation of these neutral metal nitrate species takes place with the help of dibutylalkyl phosphonate which gets extracted be the organic phase.MX+aq + X NO3 + nDBAPorg M(NO3)X.nDBAPorgFoll owing equation gives the equilibrium constant for the above reactionKeq = M(NO3)X.nDBAPorg / MX+aq NO3XDBAPorgn dispersal ratio (D) is the ratio of activity of metal ion in organic phase to that in the aqueous phase at equilibrium, which can be rearranged and represent in the following way.D = Keq NO3 XDBAPorgnDistribution ratio depends on the ducking of nitrate ions and concentration of extractant. There is always a rise in the D value as the nitrate ion concentration increases while the dismount at higher acidity indicates the extraction of nitric acid.7.4 Solvent Extraction StudiesExtraction of U (VI), Th (IV), Eu (III) and Tc (VII) with were carried out in a plastic tube with preequliberated organic phase that comprised of 1.1 M DBPrP and DBPeP in n-dodecane. 2 mL of preequliberated extractant was agitated with 2 mL of nitric acid in a shaking incubator at 25 0C for 1 hour. After the equilibration the two phases were allowed to separate and were analysed for the metal ion co ntent using commensurate technique.7.4.1 Extraction studies of nitric acidAround 2 mL of sundry(a) concentrations of nitric acid (0.1-6M) were taken in an equilibration tube and equilibrated with 1.1 M DBPrP/DBPeP, n-dodecane at room temperature for an hour. The nitric acid concentration in both the phases was contumacious by acid-base titration. Figure below depicts the uptake of nitric acid in DBPrP and DBPeP compared with the available literature values of TBP. As observed from the plot it is clear that D values in case of phosphonates are higher as compared with that of TBP which is the direct consequence of the higher basicity of the phosphonates. Prasanna et al. have reported that the changes in alkyl group structure do not have significant demand on extraction of nitric acid 18.104.22.168 Extraction Studies of U (VI)After the equilibration the two phases were separated and analysed for U (VI) content spectrophotometrically using Arsenazo-III as chromogenic mover 12. Organic p hase concentration was estimated by subtracting concentration of U (VI) in equilibrated aqueous phase from the initial feed concentration. Below figure shows the comparative data for the uptake of U (VI) in TBP, DBPeP and DBPrP in the complete nitric acid range (0.1-6 M). There was a constant increase in the uptake of U (VI) metal ion with the increase in nitric acid concentration. Also the observed increase in the uptake of U (VI) as TBP Figure 7.3 conversion of DU(VI) as the function of acid concentration for Dibutylalkyl phosphonates at 25 0C7.4.3 Extraction Studies of Th (IV)Figure 7.4 depicts the variation of extraction sort of Th (IV) by 1.1 M of TBP, DBPrP and DBPeP extraction in n-dodecane under similar conditions. As expected there is a constant rise in the D values as the concentration of nitric acid goes on increasing. Also higher analogs of neutral organophosphorus extractant shows the higher uptake which is again a direct conciquence of the increased bascicity on pho phoryl oxygen the highest uptake of Th (IV) isFigure 7.4 Variation of DTh(IV) as the function of acid concentration for Dibutylalkyl phosphonates at 25 0C7.4.4 Extraction Studies of Europium (III)Figure 7.5 Variation of DEu(III) as the function of acid concentration for Dibutylalkyl phosphonates at 25 0C7.4.5 Extraction Studies of Technetium (VII)Figure 7.3 Variation of DTc(VII) as the function of acid concentration for Dibutylalkyl phosphonates at 25 0CReferencesSchulz, W.W. Berger, L.L. Navratil, J.D. Eds. intuition and Technology of TBP RC Press Boca Raton, FL, 1990 Vol. 3.Crouse, D.J. Arnold, W.D. Hurst, F.J. Proceedings of the International Solvent Extraction crowd (ISEC83), Denver, Colorado, 1983 pp 9096.Marcus, Y. Kertes, A.S. 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