The polarographic behavior of uranium(VI)-succinate complexes was studied in 0.5M NaClO4 medium at 30°C at a dropping mercury electrode. It was found that only the doubly charged succinate ion formed the complexes stable enough to be detected. The experimental evidence for this is discussed. The stability constant of uranium(V) (succinate)2 complex was evaluated.
The synergism of the crown ethers (CE) dicyclohexano-18-crown-6 (DC18C6), dibenzo-18-crown-6 (DB18C6) and 18-crown-6 (18C6) has been investigated in the thenoyl trifluoroacetone (HTTA) extraction of americium(III) in benzene medium from an aqueous phase of ionic strength 0.5 and pH 3.50 at room temperature (23°C). The extracted synergistic species have the general formula Am(TTA)3 · CE except for DC18C6 in which case the species Am(TTA)3·2CE was also observed at high CE concentrations. The order of synergism was found to be DC18C6>DB18C6>18C6, which is the order of the basicity of CE as indicated by their ability to extract hydrogen ions from nitric acid solutions.
The stability constants of the complexes formed by U/VI/ and Pu/VI/ with succinate ions were determined in 0.5M NaClO4 medium at 30°C following the Bjerrum-Calvin pH titration technique. The stability constants obtained agreed with values reported in literature following the same technique. The values for the second complexes were reported for the first time. U/VI/ complexes were found to have stabilities higher than the corresponding Pu/VI/ complexes in accordance with the acidities of the cations.
Two isomeric monoamides, dioctyl butyramide (DOBA) and dioctyl isobutyramide (DOIBA) were synthesized for extracting uranium(VI) and plutonium(IV) from aqueous nitric acid medium into various diluents such asn-dodecane, tertiary butyl benzene and xylene. DOBA extracted uranium(VI) and plutonium(IV) efficiently whereas DOIBA extracted uranium(VI) with negligible extraction for plutonium(IV). Both these cations were extracted as their disolvates. The thermodynamic parameters involved in the extraction determined by the temperature variation method indicated the reactions in all cases to be enthalpy favoured and entropy disfavoured. Possibility of separating micrograms of plutonium(IV) from macroquantities of uranium(VI) using the mixture of these amides was explored.
The unsymmetrical diamide methylbuthylmalonamide has been synthesized and used in the extraction of U(VI), Pu(IV) and Am(III) in benzene medium. The distribution ratio for the three cations was found to increase with increasing aqueous nitric acid concentration. U(VI) and Pu(IV) were found to be extracted as disolvates while Am(III) as a trisolvate. The thermodynamic parameters determined by the temperature variation method showed the extraction reactions to be mainly enthalpy-controlled. Am(III) was found to be back-extracted with dilute nitric acid, while Pu(IV) by dilute nitric acid-hydrofluoric acid mixture and U(VI) by dilute sodium carbonate solution.
The extraction of uranium(VI) and plutonium(IV) was carried out with two isomeric monoamides, dihexylbutyramide (DHBA) and dihexylisobutyramide (DHIBA) from nitric acid medium, usingn-dodecane as diluent. The possibility of separation of the two metal ions from each other without valency adjustment was attempted. U(VI) was extracted as its disolvate, while Pu(IV) was extracted as its trisolvate. From the variation of distribution ratio with temperature, it was shown that the extraction reaction was enthalpy controlled in all the cases.
The extraction behavior of U(VI) and Pu(IV) with dioctyloctanamide (DOOA), dioctylethylhexanamide (DOEHA) and diisobutylethylhexanamide (DIBEHA) was investigated from nitric acid medium. With DOOA, U(VI) extraction is higher than that for Pu(IV) upto 5M HNO3 and the trend is reversed at higher acid concentrations. Extraction yield of U(VI) is higher than that for Pu(IV) in the case of DOEHA and DIBEHA. DIBEHA extraction of Pu(IV) is found to be very small. The lower value of the distribution ratio for Pu(IV) with branched amides was attributed to steric reasons. The possibility of using these amides for separation of U(VI) and Pu(IV) without valency adjustment was explored. Both U(VI) and Pu(IV) are extracted as their disolvates by DOOA and DOEHA.
The extraction of uranium(VI) and plutonium(IV) from nitric acid into n-dodecane was studied using two isomeric branched alkyl amides, di(2-ethyl hexyl) butyramide (DEHBA) and di(2-ethyl hexyl) isobutyramide (DEHIBA). The extraction ratios of Pu(IV) at relatively high acidities were higher than the corresponding values for U(VI) in the case of DEHBA. However, with DEHIBA the values for Pu(IV) were negligibly small. Pu(IV) was found to be extracted as trisolvate by DEHBA and as disolvate by DEHIBA. U(VI) was extracted by both the amides. From the study of the extraction reactions at different temperatures, it was shown that all the reactions in the present investigation were enthalpy favoured and entropy disfavoured. Separation of Pu(IV) from bulk of U(VI) was feasible. However, the purity of the separated plutonium was not satisfactory in batch extraction studies.
Extraction behavior of 1 × 10−2–0.1 M U(VI) from aqueous phases containing 0.86 M Th(IV) at 4 M HNO3 in 1.1 M tributyl phosphate (TBP) and 1.1 M N,N-dihexyl octanamide (DHOA) solutions in different diluents viz. n-dodecane, 10% 1-octanol + n-dodecane, and decahydronaphthalene (decalin) was studied. Third-phase formation was observed in both the extractants using
n-dodecane as diluent. There was a gradual decrease in Th(IV) concentration in the third-phase (heavy organic phase, HOP) with
increased aqueous U(VI) concentration [0.71 M (no U(VI))–0.61 M (0.1 M U(VI)) for TBP; 0.27 M (no U(VI))–0.22 M (0.1 M U(VI))
for DHOA]. The HOP volume in case of DHOA was ~2.2 times of that of TBP. Uranium concentration in HOP increased with its initial
concentration in the aqueous phase [from 1.8 × 10−2 M (0.01 M U(VI))–0.162 M (0.1 M U(VI)) for TBP; from 1.4 × 10−2 M (0.01 M U(VI))–0.14 M (0.1 M U(VI)) for DHOA] suggesting that Th(IV) was being replaced by U(VI). An empirical correlation
was developed for predicting the concentrations of uranium and thorium in HOP for both the extractants. No third-phase appeared
during the extraction of uranium and thorium from the aqueous phases employing 10% 1-octanol + n-dodecane, or decalin as diluents, and therefore, were better choices as diluent for alleviating the third-phase formation
during the reprocessing of spent thorium based fuels, and for the recovery of thorium from high-level waste solutions.
Mumbai Harbour Bay (MHB) is a recipient of low level treated effluents from BARC, Trombay. In addition, the Bay is also a
recipient of domestic and industrial wastes from the city of Mumbai and adjoining areas. The average value of uranium concentration
reported for Indian Bay water at Tarapur and Mumbai is ~3.0 ppb which is comparable with the reported value for Arabian sea.
As such the global average is reported to be ~3.3 ppb by Oceanologists. The present study deals with the distribution of uranium
in seawater of MHB. The uranium activity in MHB by alpha spectrometry was found to be between 1.0 and 4.4 ppb with an average
concentration of 2.5 ppb which is comparable with the earlier reported average activity of 2.6 ppb in the MHB as well as those
reported globally. To compare the results obtained by alpha spectrometry, uranium estimation was also carried out using Laser
fluorimeter and the levels of uranium concentration have ranged between 0.8 and 4.9 ppb with an average concentration of 2.7 ppb.