R. Veeraraghavan

Separation Studies of Uranium and Thorium Using Di-2-Ethylhexyl Isobutyramide (D2EHIBA)

The extraction behavior of di-2-ethylhexyl isobutyramide (D2EHIBA) in dodecane medium for U(VI), Th(IV), and fission products such as Zr, Ce, Eu, and Cs, and the structural material Fe, has been investigated over a wide range of nitric acid concentrations. It has been observed that whereas D U varies from < 10−3 (pH 2.0) to 4.4 (6 M HNO3) with 1 M ligand, the corresponding D Th values are 1.5 × 10−3 and 4 × 10−2. In the presence of 250 g/L of Th, D U values are 8.6 (pH 2.0) and 2.2 (6 M HNO3). D2EHIBA has been found to be a promising extractant of trace concentrations of U in the presence of macro amounts of Th. The extraction of fission products and Fe is found to be negligible. D2EHIBA is found to extract nitric acid predominantly as a 1:1 species (K H = 0.156 ± 0.048). U(VI) is extracted as a disolvate UO2(NO3)·2D2EHIBA (K ex = 0.87 ± 0.08).

Separation of uranium and thorium using tris(2-ethylhexyl) phosphate as extractant

The distribution behavior of uranium and thorium has been investigated in a biphasic system of different aqueous nitric acid concentrations and a solution of tris(2-ethylhexyl) phosphate (TEHP) inn-dodecane at 25°C. The effect of different uranium and thorium concentrations in the aqueous phase on the extraction of these metal ions is evaluated. These results indicate that TEHP is a better choice than tri-n-butyl phosphate (TBP) for the separation of233U from the irradiated thorium matrix.

Extraction of thorium(IV) by a mixture of 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone and tri-n-octyl phosphine oxide

The extraction behavior of Th(IV) from dilute nitric as well as perchloric acid medium using 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (PMBP) and its mixture with tri-n-octyl phosphine oxide (TOPO) was investigated. The species of the type Th(X)(PMBP)3·(HPMBP) and Th(X)(PMBP)3·(TOPO) were extracted for the binary and ternary extraction systems, respectively, where X=NO3− or ClO4−. The presence of 1.25·10−5M Th carrier in the aqueous phase resulted in the extracted species of the type of Th(PMBP)4 and Th(PMBP)4·(TOPO), respectively. The extraction constant (logkex) for the binary species Th(PMBP)4 was found to be 6.89±0.01 while the overall extraction constant (logK) for the ternary species Th(PMBP)4·(TOPO) was calculated to be 13.17±0.06.

Synergism with amides

Synergistic extraction of uranyl ion with 2-thenoyltrifluoroacetone (HTTA) and aliphatic amides with varying basicities, viz. dibutyl hexanamide (DBHA), dibutyloctanamide (DBOA) or dibutyldecanamide (DBDA) has been studied at various fixed temperatures of 20, 30, 40 and 50±0.1°C. Results indicate that the equilibrium constants of the organic phase addition reaction (Ks) with these amides follow their order of basicity (Kh) viz. DBHA (0.09)<0.10) H DBOA (0.13) with log Ks values of 4.91, 4.99 and 5.02, respectively. These values are much higher than those with TBP (3.8) or sulfoxides (≃4) as donors. This may be attributed to the existence of a resonance form of the amide, which has higher electron density on the carbonyl oxygen. The thermodynamic parameters associated with these systems evaluated by the temperature coefficient method indicate that the organic phase addition reaction with all the three amides is stabilized by both enthalpy and entropy changes as against UO22+/HTTA/TBP system, where only the enthalpy change contributes to the stabilization.

Extraction of americium from nitric acid medium using 3-phenyl-4-benzoyl-5-isoxazolone and tri-n-octylphosphine oxide

The extraction behavior of americium from acid solutions by a mixture of 3-phenyl-4-benzoyl-5-isoxazolone and tri-n-octyl phosphine oxide in carbon tetrachloride medium has been investigated in 1–6 M nitric acid. It is shown that Am(III) can be removed along with U(VI) and Pu(IV) quantitatively from 1 M nitric acid in a single contact and that Am(III) can be selectively stripped by using higher (>6 M) nitric acid concentrations. The distribution profile for Am(III) has been evaluated in the presence of varying amounts of U(VI) and Nd(III) in varying nitric acid media. The distribution behavior of several fission products has also been reported.

Radiation effects in plutonium and carbonate co-doped calcium hydroxy apatite: An EPR study

Electron paramagnetic resonance studies were conducted on synthetic calcium hydroxy apatite samples co-doped with 239Pu and carbonate ion. These investigations were carried out to assess the self-irradiation effects in bone and teeth on exposure to plutonium, as calcium hydroxy apatite is the major constituent of bone and teeth. On self-irradiation, in addition to the signal from O- ion arising from the radiolysis of hydroxide ion, EPR signals due to CO2-, PO22- and another signal assigned to surface O- ions were observed in the samples. In freshly quenched gamma irradiated samples, signals from CO3-, O- , PO22- and O2- ions were observed. The EPR signal of O2- ion shows a doublet splitting suggesting that O2- ion gets preferentially stabilized close to Pu4+. The radiation damage due to Pu4+ at Ca2+ sites, in the sample appears to be lower as compared to that due to external gamma-irradiation. Moreover, the alpha-dose in 239Pu doped samples has self-annealing effects. These are attributed to localized radiation damage due to alpha-particles compared to evenly distributed radical ions produced due to gamma-irradiation.

Thermally stimulated luminescence and electron paramagnetic resonance studies on uranium doped calcium phosphate

Thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) studies on uranium doped calcium phosphate yielded mechanistic information on the observed glow peaks at 365, 410 and 450 K. TSL spectral studies of the glow peaks showed that UO22+ acts as the luminescent center. Electron paramagnetic resonance studies on gamma-irradiated samples revealed that the predominant radiation induced centers are H0, PO42-, PO32- and O- ion. Studies on the temperature dependence studies of the EPR spectra of samples annealed to different temperatures indicate the role of H0 and PO42- ions in the main glow peak at 410 K.

Dioctyl sulfoxide as a stabilizer for scintillation counting

The use of dioctyl sulfoxide (DOSO) as a stabilizer for scintillation counting of uranium(VI), plutonium(IV) and americium(III) has been investigated. It has been observed that the addition of 2% DOSO to the scintillator solution results in a decrease in count rate of Am(III), which is about one third of that obtained with 2% TOPO. Uranium(VI) could be counted with almost the same efficiency with DOSO, TOPO, or as such without any stabilizer. The counting efficiency of plutonium(IV), however, is inferior for DOSO as compared to TOPO.