The role of temperature on the distribution of Am3+ and UO22+ was investigated in the extraction systems involving TBP and DOSO as the neutral oxodonors and picrate as the organophilic
counter anion. The inner-sphere water molecules and their substitution by the oxodonor molecules appeared to influence the
extraction constants of these metal ions. The conditional extraction constants for Am3+ were found to be larger (about 3 order of magnitude) than those for UO22+. From the thermodynamics data it appeared that both TBP as well as DOSO bind Am3+ ion through outer-sphere coordination. In presence of 1M NaCl, though the interaction with TBP remains unaltered DOSO tend
to form an inner-sphere complex. On the other hand, UO22+ forms inner-sphere complexes with DOSO and outer-sphere complex with TBP in the absence of salt. In the presence of 1M NaCl,
both TBP and DOSO form inner-sphere complexes. The effect of ionic strength on metal ion extraction was also investigated.
The extraction behavior of Am3+ and UO22+ is investigated employing chloroform solution of 18-crown-6 as the organic phase and picrate solution at pH 3.0 as the aqueous
phase. In contrast to the commonly observed behavior, the extraction of Am3+ is preferred to that of UO22+. This unusual separation behavior is investigated as a function of several variable parameters such as crown ether concentration,
picric acid concentration, inert electrolyte concentration, nature of diluent etc. Thermodynamic parameters are also evaluated.
With increasing global nuclear activities, there is a growing interest in understanding the migration behavior of transuranic elements in the terrestrial environment. The laboratory investigations on the adsorption behavior of AM(III) (10–7M) in aqueous solutions showed that there was not adsorption of Am(III) on glass or polyethylene vials from aqueous solutions at pH<3. The rate of adsorption was found to be inversely related to the (H+) in the pH range 4–7. It was also found to be strongly influenced by stirring/shaking as well as by the presence of particulate matter in the aqueous phase. The presence of particulate matter (>0.6 m) in the aqueous solutions significantly inhibits the adsorption rate. Attempts to fit the kinetic data (collected on filtered [particle size >0.6 m] or unfiltered distilled water at pH 6) to the reversible or irreversible first order rate equation did not successfully indicate the complexity of the adsorption process. The presence of 20mg/liter of humic acid at pH 6.3 completely inhibits the adsorption of Am on glass surfaces.
Authors:C. Pawaskar, P. Mohapatra, and V. Manchanda
The extraction behavior of several metal ions viz., Am3+, Eu3+, UO22+, Th4+, Sr2+ and Cs+ was investigated from sulphate medium employing phosphotungstic acid (PTA) and polyethylene glycol (PEG). The influence of
various parameters such as pH, PTA concentration, PEG concentration and salt concentration was studied. The order of extraction
followed the trend: Am3+>Eu3+>>Th4+>UO22+>Sr2+>Cs+ which deviate significantly from the reported order with conventional solvents. The relatively poor extraction of UO22+, Sr2+ and Cs+ was ascribed to their lack of interaction with the phosphotungstate anion. The separation behaviour of Am3+ vis-a-vis Eu3+ was also investigated under different experimental conditions.
Authors:A. Bhattacharyya, P. Mohapatra, and V. Manchanda
Separation of trivalent actinides (An(III)) and lanthanides (Ln(III)) is a challenging task in the nuclear fuel cycle due
to their similar charge and chemical behaviour. Some soft donor ligands show selectivity for An(III) over Ln(III) due to the
formation of stronger covalent bonds with the former. The extraction behaviour of Am(III) and Eu(III) is studied in the present
work with a mixture of Cyanex-301 (bis(2,4,4-trimethylpentyl)di-thiophosphinic acid) with several various ‘N’, ‘O’ or ‘S’ donor neutral ligands. Comparison of the
data was done with that of the oxygen donor analogue of Cyanex-301, i.e. Cyanex-272 (bis(2,4,4-trimethylpentyl)phosphinic acid). Effect of the organic diluent on the extraction behaviour of Am(III) using Cyanex-301
in presence of ‘N’ donor synergists was also studied. Ab initio molecular orbital calculations were carried out using GAMESS
software and charges on the donor atoms were calculated which helped in understanding the co-ordination chemistry of the ligands
and explained the separation behaviour.
Authors:P. Mohapatra, R. Veeraraghavan, and V. Manchanda
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.
Extraction behavior of137Cs was studied from nitric acid medium using dibenzo 18 crown 6 (DB18C6), 4,4'(5')di-acetylbenzo 18 crown 6 (DAB18C6), 4,
4'(5')di-hexanoylbenzo 18 crown 6 (DHB18C6), 4,4'(5')di-nonanoylbenzo 18 crown 6 (DNB18C6) and 4,4'(5')di-t-butylbenzo 18
crown 6 (DTBB18C6) in nitrobenzene medium. The stoichiometry of the species extracted with dibenzo 18 crown 6 (L) conformed
to ML+. NO3− TheDCs values were found not to be affected by the presence of aluminium nitrate in the aqueous phase. The separation behavior of
fission products obtained from an irradiated natural uranium target was also studied. Presence of 0.004M phosphotungstic acid
found to enhance theDCs values at lower acidities.
Authors:D. Raut, P. Mohapatra, P. Wattal, and V. Manchanda
Three different resins containing ammonium molybdophosphate (AMP), viz. PMMA (polymethylmethacrylate) resin, composite AMP
resin and ALIX (a bisphenol based resin), were evaluated for their irradiation stability. The studies included batch as well
as column studies and were carried out for cesium uptake behaviour at 3 M acidity. The resin beads were irradiated to varying
dose viz., 0 MRad, 10 MRad, 20 MRad, 50 MRad and 100 MRad. The time taken to attain equilibrium was rather long and about
2–5 h were found to be required for attaining equilibrium in batch studies. Batch Cs(I) uptake studies revealed no significant
effect on the Kd values in case of the PMMA resin while in case of the composite resin and ALIX resin, a decrease in the Kd was observed as a function of irradiation dose. The resin capacity indicated contrasting behaviour with irradiation dose
for the resins. Column runs have been carried out for the uptake of radio cesium using both unirradiated and irradiated resins
using feed solutions containing 3 MHNO3. The loading capacities of the resins were found to be proportional to their Cs loading capacities observed in batch studies.
Study revealed that the composite AMP had the maximum and PMMA has the least loading capacity. Results of these studies show
that these AMP based resins can be used for cesium separation from acidic nuclear waste.
Authors:A. Kanekar, P. Pathak, P. Mohapatra, and V. Manchanda
Extraction of uranium from tissue paper, synthetic soil, and from its oxides (UO2, UO3 and U3O8) was carried out using supercritical carbon dioxide modified with methanol solutions of extractants such as tri-n-butyl phosphate (TBP) or N,N-dihexyl octanamide (DHOA). The effects of temperature, pressure, extractant/nitric acid (nitrate) concentration, and of hydrogen
peroxide on uranium extraction were investigated. The dissolution and extraction of uranium in supercritical CO2 modified with TBP, from oxide samples followed the order: UO3 ≫ UO2 > U3O8. Addition of hydrogen peroxide in the modifier solution enhanced the dissolution/extraction of uranium in dynamic mode. DHOA
appeared better than TBP for recovery of uranium from different oxide samples. Similar enhancement in uranium extraction was
observed in static mode experiments in the presence of hydrogen peroxide. Uranium estimation in the extracted fraction was
carried out by spectrophotometry employing 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP) as the chromophore.