Indigenously synthesized extractant, phenyl (octyl) phosphonic acid (POPA) in tri-n-butylphosphate (TBP) and dodecane, has been investigated for the separation of americium from trivalent lanthanides in nitric
acid medium as well as diethylene triaminepentaacetic acid (DTPA) and lactic acid mixture (TALSPEAK medium). Various experimental
parameters like concentration of DTPA, lactic acid, TBP, nitrate ions and pH of the aqueous feed solution have been optimized
to obtain the highest separation factor between americium and europium. Bulk actinide–lanthanide separation reagent, tetra
(ethylhexyl) diglycolamide (TEHDGA), was equilibrated with simulated solution of americium and lanthanides, equivalent in
concentration to the reprocessing waste originating from PHWR spent fuel. DTPA/lactic acid mixture was used to strip the metal
ions from the loaded organic phase and re-extracted into POPA in TBP/dodecane to evaluate the separation factor of individual
lanthanides with respect to americium. Very good separation factors between americium and trivalent lanthanides were obtained.
The effect of -irradiation on the ion-exchange capacity, distribution coefficient and the efficiency for binary separations of some thermally stable inorganic ion exchangers have been studied. Irradiation upto 100 Mrad, has no effect on these substances, except thorium tungstate which showed changes in ion-exchange capacity, distribution behaviour and in binary separations.
Authors:C. Janardanan, P. Achuthan, A. Ramanujan, and B. Misra
Batch equilibrium distribution data for Ce3+/H+ and Am3+/H+ systems in 0.2 to 4.0M HNO3 on 1, 2, 4, 8, 10, 12 and 16% crosslinked Dowex 50W resins are reported. These data, along with the mean ionic activity coefficients of the tracer in the mixed electrolyte solutions, were used to calculate the equilibrium constant (Ka) uncorrected for the resin phase activity coefficient. The logKa values obtained at various ionic strengths were fit to a second order quadratic equation. Using the fitting parameters, logKa values were calculated for the different resins at zero ionic strength. LogK (equilibrium constant) values were computed by neglecting the changes in the activity coefficient terms in the resin phase due to resin loading. The logK values reported for Ce3+/H+ systems at a few crosslinkages are compared and the magnitude of the error in the approximate calculations is discussed.
Authors:C. Janardanan, P. Achuthan, A. Ramanujam, and B. Misra
Back-extraction of tri- and tetravalent actinides from diisodecylphosphoric acid (DIDPA) is studied using hydrazine carbonate as back-extractant. In experiments using 0.5M DIDPA–0.1M TBP n-dodecane solution, Am(III), Eu(III), Pu(IV) and Np(IV) are back-extracted, and the distribution ratios are decreased with an increase of hydrazine carbonate concentration. The back-extraction equilibria are confirmed by slope analysis in consideration of neutralization between DIDPA and hydrazine carbonate, which occurs quantitatively during back-extraction. In particular, oxidation of Np(IV) to Np(V) during back-extraction is observed by measuring absorption spectra. The hydrazinium ion acts as an oxidation reagent in the back-extraction of Np(IV). Separation factors of those metals are compared with the results of HDEHP. Hydrazine carbonate back-extracts Np(IV) more selectively from DIDPA than from HDEHP.