Studies on the use ofN,N,N′,N′-Tetra(2-Ethylhexyl) Diglycolamide (TEHDGA) for Actinide Partitioning II: Investigation on Radiolytic Stability

Abstract

N,N,N ,N -tetra(2-ethylhexyl)diglycolamide (TEHDGA) was found to be a promising extractant for actinide partitioning from high-level waste (HLW) (Part I). In order to evaluate the applicability of TEHDGA to the HLW partitioning process, investigations on its radiolytic stability were carried out. The present work deals with the studies on the uptake of americium by γ -irradiated 0.2 M TEHDGA/n-dodecane in the absence and presence of phase modifiers-di(n-hexyl)octanamide (DHOA), isodecanol and n-decanol-against the absorbed dose up to 1 × 10 6 Gy in the presence of nitric acid at varying concentrations. The addition of phase modifiers suppressed the radiolysis of TEHDGA in n-dodecane and DHOA was found to be the most effective radiolysis suppressor. Investigations were also carried out on the degradation of neat TEHDGA by γ -irradiation, and it was attempted to isolate and identify its degradation products by instrumental analysis. The radiolysis study showed that the degradation products were formed by the cleavage of the -C-N bond, to eliminate an ethylhexyl group, and the bond adjacent to the ether bond. The results obtained for TEHDGA radiolysis were compared with that of its straight-chain isomer TODGA, and TEHDGA was observed to be more resistant to radiation than TODGA. The changes in the physico-chemical properties of γ -irradiated TEHDGA against the absorbed dose were also investigated.

A Comparison of theγ-Radiolysis of TODGA and T(EH)DGA Using UHPLC-ESI-MS Analysis

“…[15] In further study of the radiolysis of T(EH)DGA, Deepika et al found that D Am values decreased more for T(EH)DGA when irradiated in the presence of the n-dodecane and HNO 3 . [4] However, these authors did not attempt to separate the effects of the diluent and the aqueous phase and erroneously concluded that nitric acid enhanced T(EH)DGA decomposition, rather than to electron transfer Downloaded by [New York University] at 23:55 14 June 2015 reactions with the n-dodecane radical cation. Thus, contradictory reports have appeared in the literature, possibly confounded by the use of the various phase modifiers.…”

“…1b) has been promoted as a cheaper alternative with less affinity for fission product complexation. [4] The weaker complexing ability of T(EH)DGA was used to advantage by Lumetta et al [5] in the design of the ALSEP (Actinide Lanthanide SEParation) solvent, where, in combination with the acidic soft-donor ligand diethylenetriamine pentaacetic acid (DTPA), it was used to give a single extraction/strip cycle separation of the actinides from the lanthanides. [5,6] A loaded organic phase consisting of 0.05 M T(EH)DGA and 0.75 M 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (HEH[EHP]) in n-dodecane, when stripped with an aqueous phase consisting of 0.01 M DTPA and 0.2 M citric acid, provided α Nd/Am values in the range 10-30.…”

Effect of irradiation on some actinide and fission product ions' extraction using several tetraalkyl diglycolamides

“…It is also important to mention here that some of the degradation products can interfere in the performance of the extraction system which is reflected in poor decontamination. Deepika, et al, reported both GC-MS as well as IR spectroscopic analysis of T2EHDGA [23]. We have tried to analyze the FT-IR spectra of the diglycolamide extractants, both unirradiated and exposed to 1000 kGy (Supporting information).…”

“…There are several reports on the radiolytic stability of diglycolamide extractants, particularly TODGA and T2EHDGA ( , , , -tetra-2-ethylhexyl diglycolamide) [17][18][19][20][21][22][23]. Radiolytic stability of TODGA was studied by Sugo and et al and the G-value (number of molecules undergo degradation after absorption of 100 eV of energy) for TODGA was found to be 8.5±0.6 molecules/100 eV [17].…”

Supported liquid membrane transport studies on Am(III), Pu(IV), U(VI) and Sr(II) using irradiated TODGA

“…The decrease in the transport rate was found to be lower for the solvent containing higher concentration of DHOA. This is due to the fact that amides such as DOHA (N,N,-di-n-octyl hexanamide, which is similar to DHOA) inhibits the radiolysis of TODGA [8] and DHOA has been reported to inhibit radiolysis of T2EHDGA (tetra-N,N,N ,N -2-ethylhexyldiglycolamide [24], which is analogous to TODGA). As a result, when 0.1 M TODGA in n-dodecane was irradiated at 100 MRad, ∼79% Am(III) got transported in ∼5 h. In sharp contrast, the transport of Am(III) increased to ∼85% under identical conditions when 0.1 M TODGA + 0.5 M DHOA in n-dodecane was used as the carrier solvent.…”