Optimization Studies for the Recovery of Thorium from Advanced Heavy Water Reactor High Level Waste (AHWR-HLW) Solutions Using Green Solvents

Investigations on Preferential Pu(IV) Extraction over U(VI) by N,N-Dihexyloctanamide versus Tri-n-butyl Phosphate: Evidence through Small Angle Neutron Scattering and DFT Studies

“…This behavior has been explained earlier in terms of the change in the stoichiometry of the extracted species of Pu(IV) at lower (mono- or disolvated complexes) and higher acidities (trisolvated complex) . Similarly, the solvent extraction studies using DHOA suggested that the dialkylamides can be used as an extractant for the reprocessing of Th-based advanced heavy water reactor (AHWR) spent fuels. ,, This offers better extraction of U(VI) and Pu(IV) over Th(IV) from nitric acid medium. Even though the use of DHOA for reprocessing of U- and Th-based spent fuels appears to be promising, there is a need to investigate its preference for Pu(IV) over U(VI) (for U-based feed solutions) and for U(VI) and Pu(IV) over Th(IV) (for AHWR feed solutions).…”

“…Extensive efforts on the development of alternative extractants to TBP have shown that straight chain amides such as N , N -dihexyloctanamide (DHOA) (Figure ) are promising alternatives for the reprocessing of irradiated uranium and thorium based fuels. − The liquid–liquid batch extraction studies have shown that U(VI) and Pu(IV) can be co-extracted living bulk of fission products in raffinate and hence can be employed in the PUREX process. , Np(V) alone has very poor or no extractability with TBP or DHOA, but if the feed contains appreciable amount of U(VI), Np(V) can be extracted to the organic phase because of the formation of a cation–cation complex of U(VI)–Np(V) . With tetravalent actinides such as Th(IV) or Pu(IV), both TBP and DHOA form a third phase, which refers to the splitting of the organic phase into diluents-rich and metal-extractant solvate-rich phases. , This is mainly guided by the species formed under the given experimental conditions. Verma et al studied the effects of extractants and diluents on third-phase formation and showed that dipole–dipole interaction between cores of a metal ligand reverse micelles causes their aggregation, which subsequently leads to third-phase formation, and such interaction is not favorable in polar diluents …”

Characterization of the Species Formed during the Extraction of Thorium Employing Tri-n-Butyl Phosphate and N,N-Dihexyl Octanamide as Extractants by Laser Desorption/Ionization Time-of-Flight Mass Spectrometry

“…20,21 We have performed systematic studies using several N,N-dialkyl amides as alternatives to TBP in the plutonium uranium reaction (PUREX) as well as in the thorium extraction (THOREX) processes. 18,[22][23][24][25][26][27][28][29][30] The straight-chain amide, N,N-dihexyl octanamide [DHOA, Figure 1(b)], was found to be the most suitable alternative to TBP for selective recovery of U and Pu from three components (U, Pu and Th) of advanced heavy water reactor (AHWR) spent fuels. [24][25][26] In addition, studies were also carried out to optimize the conditions for the recovery of ~ 100 g L −1 Th(IV) from AHWR raffinate solutions.…”

“…The choice of 1.1 M concentrations of these solvents was based on their proposed use for thorium recovery from AHWR raffinate solutions. 30 …”

“…[24][25][26] In addition, studies were also carried out to optimize the conditions for the recovery of ~ 100 g L −1 Th(IV) from AHWR raffinate solutions. 30 In this context, third-phase formation studies are of particular significance, in view of the presence of large concentrations of Th(IV) in the raffinate solutions. Similar to trialkyl phosphates, straight-chain amides showed an increase in the Th(IV)-LOC values with the total number of carbon atoms and the carbon chain length on the carbonyl group.…”