Novel polymer inclusion membranes containing T2EHDGA as carrier extractant for actinide ion uptake from acidic feeds

Abstract

Polymer inclusion membranes (PIM) containing

Polymer Inclusion Membrane Containing a Tripodal Diglycolamide Ligand: Actinide Ion Uptake and Transport Studies

“…The increase in the metal ion uptake efficiency with increasing NPOE content can be explained considering the plasticization effect, which turns the membrane into a better medium for carrier and plasticizer movements, whereas the decrease in the uptake efficiency may be due to the plasticizer exudation, prevalent in the case of PIMs . We have noticed a similar decrease in the uptake efficiency of a T2EHDGA-based PIM in the presence of NPOE as a plasticizer at a much lower concentration (17.9–30.4%) . However, with all the PIMs with NPOE content in the range of 24.5–56.8%, the uptake of Am 3+ reached a near constant value of ∼88% after 24 h (Table S2, Supporting Information).…”

“…However, as compared to solvent extraction systems, where a 100 times lower concentration of T-DGA (as compared to TODGA) was found to be enough, here a much larger concentration of T-DGA was required. The actinide uptake with the T-DGA-based PIMs follows the trend: Pu 4+ > Am 3+ ≫ UO 2 2+ > Th 4+ , which is slightly different (Am 3+ > Pu 4+ > Th 4+ ≫ UO 2 2+ ) from that reported with TODGA-containing PIMs but similar to that of T2EHDGA-containing PIMs . The sorption–desorption study indicated a limited use of the PIM as a sorbent.…”

“…However, the poor extraction of Th 4+ as compared to that of Am 3+ , though the former has a higher ionic potential, may be due to the larger amount of ligands accommodating the Th 4+ ions at a high ligand to metal ion ratio (Th 4+ < 10 –10 M) and the subsequent poor diffusion of the complex into the bulk of the PIM (mobile carrier model) and hence, resulting in an uptake only on the PIM surface. Our earlier studies with a T2EHDGA-based PIM showed the uptake trend: Pu 4+ > Am 3+ > Th 4+ > UO 2 2+ . On the other hand, a contrasting trend of actinide ion uptake was observed with a TODGA-based PIM .…”

“…The long-term usage of PIMs depends on two factors, viz., the effective stripping of the sorbed metal ions and the effective reuse of the membrane. We have previously reported that α-hydroxy- iso -butyric acid (AHIBA) is an effective strippant for the back extraction of the sorbed metal ions from PIMs . In view of this, a sorption–desorption study was performed in which the sorption was studied by following the uptake of Am 3+ from 1 M HNO 3 using a 4 cm 2 piece of the PIM (as mentioned above).…”

“…Diglycolamide (DGA) ligands are reported to be highly selective for actinide ion extraction from acidic feeds . Recently, we have demonstrated the promising extraction ability of PIMs containing two very efficient diglycolamide (DGA) extractants, viz., N , N , N ′, N ′-tetraoctyl diglycolamide (TODGA), N , N , N ′, N ′-tetra­(2-ethylhexyl) diglycolamide (T2EHDGA) and very recently with several other tetraalkyldiglycolamides to understand the role of alkyl chain length on metal ion uptake and transport . In all these cases, the extracted species contains three to four DGA ligands around the metal center and, in addition, requires special conditions for favorable extraction such as using a nonpolar diluent such as n -dodecane, which helps in the formation of molecular aggregate formation , which favors metal ion extraction in a unique manner, i.e., trivalent actinide ions are extracted to a much larger extent than the tetravalent actinide ions and a much lower extraction of uranyl ion.…”