Tri‐n‐butyl phosphate (TBP), a universally recognized solvent, has got lesser organic phase splitting or third phase formation tendency during the extraction of U(VI) as compared to tetravalent metal ions. Thus, the lighter members of trialkyl phosphates (TalP) (i. e.) tri‐n‐propyl phosphate (TPP) and triethyl phosphate (TEP) having higher third phase formation tendency would provide an opportunity to comprehend the aggregation of U(VI) loaded TalP solvents. As the above lighter TalPs exhibit higher aqueous solubility, the conventional measurement of third phase limit or Limiting Organic Concentration (LOC) by mixing organic and aqueous phases cannot be employed for the investigation of U(VI) third phase in TalPs. This has led to the development of a novel method to examine U(VI) third phase in aqueous soluble TalP solvent systems without aqueous feed solution. After validation, the newly developed method has then been utilized to determine the LOC for 1.1 M TPP in n‐alkane. The variation of extractant structure, diluent chain length, nature of metal ion and temperature on the third phase of 1.1 M TalP systems has been evaluated along with their molecular level understanding using Dynamic Light Scattering.
Even though, pyroprocessing is considered as a suitable technique for metal fuel processing, attempts are being made in our laboratory to develop a solvent extraction based process as an interim method. Since, the metallic fuels contain considerable amount of Pu(IV) and Zr(IV), the use of conventional extractant tri-n-butyl phosphate (TBP) for reprocessing may pose problems due to third phase formation. In the exploration for the identification of an alternate extractant in the organophosphate family, tris(2-methylbutyl) phosphate (T2MBP), a branched isomer of tri-n-amyl phosphate (TAP) was found to be a potential extractant for nuclear fuel reprocessing. In this context, batch wise extraction and stripping studies with a feed solution containing U(VI) and 6 wt% Zr(IV) were carried out with unirradiated and irradiated 1.1 M solution of T2MBP in n-dodecane (n-DD) and the results were compared with corresponding solutions of TBP and TAP in n-DD. Among all these systems under identical conditions, third phase formation was observed only in the case of irradiated TBP system which makes U–Zr fuel reprocessing difficult using TBP as the extractant. Furthermore, studies have also been carried out with U–Pu–Zr feed solution to understand the extraction and stripping behaviour of these extractants. The stage wise and cumulative percentage of extraction and stripping for each metal ion of these systems were evaluated. Overall, these batch studies indicated that, T2MBP system has comparable extraction and stripping behaviour with U–Zr and U–Pu–Zr feed solutions and T2MBP exhibits better separation factor than TBP.
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