The Separation Of Americium From Lanthanides By Bis(2,4,4－trimethylpentyl)dithiophosphinic Acid Extraction

The Separation of Americium from Lanthanides by Bis(2,4,4-trimethylpentyl)dithiophosphinic Acid ExtractionABSTRACTThe separation of Am from the lanthanides by bis (2,4,4-trimethylpentyl)dithio phosp-hinic acid (HBTMPDTP) extraction has been studied systematically.A method of purifying commercial Cyanex 301 (containing ~80wt% HBTMPDTP) has been studied and the purity of HBTMPDTP is >99%. >0.2mol/l HBTMPDTP mainly presents as a dimer in a non-polar solvent.The slopes of logD~pH dependencies and logD~log[(HA)2] dependencies for Am3+, Eu3" and Nd3+ are close to 3 and 2, respectively. The extraction constants (Kex) are 10~7 85 for Am3+, 10-11.62 for Eu3+ and 10-11.25 for Nd3+ at 25癈. The extraction process of Am3+ and Eu3+ by HBTMPDTP is an endothermic reaction. The extraction enthalpies of Am3+ and Eu3+ are 18.10 kJmol-1 and 43.65 kJmol-1, respectively.Compared with the hydrated ions, a red-shift and high intensity of the f-f transition supersensitive absorption spectra of HBTMPDTP - Am3+, Nd3+ complexes have been observed. The results demonstrate a great covalence of bonds between S and metal ions.High separation factors, SFAm/Eu -4700 and SFAm/pr+Nd -2100 indicate a high selectivity towards Am over macro amount of lanthanides in HBTMPDTP extraction.An empirical distribution ratio model for Am and lanthanides (Lns) in HBTMPDTP extraction has been established and a method of process parameters calculation has been proposed. The calculated values are consistent with the experimental ones. A 5 stages countercurrent HBTMPDTP extraction process can separate Am from Lns effectively. The separation of Am from Lns is >1 x 104 and the separation of Lns from Am is >260.A method of pretreating Am stripping fraction from the TRPO process by extracting Fe, Mo, Ru and Pd with HBTMPDTP or precipitating Am3+ with oxalate has been studied. The results of hot test show that Am can be well separated from fission product lanthanides (FPLns) by HBTMPDTP extraction. With a 4-stages cross-flow extraction, the extraction percentage of FPLns is <3% and the Am extraction percentage is >99.999%.The radiolytic stability of HBTMPDTP is fairly good. HBTMPDTP remains the ability to separate Am from lanthanides till a total dose of 104Gy.HBTMPDTP is an excellent extractant for Am/Ln separation and is promising for practical use in the separation of Am from FPLns. The present work develops a new research direction in the selection of extractant for trivalent actinides/lanthanides separation.