Unusual selective extraction of Pu4+ by some novel diamide ligands in a room temperature ionic liquid

Extraction of Pu4+ was carried out from nitric acid feeds employing ionic liquid solutions of four novel diamide ligands containing an aromatic bridging group. The ligands with iso-butyl, n-butyl, n-octyl and 2-ethylhexyl groups were termed as LI, LII, LIII, and LIV, respectively and showed significantly higher extraction of the tetravalent plutonium ion as compared to the hexa-valent uranyl ion. Using 0.05 M ligands, the extraction of Pu4+ was in the range of 80-95% when 3 M HNO3 was used as the feed and followed the order: LIII > LII > LI > LIV while the UO22+ ion extraction was less than 4-5% and no particular trend could be established. The extraction of UO22+ could be partly due to the anionic nitrate complex of uranyl ion which was extracted in the absence of the ligands, while the ligand assisted extraction contributing for the remaining. Out of the other metal ions studied, Cs+ showed some extraction which was not ligand assisted while almost no extraction of metal ions such as Sr2+, Am3+ and Eu3+ was noticed. Unusually high selectivity was seen for Pu4+ ion extraction out of all the metal ions studied making the solvent systems very important for a plutonium specific separation method development. The extraction was found to be increasing with the aqueous phase nitric acid concentration conforming to a 'solvation mechanism' of extraction where the extracted species conforming to Pu(NO3)4·LIL for all the four diamide extractants.