Supercritical fluid extraction of uranium and thorium employing dialkyl amides

•First report on the SFE of uranium, thorium employing a set of amides.•Extraction efficiency correlated to amide structure and nature of uranium/thorium complex.•First report on the SFE of uranium, thorium from nitric acid medium employing amides.•Systematic study of effect of various parameters.

N,N-dialkyl aliphatic amides with varying alkyl groups viz. N,N-dibutyl-2-ethyl hexanamide (DBEHA), N,N-dibutyl-3,3-dimethyl butanamide (DBDMBA), N,N-dihexyl octanamide (DHOA), N,N-di-sec-butyl pentanamide (DBPA), N,N-dibutyl octanamide (DBOA), have been evaluated for supercritical fluid extraction (SFE) of uranium and thorium from nitric acid medium as well as from tissue paper matrix. The trend in extraction efficiency could be correlated to the structure of the amides and the amide complex of uranium/thorium. Straight chain amide DBOA was found suitable for SFE of both uranium and thorium. Under optimised conditions (200 atm. pressure, 323 K temperature, 30 min static time followed by 30 min dynamic time, 0.5 M amide in methanol), (94 ± 3)% uranium and (85 ± 4)% thorium could be extracted from 4 M nitric acid medium. For tissue paper matrix, under optimised conditions (200 atm pressure, 323 K temperature, 45 min static time followed by 30 min dynamic time, 0.2 M amide in methanol) (87 ± 7)% uranium and (88 ± 7)% thorium were extractable. For the amide having branching at Cα, DBEHA, extraction efficiency of thorium was as low as 7% for 2 M HNO3 medium while extraction efficiency of uranium was still 95%. For tissue paper matrix, extraction efficiency for uranium with 0.2 M DBEHA (in methanol) was 86% while only 11% thorium was extractable under same conditions. This fact could be exploited for separation of thorium and uranium.