Supercritical fluid extraction of uranium from sintered oxides (UO_2, (U,Th)O_2), soil and ore samples using tri-n-butylphosphate and N,N-di-(2-ethylhexyl) isobutyramide as extractants

摘要

Direct extraction of uranium from different samples viz. sintered UO_2, (U,Th)O_2, soil, and ores was carried out by modifier free supercritical fluid containing tri-n-butylphosphate (TBP) and/ or N,N-di-(2-ethylhexyl)isobutyramide (D2EHIBA) as extractants. These extractants were pre-equilibrated with nitric acid prior to their use in supercritical fluid extraction experiments. Uranium extraction studies from sintered UO_2 showed that pre-equilibration with more concentrated nitric acid helped in its better dissolution and extraction. The extraction of uranium from (U,Th)O_2 samples was significantly lower for both TBP-HNO_3 (～17%) and D2EHIBA-HNO_3 (～12%) adducts in 2 h, under the conditions of present study. Modifier free supercritical fluid extraction appears attractive with respect to minimization of secondary wastes. This method resulted 80-100% extraction of uranium from different soil/ore samples. The results were confirmed by performing neutron activation analysis of original (before extraction) and residue (after extraction) samples.