Abstract
The distribution coefficient for U(VI) between an aqueous phase and a supercritical one was determined with an absorption spectrophotometer, which is corresponding to two phase measurements at a time in a high pressure vessel through sapphire windows. The distribution feature of an aqueous/supercritical phase shows the same pattern with that of an aqueous/organic phase, so, the mechanism of U(VI) extraction in TBP of both systems will be identical. The distribution of U(VI) is influenced a great deal by the concentration of nitric acid. The distribution of nitric acid was determined to fix the nitric acid concentration and the distribution of U(VI) because the nitric acid coordinated to TBP in a supercritical fluid of carbon dioxide is also stripped into an aqueous phase. The distribution coefficient for nitric acid between an aqueous phase and TBP in a supercritical fluid of carbon dioxide consists with the one between an aqueous phase and TBP. The stripping of U(VI) from a supercritical fluid of carbon dioxide to aqueous nitric acid with a countercurrent column was demonstrated and about 80% of U(VI) was collected in the aqueous phase through a column of 380 mm high.
