Supercritical fluid extraction and purification of uranium from crude sodium diuranate

Supercritical Fluid Extraction (SFE) and purification of uranium, from crude sodium diuranate (SDU) containing uranium (53%), iron (22.2% of U) and rare earth impurities (4% of U), has been studied. Adduct of tri-butyl phosphate (TBP) and nitric acid (HNO3) has been used for uranium dissolution and extraction. Carbon dioxide has been used as supercritical fluid. For 200 mg of crude SDU, operating parameters such as temperature, pressure, quantity of TBP·HNO3 adduct, static and collection time have been optimized at 323 K temperature, 15.20 MPa pressure, 1 mL of TBP·HNO3 adduct, 20 min. static time and 20 min. collection time. Under these conditions, uranium extraction efficiency was 95 ± 5%. Addition of free nitric acid leads to improvement in purity of uranium. Uranium was stripped from SFE extract and precipitated as ammonium diuranate (ADU), which was then subjected to second cycle of SFE. After two cycles of SFE, purification factor of uranium was found to be 4970, 90, 110 and 60 with respect to iron, yttrium, ytterbium and erbium respectively.