Supercritical fluid extraction of uranium and thorium from solid matrices

Supercritical fluid extraction (SFE) of uranium and thorium from solid matrices was carried out employing CO2. Direct dissolution and extraction of oxides of uranium viz. UO2 and U3O8 was performed. UO2 and U3O8 powders (0.02–0.05 g) along with 2 ml of TBP–HNO3 complex were taken in extraction vessel and CO2 was fed until 150 atm. pressure and 60°C temperature were achievable. After 20 min uranium extraction was performed by continuously flowing supercritical fluid mixture of CO2 and 10% TBP for 45 min. Uranium extraction efficiency for U3O8 was 97.05 ± 3.73% and for UO2 was 98.07 ± 4.76%. For SFE of thorium from tissue paper matrix, TBP and TOPO (0.2 M in CCl4) were investigated as complexing agents. In online complexation mode, mixture of CO2 and 10% complexing agent was fed to the extraction vessel. The vessel was maintained at pressure of 200 atm. and temperature of 60°C for 20 min followed by 20 min of extraction. TOPO was found to be more effective than TBP as extraction efficiencies with TBP and TOPO were 52.51 ± 7.54% and 65.65 ± 7.78% respectively. The efficiency was found to improve with a combination of 1: 1 volume ratio of TBP and TOPO (0.2 M in CCl4). No further improvement was observed with TOPO plus 10% methanol. In in-situ mode higher efficiency i.e. 89.83 ± 7.04% was observed with employing TOPO as a complexing agent. Uranium and thorium were determined spectrophotometrically employing arsenazo III metal indicator for color development.