COMPLEXATION AND TRANSPORT OF URANYL-NITRATE IN SUPERCRITICAL CARBON-DIOXIDE WITH ORGANOPHOSPHORUS REAGENTS

Experiments have been performed to evaluate the feasibility of extract ing solid uranyl nitrate with organophosphorus ligands using supercrit ical carbon dioxide as a solvent. Ligands investigated include tri-n-b utylphophate (TBP), tributyl phosphine oxide (TBPO), trioctyl phosphin e oxide (TOPO) and triphenyl phosphine oxide (TPPO). Of these ligands, TBP demonstrated the most favorable ligand behavior, forming stable c omplexes with uranyl nitrate, and showing excellent transport capabili ties. TOPO and TBPO showed reasonable extraction efficiencies for uran yl nitrate but the resulting complexes were difficult to transport, pr esumably due to solubility limitations. TPPO showed poor extraction ef ficiency and poor transport capabilities. Further investigation of TBP -CO2 phase behavior did not indicate secondary liquid phase formation. Kinetics of extraction were rapid, with quantitative extraction being achieved in 30-40 minutes. Solubility of UO2(NO3)(2) . xH(2)O . yTBP was estimated at 1.3 x 10(-3)-2.0 X 10(-3) M under the conditions 60 d egrees-120 degrees C and 250 atm CO2.