Extraction of uranium from solid matrices using modified supercritical fluid CO2

The equilibrium solubility of uranyl nitrate in supercritical fluid carbon dioxide (SF-CO2) in the absence and presence of different modifiers was inv estigated. In the presence of methanol and HNO3, uranyl nitrate showed a co nsiderable solubility in SF-CO2. SF-CO2 modified with different co-extracta nts such as tributylphosphate (TBP), methylisobutyl ketone (MIBK), acetylac etone (AA) and methanol (MeOH) at 60 degreesC and 250 atm was used for the extraction of uranyl nitrate from cellulose-based filter papers. The extrac tion efficiency of the system for uranyl ion was found to decrease in the o rder TBP > MIBK > AA > MeOH. The use of eight potential chelating agents bi s(2-ethylhexyl)hydrogen phosphate (HDEPH), tri-n-octylphosphine oxide (TOPO ), dicyclohexyl-18-crown-6 (DC18C6), dibenzoylmethane (DBM), 8-hydroxyquino line (HOX), diphenylaminesulfonic acid (DPASA) 1,4-bis-[4-methyl-5-phenyl-2 -oxazolyl] benzene (DMPOPOP) and TBP for uranyl ion extraction from filter paper samples by methanol modified SF-CO2 was investigated. The organophosp horous reagents TOPO and HDEPH showed the highest extraction efficiency in the series. The synergistic extraction of uranyl nitrate with HDEPH and TOP O in the presence of DC18C6 was also studied. (C) 2001 Elsevier Science B.V . All rights reserved.