Ion pairing as a strategy for extraction by modified supercritical carbon dioxide: Extraction of radioactive metal ions

Supercritical fluid carbon dioxide was investigated for its potential to ex tract perrhenate ion pairs. This has implications for radioactive waste pro cessing because Tc-99, the second row congener of Re, is produced in simila r to6% fission yield from nuclear fuel and pertechnetate is its most common chemical form in aqueous environments. The variables examined to maximize extraction of the perrhenate ion pair were temperature, pressure, solvent m odification, and ion-pairing agents. The tetrabutylammonium cation was foun d to form the most efficient ion pair for extracting perrhenate using metha nol-modified (similar to 10%) SFCO2 at 70 degreesC and 477 atm, with 0.083 mg of Re/g of SFCO2 extracted.