Partitioning of Polymeric Plutonium(IV) in Winsor II Microemulsion Systems

The hydrolysis and polymerization of Pu(IV) can cause serious problems during the aqueous processing of spent fuel and nuclear wastes. Several studies describing the liquid/liquid extraction behavior of polymeric Pu(IV) have been reported in the literature. In many cases, poor plutonium extraction was accompanied by the appearance of an interfacial crud or third phase. Invariably, poor mass balances were observed during the extraction of aged, colloidal Pu(IV). Extraction of colloidal Pu(IV) by microemulsion-based solvent extraction systems, however, is capable of attaining bulk phase mass balances for Pu of 100%. The Winsor II microemulsions discussed in this paper consisted of sodium bis(2-ethylhexyl) sulfosuccinate in hexane with either octylphenyl-N,N-diisobutylcarbamoylmethyl-phosphine oxide or tributyl phosphate as coextractant. Backextraction of plutonium from microemulsion phases was achieved by Pu encapsulation in silica particles that were produced by the acid-catalyzed hydrolysis and polymerization of tetraethoxysilane within the aqueous microdroplets of the microemulsion.