Supercritical fluid extraction of thorium from tissue paper matrix employing β-diketones

Abstract

Various β-diketones viz. acetylacetone (AA), trifluoroacetylacetone (TFA), hexafluoroacetylacetone (HFA), thenoyltrifluoroacetylacetone (TTA) and heptafluorobutanoyl-pivaroylmethane (FOD) were evaluated as chelating agents for the supercritical fluid extraction of thorium from tissue paper matrix. In-situ chelation mode was found to be more effective than online chelation mode. A combination of tributyl phosphate (TBP) and β-diketones further enhanced the extraction efficiency. The extraction efficiency trend observed in all the cases was: TTA > FOD > HFA > TFA > AA. A correlation was observed between extraction efficiency and degree of fluorination in the side arms of β-diketones. This could be attributed to the fact that in supercritical CO 2 , higher fluorination results in higher percentage of enol content, greater dissociation into enolate ion and higher solubility and stability of /?-diketones as well as of Th-β-diketone chelates. Highest extraction efficiency with TTA was probably due to the presence of aromatic thenoyl group. The spectra of the extracted Th-chelates displayed peaks in the visible region, which shifted towards UV region with increasing fluorination. In the Th-TTA chelate spectrum, red shift was observed.