Supercritical fluid extraction and chromatography of heavy metals, lanthanides and actinides

In this study, supercritical (SF) CO{dollar}sb2{dollar} containing a chelating reagent has been used for the extraction of heavy metals, lanthanides and actinides. Our results show that heavy metals can be extracted from solid and liquid matrices using SF CO{dollar}sb2{dollar} containing a fluorinated chelating agent, lithium bis(trifluoroethyl)dithiocarbamate(LiFDDC). Methylmercury chloride {dollar}rm (CHsb3HgCl){dollar} and dimethylmercury ((CH{dollar}sb3)sb2{dollar}Hg) can be extracted by SF CO{dollar}sb2{dollar} without the chelating agent and the modifier. The solubility of Hg(FDDC){dollar}sb2{dollar} in SF CO{dollar}sb2{dollar} has been determined to be {dollar}5times 10sp{lcub}-3{rcub}{dollar} M at 50{dollar}spcirc{dollar}C and 150 atm, which is about 3 orders of magnitude greater than the non-fluorinated analogue Hg(DDC){dollar}sb2.{dollar} For supercritical fluid extraction (SFE) of lanthanides and actinides, our results show that the extraction of lanthanides and actinides by neat CO{dollar}sb2{dollar} containing {dollar}beta{dollar}-diketone ligands is incomplete. One possible explanation could be the hydration of lanthanide and actinides metal chelates or incomplete shielding of center metal ions by ligands since the lanthanide and actinide elements commonly have coordination numbers of 8 or 9. Using a mixture of an organophosphorus reagent and a fluorinated {dollar}beta{dollar}-diketone as the extractant, quantitative extraction of lanthanides and actinides from soil and water samples can be achieved with neat CO{dollar}sb2.{dollar}; The synergistic extraction of lanthanides and actinides using a mixture of ligands is probably due to adduct formation. Our results from supercritical fluid chromatography (SFC) and X-ray crystallography show that hydrated metal chelates are unstable. They decompose and are irreversibly adsorbed inside the SFC column. However, the adducts of lanthanide and uranium {dollar}beta{dollar}-diketonates with organophosphorus reagents are very soluble and stable in SF CO{dollar}sb2{dollar} and exhibit great chromatographic behavior. These results indicate that adduct formation can improve the thermal stability and solubility of metal chelates in SF CO{dollar}sb2.{dollar} Therefore, the extraction of lanthanides and actinides with SF CO{dollar}sb2{dollar} containing mixed ligands is quite effective.; The adduct formation/supercritical fluid chromatography approach leads to the first successful separations of the complexes of lanthanides and divalent transition metals of the same {dollar}beta{dollar}-diketone ligand using neat CO{dollar}sb2{dollar} as the mobile phase. Solvation behavior, stability, and stoichiometry of the adducts of lanthanide and uranium {dollar}beta{dollar}-diketonates in SF CO{dollar}sb2{dollar} have also been studied by SFC. The molar ratio of a lanthanide-FOD (2,2,-dimethyl-6,6,7,7,8,8,-heptafluoro-3,5,-octanedione) chelate with an organophosphorus reagent and uranyl-HFA (hexafluoroacetylacetone) chelate with an organophosphorus reagent is 1:2 and 1:1, respectively. The stability sequence of lanthanide-FOD organophosphorus adducts follows the order of Ln(FOD){dollar}sb3cdot2{dollar} TOPO {dollar}>{dollar} Ln(FOD){dollar}sb3cdot2{dollar} TBPO {dollar}>{dollar} Ln(FOD){dollar}sb3cdot2{dollar} TBP. For Ln-FOD-TBPO systems, the relative stability of adducts increases with the atomic numbers of the lanthanides.; The extraction of U(VI) and Th(IV) from acidic nuclear waste with SF CO{dollar}sb2{dollar} modified with an organophosphorus reagent has also been demonstrated in this work. The distribution coefficients and extraction kinetics were measured. The possibility of using SF technology to replace the conventional PUREX process is discussed.