SELECTIVE EXTRACTION OF MERCURY WITH IONIZABLE CROWN-ETHERS IN SUPERCRITICAL CARBON-DIOXIDE

The solubility of a tert-butyl-substituted dibenzobistriazolo-crown ether in methanol (5 mol %) modified CO2 has been determined to be in the order of 1 x 10(-3) M at 60 degrees C and 200 atm. Using this proton-ionizable crown ether as an extractant in methanol (5%) modified CO2, quantitative extraction of Hg2+ from sand and cellulose-based filter papers can be achieved at 60 degrees C and 200 atm if a small amount of water is present in the solid matrix. Other divalent metal ions including Cd2+, Co2+, Mn2+, Ni2+ Pb2+ and Zn2+ are virtually not extractable under these conditions. Gold (AU(3+)) can be extracted by the macrocyclic ligand with a lower efficiency than Hg2+. Extraction of Hg2+ from aqueous samples can also be achieved using methanol-modified CO2 containing the macrocyclic ligand, Formation of extractable metal chelates with the ligand at the pH defined by the CO2-H2O system appears to be an important factor determining the extraction efficiencies of the metal ions by this in situ chelation-supercritical fluid extraction technique.